DESC:Field Of Invention
The present invention relates to an organoclay catalyst and a process for preparing the same.

Background Of Invention
Hydrogenation process (hydrogenation reaction) involves hydrogen at high pressure and a relatively high reaction temperature. The process can be carried out in liquid or in vapor (gas) phase.

High pressure is needed in order to improve the solubility of hydrogen in the bulk liquid, whereas the need for high reaction temperature arises from the fact that the reaction is temperature-dependent: the hydrogenation velocity is considerably enhanced by increased temperature.

Industrially, Raney nickel (Ni) and copper chromite are used in hydrogenation reactions.

Although Raney nickel is cheap and has excellent catalytic activity, it is highly pyrophoric and deactivates quickly due to leaching of nickel. Consequently, conversion rates and process selectivity are jeopardized. Any leached nickel must be removed leading to the additional cost.

On the other hand, copper chromite catalyst contains chromium trioxide which is highly toxic and can lead to severe environmental problems. In addition, the chromium species is also responsible for significant deactivation in both liquid and gas-phase hydrogenation.

Alternatively, noble metals such as ruthenium (Ru), rhodium (Rh) and palladium/ruthenium (Pd/Ru) can be used as catalyst for hydrogenation but as they are expensive, its efficiency and long-term stability must be high to be a viable alternative.

Therefore, more efforts are needed to develop efficient nickel based catalytic system with higher activity and selectivity as well as good catalyst stability.

Organoclays are modified clays obtained by treatment of clay minerals (swelling ones such as montmorillonite, vermiculite and saponite) with various surfactants and organic compounds through intercalation process and surface grafting. The hydrophilic nature of swelling clays can be rendered hydrophobic by exchanging the naturally occurring inorganic cations (Ca2+, Na+, K+) with organocations such as monoalkylammonium, tetramethylammonium, octadecyltrimethylammonium and phenyltrimethylammonium. With regard to the support, the organoclay is versatile, acidic, mesoporous and inexpensive. Among active transition metal in hydrogenation, nickel is the most inexpensive active metal.

Summary of the Invention
The present invention relates to an organoclay catalyst comprising a metal impregnated on a modified organoclay, wherein the metal is nickel and the modified organoclay is bentonite modified with cetyl trimethyl ammonium bromide.

The present invention also relates to a process for preparing an organoclay catalyst. The process comprises mixing a metal with modified organoclay, wherein the metal is nickel and the modified organoclay is bentonite with cetyl trimethyl ammonium bromide.

Further, the present invention also relates to a process of hydrogenation in presence of the organoclay catalyst.

Brief Description of Drawings
Figure 1 illustrates the temperature program of the furnace for reduction step in the process for preparation of the organoclay catalyst as per the present invention.

Figure 2 illustrates a flow chart for the hydrogenation process of hemicellulose to xylitol in liquid phase in the presence of the organoclay catalyst as per the present invention.

Figure 3 illustrates a flow chart for the hydrogenation process of hemicellulose to xylitol in vapor phase in the presence of the organoclay catalyst as per the present invention.

Description Of Invention
In an aspect, the invention relates to an organoclay catalyst comprising a metal impregnated on a modified organoclay. The metal is nickel and the modified organoclay is bentonite modified with cetyl trimethyl ammonium bromide.

The terms ‘modified bentonite’ and ‘modified organoclay’ used throughout the specification refer to bentonite modified with cetyl trimethyl ammonium bromide.

In an embodiment, the organoclay catalyst comprises nickel (Ni) in the range of 1 wt.% to 50 wt.% of the total composition, preferably nickel is present in a range of 10 wt.% to 40 wt.% of the total composition. The balance amount of modified organoclay is added to make the total to 100 wt.% such that when the organoclay catalyst contains 10 wt.% to 40 wt.% of nickel, modified organoclay is present in a range from 60 wt.% to 90 wt.%

Nickel nitrate (Ni(NO3)2•6H2O) or nickel chloride (NiCl2) is used as a source of nickel.

In an embodiment, the organoclay catalyst comprises nickel and modified organoclay in a mass ratio of 0.1 to 0.4.

In an embodiment, the organoclay catalyst is in the form of a tablet, cylindrical, trilobe or spherical ball.

The organoclay catalyst of the present invention provides high selectivity of the product, thereby reducing the impurities in the final product. The organoclay catalyst increases the rate of reaction thereby reducing the duration of the hydrogenation process. Also, the organoclay catalyst is not pyrophoric, making the handling of the catalyst easy and safe.
In another aspect, the present invention relates to a process to prepare an organoclay catalyst. The process comprises mixing a metal with modified organoclay. The metal is nickel and the modified organoclay is bentonite with cetyl trimethyl ammonium bromide.

The modified organoclay is prepared by cation exchange method. The method comprises adding bentonite and cetyl trimethyl ammonium bromide in deionized water to prepare a reaction mixture. Subsequently, stirring the reaction mixture vigorously to obtain a reaction mass. The reaction mass is then filtered, washed and dried to obtain modified organoclay (bentonite modified with cetyl trimethyl ammonium bromide).

In an embodiment, the reaction mixture of 7 g to 9 g of bentonite and 4 g to 5 g of cetyl trimethyl ammonium bromide in 80 g to 90 g of deionized water is stirred at room temperature (25°C to 30°C) for 10 hours to 14 hours to obtain a reaction mass. After washing, the reaction mass is dried in oven at a temperature in the range from 90°C to 120°C for 6 hours to 10 hours.

The modified organoclay preferably comprises 55 wt.% to 70 wt.% of bentonite and 30 wt.% to 45 wt.% of cetyl trimethyl ammonium bromide.

The organoclay catalyst is prepared from nickel and the modified organoclay described above by impregnation method. The method comprises weighing a source of nickel (nickel nitrate or nickel chloride) and modified organoclay in a mass ratio of nickel (metal) to modified organoclay in the range from 0.1 to 0.4. The modified organoclay is swelled in deionized water to obtain a modified organoclay suspension. A solution of nickel nitrate or nickel chloride is added dropwise to the organoclay suspension at room temperature with vigorous stirring. The resulting liquid is evaporated at a temperature in a range from 50°C to 80°C for 12 hours to 14 hours to produce a thick slurry. The slurry is dried at a temperature in a range from 80°C to 120°C for 10 hours to 14 hours followed by calcination at a temperature in a range from 500°C to 600°C for 2 hours to 6 hours which results in the formation of the organoclay catalyst. Further, the organoclay catalyst is reduced in tubular furnace under hydrogen gas flow.

In an embodiment, the organoclay catalyst is reduced in the tubular furnace at a temperature in a range from 500°C to 700°C for 2 hours to 4 hours under hydrogen gas flow, preferably the catalyst is reduced in the tubular furnace at the temperature of 600°C for 2 hours (See Figure 1).

When nickel chloride is used as the source of nickel, the method further includes addition of a reducing agent selected from sodium borohydride (NaBH4) or sodium hydride (NaH).

The method for preparing the organoclay catalyst is environmentally friendly and economical as the method components are cheap and available easily.

In an aspect the present invention also relates to a process for hydrogenation of hemicellulose or xylose to form xylitol by reacting hemicellulose or xylose with hydrogen in the presence of the organoclay catalyst of the present invention.

The hydrogenation process can be carried out in liquid phase or in vapor phase.

In an embodiment the invention also relates to a process for hydrogenation of hemicellulose or xylose to form xylitol in liquid phase by reacting hemicellulose or xylose with hydrogen in the presence of the organoclay catalyst of the present invention.

The reactor is an autoclave, preferably, a steel autoclave.

Industrially; xylitol is prepared from xylose or hemicellulose in a batch wise, liquid phase hydrogenation process; wherein high hydrogen pressures and relatively high temperatures are used. In the liquid phase process, a turbine impeller, coupled to a propeller mixer, is used to provide efficient gas dispersion and mixing of the reactor contents. Vigorous shaking is needed for elimination of the outer liquid-solid mass transfer.
The process of hydrogenation of hemicellulose to form xylitol in liquid phase is outlined in Figure 2 and described below:

Step 1. Aqueous hemicellulose solution (75gm to 200 gm of hemicellulose) comprising xylose, other sugars such as glucose and arabinose and impurities was neutralized with a base selected from sodium hydroxide, potassium hydroxide, calcium oxide, calcium carbonate and calcium bicarbonate, sodium carbonate, sodium bicarbonate, potassium carbonate, potassium bicarbonate or mixture thereof. The pH of the hemicellulose solution was changed to be in a range of 7 to 8.

The hemicellulose solution comprises 10 % to 15 % of xylose along with other sugars such as arabinose, glucose, fructose, galactose, etc. Total Dissolved Solid (TDS) of hemicellulose solution was 15 % to 100%, more particularly 50 % to 60%.

The hemicellulose solution was then charged in an autoclave. Hydrogen was also charged into the autoclave at a pressure in the range from 2 Kg/cm2 (1.96 bar) to 50 Kg/cm2 (49.03 bar), more particularly 20 Kg/cm2 (19.61 bar) to 25 Kg/cm2 (24.5166 bar). Hemicellulose was reacted with hydrogen gas in presence of the organoclay catalyst of the present invention under high pressure to produce a hydrogenated hemicellulose (mother liquor).

Hydrogen was continuously charged in the reactor till no consumption of hydrogen is observed.

The temperature for hydrogenation was in the range from 50°C to 150°C, more particularly 90°C to 100°C. Time for hydrogenation process was in the range from 2 hours to 20 hours, more particularly in the range from 5 hours to 10 hours.

Progress of hydrogenation was monitored on HPLC (High Performance Liquid Chromatography) system using standard calibration curve (Absolute Calibration Method) with respect to aldose and alditol standard.

All the other sugars were converted to corresponding alcohol that is arabinitol, xylitol, sorbitol, mannitol, glacitol, etc. respectively.

Step 2. The hydrogenated hemicellulose obtained by reaction of step (1) was cooled to room temperature. The catalyst was separated from the hydrogenated hemicellulose solution by filtration and was reused for the next batch of the hydrogenation reaction.

Step 3. Mother liquor (hydrogenated hemicellulose) was taken for chromatographic separation and color bodies such as inorganics salts, other impurities such as furans (hydroxymethylfurfural(HMF), furfural), some organic acid such as acetic acid, citric acid, levulinic acid, malic acid, lactic acid etc., were removed. Xylitol was separated by ion exchange (cation and anion) resin.

Step 4. Eluent from step 3 was colorless and contained crude xylitol and other sugar alcohol, was concentrated enough to remove water. This was done under vacuum and temperature not beyond 50°C to avoid color formation.

Step 5. After complete removal of water, 10 ml to 200 ml alcohol such as ethyl alcohol, isopropyl alcohol, methanol, butyl alcohol, hexanol or mixture thereof was added to the crude sugar alcohol.

Step 6. The mixture of step 5 was heated to reflux to dissolve all the crude mass in alcohol. Reflux was carried out for 2 hours to 10 hours, more particularly 2 hours to obtain a mixture of polyols (reaction mass).

Step 7. Charcoal was added, if required to remove color bodies, if any.

Step 8. The reaction mass of step (6) was chilled in ice batch to precipitate xylitol crystals.

Step 9. The precipitated xylitol crystals of step (8) was filtered to obtain a solid first crop and a filtrate. The solid subsequently was washed with alcohol and dried in oven.
Step 10. Filtrate of step (9) was concentrated, and concentrate was subjected to steps (6) to (9) to get second crop solid and a filtrate, which was also washed with alcohol and dried in oven.

The conversion of xylose was 90 % to 100 %, more particularly 100 % and the yield of xylitol was 70% to 80 % more particularly 80 %.

Step 11. Filtrate of step (10) was recycled in the next batch.

Xylitol produced by the above-mentioned process is free from metal impurities, at ppm level, which were otherwise detected in the xylitol conventionally produced by hydrogenation in liquid phase in presence of Raney nickel due to nickel leaching.

The main by-products obtained are D-arabinitol, D-xylulose, furfural, D-xylonic acid and glycerol. Their formation is primarily influenced by the factors such as temperature, pH of the reaction media and hydrogen mass transfer. The higher the temperature, the more prominent the formation of by-products. Alkaline conditions in liquid phase facilitate the formation of D-xylonic acid via the Cannizzaro reaction. At higher temperatures, some furfural formation takes place.

The process for hydrogenation described above in the presence of the organoclay catalyst of the present invention does not generate other impurities such as D-arabinitol, D-xylulose, furfural and D-xylonic acid, glycerol, etc. that are formed due to further cracking of sugars because of prolonged heating.

The above-mentioned processes, due to a shorter reaction time is advantageous as results it in the desired product xylitol, without other sugar alcohol such as arabinitol, sorbitol, mannitol and galectol.

The process of hydrogenation of xylose to xylitol in liquid phase has the same process steps as hydrogenation of hemicellulose to xylitol as described above.

In an embodiment, the invention relates to a process for hydrogenation of furfural to form furfuryl alcohol in liquid phase by reacting furfural with hydrogen in presence of the organoclay catalyst of the present invention.

The process for hydrogenation of furfural is as described below:

Step 1: 4g to 5g of furfural (95% purity), 650 mg to 750 mg of the organoclay catalyst and 20 ml to 30 ml alcohol were weighed in a 100mL stainless steel autoclave.

Step 2: The reactor was sealed and purged with nitrogen approximately three times.

Step 3: The reactor was pressurized at 2.5 Mpa (25 bar) with hydrogen.

Step 4: The reaction was stirred at 1000 rotations per minute (RPM) and heated to the desired temperature for about 2 ½ hours. Zero time (t0) was considered when the temperature of the autoclave reached the desired temperature.

The desired temperature is in the range of 100°C to 200°C, preferably 150°C.

The organoclay catalyst for hydrogenation of furfural preferably contained 30% nickel impregnated on modified organoclay.

The organoclay catalyst was recycled 1 to 10 times, more particularly at least 5 times.

In an embodiment, the invention relates to a process for hydrogenation of hemicellulose to form xylitol in vapor phase in the presence of the organoclay catalyst of the present invention. The process results in continuous production of xylitol.

The raw materials in the process for continuous production of xylitol by hemicellulose hydrogenation on trickle bed system using proposed organoclay catalyst in vapor phase are:

1. Diluted or concentrated hemicellulose
2. Nickel catalyst supported on modified bentonite organoclay as organoclay catalyst in specifically extruded form such as tablet, cylindrical, trilobe, spherical ball etc.
3. Ion exchange resin for Sequential Simulated Moving Bed (SSMB)
4. Deionized water, distilled water, arrow water or mixture thereof.
5. Ethyl alcohol, isopropyl alcohol, methanol, butyl alcohol, n-hexanol or mixture thereof.
6. Optionally charcoal.
The process of hydrogenation in vapor phase is outlined in Figure 3 and described below:

Step 1. Trickle bed system was used in series to achieve complete conversion of xylose and other aldose sugars to xylitol and other alditol sugars wherein the catalyst bed comprises of organoclay catalyst of the present invention. Hemicellulose solution along with hydrogen is passed through the catalyst bed comprising organoclay catalyst of the present invention.

The reaction temperature ranges from 30°C to 300°C. The hydrogen pressure ranges from 10 bars to 100 bars. Hemicellulose and hydrogen gas is passed through a trickle bed system. The residence time of hemicellulose in trickle bed system to contact with organoclay catalyst (nickel impregnated on modified bentonite) ranges from 0.1 to 10 minutes.

The gas hourly space velocity (GHSV) ranges from 10 h-1 to 200 h-1 & liquid hourly space velocity (LHSV) ranges from 0 h-1 to 5 h-1.

The solvent used in the above-mentioned reaction is deionized water, distilled water or arrow water in an amount of 1 ml to 200 ml. The hot reaction mass coming from trickle bed system, along with the excess vent gases, is passed through a cooling condenser to obtain a mixture of polyols comprising xylitol, arabitol, sorbitol, etc.

Step 2. The reaction mass or polyol mixture was out from vapor phase system (hydrogenated hemicellulose) which undergoes chromatographic separation to remove colored bodies such as inorganics salts, other impurities such as furans (hydroxymethylfurfural (HMF), furfural), organic acids such as acetic acid, citric acid, levulinic acid, malic acid, lactic acid etc. Cation and anion resin are used for separation of xylitol from other impurities and sugars.

Step 3. Colorless eluent, which contains only sugars and alcohol, is concentrated to remove water. This is done under vacuum and temperature does not exceed 50°C to avoid color formation.

Step 4. After removing complete water, alcohol such as ethyl alcohol, isopropyl alcohol, methanol, butyl alcohol, n-Hexanol or mixture thereof is added in an amount of 1 ml to 200 ml to crude sugar alcohol.

Step 5. To dissolve all the crude mass in alcohol, the hydrogenated hemicellulose solution is reflux heated at around 80°C. Reflux is carried out for 2 hours to 10 hours, more particularly 2 hours.

Step 6. If required, charcoal is added, in order to remove colored bodies, if any.

Step 7. The reaction mass is chilled in an ice bath to precipitate xylitol crystals.

Step 8. The precipitated solid is filtered as first crop and the solid is washed with alcohol and dried in oven.

Step 9. Concentrated filtrate is refluxed again i.e., Steps 5 and 6 are followed to get second crop solid, which is also washed with alcohol and dried in an oven.

Step 10. Mother liquor or filtrate is taken to recycle in next batch.

The process of hydrogenation in presence of the organoclay catalyst of the present invention improves selectivity of the product thereby reducing the impurities in the final product and yield of the product. The organoclay catalyst of the present invention increases the rate of the reaction thereby reducing the time required for completion of a process including hydrogenation processes.

Advantageously, the organoclay catalyst has a high selectivity towards xylitol and furfuryl alcohol. The organoclay catalyst of the present invention run for longer time i.e., it can be recycled without any processing, as compared to other conventional catalysts. The organoclay catalyst was recycled 1 to 10 times, more particularly at least 5 times.

Examples:

Example 1: Preparation of bentonite modified with cetyl trimethyl ammonium bromide (modified organoclay) as per the present invention.
7.8 g bentonite clay and 4.4 g cetyl trimethyl ammonium bromide were added in 87.75 g deionized water. The reaction mass (mixture) was stirred vigorously at 28°C for 12 hours. The reaction mass was filtered and washed with water and then dried in oven for 8 hours at 105°C. The dry weight of modified organoclay obtained was approximately 10.15 gm.

Example 2: Preparation of organoclay catalyst as per the present invention containing 20% nickel impregnated on modified organoclay
Nickel nitrate (Ni(NO3)2•6H2O) and modified organoclay prepared in Example 1 were weighed in a mass ratios of m(Ni)/m(modified organoclay) = 0.2, i.e., 2.0 g Nickel and 10.0 g modified organoclay.

The modified organoclay clay was added slowly in 100 ml of deionized water to obtain a suspension. The modified organoclay suspension was stirred vigorously at room temperature for 30 minutes to ensure the full swelling of the organoclay.

9.91 g of Ni(NO3)2.6H2O solution (equivalent to 2.0 g of nickel) was dissolved in 100ml deionized water and added dropwise into the modified organoclay suspension with vigorous stirring at room temperature. The resulting solution was evaporated slowly at 70°C for 2 hours to 4 hours to obtain thick slurry.

Finally, the slurry was dried at 100°C for 12 hours and then calcined at 550°C for 4 hours.
After calcination, the catalyst was reduced in tubular furnace at 600°C for 2 hours under hydrogen gas flow. The temperature of the furnace was programmed as described below and is shown in Figure 1:

A. Temperature was raised from 30°C to 200°C in 34 minutes (ramp of 5°C/min) under nitrogen flow (flow rate =20 ml/min to 40 ml/min).
B. Temperature was held at 200°C for 30 minutes under nitrogen flow (flow rate = 20 ml/min to 40 ml/min).
C. Temperature was raised from 200°C to 600°C in 80 minutes (ramp of 5°C/min). Nitrogen flow was kept till 400°C (Nitrogen flow rate = 20 ml/min to 40ml/min). After reaching 400°C, nitrogen flow was stopped and hydrogen flow was started (Hydrogen flow rate = 10 to 20 ml/min).
D. Temperature was held at 600°C for 120 minutes (2 hours) under hydrogen flow (flow rate = 10 to 20 ml/min). After 2 hours (i.e., after the end of program), hydrogen flow was stopped and nitrogen flow was started (Nitrogen flow rate = 20 ml/min). Nitrogen flow was continued till the furnace cooled down below 70°C and then the furnace and nitrogen flow was switched off.

Example 3: Preparation of organoclay catalyst as per the present invention containing 10% nickel impregnated on modified organoclay.
In this example 4.95g of Nickel nitrate (equivalent to 1.0 gm of nickel) was impregnated on 10 gm of modified organoclay by the process described in Example 2.

Example 4: Preparation of organoclay catalyst as per the present invention containing 30% nickel impregnated on modified organoclay.

In this example 14.86g of Nickel nitrate (equivalent to 3.0 gm of nickel) was impregnated on 10 gm of modified organoclay by the process described in Example 2.

The amount of nickel nitrate and modified organoclay in the above Examples 2-4 is shown below in Table 1
Table1:
Example Catalyst Ni(NO3)2.6H2O (g) Organoclay (g) Ratio
2 20%Ni/Organoclay 9.91 10 0.2
3 10%Ni/Organoclay 4.95 10 0.1
4 30%Ni/Organoclay 14.86 10 0.3

Example 5: Preparation of organoclay catalyst as per the present invention containing 20% nickel impregnated on modified organoclay using nickel chloride
Nickel chloride (NiCl2) and modified organoclay of Example 1 were weighed in the mass ratios of m(Ni)/m(modified organoclay) = 0.2, i.e., 2.0 g Nickel and 10.0 g modified organoclay.

Nickel chloride (taken in an amount equivalent to 2.0 gm of nickel) was reduced by adding reducing agent such as sodium borohydride (NaBH4) or sodium hydride (NaH). The nickel solution thus, obtained was used to prepare the organoclay catalyst by the process as described in Example 2 above.

Example 6: Comparison of 10% and 20%Ni/Organoclay of the present invention with other Catalyst in production of xylitol
Xylitol was prepared through the above-mentioned method in liquid phase in presence of different catalysts as described below.

1. Catalyst 1: 20% Ni/Organoclay – according to the present invention wherein the organoclay catalyst was prepared as per Example 2.

2. Catalyst 2: 10% Ni/Organoclay – according to the present invention wherein the organoclay catalyst was prepared as per Example 3.

3. Catalyst 3: 10% Ni/Bentonite – comparative example which comprises of 0.1, i.e., 1.0 g Nickel and 10.0 g bentonite only.

4. Catalyst 4: Raney Nickel[1] – comparative example, which was prepared as mentioned in Mikkola, J. P. et al. Appl. Catal. A Gen.196, 143–155 (2000).

5. Catalyst 5: Ru/NiO-TiO2[2] – comparative example, which was prepared as mentioned in Yadav, M et al, Applied Catalysis A: General vols 425–426 110–116 (2012).

6. Catalyst 6: Ru/TiO2[3] – comparative example, which was prepared as mentioned in Hernandez-Mejia, C. et al. Catal. Sci. Technol. 6, 577–582 (2016).

7. Catalyst 7: Ru/C[4] – comparative example, which was prepared as mentioned in Baudel, H. M. et al, J. Chem. Technol. Biotechnol.80, 230–233 (2005).

8. Catalyst 8: Co/SiO2[5] – comparative example, which was prepared as mentioned in Audemar, M. et al. ChemCatChem12, 1973–1978 (2020).

9. Catalyst 9: Ni/SiO2[6] – comparative example, which was prepared as mentioned in Du, H. et al. Catal. Today 1–8 (2020) doi:10.1016/j.cattod.2020.04.009.

For production of xylitol in presence of catalysts 1 to 3, hemicellulose (containing 10% xylose) was used whereas for catalysts 4 to 9, aqueous pure xylose in different amounts (1 wt. % and 20 wt. %) was used. The process parameters for the hydrogenation process are shown in Table 2.

Table 2: Comparison of 10% and 20%Ni/Organoclay of the present invention with other Catalysts
Catalyst 1 2 3 4 5 6 7 8 9
20%
Ni/Organoclay 10%
Ni/Organoclay 10%
Ni/
Bentonite Raney Nickel[1] Ru/NiO-TiO2[2] Ru/TiO2[3] Ru/C[4] Co/SiO2[5] Ni/SiO2[6]
Pure Xylose ----- ----- ----- Aq. Solution of Xylose (20wt%) Aq. Solution of Xylose (20wt%) Aq. Solution of Xylose (1wt%) 7.5 g (5
mmoles) 0.5 g (mmoles) 1.5 g (mmoles)
Hemicellulose (containing 10% Xylose) 100g 100g 100g ---- ---- ---- ---- ---- -----
Catalyst w.r.t xylose 3g (30wt%) 6g (60wt%) 6g (60wt%) 5 wt% 5 wt% 5 wt% 5 wt% 0.025g
(5 wt%) 0.3g
(20 wt%)
Solvent H2O H2O H2O H2O H2O H2O
(10 ml) H2O (150 ml) H2O
(10 ml) H2O
(30 ml)
Temperature °C 120 °C 120 °C 120 °C 120 °C 120 °C 120 °C 100-110 °C 150 °C 100 °C
Pressure in MPa 2 MPa 2 MPa 2 MPa 5.5 MPa 5.5. MPa 2 MPa 4.0-6.0 MPa 5 MPa 4 MPa
Time in h 7 h 4 h 4 h 4 h 2 h 3 h 4 h 4 h 2 h
Conversion of xylose % 95% 100% 93% 99.60% 100% 100% 100% 100% 96%
Yield of Xylitol % 92% 77% 55.32% 93.70% 99.70% 95.50% ---- 98% 95%

On comparing comparative catalyst 3 with catalyst 1 of the present invention, it was seen that conversion of xylose by catalyst 1 was 95% and yield of xylitol was 92%. Whereas, comparative catalyst 3 showed 93% conversion of xylose and resulted in only 55.32% of xylitol. This shows that less amount of catalyst 1 (3 gm) of the present invention provided a higher conversion of xylose to xylitol in comparison to comparative catalyst 3 present in twice that amount (6 gm).

On comparing comparative catalyst 3 with catalyst 2 of the present invention, wherein same amount of catalyst 2 and 3 were present, it can be observed that conversion of xylose was the highest, i.e., in presence of catalyst 2, 100% xylose was converted whereas in presence of comparative catalyst 3, only 93% of xylose was converted. Further, the yield of xylitol in the presence of catalyst 2 was 77% and in presence of comparative catalyst 3 was only 55.32%.

This shows that the organoclay catalyst containing modified organoclay had higher yield and conversion and requires less time as compared to nickel/bentonite catalyst.

For comparative catalysts 4 and 9, high pressure was required than that used in the hydrogenation process in presence of the organoclay catalyst of the present invention. Also, Raney nickel of catalyst 4 was pyrophoric and deactivated quickly due to leaching of nickel i.e., due to accumulation of organic impurities on the catalyst surface leading to poisoning of the active sites. The leached nickel was required to be removed leading to the additional cost.

For comparative catalysts 5 to 7, high pressure and high temperature were used. As Ru is one of the most expensive metal, as compared to nickel, it was difficult to have a long-term stability and efficiency in order to use Ru based catalysts. Also, no yield of xylitol was observed for catalyst 7.

For comparative catalyst 8, cobalt is expensive as compared to nickel and it requires higher temperature and higher pressure which is not preferable.

Organoclay catalyst of the present invention increases the rate of reaction and reduces the time required for completion of a process including hydrogenation processes.

Xylitol produced in the presence of organoclay catalyst of the present invention is free from metal impurities, at ppm level, which were otherwise detected in the xylitol conventionally produced by hydrogenation in liquid phase in the presence of Raney nickel due to nickel leaching.

In the presence of organoclay catalyst of the present invention, there is no generation of other impurities formed such as D-arabinitol, D-xylulose, furfural and D-xylonic acid, glycerol, etc. that are formed in batch liquid process due to further cracking of sugars because of prolonged heating in production of xylitol.

Due to less time, results in the desired xylitol product, with other sugar alcohol such as arabinitol, sorbitol, mannitol and galectol are obtained.

Example 7: Reusability of organoclay catalyst A (comparative Example) :
Catalyst A comprising nickel and modified organoclay was prepared as per the process of the present invention except the catalyst was not subjected to reduction. The catalyst was reused up to 5 times i.e., 5 cycles. The process parameters such as temperature, pressure for each cycle of reuse and results of reusing catalyst A for conversion of xylose and yield of xylitol are represented in Table 3 below.

Table 3: Reusability of 10%Ni/Organoclay catalyst A (without reducing the catalyst)
Temperature °C 120°C
Pressure in MPa 2 MPa
Cycle 1st 2nd 3rd 4th 5th
Time (in hours) 4 h 5 h 7 h 4.5 h 6.5 h
Conversion of Xylose % 100% 100% 100% 97.00% 35%
Yield of Xylitol % 79% 79% 83.00% 0.70% 10.00%

Example 8: Reusability of 10% Ni/Organoclay catalyst 2 (with reducing the catalyst)

Catalyst 2 as described in Example 3 was further reused. The catalyst was reused up to 4 times i.e., 4 cycles. Reaction time and results are described in Table 4 below:

Table 4: Reusability of 10% Ni/Organoclay catalyst 2 (with reducing the catalyst)
Cycle 1st 2nd 3rd 4th
Hemicellulose Pure hemicellulose
Time (in hours) 4 4 5 7
% conversion of xylose 99.86 100 100 99.77
% yield of xylitol 76.63 79.23 78.57 79.47

From the above tables 3 and 4, it can be inferred that the organoclay catalyst 2 is stable as it can be reused. The results show that the organoclay catalyst can be reused for at least more than 5 cycles.

Example 9: Production of furfuryl alcohol in the presence of organoclay catalyst of the present invention:

Three batches of furfural in three different solvents selected from methanol, isopropyl alcohol, ethanol, etc. were used to obtain furfuryl alcohol.

The results in terms of conversion percentage of furfural and selectivity percentage of furfuryl alcohol, tetrahydrofurfuryl alcohol (THFA) and others is represented in Table 5 below.

Table 5:
Batch. No Solvent % Conversion
Furfural % Selectivity
Furfuryl Alcohol THFA Other
Furfural Methanol 99.63 81 10 9
IPA 99.94 64 14 22
Ethanol 100 86 14 0

From the above table, it can be concluded that the organoclay catalyst of the present invention converts furfural selectively to furfuryl alcohol in highest amounts as compared to THFA and others.

Example 10: Comparison of 20%Ni/Organoclay of the present invention with other catalysts in production of furfuryl alcohol
Furfuryl alcohol was prepared through the above-mentioned method in liquid phase in presence of different catalysts as described below.

1. Catalyst 1: 20% Ni/Organoclay – according to the present invention wherein the organoclay catalyst was prepared as per Example 2.

2. Catalyst 2: 20% Ni/Bentonite - comparative example which comprises of 0.1, i.e., 1.0 g Nickel and 10.0 g bentonite only.

3. Catalyst 3: 45% Cu/Bentonite[7] – comparative example which was prepared as mentioned in Jiménez-Gómez, C. P. et al, Top. Catal.60, 1040–1053 (2017).

4. Catalyst 4: 45% Cu/Sepiolite[7] - comparative example which was prepared as mentioned in Jiménez-Gómez, C. P. et al, Top. Catal.60, 1040–1053 (2017).

5. Catalyst 5: 40% Ni/MgO-Saponite[8] – comparative example which was prepared as mentioned in Sunyol, C. et al, Applied Catalysis A: General (2020) doi:10.1016/j.apcata.2020.117903.

6. Catalyst 6: Copper chromite[9] – comparative example which was prepared as mentioned in Dillahunty, F. G. et al, United States Patent (19). (1981).

7. Catalyst 7: 5%Ru-Fe3O4/CNT[10] – comparative example which was prepared as mentioned in Li, F. et al. New J. Chem.44, 478–486 (2019).

8. Catalyst 8: CuMgAl[11] – comparative example which is prepared was mentioned in Villaverde, M. M. et al, Catal. Today213, 87–92 (2013).

For production of furfuryl alcohol using catalysts 1 to 8, furfural in different amounts was used. Further process parameters such as temperature, pressure, solvent, time etc. used in the process to prepare furfuryl alcohol are disclosed in Table 6.

Table 6: Comparison of 20%Ni/Organoclay of the present invention with other catalysts
Catalyst 1 2 3 4 5 6 7 8
20%
Ni/Organoclay 20%
Ni/Bentonite 45%
Cu/Bentonite[7] 45% Cu/Sepiolite[7] 40% Ni/MgO-Saponite[8] Copper chromite[9] 5%Ru-Fe3O4/CNT[10] CuMgAl[11]
Furfural 500 mg 500 mg Furfural (2.5-10 vol%) Furfural (2.5-10 vol%) 1.5 g 600 g 96.1 mg (1 mmoles) 9.61 mg (100 mmoles)
Catalyst w.r.t furfural 150 mg 150 mg 150 mg 150 mg 600 mg 4.5 g 20 mg 100 mg
Solvent Methanol (20 ml) Methanol (20 ml) Cyclopentyl methyl ether Cyclopentyl methyl ether H2O (30 mL) Solvent less Isopropanol (10 mL) Isopropanol (60 mL)
Temperature °C 150 °C 150 °C 210 °C 210 °C 140 °C 180 °C 180°C 110 °C
H2 Pressure in MPa 2.5 MPa 2.5 MPa 10 mL/min 10 mL/min 4.0 MPa 3.0 MPa Isopropanol as hydrogen donor 1 MPa
Time in h 3 h 15 h ----- ----- 4 h 49 min 4 h 4 h
Conversion of furfural % 97% 98% 83% 52% 60% 99.90% 99.40% 100%
Selectivity of furfuryl alcohol % 92% 97% 72% 45% 90% 99.60% 100.00% 100%

On comparing comparative catalyst 2 with catalyst 1 of the present invention, it can be observed that higher time period was required for conversion of furfural. However, under the same conditions, when furfural was converted in the presence of catalyst 1, lesser time period was required and same results were obtained as compared to catalyst 2.

On comparing comparative catalysts 3 to 5 with catalyst 1 of the present invention, from the above data, it can be observed that catalyst 1 provided higher conversion and higher selectivity of furfuryl alcohol.

For comparative catalyst 6, copper chromite was used. This catalyst usually becomes very toxic by the leaching of chromium species and hence is not sustainable or environment friendly.

As described above, Ru is very expensive. It is, therefore, difficult to have a long-term stability and efficiency of Ru based catalysts.

Cu–Cr catalyst contains toxic chromium oxides, which cause environmental pollution. In addition, there are great potential safety hazards in the transportation, storage and use of hydrogen.

Supported and/or unsupported metals (Pd/C, Cu–Pd/C, Co–Ru/C and Cu–Ni), metal oxides (Ru/RuO2/C and g-Fe2O3@HAP) and noble metal or non-noble metal catalysts are limited by high costs or low catalytic activity.

Fe3O4 is prone to coaggregation during utilization. Moreover, bare Fe3O4 is easily oxidized in air.

The organoclay catalyst of the present invention in hydrogenation of furfural to furfuryl alcohol provides higher conversion of furfural and higher yields of furfuryl alcohol without leaching, occurring additional costs or complicated process steps.

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 a person skilled in the art, the invention should be construed to include everything within the scope of the disclosure.
,CLAIMS:
1. An organoclay catalyst comprising a metal impregnated on a modified organoclay, wherein the metal is nickel and the modified organoclay is bentonite modified with cetyl trimethyl ammonium bromide.

2. The organoclay catalyst as claimed in claim 1, wherein the amount of nickel is in a range from 1 wt% to 50 wt% or 10 wt% to 40 wt%.

3. The organoclay catalyst as claimed in claim 1, wherein the mass ratio of the metal to modified organoclay is in a range from 0.1 to 0.4.

4. The organoclay catalyst as claimed in claim 1 or 2, wherein when the amount of nickel is in the range from 10wt% to 40wt%, the amount of modified organoclay is in a range from 60 wt% to 90 wt%.

5. A process to prepare the organoclay catalyst as claimed in claim 1, the process comprising mixing a metal with a modified organoclay, wherein the metal is nickel and the modified organoclay is bentonite with cetyl trimethyl ammonium bromide.

6. The process as claimed in claim 5, comprising:
i. preparing the modified organoclay by cation exchange method comprising:
a. adding bentonite and cetyl trimethyl ammonium bromide in deionized water to obtain a reaction mixture;
b. stirring the mixture of step (a) at room temperature for 10 hours to 14 hours to obtain a reaction mass;
c. filtering the reaction mass of step (b) followed by washing and drying the reaction mass at a temperature in the range from 90°C to 120°C for 6 hours to 10 hours to obtain bentonite modified with cetyl trimethyl ammonium bromide;
ii. adding bentonite modified with cetyl trimethyl ammonium bromide of step (i) in deionized water to obtain a suspension;
iii. adding a solution containing nickel to suspension of step (ii);
iv. evaporating the solution of step (iii) to produce a thick slurry;
v. drying followed by calcination of the slurry of step (iv) to obtain the organoclay catalyst.
vi. reducing the organoclay catalyst of step (v) at a temperature of 500°C to 700°C for 2 to 4 hours in a tubular furnace under hydrogen gas flow.

7. The process as claimed in claim 6, wherein the nickel solution comprises nickel nitrate or nickel chloride.

8. The process as claimed in claim 6, wherein the evaporation of solution in step (iv) is carried out at a temperature in the range from 50°C to 80°C for 12 hours to 14 hours.

9. The process as claimed in claim 6, wherein drying of the slurry in step (v) is carried out at a temperature in the range from 80°C to 120°C for 10 to 14 hours and calcination is carried out at a temperature in the range from 500°C to 600°C for 2 hours to 6 hours.

10. A process for hydrogenation of hemicellulose or xylose to form xylitol in liquid phase by reacting hemicellulose or xylose with hydrogen in the presence of the organoclay catalyst as claimed in claim 1.

11. The process as claimed in claim 10, wherein the hydrogen is supplied at a pressure in the range from 15 bar to 30 bar.

12. The process as claimed in claim 10, wherein the reaction is carried out at a temperature in the range from 50°C to 150°C.

13. The process as claimed in claim 10, wherein the organoclay catalyst comprises 10wt% to 40wt% of nickel.
14. The process as claimed in claim 10, comprising
(i) filtering the organoclay catalyst from the hydrogenated hemicellulose;
(ii) chromatographic separation of the hydrogenated hemicellulose to obtain crude xylitol and an eluent containing sugar alcohols;
(iii) subjecting crude xylitol to crystallization to obtain crystals of xylitol.

15. A process for hydrogenation of furfural to form furfuryl alcohol in liquid phase by reacting furfural with hydrogen in the presence of the organoclay catalyst as claimed in claim 1.

16. The process as claimed in claim 15, wherein hydrogen is supplied at a pressure in a range from 22 bar to 27 bar.

17. The process as claimed in claim 15, wherein the reaction is carried out at a temperature in the range from 130°C to 170°C.

18. A process to prepare xylitol in vapor phase, the process comprising:
i. passing aqueous hemicellulose, hydrogen gas and solvent through trickle bed system, wherein the trickle bed system is in contact with the organoclay catalyst as claimed in claim 1 to obtain a reaction mass;
ii. passing the reaction mass through a cooling condenser to obtain a mixture of polyol;
iii. subjecting the polyol mixture to chromatographic separation to obtain crude xylitol and an eluent containing sugar alcohols;
iv. subjecting crude xylitol to crystallization to obtain crystals of xylitol.