Field of the Invention

The present invention relates to methods for preparing aqueous solutions of (meth) acrylamide employing a biological process. The method relates to the production of aqueous (meth) acrylamide solutions of high purity with either no foaming or low levels of foaming. The invention also provides a reactor for manufacturing aqueous (meth) acrylamide solutions. Further, the present invention also provides aqueous (meth) acrylamide solutions obtainable by the inventive method, homopolymers or copolymers of said (meth) acrylamide solutions and the use of such homopolymers or copolymers for mining or oilfield applications.

Background of the Invention

Polyacrylamides are widely used as flocculants for a variety of industries including the mining industry. Other common uses of polyacrylamides include additives for enhanced oil recovery and drift reduction additives for soil treatment in agricultural applications. The raw material for polyacrylamide is typically its monomer acrylamide. In principle, there are two different methods of producing acrylamide on an industrial scale: chemical synthesis and biological synthesis, wherein the biological synthesis methods are more and more on the rise due to mild reaction conditions and inherent process safety. Due to the milder reaction conditions, the absence of copper catalyst and the quantitative conversion of the nitrile, expensive downstream processing steps such as distillation or ion exchange can be avoided in the biological synthesis, thus resulting in cheaper plants with drastically reduced plant footprint.

Both synthesis methods use acrylonitrile as starting substance. While the chemical synthesis method uses copper catalyst (e.g. US 4048226, US 3597481 ), the biological synthesis method (also known as bio-based method) employs biocatalysts to hydrate (i.e. to convert) acrylonitrile in order to obtain acrylamide. Generally, such biocatalysts are microorganisms which are capable of producing (i.e. which encode) the enzyme nitrile hydratase (IUBMB nomenclature as of September 30, 2014: EC 4.2.1.84; CAS-No. 2391-37-5; also referred to as, e.g., NHase). Nitrile hydratase producing microorganisms are largely distributed in the environment and comprise, inter alia, representatives of the species Rhodococcus rhodochrous, Rhodococcus pyridinovorans, Rhodococcus erythropolis, Rhodococcus equi, Rhodococcus ruber, Rhodococcus opacus, Aspergillus niger, Acidovorax avenae, Acidovorax facilis, Agrobacterium tumefaciens, Agrobacterium radiobacter, Bacillus subtilis, Bacillus pallidus, Bacillus smithii, Bacillus sp BR449, Bradyrhizobium oligotrophicum, Bradyrhizobium diazoefficiens, Bradyrhizobium japonicum, Burkholderia cenocepacia, Burkholderia gladioli, Klebsiella oxytoca, Klebsiella pneumonia, Klebsiella variicola, Mesorhizobium ciceri, Mesorhizobium opportunistum, Mesorhizobium sp F28, Moraxella, Pantoea endophytica, Pantoea agglomerans, Pseudomonas chlororaphis, Pseudomonas putida, Rhizobium, Rhodopseudomonas palustris, Serratia liquefaciens, Serratia marcescens, Amycolatopsis, Arthrobacter, Brevibacterium sp CH1, Brevibacterium sp CH 2, Brevibacterium sp R312, Brevi bacterium imperiale, Cory nebacteri urn nitrilophilus, Cory nebacteri urn pseudodi phteriticum, Cory nebacteri urn glutamicum, Cory nebacteri urn hoffmanii, Microbacterium imperiale, Microbacterium smegmatis, Micrococcus luteus, Nocardia globerula, Nocardia rhodochrous, Pseudonocardia thermophila, Trichoderma, Myrothecium verruca ria, Aureobasidium pullulans, Candida famata, Candida guilliermondii, Candida tropicalis, Cryptococcus flavus, Cryptococcus sp UFMG- Y28, Debaryomyces hanseii, Geotrichum candidum, Geotrichum sp JR1, Hanseniaspora, Kluyveromyces thermotolerans, Pichia kluyveri, Rhodotorula glutinis, Comomonas testosteroni, Pyrococcus abyssi, Pyrococcus furiosus, and Pyrococcus horikoshii. (see, e.g., Prasad, Biotechnology Advances (2010), 28(6): 725-741 ; FR2835531). The enzyme nitrile hydratase is either iron- or cobaltdependent (/.e. it possesses either an iron or a cobalt atom coordinated in its activity center) which is particularly characterized by its ability to catalyze conversion of acrylonitrile to obtain acrylamide by hydrating acrylonitrile (Kobayashi, Nature Biotechnology (1998), 16: 733 - 736).

EP1385972 discloses a method in which the biocatalyst is damaged as little as possible during the reaction, by-products are minimized and batch time is optimized. Therefore, a reactor with a pumping circuit is provided, in which a part of the reaction mixture is circulated by a pump and in which at least a heat exchanger is arranged. For a homogeneous content in the reactor a motor driven agitator is used. The reaction temperature is monitored by on-line measurements.

EP2267143 discloses a method for producing an amide compound from a nitrile compound using a biocatalyst that realizes low cost, energy saving and low environmental burdens. For the method a reactor is used, wherein the nitrile compound is reacted with the biocatalyst to produce the amide compound under such stirring conditions that the stirring power requirement is in the range of 0.08 to 0.7 kW/m ³

EP2518154 discloses a method for producing acrylamide from acrylonitrile by a biocatalyst method, wherein both evaporation of acrylonitrile into a gas phase and damaging of a catalyst by stirring are prevented. In EP2518154 an acrylonitrile feed tube that feeds acrylonitrile into an aqueous medium while stirring said aqueous medium is disclosed.

EP2336346 discloses a method for producing acrylamide in presence of a biocatalyst in a reactor equipped with a tubular heat exchanger for removing reaction heat by maintaining the reaction temperature in a range of 5 to 20°C in order to prevent biocatalyst deactivation by heat.

JP2015057968 discloses a manufacturing apparatus which comprises a reaction vessel equipped with a stirrer and an external circulation line including a circulating pump and heat exchanger. A supply line for supplying the nitrile compound in the external circulation line is installed in the reaction vessel. Instead of feeding a nitrile compound directly into the reaction vessel, the nitrile compound is supplied to the external circulation line and then into the reaction vessel.

JP2014176344 discloses a method of producing an amide compound using a microorganism, wherein the heat removal is monitored. The reaction tank / production apparatus is equipped with a temperature control device for calculating the heat removal of the reaction heat. A heat exchanger is installed in an external circulation line. Further the use of stirrer and/or mixer is disclosed. WO 2019081331 describes a method for preparing aqueous acrylamide solution is having low acrylic acid concentration. The method involves combining a biocatalyst, acrylonitrile and water in a reactor and performing a bioconversion. Said reactor requires an external cooling circuit and the reactor comprises no stirrer.

WO201 6/006556 describes a method for producing a compound using a continuous tank reactor which is provided with two or more reaction tanks for producing the compound and with a reaction liquid feeding pipe that feeds a reaction liquid from an upstream reaction tank to a downstream reaction tank. The tank reactor may be mounted in a portable container. The reaction liquid in the reaction vessel is agitated by stirring blades.

The aqueous (meth) acrylamide solution produced from the bio-catalysed process is generally subjected to a separation stage in order to remove the biocatalyst from the (meth) acrylamide solution. This is typically done by centrifugation although filtration can be employed sometimes. A problem that can occur is that the process of separating the biocatalyst by centrifugation or filtration can result in foaming of the clarified acrylamide solution thus produced. In some cases, this foaming can be quite excessive and lead to significant problems in handling the (meth) acrylamide solution, including problems with transfer, storage and subsequent processing in for instance producing (meth) acrylamide copolymers therefrom.

It would be desirable to provide a method for producing aqueous (meth) acrylamide solution from a bio-catalysed process which avoids the aforesaid problems. In particular, a process which enables clarified aqueous (meth) acrylamide solutions in which the biocatalyst level has been removed or reduced to access to below low levels while avoiding significant foaming would be advantageous.

Summary of the Invention

According to a first aspect of the present invention we provide a method for preparing an aqueous (meth)acrylamide solution, said method comprising the following steps: (a) adding the following components (i) to (iii) to a reactor to obtain a composition for bioconversion:

(i) a biocatalyst capable of converting (meth) acrylonitrile to (meth) acrylamide;

(ii) (meth) acrylonitrile; and

(iii) water;

(b) performing a bioconversion on the composition obtained in step (a) as a reaction mixture in the reactor to obtain a crude aqueous (meth) acrylamide solution; and

(c) passing the crude aqueous solution through at least one filter to provide a purified aqueous (meth) acrylamide solution, wherein at least one filter of step (c) has a nominal retention rating, with at least 90% efficiency, of from 4 to 22 pm, preferably from 6 to 20 pm, more preferably from 6 to 15 pm.

In a second aspect of the present invention we provide an apparatus for manufacturing aqueous (meth) acrylamide solutions according to the method of the present invention, in which the apparatus comprises a bioconversion unit; a supply of (meth) acrylonitrile to the bioconversion unit; a supply to the bioconversion unit of biocatalyst capable of converting (meth) acrylonitrile to (meth) acrylamide; and a supply of water to the bioconversion unit, wherein the apparatus comprises at least one filter for purifying crude aqueous (meth) acrylamide solution to provide a purified aqueous (meth) acrylamide solution, wherein one or more of said filter(s) has a nominal retention rating, with at least 90% efficiency, of from 4 to 22 pm, preferably from 6 to 20 pm, more preferably from 6 to 15 pm.

A further aspect of the present invention is the aqueous (meth) acrylamide solution obtainable by the aforesaid inventive method.

Homopolymers or copolymers of (meth) acrylamide obtainable by polymerising the aforesaid (meth) solutions are also provided as a further aspect of the invention. The invention further includes the use of aqueous solutions of such (meth) acrylamide homopolymers or copolymers for mining applications or oil industry applications.

The term (meth) acrylamide as defined herein means either acrylamide or methacrylamide. In the present invention it is preferred that the (meth) acrylamide is acrylamide. Similarly (meth) acrylonitrile in the present specification means either acrylonitrile or methacrylonitrile.

Brief Description of Drawings

Figure 1 schematically represents one embodiment of an apparatus for manufacturing aqueous (meth) acrylamide solutions according to the method of the present invention.

Detailed Description of the Invention

The inventors have discovered that the method according to the present invention in which the crude aqueous solution of (meth) acrylamide is passed through at least one filter, at least one filter of which has a nominal retention rating, with at least 90% efficiency, of from 4 to 22 pm, preferably from 6 to 20 pm, more preferably from 6 to 15 pm, a purified aqueous (meth) acrylamide solution with high level of purity is achieved, without exhibiting undesirable levels of foaming. Where the crude (meth) acrylamide solution is passed through more than one filter sequence, provided that at least one of those filters has the nominal retention rating, with at least 90% efficiency, of from 4 to 22 pm, preferably from 6 to 20 pm, more preferably from 6 to 15 pm, a combination of high purity and low foaming may be achieved.

In one embodiment, the crude (meth) acrylamide may be passed through a first filter which has a nominal retention rating, with at least 90% efficiency, of from 4 to 22 pm, preferably from 6 to 20 pm, more preferably from 6 to 15 pm, and then passed through an additional filter which has a nominal retention rating, with at least 90% efficiency, with a filter pore size less than the first filter. Preferably this additional filter should also have a nominal retention rating, with at least 90% efficiency, in the range of from 4 to 22 pm, preferably from 6 to 20 pm, more preferably from 6 to 15 pm.

In an alternative form the additional filter may have a nominal retention rating, with at least 90% efficiency, outside the range of from 4 to 22 pm.

In one embodiment, the crude (meth) acrylamide may be passed through a first filter which has a nominal retention rating, with at least 90% efficiency, of particle size above the range of 4 to 22 pm and then passed through an additional filter which has a nominal retention rating, with at least 90% efficiency, of from 4 to 22 pm, preferably from 6 to 20 pm, more preferably from 6 to 15 pm.

It may also be desirable to employ a series of filters in which the crude (meth) acrylamide may be passed through each of the filters in sequence, provided that at least one of the filters in the series has a nominal retention rating, with at least 90% efficiency, of from 4 to 22 pm, preferably from 6 to 20 pm, more preferably from 6 to 15 pm. Such a series of filters may comprise 2, 3, 4, 5, 6 or even more filters. Preferably for any of the filters having nominal retention ratings, with at least 90% efficiency, outside the range of from 4 to 22 pm, the nominal retention rating, at least 90% efficiency, should be greater than the range of from 4 to 22 pm. Any additional filter having nominal retention rating, with at least 90% efficiency, less than the range of from 4 to 22 pm should not have a nominal retention rating significantly below the range of from 4 to 22 pm. Preferably no additional filter having a nominal retention rating, with at least 90% efficiency, below 4 pm should be included.

In a further embodiment, the crude (meth) acrylamide may be passed through only one filter, said filter having a nominal retention rating, with at least 90% efficiency, of from 4 to 22 pm, preferably from 6 to 20 pm, more preferably from 6 to 15 pm.

Desirably filters with a nominal retention rating, with at least 90% efficiency, of from 4 to 22 pm may for instance have nominal retention ratings of from 10 to 20 pm; 8 to 20 pm; 6 to 15 pm. Suitable filters within the range of from 4 to 22 pm may also have other specific ranges, for instance from 5 to 21 pm, from 6 to 20 pm, from 7 to 19 pm, from 8 to 18 pm, from 9 to 17 pm, from 10 to 16 pm, from 11 to 15 pm. By nominal retention rating we mean the ability of the filter membrane to retain particles of a specific size. This rating is given by the particle size followed by the percentage. For instance, a nominal rating of at least 90% efficiency at 10 pm means that the filter retains 90% of the particles which are sized at 10 pm.

Preferably, the at least one filter having a nominal retention rating, with at least 90% efficiency, of from 4 to 22 pm, preferably from 6 to 20 pm, more preferably from 6 to 15 pm, has a water permeability of from 900 to 3500 L/m ² /min. Within the nominal retention rating range of 4 to 22 pm, preferably from 6 to 20 pm, more preferably from 6 to 15 pm, the water permeability may vary within the range of 900 to 3500 L/m ² /min. There is a trend that as the nominal retention rating, with at least 90% efficiency, decreases to the lower end of the scale so the water permeability decreases. Typically, for a nominal retention rating, with at least 90% efficiency, of from 10 to 20 pm the water permeability may typically vary from 1600 to 3500 L/m ² /min, suitably from 2500 to 3450 L/m ² /min; for a nominal retention rating, with at least 90% efficiency, of 8 to 20 pm the water permeability may typically vary from 1000 to 3000 L/m ² /min, suitably from 1200 to 2000 L/m ² /min; and for a nominal retention rating, with at least 90% efficiency, of from 6 to 15 pm, the water permeability may typically vary from 900 to 1700 L/m ² /min, suitably from 900 to 1200 L/m ² /min.

Where the at least one filter is used with one or more additional filters with nominal retention ratings, with at least 90% efficiency, outside the range of from 4 to 22 pm, the water permeability may also be within the range of from 900 to 3500 L/m ² /min or more typically may lie outside this range. For instance, the at least one additional filter having a nominal retention rating, with at least 90% efficiency, below the range of from 4 to 22 pm will tend to have lower water permeability than the filter with nominal retention ratings, with at least 90% efficiency, within the range of from 4 to 22 pm would. There is a trend with such filters that as the nominal retention rating, with at least 90% efficiency, is decreases below the range of from 4 to 22 pm so the water permeability decreases. It may also be desirable to subject the aqueous crude (meth) acrylamide to a centrifugation step and then subject the so formed aqueous centrate to a filtration step in which at least one filter has a nominal retention rating, with at least 90% efficiency, of from 4 to 22 pm, preferably from 6 to 20 pm, more preferably from 6 to 15 pm. More desirably the at least one filter has a water permeability of from 900 to 3500 L/m ² /min, particularly from 900 to 2000 L/m ² /min and more particularly from 900 to 1500 L/m ² /min.

In one desirable embodiment the crude aqueous (meth) acrylamide solution is passed through a first filter having a nominal retention rating, with at least 90% efficiency, from 4 to 22 pm to produce a first filtrate and then the first filtrate is passed through an additional filter having a nominal retention rating, with at least 90% efficiency, of a range below 4 to 22 pm. In one suitable aspect of this embodiment the first filter has a nominal retention rating of from 10 to 20 pm and/or a water permeability of from 2000 to 3500 L/m ² /min and the additional filter has a nominal retention rating below the nominal retention rating of the first filter, preferably from 8 to 20 pm and more preferably from 6 to 15 pm.

In another desirable embodiment the crude aqueous (meth) acrylamide solution is passed through a centrifugation stage in order to remove some of the suspended biocatalyst or other impurities suspended in the aqueous solution. Typically, this would be done prior to the filtration stage according to the present invention. It may also be desirable to include a preliminary centrifugation step in order to recover and recycle biocatalyst for reuse. Employing such a centrifugation step may enable a significant proportion of suspended matter to be removed from the crude aqueous (meth) acrylamide solution prior to the filtration stage. This may have the advantage that there would be less burden on the filtration stage in the removal of suspended matter, reduce the frequency of cleaning or replacing filters, improve the throughput of crude aqueous (meth) acrylamide solution through the filter membrane and/or even improve the efficiency of removing suspended material and purifying the aqueous (meth) acrylamide solution. Although with centrifugation it may be possible to remove a significant proportion of suspended material, including biocatalyst, from the aqueous (meth) acrylamide solution centrifugation alone would be unlikely to provide a purified aqueous (meth) acrylamide solution with sufficiently high purity while not incurring high levels of foaming.

The exact choice of filters, combinations of filters or combination of centrifugation and filters may depend upon the crude aqueous (meth) acrylamide solution produced in step (b) of the method according to the present invention. This may in turn depend upon the conditions of the bioconversion and of the particular biocatalyst, (meth) acrylonitrile or water introduced into the bioconversion step. In some cases, the crude (meth) acrylamide may be relatively more laden with suspended impurities, such as biocatalyst cellular material. A relatively low light transmission through the crude aqueous (meth) acrylamide solution may be indicative of a relatively higher level of suspended impurities.

One category of filters include polymeric membranes. Examples include polymeric membranes symmetric (polymeric) membranes which possess a uniform (pore) structure over the thickness of the membrane. Alternatively, asymmetrical (polymeric) membranes may be used. Typically, filtration membranes may be formed from polyethylene, polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE). Other polymeric filter membranes include polyester and polycarbonate membranes which can be made using irradiation and etching processes from polymers such as polypropylene, polyamides, cellulose acetate, polyether sulfone and poly sulfone. Other suitable filtration membranes may be constructed from inorganic materials, such as ceramics and metals. Suitable commercial ceramic membranes may be made by slip casting processes. Typically, this consists of 2 steps and begins with preparation of a dispersion of fine particles (referred to as slip) followed by deposition of the particles on a porous support. Inorganic membranes that are commonly available and suitable for the present invention include composite containing a thin separation barrier on a support (e.g. ceramic materials, such as titania, zirconia or alumina or combinations thereof).

Suitable filters for use in accordance with the present invention are available commercially, for instance from Pall Corporation. Suitable filters having a nominal retention rating, with at least 90% efficiency, in the range from 4 to 22 pm include Pall T1000, Pall K900 and Pall K700. The at least one filter used in the present invention may suitably be mounted in or part of a filtration unit. The filtration unit may be a dead-end filtration unit or it may be a cross-flow filtration unit. In the case of a dead-end filtration unit the aqueous (meth) acrylamide solution flow is substantially perpendicular to the filter surface. In the case of cross flow filtration the aqueous (meth) acrylamide solution flow is tangential across the surface of the filter membrane. Cross flow filtration is well documented in the literature, for instance Bertera R et al. (June 1984), “Development Studies of cross-flow filtration”, The Chemical Engineer 401 : 10; JF Richardson et al. (2002), Coulson and Richardson’s Chemical Engineering (Volume 2) (5 ^th Edition) Butterworth Heinemann.

The aqueous (meth) acrylamide solution may flow through a single filter, for instance in a filtration unit, or a series of filters, for instance in one or more filtration units, in accordance with the present invention. It may also be desirable for 2 or more filters, for instance in filtration units, to be employed in parallel. Thus, aqueous (meth) acrylamide solution produced by a single bioconversion, for instance in a single bioconversion unit, may be filtered through 2 or more filters, for instance in filtration units, in parallel. This may have the advantage that for a large bioconversion system the so produced aqueous (meth) acrylamide solution may be separately filtered through a plurality of filters in parallel simultaneously without being limited by the size of individual filter membranes. This may additionally have the advantage that if any one filter filtration unit needs to be taken off-line, for instance for cleaning, the filtration process may not need to be stopped entirely by allowing the filtration to continue through the parallel filters or filtration units. Further, each filter or filtration unit connected in parallel may be part of a series of filters or filtration units, provided that at least one of the filters has a nominal retention rating, with at least 90% efficiency, of from 4 to 22 pm, preferably from 6 to 20 pm and more preferably from 6 to 15 pm, in accordance with the present invention.

The flow rate of the aqueous (meth) acrylamide solution through the at least one filter in accordance with the present invention may be adjusted in order to achieve optimal filtration production of clarified aqueous (meth) acrylamide solution. Usually, the maximum flow rate would depend largely on the porosity or water permeability of the particular filter membrane and also the amount of impurities in the aqueous (meth) acrylamide solution being filtered. Typically, the flow rate may range from 100 to 1000 L/m ² /h, for instance from 200 to 900 L/m ² /h. One desirable range may be from 350 to 600 L/m ² /h, particularly from 400 to 550 L/m ² /h. This may be particularly suitable for filters having a nominal retention rating, with at least 90% efficiency, of from 6 to 15 pm. Another desirable range may be from 600 to 950 L/m ² /h, particularly from 650 to 900 L/m ² /h. This may be particularly suitable for filters having a nominal retention rating, with at least 90% efficiency, from 8 to 20 pm.

The clarity of the purified aqueous (meth) acrylamide solution, having been passed through at least one filter having a nominal retention rating, with at least 90% efficiency, of from 4 to 22 pm, preferably from 6 to 20 pm, more preferably from 6 to 15 pm, in step (c) according to the method of the present invention, may be determined by measuring the light transmission through the purified aqueous (meth) acrylamide solution. This can be done using a suitable instrument that measures light transmission. Suitably this may measure light with a wavelength at 600 nm using a 1 cm cuvette length against a deionised water reference. The clarity of the purified (meth) acrylamide solution may vary according to the particular choice of filter and the level of impurities present in the crude (meth) acrylamide solution or (meth) acrylamide solution to be purified if it has already been subjected to a preliminary filtration or centrifugation step.

Suitably the clarity of the purified aqueous (meth) acrylamide solution should have a light transmission of at least 75% when measured at 600 nm wavelength with a 1 cm path length against a deionised water reference. Desirably the light transmission should be at least 80%, more desirably at least 90% and preferably from 95% to 100%, more preferably from 95% to 99.5%.

Bioacrylamide

As used herein, the term “acrylamide” in the context of this invention means acrylamide that may be synthesized by partial hydrolysis of acrylonitrile using suitable catalysts. It is known in the art to use biocatalysts capable of converting acrylonitrile to acrylamide (often referred to as “bio acrylamide”). Pure acrylamide is solid. However, typically acrylamide according to the present invention is made by bio catalysis and is provided as aqueous solution, for example as aqueous solution comprising about 50 % by wt. of acrylamide. Solid acrylamide may be obtained from an aqueous solution of acrylamide by means of e.g. crystallization. Acrylamide obtained by means of biocatalysts may still comprise traces of the biocatalyst.

For the process according to the present invention an aqueous acrylamide solution is used which has been obtained by hydrolyzing acrylonitrile in water in the presence of a biocatalyst capable of converting acrylonitrile to acrylamide. As will be detailed below, using biocatalysts for hydrolyzing acrylonitrile has significant advantages for the present invention. Analogously aqueous meth acrylamide solution may be obtained by hydrolysing methacrylonitrile in water in the presence of a biocatalyst capable of converting methacrylonitrile to methacrylamide.

Biocatalyst

As used herein, the term “biocatalyst” in the context of this invention means nitrile hydratase enzymes, which are capable of catalyzing the hydrolysis of acrylonitrile to acrylamide. The conversion of acrylonitrile to acrylamide using a biocatalyst may be called “bioconversion” or “bio-catalysis”. Typically, nitrile hydratase enzymes can be produced by a variety of microorganisms, for instance microorganisms of the genus Bacillus, Bacteridium, Micrococcus, Brevibacterium, Corynebacterium, Pseudomonas, Acinetobacter, Xanthobacter, Streptomyces, Rhizobium, Klebsiella, Enterobacter, Escherichia Coli, Erwinia, Aeromonas, Citrobacter, Achromobacter, Agrobacterium, Pseudonocardia and Rhodococcus. WO 2005/054456 discloses the synthesis of nitrile hydratase within microorganisms and therein it is described that various strains of Rhodococcus rhodochrous species have been found to very effectively produce nitrile hydratase enzymes, in particular Rhodococcus rhodochrous NCIMB 41164. Such microorganisms, suitable as biocatalyst for the enzymatic conversion of acrylonitrile to acrylamide, which are known for a person skilled in the art, are able to be applied according to the present invention.

Additionally, the specific methods of culturing (or cultivation, or fermentation) and/or storing the microorganism as well as the respective sequences of polynucleotides which are encoding the enzyme, particularly the nitrile hydratase, are known in the art, e.g. WO 2005/054456, WO 2016/050816, and are applicable in context of the present invention. Within the present invention nitrile hydratase and amidase producing microorganisms may be used for converting a nitrile compound into the corresponding amide compound as it is described for example in WO 2016/050816.

As used herein, the term “nitrile hydratase (NHase) producing microorganism” or “microorganism” or “biocatalysts” or the like in the context of this invention have the meaning to be able to produce (i.e. they encode and express) the enzyme nitrile hydratase (also referred to as, e.g., NHase) either per se (naturally) or they have been genetically modified respectively. Microorganisms which have been “genetically modified” means that these microorganisms have been manipulated such that they have acquired the capability to express the required enzyme NHase, e.g. by way of incorporation of a naturally and/or modified nitrile hydratase gene or gene cluster or the like. Produced products of the microorganisms that can be used in the context of the present invention are also contemplated, e.g. suspensions obtained by partial or complete cell disruption of the microorganisms.

The terms “nitrile hydratase (NHase) producing microorganism” or “microorganism” or “biocatalysts” or the like, include the cells and/or the processed product thereof as such, and/or suspensions containing such microorganisms and/or processed products. It is also envisaged that the microorganisms and/or processed products thereof are further treated before they are employed in the embodiments of the present invention. “Further treated” thereby includes for example washing steps and/or steps to concentrate the microorganism etc. It is also envisaged that the microorganisms that are employed in the embodiments of the present invention have been pre-treated by a for example drying step. Also known methods for cultivating of the microorganisms and how to optimize the cultivation conditions via for example addition of urea or cobalt are described in WO 2005/054456 and are compassed by the embodiments of the present invention. Advantageously, the microorganism can be grown in a medium containing urea, acetonitrile or acrylonitrile as an inducer of the nitrile hydratase.

Preferably, the biocatalyst for converting acrylonitrile to acrylamide may be obtained from culturing the microorganism in a suitable growth medium. The growth medium, also called fermentation (culture) medium, fermentation broth, fermentation mixture, or the like, may comprise typical components like sugars, polysaccharides, which are for example described in WO 2005/054489 and which are suitable to be used for the culturing the microorganism of the present inventions to obtain the biocatalyst. For storage of the microorganism, the fermentation broth preferably is removed in order to prevent putrefaction, which could result in a reduction of nitrile hydratase activity. The methods of storage described in WO 2005/054489 may be applied according to the present invention ensuring sufficient biocatalyst stability during storage. Preferably, the storage does not influence biocatalytic activity or does not lead to a reduction in biocatalytic activity. The biocatalyst may be stored in presence of the fermentation broth components. Preferred in the sense of the present invention is that the biocatalyst may be stored in form of a frozen suspension and may be thawed before use. Further, the biocatalyst may be stored in dried form using freeze- drying, spray drying, heat drying, vacuum drying, fluidized bed drying and/or spray granulation, wherein spray drying and freeze drying are preferred.

The biocatalysts that are used according to the present invention can for example be cultured under any conditions suitable for the purpose in accordance with any of the known methods, for instance as described in the mentioned prior art of this specification. The biocatalyst may be used as a whole cell catalyst for the generation of amide from nitrile. The biocatalyst may be (partly) immobilized for instance entrapped in a gel or it may be used for example as a free cell suspension. For immobilization well known standard methods can be applied like for example entrapment cross linkage such as glutaraldehyde-polyethyleneimine (GA-PEI) crosslinking, cross linking to a matrix and/or carrier binding etc., including variations and/or combinations of the aforementioned methods. Alternatively, the nitrile hydratase enzyme may be extracted and for instance may be used directly in the process for preparing the amide. When using inactivated or partly inactivated cells, such cells may be inactivated by thermal or chemical treatment.

In a preferred embodiment, the microorganisms are whole cells. The whole cells may be pre-treated by a drying step. Suitable drying methods and/or drying conditions are disclosed e.g. in WO 2016/050816 and WO 2016/050861 and the known art can be applied in the context of the present invention. The microorganisms that are employed in the context of the present invention are in a preferred embodiment used in an aqueous suspension and in a more preferred embodiment are free whole cells in an aqueous suspension. The term "aqueous suspension" thereby includes all kinds of liquids, such as buffers or culture medium that are suitable to keep microorganisms in suspension. Such liquids are well-known to the skilled person and include for example storage buffers at suitable pH such as storage buffers which are used to store microorganisms, TRIS-based buffers, phosphate based buffers, saline based buffers, water in all quality grades such as distilled water, pure water, tap water, or sea water, culture medium, growing medium, nutrient solutions, or fermentation broths, for example the fermentation broth that was used to culture the microorganisms. During storage for example the aqueous suspension is frozen and thawed before use.

The biocatalyst may be provided as powder, as granulate or as aqueous suspension to the reactor for bioconversion. If provided as powder or granulate it is frequently advisable to prepare an aqueous suspension before adding the catalyst into the reactor / bioconversion unit. In an embodiment, the biocatalyst suspension may be conducted by suspending the biocatalyst powder in water in a vessel comprising at least a mixing device, for example a stirrer, one or more inlets for water, the biocatalyst and optionally further additives and one outlet for the biocatalyst suspension. The volume of the vessel may be for example from 0.1 m ³ to 1 m ³ The concentration of the biocatalyst in the aqueous biocatalyst suspension may be for example from 1 % to 30% by wt., for example from 5 to 15% by wt. relating to the total of all components of the aqueous suspension.

A biocatalyst suspension may be added directly to the bioconversion unit. In another embodiment, a concentrated suspension may be diluted before adding it to the bioconversion unit I reactor where the bioconversion takes place.

Bioconversion

The term “bioconversion” as used herein in the context with any one of the methods of the present invention in general denotes a reaction, wherein (meth) acrylonitrile is converted to (meth) acrylamide in the presence of water and a biocatalyst. The (meth) acrylamide is dissolved in the water, such that by any one of the methods described and provided herein an aqueous (meth) acrylamide solution is formed. As used herein, the term “composition” includes all components present in the reactor, such as, for example, the biocatalyst, (meth) acrylonitrile, (meth) acrylamide and water.

Particularly, the bioconversion is performed by contacting a mixture comprising water and acrylonitrile with the biocatalyst. The term “contacting” is not specifically limited and includes for example bringing into contact with, mixing, admixing, shaking, pouring into, flowing into, or incorporating into. It is thus only decisive that the mentioned ingredients come into contact with each other no matter how that contact is achieved.

Therefore, in one embodiment the present invention comprises the following steps:

(a) Adding the following components (i) to (iii) to a bioconversion unit to obtain a composition for bioconversion:

(i) a biocatalyst capable of converting (meth) acrylonitrile to (meth) acrylamide;

(ii) (meth) acrylonitrile; and

(iii) aqueous medium;

(b) performing a bioconversion on the composition obtained in step (a) as a reaction mixture in the reactor to obtain a crude aqueous (meth) acrylamide solution; and

(c) passing the crude aqueous solution to a at least one filter to provide a purified aqueous (meth) acrylamide solution, wherein at least one filter of step (c) has a nominal retention rating, with at least 90% efficiency, of from 4 to 22 pm, preferably from 6 to 20 pm, more preferably from 6 to 15 pm.

The addition of components (i) to (iii) in step (a) may take place in any order or sequence. Also preparing a pre-mix of some or all components (i) to (iii) is possible to obtain a composition for bioconversion according to step (a). The bioconversion can for example be conducted under any conditions suitable for the purpose in accordance with any of the known methods, for instance as described in the mentioned prior art of this specification like e.g. WO 2016/050817, WO 2016/050819, WO 2017/055518.

When adding the biocatalyst to the reactor in any one of the methods of the present invention, the biocatalyst may be taken directly from the fermentation broth. Alternatively, in accordance with any one of the methods described herein, the biocatalyst may have been dried before being added to the reactor. In this context the term “before” does not necessarily mean that the biocatalyst has been dried and is then directly added to the reactor. It is rather sufficient that the biocatalyst has undergone a drying step at any time before it is added to the reactor, independently of whether further steps between the drying and the addition are performed or not. As non-limiting examples, such further steps between the drying step and the addition to the reactor may be storage or reconstitution. However, it is also possible to add the biocatalyst to the reactor directly after drying. It is known from WO 2016/050816 that by using a biocatalyst, which has undergone a drying step, the concentration of acrylic acid in an aqueous acrylamide solution obtained by any one of the methods described herein is further reduced in comparison to the case that a biocatalyst is used which has not undergone drying before being employed in the bioconversion.

Regarding the drying method, in any one of the methods described and provided herein, a biocatalyst may be used which has been dried using freeze-drying, spray drying, heat drying, vacuum drying, fluidized bed drying and/or spray granulation. With this respect, spray drying and freeze drying are preferred, since in general by using a biocatalyst, which has been subjected to spray- or freeze drying, a higher reduction of the acrylic acid concentration in the obtained aqueous acrylamide solutions is achieved compared to employing a biocatalyst which has been dried using other methods.

According to any one of the methods of the present invention a dried biocatalyst may be added to the reactor. This means that the biocatalyst is added to the reactor in a dried form. In particular, the biocatalyst may have the form of a powder or a granule. As an alternative to adding a dried biocatalyst to the reactor, the dried biocatalyst may be reconstituted before being added to the reactor. For example, the biocatalyst may be reconstituted by suspending in an aqueous composition. With this respect, the aqueous composition may be water or a buffer. As a further alternative, a biocatalyst in form of a matrix bound microorganism may be added to the reactor. The conversion of acrylonitrile to the acrylamide may be carried out by any of a batch process and a continuous process, and the conversion may be carried out by selecting its reaction system from reaction systems such as suspended bed, a fixed bed, a fluidized bed and the like or by combining different reaction systems according to the form of the catalyst. Particularly, the method of the present invention may be carried out using a semi-batch process. In particular, the term "semi-batch process" as used herein may comprise that an aqueous acrylamide solution is produced in a discontinuous manner.

According to a non-limiting example for carrying out such a semi-batch process water, a certain amount of acrylonitrile and the biocatalyst are placed in the bioconversion unit. Further acrylonitrile is then added during the bioconversion until a desired content of acrylamide of the composition is reached. After such desired content of acrylamide is reached, the obtained composition is for example partly or entirely recovered from the reactor, before new reactants are placed therein. In particular, in any one of the methods of the present invention the acrylonitrile may be fed such that the content of acrylonitrile during step (b) is maintained substantially constant at a predetermined value. In general, in any one of the methods of the present invention the acrylonitrile content and/or the acrylamide content during step (b) may be monitored. Methods of monitoring the acrylonitrile contents are not limited and include Fourier Transform Infrared Spectroscopy (FTIR). In another embodiment, the heat-balance of the reaction may be used for monitoring the process. This means that monitoring via heat-balance method takes place by measuring the heat energy of the system during bioconversion and by calculating the loss of heat energy during the reaction in order to monitor the process. In yet another embodiment, the biocatalyst is recovered from the reaction mixture after the bioconversion and re-used in a subsequent bioconversion reaction. The acrylamide recovered from the reactor is then passed through a Pall K700 at a rate of 430 L/m ² /h to provide a purified aqueous acrylamide solution. Although the conversion of acrylonitrile to the acrylamide may preferably be carried out at atmospheric pressure, it may be carried out under pressure in order to increase solubility of acrylonitrile in the aqueous medium. Because biocatalysts are temperature sensitive and the hydrolysis is an exothermic reaction temperature control is important. The reaction temperature is not specifically restricted provided that it is not lower than the freezing point of the aqueous medium. However, it is desirable to carry out the bioconversion at a temperature of usually from 0 to 50°C, suitably from 5°C to 40°C, preferably from 10 to 40°C, more preferably from 15 to 30°C. It is possible that the temperature may vary over time during the bioconversion reaction. Further suitable conditions for the bioconversion according to the present invention are for example described in WO 2017/055518 and are preferably applicable for the method in a bioconversion unit of the present invention.

Preferably the bioconversion in step (b) is performed at a temperature of from 5°C to 40°C for a period of from 10 minutes to 48 hours, preferably at a temperature of from 5° to 35° for a period of from one hour to 24 hours, more preferably at a temperature of from 15°C to 30°C, for a period of from 10 minutes to 48 hours, most preferably at a temperature of from 18°C to 28°C for a period of from 3 hours to 15 hours.

Although the amount of biocatalyst may vary depending on the type of biocatalyst to be used, it is preferred that the activity of the biocatalyst, which is introduced to the reactor, is in the range of about 5 to 500 II per mg of dried cells of microorganism. Methods for determining the ability of a given biocatalyst (e.g. microorganism or enzyme) for catalyzing the conversion of acrylonitrile to acrylamide are known in the art. As an example, in context with the present invention, activity of a given biocatalyst to act as a nitrile hydratase in the sense of the present invention may be determined as follows: First reacting 100 pl of a cell suspension, cell lysate, dissolved enzyme powder or any other preparation containing the supposed nitrile hydratase with 875 pl of a 50 mM potassium phosphate buffer and 25 pl of acrylonitrile at 25°C on an Eppendorf tube shaker at 1 ,000 rpm for 10 minutes. After 10 minutes of reaction time, samples may be drawn and immediately quenched by adding the same volume of 1 .4% hydrochloric acid. After mixing of the sample, cells may be removed by centrifugation for 1 minute at 10,000 rpm and the amount of acrylamide formed is determined by analyzing the clear supernatant by HPLC. For affirmation of an enzyme to be a nitrile hydratase in context with the present invention, the concentration of acrylamide shall particularly be between 0.25 and 1 .25 mmol/l - if necessary, the sample has to be diluted accordingly and the conversion has to be repeated. The enzyme activity may then be deduced from the concentration of acrylamide by dividing the acrylamide concentration derived from HPLC analysis by the reaction time, which has been 10 minutes and by multiplying this value with the dilution factor between HPLC sample and original sample. Activities >5 U/mg dry cell weight, preferably >25 U/mg dry cell weight, more preferably >50 U/mg dry cell weight, most preferably >100 U/mg dry cell weight indicate the presence of a functionally expressed nitrile hydratase and are considered as nitrile hydratase in context with the present invention.

It is preferred, that the concentration of acrylonitrile during the bioconversion should not exceed 6 % by wt. and may for example be in the range from 0.1 % by wt. to 6 % by wt., preferably from 0.2 % by wt. to 5 % by wt., more preferably from 0.3 % by wt. to 4 % by wt., even more preferably from 0.5 % by wt. to 3 % by wt., still more preferably from 0.8 % by wt. to 2 % by wt. and most preferably from 1 % by wt. to 1 .5 % by wt., relating to the total of all components of the aqueous mixture. It is possible that the concentration may vary over time during the bioconversion reaction. In order to obtain more concentrated solutions of acrylamide the total amount of acrylonitrile should not be added all at once but it should be added stepwise or even continuously keeping the abovementioned concentration limits in mind. The disclosure of WO 2016/050818 teaches a method of additional dosing of acrylonitrile, which is suitable to be used and applied in the present invention.

The concentration of acrylamide in the obtained solution is in the range from 10% to 80%, preferably in the range from 20% to 70%, more preferably in the range from 30% to 65%, even more preferably in the range from 40% to 60%, most preferably in the range from 45% to 55% by weight, based on the complete weight of the reaction solution. The reaction should be carried out in such a manner that the final concentration of acrylonitrile in the final acrylamide solution obtained does not exceed 0.1 % by weight relating to the total of all components of the aqueous solution. Typical reaction times may be from 2 h to 20 h, in particular 4 h to 12 h, for example 6 h to 10 h. After completion of the addition of acrylonitrile, the reactor contents are allowed to further circulate for some time to complete the reaction, for example for 1 hour to 3 hours. The remaining contents of acrylonitrile should preferably be less than 100 ppm, based on the complete weight of the reaction solution.

The present invention further relates to aqueous acrylamide solutions obtainable or being obtained by any one of the methods described and provided herein.

An aqueous acrylamide solution, in particular an aqueous acrylamide solution obtainable or being obtained by any one of the methods described herein, may have an acrylic acid concentration of not more than 5000 ppm, preferably of not more than 1500 ppm, preferably of not more than 1000 ppm, more preferably of not more than 750 ppm, further preferably of not more than 500 ppm, even more preferably of not more than 300 ppm, still more preferably of not more than 200 ppm and most preferably of not more than 100 ppm, wherein indications of w/w % and ppm are each referred to the total weight of the solution, and ppm each relates to weight parts.

In any one of the aqueous acrylamide solutions, the acrylamide content and/or the acrylic acid concentration may be determined using HPLC. Preferably, an HPLC method is used as set forth below under the Examples.

Apparatus for manufacturing (meth) acrylamide

The apparatus for manufacturing aqueous (meth) acrylamide solutions according to the present invention the apparatus comprises a bioconversion unit; a supply of (meth) acrylonitrile to the bioconversion unit; a supply to the bioconversion unit of biocatalyst capable of converting (meth) acrylonitrile to (meth) acrylamide; and a supply of water to the bioconversion unit, wherein the apparatus comprises at least one filter for purifying crude aqueous (meth) acrylamide solution to provide a purified aqueous (meth) acrylamide solution, wherein one or more of said filter(s) has a nominal retention rating, with at least 90% efficiency, of from 4 to 22 pm, preferably from 6 to 20 pm, more preferably from 6 to 15 pm.

Figure 1 schematically represents one embodiment of a reactor which may be used in the method of preparing aqueous (meth) acrylamide solutions according to the present invention. The apparatus comprises a frame (1 ), said frame may be a cuboid frame, into which the bioconversion unit (3) is mounted. The bioconversion unit (3) may contain an outer wall (2) if the bioconversion unit is double-walled but not if it is single walled. The bioconversion unit is optionally equipped with a stirrer (10). Preferably bioconversion unit does not contain a stirrer (10). In other embodiments, there is no such frame (1 ) that the bioconversion unit is self-supporting. The bioconversion unit has a supply of (meth) acrylonitrile (7), a supply of biocatalyst (8) and a supply of water (9). The bioconversion unit comprises an external temperature control cycle comprising at least one pump (4) and a temperature control unit (5) and circulated through flow line (6). For cooling, the reaction mixture is circulated by means of the pump (4) from the bioconversion unit to the temperature control unit (5) and back into the bioconversion unit. Crude aqueous (meth) acrylamide solution is fed along flow line (11 ) to at least one filter or at least one filtration unit (12) containing at least one filter having a nominal retention rating, with at least 90% efficiency from 4 to 22 pm, preferably from 6 to 20 pm, more preferably from 6 to 15 pm. Purified aqueous (meth) acrylamide solution is fed from the at least one filter or filtration unit along flow line (13).

The supply of (meth) acrylonitrile to the bioconversion unit typically may be a pipe or any other conduit which conveys a supply of (meth) acrylonitrile to the bioconversion unit from a source of the (meth) acrylonitrile. Typically, this supply may comprise a storage vessel suitable for containing the (meth) acrylonitrile.

The supply of water to the bioconversion unit may be a pipe or any other conduit conveying water from a water source, such as a supply of fresh water from a natural freshwater resource, mains water or where a water source is scarce a tank or other vessel containing the water. In one desirable form the supply of water comprises a storage vessel containing water with a pipe or conduit connecting the storage vessel to the bioconversion unit.

The at least one filter for purifying the crude aqueous (meth) acrylamide solution may be connected to a flow line feeding crude aqueous (meth) acrylamide from the bioconversion unit. Specific details of the at least one filter, for instance the types of filter, arrangement of at least one filter and other specific details regarding the filter are given above in regard to the inventive method.

Preferably this at least one filter may be part of one or more filtration units. Such one or more filtration units containing said filter(s) having a nominal retention rating, with at least 90% efficiency, from 4 to 22 pm, preferably from 6 to 20 pm, more preferably from 6 to 15 pm may contain 2 or more of said filters. The one or more filtration units may additionally contain other filters with nominal retention ratings outside the aforesaid range as in accordance with the method of the present invention described above. Details of the filters and filtration units are as given above in regard to the inventive method.

The apparatus may also comprise a storage unit for the aqueous (meth) acrylamide solution. Generally, this would mean the purified aqueous (meth) acrylamide solution.

The apparatus may additionally contain a unit for further processing an aqueous (meth) acrylamide solution.

In a preferred embodiment the apparatus of the present invention is relocatable.

In one suitable embodiment such apparatus may comprise the following features:

A) the bioconversion unit is relocatable;

B) the supply of (meth) acrylonitrile comprises a storage vessel which is relocatable;

C) the at least one filter having a nominal retention rating, with at least 90% efficiency, of from 4 to 22 pm, preferably from 6 to 20 pm, more preferably from 6 to 15 pm; D) optionally, the apparatus comprises a relocatable storage unit for an aqueous (meth) acrylamide solution; and

E) optionally, the apparatus comprises at least one relocatable unit for further processing an aqueous (meth) acrylamide solution.

Desirably in this one suitable embodiment the apparatus may include additional features, for instance,

F) optionally, the apparatus comprises at least one centrifugation unit for centrifuging the crude aqueous (meth) acrylamide and located ahead of C) the at least one filter having a nominal retention rating, with at least 90% efficiency, of from 4 to 22 pm, preferably from 6 to 20 pm, more preferably from 6 to 15 pm.

The apparatus according to the present invention may be installed in any suitable location. The apparatus may be relocatable such that it may easily be relocated from one location to another. Nevertheless, when the apparatus is relocatable it may still be installed at a fixed production facility. This does not mean that the apparatus is any the less relocatable. This may offer the advantage of supplementing or complementing the activities at a fixed production facility.

Bioconversion unit

The hydrolysis of (meth) acrylonitrile to (meth) acrylamide by means of a biocatalyst is performed in a suitable bioconversion unit (also called reactor). Suitable reactors for performing the bioconversion are known to the skilled artisan. Examples comprise vessels of any shape, for example cylindrical or spherical vessels, or tube reactors. Such reactors comprise particularly a pumping circuit comprising a heatexchanger.

The bioconversion unit suitably comprises a reaction vessel. The volume of the reaction vessel is not specifically limited and may range from 10 m ³ to 150 m ³ , for example it may be about 20 m ³ to 50 m ³ Desirably the bioconversion unit comprises a double-walled reaction vessel or desirably the bioconversion unit comprises a single walled reaction vessel. Desirably, the reaction vessel may be either single walled or double walled and desirably should be horizontal. Such a construction avoids installing a pit for the collection of any leakage thereby ensuring an easier and quicker relocation of the reaction unit.

The bioconversion unit furthermore suitably should comprise means for controlling the temperature of the contents of the vessel. The hydrolysis of (meth) acrylonitrile to (meth) acrylamide is an exothermal reaction and therefore heat generated in course of the reaction should be removed in order to maintain an optimum temperature for bioconversion. The bioconversion unit furthermore usually comprises means for measurement and control, for example means for controlling the temperature or for controlling the pressure in the vessel.

For temperature control, the preferred bioconversion unit may comprise an external temperature control circuit comprising a pump which pumps the aqueous reactor contents from the storage vessel through a heat exchanger and back into the storage vessel, preferably via an injection nozzle.

In one embodiment, a separate, relocatable temperature control unit is used comprising pump and heat exchanger and which is connected with the bioconversion unit by pipes or flexible tubes. In a preferred embodiment, the temperature control circuit is integrated into the bioconversion unit. It may -for example- be located at one end of the unit next to the reaction vessel.

The external temperature control circuit described above may also be used as means for mixing. The stream of the aqueous reaction mixture which passes through the temperature control circuit and which is injected back into the reaction vessel causes a circulation of the aqueous reaction mixture within the reaction vessel which is sufficient to mix the aqueous reaction mixture.

It may be desirable that no stirrer is used for the mobile bioconversion unit (i.e. reaction vessel). A stirrer is an additional mechanical device, which increases the technical complexity. When using the external temperature control cycle for mixing instead of a stirrer, the technical complexity can be reduced while still sufficient mixing during bioconversion can be ensured. Advantageously, without a stirrer a transportation step is easier, since no stirrer as additional technical component has to be removed before transportation of the mobile bioconversion unit. Further, a bioconversion unit without a stirrer offers more flexibility in form, shape, mechanical stability requirements and size for the bioconversion unit. In particular, a horizontal set-up for the relocatable bioconversion unit can be realized easier without a stirrer and with mixing just via the external temperature control cycle.

In one desirable embodiment the apparatus comprises a relocatable bioconversion unit which comprises a frame, a reaction vessel mounted into the frame having a volume from 10 m ³ to 150 m ³ , an external temperature control circuit comprising at least one pump and a temperature control unit, wherein the reaction mixture is circulated by means of at least one pump from the reaction vessel into the temperature control unit and back into the reaction vessel, thereby simultaneously controlling the temperature and mixing the reaction mixture.

Adding (meth) acrylonitrile to the contents of the bioconversion unit may be performed in various ways. It may be added into the reaction vessel or it may be added into the temperature control circuit, for example after the pump and before the heat exchanger or after the heat exchanger. Injecting (meth) acrylonitrile into the temperature control circuit ensures good mixing of the reaction mixture with freshly added (meth) acrylonitrile. Preferably, (meth) acrylonitrile is added between pump and heat exchanger.

The amount of reaction mixture cycled per hour through the temperature control circuit is chosen such that sufficient mixing to the contents of the reactor as well as sufficient temperature control is achieved. In one embodiment, the amount of reaction mixture cycled per hour through the temperature control circuit may be from 100 % to 1000 % of the total volume of the reaction mixture in the bioconversion unit, in particular from 200 % to 1000 % and for example from 500% to 800%. Further possible is that the amount of reaction mixture cycled per hour through the temperature control circuit is from 100 % to 10000 %, preferably from 100 % to 5000 %.

Off-gases of the bioconversion unit may comprise (meth) acrylonitrile, (meth) acrylic acid and (meth) acrylamide. If necessary, according to the applicable rules such off- gases may be treated in a manner known in the art. For example, it may be possible to combust the off-gases.

In one embodiment, all off-gases containing (meth) acrylonitrile, (meth) acrylic acid and (meth) acrylamide may be washed in a scrubber. The scrubber vessel may have a volume of 1 m ³ to 100 m ³ , preferably a volume of 5 m ³ to 100 m ³ , more preferably a volume of 10 m ³ to 100 m ³ It may be for example an ISOtank or relocatable storage vessel, preferably a double walled vessel. The scrubber water may preferably be collected in a tank and it may be re-used for next bio-conversion batch.

In another embodiment of the invention, for temperature control an external temperature control circuit, for example a cooling circuit is used, which comprises a pump which pumps the monomer from the storage vessel through a heat exchanger and back into the storage vessel.

The temperature control circuit may be a separate, relocatable temperature control unit comprising pump and heat exchanger and which is connected with the storage vessel by pipes or flexible tubes.

Modular, relocatable units

In one embodiment of the invention, aqueous solutions of bio (meth) acrylamide for use in the method according to the present invention may be manufactured at a fixed chemical plant, and may be shipped to another location for further processing. However, in another preferred embodiment of the present invention the manufacture of bio (meth) acrylamide may be performed in a modular, relocatable plant. Further preferred is for example a relocatable bioconversion unit, which can be combined with installations and/or units of a fixed chemical plant. Such combination of an existing plant with a modular, relocatable bioconversion unit offers flexibility in building a production line based on case specific needs. Such production line at a certain plant can be adjusted easily in case the production requirements change.

The existing plant for example may be a fixed polymerization plant for polyacrylamide. So, the combination of a relocatable bioconversion unit offers the possibility of combining the manufacturing of bio (meth) acrylamide with units for further processing the (meth) acrylamide obtained from a relocatable bioconversion unit.

Particularly, in the light of the present invention it is possible to reduce the foot print and complexity of the bio (meth) acrylamide manufacturing site. Having a bioconversion reactor without a stirrer / no agitating element reduces the engineering and processing control significantly. Therefore, in a preferred embodiment of the invention, the bioconversion unit I bioconversion reactor is a relocatable bioconversion unit. In one embodiment, the relocatable bioconversion unit is similar to the storage unit for (meth) acrylonitrile which also may be relocatable. Therefore, it is possible to using largely the same equipment for storing the (meth) acrylonitrile and for the bioconversion step. This contributes to an economic process for manufacturing aqueous (meth) acrylamide solutions.

Due to the flexibility of having a relocatable bioconversion unit I bioconversion reactor without a mechanical stirrer I agitating device, it is possible to conduct the method for production of an aqueous acrylamide solution at the location where the further processing for example to the polymer polyacrylamide takes place.

Manufacturing bio acrylamide directly at the site of further processing the acrylamide to for example polyacrylamides saves significant transport costs. Acrylonitrile is a liquid and may be transported as pure compound to the site of further processing. The molecular weight of acrylamide is about 34 % higher than that of acrylonitrile and acrylamide is typically provided as about 50 % aqueous solution. So, for a 50 % aqueous solution of acrylamide the mass to be transported is about 2.5-fold as much as compared to transporting pure acrylonitrile. Transporting pure, solid acrylamide means transporting only about 34 % more mass as compared to transporting pure acrylonitrile, however, additional equipment for handling and dissolving the solid acrylamide is necessary at the location where further processing takes place. The analogous situation would exist with methacrylamide and methacrylonitrile.

Furthermore, acrylamide is toxic and it is therefore an advantage to reduce the transportation distance or amount of acrylamide to be transported in order to reduce the risk of accidents when transporting acrylamide. A bioconversion according to the present invention in a relocatable bioconversion unit without a stirrer enables that advantage.

Acrylonitrile for bio-catalysis may be stored in one or more than one relocatable storage units. The storage unit comprises a storage vessel. The volume of the storage vessel is not specifically limited and may range from 50 m ³ to 150 m ³ , for example it may be about 100 m ³ Preferably, the storage vessel should be double walled and should be horizontal. Such a construction avoids installing a pit for the collection of any leakage thereby ensuring an easier and quicker relocation of the storage unit. Double-walled vessels or single walled vessels may be placed on every good bearing soil. The storage unit furthermore comprises means for charging and discharging the vessel, means for controlling the pressure in the vessel, for example a valve for settling low-pressure or overpressure, and means for controlling the temperature of the acrylonitrile which preferably should not exceed 25°C. It furthermore may comprise means for measurement and control to the extent necessary.

Examples of relocatable storage units comprise relocatable cuboid, storage tanks, preferably double-walled tanks or single walled tanks. Further, any considerable form, shape and size of container is suitable and applicable for the storage and/or provision of acrylonitrile in the sense of the present invention. Particularly, standard iso-tanks are applicable for the storage and/or provision of acrylonitrile. Other examples comprise tank containers having a cuboid frame, preferably a frame according to the ISO 668 norm mentioned above and one or more storage vessels mounted into the frame. Such normed tank containers may be stacked and transported on trucks, railcars or ships in the same manner closed intermodal containers.

Several different relocatable units may be bundled together to have a relocatable plant. Each relocatable unit may have certain functions. Examples of such relocatable units comprise units for storing and optionally cooling monomers and/or other raw materials, hydrolyzing acrylonitrile, mixing monomers, further processing the acrylamide to for example an aqueous polyacrylamide solution. Details will be provided below. For performing different processes, individual units may be connected with each other in a suitable manner thereby obtaining a production line. Also bundling a relocatable bioconversion unit with non-relocatable units is possible.

“Relocatable unit” means that the unit is transportable basically as a whole and that is it not necessary to disassemble the entire unit into individual parts for transport. Transport may happen on trucks, railcars or ships.

In one embodiment, such modular, relocatable units are containerized units which may be transported in the same manner as closed intermodal containers for example on trucks, railcars or ships. Intermodal containers are large standardized (according to ISO 668) shipping containers, in particular designed and built for intermodal freight transport. Such containers are also known as ISO containers. Such ISO containers may have external dimensions of a height of ~ 2.59 m, a width of ~ 2.44 m and a length of ~ 6.05 m. Larger ISO containers have external dimensions of a height of ~ 2.59 m, a width of ~ 2.44 m and a length of ~12.19 m.

In another embodiment, the relocatable units are combined, thereby obtaining modular production plants for performing different processes according to the present invention. Such a modular construction using relocatable units provides the advantage, that the plants may be easily relocated if aqueous acrylamide solutions are no longer needed at one location but at another location.

At the site of manufacturing the aqueous acrylamide solution, at the site of further processing the acrylamide to obtain subsequent further products (e.g. polyacrylamide) and/or at the site of applying I using aqueous polyacrylamide solutions (e.g. for oilfield or mining applications) different relocatable units according to the present invention may be used and combined, for example: o a relocatable storage unit for acrylonitrile, o a relocatable bioconversion unit for hydrolyzing acrylonitrile in water in the presence of a biocatalyst capable of converting acrylonitrile to acrylamide, o at least one relocatable filter or filtration unit, comprising at least one filter having a nominal retention rating, with at least 90% efficiency, of from 4 to 22 pm, preferably 6 to 20 pm, more preferably from 6 to 15 pm, for purifying the crude aqueous acrylamide solution to produce a purified aqueous acrylamide solution, o a relocatable storage unit for an aqueous acrylamide solution, o relocatable units for further processing acrylamide with other water-soluble, monoethylenically unsaturated monomers different from acrylamide, o a relocatable unit for polymerization to obtain aqueous polyacrylamide solutions, and/or o a relocatable unit for subsequent applications.

Further processing of purified (meth) acrylamide

After having obtained the purified aqueous (meth) acrylamide solution further processing is possible. Further processing steps are for example drying the purified aqueous (meth) acrylamide solution and storing the dried (meth) acrylamide. Further processing steps are also mixing the purified aqueous (meth) acrylamide solution with other monomers in order to prepare a monomer solution which is suitable for a subsequent polymerization step to obtain homopolymers or copolymers deriving from (meth) acrylamide. The different further processing steps may be performed at different locations. For example, each further processing step may be performed at a different location. Alternatively, all or some of the further processing steps may be performed at the same location, in particular at the location of use of either the aqueous (meth) acrylamide solution or at the location of use of the aqueous polyacrylamide solution. If performed at the same location, it is possible to connect the different modular units I modular reactors with each other as needed to perform for example the different steps comprising the bioconversion of (meth) acrylonitrile to (meth) acrylamide, filtration step according to the invention and subsequent preparation of a monomer solution and polymerization to obtain polyacrylamide directly after another.

Aqueous monomer solution

During further processing, an aqueous monomer solution comprising at least water, (meth) acrylamide and optionally further water-soluble, monoethylenically unsaturated monomers is prepared. Basically, the kind and amount of water-soluble, monoethylenically unsaturated comonomers to be used besides acrylamide is not limited and depends on the desired properties and the desired use of the aqueous solutions of polyacrylamides to be manufactured. Typical monomers fall under the definitions of neutral comonomers, anionic comonomers, cationic comonomers and/or associative comonomers, which an artisan knows from the state of the art and is also applicable in the context of the present invention.

As used herein, the term “water-soluble monomers” in the context of this invention means that the monomers are to be soluble in the aqueous monomer solution to be used for polymerization in the desired use concentration. It is thus not absolutely necessary that the monomers to be used are miscible with water without any gap; instead, it is sufficient if they meet the minimum requirement mentioned. It is to be noted that the presence of acrylamide in the monomer solution might enhance the solubility of other monomers as compared to water only. In general, the solubility of the water-soluble monomers in water at room temperature should be at least 50 g/l, preferably at least 100 g/l.

Depending on the chemical nature, the water-soluble, monoethylenically unsaturated monomers to be used may be provided as pure monomers or as aqueous solutions for further processing. It is also possible to provide a mixture of two or more water- soluble, monoethylenically unsaturated monomers, in aqueous solution or as pure monomers for further processing. Acrylamide and other water-soluble, monoethylenically unsaturated monomers such as acrylic acid or salts e.g. sodium salt, ATBS (2-acrylamido-2 methyl-propane sulfonic acid or salts e.g. sodium salt), or DMA3Q (acrylroyloxy trimethylammonium chloride), or mixtures thereof preferably may be stored in suitable storage units. The monomers may be provided by road tankers, ISO tanks, or rail cars and pumped into relocatable storage units.

The aqueous monomer solution for polymerization comprises water and 5 % to 45 % by weight, preferably 15 % to 45 % by weight of water-soluble, monoethylenically unsaturated monomers, relating to the total of all components of the aqueous monomer solution. The water-soluble, monoethylenically unsaturated monomers comprise at least acrylamide, preferably bio acrylamide which preferably is manufactured as described above without a stirrer. In one embodiment of the invention, the monomer concentration is from 8 % by weight to 24.9 % by weight, preferably from 15 % by weight to 24.9 % by weight, for example from 20 to 24.9 % by weight, relating to the total of all components of the aqueous monomer solution. The monomer concentration may be selected by the skilled artisan according to his/her needs. For preparing the aqueous monomer solution, the water-soluble, monoethylenically unsaturated monomers to be used are mixed with each other. All monomers and optionally additives may be mixed with each other in a single step but it may also be possible to mix some monomers and add further monomers in a second step. Also, water for adjusting the concentration of the monomers may be added. Water eventually used for rinsing lines in course of transferring the monomer solution into the polymerization unit, needs to be taken into consideration when adjusting the concentration.

Further additives and auxiliaries may be added to the aqueous monomer solution. Examples of such further additives and auxiliaries comprise bases or acids for adjusting the pH value. In certain embodiments of the invention, the pH-value of the aqueous solution is adjusted to values from pH 5 to pH 7, for example pH 6 to pH 7. Examples of further additives and auxiliaries comprise complexing agents, defoamers, surfactants, or stabilizers are known to a person skilled in the art. Preferably, it is also possible that the pH adjustment takes place in-situ, which means that via adjusting the acrylic acid content in the acrylamide solution and/or the aqueous monomer solutions the pH can be adjusted. This adjustment can take place directly without addition of further pH adjusting additives during the reaction. This adjustment can also take place directly during the reaction by addition of for example an acrylate buffer.

In one embodiment, the preparation of the aqueous monomer solution is performed in a relocatable monomer make-up unit. In one embodiment, the monomer make-up may be the unit which is similar to the bioconversion unit as described above. Using largely the same equipment for storing acrylonitrile, for the bioconversion step, and for further processing acrylamide contributes to an economic process for manufacturing aqueous acrylamide solutions. It is possible that the bioconversion unit may also be used for monomer make-up and has particularly no stirrer / no mechanical agitation device. If the monomer make-up vessel is different to the bioconversion unit, it may be equipped with a stirrer for mixing the components of the aqueous monomer solution with each other. However, in the same manner as with the bioreactor, the external temperature control circuit may be used as means for mixing. The stream of the aqueous monomer mixture which passes through the temperature control circuit and which is injected back into the monomer make-up vessel causes a circulation of the aqueous reaction mixture within the reaction vessel which is sufficient to mix the aqueous reaction mixture.

Polymers

Furthermore, the present invention relates to an acrylamide homopolymer or copolymer obtainable or being obtained by polymerizing the acrylamide of the aqueous solution as described herein. With this respect, in case of a homopolymer the term “polymerizing” refers to a homopolymerization reaction, while in case of a copolymer the term “polymerizing” refers to a copolymerization reaction. The homopolymerization or copolymerization may be performed using an aqueous acrylamide solution obtainable or being obtained by any one of the methods described herein. In particular, an aqueous acrylamide solution may be used, from which the biocatalyst has been separated prior to the polymerization. Alternatively, the acrylamide may have been isolated from the aqueous acrylamide solution before being subjected to homopolymerization or copolymerization.

As used herein, the term “polyacrylamides” as used herein means water-soluble homopolymers of (meth) acrylamide, or water-soluble copolymers comprising at least 10 %, preferably at least 20 %, and more preferably at least 30 % by weight of acrylamide and at least one additional water-soluble, monoethylenically unsaturated monomer different from acrylamide, wherein the amounts relate to the total amount of all monomers in the polymer.

Suitable polymers may be non-ionic, anionic or cationic. Non-ionic polymers may be homopolymers of the (meth) acrylamide or copolymers of the (meth) acrylamide with other non-ionic ethylenically unsaturated monomers. Suitable non-ionic comonomers include hydroxy methyl acrylate, hydroxy ethyl acrylate and vinyl acetate. Anionic polymers may be copolymers of (meth) acrylamide with at least one anionic ethylenically unsaturated monomer. Suitable anionic ethylenically unsaturated monomers include acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, 2-acrylamido-2-methyl propane sulfonic acid, styrene sulfonic acid, vinyl sulfonic acid, styrene sulfonic acid. Each of the anionic ethylenically unsaturated monomers may be as the free acid or as salts thereof, particularly alkali metal salts, alkaline earth metal salts or ammonium salts. Preferred anionic polymers include copolymers of acrylamide with sodium acrylate, copolymers of acrylamide with calcium acrylate, copolymers of acrylamide with acrylic acid, copolymers of acrylamide with ammonium acrylate, copolymers of acrylamide with 2-acrylamido-2- methyl propane sulfonic acid, copolymers of acrylamide with sodium 2-acrylamido-2- methyl propane sulfonate, copolymers of acrylamide with maleic acid, copolymers of acrylamide with sodium maleate. Cationic polymers may be copolymers of (meth) acrylamide with at least one cationic ethylenically unsaturated monomer. Suitable cationic ethylenically unsaturated monomers include acrylroyloxy ethyl trimethylammonium chloride, methacryloyloxy ethyl trimethylammonium chloride, acrylamido propyl trimethylammonium chloride, methacrylamido propyl trimethylammonium chloride and diallyl dimethyl ammonium chloride.

The polymers produced according to the present invention may be employed in a variety of applications including additives for the oilfield industry and mining or mineral processing industry. Thus, in one embodiment of the present application the reactor according to the present invention is installed over a subterranean all bearing formation or in a mining area or in a mineral processing site.

Oilfield industry applications include additives to well injection fluids, such as viscosifiers, when conducting enhanced oil recovery procedures. Mining or mineral industry applications include flocculants to assist in solid liquid separation processes involving aqueous liquids with suspended solids, such as removal of residual solids in recovered liquors, treatment of tailings such as red mud, iron ore tailings, coal fines tailings etc.

Although the invention has been described with respect to specific embodiments and examples, it should be appreciated that other embodiments utilizing the concept of the present invention are possible without departing from the scope of the invention. The present invention is defined by the claimed elements, and any and all modifications, variations, or equivalents that fall within the true spirit and scope of the underlying principles.

Examples

Preparation of crude aqueous acrylamide solution

Acrylamide is prepared by hydrolysis of acrylonitrile using a biocatalyst Rhodococcus rhodochrous NCIMB 41164. This reaction takes place at approximately ambient temperature and normal atmospheric pressure.

The exothermic addition of water to acrylonitrile is carried out in a stirred tank reactor with an external circulating loop for cooling in a fed batch process. For this purpose, water is filled in the reactor and the biocatalyst is added as spray dried cells of Rhodococcus rhodochrous NCIMB 41164, which is previously suspended in water. In order to start the reaction acrylonitrile is dosed into the stirred tank reactor employing a process control system. A stable concentration of acrylonitrile is maintained at a constant concentration of acrylonitrile of 0.5-5% (circa 0.8%) and is controlled by the use of an online FTIR analysis, which directly interacts with the process control unit. The reaction temperature is kept at a constant 23-29°C (circa 26°C). The cycle time depends on the amount of added biocatalyst, the reaction temperature, acrylonitrile level and the final acrylamide concentration.

The addition of acrylonitrile is stopped after the addition of the total amount of acrylonitrile. After a curing reaction time and the full conversion of residual acrylonitrile (usually one hour) the reaction is finished, resulting in an aqueous 52% (w/w) acrylamide solution.

The following 3 batches of crude aqueous acrylamide solution were prepared by the above process description.

Table 1 Light Transmission was measured using light with a wavelength at 600 nm using a 1 cm cuvette length against a deionised water reference.

Filtration of crude aqueous acrylamide solution

The crude aqueous acrylamide solution is were filtered using different types of depth filter media. The specific types of filters employed are illustrated in Table 2.

Table 2

In order to assess the foaming of the crude aqueous acrylamide solution, bubbling tests were performed. 150 ml acrylamide solution was filled into a Schott bottle and gassed with air (0.7 L/min) through a metal frit.

The results of the filtration tests including the flow rate of the crude aqueous acrylamide solution through the filter are presented in Table 3. The results support the use of filters with nominal retention rating, with at least 90% efficiency, in the range from 4 to 22 pm. The results especially show the effectiveness when the nominal retention rating, with at least 90% efficiency, ranges from 6 to 20 pm. This is particularly so for the range of 6 to 15 pm. Further, the effectiveness of the inventive filters can be seen over the range of from 900 to 3500 L/m ² /min. BASF SE 180406

Table 3

BASF SE 180406

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