Process for the Production of a Saccharide Product from an Aqueous Solution

Abstract

Saccharides are produced from an aqueous solution which solution comprises saccharides and by-products, in a process, comprising: in a mixing zone admixing the aqueous solution with a carrier liquid in which the saccharides are insoluble and that has a boiling point higher than that of water to obtain an aqueous admixture; removing water from the aqueous admixture to obtain a first carrier liquid phase comprising carrier liquid, by-products and saccharides; separating the saccharides from the first carrier liquid phase to obtain a crude carrier liquid, comprising by-products and carrier liquid, and a saccharide product, wherein the process further comprises: subjecting at least a portion of the crude carrier liquid to a liquid-liquid extraction with a first solvent to obtain a by-product-rich solvent phase and a by-product-lean carrier liquid phase; and recycling at least a portion of the by-product-lean carrier liquid phase to the mixing zone.

Claims

1. A method for the production of saccharides from an aqueous solution, which solution comprises saccharides and by-products, which comprises: in a mixing zone admixing the aqueous solution with a carrier liquid in which the saccharides are insoluble and that has a boiling point higher than that of water to obtain an aqueous admixture; removing water from the aqueous admixture to obtain a first carrier liquid phase comprising carrier liquid, by-products and saccharides; separating the saccharides from the first carrier liquid phase to obtain a crude carrier liquid, comprising by-products and carrier liquid, and a saccharide product, wherein the method process further comprises: subjecting at least a portion of the crude carrier liquid to a liquid-liquid extraction with a first solvent to obtain a by-product-rich solvent phase and a by-product-lean carrier liquid phase; and recycling at least a portion of the by-product-lean carrier liquid phase to the mixing zone.

2. A method according to claim 1, wherein the aqueous solution is a hydrolysate of biomass, preferably a hydrolysate of wood.

3. A method according to claim 1, wherein the aqueous solution contains an acid selected from the group consisting of hydrochloric acid, hydrobromic acid, sulfuric acid, nitric acid, formic acid, acetic acid and combinations thereof, the aqueous solution preferably containing hydrochloric acid.

4. A method according to claim 1, wherein the aqueous solution comprises at least one selected from the group consisting of glucose, fructose, mannose, galactose, arabinose, xylose, sucrose, cellobiose, glucose dimers, glucose trimers, maltose, cellotriose, maltotriose, cellodextrins, dextrins, xylan-oligosaccharides, mannan-oligosaccharides, arabinan-oligosaccharides, oligofructans, starch, cellulose and combinations thereof.

5. A method according to claim 1, wherein the by-products comprise oxygenated organic compounds having 10 to 25 carbon atoms.

6. A method according to claim 1, wherein the aqueous solution comprises from 5 to 35% wt saccharides, 0.1 to 10% wt by-products and 5 to 45% wt acid, all percentages based on the aqueous solution.

7. A method according to claim 1, wherein the carrier liquid is immiscible with water.

8. A method according to claim 1, wherein the carrier liquid has a boiling point of at least 175 C.

9. A method according to claim 1, wherein the carrier liquid is a hydrocarbonaceous oil comprising hydrocarbons with 8 to 50 carbon atoms.

10. A method according to claim 1, wherein water and acid are removed from the aqueous admixture by evaporation in an evaporation step.

11. A method according to claim 10, wherein the evaporation step is conducted in one or more of the equipment selected from a stirrer evaporator, forced circulation evaporator, natural circulation evaporator, falling film evaporator, rising film evaporator, rising-falling film evaporator, thin film evaporator (also known as a wiped film evaporator), short path distillation evaporator, falling film short path evaporator, fluidized bed evaporator, falling film counterflow trickle evaporator, and spiral tube evaporator.

12. A method according to claim 11, wherein the evaporation step is conducted first in a falling film evaporator followed by a forced recirculation evaporator.

13. A method according to claim 10, wherein the evaporation step is carried out at a temperature in the range of 50 to 120 C.

14. A method according to claim 10, wherein the evaporation step is carried out at a pressure below 400 mbar, preferably ranging from 50 to 300 mbar.

15. A method according to claim 1, wherein saccharides are separated from the first carrier liquid phase comprising carrier liquid, by-products and saccharides, by means of settling, centrifugation, filtration, hydrocyclone separation and combinations thereof.

16. A method according to claim 1, wherein the first carrier liquid phase comprising carrier liquid, by-products and saccharides is mixed with a second solvent that is immiscible with the carrier liquid and in which saccharides are soluble to yield two liquid phases, and wherein the two liquid phases are separated to yield a second solution comprising saccharides dissolved in the second solvent as one phase, and the crude carrier liquid as the second phase.

17. A method according to claim 16, wherein the carrier liquid is immiscible with water and the second solvent is water.

18. A method according to claim 1, wherein the first solvent is an oxygen-containing organic compound.

19. A method according to claim 18, wherein the organic compound is selected from an alcohol, an ether, an aldehyde, a ketone, an ester of a carboxylic acid, a carboxylic acid and combinations thereof.

20. A method according to claim 1, wherein a portion of the by-product-rich solvent phase is subjected to evaporation to yield a purified first solvent vapor and a by-product-laden residue.

21. A method according to claim 20, wherein the purified first solvent vapor is condensed and the condensate thus obtained is recycled to the liquid-liquid extraction.

22. A method according to claim 20, wherein the by-product-laden residue is discharged.

Description

[0039] The invention will be further illustrated by means of the accompanying FIGURE showing a simplified flow scheme for a process wherein the present process can be applied.

[0040] Referring to the FIGURE a biomass material such as woodchips or wood pellets is fed via a line 1 into a hydrolysis reactor 2. When the hydrolysis reactor 2 has been filled a stream of concentrated hydrochloric acid in water, supplied by a line 3, is passed along the biomass material. The concentrated hydrochloric acid typically has a concentration of hydrochloric acid in the range of 35 to 45% wt, based on the stream. In addition to hydrochloric acid and water, the stream may comprise one or more other components, e.g. C.sub.1-C.sub.4 carboxylic acids, such as formic acid and/or acetic acid. In the FIGURE only one reactor has been shown. The skilled person will realize that the reaction section in the process described may comprise one or more reactors, e.g. up to 10 reactors, that are arranged in series. In addition, one or more spare reactors may be provided which allow for an operation in a swing method. The hydrochloric acid-containing stream achieves hydrolysis of the carbohydrate polymeric material that is present in the biomass yielding as hydrolyzate an aqueous solution of saccharides, by-products and hydrochloric acid. The hydrolyzate is withdrawn from the reactor 2 via a line 4. In the FIGURE only one hydrolyzate stream has been shown. It will be realized that the in some operations it may be advantageous to conduct the hydrolysis such that first a pre-hydrolyzate is obtained and subsequently a final hydrolyzate. The composition of the saccharides in the pre-hydrolyzate and the final hydrolyzate will be different, which may facilitate the recovery of certain saccharides.

[0041] The hydrolyzate is passed to a mixing vessel 5 wherein it is mixed with a stream of carrier liquid, supplied via a line 6. The aqueous admixture obtained is withdrawn from the mixing vessel 5 via a line 7 to an evaporation column 8. The evaporation column is provided with heat exchange surfaces (not shown) which are heated by the introduction of a heat exchange medium, such as steam, via a line 9 and the cooled heat exchange medium is withdrawn via a line 10. In the evaporation column 8 a vapor of hydrochloric acid, water and optionally low-boiling carboxylic acids, is obtained via a line 11. The vapor may be condensed and recycled to the hydrolysis reactor 2. Preferably, the vapor will be subjected to re-concentration to improve the hydrolysis (not shown). Although in the FIGURE an evaporation column has been shown as separation vessel it is evident that different methods to separate the carrier liquid with the saccharides and by-products on the one hand and the water and acid on the other hand are available, and can be used in the present process.

[0042] A first carrier liquid phase, comprising carrier liquid, saccharides and by-products, is obtained in the evaporation column 8 and is recovered via a line 12. The first carrier liquid phase is passed to a separation vessel 13. The vessel 13 may be a settling vessel or any other separator that is suitable to separate the saccharides obtained from the carrier liquid. A saccharide product is obtained from the separation vessel 13 and recovered via a line 14. A stream of crude carrier liquid comprising the carrier liquid and by-products is withdrawn from the separation vessel 13 via a line 15. The crude carrier liquid is passed to a splitter 16, wherein the crude liquid is divided into a recycle stream, withdrawn via the line 6, a waste stream, withdrawn via a line 18, and a third stream withdrawn via a line 19. The recycle stream in the line 6 is recycled to the mixing vessel 5.

[0043] The third stream of crude carrier liquid in the line 19 is passed to a liquid-liquid extraction column 20. In the column 20 the stream of crude carrier liquid is contacted with a stream of first solvent, such as methanol, ethanol, acetone or mixtures of alcohols and ketones. The first solvent is passed into the extraction column by a line 22. By-products dissolve in the first solvent to from a by-product-rich solvent phase and a by-product-lean carrier liquid phase. The by-product-lean carrier liquid phase is withdrawn from the extraction column 20 via a line 21. It is combined with line 6 to provide for a stream of carrier liquid to be recycled to the mixing vessel 5. To supplement the amount of carrier liquid that is to be fed into the mixing vessel 5 an amount of make-up carrier liquid supplied via a line 17 is added to the liquid in the line 6. In the FIGURE the make-up carrier liquid is added to the liquid in line 6.

[0044] The skilled person will realize that any make-up carrier liquid may also be fed into the mixing vessel 5 separately from the recycle liquid in line 6.

[0045] By-product-rich solvent phase is withdrawn from the extraction vessel via a line 23. It is advantageous to separate the first solvent from the by-products in this by-product-rich solvent phase. Since the first solvent can be selected such that the evaporation thereof is simple and cost-effective, a suitable separation method is evaporation. Thereto, the by-product-rich solvent phase in the line 23 is fed into a second evaporation column 24. The first solvent is evaporated on the heating surfaces that are arranged in the column 24. These heating surfaces are heated by the introduction of a heated heat transfer medium, such as steam, via a line 25 and the withdrawal of cooled heat transfer medium via a line 26. The evaporation of the by-product-rich solvent phase results in a vapor of purified first solvent that is withdrawn from the column 24 via the line 22. The purified first solvent vapor is condensed to form a liquid again (not shown). Any first solvent that is required to make up for any losses is provided via a stream of make-up first solvent supplied via a line 27. In the FIGURE the make-up first solvent is added to the liquid in line 22. The skilled person will realize that any make-up first solvent may also be fed into the column 24 separately from the condensed purified first solvent vapor in line 22.

[0046] From the column 24 also a by-product-laden residue, typically a liquid stream comprising by-products and, optionally, some carrier liquid, is obtained. This stream of by-product-laden residue is withdrawn from the evaporation column 24 via a line 28. If desired, the stream of the line 28 may be combined with the stream of the line 18 to a form a stream rich in by-products that is withdrawn via a line 29. The by-products may be isolated from this stream, if desired, or the stream, including the by-products, may be discharged or combusted.

[0047] The following example illustrates the suitability of the present invention.

EXAMPLE

[0048] Six compounds were dissolved in two different carrier liquids. The six compounds were exemplary for the by-products that may be obtained when wood is subjected to hydrolysis by the reaction of concentrated hydrochloric acid and that may be obtained when the hydrolyzate thus obtained in treated with the carrier liquid. The compounds were [0049] a) betulin, a triterpene having a pentacyclic structure and two hydroxyl groups, [0050] b) abietic acid, i.e. a diterpene compound derived from four isoprene units and a having one carboxylic acid group, [0051] c) linoleic acid, a fatty aid having 18 carbon atoms and two unsaturated bonds, [0052] d) 1-eicosanol, a linear alkanol having 20 carbon atoms, [0053] e) sitosterol, a phytosterol with a chemical structure similar to cholesterol, and [0054] f) limonene, a cyclic terpene having two unsaturated bonds.

[0055] Carrier liquid 1 is a paraffin oil with a boiling range of 388 to 709 C. and a kinematic viscosity of 481 mm.sup.2/s at 40 C. and a kinematic viscosity of about 31 at 100 C. (ASTM D445). Carrier liquid 1 is immiscible with water.

[0056] Carrier liquid 2 is a poly-alpha-olefin having a kinematic viscosity of 1240 mm.sup.2/s at 40 C. and a kinematic viscosity of 100 mm.sup.2/s at 100 C. (ASTM D445). It has a flash point of 283 C. (ASTM D92). Carrier liquid 2 is immiscible with water.

[0057] The concentrations of the six compounds in Carrier liquids 1 and 2 are shown in Table 1.

TABLE-US-00001 TABLE 1 Concentration of compounds in Carrier liquids (% wt, based on Carrier liquid). Organic compound Carrier liquid 1 Carrier liquid 2 betulin 0.009 0.018 abietic acid 0.093 0.069 linoleic acid 0.107 0.080 1-eicosanol 0.053 0.044 sitosterol 0.100 0.070 limonene 0.084 0.063

[0058] The experiments were carried out with three different organic solvents, viz. methanol, butanol and acetone.

[0059] In each experiment, 2 mL of an organic solvent was added to 3 mL of the carrier liquid solutions. The admixture obtained were shaken for 60 min at room temperature. The concentration of each compound in each of the carrier liquids was determined and the partition coefficient was calculated. By partition coefficient P is understood the ratio of concentrations of each of the compounds in an organic solvent and in a carrier liquid. The partition coefficient is expressed as

[0060] log P, being log {[compound].sub.carrier liquid/[compound].sub.organic solvent}.

[0061] The partition coefficients are shown in Table 2 for Carrier liquid 1 and in Table 3 for Carrier liquid 2. A negative coefficient indicates that the compound in question preferentially dissolves in the organic solvent.

TABLE-US-00002 TABLE 2 Partition coefficient with Carrier liquid 1 Log P Exp. abietic linoleic 1- sitos- limo- No. Solvent betulin acid acid eicosanol terol nene 1 methanol n/d 0.30 0.45 0.41 0.35 0.24 2 butanol n/d 0.19 0.26 0.79 0.45 0.23 3 acetone n/d 0.26 0.44 0.28 0.16 0.21 n/d: not determined

TABLE-US-00003 TABLE 3 Partition coefficient with Carrier liquid 2 Log P Exp. abietic linoleic 1- sitos- limo- No. Solvent betulin acid acid eicosanol terol nene 4 methanol 0.36 0.14 0.92 0.78 0.05 0.46 5 butanol 1.09 0.22 0.77 1.16 0.63 0.06 6 acetone 1.03 0.31 1.04 0.59 0.10 0.05

[0062] The experiments show that the organic compounds dissolve in each of the organic solvents. All three solvents are suitable for use in the present process. Dependent on the carrier liquid and by-product the skilled person may select the most desirable combination.