DESC:FIELD
The present disclosure relates to a process for preparation of carbon forms from biomass.
DEFINITIONS
As used in the present disclosure, the following terms are generally intended to have the meaning as set forth below, except to the extent that the context in which they are used indicate otherwise.
The term “biomass” as used herein refers to a biological material such as algae, grass, wood, agricultural crops and aquatic biomass in addition to organic wastes including urban refuse, agricultural wastes, municipal wastes and the like, which can be used as a source of fuel or energy.
The term “hydrothermal treatment (HTT)” as used herein refers to an employment of a combination of heat and water as a media to convert wet biomass into a mixture of residue and aqueous-soluble products at moderate to high temperature and at moderate to high pressure.
BACKGROUND
New forms of carbon, such as graphene and graphene oxides are being used for a wide variety of applications, including, but not limited to, electronics, optical devices, and water purification. A number of methods have been devised to prepare these new forms of carbon that include methods such as chemical vapor deposition, sputtering and the like.
The precursors used for preparing/fabricating these carbon forms include petroleum based graphite and the like. Preparation of graphene and graphene oxides using petroleum based graphite as precursors necessitates the use of very strong and corrosive acids for oxidation. The use of very strong and corrosive acids is not only hazardous but also harmful to the environment at large in the long run.
Hence, there is a need for a process that provides a way to produce carbon forms including graphene and graphene oxide that mitigates the drawbacks mentioned hereinabove.
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.
An object of the present disclosure is to provide a process for preparing carbon forms from biomass.
Another object of the present disclosure is to provide an environmentally friendly, simple, safe, and cost effective process for preparing carbon forms from biomass.
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 relates to a process for the preparation of carbon forms from biomass. The process of the present disclosure comprises admixing biomass in water, and subjecting it to a first hydrothermal treatment in the presence of a homogeneous catalyst at a first predetermined temperature, and at a first predetermined pressure using a predetermined stirring speed to obtain aqueous solution containing dissolved carbohydrates. The so obtained aqueous solution is subjected to a second hydrothermal treatment (HTT) at a second predetermined temperature and at a second predetermined pressure to obtain a reaction mass. The so obtained reaction mass is then cooled and the solid is separated to obtain the carbon forms. The carbon forms can be graphene and graphene oxide.
DETAILED DESCRIPTION
Conversion of renewable biomass into valuable products, traditionally obtained from fossil fuels, is strategically important to avoid 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 reduction 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.
New forms of carbon such as graphene and graphene oxides are being used for a wide variety of applications such as electronics, optical devices, and water purification. Conventionally, graphene/graphene oxides are prepared by using petroleum based graphite in the presence of very strong and corrosive acids and hence are not environment friendly.
The present disclosure envisages a process that provides a way to produce carbon forms (carbon solids) including graphene and graphene oxide using biomass as the base precursor or starting material by hydrothermal treatment (HTT) and without the use of the hazardous and corrosive acids. The process of the present disclosure is therefore safe and environment friendly.
In accordance with an aspect the present disclosure provides a process for preparing carbon forms from biomass. The process of the present disclosure is described in detail herein below:
Firstly, biomass is admixed in water and subjected to a first hydrothermal treatment (HTT) at a first predetermined temperature and at a first predetermined pressure, at a predetermined stirring speed in the presence of a catalyst to obtain an aqueous solution containing dissolved carbohydrates. The catalyst is a homogeneous catalyst which can be added in the aqueous slurry to enhance the rate of reaction. The predetermined stirring speed for mixing the biomass and water can be in the range of 100 rpm to 900 rpm. The predetermined time period can be in the range of 5 minutes to 90 minutes.
In one embodiment, the concentration of the biomass in the slurry can be in the range of 5% to 70 %. The biomass can be at least one selected from the group consisting of microalgae, macroalgae, cellulosic or lignocellulosic biomass, cane sugar biomass (molasses), and biomass from fruits, vegetables, and municipal wastes. Typically, the biomass is urban waste, agricultural waste and municipal solid waste. In one embodiment the biomass used in the process of the present disclosure is Picochlorum. The geographical origin of Picochlorum is Karanja, Maharashtra.
In accordance with the present disclosure, the first predetermined temperature can be in the range of 25 oC to 150 oC. In one embodiment, the first predetermined temperature is 150 oC.
In accordance with the present disclosure, the first predetermined pressure can be in the range of 1 bar to 50 bar. In one embodiment, the first predetermined pressure is 35 bar.
The dissolved carbohydrates in the aqueous solution can be at least one selected from the group consisting of monosaccharides such as hexose, pentose, to polysaccharides such as cellulose and hemicellulose. Typically the hexose carbohydrates can be glucose, mannose, fructose, galactose, and sucrose and the pentose carbohydrates can be xylose and arabinose.
In accordance with the present disclosure, the homogeneous catalyst can be acidic inorganic, organic cationic or anionic in nature. In one embodiment the catalyst is selected from water soluble ammonium salts. Typically, the water soluble ammonium salts comprise cations selected from the group consisting of ammonium, quaternary ammonium with short aliphatic chain, pyridinium, imidazolium, pyrazolium, tetraethylammonium, tetramethylammonium, and anions selected from the group consisting of chloride, bromide, iodide, and sulphonate.
Typically, the catalyst as used in the process of the present disclosure can be easily recovered and reused in the next cycle for preparing carbon solids/forms from biomass, without affecting the yield of carbon solids.
In an exemplary embodiment the catalyst is ammonium chloride, which remains in the filtrate and can be further used in the next cycle of conversion of biomass to carbon forms. Typically, the homogeneous catalyst alters the oxygen content of the carbon solids. The homogeneous catalyst promotes all the intermediate steps involved in graphene formation such as hydrolysis of carbohydrates, dehydration, and condensation of intermediates. These chemical transformations occur with simultaneous removal of small molecules such as H2O and CO2 from the intermediate. Hence, the oxygen content of the carbon solids is reduced when the catalyst is employed, which is evident from the elemental analysis.
Therefore, when the catalyst used in the process of the present disclosure, the conversion rate of biomass to graphene is comparatively higher.
Secondly, the so obtained aqueous solution is subjected to a second hydrothermal treatment at a second predetermined temperature and at a second predetermined pressure to obtain a reaction mass. The reaction mass comprises solids of carbon forms.
In one embodiment the carbon form can be graphene and graphene oxide. The formation of graphene and/or graphene oxide can be characterized by elemental analysis, FT- infrared analysis, and transmission electron microscopy (TEM).
In an exemplary embodiment the HTT of the aqueous slurry containing dissolved carbohydrates can be carried out in a batch reactor or reaction vessel. An inert gas is introduced in the reactor/reaction vessel to attain a predetermined second pressure of the slurry, present in the reactor. Use of inert gas also avoids unwanted oxygenation which can be caused by the atmospheric oxygen. Typically, nitrogen is used as the inert gas in the process of the present disclosure.
In accordance with the present disclosure the second predetermined temperature can be in the range of 350 oC to 450 oC. In one embodiment, the second predetermined temperature is 415 oC.
In accordance with the present disclosure the second predetermined pressure can be in the range of 200 bar to 300 bar. In one embodiment, the second predetermined pressure is 250 bar.
The reaction mass is then cooled and the carbon solids are separated from the cooled reaction mass. The separation of carbon solids can be carried out simply by decantation or filtration techniques.
In one embodiment a process for preparing carbon forms from biomass comprising admixing the biomass in water and subjecting it to a first hydrothermal treatment in the presence of ammonium chloride at 150 oC and at 35 bar to obtain an aqueous slurry containing dissolved carbohydrates. The weight ratio of the biomass to the catalyst is 10:1. Further, the so obtained aqueous slurry is subjected to a second hydrothermal treatment at 415 oC and at 250 bar to obtain a reaction mass. The reaction mass is cooled and the carbon forms are separated from the cooled reaction mass.
In the present disclosure, the yield of the carbon solids (carbon forms) can be in the range of 20 to 40 wt. %. In one embodiment the yield of carbon solid is 30 wt%. The process of the present disclosure is safe, simple, and environment friendly, since the reaction does not use corrosive ingredients. Further, there are no special apparatus /processes required for downstream processing i.e. filtration /separation thereby making the overall process of the present disclosure cost effective.
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.
EXPERIMENTAL DETAILS:
Experiment 1
In a reactor/reaction vessel, 20 gm of Picochlorum (biomass) in the ground/shredded form (0.01 – 10 mm) was mixed with 80 ml water under stirring at ambient temperature for 15 minutes to obtain an aqueous slurry. 2.0 g of ammonium chloride (homogenous catalyst) was added to the aqueous slurry under nitrogen gas till a pressure of 35 bars was attained and heated to 150 ºC in the reactor/reaction vessel for 15 minutes to obtain a reaction mixture. The reaction mixture was filtered after cooling to ambient temperature to obtain an aqueous solution containing dissolved carbohydrates such as glucose.
The aqueous solution so obtained was heated to 415 oC at 250 bar pressure to obtain a reaction mass.
The reaction mass was then cooled to 30 °C and the solids were separated by filtration to obtain graphene oxide. The catalyst remained in the filtrate which was used in further conversion of biomass to carbon forms.
The yield of graphene oxide was 30 wt%.
Experiment 2
Aqueous solutions of different carbohydrates (glucose, galactose and fructose) were subjected to hydrothermal treatment (conditions: temperature 250-400 °C; pressure 70-250 bar; time 30 min to 6 h; catalyst with/without) to produce solid carbon materials (carbon forms). The hydrothermal treatment of aqueous solution of different carbohydrates produced four products i.e. crude bio-oil (dichloromethane extracted), organics in aqueous phase, solid residue (carbon forms), and gaseous products are given in the table 1.
The solid residue was obtained in pure state by mere filtration and oven drying. The solid residue produced possessed enriched carbon content and depleted oxygen content in comparison to the feed carbohydrate (by elemental analysis). The IR spectroscopy confirmed the presence of hydroxyl, carbonyl, and aromatic functionalities in the product (solid residue). The solid state 13C NMR spectroscopy confirmed the presence of aromatic functionalities. The presence of a homogeneous acid catalyst during thermal treatment was also studied. The oxygen content of the solid was significantly reduced by acid catalyst. This indicates that the properties of the solid product can be altered or tuned by the reaction conditions. The results obtained are summarized in table-1
Table 1: Hydrothermal treatment of aqueous solutions of different carbohydrates
S. No. Aqueous Feed Catalyst Crude Bio-Oil (wt%) Organics in aq. Phase (wt%) Residue (carbon forms) (wt%) Gas (wt%)
1 Glucose No catalyst 15.73 53.18 27.83 3.25
2 Homogeneous cat 15.39 55.36 26.83 2.42
3 Galactose No catalyst 13.78 52.64 29.08 4.50
4 Homogeneous 11.56 53.52 29.83 5.08
5 Fructose No catalyst 12.08 52.82 30.32 4.78

From the Table 1, it is evident that HTT of mono saccharides provides solid residues in 25-30 wt% yields along with aqueous soluble organic products (50 wt% approximately).
The quantity of residue (carbon forms) obtained is more than the crude bio-oil which indicates the carbohydrate feeds are suitable for producing carbon solids containing graphene oxides. The presence of catalyst favors the production of graphene over graphene oxide.
Further, High-resolution transmission electron microscopy (HRTEM) images of the graphene obtained in the experiment 2 in accordance with the process of the present disclosure are illustrated in Figures 1 to 3.
Figure- 1 illustrates the Aberration corrected High Resolution Transmission Electron Microscopy (HRTEM) image of graphene solids obtained from HTC of Glucose. Figure-1 exhibits graphene sheets (~5-7 layers) and their ultra-high resolution images (Figure-3) of single sheet show the hexagonal typical honey comb structure of graphene. Image analysis exhibits the dimensions of the carbon rings in the graphene sheet with 0.24 Angstroms characteristic of an aromatic carbon with double bond character.
Figure-2 illustrates the HRTEM analysis of graphene solids obtained from HTC of Picochlorum sp. and exhibits carbonaceous microstructures with hollow shells formed out of hydrothermal treatment.
The present disclosure envisages a two-stage hydrothermal conversions for solid biomass feed where a low temperature hydrothermal treatment (in the order of 150 °C) to produce aqueous stream containing soluble carbohydrates and the high temperature process (250-400 °C) to convert the aqueous carbohydrates to yield the carbon containing solid materials is employed.
TECHNICAL ADVANCEMENTS
The present disclosure described herein above has several technical advantages including, but not limited to, the realization of:
? a simple, energy efficient, time saving, and environment friendly process for the preparation of carbon forms from biomass; and
? reuse of the catalyst in the next cycle in the preparation of carbon forms without affecting the yield of the carbon forms.
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.

,CLAIMS:WE CLAIM:
1. A process for preparing carbon forms from biomass, said process comprising:
a. admixing said biomass in water, and subjecting it to a first hydrothermal treatment in the presence of a homogeneous catalyst at a first predetermined temperature and at a first predetermined pressure under stirring at a predetermined stirring speed to obtain an aqueous solution containing dissolved carbohydrates;
b. subjecting said aqueous solution to a second hydrothermal treatment at a second predetermined temperature and at a second predetermined pressure to obtain a reaction mass; and
c. cooling said reaction mass followed by separation of said carbon forms from said cooled mass.
2. The process as claimed in claim 1, wherein said carbon forms comprise graphene and/or graphene oxide.

3. The process as claimed in claim 1, wherein said biomass is at least one selected from the group consisting of microalgae, macroalgae, starch, cellulosic and lignocellulosic biomass, molasses and biomass obtained through waste.

4. The process as claimed in claim 1, wherein said homogeneous catalyst is a water soluble ammonium salt.

5. The process as claimed in claim 4, wherein said water soluble ammonium salts comprise cations selected from the group consisting of ammonium, quaternary ammonium with short aliphatic chain, pyridinium, imidazolium, pyrazolium, tetraethylammonium, tetramethylammonium, and anions selected from the group consisting of chloride, bromide, iodide, and sulphonate.

6. The process as claimed in claim 1 or claim 4, wherein said homogeneous catalyst is ammonium chloride.

7. The process as claimed in claim 1, wherein said first predetermined temperature is in the range of 25 oC to 150 oC.

8. The process as claimed in claim 1, wherein said first predetermined pressure is in the range of 1 bar to 50 bar.

9. The process as claimed in claim 1, wherein said second predetermined temperature is in the range of 350 oC to 450 oC.

10. The process as claimed in claim 1, wherein said second predetermined pressure is in the range of 200 bar to 300 bar.

11. The process as claimed in claim 1, wherein said carbohydrate in the process step a) is at least one selected from the group consisting of hexose and pentose and monosaccharide to polysaccharide.

12. The process as claimed in claim 1, wherein said predetermined stirring speed is in the range of 100 rpm to 900 rpm.

13. The process as claimed in claim 1, wherein said separation is carried out by filtering or decanting.

14. A process for preparing carbon forms from biomass, said process comprising
a. admixing said biomass in water and subjecting it to a first hydrothermal treatment in the presence of ammonium chloride at 150 oC and at 35 bar to obtain an aqueous slurry containing dissolved carbohydrates, wherein the weight ratio of said biomass to said catalyst is 10:1;
b. subjecting said aqueous slurry to a second hydrothermal treatment at 415 oC and at 250 bar to obtain a reaction mass; and
c. cooling said reaction mass followed by separation of said carbon forms from said cooled mass.