Porous monolithic carbon foam from low-value carbon feedstock, and method of producing the same

Abstract

The present disclosure relates to a porous monolithic carbon foam and a method of preparation thereof, wherein the carbon foam comprises an effective amount of combination of ball-milled, acid-treated low-value carbon or waste petroleum coke and natural foaming agent - acacia gum. Said carbon foams have different low-to-high (200 nm to 20 µm) porosity and hence can be used to fabricate advanced fuel cell electrodes and their assembly components, metal-ion battery electrodes, electromagnetic interference shielding (EMI shielding) and similar carbon foam-based applications. Further, the invention adds value to petroleum coke utilization and prevents the environment from using hazardous chemical-based foaming agents.

Description

[0001] POROUS MONOLITHIC CARBON FOAM FROM LOW- VALUE CARBON FEEDSTOCK, AND METHOD OF PRODUCING THE SAME

[0002] TECHNICAL FIELD OF THE INVENTION

[0003] The invention relates to a porous monolithic carbon foam. Specifically, the present invention relates to a carbon foam feedstock composition comprising an effective amount of combination of low-value carbon and natural foaming agent to obtain highly porous and tunable carbon foam. The present invention also relates to a method of producing the carbon foam feedstock composition.

[0004] BACKGROUND AND PRIOR ART OF THE INVENTION

[0005] Carbon foams are a form of porous carbons with monolithic structures and hierarchical pores. Many researchers have reported producing carbon foams from different carbon sources but using chemical-based synthetic foaming agents like polyvinyl alcohol, N-methyl pyrrolidone, etc., which suffer mainly from chemical hazards and hence the environmental concern is limiting to prepare and arrive at the carbon foams.

[0006] Edwin P. Stankiewicz (in US6103149A) reported impregnating polyurethane foam with carbonizing resin to produce carbon foam. Murdie Neil (US6323160B 1) produced carbon foam from mesophase pitch and densified it with carbonaceous material. Tan Seng (US6339031B1) produced carbon foam from thermoplastic carbon fiber precursors. Karthik Mani (US10287412B2) reported a process for preparing porous graphitic carbon foam by impregnating polymeric foam with phenolic resin and poly-alkylene oxide compound. Li Yat (US10526203B2) reported a method of forming porous carbon foam using chitosan and glutaraldehyde for carbon foam and removable SiCh particles for creating sub-micron cavities in the foam.

[0007] Jingfeng Wu (PhD Thesis, University of Calgary, Alberta, 2019), in his doctoral research work, produced carbon foam pellets using a salt (NaCl) template method and asphaltene as a binder under hydraulic pressure of 5 MPa. The researcher chemically treated / activated petroleum coke using NaOH or KOH and ball-milled it to obtain carbon feedstock. After the carbonization, the salt was removed with water in an ultrasonic bath. Though much research has been done to produce porous monolithic carbon foam from various carbon feedstocks using some chemical-based foaming agents, inventors find no reports on producing monolithic carbon foams from a low-value carbon feedstock and plant-based natural foaming agents.

[0008] Thus, there is a need in the art to provide a modified process of preparation of monolithic carbon foams using a low-value carbon feedstock and plant-based natural foaming agent with better yield and selectivity.

[0009] OBJECTS OF THE INVENTION

[0010] Accordingly, the main objective of the present disclosure is to provide a cost-effective, environment-friendly porous monolithic carbon foam for use in energy storage applications.

[0011] An object of the present invention is to provide a porous monolithic carbon foam from a low- value carbon feedstock.

[0012] An object of the present invention is to provide an environmentally benign porous monolithic carbon foam from a low-value carbon feedstock and plant-based natural foaming agents.

[0013] Another object of the present invention is to provide a method of producing porous monolithic carbon foam from a low-value carbon feedstock and plant-based natural foaming agents.

[0014] Yet another object of the present invention is to provide electrochemical components produced using the porous monolithic carbon foam.

[0015] SUMMARY OF THE INVENTION

[0016] Accordingly, aspects of the present invention relate to a porous monolithic carbon foam. Specifically, the present invention relates to a porous monolithic carbon foam comprising an effective amount of combination of low value carbon and natural foaming agent to obtain highly porous and tunable carbon foam. The present invention also relates to a method of producing the porous monolithic carbon foam.

[0017] In one aspect, the present invention provides a method of producing porous monolithic carbon foam by utilizing low-value petroleum coke as carbon feedstock and using just the minimum required amount of acacia gum, instead of hazardous chemical-based foaming agents for carbon foaming, thus offering value addition to petroleum coke utilization and addressing the environmental concern, respectively.

[0018] In one aspect, the present invention provides a carbon foam feedstock composition, comprising: a) low value carbon feedstock; and b) naturally occurring foaming agent; wherein the low value carbon feedstock is petroleum coke comprising carbon particles having range of less than 25 pm, 25-75 pm, 75-150 pm and / or greater than 150 pm.

[0019] In another aspect, the present invention provides a process of preparation of the carbon foam feedstock composition, comprising: a) grinding low value carbon feedstock in a ball mill followed by sieving to obtain the low value carbon feedstock comprising carbon particles having range of less than 25 pm, 25- 75 pm, 75-150 pm and / or greater than 150 pm; b) treating said particles of the low value carbon feedstock of step a) with aqueous acid solution under reflux at a temperature in the range of 50-70 °C for time period in the range of 6-8 h followed by filtering, washing and drying to obtain petroleum coke-based low value carbon feedstock; c) mixing a naturally occurring foaming agent solution with said low value carbon feedstock of step b) under stirring to obtain a suspension; d) heating said suspension of step c) at temperature in the range of 50-60 °C for a time period in the range of 5-7 minutes to obtain a viscous solution of carbon foam feedstock; and e) preparing a monolith using said viscous solution of carbon foam feedstock of step d) to obtain the carbon foam.

[0020] In an embodiment, the grinding of low value carbon feedstock is done using a ball-mill reactor using one 15-25 mm of stainless-steel balls, and second 2.5-7.5 mm of stainless-steel balls at a speed of 400-500 rpm for two grinding time periods, where the one of the time periods is in the range of 30-90 minutes, and the second time period is in the range of 2.5-75 minutes. In an embodiment, the aqueous acid solution is prepared by mixing an acid with a water or distilled water.

[0021] In an embodiment, the concentration of said aqueous acid solution is in the range of 2.5 to 12.5 M.

[0022] In an embodiment, the concentration of said aqueous acid solution is in the range of 2.5 to 10 M.

[0023] In an embodiment, the concentration of said aqueous acid solution is in the range of 5 to 12.5 M.

[0024] In an embodiment, the concentration of said aqueous acid solution is in the range of 5 to 10 M.

[0025] In an embodiment, the acid is selected from but not limited to nitric acid and oxidant.

[0026] In an embodiment, the oxidant is H2O2.

[0027] In an embodiment, the filtration of step b) is done using a vacuum and polymer membrane having a 5-15 pm pore-size.

[0028] In an embodiment, the washing is done using a water, distilled water or deionized water.

[0029] In an embodiment, the drying is done at temperature in the range of 25-40 °C for time period in the range of 8-12 h followed by heating at 70-90 °C for 4-6 h to obtain the low value carbon feedstock.

[0030] In an embodiment, the naturally occurring foaming agent solution is prepared by mixing a naturally occurring foaming agent in water or distilled water.

[0031] In an embodiment, the monolith of step e) is prepared by pouring the viscous solution of carbon foam feedstock of step d) in a quartz template followed by placing in a thermal reactor and heating at a temperature gradually increasing from 30°C to 600 °C with a heating rate of 15 °C / min, followed by increasing the temperature from 600 °C to 925 °C with a heating rate of 5 °C / min to obtain a heated mixture; and thermal soaking the heated mixture at temperature in the range of 900-950 °C for 30-90 minutes to obtain the monolith of carbon foam.

[0032] In an embodiment, the quartz template is selected from but not limited to crucible, plate and tray. In an embodiment, the thermal reactor comprises but not limited to: a) a CVD apparatus equipped with a heating filament covering the top and bottom halves of the reactor tube, b) a PID temperature controller, c) a regulated current supply, and d) a rotameter for controlling argon gas flow.

[0033] In an embodiment, the step e) is done under inert conditions using a gas selected form argon, nitrogen and helium at the flow rate of 100-200 litre per hour (LPH).

[0034] In an embodiment, the petroleum coke comprises combination of carbon particles having range of less than 25 pm, 25-75 pm, 75-150 pm and greater than 150 pm.

[0035] In an embodiment, the petroleum coke comprises combination of carbon particles having range of 5-25 pm, 25.1-75 pm, 75.1-150 pm and / or 150-300 pm.

[0036] In an embodiment, the petroleum coke comprises combination of carbon particles having range of 10-25 pm, 25.1-75 pm, 75.1-150 pm and / or 150-250 pm.

[0037] In an embodiment, the petroleum coke comprises combination of carbon particles having range of 15-25 pm, 25.1-75 pm, 75.1-150 pm and / or 150-200 pm.

[0038] In an embodiment, the petroleum coke comprises combination of carbon particles having range of 20-25 pm, 25.1-75 pm, 75.1-150 pm and / or 150-200 pm.

[0039] In an embodiment, the naturally occurring agent is selected from but not limited to acacia gum, tragacanth (Katira) gum, karaya gum, ghatti gum, guar (goma) gum and xanthan gum.

[0040] In an embodiment, the acacia gum is selected from but not limited to Arabic gum, Sudani gum, Senegal gum, and Kordofan gum.

[0041] In an embodiment, the weight ratio of low value carbon feedstock: naturally occurring foaming agent is in the range of 2: 1 to 1: 2.

[0042] In an embodiment, the weight ratio of low value carbon feedstock: naturally occurring foaming agent is in the range of 2: 1 to 1: 1.

[0043] In an embodiment, the weight ratio of low value carbon feedstock: naturally occurring foaming agent is 2: 1. In an embodiment, the weight % of the naturally occurring foaming agent is in the range of 30- 70% of the total composition.

[0044] In an embodiment, the weight % of the naturally occurring foaming agent is in the range of 33- 67% of the total composition.

[0045] In an embodiment, the weight % of the naturally occurring foaming agent is in the range of 33- 50% of the total composition.

[0046] In an embodiment, the weight % of the naturally occurring foaming agent is in the range of 50- 67% of the total composition.

[0047] In an embodiment, the weight % of the naturally occurring foaming agent is in the range of 35- 67% of the total composition.

[0048] In an embodiment, the weight % of the naturally occurring foaming agent is in the range of 40- 67% of the total composition.

[0049] In an embodiment, the weight % of the naturally occurring foaming agent is in the range of 45- 67% of the total composition.

[0050] In an embodiment, the weight % of the naturally occurring foaming agent is in the range of 55- 67% of the total composition.

[0051] In an embodiment, the weight % of the naturally occurring foaming agent is in the range of 60- 67% of the total composition.

[0052] In an embodiment, the weight % of the naturally occurring foaming agent is in the range of 33- 60% of the total composition.

[0053] In an embodiment, the weight % of the naturally occurring foaming agent is in the range of 33- 55% of the total composition.

[0054] In an embodiment, the weight % of the naturally occurring foaming agent is in the range of 33- 45% of the total composition.

[0055] In an embodiment, the weight % of the naturally occurring foaming agent is in the range of 33- 40% of the total composition. In an embodiment, the weight % of the naturally occurring foaming agent is 33% of the total composition.

[0056] In an embodiment, the carbon foam is monolithic in nature.

[0057] In an embodiment, the carbon foam is porous in nature.

[0058] In an embodiment, the carbon foam comprises pore size(s) is / are in the range of 200 to 300 nm, 1 to 3 pm, and / or 6-20 pm.

[0059] In an embodiment, the carbon foam comprises bimodal pore distribution. Here, the bimodal pore (size) distribution means having two sets of (different) pore size ranges.

[0060] In an embodiment, the total porosity of the carbon foam is in the range of 5-60% based on the total volume / mass.

[0061] In an embodiment, the elemental composition of the low value carbon feedstock, comprises: i. carbon is present in the range of 69-87 wt. %; ii. nitrogen is present in the range of 6-9 wt. %; iii. oxygen is present in the range of 3-22 wt. %; and / or iv. sulfur is present in the range of 1-5 wt. %.

[0062] In an embodiment, the elemental composition of the low value carbon feedstock, comprises: i. carbon is present in the range of 69.14-86.74 wt. %; ii. nitrogen is present in the range of 6.11-8.39 wt. %; iii. oxygen is present in the range of 2.55-21.32 wt. %; and / or iv. sulfur is present in the range of 1.15-4.6 wt. %.

[0063] In an embodiment, the low value carbon feedstock comprises graphitic carbons with structural disorder or defects.

[0064] DETAILED DESCRIPTION OF THE DRAWINGS The invention has other advantages and features which will be more readily apparent from the following detailed description of the invention and the appended claims, when taken in conjunction with the accompanying drawings, in which:

[0065] Figure 1 depicts the FES EM images of petroleum coke particles of different particle sizes (PS),

[0066] (a) PS < 25 pm, (b) PS 25-75 pm, (c) PS 75-150 pm and (d) PS > 150 pm, complying to the sieving process. [Magnifications: (a) 1600 x, (b) 400 x, (c) 200 x, (d) 400 x / 400 x / 200 x].

[0067] Figure 2 depicts the FESEM images of carbon foams produced from petroleum coke (5 M HNO3 treated) using acacia gum as foaming agent with varying content, (a) 33%, (b) 50%, (c) 67% and (d) 0% (i.e., without foaming agent). [Magnifications: (a) 2500 x, (b) 2500 x, (c) 2000 x, (d) 4000 x].

[0068] Figure 3 depicts the FESEM images of carbon foams produced from petroleum coke (5 M HNO3 treated) of different particle sizes (PS), (a) PS < 25 pm, (b) PS 25-75 pm, (c) PS 75-150 pm and (d) PS > 150 pm, keeping the foaming agent (acacia gum) content at 33% unvaried. [Magnifications: (a) 30000 x, (b) 8000 x, (c) 2000 x, (d) 4000 x].

[0069] Figure 4 depicts the FESEM images of carbon foam produced from 25-75 pm, 10 M HNO3 treated petroleum coke and 33% foaming agent (acacia gum). [Magnifications: 500 x / 1000 x].

[0070] Figure 5 depicts the Raman spectra of (a) ball-milled petroleum coke before acid treatment,

[0071] (b) ball-milled petroleum coke after acid treatment with 5 M HNO3, (c) ball-milled petroleum coke after acid treatment with 10 M HNO3.

[0072] Figure 6 depicts the Raman spectra of carbon foams produced from petroleum coke (5 M HNO3 treated) using acacia gum as foaming agent with varying content, (a) 33%, (b) 50%, (c) 67% and (d) 0% (i.e., without foaming agent).

[0073] Figure 7 depicts the Raman spectra of carbon foams produced from petroleum coke (5 M HNO3 treated) of different particle sizes (PS), (a) PS < 25 pm, (b) PS 25-75 pm, (c) PS 75-150 pm, and (d) PS > 150 pm, keeping the foaming agent (acacia gum) content at 33% unvaried.

[0074] Figure 8 depicts the Raman spectrum of carbon foam produced from 25-75 pm, 10 M HNO3 treated petroleum coke and 33% foaming agent (acacia gum). Figure 9 depicts the photographs of carbon foam monoliths formed in different quartz templates, (a) crucible, = 3.5 cm, (b) plates, L x W x T = 7.3 cm x 5 cm x 0.5 mm, and (c) tray, L x W x T = 4.5 cm x 2.5 cm x 4 mm.

[0075] SOURCE OF BIOLOGICAL MATERIAL: No biological material is used in the present invention.

[0076] DETAILED DESCRIPTION OF THE INVENTION:

[0077] While the invention has been disclosed with reference to certain embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the scope of the invention. In addition, many modifications may be made to adapt to a particular situation or material to the teachings of the invention without departing from its scope.

[0078] Throughout the specification and claims, the following terms take the meanings explicitly associated herein unless the context clearly dictates otherwise. The meaning of "a", "an", and "the" include plural references. The meaning of "in" includes "in" and "on." Referring to the drawings, like numbers indicate like parts throughout the views. Additionally, a reference to the singular includes a reference to the plural unless otherwise stated or inconsistent with the disclosure herein.

[0079] The tables, figures and protocols have been represented where appropriate by conventional representations in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present disclosure so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having benefit of the description herein.

[0080] The term “monolithic” or “monolith” used herein means a solid structure of carbon foam containing pores.

[0081] The term “low-value” used in the specification (e.g. low value carbon feedstock) means a material having no significant usefulness or obtained from waste material or is a waste material.

[0082] The carbon foam is a form of porous carbon with monolithic structures and hierarchical pores. Accordingly, embodiments of the present invention relate to a porous monolithic carbon foam. Specifically, the present invention relates to a porous monolithic carbon foam comprising an effective amount of combination of low value carbon and natural foaming agent to obtain highly porous and tunable carbon foam. The present invention also relates to a method of producing the porous monolithic carbon foam.

[0083] The terms “porous monolithic carbon foam”, “carbon foam”, “carbon foam feedstock composition”, and “carbon foam feedstock formulation” used throughout the specification are same and can be used interchangeably.

[0084] In an embodiment of the present invention, the low-value carbon is petroleum coke, which is powdered to be used as a feedstock.

[0085] In one embodiment, the present invention provides a method of producing porous monolithic carbon foam by utilizing low-value petroleum coke as carbon feedstock and using just the minimum required amount of acacia gum, instead of hazardous chemical-based foaming agents for carbon foaming, thus offering value addition to petroleum coke utilization and addressing the environmental concern, respectively.

[0086] In an embodiment of the present invention, the individual fractions of low-value carbon feedstock powder comprise particle size in the range of < 25 pm, 25-75 pm, 75-150 pm and > 150 pm.

[0087] In one embodiment, the present invention provides a method of producing low-value carbon feedstock powder comprising the steps of:

[0088] (i) providing petroleum coke granules of size 2-3 mm;

[0089] (ii) ball-milling the petroleum coke granules using stainless steel balls for 5 min to 1 h;

[0090] (iii) sieving the ball-milled petroleum coke powder to obtain the individual fractions of low- value carbon feedstock powder comprising particle size in the range of < 25 pm, 25-75 pm, 75-150 pm and > 150 pm.

[0091] In an embodiment of the present invention, the ball milling is effected at 100-500 rpm. For example, 100 rpm, 150 rpm, 200 rpm, 250 rpm, 300 rpm, 350 rpm, 400 rpm, 450 rpm, or 500 rpm. Preferably 450 rpm. In an embodiment of the present invention, the low-value carbon feedstock powder may be analyzed by field-emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDX) and Raman spectroscopy to study their morphological, compositional and structural properties.

[0092] In one embodiment, the present invention provides a porous monolithic carbon foam formulation / composition, comprising (i) carbon precursor petroleum coke feedstock powder and (ii) foaming agent selected from the group consisting of acacia gum, tragacanth (Katira) gum, karaya gum, ghatti gum, guar (goma) gum and xanthan gum.

[0093] In an embodiment of the present invention, the foaming agent content present in the carbon foam formulation is 33%, 50% and 67%. Preferably 33%.

[0094] In an embodiment of the present invention, the carbon-to-foaming agent ratio of 2: 1, 1: 1 and 1:2, respectively. Preferably, the carbon-to-foaming agent ratio is 2: 1.

[0095] In an embodiment of the present invention, the individual fractions of low-value carbon feedstock powder obtained by said process having particle sizes in the range of 2 to 25 pm, 25 to 75 pm, 75 to 150 pm, and / or more than 150 pm.

[0096] In another embodiment, the present invention provides a method of preparing porous monolithic carbon foam comprising the steps of:

[0097] (i) providing acacia gum powder, followed by dissolving the same in water to obtain a viscous solution;

[0098] (ii) adding petroleum coke feedstock powder to the viscous solution from step (i) and stirring, wherein the amount of carbon foam feedstock formulation totaling 1.5 to 150 cc; and

[0099] (iii) heating the carbon foam feedstock formulation obtained from step (ii) with continuous stirring to obtain the highly viscous formulation, which may be used in the production of carbon foam monoliths.

[0100] In one embodiment, the present invention provides a porous monolithic carbon foam comprising low-value carbon feedstock and a plant-based binder.

[0101] In yet another embodiment, the present invention provides a method of producing porous monolithic carbon foam comprising the steps of: (i) providing highly viscous suspension containing petroleum coke feedstock powder and acacia gum in water;

[0102] (ii) pouring the suspension in a quartz template of suitable design, followed by placing the same in a horizontal tubular quartz thermal reactor of a Chemical Vapor Deposition (CVD) apparatus equipped with a heating filament;

[0103] (iii) heating the reactor containing the suspension under inert atmosphere.

[0104] In an embodiment of the present invention, the suspension containing the wet product is first exposed to a heat treatment step effective to remove the water, preferably in a manner that minimizes or prevents collapse of the pore structure, followed by heating and maintaining the dry product at the binder decomposition temperature.

[0105] In some embodiments, the reactor is heated first from room temperature to 600 °C with a heating rate of 15 °C / min, then continued from 600 °C to 925 °C with a heating rate of 5 °C / min. Further, the suspension is allowed to undergo thermal soaking at 925 °C for 1 h.

[0106] In an embodiment of the present invention, the inert atmosphere such as nitrogen, argon, another inert gas or a combination of inert gases can be used to prevent exposure to atmospheric oxygen. Preferably, the inert atmosphere is argon atmosphere at the flow rate of 150 LPH.

[0107] In an embodiment of the present invention, the carbon foam monoliths are produced by utilizing low-value petroleum coke as carbon feedstock and using just the minimum required amount of acacia gum instead of hazardous chemical-based foaming agents for carbon foaming, thus offering value addition to petroleum coke utilization and addressing the environmental concern, respectively.

[0108] In an embodiment of the present invention, the porous monolithic carbon foam produced using different carbon foam formulations contained pores of sizes ranging from nano to micro meter. In some embodiments, the porous monolithic carbon foams produced using different carbon foam formulations have different pore distributions in the range of 200 - 300 nm, 1-3 pm, and 6-20 pm. The porous monolithic carbon foam may have a bimodal pore distribution.

[0109] The structural changes, especially the porosity of the porous monolithic carbon foam, can be monitored by varying the carbon-to-foaming agent composition ratio and the particle size of the carbon feedstock. The porosity is enhanced systematically as the carbon-to-foaming agent ratio varies from high to low. Alternatively, the porosity can also be enhanced by increasing the particle size of the carbon feedstock. Therefore, the carbon-to-foaming agent composition ratio of 2: 1 is employed for producing carbon foam monoliths, and monitoring its porosity by varying the carbon feedstock particle size: < 25 pm for low-density 200-300 nm pores, 25-75 pm for moderate-density 1-3 pm pores, and 75-150 pm for high density 6-20 pm pores in the carbon foams.

[0110] In an embodiment of the present invention, the carbon feedstock having particle size < 25 pm generated very low density, 200-300 nm pores; the carbon feedstock having particle size in the range of 25-75 pm generated 1-3 pm pores in a moderate density, and the carbon feedstock having particle size in the range of 75-150 pm generated high density, 6-20 pm pores; while the carbon feedstock having particle size > 150 pm showed inconsistency in the formation of pores with an uneven pore distribution with an average pore size of around 10 pm.

[0111] In an embodiment of the present invention, the porous monolithic carbon foam has a total amount of porosity of at least 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55% or higher based on the total volume. In many cases, the total porosity is within the range of from 5 to 10%; from 10 to 15%; from 15 to 20%; from 20 to 25%; from 25 to 30%; from 30 to 35%; from 35 to 40%; from 40 to 40%; from 40 to 45%; from 45 to 50%; from 50 to 55% based on the total volume. In some embodiments, the total porosity can be 30 to 45% or from 35 to 50% based on the total volume. Higher or lower levels of total porosity also can be obtained.

[0112] In an advantageous embodiment, the present invention utilizes low-value petroleum coke, addressing the environmental concern, to produce monolithic carbon foams using acacia gum for foaming the carbon. Thus, utilizing a low-value carbon such as petroleum coke that addresses the environmental concern and offers value addition is advantageous over using naturally valuable material, such as acacia gum, to produce carbon foams. It is righteous only when such a valuable natural material (acacia gum) is used in the minimum required amount for carbon foaming, which is environmentally advantageous over any chemical-based synthetic foaming agents.

[0113] In yet another embodiment, the present invention provides advanced fuel cell electrodes and their assembly components, metal-ion battery electrodes, supercapacitors, EMI shielding, fabricated using the porous monolithic carbon foam as disclosed herein. In yet another embodiment of the present invention, carbon foam monoliths are mainly intended for their use in the fabrication of advanced fuel cell electrodes and assembly components to improve the fuel cell’s overall performance. Other possible applications include metal-ion battery electrodes, supercapacitors, EMI shielding, and the like.

[0114] Simple porous carbon (micro- and meso-) is a refined carbon product, preferably with tuned porosity. In contrast, low-value petroleum coke (disclosed herein) is a carbon produced as a byproduct in a petroleum refining process (thermal cracking of heavy oil residues). Using low- value carbon sources such as petroleum coke or any waste carbon to produce carbon foam is very cost-effective, offers value-addition to refineries and prevents the environment from their disposal.

[0115] EXAMPLES

[0116] The following examples, which include preferred embodiments, will serve to illustrate the practice of this invention, it being understood that the particulars shown are by way of example and for purpose of illustrative discussion of preferred embodiments of the invention.

[0117] MATERIALS;

[0118] The materials used in the present invention include: 1) petroleum coke supplied by Cleantech International Foundation, 128, South Park Apartments, Kalkaji, New Delhi 110019, INDIA, industrial grade, granular, ground to fine powder of different micron-sized particles; 2) nitric acid LOB A Chemie, purchased from Vijay Chemicals, Pune 411009, INDIA, AR grade, 69%, diluted to 5 M and 10 M concentrations; 3) polymer filter membrane Merck Millipore, purchased from Raut Scientific, Pune 411003, INDIA, 10 micrometer pore- size, 47 mm diameter; 4) acacia gum and other naturally occurring foaming agent is purchased from a local market shop located in Baner, Pune 411045, INDIA, domestic grade, ground to powder, readily available water; 5) quartz templates purchased from Star Scientific, Pune 411027, INDIA, crucible, plate and tray; and 6) high-purity argon gas (high-purity nitrogen gas can be used in place of argon gas).

[0119] EXAMPLE 1: PREPARATION OF CARBON FEEDSTOCKS

[0120] Petroleum coke granules of size 2-3 mm were ball-milled in a Retsch PM- 100 planetary ball mill grinder using one 20 mm and two 5 mm stainless steel balls at 450 rpm for two different grinding times, 1 h for producing carbon foams with varying content of foaming agent and 5 min for producing carbon foams from petroleum coke having different particle sizes. The 5- min ball-milled petroleum coke powder was sieved using different micro-sieves to get four individual fractions containing < 25 pm, 25-75 pm, 75-150 pm and > 150 pm sized particles. All the powdered and sieved petroleum coke were acid-treated by refluxing them in 5 M HNO3 aqueous solutions at 60 °C for 7 h, vacuum-filtered using 10 pm pore-size polymer membrane, washed with distilled water and dried at room temperature overnight, followed by heating at 80 °C for 5h to obtain the petroleum coke -based carbon feedstocks. One of the petroleum coke fractions, 25-75 pm, was also refluxed in 10 M HNO3 to study the oxidative effect of acid strength and, ultimately, its effect on the porosity of carbon foam.

[0121] EXAMPLE 2: PREPARATION OF CARBON FOAM FORMULATIONS

[0122] The carbon foam formulations comprising carbon precursor petroleum coke and foaming agent acacia gum were prepared with variations of the (a) foaming agent content as 33%, 50% and 67% (carbon-to-foaming agent ratio of 2: 1, 1: 1 and 1:2, respectively) in the feedstock compositions, and (b) carbon feedstock particle size in the range of < 25 pm, 25-75 pm (both, 5 M HNOs-treated and 10 M HNCh-treated), 75-150 pm and > 150 pm in the feedstock compositions containing 33% foaming agent (carbon-to-foaming agent ratio of 2: 1). As a standard process, the specified amount of acacia gum was dissolved in water followed by the addition of the specified amount of petroleum coke powder, each carbon foam formulation totalling 1.5 cc, with standard regular manual mixing using a glass rod. The formulation was heated slightly in a water bath with continuous manual mixing using a glass rod to make it highly viscous. The viscous formulation was then transferred into / onto a quartz template such as a crucible, plate or tray.

[0123] EXAMPLE 3: PROCESS OF PRODUCING CARBON FOAMS

[0124] Carbon foam monoliths (Figure 9) were prepared from the carbon foam formulations mentioned above. The quartz template (crucible / plate / tray) containing the premix formulation was placed in a horizontal tubular quartz thermal reactor of a Chemical Vapour Deposition (CVD) apparatus equipped with a heating filament covering the top and bottom halves of the reactor tube, a PID [(proportional-integral-derivative (main control actions to regulate and maintain a set temperature)] temperature controller, regulated current supply, and a rotameter for controlling argon gas flow. The reactor, with the formulation placed in it, was heated first from room temperature to 600 °C with a heating rate of 15 °C / min, then continued from 600 °C to 925 °C with a heating rate of 5 °C / min. Later, the formulation was allowed to undergo thermal soaking at 925 °C for 1 h. All the thermal processing was carried out in an inert argon atmosphere at the flow rate of 150 LPH.

[0125] EXAMPLE 4: CHARACTERIZATION OF THE CARBON FEEDSTOCK OF EXAMPLE 1 AND CARBON FOAM OF EXAMPLE 3

[0126] All the carbon samples, including petroleum coke powders of different particle sizes and carbon foams produced at all variations, were characterized by field-emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDX) and Raman spectroscopy to study their morphological, compositional and structural properties. The FESEM imaging and EDX elemental quantification were done on FEI Nova NanoSEM 450 at the accelerating voltage of 20 kV and different magnifications. The Raman measurements were carried out on a Horiba JY LabRAM HR 800 Raman spectrometer with 17 mW, 632.8 nm He- Ne laser excitation. For FESEM and EDX studies, the samples were dispersed in toluene and drop-casted on silicon wafer pieces. For Raman measurements, the powder-form samples were spread on glass plates.

[0127] RESULTS AND DISCUSSION

[0128] A) FIELD-EMISSION SCANNING ELECTRON MICROSCOPY (FESEM):

[0129] From the FESEM (images not shown here) study of the particle size dependency on grinding time, it was observed that increasing the grinding time from 5 min to 1 h reduced the particle size (max) from 66 pm to 27 pm, thus narrowing down the particle size distribution to 2 - 27 pm. The particle size (min) in both cases was 2 pm.

[0130] FESEM images of the carbon feedstocks of different particle sizes and carbon foams produced with different feedstock compositions and particle sizes of carbon feedstock are given below. Figure 1 shows the FESEM images of petroleum coke particles of varying particle sizes after micro-sieving.

[0131] The porosity of the carbon foams in terms of the pore size and number affected due to these variations can be discussed. In the first variation study, the acacia gum foaming agent content varied as 33%, 50% and 67% (carbon-to-foaming agent ratio of 2: 1, 1: 1 and 1:2, respectively) in the feedstock compositions. As seen in the FESEM images of the carbon foams (Figure 2), the porosity increased significantly with the increase in the content of acacia gum foaming agent from 33% to 67%. Just carbon feedstock with no acacia gum foaming agent failed to produce carbon foam; it only turned into porous carbon.

[0132] From the study of varying foaming agent’s content in the feedstock, the feedstock containing 33% acacia gum foaming agent (carbon-to-foaming agent ratio of 2: 1) was opted for further variation study, thus allowing the maximum utilization of low-value petroleum coke as a carbon feedstock and minimal use of the foaming agent.

[0133] In the second variation study, the carbon feedstock, i.e., petroleum coke, particle size varied in the range of < 25 pm, 25-75 pm, 75-150 pm and > 150 pm, all with 33% acacia gum foaming agent (carbon-to-foaming agent ratio of 2: 1), to produce carbon foams with different porosity. Figure 3 shows an apparent change in the formation of pores in the carbon foams with the change in the particle size. The carbon feedstock having particle size < 25 pm generated very low density, 200-300 nm pores. The carbon feedstock having particle size in the range of 25- 75 pm generated 1-3 pm pores in a moderate density, and that in the range of 75-150 pm generated high density, 6-20 pm pores. The carbon foam produced from the carbon feedstock having particle size > 150 pm showed inconsistency in the formation of pores with an uneven pore distribution. The average pore size, in this case, was around 10 pm.

[0134] Figure 4 shows the FESEM images of the carbon foam produced from 10 M HNCh-treated, 25- 75 pm sized petroleum coke. As evident, the pore density in this carbon foam is more than that in the carbon foam produced from 5 M HNO3- treated 25-75 pm sized petroleum coke. Here, referring to Figure 3(b) for 5 M HNO3 -treated carbon feedstock and Figure 4 for 10 M HNO3- treated carbon feedstock, the results / inference is based on the visual indication. Further, the pores are uniformly formed and widespread throughout the matrix. The pore size distribution in this carbon foam is broader than that in the carbon foam produced from 5 M HNO3- treated 25-75 pm sized petroleum coke, up to 28 pm in the former as compared to 3 pm in the latter.

[0135] B) ENERGY DISPERSIVE X-RAY SPECTROSCOPY (EDX)

[0136] The EDX micro-analysis revealed the C-N-O-S elemental quantifications in the ball-milled, acid-treated petroleum coke samples, as detailed in Table 1. The EDX data suggest largely increased O-content (3.7 times in 5 M HNO3 and 8.4 times in 10 M HNO3), slightly increased N-content (1.2 times in 5 M HNO3 and 1.4 times in 10 M HNO3), and reduced S-content (nearly half in 5 M HNO3 and 174thin 10 M HNO3) due to the acid-treatment.

[0137] Table. 1. EDX data for ball-milled, acid-treated petroleum coke

[0138] C) RAMAN SPECTROSCOPY All the raman spectra of the carbon feedstock and carbon foam samples show two prominent peaks, the G-band resulting from the in-plane oscillations of graphitic carbon and the D-band for the structural disorder or defects in the carbons. The structural disorder in graphitic carbon is usually estimated by ID / IG, the ratio of intensities of D-band to G-band. The higher the ID / IG value, the more the structural disorder or defects in graphitic carbons. Figure 5 shows the G-band around 1585 cm-1(a) for ball-milled petroleum coke before the acid treatment, 1583 cm-1(b) for ball-milled petroleum coke after the acid treatment with 5 M HNO3, and 1582 cm-1(c) for ball-milled petroleum coke after the acid treatment with 10 M HNO3. The G-band of the carbon sample (a) is blue-shifted (shift to higher wavenumber) from the standard 1580 cm-1G-band peak position of graphitic carbon to 1585 cm-1, suggesting a compressive local strain in the material. After the acid treatment, the G-band of the ball-milled petroleum coke is seen red-shifted (shift to lower wavenumber) from 1585 cm-1(a) to 1583 cm-1(b) for 5 M HNOs-trcatcd petroleum coke, and 1582 cm-1(c) for 10 M HNOs-trcatcd petroleum coke due to the improved purity of the petroleum coke carbon. The D-band is seen around 1350 cm-1for sample (a), 1353 cm-1for sample (b), and 1352 cm-1for sample (c), conforming to the reported peak position in the range 1300 - 1400 cm-1. The ID / IG value for all these petroleum coke samples lies in the range of 0.92 - 0.99 (ID / IG < 1), indicating the extent of structural disorder / defects already present in the petroleum coke, the starting carbon material for the carbon foams.

[0139] Figure 6 shows the G and D bands of carbon foams produced from 5 M HNOs-treated petroleum coke with varying content of the foaming agent. For all these carbon foam samples except sample (d), the G-band is seen in the range of 1593 - 1590 cm-1. This further blue shift of the G-band from 1583 cm-1(Figure 5b) may be attributed to the additional local strain induced by the carbon foam processing. The D-band is seen around 1335 cm-1for sample (a), 1337 cm-1for sample (b), and 1333 cm-1for sample (c). The G-band and D-band for sample (d), a form of porous carbon produced without using the foaming agent, are seen at 1582 cm-1and 1342 cm-1, respectively. The ID / IG value for these carbon foam samples and the porous carbon sample (d) lies in the range 1.2 - 1.3 (ID / IG > 1), which is higher than that of its starting carbon material - the petroleum coke having ID / IG < 1. This increased ID / IG suggests the increased structural disorder / defects caused by carbon foaming in the carbon foam samples and the increased structural disorder / defects due to porosity in the porous carbon sample (d).

[0140] Figure 7 shows the G and D bands of carbon foams produced from 5 M HNOs-trcatcd petroleum coke of different particle sizes ranging from < 25 pm to > 150 pm, and keeping the content of the foaming agent at 33% unvaried. Like the carbon foam samples shown in Figure 6, the carbon foam samples shown in Figure 7, except sample (a), exhibit the G-band in the range of 1587 - 1590 cm-1. The D-band of the carbon foams in Figure 7 is seen around 1335 cm-1for sample (b), 1332 cm-1for sample (c), and 1333 cm-1for sample (d). The G-band and D-band of the carbon foam sample (a) in Figure 7 are seen at 1582 cm-1and 1340 cm-1, respectively. The ID / IG value for all these carbon foam samples in Figure 7 lies in the range of 1.2 - 1.3 (ID / IG > 1), the same as for the carbon foam samples shown in Figure 6.

[0141] The Raman spectrum of the carbon foam produced from 25-75 pm, 10 M HNOs-trcatcd petroleum coke using 33% foaming agent shows the G-band at 1590 cm-1and the D-band at 1332 cm-1(Figure 8). The ID / IG value for this carbon foam sample is around 1.3.

[0142] D) CARBON FOAM MONOLITHS: Figure 9 depicts the photographs of some carbon foam monoliths produced in different quartz templates, (a) crucible, = 3.5 cm, (b) plates, L x W x T = 7.3 cm x 5 cm x 0.5 mm, and (c) tray, L x W x T = 4.5 cm x 2.5 cm x 4 mm.

[0143] ADVANTAGES OF THE INVENTION • The present disclosure provides an environment-friendly and inexpensive feedstock formulation for producing monolithic carbon foams.

[0144] • The present disclosure provides a value-addition to petroleum coke, which is abundantly available in the oil and gas industries.

[0145] • The present disclosure provides a natural, plant-based carbon foaming agent, replacing hazardous chemical-based foaming agents

[0146] • The present disclosure provides a simple method to produce monolithic carbon foams of different porosity.

[0147] The present disclosure provides a scope for producing monolithic carbon foams of varying porosity that might be useful in fabricating high-performance fuel cell and battery electrodes, EMI shielding devices, and the like.

Claims

WE CLAIM:

1. A carbon foam feedstock composition, comprising: a) low value carbon feedstock; and b) naturally occurring foaming agent; wherein the low value carbon feedstock is petroleum coke comprising carbon particles having range of less than 25 pm, 25-75 pm, 75-150 pm and / or greater than 150 pm.

2. The carbon foam feedstock composition as claimed in claim 1, wherein the petroleum coke comprises combination of carbon particles having range of less than 25 pm, 25-75 pm, 75-150 pm and greater than 150 pm.

3. The carbon foam feedstock composition as claimed in claim 1, wherein the naturally occurring agent is selected from acacia gum, tragacanth (Katira) gum, karaya gum, ghatti gum, guar (goma) gum and xanthan gum.

4. The carbon foam feedstock composition as claimed in claim 1, wherein a weight ratio of low value carbon feedstock: naturally occurring foaming agent is in the range of 2: 1 to 1: 2; and wherein a weight % of the naturally occurring foaming agent is in the range of 33-67% of the total composition.

5. The carbon foam feedstock composition as claimed in claim 1, wherein the carbon foam is monolithic in nature; and wherein the carbon foam comprises pore size(s) is / are in the range of 200 to 300 nm, 1 to 3 pm, and / or 6-20 pm.

6. The carbon foam feedstock composition as claimed in claim 1, wherein elemental composition of the low value carbon feedstock, comprises: i. carbon is present in the range of 69-87 wt. %; ii. nitrogen is present in the range of 6-9 wt. %; iii. oxygen is present in the range of 3-22 wt. %; and / or iv. sulfur is present in the range of 1-5 wt. %.

7. A process of preparation of the carbon foam feedstock composition as claimed in claim 1, comprising:a) grinding low value carbon feedstock in a ball mill followed by sieving to obtain the low value carbon feedstock comprising carbon particles having range of less than 25 pm, 25-75 pm, 75-150 pm and / or greater than 150 pm; b) treating said particles of the low value carbon feedstock of step a) with aqueous acid solution under reflux at a temperature in the range of 50-70 °C for time period in the range of 6-8 h followed by filtering, washing and drying to obtain petroleum cokebased low value carbon feedstock; c) mixing a naturally occurring foaming agent solution with said low value carbon feedstock of step b) under stirring to obtain a suspension; d) heating said suspension of step c) at temperature in the range of 50 - 60 °C for a time period in the range of 5-7 minutes to obtain a viscous solution; and e) preparing a monolith using said viscous solution of step d) to obtain the carbon foam feedstock composition.

8. The process as claimed in claim 7, wherein the grinding of low value carbon feedstock in step a) is done using a ball-mill reactor using one 15-25 mm of stainless- steel balls, and second 2.5-7.5 mm of stainless-steel balls at a speed of 400-500 rpm for two grinding time periods, wherein the one of the time periods is in the range of 30-90 minutes, and the second time period is in the range of 2.5-75 minutes.

9. The process as claimed in claim 7, wherein the aqueous acid solution is prepared by mixing an acid with a water or distilled water, wherein concentration of said aqueous acid solution is in the range of 2.5 to 12.5 M.

10. The process as claimed in claim 7, wherein the monolith of step e) is prepared by pouring the viscous solution of carbon foam feedstock of step d) in a quartz template followed by placing in a thermal reactor and heating at a temperature gradually increasing from 30°C to 600 °C with a heating rate of 15 °C / min, followed by increasing the temperature from 600 °C to 925 °C with a heating rate of 5 °C / min to obtain a heated mixture; and thermal soaking the heated mixture at temperature in the range of 900-950 °C for 30-90 minutes to obtain the monolith of carbon foam feedstock composition.

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