METHOD AND EQUIPMENT FOR DECOMPOSING BIOMASS MOLECULAR COMPONENTS CONTINUOUSLY

Cellulose is the most common natural polymer. In wood the cellulose fibres are bound together by lignin, thus wood is a natural composite material. The interest to utilize wood and other biomass in a non traditional way as a renewable non-fossil crude material is increasing due to the developments of biorefineries, in other words the chemical or energy technological utilisation of different kinds of biomasses.

For the use of wood in paper making, but also for the separation of the valuable components existing in the wood materials, it is of central importance to separate the cellulose fibres from lignin by an efficient, economic and environmentally feasible way. In addition to separate the essential components of wood or biomass it is interesting and also industrially significant to be further able to destruct the components of the biomass into fragments of essentially smaller molecular weights having industrial use. This very central problematic has been solved in this invention by a novel and technically feasible way.

As novel area of use for biomass like especially plants and plant components or the structural components of their structures like polysaccharides, oligosaccharides and lignin one can mention the refining of them in a biorefinery to chemical products or energy sources.

To decompose the natural structure of wood, and especially to separate the lignin and cellulose fibres from each other several alternative methods are known. Some of which are in a wide industrial use and well researched.

Wood and other cellulose based biomasses can be refined by using several different technologies, such as mechanical, chemical, thermomechanical or thermal conversion methods. Cellulose can be separated from wood material by using different technologies chemically, mechanically or by using a combination of these. The most important use of the cellulose is in papermaking, but also derivatives like viscose and rayon can be manufactured out of it.

SUBSTITUTE SHEET (R" ¹ ** 26)

In a sulphate process, so-called white alkali consists of sodium hydroxide and sodium sulphide, which are present in the boiling of wood chips. Thus, so-called black liquor is formed when lignin degrades and dissolves, and cellulose fibres separate to their own fibrous phase. In this method the cooking is performed at high pressure and temperature and it requires long cooking tune. Black liquor is concentrated in a multi-stage evaporator and burned for the production of energy. Sodium carbonate and sodium sulphide and small amount of sodium sulphate are formed. Moreover in the process, sodium carbonate is converted to sodium hydroxide at which the original white alkali can be regenerated. The sulphate process is the leading technology for the production of cellulose.

In a sulphite process, active sulphur containing compounds are sulphur dioxide, hydrogen sulphite ions and sulphite ions. According to the acidity of the cooking can be separated acidic sulphite process, bisulphite process, neutral sulphite process and alkaline sulphite process. Disadvantage of the sulphite process is the sulphur containing compounds used in it, which are problematic from an environmental point of view.

In the thermal mechanical pulping process the fibre mass is produced from wood by mechanical shearing and elevated temperature. The required energy consumption of the process is high, and lignin in wood stays in the product mass.

In addition to water, organic solvents are used in the so-called organosolv processes. These processes are presented among others in the reference publications: Heitz, M. et al.. Solvent effects on liquefaction: solubilization profiles of a Canadian prototype wood, Populus deltoides, in the presence of different solvents, Can.J.Chem.Eng. 72(1994)No.l2, 1021-1027, seka Gullichsen, J. ja Fogelholm, C-J., Papermaking Science and Technology, Book 6B: Chemical pulping, PI/TAPPI/Fapet Oy, Helsinki, 1999, 427 s.

So-called Alcell process uses mixture of ethanol and water in the cooking of cellulose at approximate temperature of 190-200 ⁰ C.

In the Organocell process, the cooking is performed in a mixture of methanol and alkali at temperature of 160-180 ⁰ C.

Formic acid together with peroxy formic acid has successfully been used in so-called Milox process.

Lignin is a high molecular weight, crosslinked polymer, which contains abundantly phenolic units. Thus, the separation of lignin from wood mass is not solely physical solubilization process, but it is a question of partial degradation of crosslinked lignin molecule into smaller dissolving fragments.

The patent application FI 20050811 presents a method to decompose the natural structure of biomass essentially only by using lactic acid and/or its oligomers. The method produces advantageously a water based fibre suspension that contains in addition to lactic acid and/or its oligomers lignin brought into the liquid phase and other corresponding components known to exist in a fibrous biomass and the lower molecular weight degradation products of those.

There is a great demand for the methods to decompose the binder agent components of the biomass since today the lignin produced in the forest industry is mainly combusted to produce energy although it would have a great potential value as a crude material for higher valued refined uses, and especially in the near future so called biorefinery use.

The present invention describes a continuous method and process technological solution that allows a continuous production of great amounts of lignin and other components in the fibrous biomass, and especially degradation compounds having lower molecular weight, and located into lactic acid containing liquid phase. The present invention largely solves the problems known to be present in the intensively researched pyrolytic and catalytic degradation methods based on the use of high temperatures, where degradation has been possible to achieve to a certain degree. In these processes although an essential problem has become the excessive coke formation, which reduces the yield and leads to fouling and plugging of the equipment, and thus in practice prevents the economic and technically feasible operation of the process. Now in the present method there is no such a coke formation but the reaction liquid remains in the liquid phase and easily flowing throughout the entire process. This character enables applying a genuinely continuous process design.

Regarding the entire degradation, i.e. the degradation of the biomass into the liquid phase brought macromolecular components, like lignin and polysaccharides, into compounds of essentially smaller molecular weight, the reaction conditions and process technology to be such that the said compounds originating from the biomass, at least hi part, degrade to form smaller molecular weight degradation products. The degradation products of smaller molecular weight mean in this connection molecular fragments having molecular weights of essentially less than lOOOg/mol, most often at a level of 100 - 300g/mol. These kinds of degradation products, mostly based on renewable crude materials and being typically on phenolic groups containing aromatic hydrocarbons, furanes or mono-, di- or oligosaccharides, have great interest in respect to technical use. These areas of technical uses are liquid fuel components or the precursors of those, use as a feedstock material in biotechnical processes or the use as a component in chemical industry such as a reactive component or as polymerizing monomers.

Quite a special need is to find new technologies to utilize the lignin separated from wood fibres. The degradation reactions of lignin have been researched a lot, as an example one can mention among others Doctoral dissertation by Vuori, A.: "Thermal and catalytic reactions of the C-O bond in lignin and coal related aromatic methyl esters", Acta Polytechnica Scandinavica Ser. Ch 176 (1986). The catalytic degradation methods have however faced strong side reactions as problems such as coke formation and uncontrolled polymerization. The present invention presents now a novel solution and a better process technical solution to overcome these problems.

Earlier has been observed that the natural structure of a cellulose based biomaterials, especially wood, can be decomposed partially or entirely and thus transform the wood material into a plastic and partially solubilised form. This means thus that the main components like lignin and cellulose separate from each other in a way that the lignin component at least partially or even totally will be solubilised and the cellulose component remains dispersed in a fibrous form into the liquid phase. The above described degradation occurs when the cellulose based biomaterials such as chopped wood or wood in another suitable form will be heat treated, for example cooked or refluxed in a liquid containing as the main or only component lactic acid, aqueous solution of lactic acid or oligomeric or polymeric lactic acid. Now in the present invention the degradation process of the biomass has been progressed essentially longer and into a level that has not been able to reach

before. This means in our invention that the components of solubilised lignin fragments molecules from biomass among others can be successfully decomposed with a good yield and essentially without harmful side reactions to form compounds having the molecular weight even below lOOOg/mol.

Especially unexpected and inventive is the fact that the method and equipment according to the present invention enables effectively a batchwise or continuous process that degrades large quantities of biomass and/or its components like lignin into molecules of essentially lower molecular weights such as monomers or oligomers. So there is to be seen a great potential for the exploitation of the method according to this invention as a crude material source for further refining. Its applications include the possibility to construct closed, energy saving, renewable materials using degradation, recovery and refining methods to form useful compounds from biomass, especially from degradation products of lignin molecules. The biomass being like wood, wood chops or dust, or straw type of non- woods or their components, or even peat or its components.

A significant benefit of the use of lactic acid to degrade the structure of wood, and separate them from each other and to transform them into solubilised form is that there is no need to use sulphur containing compounds in the process. The method is suitable also for the exploitation, separation, molecular fragmentation and/or recovery of other biomasses such as straw biomass and peat, different valuable components, like betulin, hemicellulose, lignin, lignanes, phenolic compounds and saccharides just to mention a few.

There is a significant environmental aspect in the method according to this invention. Lactic acid can namely be produced by using some biomass based crude sugar source through a fermentation process. This is thus a technology and a method that utilizes renewable crude materials sources. Lactic acid exists in two different stereoforms, L- and D-form. In addition their blend i.e. racemic lactic acid is known. According to this invention all the different forms of lactic acid are possible to use One also has to notice that lactic acid exists most commonly in an aqueous solution, but it starts to polymerize when water is removed, first to form oligomers and then later on to form larger molecular weight polymers. The polymerization is a natural and easily detectable phenomenon and it can be accelerated by using suitable catalysts such as stannous-octoate. In suitable

conditions lactic acid forms a dimer i.e. lactide, that also alternatively can be used as a chemical for degradation according to the invention.

The method according to this invention enables also a production process that is based almost entirely on closed circulations, because lactic acid can be recovered from the product stream after cooking and thereafter it can be recirculated back in the process.

In the method according to this invention the lactic acid and/or an aqueous solution of its oligomers and the biomass or its fragments are mixed together to form a mixture or a solution. In one of the advantageous forms of applications the capability of lactic acid to dissolve lignin at very high concentrations to form a homogeneous solution that can be pumped continuously through a continuous reactor. We have namely observed as an essential part of the present invention that lignin that is produced in large quantities as a side product in forest industry, can be solubilised in an extremely wide concentration range into lactic acid from for example dry powder form. As much as over 80wt% of lignin has been solubilised into 88% aqueous lactic acid solution. The solubilised form of the feed together with the fact that there are no significant side reactions, like coke formation, enable an essentially continuous operation of the process.

The lignin in the feed of a continuous process can originate from a conventional cellulose process, or from a process described in the patent application FI 20050811 that utilizes lactic acid in a cellulose fibre production process.

The degradation process according to the invention can be operated either by using a batch wise or a continuous process, by using a stirred tank reactor or a pipe reactor. The applicable pressure and temperature range is wide, and its selection depends essentially on the quality of the used biomass. Typically the temperature can be in the range of 130 -350

⁰ C, and the residence time in the reactor typically from 10 minutes up to several hours, depending on the reaction conditions and the quality of the feed and also on the demand of the extent of the degradation and scission of the molecules.

The most essential characteristic features of the invention are presented in the claims.

One advantageous form and process of performing the invention has been presented as a block diagram in Figure 1 , which thus presents one form of performing the invention however not to exclude other possible industrial ways and possibilities.

Through line 1 the lactic acid containing aqueous solution, for example lignin solubilised into lactic acid, or a mixture after cooking containing also other components in addition to lignin, such as fibre fractions, polysaccharides and hemicellulose included, is fed from the storage tank into the pump 2. Pump 2 can advantageously be any kind of a pump capable of pumping the fluids of this connection, and possibly also liquids containing solid particles to a certain extent into an appropriate pressure, possibly more than lOObars. The pump can advantageously be a piston pump or a gear pump. The pressure level on the pressure side can be followed with a pressure indicator 3. The biomass containing feed stream essentially mixed or solubilised with lactic acid will be then flowing into a reactor 4, which most likely is a pipe reactor or a plug flow reactor having a length of several meters, up to a length of hundreds of meters, or alternatively into an autoclave reactor, with a agitation or not. Both of the reactors being advantageously filled with liquid without a gas phase. Additionally the reactors can be equipped with dynamic or static mixers, that however being not always necessary. The reactor is having strength to resist the required pressure levels and temperatures and being manufactured out of a material that resists lactic acid advantageously out of a acid resistant steel. Several of these kinds of reactors can be installed in parallel or in series together if necessary. The reactor or reactors are installed into a heated chamber 5 or they are heated by using another suitable heating technology such as heating jacket, that enables the reaction mass to reach the necessary elevated reaction temperature , that is advantageously in the range of 150 ... 350 ⁰ C. The reactor over pressure is maintained with a pressure valve 6. The product stream is cooled down at the end of the continuous reaction stream or at the outlet stream with a cooling stream of water or another cooling medium 7 in the jacket 8, and will be conducted through the pressure valve 6 and the product pipeline 9 into a product tank (not indicated in the Figure 1), and further into the separation of lactic acid and water from the product. The lactic acid and water will be circulated in the process.

The method enables a very complete degradation of the biomass, and especially advantageous degradation of the lignin molecules to form essentially smaller molecular size fragments. The molecular weight levels can be measured by using gel permeation

chromatography, which indicates the levels of typically below 3000g/mol, advantageously below lOOOg/mol, and especially advantageously in the range of 50 -300 g/mol.

The present invention will be illustrated more in detail by the following examples in which the biomass and aqueous lactic acid together forming a reaction mass and a liquid phase will be called together with a term "black liquor":

Example 1

The cooking of lactic acid and chopped wood

The cooking was performed in 100ml glass flask, which was equipped with a vertical cooler and a magnetic stirrer. Into the flask was weighted 40g of lactic acid (88-% aqueous solution, 97.5 weight -%) and Ig of chopped wood (2.5 wt-%). The flask was immersed into an oil bath at 100 ⁰ C, where it was held for 4 hours, meanwhile the mixture was refluxing. The temperature was increased into 145 ⁰ C and the mixture cooking was still for 4 hours. As a product a dark mixture was recovered, in which the lignin was significantly dissolved and the wood material was plasticized. The fibres were separated from the liquid form black liquor by filtration and the black liquor was recovered.

Thus prepared black liquor was conducted into a pipe reactor with a pump. The pipe reactor being 3 mm of its diameter and 3 m in length. The residence time in the reactor was adjusted stepwise with the pumping speed between 5 min ... 2 h. Samples were recovered corresponding each of the residence times at the outlet of the pipe reactor. The molecular weight distributions were measured and lignin was observed to be in a form of significant degradation, molecular weight level 200 - 1000g/mol.

Example 2

The cooking of lactic acid and chopped wood by using higher solids content

The cooking was performed as described in the example 1, but by using the following amounts, and by keeping the temperature all the time at 145 ⁰ C. 50 g of lactic (88-% aqueous solution, 85 weight -%) acid and 1Og (15 wt-%) of chopped wood were added

into the flask and were refluxed for 5h. Black slurry was recovered as a product, in which the lignin contained in the wood material was in a solubilised form and the cellulose fibres clearly separated and observable. The cellulose fibres were filtered out of the black liquor, which was recovered for the further processing. Furthermore the black liquor was conducted by a pump into a pipe reactor having a diameter of 3 mm and a length of 3 m. The residence time in the reactor was regulated by the pumping speed to be around Ih. The temperature of the pipe reactor was adjusted by regulating the sand bath temperature to the levels: 150 ⁰ C, 180 ⁰ C, 250 ⁰ C and 300 ⁰ C. Samples were recovered from the outlet for each of the temperatures. The molecular weight distributions were measured for each of the samples, and highly degraded lignin fragments detected, molecular weights in the range of200 - 1000 g/mol.

Example 3

Cooking of aqueous lactic acid and chopped wood under stirred conditions

The cooking was performed by using a 250ml reaction flask that was equipped with a vertical condenser and a propeller type agitator. The flask was charged with 150g lactic acid ( 88 wt-% aqueous solution, 85 wt-% of the total mass) and 30g of chopped wood (15 wt-%). The flask was immersed to an oil bath and the mixing was started with a stirrer speed of 70rpm, so that the torque of the agitation was 23,5 Ncm. The temperature was rapidly increased to 145 ⁰ C, with a torque value of 18,6 Ncm. After an hour the stirring speed was increased to 140 rpm, under which conditions the mixture was let to cook for 10 hours. As the product black slurry was recovered, where the lignin and corresponding components were solubilised in the liquid phase, and cellulose separately as a phase dispersed in the solution. The fibres were filtered separately from the solution, and the black liquor was stored for a later use.

Example 4

Chopped pine particles ( 10 g) were charged into an open beaker. 40 g of aqueous solution of 88 wt-% lactic acid was added. The temperature was increased to 140 - 160 ⁰ C and the mixture was agitated by using a magnetic stirrer. These conditions were maintained for 3 hours.

Some separation of lignin from the wood mass was observed already after 15 minutes cooking time. As a result a dark viscous mass was recovered formed out of the wood particles from the cooking, where lignin was solubilised and fibers separated. The fibers were separated by using filtration.

Example 5

The experiment in example 4 was repeated, however with the difference that now the temperature was all the time 130 -140 ⁰ C and the time of the cooking was 4 hours. During the cooking the water that was evaporated from the beaker was replaced so that the volume of the mass remained constant and the viscosity remained at a low level.

The wood material was observed to become softer in the beginning, lignin to dissolve into the liquid phase and the cellulose fibres to be separated from the wood material. Finally the wood particles disappeared totally when lignin was dissolved and cellulose fibres were separated from each other. The black liquor was separated as a permeate in fibre filtration.

Example 6

Pieces of bamboo were crushed mechanically to make grinded particles. 1Og of this bamboo mass was placed into a flask with a vertical cooler and which was placed into an oil bath. Into the flask was added 50 ml of solution containing 88% lactic acid in water. The mixture was refluxed for 4 hours, where after the natural structure of bamboo was visibly degraded and the cellulose fibres separated to form an own dispersed phase so that they could be separated by filtration, washed and dried. A lignin containing liquid fraction i.e. black liquor was recovered as a permeate.

Example 7

The experiment according to the example 6 was repeated, however in the way that the biomass used was smashed straw.

The natural structure of the biomass was observed to have degraded and the cellulose fibres to have been separated. The fibrous component was separated and recovered and as the filtrate a lignin containing liquid so called black liquor was recovered.

Example 8

Degradation of chopped wood to form low molecular weight fragments

The cooking of lactic acid and wood chops. The cooking was performed in a 1000ml pressure reactor. The reactor was charged with 40Og of lactic acid ( 88-% aqueous solution,

97.5 weight % of the total mass and 1Og ( 2.5 wt-%) of chopped wood. The reactor was immersed into an oil bath and the temperature was elevated into 180 ⁰ C and cooking was continued until 4 hours. As the product a dark mixture was recovered, in which the lignin was significantly solubilised and wood material disintegrated. The fibre structure was also largely degraded, and thus a fluid was formed that was easy to pump.

Thus recovered black liquor was conducted into a pipe reactor having a diameter of 3 mm and length of 3 m. The residence time was controlled stepwise through the pumping speed into the range between 5 min ... 2 hours. Samples were recovered corresponding each residence time at the outlet. The molecular weights were measured for each of the samples, and lignin was detected to be in a form of far reached degradation, the molecular weight range being 200 - lOOOg/mol.

Example 9

The degradation of straw mass

The experiment was repeated according to the example 8, but now by using wheat straw as the biomass.

As an end product highly degraded biomass was recovered, molecular weight level being below 1000g/mol.

Example 10

The degradation of sulphate lignin

5Og of powder form lignin produced by sulphate method was solubilised into 40Og of 88% aqueous solution of lactic acid by mixing the components and thereafter heating.

The cooking was performed in a 1000ml pressurized reactor. The above mentioned lignin solution was fed to the reactor. The reactor was immersed into an oil bath of 100 ⁰ C and the temperature was increased into the temperature of 180 ⁰ C and the mixture was cooked further up to 4 hours. As the product a dark mixture was recovered in which the lignin was significantly degraded and the end product was an easily flowing mass that could be pumped.

Thus recovered black liquor was conducted into a pipe reactor having a diameter of 3mm and length of 3m. The residence time was controlled stepwise through the pumping speed into the range between 5min ... 2hours. The pipe reactor was installed into a sand bath having a temperature of 180 ⁰ C. Samples were recovered corresponding each residence time at the outlet. The molecular weights were measured for each of the samples, and lignin was detected to be in a form of far reached degradation, the molecular weight range being 200 - lOOOg/mol.

Example 11

The previous experiment number 10 was repeated however in the way, that now the reactor was a pipe reactor, into which the lignin solubilised into a lactic acid was fed by using a pump. Samples were recovered corresponding each residence time at the outlet. The molecular weights were measured for each of the samples, and lignin was detected to be in a form of far reached degradation, the molecular weight range being 200 - 1000g/mol.

Example 12

The fragmentation of the lignin recovered in a lactic acid cooking

Black liquor produced and recovered as a permeate with a method according to the example 3 was fed with a pump into a pipe reactor having the diameter of 3 mm and the length of 3 m. The residence time was controlled stepwise through the pumping speed into the range between 5 min ... 2 hours. The pipe reactor was installed into a sand bath having a temperature of 180 ⁰ C. Samples were recovered corresponding each residence time at the outlet. The molecular weights were measured for each of the samples, and lignin was detected to be in a form of far reached degradation, the molecular weight range being 200 - lOOOg/mol.

It is clear to a person skilled in the art that the possible forms to apply this invention are wide and are not limited to these examples but can be variable in wide range of variations within the characteristic features presented in the claims of this patent.