DESC:TECHNICAL FIELD
The present disclosure relates to ionic and non-ionic DES based system for selective delignification of biomass and a process for the same. The present invention provides an effective pretreatment which recover maximum amount of carbohydrates (cellulose and hemicelluloses) and accomplish higher delignification, and thus enzymes in the downstream saccharification can hydrolyse the polymeric sugars to fermentable sugars more efficiently.
BACKGROUND
Lignocellulose is the most abundantly available plant-based material on the Earth. This organic matter can be converted into liquid green fuel such as bioethanol through pretreatment, enzymatic hydrolysis and fermentation processes. Among the three important stages in the process of biomass conversion to ethanol, pretreatment is the most critical step as it determines the overall process economics. An effective pretreatment should recover maximum amount of carbohydrates (cellulose and hemicelluloses) and accomplish higher delignification, and thus enzymes in the downstream saccharification can hydrolyse the polymeric sugars to fermentable sugars more efficiently. Unavailability of a cost-effective pretreatment process is one of the major limitations in making the existing 2G ethanol technologies commercially viable. Therefore, an effective pretreatment is desired for removing or break-opening the lignin-hemicellulose barrier.
SUMMARY
This summary is provided to introduce a selection of concepts in a simplified format that are further described in the detailed description of the invention. This summary is not intended to identify key or essential inventive concepts of the claimed subject matter, nor is it intended for determining the scope of the claimed subject matter.
In accordance with the present subject matter, a system ionic and non-ionic DES based system for selective delignification of biomass is provided.
In yet another embodiment of the present disclosure, ionic and non-ionic DES based process for selective delignification of biomass is provided.
In accordance with another embodiment, the present invention provides an ionic and non-ionic DES based process for selective delignification of biomass, said process comprising the steps of:
a) milling the feedstock to reduce biomass size in the range of about 20-25 mm;
b) preparing Deep Eutectic Solvent (DES) system by mixing 1 equivalent of Tetra Butyl Ammonium Bromide (TBAB) in three equivalents of Mono-ethanolamine;
c) mixing the reduced sized biomass obtained in step a) with DES (6 parts): THF (4 parts) at solid to liquid ratio of 1: 10;
d) carrying out delignification reaction for about 3 hour at around 100 °C and subjecting the slurry for solid-liquid separation after completion of delignification reaction;
e) washing the delignified solid rich in cellulose & hemicelluloses obtained in step d) with ethanol and subsequently washing with water to remove residual lignin and DES;
f) pooling all the liquid streams obtained from steps d) and (e) and allowing for lignin settling at <10°C for 60 to 120 minutes and solid/liquid separation for obtaining lignin; and
g) subjecting the liquid stream obtained in step (f) for distillation to recover ethanol and DES-THF system; and recycling back the DES-THF system to step (c) for delignification of fresh feedstock.

In accordance with another embodiment, the present invention provides a process for selective delignification of biomass, said process comprising the steps of:
a) milling the feedstock to reduce biomass size in the range of about 20-25 mm;
b) mixing the reduced sized biomass obtained in step a) with 1% w/v NaOH + 3 % w/v Tetra Butyl Ammonium Bromide (TBAB) in Ethanol at solid to liquid ratio of 1: 10;
c) carrying out delignification reaction for about 3 hour at around 100 °C and subjecting the slurry for solid-liquid separation after completion of delignification reaction;
d) washing the delignified solid rich in cellulose & hemicelluloses obtained in step c) with ethanol to remove residual lignin and DES;
e) pooling all the liquid streams obtained from steps c) and (d) and subjected for DCM extraction to remove lignin; and
f) subjecting the liquid stream having DES + DCM obtained in step (e) for distillation to recover DCM and ethanol (partially) and recycling back the Ethanol.NaOH-TBAB to step (b) for delignification of fresh feedstock.

In accordance with another embodiment, the present invention provides a process for selective delignification of biomass, said process comprising the steps of:
a) milling the feedstock to reduce biomass size in the range of about 20-25 mm;
b) mixing the reduced sized biomass obtained in step a) with 5% w/v NH3 + 3 % w/v Tetra Butyl Ammonium Bromide (TBAB) in Ethanol at solid to liquid ratio of 1: 10;
c) carrying out delignification reaction for about 3 hour at around 100 °C and subjecting the slurry for solid-liquid separation after completion of delignification reaction;
d) washing the delignified solid rich in cellulose & hemicelluloses obtained in step c) with ethanol to remove residual lignin and DES;
e) pooling all the liquid streams obtained from steps c) and (d) and subjected for distillation to recover ethanolic ammonia; and
f) subjecting the liquid stream having TBAB + lignin obtained in step (e) for DCM extraction followed by distillation to recover DCM and TBAB and recycling back the Ethanol.NH3-TBAB to step (b) for delignification of fresh feedstock.

The details of one or more embodiments are set forth in the accompanying drawings and description below. Other features and advantages will be apparent from a reading of the following detailed description and a review of the associated drawings. It is to be understood that the following detailed description is explanatory only and is not restrictive of the invention as claimed.

BRIEF DESCRIPTION OF DRAWINGS:

To further clarify advantages and aspects of the invention, a more particular description of the invention will be rendered by reference to specific embodiments thereof, which is illustrated in the appended drawings. It is appreciated that the drawings depict only typical embodiments of the invention and are therefore not to be considered limiting of its scope.

Figure 1 provides Lignin appearance in untreated (a) and DES pretreated (b) rice straw. Rice straw (b) pretreated with DES is in accordance with the present invention.

Figure 2 provides FTIR spectra of untreated (UT-RS) and DES pretreated rice straw (PT-RS). FTIR spectra of DES pretreated rice straw (PT-RS) is in accordance with the present invention.

Figure 3 provides Enzymatic conversion of untreated (UT-RS) and pretreated rice straw (PT-RS) in comparison with MCC (control) at different cellulase dosages incubated at 50 °C for 48 h. Pretreated rice straw (PT-RS) at different cellulase dosages incubated at 50 °C for 48 h is in accordance with the present invention.

Figure 4 provides Scheme -I in accordance with example 1 of the present invention.

Figure 5 provides Scheme -II in accordance with example 2 of the present invention.

Figure 6 provides Scheme -III in accordance with example 3 of the present invention.

Further, those of ordinary skill in the art will appreciate that elements in the drawings are illustrated for simplicity and may not have been necessarily drawn to scale. For example, the dimensions of some of the elements in the drawings may be exaggerated relative to other elements to help to improve understanding of aspects of the invention. Furthermore, one or more elements may have been represented in the drawings by conventional symbols, and the drawings may show only those specific details that are pertinent to understanding the embodiments of the invention so as not to obscure the drawings with details that will be readily apparent to those of ordinary skill in the art having benefit of the description herein.

DETAILED DESCRIPTION:

For the purpose of promoting an understanding of the principles of the invention, reference will now be made to the embodiments and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications in the illustrated system, and such further applications of the principles of the invention as illustrated therein being contemplated as would normally occur to one skilled in the art to which the invention relates.

It will be understood by those skilled in the art that the foregoing general description and the following detailed description are explanatory of the invention and are not intended to be restrictive thereof.

Reference throughout this specification to “an aspect”, “another aspect” or similar language means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrase “in an embodiment”, “in another embodiment” and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment.

The terms "comprises", "comprising", or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a process or method that comprises a list of steps does not include only those steps but may include other steps not expressly listed or inherent to such process or method. Similarly, one or more devices or sub-systems or elements or structures or components proceeded by "comprises... a" does not, without more constraints, preclude the existence of other devices or other sub-systems or other elements or other structures or other components or additional devices or additional sub-systems or additional elements or additional structures or additional components.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The system, methods, and examples provided herein are illustrative only and not intended to be limiting.

In accordance with an embodiment of the present disclosure, the present invention provides a water-free solvent system and process for selective delignification (up to ~50%) of biomass.
In yet another embodiment of the present disclosure, the present invention provides about 5-fold reduction in water consumption compared to conventional acid processes.
In accordance with an embodiment of the present disclosure, the present invention provides multi-feedstock processing (Rice straw, Sugarcane bagasse & Wheat straw).
The present invention discloses novel and efficient recyclable DES Deep eutectic solvent (Ionic & Non-Ionic) systems that have been developed for delignification of biomass (rice straw/ wheat straw/ sugarcane bagasse). All these systems utilize a mixture of eutectic solvents explicitly designed for selective delignification of biomass under the process conditions of low severity (at around 100 °C). The solvents used for delignification have been successfully recycled (with ~85 % recovery) for 10 number of subsequent pretreatment cycles with similar delignification efficiency (~50 %). The carbohydrate recoveries were observed to be around 91 % and 62 % for cellulose and hemicelluloses, respectively.
EXAMPLES

Example 1:
During process of biomass conversion to ethanol, pretreatment is the most critical step as it determines the overall process economics. The present invention provides an effective pretreatment which recover maximum amount of carbohydrates (cellulose and hemicelluloses) and accomplish higher delignification, and thus enzymes in the downstream saccharification can hydrolyse the polymeric sugars to fermentable sugars more efficiently.
In one of the embodiment, the feedstock is initially subjected to milling to obtain a feed with a size of ~20-25 mm. Then, the size reduced biomass is mixed with a DES (6 parts): THF tetra hydro furan (4 parts) at solid to liquid ratio of 1: 10. DES means Deep eutectic solvent and THF means Tetrahydrofuran. DES system is prepared by mixing 1 equivalent of Tetra Butyl Ammonium Bromide (TBAB) in three equivalents of Mono-ethanolamine. The delignification reaction is carried out for about 3 hour at around 100 °C. After completion of the reaction, the slurry will be subjected for solid-liquid separation. Before sending for enzymatic hydrolysis, the delignified solid (rich in cellulose & hemicelluloses) is washed with ethanol followed by water to remove residual lignin and DES. In order to recycle the DES system back, all the liquid streams generated in the process are pooled and allowed for lignin settling at <10°C for 60 to 120 minutes. Afterwards, the liquid stream having DES will be subjected for distillation to recover ethanol and then recycled back for delignification of fresh feedstock. Scheme -I (Figure 4) describes the process of example 1 in detailed manner.

Example 2:
In another embodiment, the feedstock is initially subjected to milling to obtain a feed with a size of ~20-25 mm. Then, the size reduced biomass is mixed with 1% w/v NaOH + 3 % w/v Tetra Butyl Ammonium Bromide (TBAB) in Ethanol at solid to liquid ratio of 1: 10. The delignification reaction is carried out for about 3 hour at around 100 °C. After completion of the reaction, the slurry will be subjected for solid-liquid separation. Before sending for enzymatic hydrolysis, the delignified solid (rich in cellulose & hemicelluloses) is washed with ethanol to remove residual lignin & DES. In order to recycle the DES system back, all the liquid streams generated in the process are pooled and subjected for DCM extraction to remove lignin. Afterwards, the liquid stream having DES + DCM will be subjected for distillation to recover DCM and ethanol (partially) before sending it back for delignification of fresh feedstock. Scheme -II (Figure 5) describes the process of example 2 in detailed manner.

Example 3:
In yet another embodiment, the feedstock is initially subjected to milling to obtain a feed with a size of ~20-25 mm. Then, the size reduced biomass is mixed with 5% w/v NH3 + 3 % w/v Tetra Butyl Ammonium Bromide (TBAB) in Ethanol at solid to liquid ratio of 1: 10. The delignification reaction is carried out for about 3 hour at around 100 °C. After completion of the reaction, the slurry will be subjected for solid-liquid separation. Before sending for enzymatic hydrolysis, the delignified solid (rich in cellulose & hemicelluloses) is washed with ethanol to remove residual lignin & DES. In order to recycle the DES system back, all the liquid streams generated in the process are pooled and subjected for distillation to recover ethanolic ammonia. Afterwards, the liquid stream having TBAB + lignin will be subjected for DCM extraction followed by distillation to recover DCM and TBAB before sending it back for delignification of fresh feedstock. Scheme -III (Figure 6) describes the process of example 3 in detailed manner.

In yet another embodiment of the present disclosure:
a. The biomass (rice straw/wheat straw/ sugarcane bagasse) is selectively delignified by recyclable ionic and non-ionic DES systems.
b. Biomass delignification is carried out at ~100°C in a system of DES (6 parts): THF (4 parts) at solid to liquid ratio of 1: 10. DES system is prepared by mixing 1 equivalent of Tetra Butyl Ammonium Bromide (TBAB) in 3 equivalents of Mono-ethanolamine at a solid to liquid ratio of 1: 5 or 1: 10.
c. The solvents and DES separated from treated solids are recycled for several cycles delignification of fresh biomass.

In yet another embodiment, the present invention provides an ionic and non-ionic DES based process for selective delignification of biomass, said process comprising the steps of:
a) milling the feedstock to reduce biomass size in the range of about 20-25 mm;
b) preparing Deep Eutectic Solvent (DES) system by mixing 1 equivalent of Tetra Butyl Ammonium Bromide (TBAB) in three equivalents of Mono-ethanolamine;
c) mixing the reduced sized biomass obtained in step a) with DES (6 parts): THF (4 parts) at solid to liquid ratio of 1: 10;
d) carrying out delignification reaction for about 3 hour at around 100 °C and subjecting the slurry for solid-liquid separation after completion of delignification reaction;
e) washing the delignified solid rich in cellulose & hemicelluloses obtained in step d) with ethanol and subsequently washing with water to remove residual lignin and DES;
f) pooling all the liquid streams obtained from steps d) and (e) and allowing for lignin settling at <10°C for 60 to 120 minutes and solid/liquid separation for obtaining lignin; and
g) subjecting the liquid stream obtained in step (f) for distillation to recover ethanol and DES-THF system; and recycling back the DES-THF system to step (c) for delignification of fresh feedstock.

In yet another embodiment, the present invention provides a process for selective delignification of biomass, said process comprising the steps of:
a) milling the feedstock to reduce biomass size in the range of about 20-25 mm;
b) mixing the reduced sized biomass obtained in step a) with 1% w/v NaOH + 3 % w/v Tetra Butyl Ammonium Bromide (TBAB) in Ethanol at solid to liquid ratio of 1: 10;
c) carrying out delignification reaction for about 3 hour at around 100 °C and subjecting the slurry for solid-liquid separation after completion of delignification reaction;
d) washing the delignified solid rich in cellulose & hemicelluloses obtained in step c) with ethanol to remove residual lignin and DES;
e) pooling all the liquid streams obtained from steps c) and (d) and subjected for DCM extraction to remove lignin; and
f) subjecting the liquid stream having DES + DCM obtained in step (e) for distillation to recover DCM and ethanol (partially) and recycling back the Ethanol.NaOH-TBAB to step (b) for delignification of fresh feedstock.

In yet another embodiment, the present invention provides a process for selective delignification of biomass, said process comprising the steps of:
a) milling the feedstock to reduce biomass size in the range of about 20-25 mm;
b) mixing the reduced sized biomass obtained in step a) with 5% w/v NH3 + 3 % w/v Tetra Butyl Ammonium Bromide (TBAB) in Ethanol at solid to liquid ratio of 1: 10;
c) carrying out delignification reaction for about 3 hour at around 100 °C and subjecting the slurry for solid-liquid separation after completion of delignification reaction;
d) washing the delignified solid rich in cellulose & hemicelluloses obtained in step c) with ethanol to remove residual lignin and DES;
e) pooling all the liquid streams obtained from steps c) and (d) and subjected for distillation to recover ethanolic ammonia; and
f) subjecting the liquid stream having TBAB + lignin obtained in step (e) for DCM extraction followed by distillation to recover DCM and TBAB and recycling back the Ethanol.NH3-TBAB to step (b) for delignification of fresh feedstock.

In yet another embodiment, the present invention provides a process wherein the feedstock comprises one or more of rice straw, wheat straw and sugarcane bagasse.

In yet another embodiment, the present invention provides a process, wherein solvents used for delignification are recycled with about 85 % recovery from at least ten subsequent pretreatment cycles and exhibiting about 50 % delignification efficiency even at tenth pretreatment cycle.

In yet another embodiment, the present invention provides a process, wherein the process provides a water-free solvent system.

In yet another embodiment, the present invention provides a process, wherein recovered carbohydrates comprises cellulose and hemicelluloses in the range of about 91 % and 62 % respectively.
In yet another embodiment, the present invention provides a process, wherein said process exhibits 100 % DES recovery, 67 % solid recovery, 87.8 % cellulose recovery, 58.6 % hemicellulose recovery, and 52.6 % delignification efficiency after tenth pretreatment cycle.

In yet another embodiment, the present invention provides a process, wherein the water-free solvent system is recovered almost 85%.
In yet another embodiment, the present invention provides a process, wherein the DES-pretreated feedstock is highly amenable to cellulolytic enzymes, and it is hydrolysed at low enzyme loadings of 5 FPU/g with 58% efficiency and at 10 FPU/g with 84.5% efficiency.

Example 4: Effect of pretreatment on chemical composition of biomass

The changes occurring in rice straw upon pretreatment with DES- solvent systems were determined by compositional, histochemical and spectroscopic (FTIR & EDX) analyses. The histochemical analysis of phloroglucinol (PG)-stained rice straw samples showed that untreated samples appeared dark brown (possibly due to the binding of phloglucinol with hydroxybenzaldehyde in lignin) (Figure 1a), whereas the pretreated samples appear lighter or yellowish (probably due to the decreased lignin content and exposed cellulose microfibrils) (Figure 1b). Microscopic observations of DES- solvent treated and untreated samples matched with the results of compositional analysis which indicated that the pretreated rice straw samples had lower lignin content (~46 %) and increased glucan content (~ 36 %) over 10 solvent recycles (Table 1). The analysis of DES- solvent treated solids by FTIR showed intensification of the corresponding peaks (1031 cm-1 and 3400 cm-1) due to C-O stretching and O-H bending (Figure 2), thereby indicating no changes in cellulose and hemicellulose concentrations. As expected, the peak intensities at 1549 cm-1, 1644 cm-1 (due to C=O stretching of aromatic ketones in lignin) and 2885 cm-1 (related to C-H stretching of lignin) had reduced (Figure 2) due to the reduced lignin content.

Table 1. Composition analysis of untreated (UT-RS) and pretreated rice straw (PT-RS) samples during subsequent solvent reuses (C1-C10); all of the percentage compositions of raw and pretreated solid samples were calculated based on their dry weights.
Sample Glucan (%) Xylan (%) Arabinan (%) Lignin (%) Ash (%) Ext. (%)

UT-RS 31.4 ± 0.5 19.9 ± 0.8 2.7 ± 0.2 19.1 ± 0.7 11.4 ± 1.5 12.5 ± 1.2
PT-RS C-1 solids 41.1 ± 0.7 18.1 ± 0.7 2.9 ± 0.0 10.5 ± 0.1 14.8 ± 1.2 ND
PT-RS
C-2 solids 41.9 ± 0.6 18.4 ± 0.0 2.6 ± 0.0 10.17 ± 0.3 14.3 ± 1.8
PT-RS
C-3 solids 41.9 ± 0.2 18.4 ± 0.1 2.8 ± 0.0 10.33 ± 0.2 15.0 ± 1.1
PT-RS
C-4 solids 44.1 ± 0.2 19.8 ± 0.2 2.3 ± 0.5 10.0 ± 0.5 10.0 ± 0.8
PT-RS
C-5 solids 46.0 ± 1.0 20.5 ± 0.1 3.0 ± 0.1 10.3 ± 0.1 12.3 ± 1.2
PT-RS
C-6 solids 43.6 ± 0.6 20.3 ± 3.1 2.5 ± 0.3 11 ± 0.6 8.3 ± 1.5
PT-RS
C-7 solids 44.2 ± 0.3 24.5 ± 0.4 3.3 ± 0.5 10.0 ± 0.4 14.0 ± 0.9
PT-RS
C-8 solids 43.9 ± 0.8 24.9 ± 0.7 3.3 ± 0.2 12.7 ± 0.8 13.0 ± 1.1
PT-RS
C-9 solids 40.6 ± 0.5 16.4 ± 0.9 1.85 ± 0.5 8.0 ± 1.1 13.0 ± 0.9
PT-RS
C-10 solids 41.2 ± 1.1 17.4 ± 0.5 2.3 ± 0.2 9.0 ± 0.5 13.2 ± 0.5
Note: Ext., extractives; ND, not determined.

Rice straw contains several metals such as K+, Al3+, Mn2+, Fe3+, Cu2+, Zn2+ etc., which can interfere with the action of cellulases during hydrolysis. To ascertain the effect of DES- solvent pretreatment on the metal content of rice straw, elemental analysis of untreated and pretreated rice straw samples was carried out using ED-XRF. The results indicated that pretreatment of rice straw containing the elements S, K, Mg, P, Ca Si, O, C, Al caused a reduction in contents of S and K and the removal of Mg, P and Ca (Table 2). The relative concentrations of Si and O increased due to removal of lignin and the corresponding increase in the carbohydrate content after DES- solvent pretreatment. Another evidence for the selective removal of lignin comes from the determination of the oxygen: carbon (O/C) ratios of separated lignin and treated /untreated biomass samples. Usually, the O/C ratios of lignin and biomass samples are 0.511 and 1.23, respectively. In the present invention, it was found that the O/C ratio of pretreated rice straw (1.26) was three times higher than the untreated biomass samples (0.42), due to reduced O and increased C contents possibly due to the selective removal of lignin.

Table 2. Surface elemental analysis of untreated (UT-RS) and pretreated rice straw (PT-RS) samples, and their oxygen to carbon ratios.

Element Untreated rice straw Pretreated rice straw
Weight % Atomic % Weight % Atomic %
C 59.77 71.13 38.8 48.02
O 25.16 22.48 49.13 45.63
Mg 0.48 0.28 -- -
Al 0.73 0.39 0.74 0.41
Si 3.17 1.61 10.88 5.76
P 0.91 0.42 - -
S 0.50 0.22 0.25 0.11
Ca 1.07 0.38 - -
K 6.13 2.24 0.20 0.08
O/C 0.42 1.26
Example 5: Evaluation of solvent system recyclability and its efficacy
The process cost can be substantially lowered by the reuse of catalysts if the final product quality remains unaffected. During our study, the DES- solvent mixture recovered after pretreatment was reused for upto 10 subsequent pretreatments with an average solvent recovery ranging from 74 to as much as 100 % (Table 3). The average cellulose and hemicelluloses recoveries were consistent and remained higher ~91% and ~68 %, respectively, even after 10 recycles (Table 3). Similarly, the concentration of lignin removed from biomass (~46 %) remained comparable during solvent reuse while the glucan concentrations varied only marginally (+/? 1.75) (Table 3). These minor variations in concentrations of different components (Table 3) could also be attributed to handling errors. Overall, our results indicate that the newly developed DES- solvent system can be effectively used for biomass pretreatment under milder conditions and recycled multiple times without generating any additional by-products.

Table 3. Effect of recycling DES-solvent system on delignification, cellulose & hemicellulose recoveries during rice straw pretreatment (Values presented are mean for n=2 analyses)
Cycle No. Volume of fresh dDES-Solvent mix (mL) Recycled DES-Solvent (mL) DES Recovery (%) Solid recovery (%) Cellulose recovery (%) Hemicellulose recovery (%)

Delignification

efficiency (%)

Control-A 380 (only DES) 82.7 95.3 70.1 32.9
Control-B 380 (only THF) 93 98.5 93.6 2.6
C-1 380 74 72 94.4 67.3 44.7
C-2 100 280 79 69 91.5 64.6 46.5
C-3 80 300 79 68 91.0 64.0 45.6
C-4 80 300 79 64 89.2 62.4 47.4
C-5 70 310 82 64 93.8 66.9 45.8
C-6 60 320 84 69 95.9 70.0 42.1
C-7 50 330 87 67 93.9 86.9 47.4
C-8 40 340 89 65 91.4 81.9 33.2
C-9 20 360 95 66 85.7 53.9 57.9
C-10 0 380 100 67 87.8 58.6 52.6
*AVG-10 85 67 91.5 67.6 46.3

Note: BDW (bone dry weight) of raw rice straw used in each cycle of pretreatment was 55 g (solids concentration ~15 % w/v).
dThe solvent mentioned above contains six parts of original DES and four parts of THF solvent.
*AVG-10: Average recoveries of DE-THF solvent, treated solids, cellulose, hemicellulose & average delignification efficiency over ten subsequent pretreatment cycles.

Example 6: Hydrolysability of pretreated biomass to cellulolytic enzymes

The effectiveness of the newly developed DES- solvent system was established by the extent of lignin removal and by determining the ease of cellulose hydrolysability (Figure 3). The enzymatic hydrolysis of DES- solvent treated biomass showed that the percentage hydrolysis (~58%) obtained at lower enzyme dosage of 5 FPU g-1 was ~2-fold higher than that obtained with untreated rice straw and MCC (Figure 3). Further increase in enzyme dosages to 10 FPUg-1 and 15 FPUg-1 resulted in rice straw hydrolysis of 84.5 and 95.3 % respectively while on adding 20 FPUg-1 of enzyme, the improvement in hydrolysis (96 %) was marginal. On the other hand, the percentage hydrolysis of UT rice straw and MCC at 20 FPU was around 40 % and 27 %, respectively (Figure 3). The results indicated that DES- solvent pretreated rice straw was highly amenable to lower enzyme dosages.

ADVANTAGES:
a) Water-free solvent system (example 1) for selective delignification (up to ~50%) of biomass.
b) Overall, the process is carried out under low severity (at around 100° C).
c) About 5-fold reduction in water consumption (examples 2 and 3) compared to conventional acid processes.
d) Lesser inhibitor formation than that observed in the conventional acid pretreatments and recyclability of pretreatment chemicals is possible.
e) Multi-feedstock processing (Rice straw, Sugarcane bagasse & Wheat straw).

While the invention has been described and illustrated with reference to certain particular embodiments thereof, those skilled in the art will appreciate that various adaptations, changes, modifications, substitutions, deletions, or additions of procedures and protocols may be made without departing from the spirit and scope of the invention.
While specific language has been used to describe the present subject matter, any limitations arising on account thereto, are not intended. As would be apparent to a person in the art, various working modifications may be made to the method in order to implement the inventive concept as taught herein. The drawings and the foregoing description give examples of embodiments. Those skilled in the art will appreciate that one or more of the described elements may well be combined into a single functional element. Alternatively, certain elements may be split into multiple functional elements. Elements from one embodiment may be added to another embodiment.
,CLAIMS:1. An ionic and non-ionic DES based process for selective delignification of biomass, said process comprising the steps of:
a) milling the feedstock to reduce biomass size in the range of about 20-25 mm;
b) preparing Deep Eutectic Solvent (DES) system by mixing 1 equivalent of Tetra Butyl Ammonium Bromide (TBAB) in three equivalents of Mono-ethanolamine;
c) mixing the reduced sized biomass obtained in step a) with DES (6 parts): THF (4 parts) at solid to liquid ratio of 1: 10;
d) carrying out delignification reaction for about 3 hour at around 100 °C and subjecting the slurry for solid-liquid separation after completion of delignification reaction;
e) washing the delignified solid rich in cellulose & hemicelluloses obtained in step d) with ethanol and subsequently washing with water to remove residual lignin and DES;
f) pooling all the liquid streams obtained from steps d) and (e) and allowing for lignin settling at <10°C for 60 to 120 minutes and solid/liquid separation for obtaining lignin; and
g) subjecting the liquid stream obtained in step (f) for distillation to recover ethanol and DES-THF system; and recycling back the DES-THF system to step (c) for delignification of fresh feedstock.

2. A process for selective delignification of biomass, said process comprising the steps of:
a) milling the feedstock to reduce biomass size in the range of about 20-25 mm;
b) mixing the reduced sized biomass obtained in step a) with 1% w/v NaOH + 3 % w/v Tetra Butyl Ammonium Bromide (TBAB) in Ethanol at solid to liquid ratio of 1: 10;
c) carrying out delignification reaction for about 3 hour at around 100 °C and subjecting the slurry for solid-liquid separation after completion of delignification reaction;
d) washing the delignified solid rich in cellulose & hemicelluloses obtained in step c) with ethanol to remove residual lignin and DES;
e) pooling all the liquid streams obtained from steps c) and (d) and subjected for DCM extraction to remove lignin; and
f) subjecting the liquid stream having DES + DCM obtained in step (e) for distillation to recover DCM and ethanol (partially) and recycling back the Ethanol.NaOH-TBAB to step (b) for delignification of fresh feedstock.

3. A process for selective delignification of biomass, said process comprising the steps of:
a) milling the feedstock to reduce biomass size in the range of about 20-25 mm;
b) mixing the reduced sized biomass obtained in step a) with 5% w/v NH3 + 3 % w/v Tetra Butyl Ammonium Bromide (TBAB) in Ethanol at solid to liquid ratio of 1: 10;
c) carrying out delignification reaction for about 3 hour at around 100 °C and subjecting the slurry for solid-liquid separation after completion of delignification reaction;
d) washing the delignified solid rich in cellulose & hemicelluloses obtained in step c) with ethanol to remove residual lignin and DES;
e) pooling all the liquid streams obtained from steps c) and (d) and subjected for distillation to recover ethanolic ammonia; and
f) subjecting the liquid stream having TBAB + lignin obtained in step (e) for DCM extraction followed by distillation to recover DCM and TBAB and recycling back the Ethanol.NH3-TBAB to step (b) for delignification of fresh feedstock.

4. The process as claimed in claims 1 to 3, wherein the feedstock comprises one or more of rice straw, wheat straw and sugarcane bagasse.

5. The process as claimed in claims 2 and 3, wherein the process provides a water-free solvent system.
6. The process as claimed in claims 1 to 3, wherein said process exhibits 100 % DES recovery, 67 % solid recovery, 87.8 % cellulose recovery, 58.6 % hemicellulose recovery, and 52.6 % delignification efficiency after tenth pretreatment cycle.
7. The process as claimed in claims 1 to 3, wherein the water-free solvent system is recovered almost 85%.
8. The process as claimed in claims 1 to 3, wherein the DES-pretreated feedstock is highly amenable to cellulolytic enzymes, and it is hydrolysed at low enzyme loadings of 5 FPU/g with 58% efficiency and at 10 FPU/g with 84.5% efficiency.