A single step process for the delignification of agricultural residue

Abstract

The present invention discloses a process for delignification of agricultural residue, the process comprising mixing the agricultural residue with a molybdenum-peroxy catalyst having formula [MoO2(OH)(OOH)] and hydrogen peroxide at a temperature in a range from 75℃ to 100℃.

Description

[0001] PT / 2025 / 17077

[0002] A SINGLE STEP PROCESS FOR THE DELIGNIFICATION OF AGRICULTURAL RESIDUE

[0003] FIELD OF THE INVENTION

[0004] The present invention relates to a simple process for delignification of agricultural residue. More particularly, the present invention relates to a single step process for delignification of agricultural residue using homogeneous molybdenum-based catalyst and hydrogen peroxide.

[0005] BACKGROUND OF THE INVENTION

[0006] Agricultural residues, which are waste products left in fields after crop harvesting, include processing residues like sugarcane bagasse, husk and field debris such as stalks, leaves, and seed pods, which are composed primarily of lignocellulosic biomass. Agricultural residues hold significant potential for various industrial applications, including the paper and pulp industry, microcrystalline cellulose production, second-generation (2G) ethanol production, biodegradable plastic production, and cellulose composite material production.

[0007] For agricultural residues to be utilized effectively, a pretreatment is essential to remove lignin. Conventional methods for lignin removal from biomass involve processes such as steam explosion, alkaline treatment, and acid pretreatment. Steam explosion requires temperatures between 160-260°C and pressures of 0.7-4.83 MPa. Alkaline treatments typically use sodium hydroxide solutions at high temperatures ranging from 100-150°C, while acid pretreatments employ dilute sulfuric acid at elevated temperatures. These methods present several drawbacks, including harsh reaction conditions (high temperature and pressure), the necessity of neutralization post-treatment, and additional steps such as organosolv treatment following acid pretreatment.

[0008] The Kraft process, a commonly used method for lignin removal, involves the use of sodium hydroxide and sodium sulfite at high temperatures and pressures. In this process, lignin is extracted as a sodium salt, and the resulting cellulose and hemicellulose pulp remain brown, necessitating multiple bleaching cycles to achieve the desired whiteness for paper production or microcrystalline cellulose production. This process operates at a pH of around 10-12 and results in products containing sodium and sulfur, making their removal challenging.PT / 2025 / 17077

[0009] The drawbacks in prior art include severe reaction conditions, highly acidic or basic media, corroding reactors, and the difficulty of catalyst separation. Therefore, there is a need in the art to provide a simple, green process to obtain lignin-free biomass with minimal use of harmful chemicals.

[0010] OBJECTS OF THE INVENTION

[0011] Main object of the present invention is to provide a process for delignification of agricultural residue by employing a molybdenum-peroxy catalyst and hydrogen peroxide.

[0012] Another object of the present invention is to provide a single-step method for the delignification of biomass that does not require high temperatures, high pressures, acids, alkalis, or digesters and involves use of water as reaction media. This simplification aims to make the process more accessible and less resource intensive.

[0013] Another object of the present invention is to provide a process for the delignification of biomass to facilitate the easy separation of delignified pulp, thereby making the downstream processing more efficient and significantly reducing water usage.

[0014] Yet another object of the present invention is to provide a process for delignification of biomass to produce dry pulp / cellulose that is white in appearance, thus eliminating the need for multiple bleaching cycles typically required in traditional processes.

[0015] Still another object of the present invention is to provide a process for the delignification of biomass to minimize the environmental impact by avoiding the use of harsh chemicals like acid, alkali, elemental chlorine, sulfur compounds etc.

[0016] SUMMARY OF THE INVENTION

[0017] In an aspect, the present invention relates to a process for delignification of agricultural residue, the process comprising mixing the agricultural residue with a molybdenum-peroxy catalyst having formula [MoO2(OH)(OOH)] and hydrogen peroxide at a temperature in a range from 75°C to 100°C.PT / 2025 / 17077

[0018] BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 depicts UV-Vis spectra of isolated lignin obtained in a) Example 4; b) Example 5; c) Example 6; d) Example 7; e) Example 8; f) Example 9; g) Example 10; h) Example 11; i) Example 12; j) Example 13; k) Standard lignin.

[0020] Figure 2 depicts FTIR spectra of standard commercial lignin and isolated lignin of Example 4.

[0021] Figure 3 depicts FTIR of bagasse and pulp obtained in Example 19.

[0022] Figure 4 depicts FTIR spectra of Pulp of Sugar Cane Bagasse from Example 19 and commercial microcrystalline cellulose ‘AviceF.

[0023] Figure 5 depicts PXRD of pulp obtained in Example 19 and commercial Microcrystalline cellulose Avicel.

[0024] Figure 6 depicts PXRD of the delignified pulp (Examples 16-19).

[0025] Figure 7 depicts TGA of the microcrystalline cellulose (MCC) commercial Avicel and pulp obtained from examples 16 to 19.

[0026] Figure 8 depicts photographs of bagasse before and after delignification as carried out in Example 5.

[0027] Figure 9 depicts SEM images of bagasse after delignification as carried out in Example 5.

[0028] Figure 10 depicts photographs of hemp stalk before and after delignification as carried out in Example 16.

[0029] DETAILED DESCRIPTION OF THE INVENTION

[0030] In an embodiment, the present invention provides a process for delignification of agricultural residue, the process comprising mixing the agricultural residue with a molybdenum -peroxy catalyst having formula [MoO2(OH)(OOH)] and hydrogen peroxide at a temperature in a range from 75°C to 100°C.PT / 2025 / 17077

[0031] The agricultural residue in a concentration ranging from 3 wt / vol% to 10 wt / vol% is mixed with the molybdenum-peroxy catalyst having concentration in a range from 0.1% wt. to 5% wt. with respect to biomass and with hydrogen peroxide in a concentration ranging from 0.25 to 2 weight equivalent with respect to biomass. The agricultural residue includes biomaterial, which are mostly left on the fields after harvests and used for fodder and as landfill material or burnt in many places such as but not limited to rice straw, wheat straw, rice husk, sugarcane bagasse, corn stover, banana stem, hemp stalks, banana stem fiber, corncob, hemp fiber or mixtures thereof. Preferably, the agricultural residue is sugarcane bagasse.

[0032] The molybdenum peroxy complex catalyst [MoO2(OH)(OOH)] may be prepared by known processes in the literature by using molybdenum precursors selected from MOO2CI2.2DMSO, MOO2CI2.2DMF or molybdenum trioxide. In an exemplary embodiment, the molybdenum peroxy complex catalyst is prepared by dissolving molybdenum tri oxide, 7 to 10 times by weight of hydrogen peroxide. Advantageously, the process of the present invention by employing the molybdenum peroxy complex catalyst enables the recovery of almost quantitative lignin from initial biomass thereby improving overall efficiency of the process and providing a delignified product with a white appearance similar to commercially available microcrystalline cellulose. Further the process of the present invention requires less than 1% of the catalyst thus reducing chemical consumption and improving the economic and environmental sustainability of the process. Additionally, the process of the present invention by employing the molybdenum peroxy complex catalyst results in delignified product which is free from sodium (Na) and sulfur (S) as compared to conventionally known processes.

[0033] Preferably, the process of the present invention is carried out using water as solvent. The process of the present invention is carried out for a time period in a range from 8 hours to 24 hours. Preferably, the process of the present invention further comprises the steps of filtration and washing the filtrate obtained with water, to recover the water-soluble homogeneous molybdenum peroxy complex catalyst.

[0034] The process of the present invention is a simple, and a green single step process for delignification of agricultural residues. The process of the present invention minimizes environmental impact by avoiding the use of harsh chemicals such as acids, alkalis, elemental chlorine, sulfur compounds, and the like, as well as severe reaction conditions, highly acidic or basic media, and corrosive reactors typically employed for delignification. Further, thePT / 2025 / 17077

[0035] process of the present invention produces delignified product / pulp in a single step whereas the conventionally known processes such as Kraft process involve multi-step process for delignification. Additionally, the process of the present invention involves use of water as a solvent which is inexpensive and easily available and hence eliminates the use of expensive and toxic / hazardous solvent. Further, the process of the present invention enables the valorization of agricultural residues, thereby converting waste materials into value-added products. Thus, the process of the present invention offers an environmentally friendly and sustainable approach.

[0036] Further, the process of the present invention enables the easy separation of delignified pulp / product obtained thereby making the downstream processing more efficient and further reduces water usage compared to conventional processes. Further, the catalyst employed in the process of the present invention is recyclable for at least five times thereby making the process inexpensive and economically friendly on an industrial scale.

[0037] Furthermore, the delignified product or dry pulp or cellulose produced by the process of the present invention is white in appearance thus eliminating the need for multiple bleaching cycles typically required in traditional process for paper production or microcrystalline cellulose production.

[0038] In a preferred embodiment, the present invention provides a process for delignification of agricultural residue the process comprising the steps of:

[0039] a) mixing agricultural residue with molybdenum peroxy complex catalyst and hydrogen peroxide in water to obtain a reaction mixture;

[0040] b) maintaining the reaction mixture at a temperature in a range from 75-100°C for the period in a range from 8-24 hours;

[0041] c) filtering the reaction mixture obtained in step b) and washing with water to remove the water-soluble homogeneous molybdenum-peroxy catalyst; and

[0042] d) drying the residue obtained in step c) at a temperature in the range from 95-100°C for the period in a range from 8-10 hours to get the delignified product.PT / 2025 / 17077

[0043] The process of the present invention is illustrated below by non-limiting examples.

[0044] EXAMPLES

[0045] The following examples are given by way of illustration and therefore should not be construed to limit the scope of the invention.

[0046] Procurement Details:

[0047]

[0048] Example 1: Process for preparation of the catalyst

[0049] The molybdenum per-oxy catalyst was prepared by dissolving 10 g molybdenum tri oxide (MoOs) in 75 ml hydrogen peroxide (H2O2) (50%) in a beaker. The solution was stirred till complete dissolution of MoOs forming transparent yellow solution. The solution was then evaporated at 70 °C to obtain yellow solid and was named as molybdenum per-oxy catalyst, having molecular formula [MoO2(OH)(OOH)] according to the literature (ref: Bulletin of the Chemical Society of Japan 54.1 (1981): 293-294.).

[0050] Example 2: Process for preparation of the catalyst

[0051] The MOO2CI2.2DMSO was prepared according to literature procedure (ref: Current Catalysis 2.3 (2013): 237-243). The MOO2CI2.2DMSO catalyst was prepared by dissolving 10 g molybdenum tri oxide in 80 mL concentrated HC1 in a round bottom flask. The mixture was heated at 80 °C with stirring till complete dissolution of MoOs and formation of transparent solution. After complete dissolution of MoOs in HC1, 20 mL dimethyl sulphoxide (DMSO) was added drop wise to the same solution to form a precipitate. The precipitatePT / 2025 / 17077

[0052] formed was filtered and recrystallized in acetonitrile to obtain MOO2CI2.2DMSO catalyst. The 10 g MOO2CI2.2DMSO catalyst thus obtained was then treated with 50% H2O2...30 ml... to obtain molybdenum per-oxy catalyst, having molecular formula [MoO2(OH)(OOH)].

[0053] Example 3: Process for preparation of the catalyst

[0054] The MOO2CI2.2DMF was prepared according to literature procedure (ref: Journal of Molecular Catalysis A: Chemical 297.2 (2009): 110-117) The MOO2CI2.2DMF catalyst was prepared by dissolving 10 g molybdenum trioxide in 80 mL concentrated HC1 in a round bottom flask. The mixture was heated at 80 °C with stirring till complete dissolution of MoOs and formation of transparent solution. After complete dissolution of MoOs in HC1, 20 mL dimethylformamide (DMF) was added drop wise to the same solution to form a precipitate. The precipitate formed was filtered and recrystallized in acetonitrile to obtain MOO2CI2.2DMSO catalyst. The 10 g MOO2CI2.2DMF catalyst thus obtained was then treated with 50% H2O2...3I mL to obtain molybdenum per-oxy catalyst, having molecular formula [MOO2(OH)(OOH)]

[0055] Example 4: Process for delignification using the catalyst of Example 1

[0056] To the slurry of sugar cane bagasse (9.602 g on dry basis) in 200 ml water was added 0.1 g molybdenum peroxy complex as prepared in Example 1 and 33 g H2O2 (30%) in 500 ml round bottom flask. The mixture was heated at 100 °C for 8h. The reaction mixture was filtered using filter paper and washed with water. The filtrate was concentrated till dryness to recover lignin. Residue was dried at 100°C for 8 h to calculate percent weight loss. Weight loss of bagasse on dry basis was 17.82%.

[0057] Example 5: Process for delignification using the catalyst of Example 1

[0058] To the slurry of sugar cane bagasse (9.620 g on dry basis) in 200 ml water was added 0.1 g molybdenum peroxy complex as prepared in Example 1 and 67 g H2O2 (30%) in 500 ml round bottom flask. The mixture was heated at 100 °C for 8h with constant stirring. The reaction mixture was filtered using filter paper and washed with. The filtrate was concentrated till dryness to recover lignin. Residue was dried at 100°C for 8 h to calculate percent weight loss. Weight loss of bagasse on dry basis was 23.11%.

[0059] Example 6: Process for delignification using the catalyst of Example 1PT / 2025 / 17077

[0060] To the slurry of sugar cane bagasse (9.742 g on dry basis) in 200 ml water was added 0.05 g molybdenum peroxy complex as prepared in Example 1 and 33 g H2O2 (30%) in 500 ml round bottom flask. The mixture was heated at 100°C for 8h with continuous stirring. The reaction mixture was filtered using filter paper and washed with water. The filtrate was concentrated till dryness to recover lignin. Residue was dried at 100°C for 8 h to calculate percent weight loss. Weight loss of bagasse on dry basis was 24.06%.

[0061] Example 7: Process for delignification using the catalyst of Example 1

[0062] To the slurry of sugar cane bagasse (10.474 g on dry basis) in 200 ml water was added 0.5 g molybdenum peroxy complex as prepared in Example 1 and 33 g H2O2 (30%) in 500 ml round bottom flask. The mixture was heated at 100°C for 8h. The reaction mixture was filtered using filter paper and washed with water. The filtrate was concentrated till dryness to recover lignin. Residue was dried at 100°C for 8 h to calculate percent weight loss. Weight loss of bagasse on dry basis was 29.81% which approximately corresponds to the amount of lignin separated from the bagasse.

[0063] Example 8: Process for delignification using the catalyst of Example 1

[0064] To the slurry of sugar cane bagasse (9.657 g on dry basis) in 200 ml was added 0.1 g molybdenum peroxy complex as prepared in Example 1 and 33 g H2O2 (30%) in 500 ml round bottom flask. The mixture was heated at 80°C for 8h. The reaction mixture was filtered using filter paper and washed with water. The filtrate was concentrated till dryness to recover lignin. Residue was dried at 100°C for 8 h to calculate percent weight loss. Weight loss of bagasse on dry basis was 2.43%.

[0065] Example 9: Process for delignification using the catalyst of Example 1

[0066] To the slurry of sugar cane bagasse (9.620 g on dry basis) in 200 ml water was added 0.1 g molybdenum peroxy complex as prepared in Example 1 and 33 g H2O2 (30%) in 500 ml round bottom flask. The mixture was heated at 120°C for 8h. The reaction mixture was filtered using filter paper and washed with water. The filtrate was concentrated till dryness to recover lignin. Residue was dried at 100°C for 8 h to calculate percent weight loss. Weight loss of bagasse on dry basis was 23.25%.

[0067] Example 10: Process for delignification using the catalyst of Example 1PT / 2025 / 17077

[0068] To the slurry of sugar cane bagasse (9.657 g on dry basis) in 400 ml water was added 0.1 g molybdenum peroxy complex as prepared in Example 1 and 33 g H2O2 (30%) in 500 ml round bottom flask. The mixture was heated at 100°C for 8h. The reaction mixture was filtered using filter paper and washed with water. The filtrate was concentrated till dryness to recover lignin. Residue was dried at 100°C for 8 h to calculate percent weight loss. Weight loss of bagasse on dry basis was 6.89%.

[0069] Example 11: Process for delignification using the catalyst of Example 2

[0070] To the slurry of sugar cane bagasse (9.602 g on dry basis) in 200 ml water was added 0.1 g MOO2CI2.2DMSO complex as prepared in Example 2 and 33 g H2O2 (30%) in 500 ml round bottom flask. The mixture was heated at 100°C for 8h. The reaction mixture was filtered using filter paper and washed with water. The filtrate was concentrated till dryness to recover lignin. Residue was dried at 100°C for 8 h to calculate percent weight loss. Weight loss of bagasse on dry basis was 19.04%.

[0071] Example 12: Process for delignification using the catalyst of Example 3

[0072] To the slurry of sugar cane bagasse (9.605 g on dry basis) in 200 ml water was added 0.1 g MOO2C12(DMF)2 complex as prepared in Example 3 and 33 g H2O2 (30%) in 500 ml round bottom flask. The mixture was heated at 100°C for 8h. The reaction mixture was filtered using filter paper and washed with water. The filtrate was concentrated till dryness to recover lignin. Residue was dried at 100°C for 8 h to calculate percent weight loss. Weight loss of bagasse on dry basis was 20.86%.

[0073] Example 13: Process for delignification using the catalyst of Example 3

[0074] To the slurry of corncobs (9.358 g on dry basis) in 200 ml water was added 0.1 g MOO2C12(DMF)2 complex as prepared in Example 3 and 33 g H2O2 (30%) in 500 ml round bottom flask. The mixture was heated at 100°C for 8h. The reaction mixture was filtered using filter paper and washed with water. The filtrate was concentrated till dryness to recover lignin. Residue was dried at 100°C for 8 h to calculate percent weight loss. Weight loss of bagasse on dry basis was 14.78%.

[0075] Example 14: Process for delignification using the catalyst of Example 1PT / 2025 / 17077

[0076] To the slurry of wheat straw (9.20 g on dry basis) in 200 ml water was added molybdenum peroxy complex (0.1 g) as prepared in Example 1 and 33 g H2O2 (30%) in 500 ml round bottom flask. The mixture was heated at 100°C for 8h. The reaction mixture was filtered using filter paper and washed with water. The filtrate was concentrated till dryness to recover lignin. Residue was dried at 100°C for 8 h to calculate percent weight loss. Weight loss of wheat straw on dry basis was 8.00%.

[0077] Example 15: Process for delignification using the catalyst of Example 1

[0078] To the slurry of sugar cane bagasse (130.21 g on dry basis) in 2500 ml water was added 0.151 g molybdenum peroxy complex as prepared in Example 1 and 100 mL H2O2 (50%) in 5000 ml round bottom flask. The mixture was heated at 90°C for 24h. The reaction mixture was filtered using filter paper and washed with water. The filtrate was concentrated till dryness to recover lignin. Residue was dried at 100°C for 8 h to calculate percent weight loss. Weight loss of bagasse on dry basis was 37%.

[0079] Example 16: Process for delignification using the catalyst of Example 1

[0080] To the slurry of crushed and sieved Hemp Stalks (135.22 g on dry basis) in 3 L water was added 1.50 g molybdenum peroxy complex as prepared in Example 1 and 1 L H2O2 (30%) . The mixture was heated at 100°C for 24h. The reaction mixture was filtered using filter paper and washed with water. Residue was dried at 100°C overnight to calculate percent weight loss. Weight loss of Hemp Stalks on dry basis was 30.45% which corresponds to approximately the amount of the lignin separated from the stalk and a bright white pulp was obtained which has 71 % Segal crystallinity index. Further the FTIR showed the absence of lignin aromatic peak in the pulp and it had less than 1% Klason Lignin which was estimated by the TAPPI T 222 om-02.

[0081] Example 17: Process for delignification using the catalyst of Example 1

[0082] To the slurry of hemp fiber as received (27.46 g on dry basis) in 600 ml water was added 0.30 g molybdenum peroxy complex as prepared in Example 1 and 200 ml H2O2 (30%) in 2 L round bottom flask in an oil bath. The mixture was heated at 100°C for 24h. The reaction mixture was filtered using filter paper and washed with water. Residue was dried at 100°C overnight to calculate percent weight loss. Weight loss of hemp fiber on dry basis was 35.86 % and a bright white fibrous pulp was obtained which has 85 % Segal crystallinity index,PT / 2025 / 17077

[0083] further, FTIR showed the absence of lignin aromatic peak in the pulp and it had less than 0.05 % Klason Lignin which was estimated by the TAPPI T 222 om-02.

[0084] Example 18: Process for delignification using the catalyst of Example 1

[0085] To the slurry of fresh green banana stem which already have more than 90 % moisture (10 g on dry basis) in 100 ml water was added 0.10 g molybdenum peroxy complex as prepared in Example 1 and 70 ml H2O2 (30%) in 1 L round bottom flask in a oil bath . The mixture was heated at 100°C for 24h. The reaction mixture was filtered using filter paper and washed with water. Residue was dried at 100°C overnight to calculate percent weight loss. Weight loss of green banana stem on dry basis was around 40 % and a bright white fibrous pulp was obtained which has 78 % Segal crystallinity index, further FTIR showed the absence of lignin aromatic peak in the pulp and it had less than 0.1 % Klason Lignin which was estimated by the TAPPI T 222 om-02.

[0086] Example 19: Process for delignification using the catalyst of Example 1

[0087] To the slurry of crushed and sieved sugarcane bagasse (180.60 g on dry basis) in 4 L water was added 1.80 g molybdenum peroxy complex as prepared in Example 1 and 1.33 L H2O2 (30%). The mixture was heated at 100°C for 24h. The reaction mixture was filtered using filter paper and washed with water. Residue was dried at 100°C overnight to calculate percent weight loss. Weight loss of Sugarcane bagasse on dry basis was 67.71 % and a bright white pulp was obtained which has 78 % Segal crystallinity index.

[0088] Example 20: Recyclability study of the catalyst of the present invention:

[0089] To the slurry of sugar cane bagasse (83.8 g on dry basis) in 1500 ml water was added 0.11 g molybdenum peroxy complex as prepared in Example 1 and 70 mL H2O2 (50%) in 5000 ml round bottom flask. The mixture was heated at 90°C for 24h. The reaction mixture was filtered using filter paper and washed with water. Residue was dried at 100°C for 8 h to calculate percent weight loss. The weight loss of the treated bagasse residue on dry basis was 34%. The filtrate obtained was used for next cycle as such.

[0090] First recycle - To the filtrate obtained above was added fresh bagasse (84.79 g on dry basis) and 50 mL H2O2 (50%). The mixture was heated at 90°C for 24h. The reaction mixture was filtered using filter paper and washed with water. Residue was dried at 100°C for 8 h toPT / 2025 / 17077

[0091] calculate percent weight loss. The weight loss of the treated bagasse residue on dry basis was 18%. The filtrate obtained was used for next cycle as such.

[0092] Second recycle - In the filtrate obtained above was added fresh bagasse (82.16 g on dry basis) and 100 mL H2O2 (50%). The mixture was heated at 90°C for 24h. The reaction mixture was filtered using filter paper and washed with water. Residue was dried at 100°C for 8 h to calculate percent weight loss. The weight loss of the treated bagasse residue on dry basis was 30%. The filtrate obtained after second recycle was concentrated till dryness to recover lignin. The total lignin obtained was 55 g (21.93% with respect to original bagasse). This suggests the recyclability of the catalyst of the present invention when employed in subsequent processes.

[0093] Example 21: Characterization studies of the isolated lignin and the delignified pulp obtained in Examples 4 to 19.

[0094] Characterization of the isolated lignin by UV-Visible spectrometer

[0095] The UV-Vis spectra of all the lignin samples were recorded on a PerkinElmer Lambda 650 UV-vis spectrometer. The spectra were obtained in the range of 200-800 nm using a path length of 10 mm, a bandwidth of 1.0 nm and a scan speed of 250 nm / min against water as reference. The sample was prepared by adding 0.001g of the lignin to 1 mL water. The UV-Vis spectrum of lignin obtained in examples 4 to 13 was compared with commercial lignin obtained from Praj Industries, Pune India as shown in Figure 1. The UV-Vis spectrum of lignin obtained in all examples (4-13) mentioned above matched very well with standard lignin at 280 nm (Figure 1) demonstrating the successful recovery of lignin.

[0096] Characterization of the isolated lignin by FT-IR

[0097] The Fourier transform infrared (FT-IR) spectra of isolated lignin sample (Example 4) was recorded on a Thermo Nicolet Nexus 670 IR instrument using KBr pellets with a resolution of 4 cm-1in the range of 4000-400 cm-1averaged over 100 scans. Sample was prepared by mixing KBr (100 mg) and lignin isolated, for Example 4 (2 mg) and grinded well for making homogeneous mixture and further were made into pallets. The prepared pallet was scanned with KBr as a reference. The IR of lignin sample was compared with standard lignin obtained from industry as depicted in Figure 2. All the peaks of lignin isolated in Example 4PT / 2025 / 17077

[0098] matched very well with standard commercial lignin thus confirming the successful recovery of lignin.

[0099] Characterization of obtained bright white pulp by FT-IR

[0100] The sugar cane bagasse and the delignified pulp obtained in Example 19 was subjected to FTIP analysis as depicted in Figure 3. As observed from the said Figure the pulp obtained showed no characteristic peak of lignin thus suggesting the successful delignification by the process of the present invention and it had less than 0.1% Klason Lignin which was estimated by the TAPPI T 222 om-02. Similar absence of peaks corresponding to lignin were obtained for the pulp obtained in Examples 16 to 18. Further, using above setup, characterization of bright white pulp / delignified pulp obtained in Example 19 was done and compared with commercially available microcrystalline cellulose viz. AVICEL as depicted in Figure 4. The said Figure showed similarity in the peaks which confirmed the formation of microcrystalline cellulose in a single step as per the process of the present invention.

[0101] Characterization of the obtained dry pulp by PXRD

[0102] The Powder X-Ray Diffraction (PXRD) analysis was used to establish the crystallinity of the obtained pulp of Examples 16-19 as depicted in Figures 5 and 6, which showed high crystallinity of the microcrystalline cellulose obtained, which was comparable with the commercial microcrystalline cellulose Avicel. PXRD was done using Rigaku miniplex 600 X-Ray diffractometer in NCL. And crystallinity was calculated by the Segal crystallinity formula.

[0103] & &

[0104]

[0105] Where Jc is the maximum intensity of the diffraction peak at 29 ~ 22.5°, which corresponds to the crystalline cellulose (002) plane. Fa is the intensity at the minimum between the 002 and 101 peaks, which represents the amorphous contribution.

[0106] Characterization of pulp by TGA-DTA

[0107] Thermogravimetric Analysis - Differential Thermal Analysis (TGA-DTA) was done in Diamond -TG / DTA instrument. The TGA, DTA, and DTG analyses conducted on both thePT / 2025 / 17077

[0108] microcrystalline cellulose samples, commercial Avicel and pulp obtained from examples 16-19 are depicted in Figure 7. Notably, as observed from the said Figure, the pulp obtained from Examples 16-19 demonstrated almost similar decomposition temperatures compared to commercial Avicel thus indicating similar thermal stability of the pulp obtained by the process of the present invention.

[0109] Example 26:

[0110] Figure 8 demonstrates the photographic images of the bagasse before and after delignification carried out according to the process of Example 5 while Figure 9 depicts the Scanning Electron Microscope (SEM) images of the said bagasse after delignification. Figure 10 depicts the photographic images of hemp stalk before and after delignification as carried out in Example 16.

[0111] ADVANTAGES OF THE INVENTION

[0112] 1. A simple process using a cheaper homogeneous catalyst without any use of acids or alkali is provided.

[0113] 2. The process is environment benign process as it does not need any additional effluent treatment.

[0114] 3. The process is able to remove almost complete lignin from the agriculture residue in a single step.

[0115] 4. The process yields highly crystalline microcrystalline cellulose from different biomass sources in a single step.

[0116] 5. Obtained pulp in this single step process resembles commercial microcrystalline cellulose as confirmed by the FTIR, TGA, and PXRD analysis.

[0117] The foregoing description of the invention has been set merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to person skilled in the art, the invention should be construed to include everything within the scope of the disclosure.

Claims

PT / 2025 / 17077WE CLAIM:

1. A process for delignification of agricultural residue, the process comprising mixing the agricultural residue with a molybdenum-peroxy catalyst having formula [MOO2(OH)(OOH)] and hydrogen peroxide at a temperature in a range from 75°C to 100°C.

2. The process as claimed in claim 1, wherein the agricultural residue in a concentration ranging from 3 wt / vol% to 10 wt / vol% is mixed with the molybdenum-peroxy catalyst having concentration in a range from 0.1% wt. to 5% wt. with respect to biomass and with hydrogen peroxide in a concentration ranging from 0.25 to 2 weight equivalent with respect to biomass.

3. The process as claimed in claim 1, wherein the agricultural residue is selected from rice straw, wheat straw, rice husk, sugarcane bagasse, com stover, banana stem, hemp stalks, banana stem fiber, corncob, hemp fiber or mixtures thereof.

4. The process as claimed in claim 1, wherein the process is carried out using water as a solvent.

5. The process as claimed in claim 1, wherein the process is carried out for a time period in a range from 8 hours to 24 hours.

6. The process as claimed in claim 1, wherein the process further comprises the steps of filtration and washing to recover the molybdenum-peroxy catalyst.

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