Claims:1. A method for synthesizing 5-hydroxymethylfurfural (HMF), said method comprising reacting at least one biomass with at least one substituted heterocyclic salt in the presence of at least one ionic liquid.
2. The method as claimed in claim 1, wherein said at least one substituted heterocyclic salt acts as a solvent.
3. The method as claimed in claim 1, wherein said at least one substituted heterocyclic salt is selected from the group consisting of 1-butyl-3-methylimidazolium chloride, 1-butyl-3-methylimidazolium bromide, 1-butyl-3-methylimidazolium acetate, 1-butyl-3-methylimidazolium tetrafluroborate, 1-butyl-3-methylimidazolium thiocyanate, 1-allyl-3-methyl imidazolium chloride and 1-ethyl-2,3-dimethylimidazolium chloride.
4. The method as claimed in claim 1, wherein said at least one ionic liquid is selected from the group consisting of Triethylamine-chromium chloride, ChCl-CrCl3, Thiourea-CrCl3, Urea-CrCl3 and DMSO-CrCl3.
5. A method for synthesizing 5-hydroxymethylfurfural (HMF), said method comprising:
i. reacting at a temperature in the range of 100 to 150 °C, a predetermined amount of at least one biomass with 1-butyl-3-methylimidazolium chloride and Triethylamine-chromium chloride ionic liquid in an amount in the range of 1M to 7M, followed by agitating at a predetermined rpm to form a first reaction mixture;
ii. heating said first reaction mixture at a temperature in the range of 100 to 150 °C for a set time followed by cooling to a temperature ranging from 15 to 40 °C to form a second reaction mixture; and
iii. separating said 5-hydroxymethylfurfural from said second reaction mixture by adding a predetermined amount of at least one organic solvent;
wherein said at least one organic solvent is selected from the group consisting of ethylacetate, diethyl ether and combinations thereof;
wherein said 5-hydroxymethylfurfural has a purity of at least 90%.
6. The method as claimed in claim 1 or claim 5, wherein said at least one biomass is a cellulosic biomass, preferably lignocellulosic biomass.
7. The method as claimed in claim 6, wherein said biomass is selected from the group consisting of cotton stalk, castor stalk and red gram.
8. A method for preparing Triethylamine-chromium chloride ionic liquid, said method comprising reacting CrCl3.6(H2O) with Triethylamine in a nitrogen environment at a temperature in the range of 50 to 120 °C to obtain said Triethylamine-chromium chloride ionic liquid. , Description:FIELD
The present disclosure relates to the synthesis of 5-hydroxymethyl furfural from biomass.
BACKGROUND
Conversion of the renewable biomass into chemicals and fuels, traditionally obtained from petroleum, is strategically important to avoid the depletion of non-renewable energy reserves. Non-renewable energy sources have fuelled the world’s industrial complex for many years and have reached a point where the world is facing rapid starvation of these non-renewable energy sources. There are also other associated effects with an increase in the exploitation of these non-renewable energy sources, like land pollution and air pollution which in turn affect both animal and plant life.
For many years, countless chemical compounds required in the industries have been derived from fossil fuels. The rapid industrial growth coupled with a huge demand for the products obtained from the non-renewable energy sources, has led to rapid depletion in the non-renewable energy sources reserves. Moreover, the far-reaching consequences of the non-renewable energy sources and the concern of climate change and anticipation of dwindling fossil resources have accelerated the transition of today’s fossil-based economy to a sustainable economy based on renewable biomass.
Cellulosic and lignocellulosic feedstocks (e.g., plant-derived biomass) provide a large renewable source of potential starting materials for the production of a variety of chemicals, fuels and feeds. Lignocellulose based biomass can be converted into chemicals and biofuels without having food verses fuel issues. 5-Hydroxymethylfurfural (HMF) is an example of such a compound which is derived from dehydration of sugars making it derivable from renewable biomass resources. The biomass derived 5-hydroxymethylfurfural (HMF) has emerged as an important platform for the production of value added chemicals and liquid fuels that are currently obtained from petroleum.
HMF obtained from renewable resources acts as a key compound that bridges the gap between biomass and bio-refinery. HMF has been of great interest due to the wide range of chemical intermediates and end products that can be obtained from HMF which is used in polymer, fuel and pharmaceutical industries. HMF has numerous applications, especially in the synthesis of dialdehydes, glycols, ethers, aminoalcohols and acetals, and other organic intermediates which can lead to the production of numerous chemical products such as solvents, surface-active agents, phytosanitary products, resins and the like. Furthermore, HMF also serves as a precursor for production of FDCA (furan dicarboxylic acid) which is used in the synthesis of PEF (polyethylene furanoate), liquid alkanes (C7-C15) that serve as diesel fuel components and pharmaceutical intermediates.
There is, therefore, felt a need to provide a method that efficiently transforms the renewable sources of energy into 5-Hydroxymethylfurfural (HMF) without having food verses fuel issues.
OBJECTS
Some of the objects of the present disclosure, which at least one embodiment herein satisfies, are as follows:
It is an object of the present disclosure to ameliorate one or more problems of the prior art or to at least provide a useful alternative.
It is an object of the present disclosure to provide a method for synthesizing 5-hydroxymethylfurfural (HMF).
It is another object of the present disclosure is to provide a method for synthesizing 5-hydroxymethylfurfural (HMF) from renewable sources of energy.
It is yet another object of the present disclosure is to provide a method for preparing Triethylamine-chromium chloride ionic liquid.
Other objects and advantages of the present disclosure will be more apparent from the following description, which is not intended to limit the scope of the present disclosure.
SUMMARY
The present disclosure envisages a method for synthesizing 5-hydroxymethylfurfural (HMF). More particularly, the present disclosure discloses a method for synthesizing HMF directly from biomass by reacting the biomass with at least one substituted heterocyclic salt in presence of at least one ionic liquid.
The present disclosure also envisages a method for preparing Triethylamine-chromium chloride ionic liquid by reacting CrCl3.6(H2O) with Triethylamine in a nitrogen environment at a predetermined temperature to obtain the Triethylamine-chromium chloride ionic liquid.
The substituted heterocyclic salt of the present disclosure is selected from the group consisting of, but not limited to, 1-butyl-3-methylimidazolium chloride, 1-butyl-3-methylimidazolium bromide, 1-butyl-3-methylimidazolium acetate, 1-butyl-3-methylimidazolium tetrafluroborate, 1-butyl-3-methylimidazolium thiocyanate, 1-allyl-3-methyl imidazolium chloride and 1-ethyl-2,3-dimethylimidazolium chloride.
The ionic liquid is selected from the group consisting of, but not limited to, Triethylamine-chromium chloride, ChCl-CrCl3, Thiourea-CrCl3, Urea-CrCl3 and DMSO-CrCl3. The biomass is a cellulosic biomass, preferably lignocellulosic biomass, selected from the group consisting of, but not limited to, cotton stalk, castor stalk and red gram.

DETAILED DESCRIPTION
Massive availability of agricultural waste, left unutilized in the field, and its potential to be converted to environmentally friendly biofuel coupled with the need for generating alternate sources of energy has led to an increasing attention towards the advancement of methods to generate biofuel. Further, Ionic liquids have gained wide attention due to it being environmentally friendly and economical. Ionic liquids are non-flammable, thermally stable, exhibit negligible vapor pressure, and offer the potential for recyclability.
In accordance with the present disclosure, there is envisaged a method for direct conversion of biomass to organic bulk chemicals such as 5-hydroxymethylfurfural (HMF) by using at least one ionic liquid as a catalyst. The method involves selective hydrolysis of the biomass followed by dehydration to produce HMF in one step process using Triethylamine-chromium chloride ionic liquid as a catalyst.
In an embodiment of the present disclosure, the method for synthesizing 5-hydroxymethylfurfural (HMF) comprises reacting at least one biomass with at least one substituted heterocyclic salt in presence of at least one ionic liquid.
Typically, the biomass is a cellulosic biomass, preferably lignocellulosic biomass, selected from the group consisting of, but not limited to, cotton stalk, castor stalk and red gram.
Typically, the biomass can be cotton stalk.
Typically, the at least substituted heterocyclic salt of the present disclosure is selected from the group consisting of, but not limited to, 1-butyl-3-methylimidazolium chloride, 1-butyl-3-methylimidazolium bromide, 1-butyl-3-methylimidazolium acetate, 1-butyl-3-methylimidazolium tetrafluroborate, 1-butyl-3-methylimidazolium thiocyanate, 1-allyl-3-methyl imidazolium chloride and 1-ethyl-2,3-dimethylimidazolium chloride.
Typically, the at least one substituted heterocyclic salt can be 1-butyl-3-methylimidazolium chloride.
Typically, the ionic liquid is selected from the group consisting of, but not limited to, Triethylamine-chromium chloride, ChCl-CrCl3, Thiourea-CrCl3, Urea-CrCl3 and DMSO-CrCl3.
Typically, the at least one ionic liquid can be Triethylamine-chromium chloride.
In an embodiment of the present disclosure, the method for synthesizing 5-hydroxymethylfurfural (HMF) comprises:
i. reacting at a temperature in the range of 100 to 150 °C, a predetermined amount of at least one biomass with 1-butyl-3-methylimidazolium chloride and Triethylamine-chromium chloride ionic liquid in an amount in the range of 1M to 7M, followed by agitating at a predetermined rpm to form a first reaction mixture;
ii. heating the first reaction mixture at a temperature in the range of 100 to 150 °C for a set time followed by cooling to a temperature ranging from 15 to 40 °C to form a second reaction mixture; and
iii. separating the 5-hydroxymethylfurfural from the second reaction mixture by adding a predetermined amount of at least one organic solvent;
wherein the at least one organic solvent is selected from the group consisting of, but not limited to, ethylacetate, diethyl ether and combinations thereof;
wherein the 5-hydroxymethylfurfural has a purity of at least 90%.
Typically, the at least one biomass can be cotton stalk.
Typically, the predetermined rpm to form the reaction mixture can be in the range of 500 rpm to 5000 rpm.
Typically, the set time can be in the range of 50 to 150 minutes.
Typically, the at least one substituted heterocyclic salt acts as a solvent.
Typically, the catalyst obtained after the isolation of HMF can be further recycled as such or after regeneration.
In an embodiment of the present disclosure, envisaged is a method for preparing Triethylamine-chromium chloride ionic liquid. The method comprises reacting CrCl3.6(H2O) with Triethylamine in a nitrogen environment at a predetermined temperature to obtain said Triethylamine-chromium chloride ionic liquid.
Typically, the predetermined temperature to obtain said Triethylamine-chromium chloride ionic liquid is in the range of 50 to 120 °C.
In the method of the present disclosure, when carried at an industrial/commercial scale, typically a glass lined reactor or a stainless steel reactor is used in an inert gas atmosphere for synthesizing 5-hydroxymethylfurfural (HMF). Typically nitrogen is used as an inert gas.
Typically the isolation of HMF at an industrial scale is carried out using a filter cloth or a centrifuge.
In an embodiment of the present disclosure, the method to obtain Triethylamine-chromium chloride ionic liquid comprises reacting a first predetermined amount of CrCl3.6H2O with predetermined amount of Triethylamine in a nitrogen environment for 15 to 30 minutes. The temperature is increased to 50 to 100 °C and a second predetermined amount of CrCl3.6H2O is added under stirring conditions to obtain the deep green colored semi solid paste, i.e. Triethylamine-chromium chloride ionic liquid.
In an embodiment of the present disclosure, triethylamine-chromium chloride ionic liquid TEA-CrCl3 ionic liquid is used for the synthesis of HMF directly from biomass.
In another embodiment of the present disclosure, the HMF yield was found to be 38% from biomass and 40% from cellulose.
Typically, the HMF yield was found to be 38% from cotton stalk, 32% from castor stalk and 31% from red gram respectively.
In yet another embodiment of the present disclosure, the method for synthesizing 5-hydroxymethylfurfural (HMF) as disclosed in the present disclosure is economical due to use of the low cost of TEA-CrCl3 ionic liquid and by the use of biomass.
The present disclosure is further described in light of the following experiments which are set forth for illustration purpose only and not to be construed for limiting the scope of the disclosure. The following experiments can be scaled up to industrial/commercial scale and the results obtained can be extrapolated to industrial scale.
Experiments:
In the method of the present disclosure, when carried at an industrial/commercial scale, typically a glass lined reactor or a stainless steel reactor is used in an inert gas atmosphere for synthesizing 5-hydroxymethylfurfural (HMF). Typically nitrogen is used as an inert gas.
Experiment No 1:
Preparation of TEA-CrCl3 and ChCl-CrCl3 ionic liquids:
TEA-CrCl3 ionic liquid:
Initially one mole of CrCl3.6H2O was added to a reaction vessel. Further, three moles of TEA was added dropwise with constant stirring in N2 atmosphere to the reaction vessel containing one mole of CrCl3.6H2O. Stirring was carried out for 20 mins to obtain a TEA-CrCl3 adduct in form of a solid mass. The temperature of the TEA-CrCl3 adduct was increased to 70 °C followed by addition of 6 moles of CrCl3.6H2O under constant stirring to obtain a deep green colored semi solid paste, i.e. TEA-CrCl3 ionic liquid.

ChCl·CrCl3: One mole of CrCl3.6H2O was added to a reaction vessel. The reaction vessel was kept in an oil bath. One mole of choline chloride was added to the reaction vessel containing CrCl3.6H2O followed by stirring in N2 atmosphere for 10 minutes. Further, temperature of the oil bath was increased to 100 °C to obtain a deep green colored semi solid paste, i.e. ChCl-CrCl3 ionic liquid.
Experiments 2:
Effect of temperature on HMF Yield: 5 experiments were carried out in batch operations with temperatures of 110 °C, 120 °C, 130 °C, 140 °C and 150 °C respectively.
A reaction vessel was charged with 0.5 grams of cotton stalk, 10.0 g of 1-butyl-3-methylimidazolium chloride and 2 wt% w.r.t. to total reaction wt. of TEA-CrCl3 ionic liquid and was agitated at 1000 rpm by using a magnetic bar. The reaction was heated to respective temperatures as summarized in table 1 for 60 minutes to form a reaction mixture. The reaction mixture was cooled to a temperature of 28 °C. Distilled water was added to make the total volume to 25 ml and percentage yield of 5-hydroxymethyl furfural (HMF) formation was calculated by HPLC analysis. The effect of temperature on yield of HMF is summarized in table 1. It was found that with an increase in reaction temperature beyond 130 °C; HMF yield decreased. This decrease in HMF yield is due to the thermal degradation of HMF which occurred at the higher temperature.
Table 1
Sr. No. Temperature °C HMF Yield (%)
Biomass Cellulose
1 110 8 12
2 120 9 32
3 130 31 35
4 140 20 30
5 150 6 17

Experiments 3:
Effect of TEA-CrCl3 ionic liquid amount on HMF Yield: 4 experiments were carried out in batch operations with TEA-CrCl3 ionic liquid in an amount of 0.5, 1.0, 2.0 and 3.0 wt% w.r.t. to total reaction wt.
A reaction vessel was charged with 0.5 grams of cotton stalk, 10.0 g of 1-butyl-3-methylimidazolium chloride and respective amounts of TEA-CrCl3 ionic liquid as summarized in table 2, and was agitated at 1000 rpm by using a magnetic bar. The reaction was heated to 130 °C for 60 minutes to form a reaction mixture. The reaction mixture was cooled to a temperature of 28 °C. Distilled water was added to make the total volume to 25 ml and percentage yield of 5-hydroxymethyl furfural (HMF) formation was calculated by HPLC analysis. The effect of TEA-CrCl3 on yield of HMF is summarized in table 2. It was found that 2.0 and 3.0 wt% w.r.t. to total reaction wt of TEA-CrCl3 ionic liquid gave better HMF yield.

Table 2
Sr. No. TEA-CrCl3 ionic liquid amount
(wt% w.r.t. to total reaction wt) HMF Yield (%)
Biomass Cellulose
1 0.5 18 20
2 1.0 31 35
3 2.0 34 37
4 3.0 34 38

Experiments 4:
Effect of reaction time on HMF Yield: 4 experiments were carried out in batch operations with reaction time of 60 minutes, 90 minutes, 120 minutes and 240 minutes respectively.
A reaction vessel was charged with 0.5 grams of cotton stalk, obtained from Jetpur, Rajkot district, Gujrat, 10.0 g of 1-butyl-3-methylimidazolium chloride and 2.0 wt% w.r.t. to total reaction wt. of TEA-CrCl3 ionic liquid and was agitated at 1000 rpm by using a magnetic bar. The reaction was heated to 130 °C for respective time period, as summarized in table 3, to form a reaction mixture. The reaction mixture was cooled to a temperature of 28 °C. Distilled water was added to make the total volume to 25 ml and percentage yield of 5-hydroxymethyl furfural (HMF) formation was calculated by HPLC analysis. The effects of different reaction time on HMF yield are summarized in table 3. It was found that beyond 120 minutes, the HMF yield decreases due to self-degradation of HMF. Hence, 120 min was considered as optimum reaction time for HMF synthesis.

Table 3
Sr. No. Reaction time (minutes) HMF Yield (%)
Biomass Cellulose
1 60 32 36
2 90 34 38
3 120 38 40
4 240 31 35

Experiments 5:
Effect of Biomass/cellulose amount on HMF Yield: 2 experiments were carried out in batch operations with biomass in an amount of 0.5g and 1.0g respectively.
A reaction vessel was charged with respective amounts of cotton stalk, as summarized in table 4, 10.0 g of 1-butyl-3-methylimidazolium chloride and 2.0 wt% w.r.t. to total reaction wt. of TEA-CrCl3 ionic liquid and was agitated at 1000 rpm by using a magnetic bar. The reaction was heated to 130 °C for 120 minutes to form a reaction mixture. The reaction mixture was cooled to a temperature of 28 °C. Distilled water was added to make the total volume to 25 ml and percentage yield of 5-hydroxymethyl furfural (HMF) formation was calculated by HPLC analysis. The effects of biomass amount on HMF yield are summarized in table 4. It was found that with increase in amount of the biomass/cellulose amount from 0.5g to 1.0g, the HMF yield was found to decrease due to increase in viscosity of the reaction. 0.5g of biomass/cellulose amount gave optimum HMF yield.

Table 4
Sr. No. Biomass/cellulose amount HMF Yield (%)
Biomass Cellulose
1 0.5g 38 40
2 1.0g 26 32

Experiments 6:
Effect of different ionic liquids on HMF Yield: 5 experiments were carried out in batch operations with different ionic liquids.
A reaction vessel was charged with 0.5 grams of cotton stalk, 10.0 g of 1-butyl-3-methylimidazolium chloride and 2.0 wt% w.r.t. to total reaction wt. of different ionic liquids, as summarized in table 5 and was agitated at 1000 rpm by using a magnetic bar. The reaction was heated to 130 °C for 120 minutes to form a reaction mixture. The reaction mixture was cooled to a temperature of 28 °C. Distilled water was added to make the total volume to 25 ml and percentage yield of 5-hydroxymethyl furfural (HMF) formation was calculated by HPLC analysis. The effects of different ionic liquids on HMF yield are summarized in table 5. It was found that TEA-CrCl3 ionic liquid gives better yield of HMF as compared with ChCl·CrCl3, Thiourea·CrCl3, Urea·CrCl3 and DMSO·CrCl3 which can be due to the strong Lewis acid characteristic of TEA-CrCl3 ionic liquid.

Table 5
Sr. No Ionic liquids HMF Yield (%)
Biomass Cellulose
1 TEA-CrCl3 38 40
2 ChCl-CrCl3 21 30
3 Thiourea-CrCl3 25 29
4 Urea-CrCl3 10 13
5 DMSO·CrCl3 8 10

Experiment 7:
Experiment was carried out for isolating the HMF produced in the above experiments. HMF was isolated by using ethyl acetate or diethyl ether or both by solvent extraction technique.
50 ml of ethyl acetate or 50 ml of diethyl ether or both was added to the second reaction mixture and stirred for 15 mins. Thereafter, ethyl acetate/diethyl ether layer is separated out. The procedure is repeated twice. Then, ethyl acetate/diethyl ether is evaporated under reduced pressure in rota vacuum to obtain the isolated 5-hydroxymethyl furfural.
TECHNICAL ADVANCEMENTS
The present disclosure described herein above has several technical advantages including, but not limited to, the realization of:
? a method for synthesizing 5-hydroxymethylfurfural (HMF) which is environmental friendly, economical and utilizes renewable sources of energy; and
? a simple and easy method for isolating 5-hydroxymethylfurfural (HMF).
Throughout this specification the word “comprise”, or variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.
The use of the expression “at least” or “at least one” suggests the use of one or more elements or ingredients or quantities, as the use may be in the embodiment of the invention to achieve one or more of the desired objects or results. While certain embodiments of the inventions have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Variations or modifications to the formulation of this invention, within the scope of the invention, may occur to those skilled in the art upon reviewing the disclosure herein. Such variations or modifications are well within the spirit of this invention.
The numerical values given for various physical parameters, dimensions and quantities are only approximate values and it is envisaged that the values higher than the numerical value assigned to the physical parameters, dimensions and quantities fall within the scope of the invention unless there is a statement in the specification to the contrary.
While considerable emphasis has been placed herein on the specific features of the preferred embodiment, it will be appreciated that many additional features can be added and that many changes can be made in the preferred embodiment without departing from the principles of the disclosure. These and other changes in the preferred embodiment of the disclosure will be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the disclosure and not as a limitation.