NL1039316C2

NL1039316C2 - Process for the production of substantially pure monomers from biopolymers.

Info

Publication number: NL1039316C2
Application number: NL1039316A
Authority: NL
Inventors: Jacob Spronsen; Geert-Jan Witkamp
Original assignee: Univ Delft Tech
Priority date: 2012-01-23
Filing date: 2012-01-23
Publication date: 2013-07-25

Description

Title: Process for the production of substantially pure monomers from biopolymers

The present invention is directed to the production of substantially pure monomers from biopolymers in an aqueous system.

In chemical industry, there is a need for new or alternative feedstocks for producing various chemicals. Also there is a need for processes 5 to produce pure monomers from biopolymers.

Biopolymers form a promising source of chemicals, provided there is a suitable way of recovering the chemicals, or precursors in an efficient and economic way. Also the materials need to be pure enough to be used in subsequent processes.

10 Such biopolymers are, for example, present in biomass (especially lignocellulosic biomass), but also in plants and other natural materials, such as waste from the bio-industry. Also some biopolymers may be produced in plants or otherwise, using genetic modification.

Other biopolymers may be in the form of proteins, sugar polymers, 15 or amino acid polymers. The monomeric components of the biopolymers may be of one type, i.e. glucose, xylose or a specific other sugar or amino acid, but it is also possible that a mixture of monomers is present, such as in proteins.

Lignocellulosic biomass refers to plant biomass that is composed of cellulose, hemicellulose, and lignin. The carbohydrate polymers (cellulose and 20 hemicelluloses) are tightly bound to the lignin. Lignocellulosic biomass can be grouped into four main categories: agricultural residues (including corn stover and sugarcane bagasse), dedicated energy crops, wood residues (including sawmill and paper mill discards), and municipal paper waste.

Biomass is an important source of raw materials for chemical 25 products. More in particular, biomass may be decomposed into smaller molecules, more in particular sugars, by hydrolysis and after recovery the sugars can be used as such or as raw material for further reaction.

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In order to be able to use these sugars in an economically attractive way, it is important to have an efficient process for recovery of the sugars that results in a very pure material.

It is an object of the present invention to provide a process for a 5 process for the production of monomers from biopolymers, which is economic, while at the same time producing substantially pure monomers, that may be used as such or can be used as starting material in the production of other chemicals. Other objects of the invention will be apparent from the further description.

10 The process of the present invention is accordingly directed to a process for the production of substantially pure monomers from a biopolymer, which process comprises feeding an aqueous solution or slurry of at least one biopolymer to a catalytic hydrolysis step using a catalyst, optionally removing solids from the reaction mixture obtained in the hydrolysis step, subjecting the 15 said reaction mixture to eutectic freeze crystallization, thereby obtaining an ice fraction, substantially pure monomer in solid form and a mother liquor containing said catalyst dissolved therein, and recycling at least part of the said mother liquor to the said hydrolysis step.

This integrated process produces substantially pure monomers, as 20 well as ice, which may be used to produce pure water, for example for use elsewhere in the production facilities, such as for producing steam, or as drinking water.

In the first step, the biopolymer is hydrolysed. The hydrolysis is preferably acid catalysed, but it is also possible to have an enzymatic or a base 25 catalysis. The catalyst may be dissolved in the aqueous solution.

In case the biopolymer is not dissolved in the aqueous system, the catalyst is preferably dissolved. When using a solution of a biopolymer in water, the catalyst may be dissolved, but can also be in solid form or present on a support material.

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An acidic catalyst has preferably a pKa of <2, resulting in an efficient hydrolysis of the biomass into the constituent molecules. Various acids may be used, with a preference for mineral acids, such as sulphuric acid, nitric acid, phosphoric acid, hydrochloric acid and the like. When a base 5 catalyst is used, the pK is preferably >12.

The resulting reaction mixture contains the monomers, the catalyst, and possibly various byproducts, such as acetic acid. The reaction mixture is fed to a eutectic freeze crystallization step, in which step the reaction mixture is split into three flows, namely an ice fraction, a sugar fraction and a mother 10 liquor.

The mother liquor is recycled and reintroduced into the hydrolysis step, or upstream thereof. The mother liquor may be subjected to an additional treatment step, for example stripping, to remove components that are preferably not recycled or that will build up in the system. Stripping may be 15 used to remove acetic acid. In addition a small bleed stream may be applied to prevent other components from building up in the system.

The present invention is i.a. based on the use of an eutectic freeze crystallization step. This is a well-known process, for example described in US patent specification No. 7,127,913, the contents of which is incorporated herein 20 by way of reference.

Eutectic freeze crystallisation is a process based on separation of components at a eutectic freezing point. Eutectic freeze crystallisation has been described in EP-A 1,230,194 and in Chem.Eng.Proc. 37, (1998), pp 207-213.

25 In freeze crystallisation at a eutectic freezing point (Eutectic freeze crystallisation; EFC) on the one hand crystalline material is obtained, and on the other hand ice crystals.

As has been described in the cited references, EFC is based on the principle that a solution of a salt in water exhibits a eutectic freezing point. In 30 the phase diagram water-salt, it can be seen that in case an undersaturated 4

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water salt mixture is cooled down to the freezing point thereof, ice crystals form first. This increases the salt concentration in the solution and decreases the temperature along the freezing point depression line, until the solution is saturated. At this composition the eutectic freezing point is reached. Further 5 heat withdrawal results in simultaneous formation of both ice crystals and crystals of salt. In case the solution becomes (or is) saturated, first the salt will crystallise and the temperature will decrease along the solubility line, until an eutectic freezing point is reached. Then simultaneous formation of both ice crystals and crystals of salt occurs again at or near the eutectic point of the 10 specific combination of compounds. In continuous operation, the operation point will therefore lie close to the eutectic point, irrespective of the feed composition.

Due to the difference in density and/or particle size, the crystals of salt and the ice can be recovered separately.

15 The monomers produced by the process will depend on the nature of the feed stream. Suitable feed streams are cellulose, hemicellulose, lignocellulose containing materials, sugar polymers, polylactic acid and polyleucine containing materials. Other suitable materials are waste streams from the agro and food-industry, such as slaughter waste (collagen and the 20 like), starch.

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The invention is now elucidated on the basis of the following, nonlimiting examples.

5 EXAMPLE

Production of glucose from starch.

350 G. of starch was added to 650 g of water and 1000 U/kg alpha 10 amylase. After 2 hours at 100°C the mixture was cooled to 65°C and 200 U/kg amyloglucosidase was added. After stirring for 48 hours the resulting solution containing D-glucose and the enzymes was cooled down. In the second part of the process the D-glucose solution was fed into a cooling crystallizer that was operated in a continuous mode. The temperature inside the crystallizer was 15 kept just below the eutectic point at -9°C. At this temperature ice and D- glucose monohydrate crystallized from the solution. The ice and the D-glucose were separated by gravitation, filtered and washed yielding pure ice and pure D-glucose monohydrate. The motherliquors from the filtration and the washing liquids were fed back into the crystallizer. A small bleed stream (10% 20 of the main stream) containing all the enzymes was obtained from the crystallizer.

The bleed stream with the enzymes was used in the starch hydrolysis step. 350 G. of starch was added to 550 g of water and 100 g of bleed stream. After 2 hours at 100°C the mixture was cooled to 65°C. After stirring 25 for 48 hours the resulting solution containing mainly D-glucose was cooled down and fed into the cooling crystallizer.

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Claims

A method for the production of substantially pure monomers from a biopolymer, the method comprising: supplying an aqueous solution or slurry of at least one biopolymer to a catalytic hydrolysis step using a catalyst, optionally removing solids from the reaction mixture obtained in the hydrolysis step, subjecting said reaction mixture to eutectic freeze crystallization, thereby obtaining an ice fraction, substantially pure monomer in solid form and a mother liquor containing said catalyst dissolved therein, and recycling at least 10 a portion of said mother liquor to said hydrolysis step.

The method of claim 1, wherein the catalytic hydrolysis step is an acid, base or enzyme catalyzed hydrolysis step.

The method of claim 2, wherein the pKa of the acid is <2.

4. Process according to claim 3, wherein the sulfuric acid is used as the catalyst.

The method of claims 1 to 4, wherein the recycle of the mother liquor is purified.

The method of claim 5, wherein said purification comprises stripping the mother liquor to remove acetic acid.

The method of claims 1 to 6, wherein the feed containing said biopolymer is a biomass.

The method of claim 7, wherein said biomass is selected from the group of cellulose, hemicellulose, lignocellulose-containing materials, sugar polymers, and polyleucine-containing materials.

The method of claims 1 to 6, wherein said biopolymer is a sugar polymer, a protein, an amino acid polymer, DNA, RNA.

The method of claims 1 to 9, wherein the sugars produced are xylose or glucose.