FIELD

[0001] The present invention relates to a method of recovering butanol. In particular the present invention relates to a method of recovering butanol from an effluent obtained by fermentation. Further, the present invention relates to a method of recovering butanol comprising extracting the butanol with butyl butyrate. Additionally the present invention relates to uses of butanol and other products recovered by the method. The present invention also relates to an apparatus for recovering butanol.

BACKGROUND

[0002] Environmental pollution and global warming linked with the exploitation of fossil fuels is a major concern of the 21 ^st century. Such pollution can be alleviated by substituting a part of fossil fuels with biofuels that have been extracted from e.g. fermentation broths .

[0003] The cost of feedstock and the cost of separating acetone-butanol-ethanol

(ABE) components from dilute fermentation broth are the two most important factors affecting the economics of ABE fermentation.

[0004] Conventionally, products from fermentation broths are separated by distillation using effective, robust and well-known, but energy-intensive technology. Due to the energy-intensive distillation, it is a well-recognised problem that fermentation to produce butanol is not economically favourable compared to production by a synthetic route.

[0005] Catalytic methods of manufacturing butanol are also known in the art e.g. WO 2009/008618 Al discloses a method for manufacturing bio butanol by producing butyric acid using bacteria and then producing butanol through chemical catalysis using hydrogen produced as a by-product with butyric acid.

[0006] Esterification of bio butanol followed by immediate extraction into diesel or kerosene provides an immediate bio fuel as is disclosed by TU-Delft at http://ww udelft.nl/fileadminAJD/MenC/Support/Intemet/TU_Website/TU_De lft_portal/ Samenwerken/Patenten_vitrine/Patenten_IPMS_pdf/OCT- 11 -005_Biofuel.pdf

[0007] Although butanol compares favourably to ethanol as a bio fuel, ethanol is more economically viable. One aggravating factor making the recovery of butanol expensive and difficult is the toxicity of butanol to fermenting bacteria. When fermenting sugar solutions with Clostridia bacteria to produce butanol, the butanol yield is low. Due to its toxicity butanol is only present in low product concentrations in fermented solutions. The concentration of butanol in a fermented solution usually amounts to about 12 g/1. At concentrations above this butanol is toxic to Clostridia bacteria. A further difficulty is that butanol forms an azeo trope with water making distillation processes more complicated and energy intensive.

[0008] In the past, methods have been devised to overcome the low butanol concentration by extracting butanol directly from the fermentation solution as it is being produced with water insoluble organic solvents e.g. a mixture of oleyl alcohol and n- decanol. Other methods include continuous gas phase stripping of butanol (and ethanol and acetone) from the fermentation solution. These methods, however, have high energy costs.

SUMMARY OF THE INVENTION

[0009] It is an aim of the present invention to provide a method of recovering butanol and optionally other biomolecules from a liquid effluent. It is a further aim of the present invention to provide uses of the recovered butanol and other biomolecules. One still further aim of the invention to provide an apparatus for recovering butanol.

[0010] The invention is defined by the features of the independent claims. Some specific embodiments are defined in the dependent claims. [0011] According to a first aspect of the present invention, there is provided a method of recovering butanol from a liquid effluent obtained by fermentation of a sugar solution comprising the step of extracting butanol with butyl butyrate.

[0012] According to a second aspect of the present invention, there is provided a use of butanol as an additive in fuels, e.g. fossil fuels. [0013] According to a third aspect of the present invention, there is provided a use of esters as an additive in fuels, e.g. fossil fuels.

[0014] According to a fourth aspect of the present invention, there is provided a use of esters as an additive in cosmetic preparations. [0015] According to a fifth aspect of the present invention, there is provided a use of esters as a flavouring.

[0016] According to a sixth aspect of the invention, there is provided an apparatus for carrying out the method of the invention.

[0017] The present invention addresses the low yield and high energy consumption problems by using reactive distillation to produce a mixture of esters, mainly butyl butyrate and butyl acetate, from the liquid fermentation products. These esters are then used for in- situ solvent removal from the fermentation broth by liquid-liquid extraction. The water produced during the reactive distillation can be easily removed by decantation from the condensed mixed ester stream, or by adsorption using molecular sieve or other water adsorbing substances. In the reactive distillation the esters are formed from the reaction between the acids and the alcohols, mainly butanol, while the remaining butanol, acetone and ethanol can be separated by regular distillation. Another advantage of the proposed scheme is that the produced esters are desirable products with a higher value than the acids.

[0018] Aspects of the present invention provide several advantages over the art e.g. butyric acid and acetic acid can be extracted efficiently, products can be recovered simply and economically, capital costs and energy consumption are low e.g. the ester extraction medium has a lower boiling point than conventional extractants. Esters valuable for example to food, pharmaceutical and cosmetics industries and usable as biosolvents and in biofuels are recoverable. Further advantages will become apparent from the description of embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] FIGURE 1 illustrates a method for the extraction of butanol from a dilute

ABE fermentation broth in accordance with at least some embodiments of the present invention. [0020] FIGURE 2 illustrates an apparatus and method for the extraction of acetone, butanol, ethanol from a dilute ABE fermentation broth in accordance with at least some embodiments of the present invention

EMBODIMENTS

[0021] The present invention relates to the extraction of useful biomolecules, in particular alcohols, acids and esters from a broth fermented from a sugar solution. In particular the present invention relates to a method of extracting bioalcohols selected from the group consisting of ethanol, butanol and a mixture thereof, and bioesters selected from the group consisting of butyl butyrate, butyl acetate, ethyl butyrate, ethyl acetate and a mixture thereof from a fermentation broth, comprising a pre-extraction and a main extraction, said pre-extraction comprising the steps of providing a feedstock comprising a fermentation broth, carrying out an extraction on the feedstock with an extraction medium comprising butyl butyrate to provide an organic phase and an inorganic phase, said organic phase comprising the extraction medium and one or more biomolecules selected from the group consisting of alcohols, esters, carboxylic acids and carbonyl compounds, conducting the organic phase to a first reactive distillation column for reactive distillation, said reactive distillation comprising the steps of reacting the alcohols and carboxylic acids to provide esters, removing water e.g. by absorption with a water absorption medium, such as a molecular sieve, withdrawing an ester product from a bottom portion of the first reactive distillation column to an (lights) ester separation column, withdrawing a vapour distillate comprising butanol, ethanol and acetone from a top portion of the column to a butanol column for separation of solvents, separating esters in the ester separation column, withdrawing a top fraction from the ester separation column to a butanol column, recycling a bottom fraction comprising butyl butyrate to the first pre extraction step, and conducting the fermentation broth comprising butanol, ethanol and acetone, and acetic acid and butyric acid to the main extraction, which comprises the steps of contacting the effluent with butyl butyrate to extract one or more biomolecules into an organic phase into which biomolecules such as butanol, acetone, ethanol, acetic acid and butyric acid are extracted, such molecules as butanol, acetone and ethanol being recovered from the extraction medium by distillation, and the extracted effluent is recycled to the fermentation broth. [0022] The fermentation broth may be a Clostridium fermentation that produces butanol. Clostridium fermentation in an acetogenic phase produces butyric acid and acetic acid in a higher yield than conventional Clostridium fermentation. Clostridium bacteria ferment sugars acetogenically producing butyric and acetic acids before shifting to a solvetogenic phase producing solvents (acetone, ethanol and butanol). The acids are extracted as described above in the pre-extraction with butyl butyrate before being reacted to product in the reactive distillation column. The product esters butyl butyrate, ethyl butyrate, ethyl acetate and butyl acetate can then be reacted with hydrogen obtained from fermentation gas in a hydrogenation reaction to provide butanol and ethanol. If desirable, the fermentation can be kept in the acetogenic phase yielding acids only that can then be converted to esters in reactive distillation in the presence of butanol and ethanol. The esters can be used as product as is described below or can be further reacted with hydrogen obtained from the fermentation gas to alcohols, uses of which are described below. In one embodiment the alcohols produced, ethanol and butanol, are recycled to the reactive distillation column. A further advantage of esters and alcohols recovered by means of the present invention, is that they are free of aromatic compounds, which are a known health concern due to both mutagenic and non-mutagenic effects.

[0023] FIGURE 1 illustrates a method in accordance with at least one embodiment of the present invention. A liquid effluent obtained by fermentation of a sugar solution is pre-extracted with butyl butyrate to provide a rich pre-extraction medium comprising alcohols and acids, in particular ethanol, butanol, acetic acid and butyric acid. The pre- extracted liquid effluent contains a suitable ratio of butyric acid and acetic acid compared to butanol and ethanol, e.g. up to 3 times the amount of butyric acid and acetic acid. The alcohols and esterified , esters including butyl acetate, ethyl acetate and butyl butyrate are recovered and butyl butyrate is recycled to the pre extraction medium, which is then directed to a main extraction in which alcohols and acetone are extracted into a main extraction medium. The main extraction medium is distilled to regenerate the extraction medium which is recycled to the main extraction. . The distillate from which the extraction medium is recycled undergoes further fractionation to yield butanol, acetone and ethanol. [0024] FIGURE 2 illustrates an apparatus and method according to at least one embodiment of the present invention. Biomass hydrolysate comprising a sugar solution is directed into an ABE reactor where the sugars are fermented via an inlet. [0025] The mass flow rate of the biomass hydrolysate into the ABE reactor is in the range of 3200 to 3600 kg/h, suitably 3437 kg/h. The temperature of the biomass hydrolysate is in the range of 30 to 50 °C, particularly the temperature of the biomass hydrolysate is 37 °C. [0026] The fermenting sugars produce fermentation gases which are drawn from the reactor via an outlet valve at atmospheric pressure and a mass flow rate of 200 to 250 kg/h, for instance 220 kg/h and a temperature of 0 to 30 °C, preferably 2 °C. From the fermentation gases, hydrogen can be recovered for the optional hydrogenation of esters recovered from the reactive distillation column to alcohols, such as butanol and ethanol. Condensate is recovered from the fermentation gases at a mass flow rate in the range of 10 to 20 kg/h, especially 14 kg/h at a temperature in the range of 0 to 10 °C, suitably at 2 °C. The condensate comprises solvents selected from the group consisting of acetone butanol and ethanol. Optionally, the condensate further comprises acetic acid, butyl acetate, and butyl butyrate. [0027] From a second outlet valve a liquid effluent is directed to a first inlet of a first extraction column, Extraction 1 , where the liquid effluent is extracted with butyl butyrate added to Extractionl via a second inlet at a mass flow rate of 0 to 20 kg/h, e.g. 5 kg/h, preferably 0 kg/h as a Makeup Solvent.

[0028] From a first outlet of Extraction 1 an organic phase, Orgl is directed to an inlet of a reactive distillation column at a mass flow rate in the range of 600 to 700 kg/h, for instance 650 kg/h. The reactive distillation column has for example 20 stages, the bottom stage of which is reactive. Org 1 typically comprises esters, alcohols, acids and carbonyl compounds. Org 1 typically comprises compounds selected from the group consisting of, butanol, ethanol acetone, butyric acid, acetic acid and mixtures thereof. [0029] In the reactive distillation column, Orgl is refluxed, for instance at a reflux ratio of 15 by mass at a pressure of, for example 1.2 bar and components of Orgl are esterified. A first unreacted fraction comprising ethanol and acetone is withdrawn from a first outlet of the reactive distillation column to an adsorption medium Adsl and a dewatered fraction is directed to an inlet of a solvent regeneration column at a mass flow rate of 10 to 60 kg/h, typically 32 kg/h at a temperature of 60 to 1 10 °C, suitably 97 °C Water produced in the reactive distillation column is removed by a solid adsorbing material at a mass flow rate of 5 to 10 kg/h, for instance 7 kg/h, such as a molecular sieve, and acetone and ethanol are recovered.

[0030] The recovered acetone and ethanol are recovered as separate fractions, each fraction having a purity in excess of 90 %, preferably in excess of 95 %, most preferably in excess of 99 %. Alternatively the acetone and ethanol are recovered in one single fraction and directed to separation at a later stage.

[0031] From a second outlet of the reactive distillation column is recovered a mixture comprising one or more esters, e.g. butyl butyrate, butyl acetate, ethyl acetate and ethyl butyrate may be recovered. The mixture comprising one or more esters are directed to an inlet of a lights column having for example 20 stages, at a mass flow rate in the range of 550 to 750 kg/h, suitably 610 kg/h and at a temperature in the range of 100 to 200 °C, for example 163 °C. In the lights distillation column the mixture is refluxed at a reflux ratio of 15 by mass and at a pressure of 1 bar. From a first outlet of the lights column is withdrawn a first fraction at a mass flow rate of about 0 to 10 kg/h, preferably 0.4 kg/h, to a first inlet of a butanol column having 20 stages. Optionally, the first fraction comprising a liquid ester rich distillate is withdrawn from the light column at a mass flow rate of 0 to 50 kg/h, particularly 8 kg/h and at a temperature in the range of 80 to 120 °C, suitably 94 °C. This first fraction may optionally mixed with used extraction medium for solvent extraction. [0032] From a second outlet of the lights column is withdrawn a second fraction at a mass rate flow in the range of 550 to 650 kg/h, for instance 602 kg/h at a temperature in the range of 100 to 200 °C, especially 163 °C.

[0033] The bottom product from the solvent regeneration column is divided into two streams: Solvl which is directed to a third inlet of the first extraction column Extraction 1 at a mass flow rate of about 1 to 10 kg/h, particularly 5 kg/h and at a temperature of about 30 to 40 °C, preferably 37 °C; and Solv2. Solv2 further comprises a fraction from an outlet of the above-mentioned solvent regeneration column. Solv 2 is directed to a second inlet of a second extraction column, Extraction 2, at a mass flow rate of about 2800 to 3200 kg/h, for example 3060 kg/h at a temperature of about 40 to 60 °C, particularly 44 °C. [0034] To a first inlet of the second extraction column Extraction 2 is directed from a second outlet of the first extraction column Extraction 1 an inorganic phase at a mass flow rate in the region of 15000 to 20000 kg/h, for instance 17570 kg/h. Makeup Solvent comprising butyl butyrate is added to the second extraction column Extraction 2 via a third inlet at a mass flow rate in the range of 0 to 15 kg/h, preferably 3 kg/h. A second organic phase, Org2, is directed via a first outlet to the solvent regeneration column at a mass flow rate in the region of 3100 to 3400 kg/h, for instance 3242 kg/h.

[0035] From a second outlet of the second extraction column Extraction 2 an inorganic phase is withdrawn to undergo aqueous purging at a mass flow rate of about 2700 to 3100 kg/h, particularly 2985 kg/h at a temperature in the range of 25 to 40 °C, preferably 30 °C. The purged inorganic phase is then recycled to the fermentation broth. Extraction medium recycled to the fermentation broth hydro lyses to butanol and butyric acid.

[0036] In the solvent regeneration column, butyl butyrate is separated from butanol, acetone and ethanol (regenerated) in a first fraction, withdrawn from a first outlet and recycled with Solv2 as described above. A second fraction comprising butanol, ethanol and acetone is directed via a second outlet to a solid water adsorption medium, Ads2, where water is adsorbed from the second fraction.

[0037] After water is adsorbed from the second fraction, the dewatered second fraction passes through heat recovery at a mass flow rate in the range of 1800 to 2200 kg/h, preferably 2108 kg/h at a temperature of about 100 to 140°C, particularly 120 °C, to the first inlet of the butanol column.

[0038] The contents of the butanol column are refluxed at a reflux ratio of 15 and at a pressure of about 1 bar. From a first outlet of the butanol column is withdrawn a fraction comprising ethanol and acetone. This fraction comprising ethanol and acetone is directed to an inlet of an ethanol acetone column having 20 stages at a mass flow rate in the range of 40 to 75 kg/h, for example 61 kg/h and at a temperature of 60 to 70 °C, for instance 66 °C.

[0039] From a second outlet of the butanol column, butanol is recovered at a mass flow rate in the range of 80 to 140 kg/h, for example 1281 kg/h and a temperature of about 30 to 80 °C, preferably 64 °C. [0040] The fraction comprising ethanol and acetone is refluxed at a reflux ratio of 8 in the ethanol acetone column. From a first outlet non condensable gases are vented e.g. to combustion etc. at mass flow rate in the range of 2 to lO kg/h, suitably 6 kg/h and a temperature in the range of 22 to 28 °C, particularly 25 °C. From a second outlet acetone is recovered at a mass flow rate in the range of 35 to 45 kg/h, preferably, 36 kg/h and a temperature in the range of 20 to 30 °C, for instance 25 °C. From a third outlet, ethanol is recovered at a mass flow rate in the range of 10 to 30 kg/h, suitable 21 kg/h and at a temperature of about 60 to 90 °C, for example at 69 °C.

[0041] The dotted lines in the Figure represent heat transfer from hot stream to cold stream.

[0042] The ethanol recovered from the ethanol acetone column is of high purity, typically of commercial purity, particularly the ethanol recovered is in excess of 95 % ethanol by volume, preferably 97 to 100 % ethanol by volume, suitably 98 to 99.5 % ethanol by volume.

[0043] Similarly, acetone recovered from the ethanol acetone column is of high purity typically of commercial purity, particularly the ethanol recovered is in excess of 95 % acetone by volume, preferably 97 to 100 % acetone by volume, suitably 98 to 99.5 % acetone by volume.

[0044] Likewise, butanol recovered from the butanol column is of high purity typically of commercial purity, particularly the butanol recovered is in excess of 95 % butanol by volume, preferably 97 to 100 % butanol by volume, suitably 98 to 99.5 % butanol by volume.

[0045] As discussed above butanol compares favourably to ethanol as a bio fuel.

Butanol has about 1.5 times more energy content per unit volume than ethanol. Due to its poor solubility in water compared with that of ethanol, it can be used as both an additive in fuels and as a standalone fuel that can be used in conventional engines. Butanol's suitablility as an additive in fuel is recognised by the European Commission. According to Active Standard ASTM D7862, up to 12.5 volume % of butanol can be blended with petrol for use as an automotive spark ignition engine fuel.

[0046] In the following are described certain further embodiments of the invention.

[0047] In an embodiment butanol is recovered from a liquid effluent obtained by fermentation of a sugar solution, in a method comprising the step of extracting butanol with an extraction medium comprising butyl butyrate. Butyl butyrate is particularly advantageous as an extraction medium as it is non-toxic to fermenting bacteria and thus, does not inhibit fermentation. In an embodiment the extraction medium further comprises esters selected from the group consisting of ethyl butyrate, butyl acetate and mixtures thereof.

[0048] In a further embodiment the extraction is carried out in a first pre-extraction step and a second main extraction step. In another embodiment the pre-extraction comprises an acid extraction step and a reactive distillation step. In a still further embodiment the acid extraction comprises contacting the liquid effluent with butyl butyrate to extract one or more biomolecules selected from the group of esters, alcohols and mixtures thereof into an organic phase and conducting the organic phase to the reactive distillation step. In an embodiment the biomolecules are selected from the group consisting of butyric acid, acetic acid, butanol, ethanol, and acetone. Such an acid extraction provides an inexpensive, low energy means of separating low value acids from the fermentation broth.

[0049] In an embodiment the reactive distillation comprises esterifying alcohols and carboxylic acids present in the organic phase in a reactive distillation column to provide an ester product comprising one or more esters. In a further embodiment the ester product comprises esters selected from the group consisting of butyl acetate, ethyl acetate, ethyl butyrate, butyl butyrate and mixtures thereof. In another embodiment the reactive distillation column is connected to a bed with water adsorbing solid substance for removal of water produced in esterification. Removing water mechanically provides the advantage that it does not need to be boiled off in a distillation step and thus improving the energy economy of the method. Removing water provides for simpler distillation since azeotropes are formed between butanol, esters, and water.

[0050] After water has been removed, the esters are withdrawn to an ester separation column. In an embodiment the esters are at least partly separated from butyl butyrate in an ester separation column. In another embodiment the butyl butyrate is withdrawn from a bottom portion of the ester separation column and recycled to the first acid extraction step. In a still further embodiment further butyl butyrate is added to the first acid extraction step.

[0051] After pre-extraction of the liquid effluent, a main extraction is carried out. In an embodiment the liquid effluent is conducted to the second main extraction step. In one embodiment the main extraction step comprises contacting the effluent with butyl butyrate to extract and recover one or more biomolecules into a second organic phase. In another embodiment the extracted and recovered biomolecules are selected from the group consisting of butanol, acetone, ethanol and mixtures thereof. In a further embodiment, acetic acid and optionally butyric acid are also extracted. In yet another embodiment the extracted effluent is recycled to the fermentation broth.

[0052] After extraction into the second organic phase. The second organic phase is distilled. In an embodiment the second organic phase is distilled at a temperature in the range of 100 - 220 °C, preferably at a temperature of 170 °C for recovery of butyl butyrate.

[0053] Following the distillation, fractions of distillate are recovered. In an embodiment at least a portion of the recovered butyl butyrate is recycled to the main extraction. In a further embodiment a fraction comprising butanol is recovered. In one embodiment a fraction comprising ethanol is recovered. In another embodiment a fraction comprising acetone is recovered.

[0054] Products recovered by the method have diverse uses. In one embodiment butanol recovered by embodiments of the method is used as an additive in fossil fuels. In a further embodiment esters recovered by embodiments of the method is used as an additive in fossil fuels. [0055] Not only are the products suitable for uses in fuels but they are also suitable for uses in cosmetic preparations. In one embodiment esters recovered by embodiments of the method are used as an additive in cosmetic preparations. Each ester may be either used alone or in combination with other esters recovered by the method. In a further embodiment esters recovered by embodiments of the method are used as a flavouring. Each ester may be either used alone or in combination with other esters recovered by the method. In an embodiment the esters used in the flavouring are selected from the group consisting of butyl butyrate, butyl acetate, ethyl acetate, ethyl butyrate and mixtures thereof. In a further embodiment, the esters used in the cosmetics preparations are selected from the group consisting of butyl butyrate, butyl acetate, ethyl acetate, ethyl butyrate and mixtures thereof. In one embodiment the esters are used as a flavouring in foodstuffs or in medicines. In another embodiment the esters are used in a pineapple flavouring. [0056] A further aspect of the invention relates to an apparatus for the extraction of butanol from a liquid effluent obtained by fermentation of a sugar solution. In an embodiment the apparatus comprises a first extraction column, a second extraction column, a reactive distillation column, a first water adsorbing medium, a solvent regeneration column, a second water adsorbing medium, a butanol column an ethanol- acetone column and a heat recovery system. In one embodiment, the apparatus optionally comprises a lights column. In a further embodiment the first extraction column has a first inlet for receiving a liquid effluent obtained by fermentation of a sugar solution, a second inlet for receiving makeup solvent for extracting a first organic phase, a third inlet for receiving solvent from a second outlet of the lights distillation column, a first outlet for directing a first organic phase to an inlet of the reactive distillation column, and a second outlet for directing a first inorganic phase to a first inlet of the second extraction column.

[0057] In a further embodiment the second extraction column has a first inlet or receiving an inorganic phase from the first extraction column, a second inlet for receiving makeup solvent for extracting a second organic phase, a third inlet for receiving solvent from a first outlet of the solvent regeneration column and from the second outlet of the lights column, a first outlet for conducting the second organic phase to a first inlet of the solvent regeneration column, and a second outlet for conducting a second inorganic phase to aqueous purging in a purge stream. This purge stream contains mainly water, but also some unfermented sugars and ABE products are also present. The purge stream can be directed to further treatment to recover ABE products or it can be directed to biogas production.

[0058] In another embodiment the reactive distillation column has an inlet for receiving the first organic phase from the first extraction column, a first outlet for conducting a first fraction to an inlet of a first water adsorption medium, and a second outlet for conducting a second fraction to an inlet of the lights column.

[0059] In a still further embodiment the lights column has an inlet for receiving the second fraction from the reactive distillation column, a first outlet for the recovery of a first lights distillate or for conducting the first lights distillate to an inlet of the butanol column, and a second outlet for conducting a second lights distillate to the first extraction column or the second extraction column or both.

[0060] In one embodiment the first water adsorption medium has an inlet for receiving the first fraction from the reactive distillation column, and an outlet for conducting a dewatered fraction to a second inlet of the solvent regeneration column.

[0061] In an embodiment the solvent regeneration column has a first inlet for receiving the second organic phase from the second extraction column, a second inlet for receiving the dewatered fraction from the outlet of the first water adsorption medium, a first outlet for conducting solvent to the third inlet of the second extraction column and a second outlet, and a second outlet for conducting a fraction to an inlet of the second water adsorbing medium.

[0062] In a further embodiment the second water adsorbing medium has an inlet for receiving a fraction from the second outlet of the solvent regeneration column, and an outlet for conducting a dewatered fraction to an inlet of the heat recovery system.

[0063] In another embodiment the heat recovery system has an inlet for receiving the dewatered fraction from the outlet of the second water adsorbing medium, and an outlet for further conducting the dewatered fraction to an inlet of the butanol column.

[0064] In one embodiment the butanol column has an inlet for receiving the fraction from the outlet of the heat recovery system and for receiving the first lights distillate from the first outlet of the lights distillation column, a first outlet for conducting a first fraction to an inlet of the ethanol-acetone column, and a second outlet for recovering a butanol fraction.

[0065] In a still further embodiment the ethanol-acetone column has an inlet for receiving the first fraction from the first outlet of the butanol column, a first outlet for the recovery of non-condensable gases, a second outlet for the recovery of acetone, and a third outlet for the recovery of ethanol.

[0066] In a further embodiment, the apparatus is used for the extraction of butanol by any of the methods disclosed hereinabove. [0067] It is to be understood that the embodiments of the invention disclosed are not limited to the particular structures, process steps, or materials disclosed herein, but are extended to equivalents thereof as would be recognized by those ordinarily skilled in the relevant arts. It should also be understood that terminology employed herein is used for the purpose of describing particular embodiments only and is not intended to be limiting. [0068] Reference throughout this specification to one embodiment or an embodiment means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases "in one embodiment" or "in an embodiment" in various places throughout this specification are not necessarily all referring to the same embodiment. Where reference is made to a numerical value using a term such as, for example, about or substantially, the exact numerical value is also disclosed.

[0069] As used herein, a plurality of items, structural elements, compositional elements, and/or materials may be presented in a common list for convenience. However, these lists should be construed as though each member of the list is individually identified as a separate and unique member. Thus, no individual member of such list should be construed as a de facto equivalent of any other member of the same list solely based on their presentation in a common group without indications to the contrary. In addition, various embodiments and example of the present invention may be referred to herein along with alternatives for the various components thereof. It is understood that such embodiments, examples, and alternatives are not to be construed as de facto equivalents of one another, but are to be considered as separate and autonomous representations of the present invention.

[0070] Furthermore, the described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. In the following description, numerous specific details are provided, such as examples of lengths, widths, shapes, etc., to provide a thorough understanding of embodiments of the invention. One skilled in the relevant art will recognize, however, that the invention can be practiced without one or more of the specific details, or with other methods, components, materials, etc. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of the invention. [0071] While the forgoing examples are illustrative of the principles of the present invention in one or more particular applications, it will be apparent to those of ordinary skill in the art that numerous modifications in form, usage and details of implementation can be made without the exercise of inventive faculty, and without departing from the principles and concepts of the invention. Accordingly, it is not intended that the invention be limited, except as by the claims set forth below.

[0072] The verbs "to comprise" and "to include" are used in this document as open limitations that neither exclude nor require the existence of also un-recited features. The features recited in depending claims are mutually freely combinable unless otherwise explicitly stated. Furthermore, it is to be understood that the use of "a" or "an", that is, a singular form, throughout this document does not exclude a plurality.

EXAMPLES

Example 1

[0073] Biomass hydrolysate or other concentrated sugar solution was fed to a continuous fermentation process to provide a fermentation broth. The liquid effluent from the fermentor contained around 7 g/L acetic acid,2 g/L of ethanol, 5 g/L of acetone, 8 g/L of butanol, approximately 1 g/L of butyric acid and 33 g/1 unfermented sugars. A small amount of evaporated solvents were recovered from the fermentation gas by cooling the fermentation gas to condense the solvents. The fermented solution was then fed to a concurrent pre-extraction stage with 3 stages. Here a small amount of butyl butyrate (0.6 t/h) was used to extract the main part of the acids. Butyric acid and acetic acid were extracted. Fractions of butanol, acetone and ethanol were also extracted. The extraction medium was then fed to a reactive extraction column where the mixture was esterified:

[0074] Reactive esterification was performed at the lowest stage in the reactive distillation column with 20 equilibrium stages operated at 1.2 bar. The reactive extraction was performed so that the water formed in the reaction and the water contained in the extraction medium was removed by a molecular sieve or other adsorption medium. From the top of the reactive extraction column a small vapour distillate flow was withdrawn. This stream was sent to the butanol column in order to separate the solvents from each other. The bottom product is sent to a further lights distillation column where the acetone, ethanol, butanol and lighter esters were separated from butyl butyrate as a liquid distillate. A part of the distillate was not condensed and this stream was sent to the lights separation column. The bottom product was returned to the pre-extraction.

[0075] The fermentation broth was sent after pre-extraction to a 5 stage solvent extraction. After extraction the main part of the extracted solution was returned to the fermentation feed. A purge stream was directed to anaerobic digestion in order to prevent accumulation of water in the process.

[0076] The extracted solution was fed to a solvent regeneration column with 30 equilibrium stages at 1.2 bar. Overhead vapour distillate from the reactive extraction was feed to the top of the column. Here the butanol, ethanol and acetone were separated from butyl butyrate. A small amount of butyl acetate, ethyl butyrate and butyl butyrate remain in the vapour distillate stream. In order to minimise this, the main part of the butanol column bottom product (from which ethanol and acetone was removed) was fed as a reflux stream to the top of the solvent regeneration column. The vapour distillate from the solvent regeneration column was directed through a molecular sieve bed in order to remove water and avoid separation of a butanol/water azeotropic mixture. The mixture was partially condensed and the condensation heat was recovered. Next ethanol and acetone were separated from the solvent regeneration column overhead in the butanol column. The butanol column has 20 equilibrium stages and was operated at 1 bar. The bottom product was partly directed as reflux to the solvent regeneration column and partly recovered as butanol product. Finally the distillate from the light fractionation column was directed to further fractionation in the lights fractionation column at 1 bar with 20 equilibrium stages.

Simulation Model and Calculations [0077] The simulation was performed with Aspen Plus version 8.4. The distillation columns and extraction stages were modelled as ideal equilibrium stages. According the following section the Liquid Liquid (LLE) distribution coefficients between the phases were measured experimentally. Based on the measurements parameters LLE parameters were regressed. For the extraction stages NRTL thermodynamics with regressed LLE parameters were used. For the rest of the flowsheet standard NRTL thermodynamics with Aspen databank VLE interaction parameters were used in order not to compute the Vapour Liquid Equilibrium with the regressed LLE parameters.

[0078] The reactive extraction was modelled with reaction 1 to 4. For them a chemical equilibrium was assumed at 10° C above the real temperature. The K value as function of temperature was obtained from literature. The following K values were used for butyl butyrate : K(T) = exp(6.88-1365/T) for ethyl butyrate : K(T) exp(8.18-2654/T) according (Santhanakrishnan et al 2013 p.1849) for butyl acetate Ka = 3.8207 exp(3581.7/RT) according to Gangadwala (2003) and ethyl acetate K value was estimate by Gibbs Energy minimization calculation.

[0079] This approach was used since based on the literature it can be concluded that equilibrium could be reached within a reasonable time (less than 1 h) when an effective catalyst such as Amberlyst was employed. The temperature approach accounts for deviation from the chemical equilibrium since the K values are lower at higher temperature. In addition kinetic data was not available in the literature for the same catalyst for reactions 1 -4.

[0080] Efficient heat integration was performed in order to minimize the energy consumption for the described flowsheet. The feed to the reactive distillation was preheated with the bottom product from the esterification column. The feed to the solvent stripper was heated first with the butanol product and subsequently with the solvent stripper bottom product. The light fractionation column feed was heated with the product. For the heat-exchangers the minimum temperature difference 10 °C was specified. Liquid-liquid equilibrium measurements

[0081] Butylbutyrate, butanol, acetone, acetic acid and butyric acid were from

Sigma Aldrich and their purities were 99.9%. Ethanol was purchased from Altia oyj, and its purity was 99.6%.

[0082] To measure the LLE behavior of the selected solvents with ABE broth, an aqueous mixture containing 0.8, 0.4, 0.167, 0.1 and 0.1 m-%> of butanol, acetone, ethanol, acetic acid and butyric acid respectively, was mixed in a mass ratio of 1 : 10 with an organic phase consisting of one of the selected extraction solvents.

[0083] The experiments were carried out in 100 ml glass bottles. The bottles were filled so that the gas volume inside was small, approximately 5 ml. The relatively small gas volume ensured that any errors caused by VLE would be minimized. All the experiments were carried out at 37 °C with constant mixing for 24 hours, after which the bottles were stored at 37 °C. The temperature was controlled within 0.05 °C. During these experiments the mixtures were monitored to verify that no stable emulsions were formed. Both of the phases were analyzed using a gas chromatograph with flame ionization detector (GC-FID). The organic phases were further analyzed with a gas chromatograph with a mass spectrometer (GC-MS) to determine their water content. The aqueous phase water content was calculated from mass balance. For the calculation of each distribution coefficient the results from two GC-FID and one GC-MS analyses were combined. The reproducibility was ±5%. To make our results more reliable we averaged the results from four analyses. We can assume that evaporative losses and error from weighing are negligible when compared to the error from GC. The distribution coefficients for the components were calculated as mass fraction ratios in organic and aqueous phases

where is the distribution coefficient for component is the mass fraction of

component i in organic phase and is the mass fraction of component i in aqueous

phase.

Analysis methods

[0084] The GC-FID was a Hewlett Packard 6890 Series gas chromato graph, with a 60 m long Zebron ZB Wax plus column, with 0.25 mm inner diameter and 0.25 μιη phase thickness. The carrier gas was helium, the injection volume was 0.5 μΐ and split ratio was 1 :50. The temperature program began with a ten minutes hold at 40 °C after which the temperature was elevated 10 °C min ¹ to 230 °C followed by a hold of two minutes at that temperature.

[0085] The GC-MS was manufactured by Agilent Technologies: the gas chromatograph was 7890A and the mass spectrometer was 5975C VL MSD. The used column was 30 m long Agilent Technologies Innowax with 0.25 mm inner diameter and 0.25 μιη phase thickness. The carrier gas was helium, the injection volume was 0.5 μΐ and split ratio was 1 :50. The temperature program begun with a 15 minutes hold at 40 °C after which the temperature was elevated 7.5 °C min ^-1 to 200 °C followed by a hold of 15 minutes.

Results and Discussion

[0086] The fermentation product as well as derivatives obtained in the fermentation are described in Table 1. Solvents can be efficiently recovered with the method. In addition valuable ester byproducts are obtained. An excess amount of butyl butyrate which is used as extraction medium is produced. In order to increase the recovery of products an additional extraction step of purge water could be considered.

[0087] The various contributions of energy consumers in the process are shown in

Table 2. The solvent stripper consumes the greatest amount of energy. This is because a significant amount of reflux is needed 2000 kg/h to recover the solvents from the extraction medium and prevent a significant amount of ester going to the distillate product. If the overhead product contains esters, they cannot be easily separated from butanol. It was not possible to reduce the energy demand of the solvent stripper, or effective heat- integration. However, heat can be recovered from the overhead product at a temperature around 110 °C. This heat could be used elsewhere in a biofuel plant process for evaporation, drying etc.

Table 1 : Species produced in the fermentation, recovered as products and the fraction that goes to the biogas process with the purge water.

Table 3: Measured distribution of the selected components between aqueous phase butyl butyrate

Table 4: Interaction parameters used in the simulation which was fitted based on experiments

INDUSTRIAL APPLICABILITY

[0088] At least some embodiments ofthe present invention find

industrial application in the production ofbiofuels and in the production of additives for biofuels. Further embodiments ofthe present invention find industrial application in food industry, in the pharmaceutical industry and in the cosmetics industry.