Description:FORM 2
THE PATENT ACT 1970
(39 of 1970)
&
The Patents Rules, 2003
COMPLETE SPECIFICATION
(Section 10 and rule13)

ECO-FRIENDLY ROUTE FOR SYNTHESIS OF ACTIVATED CARBON WITH HIGH SPECIFIC SURFACE AREA AND POROSITY

BRIDGR INNOVATIONS PRIVATE LIMITED
INDIA
Building No.65/614, Fourth Floor Finance Tower, Kaloor, Ernakulam, Kerala, 682017, India

The following specification particularly describes the invention and the manner in which it is to be performed.

FIELD OF INVENTION
The present invention relates to the field of activated carbon. More specifically, the present invention relates to facile, efficient and eco-friendly route for synthesis of activated carbon with high specific surface area and porosity.

BACKGROUND OF THE INVENTION
When it comes to chemical activation, a broad range of substances (activating agents) are frequently utilized, such as acids, bases, and salts (such as H3PO4, KOH, NaOH, ZnCl2, and FeCl3), which are then heated at various activation temperatures (Tact) to create activated carbon material.

For the synthesis of activated carbon with high surface area, a variety of techniques have been reported. These include physical activation using suitable oxidizing gases like steam, carbon dioxide, etc. at high temperatures of 600–1200oC and chemical activation using chemical activating agents like potassium hydroxide (KOH), zinc chloride (ZnCl2), phosphoric acid (H3PO4), sodium hydroxide (NaOH), and ferric chloride (FeCl3). Due to improved yield, high porosity/surface area, and well-developed/interconnected pore structures, chemical activation is typically favored over physical activation. The use and effectiveness of activated carbon are heavily influenced by its surface area and porosity, which are in turn connected to the activating agent employed. The main drawbacks, however, are the poisonous nature of these activation chemicals, the laborious and time-consuming methods required to remove them from the product, as well as their high price. It's interesting that the current incarnation presents a brand-new, economically viable, environmentally beneficial, and quicker method for producing activated carbon aerogels.

CA1334192C discloses the activation of carbonaceous cellulose materials with ZnCl2. Aqueous ZnCl2 was mixed with carbon material in the ratio 1:4 followed by carbonization temperatures between 400-700 ºC. The synthesized activated carbon had a specific surface area of 1800 m2·g-1 and bulk density of 0.35 g·cm-3.
US5614459A discloses a similar method for the synthesis of activated carbon using ZnCl2 and SnCl2 and obtained a maximum surface area of 1047 m2·g-1.

WO1994000382A1 discloses the synthesis of activated carbon from lignite using KOH /NaOH as activating agent and claimed an improvement in hexane absorption properties.

US2013028061 discloses the synthesis of activated carbon aerogel (with a surface area of 898 m2·g-1) through physical activation using CO2 gas at temperatures ranging from 800-1000 ºC.

US8563467B2 discloses the synthesis of activated carbon from petroleum coke using microwave irradiation in the presence of water.

Thus, it is claimed that the current techniques for making activated carbon have severe drawbacks, such as high costs, extended activation times, laborious processes required to remove the activating agent, environmental pollution, and toxicity. Research aimed at finding solutions for these issues gave rise to the current invention. As a result, the primary goal of the current invention is to provide a better process for the one-shot synthesis of activated carbon aerogel with extremely high surface area and porosity.

Taking into account the above-mentioned problems, there arise a need to develop a simple, cost effective and eco-friendly route for the development of carbon aerogel having ultra-high surface area and porosity. Carbon aerogels are quite extensively used as electrode material in batteries, supercapacitors, hydrogen storage devices etc. materials for CO2 sequestration, and catalyst support systems and the performance is largely dependent on surface area and porosity.

OBJECTOF THE INVENTION:

An object of the present invention is to provide a process for synthesis of activated carbon with ultra-high surface area/porosity through in situ doping of activating agent followed by one step pyrolysis/activation process.
Another object of the present invention is to provide Mn(OAc)4.4H2O as a novel eco-friendly and effective catalyst/activating agent.
Another object of the present invention is to develop a process for cost effective route for the synthesis of carbon aerogel with high porosity and surface area.
SUMMARY OF THE INVENTION
This summary is provided to introduce a selection of concepts in a simplified form that are further disclosed in the detailed description of the invention. This summary is not intended to identify key or essential inventive concepts of the claimed subject matter, nor is it intended for determining the scope of the claimed subject matter.
Accordingly, the present invention provides a process for the synthesis of carbon aerogels with ultra-high surface area and porosity comprising the steps of preparation of sol by mixing resorcinol, formalin and catalyst system to obtain a homogenous solution; converting the solution to gel at ambient conditions followed by solvent exchange using acetic acid solution and acetone; drying of the gel; and carbonization of the aerogel to obtain activated carbon aerogels.
In an embodiment, the present invention provides that the catalyst system is (Mn(OAc)4.4H2O.
In another embodiment, the present invention provides that the ratio of the resorcinol, formalin ranges from 1:2 and the catalyst is about 5 to 25% of the weight of resorcinol.
In another embodiment, the present invention provides that the conversion of the solution to gel followed by the solvent exchange with solvents selected from acetic acid solution and acetone.
In another embodiment, the present invention provides that the amount of acetic acid is 1-5%.
In another embodiment, the present invention provides that the carbon aerogel is formed from the condensation reaction between resorcinol and formaldehyde.
In another embodiment, the present invention provides that the carbonization of the aerogel at performed at 900- 1100ºC with heating rate of 1-5ºC/min-1, and residence time of 1h- 3h under argon atmosphere.
In another embodiment, the present invention provides that the obtained activated carbon aerogel is etched with nitric acid to obtain carbon derived carbon with increased porosity, surface area and pore volume.

BRIEF DESCRIPTION OF THE DRAWINGS
The foregoing summary, as well as the following detailed description of the invention, is better understood when read in conjunction with the appended drawings. For the purpose of illustrating the invention, exemplary constructions of the invention are shown in the drawings. However, the invention is not limited to the specific methods and components disclosed herein. The description of a method step or a component referenced by a numeral in a drawing is applicable to the description of that method step or component shown by that same numeral in any subsequent drawing herein.

Figure 1: shows a schematic presentation reaction between resorcinol and formaldehyde for the synthesis of carbon aerogel;

Figure 2: shows a diagram illustrating the implant at an angle perpendicular to the illustration of Fig. 1;

Figure 3: XRD studies on activated carbon aerogel with different dopant concentration; and
Figure 1: Raman spectra of neat carbon aerogel and MnO doped carbon aerogels.
Further, skilled artisans will appreciate that elements in the drawings are illustrated for simplicity and may not have been necessarily been drawn to scale. Furthermore, the drawings may show only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the drawings with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.

DETAILED DESCRIPTION OF THE DRAWINGS
To promote an understanding of the principles of the invention, reference will now be made to the embodiment illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications in the illustrated system, and such further applications of the principles of the invention as illustrated therein being contemplated as would normally occur to one skilled in the art to which the invention relates.

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

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

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

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

Exemplary methods and systems are described herein. Any example embodiment or feature defined herein is not essentially to be interpreted as favored or advantageous over other embodiments or features. The example embodiments explained in this disclosure are not meant to be restrictive within a limit. It will be readily understood that certain aspects of the described systems and methods may be oriented and joined together in a broad variety of different arrangements, all of which are anticipated herein.
The procedure for creating activated carbon aerogels with enhanced surface area, porosity, and pore volume is disclosed in the current invention. It involves a revolutionary one-step pyrolysis/activation approach. The current embodiment describes a more effective method for creating activated carbon aerogels using Mn(OAc)4.4H2O. Low-cost carbon aerogels with high surface area and porosity find application in a variety of fields thanks to in-situ pyrolysis/activation and a straightforward washing procedure. Mn(OAc)4.4H2O is utilized in the present invention as an activating agent and catalyst for the production of activated carbon.
In one aspect of the present invention, the current invention offers a straightforward, effective, and environmentally friendly method for producing activated carbon with a very high specific surface area and porosity in a single step. The current embodiment describes the development of low cost activated carbon for use in stealth devices, CO2 sequestration, water purification, batteries, supercapacitors, and hydrogen storage. It uses non-toxic chemicals, a time-shortened one pot synthesis route, and tunable porosity/surface area. Depending on the quantity of dopant utilized, the synthetic activated carbon has a very high specific surface area of 4750 m2g-1.

Aerogels are very porous substances with a 100% open pore structure, sub-nanometer-sized pore diameters, and low density. Carbon aerogels have surface areas ranging from 900 to 1300 m2·g-1. The typical method used to create carbon aerogels is sol-gel production, followed by super critical drying and carbonization in inert gas. Aerogels are often created using the sol-gel method, which involves the reaction of resorcinol and formaldehyde in the presence of a suitable catalyst, followed by ambient pressure drying. As indicated in Figure 1, the synthesized aerogels are subsequently carbonized at a particular carbonization temperature in an inert environment. Carbon aerogel, which has a density of 1.5–2.7 g/cc, is widely utilized to create supercapacitors, batteries, catalyst support systems, and adsorbent for a variety of gases, including volatile organic gases, hydrogen storage devices, photocatalyst etc.

Aerogels are highly porous materials having sub-nanometer-sized pores, huge surface areas that typically surpass 1000 m2·g-1, and extremely low densities in the range of 0.008 to 0.1 g·cc-1. Figure 1(a) illustrates the polycondensation reaction that results in the formation of a gel during the creation of carbon aerogels. Following that, the gel is solvent-free thanks to an ambient pressure drying process, as seen in Figure 1(b).
To create porous carbon aerogels, the aerogels are subsequently carbonised or pyrolyzed at various temperatures. Activation of carbon aerogel using KOH proceeds through:
(a) Redox reaction between various potassium compounds and carbon resulting in an etching of carbon framework;
(b) The formation of H2 and CO2 provides physical activation; and
(c) Intercalation of potassium in the carbon matrix and its removal by washing leaves micro/meso pores in the lattice.
In an embodiment, the present invention provides a process for the synthesis of carbon aerogels with ultra-high surface area and porosity using a novel catalyst and activating agent (Mn(OAc)4.4H2O. The aerogel is formed from the condensation reaction between resorcinol and formaldehyde. The porous carbon is formed by the usage of Mn(OAc)4.4H2O as insitu activating agent capable of producing high quality carbon aerogels with very high surface area/porosity. The oxygen moieties in Mn(OAc)4.4H2O serve to produce porous carbon through a combination of physical and chemical activation. The in situ incorporation of Mn(OAc)4.4H2O enables the uniform dispersion in resorcinol-formaldehyde sol. This eventually helps in the production of high-quality activated carbon aerogels. The porous carbon is produced through an eco-friendly route without the usage of any toxic chemicals. The porous carbon provides ultra-high surface area depending on the loading of Mn(OAc)4.4H2O. The porous carbon is having micropores with size in the range of 4nm. A porous carbon with ultra-high surface area, low density and porosity. Etching of the obtained porous carbon using nitric acid provides derived carbon with increased porosity, surface area and pore volume.
The activated carbon aerogel of the present invention is used as insulation systems for use in launch vehicles, as electrode material for lithium-ion batteries, other types of batteries and supercapacitors, photocatalyst for the waste water purification. It is the best material for hydrogen storage, hydrogen storage capacity is directly related to specific surface area. Further, the activated carbon aerogel of the present invention is effective adsorbent for CO2 sequestration process.

The following examples define the invention by way of illustration which does not limit the scope of the invention.
EXAMPLE 1:
The porous carbon aerogels are then activated using suitable activating agent to increase the surface area and porosity. Wide varieties of activating agents are commonly used to achieve an increase in surface area and porosity. Few of the commonly used activating agents and their limitations are listed in Table 1.
Table 1: Activating agents commonly used for the synthesis of porous carbon with high surface area and porosity:
Activating agent (s) Molar ratio Advantages Limitations
Potassium Hydroxide (KOH) 1:1, 1:2, 1:3, 1:4 Most widely used activating agent, High surface area, porosity Difficulty in removing potassium from the carbon matrix.
Zinc Chloride (ZnCl2) 1:4 Formation of aromatic graphitic structure. Increased carbon yield. Highly corrosive and usually destroys the chamber of the furnace. Highly toxic.
o-Phosphoric Acid (H3PO4) 1:4 Low temperature activating agent used for carbon from biosource. Toxic and difficulty in cleaning the furnace
ZnCl2-H3PO4 mixture 1:4 High surface area and porosity Highly corrosive and difficulty in cleaning the activated carbon
(Mn(OAc)4.4H2O 1:4 High-quality activated carbon aerogels through an eco-friendly route without the usage of any toxic chemicals. Low density and porosity

EXAMPLE 2:
The present invention discloses the synthesis of activated carbon aerogels through an in-situ doping process. The polycondensation reaction between resorcinol and formaldehyde was carried out in the presence of Mn(OAc)4.4H2O catalyst. Loading of Mn(OAc)4.4H2O was fixed with respect to resorcinol. Accordingly, 0, 5, 10, 15, and 20 wt% of the weight of resorcinol was added to the sol followed by stirring for 1h and allowed to gel in room temperature. The gel was strengthened at 50 ºC for 1 day and 90 ºC for 3 days, respectively. The strengthened gel was subjected to solvent exchange using 1% acetic acid and acetone followed by drying the gel at 60 ºC for 2 days. The xerogel was subjected to pyrolysis at 1000 ºC for 1 h under inert (argon) atmosphere. The synthesized porous activated carbon was subjected to detailed analysis.
Steps involved in the synthesis of in-situ activated carbon aerogels:
1. Preparation of sol by mixing required quantity of resorcinol, formalin and catalyst system;
2. Dissolution of required quantity of Mn(OAc)4.4H2O (In the present embodiment, the loading was fixed with respect to the quantity of resorcinol) with constant stirring so as to obtain a homogenous sol;
3. Conversion of the sol to gel at ambient conditions followed by solvent exchange using acetic acid solution (2%) and acetone;
4. Drying of the gel;
5. Carbonization of the aerogel at 1000ºC with heating rate of 3ºC·min-1, and residence time of 1h under argon atmosphere.

EXAMPLE 3:
Analysis of the in situ activated carbon aerogel:
Morphology: Morphology of the synthesised activated carbon aerogel analysed using scanning electron microscopy (SEM) confirms a pearl and neck morphology as presented in Figure 2(a). The TEM images presented in Figure 2 (b) confirm a highly porous structure with a uniform dispersion of the MnO.

EXAMPLE 4:
X-ray diffraction studies confirm the presence of MnO as evidenced by Figure 3. The XRD spectra consisted of peaks at 39.94º, 40.6º, 58.57º, 70.19º with the intensity of the peaks increasing as a function of MnO loading. Raman spectra of activated carbon consist of two main peaks as presented in Figure 4.

One at 1332 cm-1 corresponding to deffect band and arise due to edge induced structural defects. The second peak is centered around 1587 cm-1 correspond to G band and arise due to the zone centre vibration of C atoms against each other in the layer plane. In addition to this a broad band can be observed around 640 cm-1 which corresponds to Mn-O vibration modes. BET studies shows a combination of type I and type IV isotherms confirming the microporous nature of the synthesized aerogels. The surface area increases with increase in Mn(OAc)4.4H2O loading attaining a maximum of 4764 m2·g-1 for the 20 wt% doped system as given in Table 2. However, Mn(OAc)4.4H2O loading beyond this limit is not possible due to practical difficulties.

Table 2: Surface area porosity and pore volume obtained from BET studies:
Surface area (m2·g-1) Pore volume (cm3·g-1) Average pore diameter (nm)
0% doped 965.4 1.067 4.423
5 wt% doped 1399 1.627 4.653
10 wt% doped 2351 2.867 4.877
15 wt% doped 2287 2.773 4.850
20 wt% doped 4764 5.767 4.842

TGA studies prove two stage decomposition with the first stage decomposition centered on 275 ºC and second stage decomposition around 390 ºC.
, Claims:We Claim,

1. A process for the synthesis of carbon aerogels with ultra-high surface area and porosity comprising the steps of:
a. preparation of sol by mixing resorcinol, formalin and catalyst system to obtain a homogenous solution;
b. converting the solution to gel at ambient conditions followed by solvent exchange using acetic acid solution and acetone;
c. drying of the gel; and
d. carbonization of the aerogel to obtain activated carbon aerogels.
2. The process as claimed in claim 1, wherein the catalyst system is (Mn(OAc)4.4H2O.
3. The process as claimed in claim 1, wherein the ratio of the resorcinol, and formalin is 1:2 and catalyst loading from 5 to 20 wt%.
4. The process as claimed in claim 1, wherein the conversion of the solution to gel followed by the solvent exchange with solvents selected from acetic acid solution and acetone.
5. The process as claimed in claim 1, wherein the amount of acetic acid is 1-5%.
6. The process as claimed in claim 1, wherein the carbon aerogel is formed from the condensation reaction between resorcinol and formaldehyde.
7. The process as claimed in claim 1, wherein the carbonization of the aerogel at performed at 900- 1100ºC with heating rate of 1-5ºC/min-1, and residence time of 1h- 3h under argon atmosphere.
8. The process as claimed in claim 1, wherein the obtained activated carbon aerogel is etched with nitric acid to obtain carbon derived carbon with increased porosity, surface area and pore volume.

Dated this 16th day of September 2023

Bency Varghese
Patent Agent for the applicant (INPA/2313)