DESC:FIELD OF THE INVENTION
[0001] The present disclosure relates to a method for extraction of xylose from the black liquor. The developed process requires low energy and generates minimal waste as compared to conventional process.

BACKGROUND OF THE INVENTION
[0002] Background description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.
[0003] Xylose is the second highest available sugar from lignocellulosic biomass after glucose. It is a value-added chemical used to produce xylitol, flavoring agents, and find further applications in dental and chewing gums. The acidic hydrolysate produced during the pretreatment of lignocellulosic biomass is rich in xylose, which could be used to produce xylose commercially, increasing the economics of biorefinery. Commercially available processes are based on ion-exchange or solvent extraction, which are energy intensive processes and produce large amount of chemical waste. Thus, opportunities are available to develop sustainable and energy efficient processes to extract and isolate xylose in a biorefinery context.
[0004] Griffin G. J. [Sep. Sci. Technol., 2005, 40: 2337–2351] discloses purification and concentration of xylose and glucose from neutralized bagasse hydrolysates using 3,5-dimethylphenylboronic acid and modified aliquat 336 as Coextractants. The drawback of this article is that pH was adjusted to 6-7 using calcium hydroxide before extraction of sugars. Hence, the process cannot be readily applied to acidic hydrolysates.
[0005] Gori et al. [ACS Sustainable Chem. Eng. 2015, 3, 2452-2457] discloses isolation of C5-Sugars from the hemicellulose-rich hydrolyzate of distillers dried Grains. The drawback of this article is that no concentration step involved to improve the sugar concentration in acidic hydrolysate. Hence, higher PBA: xylose molar ratio was required to achieve higher esterification efficiency.
[0006] US 10,407,453 B2 discloses a process for isolating hemicellulose-based sugar from a biomass. The process includes providing a biomass hydrolyzate including a C5 sugar , forming a boronic ester or diester of the C5 sugar , extracting the boronic ester of diester of the C5 sugar , precipitating the C5 sugar using a boron capture agent , and isolating the C5 sugar from the precipitate . The isolated C5 sugar is provided in dry form. The drawback of this process is neutralization step included where the pH was adjusted to about 7 to 9. Higher PBA: xylose molar ratio equivalents (4:1) was used in the process.
[0007] Thus, there is a need to develop a new method for extraction of xylose from the black liquor which can overcome the drawbacks of the above mentioned prior arts. Biorefinery involves the processing of lignocellulosic biomass to derive valuable biofuels/biochemicals. To enhance the overall economics of the biorefineries, valorization of the side streams/ waste streams is necessary. Black liquor is one of the important streams generated after the acid pretreatment of the lignocellulosic biomass. This stream is rich in hemi cellulosic sugars, which could be extracted to produce valuable products. Hence, an innovative and cost-effective process is required to produce these sugars from the acidic liquor.

OBJECTS OF THE INVENTION
[0008] An objective of the present invention is to provide a method for extraction of xylose from the black liquor.
[0009] Another objective of the present invention is to provide cost effective extraction of xylose.
[0010] Another objective of the present invention is to provide a method for extraction of xylose without neutralization step and without use of transfer agent.
[0011] Another objective of the present invention is to provide a method to use reduced amount of reagent in the esterification reaction.
[0012] Yet another objective of the present invention is to provide a method for recovery of one or more reagent used in the process.
SUMMARY OF THE INVENTION
[0013] This summary is provided to introduce a selection of concepts in a simplified form that are further described below in Detailed Description section. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.
[0014] In an aspect, the present invention provides a method for extraction of xylose from the black liquor comprising: a) pre-treating 5 % to 25 % w/v of a lignocellulosic biomass with 0.5 % to 2.5 % w/v of a first acid to obtain an acidic filtrate of black liquor; b) concentrating the acidic filtrate under condition to obtain a concentrated acidic liquor; c) subjecting the concentrated acidic liquor from step b) to scheme 1 or scheme 2 to obtain pure xylose solids,
wherein, the scheme 1 comprises the steps of (i) contacting the concentrated acidic liquor containing xylose with phenyl boronic acid (PBA) in the molar ratio of (1:2 to 1:10) for esterification reaction under condition to obtain a first solid phase and a first liquid phase, wherein the first liquid phase is recycled back to pre-treatment step a); (ii) subjecting the solid phase from step (i) to either step (ii-a) hydrolysis under condition at alkaline/acidic pH resulting in the extraction of xylose in aqueous phase or step (ii-b) to transesterification reaction under condition using solvent and vicinal diol resulting in the extraction of xylose in solid phase, followed by solid-liquid separation wherein the solid phase containing the xylose from transesterification reaction is dried or the liquid phase containing the xylose from hydrolysis reaction is crystallized to obtain the purified xylose,
wherein, the scheme 2 comprises the steps of: c) contacting one part of the concentrated acidic liquor in 0.5 to 2 parts of an organic solvent containing phenyl boronic acid (PBA) for esterification under condition to obtain a first organic phase and a first aqueous phase; d) separation of the both phases and recycling the first aqueous phase of step c) back to step a); e) subjecting the first organic phase to transesterification reaction by adding a vicinal diol with/without combining with a second acid to obtain a second organic phase and a second aqueous phase or a second organic phase and a humectant precipitate; f) recycling the second organic phase of step e) back to esterification step c); g) crystallizing the second aqueous phase of step e) to obtain pure xylose; or h) washing the humectants precipitate of step e) with a second solvent followed by drying to obtain a dry powder of xylose.
[0015] In an aspect, the lignocellulosic biomass is selected from a group consisting of rice straw, wheat straw, sugarcane bagasse, soya stalk, rice husk, maize stalk, cotton stalk and combination thereof.
[0016] In an aspect, the first acid in step a) is selected from a group consisting of sulphuric acid, hydrochloric acid, formic acid, acetic acid, phosphoric acid, boric acid, nitric acid, succinic acid, lactic acid, and combination thereof.
[0017] In an aspect, the acidic filtrate of black liquor of step a) has a pH in the range of 0.5 to 5.5.
[0018] In an aspect, the acidic filtrate is concentrated at a temperature in the range of 40 to 60 °C under vacuum in the range of 70-150 mbar.
[0019] In an aspect, the concentrated acidic liquor of step b) has a pH in the range of 0.5 to 1.5.
[0020] In an aspect, the condition in step (i) of scheme 1 includes temperature in the range of 15 to 35°C for a period in the range of 0.5 to 3 hrs with agitation at a speed in the range of 100 to 1000 rpm
[0021] In an aspect, the conditions in step (ii-a) of scheme 1 includes temperature in the range of 15 to 100 °C for a period of 0.5 to 3 hrs and modulation of pH in the range of 1-14.
[0022] In an aspect, the molar ratio of Ethyl acetate and propylene glycol in step (ii-b) is in the range of 2:1 to 10:1.
[0023] In an aspect, the pH in step (ii-a) of scheme 1 is 1-14.
[0024] In an aspect, the pH in step (ii-a) of scheme 1 is adjusted to alkaline pH by the addition of sodium hydroxide, potassium hydroxide, calcium hydroxide, magnesium hydroxide, ammonium hydroxide etc
[0025] In an aspect, the pH in step (ii-a) of scheme 1 is adjusted to acidic pH by the addition of sulphuric acid, hydrochloric acid, formic acid, acetic acid, phosphoric acid, boric acid, nitric acid, succinic acid, lactic acid, etc.
[0026] In an aspect, the condition in step (ii-b) includes temperature in the range of 20 to 50°C for a period in the range of 2 to 24 hrs.
[0027] In an aspect, the drying in step (ii) is carried out at a temperature in the range of 40 to 80°C until a constant weight is obtained.
[0028] In an aspect, the liquid phase comprising of xylose obtained from the hydrolysis reaction of step (ii-a) is recycled back followed by effecting the same through step (ii-a).
[0029] In an aspect, the organic solvent in step c) of scheme 2 is selected from a group consisting of toluene, dichloromethane, hexane, pentane, benzene, chloroform, diethyl ether, xylene and combination thereof.
[0030] In an aspect, the condition in step c) of scheme 2 includes temperature in the range of 15 to 35°C for a period in the range of 0.5 to 3 hrs with agitation at a speed in the range of 100 to 1000 rpm
[0031] In an aspect, the PBA and xylose molar ratio in step c) of scheme 2 is in the range of 2:1 to 10:1, and the vicinal diol and xylose diester molar ratio in step e) is in the range of 2:1 to 10:1.
[0032] In an aspect, the vicinal diol in step (ii-b) or step e) is selected from a group consisting of propylene glycol, pinacol, ethylene glycol, glycerol and combination thereof.
[0033] In an aspect, the step e) further comprises a second acid in transesterification reaction and the second acid is selected from a group consisting of sulphuric acid, hydrochloric acid, nitric acid and combination thereof.
[0034] In an aspect, the condition in step e) includes temperature in the range of 20 to 100°C for a period in the range of 1 to 16 hrs.
[0035] In an aspect, the solvent of step (ii-b) or the second solvent of step h) is selected from a group consisting of ethyl acetate, ethanol, methanol, methyl acetate and combination thereof.
[0036] In an aspect, the drying in step h) is carried out at a temperature in the range of 40 to 80°C until a constant weight is obtained.
[0037] Various objects, features, aspects and advantages of the inventive subject matter will become more apparent from the following detailed description of preferred embodiments.

DESCRIPTION OF THE FIGURES
[0038] The accompanying drawings are included to provide a further understanding of the present disclosure, and are incorporated in and constitute a part of this specification. The drawings illustrate exemplary embodiments of the present disclosure and, together with the description, serve to explain the principles of the present disclosure.
[0039] FIG. 1 illustrates a flow chart of method for extraction of xylose from the black liquor (includes both Scheme 1 and Scheme 2).

DETAILED DESCRIPTION OF THE INVENTION
[0040] The following is a detailed description of embodiments of the disclosure. The embodiments are in such detail as to clearly communicate the disclosure. However, the amount of detail offered is not intended to limit the anticipated variations of embodiments; on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present disclosure as defined by the appended claims.
[0041] Unless the context requires otherwise, throughout the specification which follow, the word “comprise” and variations thereof, such as, “comprises” and “comprising” are to be construed in an open, inclusive sense that is as “including, but not limited to.”
[0042] As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the content clearly dictates otherwise. It should also be noted that the term “or” is generally employed in its sense including “and/or” unless the content clearly dictates otherwise.
[0043] In some embodiments, the numbers expressing quantities of ingredients, properties such as concentration, reaction conditions, and so forth, used to describe and claim certain embodiments of the invention are to be understood as being modified in some instances by the term “about.” Accordingly, in some embodiments, the numerical parameters set forth in the written description are approximations that can vary depending upon the desired properties sought to be obtained by a particular embodiment. In some embodiments, the numerical parameters should be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. Notwithstanding that the numerical ranges and parameters setting forth the broad scope of some embodiments of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as practicable.
[0044] The recitation of ranges of values herein is merely intended to serve as a shorthand method of referring individually to each separate value falling within the range. Unless otherwise indicated herein, each individual value is incorporated into the specification as if it is individually recited herein.
[0045] All processes described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided with respect to certain embodiments herein is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention otherwise claimed. No language in the specification should be construed as indicating any non-claimed element essential to the practice of the invention.
[0046] The headings and abstract of the invention provided herein are for convenience only and do not interpret the scope or meaning of the embodiments.
[0047] The following discussion provides many example embodiments of the inventive subject matter. Although each embodiment represents a single combination of inventive elements, the inventive subject matter is considered to include all possible combinations of the disclosed elements. Thus, if one embodiment comprises elements A, B, and C, and a second embodiment comprises elements B and D, then the inventive subject matter is also considered to include other remaining combinations of A, B, C, or D, even if not explicitly disclosed.
[0048] All publications herein are incorporated by reference to the same extent as if each individual publication or patent application were specifically and individually indicated to be incorporated by reference. Where a definition or use of a term in an incorporated reference is inconsistent or contrary to the definition of that term provided herein, the definition of that term provided herein applies and the definition of that term in the reference does not apply.
[0049] Groupings of alternative elements or embodiments of the invention disclosed herein are not to be construed as limitations. Each group member can be referred to and claimed individually or in any combination with other members of the group or other elements found herein. One or more members of a group can be included in, or deleted from, a group for reasons of convenience and/or patentability. When any such inclusion or deletion occurs, the specification is herein deemed to contain the group as modified thus fulfilling the written description that follows, and the embodiments described herein, is provided by way of illustration of an example, or examples, of particular embodiments of the principles and aspects of the present disclosure. These examples are provided for the purposes of explanation, and not of limitation, of those principles and of the disclosure.
[0050] It should also be appreciated that the present invention can be implemented in numerous ways, including as a system, a method or a device. In this specification, these implementations, or any other form that the invention may take, may be referred to as processes. In general, the order of the steps of the disclosed processes may be altered within the scope of the invention.
[0051] Various terms as used herein are shown below. To the extent a term used in a claim is not defined below, it should be given the broadest definition persons in the pertinent art have given that term as reflected in printed publications and issued patents at the time of filing.
[0052] Biorefinery operation involves pre-treatment of lignocellulosic biomass with the objective of reducing the recalcitrance and thereby increasing the hydrolysability. This involves treatment of biomass using various chemicals like oxidizing agents, alkalis, acids, organic solvents, and salts. Among these treatments, acid pre-treatment is one of the widely used method to solubilize hemicellulose portion and expose cellulose fibers for enzymatic hydrolysis. The aqueous black liquor, which is acidic in nature, generated during this process contains valuable xylose along with minor quantities of glucose, arabinose etc. The process of present disclosure developed is a chemical treatment-based process to selectively extract xylose from the acidic black liquor obtained after the acid pretreatment. The process involves esterification using solvents to produce xylose-diester and separate it from the impurities in the aqueous phase. Subsequently, xylose diester has been subjected to transesterification/hydrolysis reaction using suitable acid, alkali or vicinal diols to release free xylose into aqueous phase or obtain as a dry powder. Post transesterification/hydrolysis, the byproducts can be recycled back to esterification reaction step. Overall, the developed process requires low energy as it avoids distillation and generates minimal waste since it doesn’t require acid neutralization compared to conventional process.
[0053] An embodiment of the present disclosure is to provide a method for extraction of xylose from the black liquor comprising: a) pre-treating 5 % to 25 % w/v of a lignocellulosic biomass with 0.5 % to 2.5 % w/v of a first acid to obtain an acidic filtrate of black liquor; b) concentrating the acidic filtrate under condition to obtain a concentrated acidic liquor; c) subjecting the concentrated acidic liquor from step b) to scheme 1 or scheme 2 to obtain pure xylose solids. A flow chart of extraction of xylose is given in Figure. 1.
[0054] In an embodiment of the present invention, the scheme 1 comprises the steps of (i) contacting the concentrated acidic liquor containing 2.5 – 12 % w/v xylose with 4 - 20 w/v% of phenyl boronic acid (PBA) for esterification under condition to obtain a first solid phase and a first liquid phase, wherein both the phases are separated by solid liquid separation and the liquid phase is recycled back to pre-treatment step a); (ii) subjecting the solid phase from step (i) to either step (ii-a) hydrolysis at alkaline/acidic pH resulting in the extraction of xylose in aqueous phase or step (ii-b) to transesterification reaction using solvent and vicinal diol resulting in the extraction of xylose in solid phase, followed by solid-liquid separation wherein the solid phase containing the xylose from transesterification reaction is dried or the liquid phase containing the xylose from hydrolysis reaction is crystallized to obtain the purified xylose.
[0055] In an embodiment of the present invention, the liquid phase comprising limited xylose obtained from the esterification reaction is recycled back to step (a) or step (b), followed by effecting the same through steps (i), and (ii-a). In some embodiments, the recycling steps are repeated for as many times (for example, one time, twice, thrice, four times, and the like) until the recycled liquid phase does not contain xylose.
[0056] In an embodiment of the present invention, the liquid phase comprising of xylose obtained from the hydrolysis reaction of step (ii-a) is recycled back followed by effecting the same through step (ii-a). In some embodiments, the recycling steps are repeated for as many times (for example, one time, twice, thrice, four times, and the like) and the same is stopped once the solubilization ceased.
[0057] In an embodiment of the present invention, the solid phase comprising Phenyl Boronic Acid (PBA) obtained from the hydrolysis reaction is recycled back to esterification reaction of step (i), which then follows the step (ii-a) to obtain the purified xylose. In some embodiments, the recycling steps are repeated for as many times (for example, one time, twice, thrice, four times, and the like) to reduce the consumption of (PBA).
[0058] In an embodiment of the present invention, the pH of the hydrolysis step (ii-a) is adjusted to alkaline pH by the addition of sodium hydroxide, potassium hydroxide, calcium hydroxide, magnesium hydroxide, ammonium hydroxide and the like.
[0059] In an embodiment of the present invention, the pH of the hydrolysis step (ii-a) is adjusted to acidic pH by the addition of sulphuric acid, hydrochloric acid, formic acid, acetic acid, phosphoric acid, boric acid, nitric acid, succinic acid, lactic acid, and the like.
[0060] In an embodiment of the present invention, the pH of the hydrolysis step (ii-a) ranges from 1 to 14. For example 1-2, 2-3, 3-4, 4-5, 5-6, 6-7, 7-8, 8-9, 9-10, 10-11, 11-12, 12-13, or 13-14. Preferably, the pH is 1-2, 6-7 or 10-11.
[0061] In an embodiment of the present invention, the scheme 2 comprises the steps of: c) contacting one part of the concentrated acidic liquor in 0.5 to 2 parts of a first solvent containing phenyl boronic acid (PBA) for esterification under condition to obtain a first organic phase and a first aqueous phase; d) separation of the both phases and recycling the first aqueous phase of step c) back to step a); e) subjecting the first organic phase to transesterification reaction by adding a vicinal diol with/ without combining with a second acid to obtain a second organic phase and a second aqueous phase or a second organic phase and a humectant precipitate; f) recycling the second organic phase of step e) back to esterification step c); g) crystallizing the second aqueous phase of step e) to obtain a pure xylose; or h) washing the humectants precipitate of step e) with a second solvent followed by drying to obtain a dry powder of xylose, wherein the PBA and xylose molar ratio in step c) is in the range of 2:1 to 10:1, and the vicinal diol and xylose diester molar ratio in step e) is in the range of 2:1 to 10:1.
[0062] In an embodiment, the lignocellulosic biomass is selected from a group consisting of rice straw, wheat straw, sugarcane bagasse, soya stalk, rice husk, maize stalk, cotton stalk and combination thereof. Preferably, the lignocellulosic biomass is rice straw.
[0063] In an embodiment, the first acid in step a) is selected from a group consisting of sulphuric acid, hydrochloric acid, formic acid, acetic acid, phosphoric acid, boric acid, nitric acid and combination thereof. Preferably, the first acid is sulphuric acid.
[0064] In an embodiment, the acidic filtrate of black liquor of step a) has a pH in the range of 0.5 to 5.5. Preferably, the acidic filtrate has a pH of 1.5 to 2.5.
[0065] In an embodiment, the acidic filtrate is concentrated in a rota evaporator at a temperature in the range of 40 to 60 °C under vacuum in the range of 70-150 mbar. Preferably, the temperature of the rota evaporator is 50 °C and vacuum is 75 mbar.
[0066] In an embodiment, the concentrated acidic liquor of step b) has a pH in the range of 0.5 to 1.5. Preferably, the concentrated acidic liquor has a pH of 1.2.
[0067] In an embodiment, the condition in step (i) of scheme 1 includes temperature in the range of 15 to 35°C for a period in the range of 0.5 to 3 hrs with agitation at a speed in the range of 100 to 1000 rpm, and the reaction mixture has a pH in the range of 0.5 to 1.5.
[0068] In an embodiment, the condition of step (ii-a) of scheme 1 includes temperature in the range of 15 to 100 °C for a period of 0.5 to 3 hrs. Preferably, the temperature is 25 oC and the pH is 10 or the temperature is 80 °C and pH is 7 or 1.
[0069] In an embodiment, the PBA and xylose molar ratio in step (i) of scheme 1 is in the range of 2:1 to 10:1.
[0070] In an embodiment, the molar ratio of vicinal diol and xylose diester in step (ii-b) of scheme 1 is in the range of 2:1 to 10:1.
[0071] In an embodiment, the molar ratio of Ethyl Acetate and propylene glycol in step (ii-b) of scheme 1 is in the range of 2:1 to 10:1.
[0072] In an embodiment, the condition in step (ii-b) includes temperature in the range of 20 to 50°C for a period in the range of 2 to 24 hrs. Preferably, the condition in step (ii-b) includes temperature at 25 to 30 °C for a period of 2 to 3 hrs.
[0073] In an embodiment, the drying in step (ii-b) is carried out at a temperature in the range of 40 to 80 °until constant weight is obtained. Preferably, the drying is carried out at 45°C.
[0074] In an embodiment, the first solvent in step c) of scheme 2 is selected from a group consisting of toluene, dichloromethane, hexane, pentane, benzene, chloroform, diethyl ether, xylene and combination thereof. Preferably, the first solvent is toluene, dichloromethane and combination thereof.
[0075] In an embodiment, the condition in step c) includes temperature in the range of 15 to 35°C for a period in the range of 0.5 to 3 hrs with agitation at a speed in the range of 100 to 1000 rpm, the reaction mixture has a pH in the range of 0.5 to 1.5. Preferably, the condition includes temperature at 20 to 35 °C for a period of 1 to 2 hrs with agitation at a speed of 600 rpm.
[0076] In an embodiment, the vicinal diol in step e) is selected from a group consisting of propylene glycol, pinacol, ethylene glycol, glycerol and combination thereof. Preferably, the vicinal diol is propylene glycol and pinacol.
[0077] In an embodiment, the step e) further comprises a second acid when pinacol is used for transesterification reaction. The second acid is sulphuric acid, hydrochloric acid, nitric acid and combination thereof. Preferably, the second acid is sulphuric acid.
[0078] In an embodiment, the condition in step e) includes temperature in the range of 20 to 100°C for a period in the range of 1 to 16h hrs. Preferably, the condition in step e) includes temperature at 60 to 90 °C for a period of 2 hrs when pinacol is used in combination with a second acid for transesterification reaction and temperature of 25 to 35°C for a period of 16h when propylene glycol is used.
[0079] In an embodiment, the second solvent of step h) is selected from a group consisting of ethyl acetate, ethanol, methanol, methyl acetate and combination thereof. Preferably, the second solvent is ethyl acetate.
[0080] In an embodiment, the drying in step h) is carried out at a temperature in the range of 40 to 80°C until constant weight is attained. Preferably, the drying is carried out at 45°C.
[0081] Another embodiment of the present disclosure is to provide a method to reduce the amount of reactants in the esterification reaction by concentrating the acidic liquor obtained after the pretreatment of biomass by solvent extraction. This reduces the cost of the process.
[0082] Another aspect of the present disclosure is to provide a method for recovery of one or more reagent used in the process. Recovery of one or more reagents reduces the cost of the process.

ADVANTAGES OF THE PRESENT INVENTION
[0083] The developed process scheme offers flexibility and is more economical and environmentally friendly. Since the use of organic solvents is completely eliminated in one of the schemes, this allows the produced product to be used in applications within the food industry, while the other scheme offers the product for applications in chemical industries..
[0084] The developed process requires low energy as it avoids distillation and generates minimal waste since it doesn’t require acid neutralization compared to conventional process.
[0085] Earlier literature suggests the use of liquid-liquid extraction strategy at basic or alkaline pH conditions and uses a phase transfer agent to form a hydrophobic ion-pair complex. However, the present invention obviates the need for neutralizing acidic hydrolysates obtained after pretreatment in the lignocellulosic biorefinery and avoids the use of phase transfer agent. This, in turn, enhances the overall economics of the process. Moreover, the present invention also suggests concentrating the acidic hydrolysates before esterification reaction, which enhances the rate of reaction and minimizes the volume of liquid handled.
[0086] There is removal of two unit operations in the present invention i.e. neutralizing step is not carried out in the present invention and no use of phase transfer agent which makes the invention cost effective and economic as compared to the prior arts.
[0087] The present invention provides a method in which reduced amount of reagent used in the esterification reaction. Further, the present invention also recovers one or more reagent which reduces the cost of the process.
[0088] While the foregoing describes various embodiments of the disclosure, other and further embodiments of the disclosure may be devised without departing from the basic scope thereof. The invention is not limited to the described embodiments, versions or examples, which are included to enable a person having ordinary skill in the art to make and use the invention when combined with information and knowledge available to the person having ordinary skill in the art.

EXAMPLES
[0089] The present invention is further explained in the form of following examples. However, it is to be understood that the following examples are merely illustrative and are not to be taken as limitations upon the scope of the invention.
Example 1
[0090] Acid filtrate obtained after the pretreatment of rice straw (pH-1.6) was concentrated to increase the xylose concentration to 50 g/L. Concentrated acid liquor (100mL, pH-0.7) was contacted with 8.17g of phenyl boronic acid. Reaction was carried out at room temperature under agitation at 600rpm. After 30 min the reaction was stopped, and solid and liquid phase was separated. The solids were washed until the washed liquid attained pH 7. Thereafter, the solids were subjected to hydrolysis using alkaline water maintained at pH 10. Further, the solids were repeatedly added to the same reaction mixture and addition was stopped once the solubilization ceased. The aqueous phase was removed and subjected to HPLC analysis. The aqueous phase contained 275 g/L of xylose resulting in 83% overall xylose recovery. This stream could be crystallized to obtain pure xylose solids.
Example 2
[0091] Acid filtrate obtained after the pretreatment of rice straw (pH-1.6) was concentrated to increase the xylose concentration to 50 g/L. Concentrated acid liquor (100mL, pH-0.7) was contacted with 8.17g of phenyl boronic acid. Reaction was carried out at room temperature under agitation at 600rpm. After 30 min the reaction was stopped, and solid and liquid phase was separated. The solids were washed until the washed liquid attained pH-7. Thereafter, the solids were subjected to hydrolysis using acidic water maintained at pH 1 at 80°C. The aqueous phase was removed and subjected to HPLC analysis. The aqueous phase contained 15 g/L of xylose resulting in 70% overall xylose recovery. This stream could be crystallized to obtain pure xylose solids.
Example 3
[0092] Acid filtrate obtained after the pretreatment of rice straw (pH-1.6) was concentrated to increase the xylose concentration to 50 g/L. pH of concentrated acid liquor (100mL, pH-0.7) was adjusted to 5.7 and subsequently it was contacted with 8.17g of phenyl boronic acid. Reaction was carried out at room temperature under agitation at 600rpm. After 30 min the reaction was stopped, and solid and liquid phase was separated. The solids were washed until the washed liquid attained pH-7. Thereafter, the solids were subjected to hydrolysis using alkaline water maintained at pH 10. Further, the solids were repeatedly added to the same reaction mixture. Addition of solids was stopped once the solubilization ceased. The aqueous phase was removed and subjected to HPLC analysis. The aqueous phase contained 260 g/L of xylose resulting in 80% overall xylose recovery. This stream could be crystallized to obtain pure xylose solids.
Example 4
[0093] Acid filtrate obtained after the pretreatment of rice straw (pH-1.6) was concentrated to increase the xylose concentration to 50 g/L. pH of concentrated acid liquor (100mL, pH-0.7) was adjusted to 10 and subsequently it was contacted with 8.17g of phenyl boronic acid. Reaction was carried out at room temperature under agitation at 600rpm. After 30 min the reaction was stopped, and solid and liquid phase was separated. The solids were washed until the washed liquid attained pH-7. Thereafter, the solids were subjected to hydrolysis using alkaline water maintained at pH 10. Further, the solids were repeatedly added to the same reaction mixture and addition was stopped once the solubilization ceased. The aqueous phase was removed and subjected to HPLC analysis. The aqueous phase contained 265 g/L of xylose resulting in 80% overall xylose recovery. This stream could be crystallized to obtain pure xylose solids.
Example 5
[0094] Acid filtrate obtained after the pretreatment of rice straw (pH-1.6) was concentrated to increase the xylose concentration to 50 g/L. Concentrated acid liquor (100mL, pH-0.7) was contacted with 8.17g of phenyl boronic acid. Reaction was carried out at room temperature under agitation at 600rpm. After 30 min the reaction was stopped, and solid and liquid phase was separated. The solids were washed until the washed liquid attained pH 7. The solids (13g) were dissolved in 40 mL of ethyl acetate and propylene glycol (12.8 mL) was added. The reaction mixture was stirred at 600 rpm for 2h. The humectant precipitate formed was filtered and dried in an oven at 45°C. Xylose (4.51 g) was extracted.
Example 6
[0095] Acid filtrate obtained after the pretreatment of rice straw (pH-1.6) was concentrated to increase the xylose concentration to 34.16g/L. Concentrated acid liquor (100mL, pH-1.2) was contacted with 100mL of toluene containing 5.5g of phenyl boronic acid. Reaction was carried out at room temperature under agitation at 600rpm. After 1-2h the reaction was stopped, and organic and aqueous phases were separated. The organic phase was contacted with 10mL of propylene glycol under agitation for 16h. The pH of the reaction mixture was observed to be 4.3. The humectant precipitate formed was filtered and washed with ethyl acetate and dried in an oven at 45°C. Xylose (2.48g) was extracted.
Example 7
[0096] Acid filtrate obtained after the pretreatment of rice straw (pH-1.6) was concentrated to increase the xylose concentration to 27.7g/L. Concentrated acid liquor (100mL, pH-1.2) was contacted with 100mL of toluene containing 3.15g of phenyl boronic acid. Reaction was carried out at room temperature under agitation at 600rpm. After 1-2h the reaction was stopped, and organic and aqueous phases were separated. Pinacol (2.7g) was dissolved in the organic phase and this mixture was refluxed with 10mL of 5N sulphuric acid at 60°C for 2h. The aqueous phase was removed and subjected to HPLC analysis. The aqueous phase contained 135.6g/L of xylose.
Example 8
[0097] Acid filtrate obtained after the pretreatment of rice straw (pH-1.6) was concentrated to increase the xylose concentration to 27.7g/L. Concentrated acid liquor (100mL, pH-1.2) was contacted with the mixture of toluene (50mL) and dichloromethane (50mL) containing 3.15g of phenyl boronic acid. Reaction was carried out at room temperature under agitation at 600rpm. After 1-2h the reaction was stopped, and organic and aqueous phases were separated. Pinacol (3g) was dissolved in the organic phase and this mixture was refluxed with 10mL of 5N sulphuric acid at 90°C for 2h. The aqueous phase was removed and subjected to HPLC analysis. The aqueous phase contained 105.6g/L of xylose.
Example 9
[0098] Acid filtrate obtained after the pretreatment of rice straw (pH-1.6) was concentrated to increase the xylose concentration to 30.97g/L. Concentrated acid liquor (100mL, pH-1.2) was contacted with 100mL of toluene containing 5g of phenyl boronic acid. Reaction was carried out at room temperature under agitation at 600rpm. After 2h the reaction was stopped, and organic and aqueous phases were separated. Pinacol (3.83g) was dissolved in the organic phase and this mixture was refluxed with 10mL of 5N sulphuric acid at 60°C for 2h. The aqueous phase was removed and subjected to HPLC analysis. The aqueous phase contained 134. 94g/L of xylose.
Example 10
[0099] Acid filtrate obtained after the pretreatment of rice straw (pH-1.6) was concentrated to increase the xylose concentration to 29.61g/L. Concentrated acid liquor (1670mL, pH-1.2) was contacted with 1670mL of toluene containing 80.4g of phenyl boronic acid. Reaction was carried out at room temperature under agitation at 250rpm. After 2h the reaction was stopped, and organic and aqueous phases were separated. Pinacol (60.3g) was dissolved in the organic phase and this mixture was refluxed with 170mL of 5N sulphuric acid at 60°C for 2h. The aqueous phase was removed and subjected to HPLC analysis. The aqueous phase contained 158.10g/L of xylose.
Example 11
[00100] Acid filtrate obtained after the pretreatment of rice straw (pH-1.6) was concentrated to increase the xylose concentration to 50 g/L. Concentrated acid liquor (100mL, pH-0.7) was contacted with 8.17g of phenyl boronic acid. Reaction was carried out at room temperature under agitation at 600rpm. After 30 min the reaction was stopped, and solid and liquid phase was separated. The solids were washed until the washed liquid attained pH-7. Thereafter, the solids were subjected to hydrolysis using water maintained at pH 7 at 80°C for 21h. The aqueous phase was removed and subjected to HPLC analysis. The aqueous phase contained 14.42 g/L of xylose resulting in 67.3% overall xylose recovery. This stream could be crystallized to obtain pure xylose solids.
[00101] The foregoing examples are merely illustrative and are not to be taken as limitations upon the scope of the invention. Various changes and modifications to the disclosed embodiments will be apparent to those skilled in the art. Such changes and modifications may be made without departing from the scope of the invention.
,CLAIMS:1. A method for extraction of xylose from the black liquor comprising: a) pre-treating 5 % to 25 % w/v of a lignocellulosic biomass with 0.5 % to 2.5 % w/v of a first acid to obtain an acidic filtrate of black liquor; b) concentrating the acidic filtrate under condition to obtain a concentrated acidic liquor; c) subjecting the concentrated acidic liquor from step b) to scheme 1 or scheme 2 to obtain pure xylose solids,
wherein, the scheme 1 comprises the steps of (i) contacting the concentrated acidic liquor containing xylose with phenyl boronic acid (PBA) in the molar ratio of (1:2 to 1:10) for esterification reaction under condition to obtain a first solid phase and a first liquid phase, wherein the first liquid phase is recycled back to pre-treatment step a); (ii) subjecting the solid phase from step (i) to either step (ii-a) hydrolysis under condition at alkaline/acidic pH resulting in the extraction of xylose in aqueous phase or step (ii-b) to transesterification reaction under condition using solvent and vicinal diol resulting in the extraction of xylose in solid phase, followed by solid-liquid separation wherein the solid phase containing the xylose from transesterification reaction is dried or the liquid phase containing the xylose from hydrolysis reaction is crystallized to obtain the purified xylose,
wherein, the scheme 2 comprises the steps of: c) contacting one part of the concentrated acidic liquor in 0.5 to 2 parts of an organic solvent containing phenyl boronic acid (PBA) for esterification under condition to obtain a first organic phase and a first aqueous phase; d) separation of both the phases and recycling the first aqueous phase of step c) back to step a); e) subjecting the first organic phase to transesterification reaction by adding a vicinal diols to obtain a second organic phase and a second aqueous phase or a second organic phase and a humectant precipitate; f) recycling the second organic phase of step e) back to esterification step c); g) crystallizing the second aqueous phase of step e) to obtain pure xylose; or h) washing the humectants precipitate of step e) with a second solvent followed by drying to obtain a dry powder of xylose.
2. The method as claimed in claim 1, wherein the lignocellulosic biomass is selected from a group consisting of rice straw, wheat straw, sugarcane bagasse, soya stalk, rice husk, maize stalk, cotton stalk and combination thereof.
3. The method as claimed in claim 1, wherein the first acid in step a) is selected from a group consisting of sulphuric acid, hydrochloric acid, formic acid, acetic acid, phosphoric acid, boric acid, nitric acid, succinic acid, lactic acid, and combination thereof.
4. The method as claimed in claim 1, wherein the acidic filtrate of black liquor of step a) has a pH in the range of 0.5 to 5.5.
5. The method as claimed in claim 1, wherein the acidic filtrate is concentrated at a temperature in the range of 40 to 60 °C under vacuum in the range of 70-150 mbar.
6. The method as claimed in claim 1, wherein the concentrated acidic liquor of step b) has a pH in the range of 0.5 to 1.5.
7. The method as claimed in claim 1, wherein the condition in step (i) of scheme 1 includes temperature in the range of 15 to 35°C for a period in the range of 0.5 to 3 hrs with agitation at a speed in the range of 100 to 1000 rpm
8. The method as claimed in claim 1, wherein the conditions in step (ii-a) of scheme 1 includes temperature in the range of 15 to 100 °C for a period of 0.5 to 3 hrs and modulation of pH in the range of 1-14.
9. The method as claimed in claim 1, wherein the molar ratio of Ethyl acetate and propylene glycol in step (ii-b) is in the range of 2:1 to 10:1.
10. The method as claimed in claim 1, wherein the pH in step (ii-a) of scheme 1 is 1-14.
11. The method as claimed in claim 1, wherein the pH in step (ii-a) of scheme 1 is adjusted to alkaline pH by the addition of sodium hydroxide, potassium hydroxide, calcium hydroxide, magnesium hydroxide, ammonium hydroxide etc
12. The method as claimed in claim 11, wherein the pH in step (ii-a) of scheme 1 is adjusted to acidic pH by the addition of sulphuric acid, hydrochloric acid, formic acid, acetic acid, phosphoric acid, boric acid, nitric acid, succinic acid, lactic acid, etc.
13. The method as claimed in claim 1, wherein the condition in step (ii-b) includes temperature in the range of 20 to 50°C for a period in the range of 2 to 24 hrs.
14. The method as claimed in claim 1, wherein the drying in step (ii) is carried out at a temperature in the range of 40 to 80°C until a constant weight is obtained.
15. The method as claimed in claim 1, wherein the liquid phase comprising of xylose obtained from the hydrolysis reaction of step (ii-a) is recycled back followed by effecting the same through step (ii-a).
16. The method as claimed in claim 1, wherein the organic solvent in step c) of scheme 2 is selected from a group consisting of toluene, dichloromethane, hexane, pentane, benzene, chloroform, diethyl ether, xylene and combination thereof.
17. The method as claimed in claim 1, wherein the condition in step c) of scheme 2 includes temperature in the range of 15 to 35°C for a period in the range of 0.5 to 3 hrs with agitation at a speed in the range of 100 to 1000 rpm
18. The method as claimed in claim 1, wherein the PBA and xylose molar ratio in step c) of scheme 2 is in the range of 2:1 to 10:1, and the vicinal diol and xylose diester molar ratio in step e) is in the range of 2:1 to 10:1.
19. The method as claimed in claim 1, wherein the vicinal diol in step (ii-b) or step e) is selected from a group consisting of propylene glycol, pinacol, ethylene glycol, glycerol and combination thereof.
20. The method as claimed in claim 1, wherein the step e) further comprises a second acid in transesterification reaction and the second acid is selected from a group consisting of sulphuric acid, hydrochloric acid, nitric acid and combination thereof.
21. The method as claimed in claim 1, wherein the condition in step e) includes temperature in the range of 20 to 100°C for a period in the range of 1 to 3 hrs.
22. The method as claimed in claim 1, wherein the solvent of step (ii-b) or the second solvent of step h) is selected from a group consisting of ethyl acetate, ethanol, methanol, methyl acetate and combination thereof.
23. The method as claimed in claim 1, wherein the drying in step h) is carried out at a temperature in the range of 40 to 80°C until a constant weight is obtained.