Xylose crystals

Abstract

A method for producing xylose crystals is disclosed. The method comprises conducting the following steps one after the other in this order: - providing a crude feedstock of hardwood-derived carbohydrates in the form of a crude liquid fraction; - subjecting the crude liquid fraction to a first chromatographic treatment; - optionally subjecting the first purified liquid fraction to evaporation; - subjecting the first purified, and optionally evaporated, liquid fraction to a second chromatographic treatment to recover a second purified liquid fraction; - optionally subjecting the second purified liquid fraction to evaporation; - subjecting the second purified, and optionally evaporated, liquid fraction to crystallization treatment; to produce xylose crystals.

Description

[0001] XYLOSE CRYSTALS

[0002] TECHNICAL FIELD

[0003] The present disclosure relates to a method for producing xylose crystals . Further, the present disclosure relates to an arrangement for producing xylose crystals . Further, the present disclosure relates to xylose crystals .

[0004] BACKGROUND

[0005] Xylose is a sugar that may be isolated from wood and that finds several applications . Typical process to produce pure crystalline xylose from lignocellulosic raw materials includes many purification steps such as chromatography, adsorption, ion exchange , and batchwise crystalli zation . Such a process concept is capex intensive while numerous wastewater streams are produced, and the chemical consumption is high . A more efficient process for producing xylose crystals is needed .

[0006] SUMMARY

[0007] A method for producing xylose crystals is disclosed . The method comprises conducting the following steps one after the other in this order :

[0008] - providing a crude feedstock of hardwood-derived carbohydrates in the form of a crude liquid fraction having a total dry matter content of 30 - 70 weight- % and having a xylose content of 40 - 60 weight-% based on the total dry matter content of the crude liquid fraction ;

[0009] - subj ecting the crude liquid fraction to a first chromatographic treatment to recover a first puri fied l iquid fraction having a xylose content that is increased by at least 20 % compared to the xylose content of the crude liquid fraction ;

[0010] - optionally subj ecting the first purified liquid fraction to evaporation ;

[0011] - subj ecting the first purified, and optionally evaporated, liquid fraction to a second chromatographic treatment to recover a second purified liquid fraction having a xylose content that is increased by at least 8 % compared to the xylose content of the f irst purif ied liquid fraction, wherein the second chromatographic treatment is carried out by using a gel-type strong bas ic anion-exchange resin, which i s composed of a matrix functionali zed with quaternary ammonium groups and which is in sulphate anion form;

[0012] - optionally subj ecting the second purified liquid fraction to evaporation ; and

[0013] - subj ecting the second purified, and optionally evaporated, liquid fraction to a crystalli zation treatment ; in order to produce xylose crystals , having a xylose content of at least 96 weight-% , with a yield of at least 50 % .

[0014] Further is disclosed an arrangement for producing xylose crystals . The arrangement comprises the following configured to be implemented one after the other in this order :

[0015] - a first chromatographic device configured to subj ect a crude feedstock of hardwood-derived carbohydrates in the form of a crude liquid fraction having a total dry matter content of 30 - 70 weight-% and having a xylose content of 40 - 60 weight-% based on the total dry matter content of the crude liquid fraction, to a first chromatographic treatment to recover a first puri fied l iquid fraction having a xylose content that is increased by at least 20 % compared to the xylose content of the crude liquid fraction ; - optionally a first evaporator configured to subj ect the first purified liquid fraction to evaporation ;

[0016] - a second chromatographic device configured to subj ect the first purified, and optionally evaporated, liquid fraction to a second chromatographic treatment , by using a gel-type strong basic anion-exchange resin, which is composed of a matrix functionali zed with quaternary ammonium groups and which is in sulphate anion form, to recover a second purified liquid fraction having a xylose content that is increased by at least 8 % compared to the xylose content of the first purified liquid fraction ;

[0017] - optionally a second evaporator configured to subj ect the second purified liquid fraction to evaporation ; and

[0018] - a crystalli zation unit configured to subj ect the second purified, and optionally evaporated, liquid fraction to a crystalli zation treatment ; in order to produce xylose crystals , having a xylose content of at least 96 weight-% , with a yield of at least 50 % .

[0019] Further is disclosed xylose crystals obtainable by the method as disclosed in this specification, wherein the xylose crystals have a xylose content of at least 96 weight-% and the xylose crystals are produced with a yield of at least 50 % .

[0020] BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The accompanying drawings , which are included to provide a further understanding of the embodiments and constitute a part of this specification, illustrate embodiments and together with the description help to explain the principles of the invention . In the drawings :

[0022] FIG . 1 illustrates one embodiment of producing xylose crystals ; and Figs . 2a and 2b present results from example

[0023] 1 .

[0024] DETAILED DESCRIPTION

[0025] A method for producing xylose crystals is disclosed . The method comprises conducting the following steps one after the other in this order :

[0026] - providing a crude feedstock of hardwood-derived carbohydrates in the form of a crude liquid fraction having a total dry matter content of 30 - 70 weight- % and having a xylose content of 40 - 60 weight-% based on the total dry matter content of the crude liquid fraction ;

[0027] - subj ecting the crude liquid fraction to a first chromatographic treatment to recover a first puri fied l iquid fraction having a xylose content that is increased by at least 20 % compared to the xylose content of the crude liquid fraction,

[0028] - optionally subj ecting the first purified liquid fraction to evaporation ;

[0029] - subj ecting the first purified, and optionally evaporated, liquid fraction to a second chromatographic treatment to recover a second purified liquid fraction having a xylose content that is increased by at least 8 % compared to the xylose content of the f irst purif ied liquid fraction, wherein the second chromatographic treatment is carried out by using a gel-type strong bas ic anion-exchange resin, which i s composed of a matrix functionalized with quaternary ammonium groups and which is in sulphate anion form;

[0030] - optionally subj ecting the second purified liquid fraction to evaporation ; and

[0031] - subj ecting the second purified, and optionally evaporated, liquid fraction to a crystalli zation treatment ; in order to produce xylose crystals, having a xylose content of at least 96 weight-%, with a yield of at least 50 % .

[0032] The expression "total dry matter content" may refer to the total amount of solids including soluble or dissolved solids. The crude feedstock of hardwood- derived carbohydrates may be free of suspended solids and contain only soluble solids.

[0033] In this specification the term "total dry matter content of the liquid fraction" may refer to the weight of the liquid fraction as determined after removing any solid particles or material from the liquid fraction, e.g. by filtering, and subjecting the filtrate to drying at a temperature of 45 °C for 24 hours. The effectiveness of the drying may be assured by weighing the sample, drying for a further two hours at the specified temperature, and reweighing the sample. If the measured weights are the same, the drying has been complete, and the total weight may be recorded.

[0034] Xylose is a monosaccharide. The monosaccharide content, and thus the xylose content, based on the total dry matter content of the liquid fractions may be determined both qualitatively and quantitatively by high- performance liquid chromatography (HPLC) by comparing to standard samples. Examples of analysis methods can be found in e.g. Sluiter, A., et al., "Determination of sugars, byproducts, and degradation products in liquid fraction process samples", Technical Report, National Renewable Energy Laboratory, 2008, and Sluiter, A., et al., "Determination of Structural Carbohydrates and Lignin in Biomass", Technical Report, National Renewable Energy Laboratory, revised 2012.

[0035] The inventors surprisingly found out that using a method wherein two chromatographic treatments are used one after the other, with merely a possible evaporation step in between, it is possible to decrease the loss in yield of xylose crystals. It was also noted that the using a cascade of two chromatographic treatments has the added utility of decreasing the amount of lignin in the fraction and thus decreasing unwanted colour of the xylose crystals to a surprisingly large extend .

[0036] In one embodiment, the xylose crystals exhibit an ICUMSA color value of 10 - 1000 IU, or 15 - 500 IU, or 20 - 200 IU . The xylose crystals are firstly dissolved in water before the ICUMSA color measurement (max 50 % brix dissolution, 1 % brix = 1 g sugar per 100 g solution) . The ICUMSA color value may then be measured using a modified ICUMSA GS 1 method without adj usting the pH of the sample to be analyzed and filtering the sample through a 0 . 45 pm filter before analysis . The measurement is conducted in room temperature .

[0037] Further is disclosed an arrangement for producing xylose crystals . The arrangement comprises the following configured to be implemented one after the other in this order :

[0038] - a first chromatographic device configured to subj ect a crude feedstock of hardwood-derived carbohydrates in the form of a crude liquid fraction having a total dry matter content of 30 - 70 weight-% and having a xylose content of 40 - 60 weight-% based on the total dry matter content of the crude liquid fraction, to a first chromatographic treatment to recover a first puri fied l iquid fraction having a xylose content that is increased by at least 20 % compared to the xylose content of the crude liquid fraction ;

[0039] - optionally a first evaporator configured to subj ect the first purified liquid fraction to evaporation ;

[0040] - a second chromatographic device configured to subj ect the first purified, and optionally evaporated, liquid fraction to a second chromatographic treatment , by using a gel-type strong basic anion-exchange resin, which is composed of a matrix functionali zed with quaternary ammonium groups and which is in sulphate anion form, to recover a second purified liquid fraction having a xylose content that is increased by at least 8 % compared to the xylose content of the first purified liquid fraction ;

[0041] - optionally a second evaporator configured to subj ect the second purified liquid fraction to evaporation ; and

[0042] - a crystalli zation unit configured to subj ect the second purified, and optionally evaporated, liquid fraction to a crystalli zation treatment ; in order to produce xylose crystals , having a xylose content of at least 96 weight-% , with a yield of at least 50 % .

[0043] Thus , in the arrangement , the above chromatographic devices , ( optional ) evaporators , and crystallization unit , are configured to be implemented one after the other in a predetermined order . These may be physically arranged one after the other . Alternatively, the separate chromatographic devices , ( optional ) evaporators , and crystalli zation unit may be physically placed in different locations . However, the process carried out with the arrangement is performed in a specific order as disclosed in the current specification .

[0044] Further is disclosed xylose crystals obtainable by the method as disclosed in this specification, wherein the xylose crystals have a xylose content of at least 96 weight-% and the xylose crystals are produced with a yield of at least 50 % .

[0045] In one embodiment , the xylose crystals have a xylose content of 96 - 99 . 9 weight-% , or 97 - 99 . 8 weight-% , or 98 - 99 . 7 weight-% . In one embodiment , the xylose crystals are produced with a yield of at least 60 % , or at least 70 % , or at least 80 % , or at least 90 % , or at least 95 % , or at least 98 % . The method as disclosed in the current disclosure has the added utility of providing a process that is eff icient from economical and industrial point of view while simultaneously resulting in xylose crystals being produced with a high xylose content.

[0046] The method for producing xylose crystals comprises providing a crude feedstock of hardwood-derived carbohydrates in the form of a crude liquid fraction having a total dry matter content of 30 - 70 weight-% and having a xylose content of 40 - 60 weight-% based on the total dry matter content of the crude liquid fraction. Such a crude feedstock may be recovered from different processes where carbohydrate compositions are produced. One example of providing such a crude feedstock of hardwood-derived carbohydrates may include the following :

[0047] A feedstock of wood chips, such as hardwood chips, may be subjected to an impregnation treatment with an impregnation liquid. The impregnation liquid may be e.g. a liquid of 0.5 - 2 % sulfuric acid. The impregnation treatment may be carried out at a temperature of 40 - 100 °C for 1 - 30 minutes. The impregnated feedstock may then be subjected to steam explosion treatment. The steam explosion treatment may be carried out by treating the impregnated wood-based feedstock with steam having a temperature of 130 - 240 °C, or 180 - 200 °C, or 185 - 195 °C under a pressure of 0.17 - 3.25 MPaG followed by a sudden, explosive decompression of the feedstock. The feedstock may be treated with the steam for 1 - 20 minutes, or 1 - 18 minutes, or 2 - 15 minutes, or 4 - 13 minutes, or 3 - 10 minutes, or 3 - 8 minutes, before the sudden, explosive decompression of the steam-treated feedstock. As a result of the hemihydrolysis of the feedstock affected by the steam explosion treatment, the hemicellulose present in the wood chips of feedstock may become hydrolyzed or degraded into e.g. xylose oligomers and / or monomers. The hemicellulose comprises polysaccharides such as xylan, mannan and glucan. Xylan is thus hydrolyzed into xylose that is a monosaccharide. Thus, steam explosion of the feedstock may result in the formation of an output stream. The output stream from the steam explosion may be subjected to steam separation. The output stream from the steam explosion may be mixed or combined with a liquid, e.g. water, to form a slurry. The slurry may comprise a liquid phase and a solid phase. The slurry may be separated into a liquid fraction and a fraction comprising solid cellulose particles. The liquid fraction may then be subjected to concentration, e.g. by evaporation, and, if necessary, the pH of the liquid fraction may be adjusted to 5.5 - 6, e.g. with sodium hydroxide (NaOH) or potassium hydroxide (KOH) , to provide a crude liquid fraction .

[0048] In one embodiment, the crude liquid fraction has a total dry matter content of 30 - 70 weight-%, or 40 - 60 weight-%, or 45 - 55 weight-%, or 40 - 50 weight- % . In one embodiment, the crude liquid fraction has a xylose content of 40 - 60 weight-%, or 45 - 55 weight- % , based on the total dry matter content of the crude liquid fraction.

[0049] The total dry matter content of the crude liquid fraction affects the size of the chromatographic devices needed to be used. With a too low total dry matter content, a high flow rate needs to be used resulting in a bigger chromatographic column volume needed. This would increase the investment and operational costs. The total dry matter content of the crude liquid fraction being at most 70 weight-% has the added utility of the viscosity of the crude liquid fraction remaining on a suitable level such that no runnability issues may appear and the pressure over the chromatographic columns may be kept on a suitable level.

[0050] A crude liquid fraction having xylose content of 40 - 60 weight-% may be provided e.g. when extracting a hemicellulosic fraction by acid hydrolysis from hardwood, such has beech and / or birch. The hydrolysis results in solubili zation of the hemicellulosic components l ike xylose . By extracting and washing the solubili zed components from solids a crude feedstock fraction containing 40 - 60 weight-% of xylose may be provided . A crude liquid feedstock having a xylose content of 45 - 55 weight-% may be provided when using e . g . beech wood as a raw material . Providing a crude feedstock of hardwood-derived carbohydrates in the form of a crude liquid fraction having a xylose content of 40 - 60 weight-% has the added utility of enabling industrially feas ible separation without the need of too large chromatographic devices .

[0051] In one embodiment , the crude liquid fraction is subj ected to a first chromatographic treatment to recover a first purified liquid fraction having a xylose content that is increased by at least 20 % , or at least 25 % , or at least 30 % , compared to the xylose content of the crude liquid fraction . In one embodiment , the crude liquid fraction is subj ected to a first chromatographic treatment to recover a first purified liquid fraction having a xylose content that is increased by 20 - 40 % , or 25 - 35 % , or 25 - 33 % , compared to the xylose content of the crude liquid fraction . In one embodiment , the first purified liquid fraction has a xylose content of 50 - 80 weight-% , or 55 - 75 weight- % , or 60 - 73 weight-% , or 65 - 72 weight-% , based on the total dry matter content of the first purified liquid fraction .

[0052] In one embodiment , the first chromatographic treatment is carried out by using a gel-type strong cation exchange ( SAC) resin . The gel-type strong cation exchange ( SAC) resin may be in Na+or K+ form . The SAC resin may have a cross-linking degree of 4 - 7 % . By the term "cross-inking degree of the resin" may refer to the divinylbenzene ( DVB) content in the resin which correlates with the internal pore diameter of the resin . In chromatographic treatment the resin is used as the separation material . In one embodiment , the first chromatographic device is configured to subj ect the crude feedstock of hardwood-derived carbohydrates in the form of a crude liquid fraction to a first chromatographic treatment by using a gel-type strong cation exchange ( SAC) resin .

[0053] The first chromatographic treatment may assist in removal of salts , such as sodium sulphate , colors , oligomers , large molecules , salts of organic acids , and uranes etc . Especially, the first chromatographic treatment may be used in order to decrease the lignin content of the liquid fraction to such an extent that the resin used in the second chromatographic treatment is able to work in an efficient manner . The inventors found out that by using the gel-type strong cation exchange ( SAC) resin in the first chromatographic treatment it is possible to remove a large amount of lignin present in the crude liquid fraction .

[0054] The inventors thus also surprisingly found out that the presence of lignin in the second chromatographic treatment cause undesired effect of hindering proper recovery of the second purified liquid fraction in a high xylose content , and thus efficiently removing lignin before entering the second chromatographic treatment highly affected the overall efficiency of the whole method .

[0055] The lignin present in the liquid fractions may be considered to be mostly soluble lignin . The amount of soluble lignin may be determined by UV-VI S absorption spectroscopy in the following manner : The amount of soluble lignin present in the carbohydrate composition is determined by diluting a sample of carbohydrate composition so that its absorbance at 205 nm is 0 . 2 - 0 . 7 AU when compared to a reference sample of pure water and using a cuvette with a path length of 1 cm . The soluble lignin content of the sample in mg / 1 may then be calculated using the following equation where A is absorbance of the sample , a is the absorptivity coefficient 0 . 110 1 / mgcm, and D is a dilution factor .

[0056] The method may comprise subj ecting the first purified liquid fraction to evaporation before being subj ected to the second chromatographic treatment . In one embodiment , the arrangement comprises a first evaporator configured to subj ect the first purified liquid fraction to evaporation before being fed into the second chromatographic device . Evaporating the first liquid fraction prior to the second chromatographic treatment has the added utility of keeping the si ze of the chromatography column ( s ) on an economical level for industrial use . Reducing the amount of water going to the chromatographic treatment has the added utility of making the process more efficient for industrial use .

[0057] In one embodiment , the first purified, and optionally evaporated, liquid fraction is subj ected to a second chromatographic treatment to recover a second purified liquid fraction having a xylose content that is increased by at least 8 % , or at least 9 % , or at least 10 % , or at least 11 % , compared to the xylose content of the first purified liquid fraction . In one embodiment , the first purified, and optionally evaporated, liquid fraction is subj ected to a second chromatographic treatment to recover a second purified liquid fraction having a xylose content that is increased by 8 - 45 % , or 9 - 40 % , or 10 - 35 % , or 11 - 30 % , compared to the xylose content of the first purified liquid fraction . In one embodiment , the second purified liquid fraction has a xylose content of 75 - 90 weight-% , or 79 - 88 weight-% , or 80 - 85 weight-% , based on the total dry matter content of the second purified liquid fraction . The second chromatographic treatment is carried out by using a gel-type strong basic anion-exchange ( SBA) resin, which i s composed of a matrix functionali zed with quaternary ammonium groups and which is in sulphate anion ( counterion) form . The strong basic anion-exchange resin is thus in sulphate anion form . The sulphate anions may be bonded through ionic bonding to the ammonium groups . The SBA resin may have a crosslinking degree of 4 - 8 % .

[0058] The inventors surprisingly found out that the sulphate anions affected the sorption of the monosaccharides enabling the separation of xylose from the other monosaccharides . The sorption is governed by a ligand exchange type mechanism, in which the OH-groups in the monosaccharides form coordination complexes with the sulfate ions , and si ze exclusion . These interactions are different for each monosaccharide and thus result in their separation .

[0059] The matrix of the strong basic anion-exchange resin may be a divinylbenzene ( DVB) -based matrix . The matrix of the strong basic anion-exchange resin may be a styrene-divinylbenzene matrix or a methacrylate-divi- nylbenzene matrix . The inventors surprisingly found out that the use of the specific type of resin in the second chromatographic treatment has the added utility of efficiently increasing the xylose content to a level such that crystalli zation of the second purified liquid fraction can be carried out in an efficient manner while producing xylose crystals having a high xylose content . The use of a gel-type strong basic anion-exchange resin composed of a matrix functionali zed with quaternary ammonium groups and being in sulphate anion form has the added utility of reducing especially small molecular weight lignin from the fraction to a great extent . Being able to efficiently remove lignin affects especially the color of the produced xylose crystals as lignin tends to provide a brownish color . Further, the crystalli zation treatment following the second chromatographic treatment may be carried out with a rather short crystalli zation residence time as a result of the second chromatographic treatment providing an outcome with properties making the crystalli zation treatment efficient . Further, xylose may be separated from other sugars present in the first purif ied liquid fraction during the second chromatographic treatment resulting in a higher xylose content .

[0060] In one embodiment , the xylose yield after the first and second chromatographic treatments is 60 - 98 % , or 70 - 96 % , or 80 - 94 % .

[0061] The second purified liquid fraction may be subj ected to evaporation before the crystalli zation treatment . In one embodiment , before the crystalli zation treatment , the recovered second purified liquid fraction is subj ected to evaporation until the total dry matter content of the second purified liquid fraction is 75 - 90 weight-% , or 75 - 88 weight-% . In one embodiment , the arrangement comprises , before the crystalli zation unit , a second evaporator configured to subj ect the recovered second purified liquid fraction to evaporation . In one embodiment , the arrangement comprises , before the crystalli zation unit , a second evaporator configured to subj ect the recovered second purified liquid fraction to evaporation until the total dry matter content of the second purified liquid fraction is 75 - 90 weight-% , or 75 - 88 weight-% . Evaporating the second purified liquid fraction before the crystalli zation treatment has the added utility of one being able to reach an optimal supersaturation level for xylose during the crystallization .

[0062] In one embodiment , the method comprises recovering a first raffinate stream of impurities from the first chromatographic treatment . The first raffinate stream of impurities may comprise impurities such as salts , soluble lignin, organic acids , and / or oligosaccharides .

[0063] In one embodiment , the method comprises recovering a second raffinate stream of impurities from the second chromatographic treatment . The second raffinate stream of impurities may comprises impurities such as remaining salts , lignin, oligosaccharides , and / or organic acids .

[0064] In one embodiment , the method comprises recovering a stream of C6 sugars from the second chromatographic treatment . Such a stream of C6 sugars may be used in further applications . The method as disclosed in the current disclosure thus has the added utility that C6 sugars present in the crude feedstock of hard- wood-derived carbohydrates may be separated during the process for further use , instead of being part of a raffinate stream . In one embodiment , the method comprises recovering C6 sugars from the second chromatographic treatment together with the second raffinate stream of impurities .

[0065] In one embodiment , the crystalli zation treatment comprises crystallization, followed by washing and / or drying the formed xylose crystals . In one embodiment , the crystalli zation treatment comprises cooling crystalli zation, followed by washing and / or drying the formed xylose crystals . In one embodiment , the crystalli zation treatment comprises evaporation crystalli zation, followed by washing and / or drying the formed xylose crystals .

[0066] The crystalli zation may comprise evaporation crystalli zation, cooling crystalli zation, or both . In one embodiment , the crystalli zation comprises evaporation crystalli zation followed by cooling crystalli zation .

[0067] In evaporation crystalli zation, the liquid part is removed by heating the second purified liquid fraction under vacuum until a predetermined part of the liquid is evaporated and xylose is crystalli zed . In cooling crystalli zation, the liquid is cooled until the solubility of the xylose involved is reduced, causing it to separate from the liquid through crystalli zation .

[0068] The residence time of the crystalli zation may be 1 - 50 hours . The residence time of evaporation crystalli zation may be 1 - 5 hours . The residence time of cooling crystallization may be 20 - 50 hours . The evaporation crystalli zation may be carried out at a temperature of 50 - 80 °C . The cooling crystalli zation may be carried out at a temperature starting from 60 - 80 °C and ending at 25 - 45 °C .

[0069] In one embodiment , the crystalli zation treatment comprises a washing step, in which the xylose crystals formed in the crystalli zation treatment are washed with a washing liquid . In one embodiment , the method comprises washing liquid from the crystalli zation treatment to be recycled by combining an amount of the washing liquid with the recovered second purif ied liquid fraction .

[0070] In one embodiment , the method comprises recovering a mother liquor stream compris ing C6 sugars from the crystalli zation treatment . In one embodiment , the method comprises recovering a mother liquor stream comprising C6 sugars from the crystalli zation treatment and recycling at least part of the recovered mother liquor stream to be combined with the first purified, and optionally evaporated, liquid fraction .

[0071] The method as disclosed in the current disclosure has the added util ity that the proces s al lows for continuous chromatographic separation to improve the xylose content of xylose crystals by a more straightforward method and process steps than previously used .

[0072] The method as disclosed in the current disclosure has the added util ity of being a method suitable for industrial use for producing xylose crystals . The method as discussed in the current disclosure has the added utility of one being able to receive xylose crystals in high yield and purity with an industrially and economically straightforward process . The internal recovery and circulation of streams has the further added utility of increasing the yield even further .

[0073] EXAMPLES

[0074] Reference will now be made in detail to the described embodiments , an example of which is illustrated in the accompanying drawing .

[0075] The description below discloses some embodiments in such a detail that a person skilled in the art is able to uti li ze the method based on the di sclosure . Not all steps of the embodiments are discussed in detail , as many of the steps will be obvious for the person skilled in the art based on this specification .

[0076] For reasons of simplicity, item numbers will be maintained in the following exemplary embodiments in the case of repeating components .

[0077] Fig . 1 illustrates one embodiment of producing xylose crystals . The following steps may be carried out one after the other in the presented order .

[0078] Firstly, a crude feedstock of hardwood-derived carbohydrates is provided in the form of a crude liquid fraction 5a having a total dry matter content of 30 - 70 weight-% and having a xylose content of 40 - 60 weight-% based on the total dry matter content of the crude liquid fraction .

[0079] The crude liquid fraction 5a is subj ected to a first chromatographic treatment in a first chromatographic device la to recover a first purified liquid fraction 5b having a xylose content that is increased by at least 20 % compared to the xylose content of the crude liquid fraction 5a . After the first chromatographic treatment la, the f irst puri fied l iquid fraction 5b may be subj ected to evaporation in a first evaporator 2a to recover a first purified and evaporated liquid fraction 5c . Alternatively the first purified liquid fraction 5b may be directly subj ected to the second chromatographic treatment in the second chromatographic device lb .

[0080] From the second chromatographic treatment in the second chromatographic device lb a second purified liquid fraction 5d is recovered having a xylose content that is increased by at least 8 % compared to the xylose content of the first purified liquid fraction 5b . The second chromatographic treatment is carried out by using a gel-type strong basic anion-exchange resin, which is composed of a matrix functionali zed with quaternary ammonium groups and which is in sulphate anion form .

[0081] Again, the second purified liquid fraction 5d may be subj ected to evaporation in a second evaporator 2b to recover a second purified and evaporated liquid fraction 5e . Alternatively, the second purified liquid fraction 5d may be directly subj ected to the crystallization treatment 3 . The crystalli zation treatment 3 may comprise crystalli zation, followed by washing and / or drying the formed xylose crystals .

[0082] As a result of the method carried out in the disclosed arrangement xylose crystals 9 are produced . The produced xylose crystals have a xylose content of at least 96 % . The xylose crystals are produced with a yield of at least 50 % .

[0083] In addition to the above presented steps and units , in Fig . 1 is also presented the following features that may be included in the method or arrangement , respectively, either alone or in any combination with each other :

[0084] A first raffinate stream of impurities 4a is recovered from the first chromatographic treatment la . A second raffinate stream of impurities 4b is recovered from the second chromatographic treatment lb . A stream of C6 sugars 7 is recovered from the second chromatographic treatment lb . C6 sugars may also be recovered from the second chromatographic treatment together with the second raffinate stream of impurities 4b .

[0085] A washing liquid 8 is recycled from the crystalli zation treatment 3 to be combined with the recovered second purified liquid fraction 5d . A mother liquor stream comprising C6 sugars 6a is recovered from the crystalli zation treatment 3 . At least a part of the mother liquor stream comprising C6 sugars 6b recovered from the crystalli zation treatment 3 is recycled to be combined with the first purified, and optionally evaporated, liquid fraction 5b, 5c .

[0086] Example 1 - Producing xylose crystals

[0087] In this example xylose crystals were produced by three di fferent methods . In all of the examples the crude feedstock of hardwood-derived carbohydrates in the form of a crude liquid fraction had the following properties : total dry matter content : 50 weight-% xylose content : 51 . 6 weight-% amount of xylose of total sugars 70 . 9 weight-% lignin content : 6 . 3 weight-%

[0088] ICUMSA color value (measured at a pH value of 5 . 9 ) : 165 000 IU

[0089] The different methods included the following steps one after the other as disclosed in the current disclosure :

[0090] Comparative example A : 1) providing a crude feedstock of hardwood-derived carbohydrates in the form of a crude liquid fraction ii) first chromatographic treatment resin: gel-type strong cation exchange (SAC) resin, with a cross-linking degree of 6.5 % , in Na+form

[0091] Comparative example B: i) providing a crude feedstock of hardwood-derived carbohydrates in the form of a crude liquid fraction ii) first chromatographic treatment resin: gel-type strong cation exchange (SAC) resin with a cross-linking degree of 6.5 % , in Na+form iii) second chromatographic treatment resin: gel-type strong cation exchange (SAC) resin, with a cross-linking degree of 6.5 % , in Na+form iv) crystallization treatment

[0092] Example C: i) providing a crude feedstock of hardwood-derived carbohydrates in the form of a crude liquid fraction ii) first chromatographic treatment resin: gel-type strong cation exchange (SAC) resin, with a cross-linking degree of 6.5 % , in Na+form iii) second chromatographic treatment resin: gel-type strong anion exchange (SBA) resin, with a cross-linking degree of 5 % , in SO42’ form iv) crystallization treatment The results of the above methods are presented in the below tables 1 and 2 :

[0093] Table 1 . Results after the chromatographic treatments

[0094] *For comparative example A, the yield after the first chromatographic treatment , and for comparative example B and example C, the yield after both the first and the second chromatographic treatments had been carried out . * * simulation of the method showed that yield of 90 % can be achieved

[0095] From the results one may see that the lignin content and ICUMSA color value of example C has relevantly decreased compared to comparative example A and comparative example B . Also the xylose content of the produced xylose crystals is increased when using the method of example C .

[0096] Fig . 2a shows the spatial profiles inside the second chromatographic device ( intermittent simulated moving bed ( I SMB) chromatographic unit ) loaded with the SAC resin in Na+form at steady state conditions for comparative example B . From Fig . 2a one can see that the liquid fraction recovered from the outlet of column 1 during the ongoing step had the same ratio of xylose to other sugars as the liquid fraction fed into the second chromatographic device. Thus, mostly only lignin and salts were separated.

[0097] Fig. 2b shows the spatial profiles inside the second chromatographic device (ISMB chromatographic unit) loaded with the SBA resin in SO42- at steady state conditions for example C. From Fig. 2b one can see that the second purified liquid fraction recovered from the outlet of column 1 during the ongoing step was enriched in xylose.

[0098] Comparative example B and example C were continued into the crystallization treatment in the following manner:

[0099] After the second chromatographic treatment comparative example B having a xylose content of 76.5 weight-% was subjected to evaporation in order to increase the total dry matter content to 77.4 weight-%. Then the chromatographically purified and evaporate liquid fraction was subjected to crystallization treatment as follows:

[0100] Seed crystals were added in an amount of 3 % of xylose at 64 °C. The liquid fraction was subjected to cooling crystallization for 18 hours in which time it was cooled from 64 °C to 28 °C. After the crystallization, the formed crystal suspension was vacuum filtered in Buchner funnel.

[0101] Similarly as above, after the second chromatographic treatment Example C having a xylose content of 81.4 weight-% was subjected to evaporation in order to increase the total dry matter content 75.7 weight-%. Then the chromatographically purified and evaporated liquid fraction was subjected to cooling crystallization for 18 hours in which time it was cooled from 64 °C to 28 °C. After the crystallization, the formed crystal suspension was vacuum filtered in Buchner funnel.

[0102] After the crystallization treatment, the viscosity of both examples was about 15000 cP (Brookfield, 10 rpm, measured at 28 °C) . The yield of comparative example B was 58 % and of example C 66 % . Displacement washing was executed by washing the xylose crystals with 0 . 7 m3of water per ton of xylose crystals based on the total dry matter content thereof .

[0103] The results are presented in Table 2 below .

[0104] Table 2 . Results after the crystalli zation treatment

[0105] *The lignin content was measured by UV 205 nm method applicable to soluble lignin .

[0106] From the results one may see that the lignin content of example C has relevantly decreased compared to comparative example B . Also the xylose content of the produced xylose crystals is increased when using the method of example C .

[0107] Example 2 - Subj ecting crude liquid fractions to the first and the second chromatographic treatment

[0108] In this example different crude feedstocks of hardwood-derived carbohydrates in the form of crude liquid fractions with varying xylose contents were subj ected to the first chromatographic treatment and the second chromatographic treatment as presented below : i ) providing a crude feedstock of hardwood-derived carbohydrates in the form of a crude liquid fraction with varying xylose contents ii ) first chromatographic treatment resin : gel-type strong cation exchange ( SAC) resin, with a cross-linking degree of 6 . 5 % , in Na+form iii ) second chromatographic treatment resin : gel-type strong anion exchange ( SBA) resin, with a cross-linking degree of 5 % , in SO42’ form

[0109] The results are presented in Table 3 below .

[0110] Table 3 . Increase in xylose content

[0111] From table 3 one can see that the xylose content was efficiently increased for the samples when using the method as disclosed in the current disclosure .

[0112] It is obvious to a person skil led in the art that with the advancement of technology, the basic idea may be implemented in various ways . The embodiments are thus not limited to the examples described above ; instead they may vary within the scope of the claims . The embodiments described hereinbefore may be used in any combination with each other . Several of the embodiments may be combined together to form a further embodiment . A method, an arrangement , or xylose crystals , as disclosed herein, may comprise at least one of the embodiments described hereinbefore . It will be understood that the benefits and advantages described above may relate to one embodiment or may relate to several embodiments . The embodiments are not limited to those that solve any or all of the stated problems or those that have any or all of the stated benefits and advantages . It will further be understood that reference to ' an ' item refers to one or more of those items . The term "comprising" is used in this specification to mean including the feature ( s ) or act ( s ) followed thereafter, without excluding the presence of one or more additional features or acts .

Claims

CLAIMS1 . A method for producing xylose crystals , wherein the method comprises conducting the following steps one after the other in this order :- providing a crude feedstock of hardwood-derived carbohydrates in the form of a crude liquid fraction having a total dry matter content of 30 - 70 weight- % and having a xylose content of 40 - 60 weight-% based on the total dry matter content of the crude liquid fraction ;- subj ecting the crude liquid fraction to a first chromatographic treatment to recover a first purified liquid fraction having a xylose content that is increased by at least 20 % compared to the xylose content of the crude liquid fraction,- optionally subj ecting the first purified liquid fraction to evaporation ;- subj ecting the first purified, and optionally evaporated, liquid fraction to a second chromatographic treatment to recover a second purified liquid fraction having a xylose content that is increased by at least 8 % compared to the xylose content of the f irst purif ied liquid fraction, wherein the second chromatographic treatment is carried out by using a gel-type strong bas ic anion-exchange resin, which i s composed of a matrix functionali zed with quaternary ammonium groups and which is in sulphate anion form;- optionally subj ecting the second purified liquid fraction to evaporation ;- subj ecting the second purified, and optionally evaporated, liquid fraction to crystalli zation treatment ; to produce xylose crystals , having a xylose content of at least 96 % , with a yield of at least 502 . The method of claim 1 , wherein the crude liquid fraction has a total dry matter content of 40 - 60 weight-% , or 45 - 55 weight-% , or 40 - 50 weight-% .3 . The method of any one of the preceding claims , wherein the crude liquid fraction has a xylose content of 45 - 55 weight-% based on the total dry matter content of the crude liquid fraction .4 . The method of any one of the preceding claims , wherein the first purified liquid fraction has a xylose content of 50 - 80 weight-% , or 55 - 75 weight- % , or 60 - 73 weight-% , or 65 - 72 weight-% , based on the total dry matter content of the first purified liquid fraction .5 . The method of any one of the preceding claims , wherein the second purified liquid fraction has a xylose content of 75 - 90 weight-% , or 79 - 88 weight- % , or 80 - 85 weight-% , based on the total dry matter content of the second purified liquid fraction .6 . The method of any one of the preceding claims , wherein the first chromatographic treatment is carried out by using a gel-type strong cation exchange ( SAC) resin .7 . The method of any one of the preceding claims , wherein the matrix of the strong basic anion- exchange resin is a styrene-divinylbenzene matrix or a methacrylate-divinylbenzene matrix .8 . The method of any one of the preceding claims , wherein the method comprises subj ecting the first purified liquid fraction to evaporation before being subj ected to the second chromatographic treatment .9 . The method of any one of the preceding claims , wherein, before the crystalli zation treatment , the recovered second purified liquid fraction is subj ected to evaporation until the total dry matter content of the second purified liquid fraction is 75 - 90 weight-10 . The method of any one of the preceding claims , wherein the method comprises recovering a first raffinate stream of impurities from the first chromatographic treatment .11 . The method of any one of the preceding claims , wherein the method comprises recovering a second raffinate stream of impurities from the second chromatographic treatment .12 . The method of any one of the preceding claims , wherein the method comprises recovering a stream of C6 sugars from the second chromatographic treatment .13 . The method of any one of the preceding claims , wherein the crystalli zation treatment comprises crystalli zation, followed by washing and / or drying the formed xylose crystals .14 . The method of claim 13 , wherein the method comprises washing liquid from the crystalli zation treatment to be recycled by combining an amount of the washing liquid with the recovered second purif ied liquid fraction .15 . The method of any one of the preceding claims , wherein the method comprises recovering a mother liquor stream comprising C6 sugars from the crystallization treatment .16 . The method of any one of the preceding claims , wherein the method comprises recovering a mother liquor stream comprising C6 sugars from the crystallization treatment and recycling at least part of the recovered mother liquor stream to be combined with the first purified, and optionally evaporated, crude liquid fraction .17 . An arrangement for producing xylose crystals , wherein the arrangement comprises the following configured to be implemented one after the other in thi s order :- a first chromatographic device ( la) configured to subj ect a crude feedstock of hardwood-derivedcarbohydrates in the form of a crude liquid fraction (5a) having a total dry matter content of 30 - 70 % and having a xylose content of 40 - 60 weight-% based on the total dry matter content of the crude liquid fraction, to a first chromatographic treatment to recover a first purified liquid fraction (5b) having a xylose content that is increased by at least 20 % compared to the xylose content of the crude liquid fraction (5a) ;- optionally a first evaporator (2a) configured to subject the first purified liquid fraction (5b) to evaporation;- a second chromatographic device (lb) configured to subject the first purified, and optionally evaporated, liquid fraction (5b, 5c) to a second chromatographic treatment by using a gel-type strong basic anion-exchange resin composed of a matrix functionalized with quaternary ammonium groups to recover a second purified liquid fraction (5d) having a xylose content that is increased by at least 8 % compared to the xylose content of the first purified liquid fraction;- optionally a second evaporator (2b) configured to subject the second purified liquid fraction (5d) to evaporation; and- a crystallization unit (3) configured to subject the second purified, and optionally evaporated, liquid fraction (5d,5e) to crystallization treatment; to produce xylose crystals (9) , having a xylose content of at least 96 weight-%, with a yield of at least 50 % .

18. The arrangement of claim 17, wherein the first chromatographic device (la) is configured to subject the crude feedstock of hardwood-derived carbohydrates in the form of a crude liquid fraction (5a) to a first chromatographic treatment by using a gel-type strong cation exchange (SAC) resin.

19. The arrangement of any one of claims 17 - 18, wherein the arrangement comprises a first evaporator(2a) configured to subject the first purified liquid fraction (5b) to evaporation before being fed into the second chromatographic device (lb) .

20. The arrangement of any one of the claims 17 - 19, wherein the arrangement comprises, before the crystallization unit (3) , a second evaporator (2b) configured to subject the recovered second purified liquid fraction (5d) to evaporation until the total dry matter content of the second purified liquid fraction is 75 - 90 weight-%.

21. Xylose crystals obtainable by the method of any one of claims 1 - 16, wherein the xylose crystals have a xylose content of at least 96 weight-% and the xylose crystals are produced with a yield of at least 50 %.

22. The xylose crystals of claim 21, wherein the xylose crystals have a xylose content of 96 - 99.9 weight-%, or 97 - 99.8 weight-%, or 98 - 99.7 weight-%.

23. The xylose crystals of any one of claims 21 - 22, wherein the xylose crystals are produced with a yield of 60 % , or at least 70 % , or at least 80 % , or at least 90 % , or at least 95 % , or at least 98 % .

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