DESC:FIELD
The present disclosure relates to a process for the preparation of graphite plates.
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 indicates otherwise.
Petroleum Pitch: The term “petroleum pitch” refers to a residue obtained from heat treatment and distillation of petroleum fractions. It is a solid at room temperature and consists of a complex mixture of numerous predominantly aromatic and alkyl-substituted aromatic hydrocarbons, thereby exhibiting a broad softening range instead of a defined melting temperature.
Mesophase Pitch: The term “mesophase pitch” refers to a pitch obtained from the heating of an isotropic pitch. Mesophase pitch is made by polymerizing isotropic pitch to a higher molecular weight. The mesophase pitch forms a thermotropic crystal, which allows the pitch to become organized and form linear chains without the use of tension.
Carbonization: The term “carbonization” refers to the removal of all non-carbon material from a substance.
Dwell time: The term “dwell time” refers to the time spent at the same conditions, stage of a process, and the like.
Green plate: The term “green plate” refers to a solid material obtained by compressing the mesophase pitch before the carbonization process.
Softening point: The term ‘softening point’ refers to a temperature at which a substance has flown a certain distance under defined test conditions.
BACKGROUND
The background information herein below relates to the present disclosure but is not necessarily prior art.
Graphite plates are widely used in various industries, having their application in the field of electrode materials such as electrode bars used in metallurgical industries, nuclear reactors, hearths for blast furnaces, radiating components, and the like.
Conventionally, graphite plates are prepared by using graphite powder and a binder (20% to 30%) followed by repeated impregnation and calcination processes to reduce volumetric shrinkages and porosity. However, the cost of graphite powder is high, thereby making the product not economical. Further, graphite plates are prepared by using other carbon rich sources such as mesophase pitch or needle coke. However, these materials require to undergo air-stabilization to make them infusible during carbonization/graphitization processes. Moreover, the thicker graphite plates provided by using alternative carbon sources such as mesophase pitch or needle coke is difficult to produce due to limited diffusion of air into thicker sections. Furthermore, the kinetics of the air-stabilization process is slow and incomplete stabilization causes melting or swelling of the plate during the carbonization/graphitization process leading to loss of product shape. Several approaches were considered to reduce swelling during the carbonization of the pitch. One such approach reported the use of carbon black as an additive in the graphite plate that absorbs the released volatile compounds from the pitch and hence, reduces swelling.
Alternatively, quinone type compounds, iodine vapor, and dicumyl peroxide can be added to mesophase pitch to stabilize and reduce the swelling. These quinone structures cross-link with mesophase pitch to make it infusible. These compounds reduce the swelling in making graphite plates; however, large amounts are required to be added to avoid swelling. Although, the addition of these compounds increases the stabilization processes it also increases the cost of the overall process.
Therefore, there is felt a need to provide a process for the preparation of graphite plates from mesophase pitch that mitigates the aforestated drawbacks or at least provide an alternative solution.
OBJECTS
Some of the objects of the present disclosure, which at least one embodiment herein satisfies, are as follows:
An object of the present disclosure is to ameliorate one or more problems of the background or to at least provide a useful alternative.
Another object of the present disclosure is to provide a process for the preparation of graphite plates.
Still another object of the present disclosure is to provide a process for the preparation of carbon plates.
Yet another object of the present disclosure is to provide a graphite plate without a binder.
Still another object of the present disclosure is to provide a graphite plate by using a chemically modified mesophase pitch.
Another object of the present disclosure is to provide a simple and economically viable process for the preparation of graphite plates.
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 graphite plates. The process comprises distilling petroleum pitch at a first predetermined temperature for a first predetermined time period in an inert atmosphere to obtain a mesophase pitch. The mesophase pitch is treated with nitric acid under stirring at a second predetermined temperature for a second predetermined time period to obtain a mesophase pitch slurry. The mesophase pitch slurry is filtered followed by drying at a third predetermined temperature for a third predetermined time period to obtain a modified mesophase pitch. The modified mesophase pitch is moulded at a fourth predetermined temperature for a fourth predetermined time period at a predetermined pressure to obtain a green plate. The green plate is carbonized in an inert atmosphere at a first predetermined heating rate till a temperature reaches to 1200°C using a dwell time in the range of 3 minutes to 10 minutes to obtain the carbon plates. The carbon plates are graphitized in a graphitization furnace in an inert atmosphere at a second predetermined heating rate till a temperature reaches to 2800°C using a dwell time in the range of 1 hour to 3 hours to obtain the graphite plates.
In an embodiment of the present disclosure the mesophase pitch is milled to obtain a mesophase pitch in the form of granules.
In an embodiment of the present disclosure, the particle size of said granules is in the range of 1 µm to 45 µm.
In an embodiment of the present disclosure, the mesophase pitch is characterized by having
a) a softening point in the range of 150°C to 300°C;
b) toluene insoluble in the range of 30% to 90%; and
c) quinoline insoluble in the range of 15% to 70%.
In an embodiment of the present disclosure, the mesophase pitch obtained is reinforced with a predetermined amount of carbon fibers prior to treating with nitric acid.
In an embodiment of the present disclosure, the predetermined amount of carbon fibers is in the range of 0.1 wt% to 10 wt% with respect to the total weight of mesophase pitch.
In an embodiment of the present disclosure, the first predetermined temperature is in the range of 300°C to 450°C.
In an embodiment of the present disclosure, the first predetermined time period is in the range of 2 hours to 30 hours.
In an embodiment of the present disclosure, the inert atmosphere is selected from nitrogen and argon.
In an embodiment of the present disclosure, the second predetermined time period is in the range of 30 minutes to 120 minutes.
In an embodiment of the present disclosure, the second predetermined temperature is in the range of 20°C to 55°C.
In an embodiment of the present disclosure, the nitric acid has a concentration in the range of 25% to 45%.
In an embodiment of the present disclosure, the predetermined third time period is in the range of 100 minutes to 200 minutes.
In an embodiment of the present disclosure, the third predetermined temperature is in the range of 70°C to 130°C.
In an embodiment of the present disclosure, the moulding is done by using a method selected from hand pressed moulding, compression moulding, and channel flow pattern moulding.
In an embodiment of the present disclosure, the fourth predetermined temperature is in the range of 200°C to 350°C.
In an embodiment of the present disclosure, the fourth predetermine time period is in the range of 20 minutes to 60 minutes.
In an embodiment of the present disclosure, the predetermined pressure is in the range of 0.1 tonne per sq.cm to 1 tonne per sq.cm.
In an embodiment of the present disclosure, the first predetermined heating rate and the second predetermined heating rate are independently in the range of 5°C/min to 15°C/min.
In an embodiment of the present disclosure, the mesophase pitch contains C/N and C/O weight ratios in the range of 20 to 55 and 5 to 15 respectively.
In an embodiment of the present disclosure, a density of the graphite plates is in the range of 1.4 g/cm3 to 1.8 g/cm3.
In an embodiment of the present disclosure, the graphite plates are used as bipolar plates in fuel cells.
BRIEF DESCRIPTION OF THE DRAWING
Figure 1 illustrates a digital image for the conversion of mesophase pitch into a carbon plate (a) with chemical modification of mesophase pitch carried out using 30% nitric acid concentration and (b) with air-stabilization of mesophase pitch;
Figure 2a illustrates a plate formation using chemically modified mesophase pitch using 10% nitric acid;
Figure 2b illustrates a plate formation using chemically modified mesophase pitch using 20% nitric acid;
Figure 2c illustrates a plate formation using chemically modified mesophase pitch using 25% nitric acid;
Figure 2d illustrates a plate formation using chemically modified mesophase pitch using 28% nitric acid;
Figure 2e illustrates a plate formation using chemically modified mesophase pitch using 30% nitric acid;
Figure 2f illustrates a plate formation using chemically modified mesophase pitch using 40% nitric acid;
Figure 2g illustrates a plate formation using chemically modified mesophase pitch using 42% nitric acid;
Figure 2h illustrates a plate formation using chemically modified mesophase pitch using 45% nitric acid;
Figure 2i illustrates a plate formation using chemically modified mesophase pitch using 50% nitric acid;
Figure 2j illustrates a plate formation using chemically modified mesophase pitch using 70% nitric acid;
Figure 3 illustrates a large-sized compact carbon plate formed by the process of the present disclosure;
Figure 4a illustrates a plate formation using chemically modified mesophase pitch using 25% nitric acid at 50°C;
Figure 4b illustrates a plate formation using chemically modified mesophase pitch using 45% nitric acid at 25°C for 45min;
Figure 5 illustrates an FTIR analysis (a) after chemical modification to mesophase pitch (MP) and (b) after compression moulding and carbonization process; and
Figure 6 illustrates reaction pathway to generate functional groups after chemical treatment of the mesophase pitch with nitric acid to form cross-linked green plate.
DETAILED DESCRIPTION
The present disclosure relates to a process for the preparation of graphite plates.
Embodiments, of the present disclosure, will now be described with reference to the accompanying drawings.
Embodiments are provided so as to thoroughly and fully convey the scope of the present disclosure to the person skilled in the art. Numerous details are set forth, relating to specific components, and methods, to provide a complete understanding of embodiments of the present disclosure. It will be apparent to the person skilled in the art that the details provided in the embodiments should not be construed to limit the scope of the present disclosure. In some embodiments, well-known processes, well-known apparatus structures, and well-known techniques are not described in detail.
The terminology used, in the present disclosure, is only for the purpose of explaining a particular embodiment and such terminology shall not be considered to limit the scope of the present disclosure. As used in the present disclosure, the forms "a,” "an," and "the" may be intended to include the plural forms as well, unless the context clearly suggests otherwise. The terms "comprises," "comprising," “including,” and “having,” are open ended transitional phrases and therefore specify the presence of stated features, integers, steps, operations, elements, modules, units and/or components, but do not forbid the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. The particular order of steps disclosed in the method and process of the present disclosure is not to be construed as necessarily requiring their performance as described or illustrated. It is also to be understood that additional or alternative steps may be employed.
As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed elements.
The terms first, second, third, etc., should not be construed to limit the scope of the present disclosure as the aforementioned terms may be only used to distinguish one element, component, region, layer or section from another component, region, layer or section. Terms such as first, second, third etc., when used herein do not imply a specific sequence or order unless clearly suggested by the present disclosure.
Conventionally, graphite plates are prepared by using graphite powder and a binder (20% to 30%) followed by repeated impregnation and calcination processes to reduce volumetric shrinkages and porosity. However, the cost of graphite powder is high, thereby making the product not economical. Further, graphite products are prepared by using other carbon rich sources such as mesophase pitch or needle coke. However, these materials require to undergo air-stabilization to make them infusible during carbonization/graphitization processes. Moreover, the thick graphite plates provided by using alternative carbon sources such as mesophase pitch or needle coke are difficult to produce due to the limited diffusion of air into thicker sections. Furthermore, the kinetics of the air-stabilization process is slow and incomplete stabilization causes melting or swelling of the plate during the carbonization/graphitization process leading to loss of product shape. Several approaches were considered to reduce swelling during carbonization of the pitch. One such approach reported the use of carbon black as an additive in the graphite plate absorbs the released volatile compounds from the pitch and hence, reduces swelling.
The process of the present disclosure provides a simple and cost-efficient process for the preparation of graphite plates.
In accordance with the present disclosure, there is provided a process for the preparation of graphite plates.
The process is described in detail.
In a first step, a predetermined amount of petroleum pitch is distilled at a first predetermined temperature for a first predetermined time period in an inert atmosphere to obtain a mesophase pitch.
In an embodiment, the petroleum pitch is characterized by having
• a softening point in the range of 50°C to 180°C;
• toluene insoluble in the range of 2% to 35%; and
• quinoline insoluble in the range of 0.1% to 10%.
In an exemplary embodiment of the present disclosure, the petroleum pitch has a softening point of 90°C, toluene insoluble content of 5%, and quinoline insoluble content of less than 0.5%.
In an embodiment of the present disclosure, the first predetermined temperature is in the range of 300°C to 450°C. In an exemplary embodiment of the present disclosure, the first predetermined temperature is 420°C.
In an embodiment of the present disclosure, the first predetermined time period is in the range of 2 hours to 30 hours. In an exemplary embodiment of the present disclosure, the first predetermined time period is 5 hours.
In an embodiment of the present disclosure, the inert atmosphere is selected from nitrogen and argon. In an exemplary embodiment of the present disclosure, the inert atmosphere is nitrogen during the preparation of the carbon plates. In another exemplary embodiment, the inert atmosphere is argon during the preparation of the graphite plates.
In an embodiment of the present disclosure, the petroleum pitch is to be distilled for less time at a higher temperature and vice versa to obtain the desired quality of mesophase pitch.
The mesophase pitch is formed by the distillation process, wherein temperature and duration of the distillation are the critical parameters to obtain the desired quality of mesophase pitch. The desired quality of mesophase pitch can be obtained by performing distillation at a higher temperature for less time or by performing distillation at a lower temperature for a longer period. Any deviation in the distillation conditions will directly affect the quality of the mesophase pitch.
The inert gas is continuously purged during the distillation process so as to enable easy removal of low molecular weight components from petroleum pitch during the distillation process. On completion of the distillation, the mesophase pitch is cooled to room temperature in an inert atmosphere to avoid oxidation of the synthesized mesophase pitch. The so obtained mesophase pitch is brittle in nature and milled to obtain a mesophase pitch in the form of granules.
In an embodiment of the present disclosure, the particle size of the granules of mesophase pitch is in the range of 1 µm to 45 µm. In an exemplary embodiment of the present disclosure, the particle size of the granules is less than 25 µm.
In an embodiment, the mesophase pitch is characterized by having
a) a softening point in the range of 150°C to 300°C;
b) toluene insoluble in the range of 30% to 90%; and
c) quinoline insoluble in the range of 15% to 70%.
In an exemplary embodiment of the present disclosure, the mesophase pitch has a softening point of 220°C, toluene insoluble content of 58%, and quinoline insoluble content of 33%.
In a second step, the mesophase pitch is treated with nitric acid under stirring at a second predetermined temperature for a second predetermined time period to obtain a mesophase pitch slurry.
In an embodiment of the present disclosure, the mesophase pitch is reinforced with a predetermined amount of carbon fibers before treating with nitric acid.
In an embodiment of the present disclosure, the predetermined amount of carbon fibers is in the range of 0.1 wt% to 10 wt% with respect to the total weight of mesophase pitch. In an exemplary embodiment, the predetermined amount of carbon fibers is 5 wt% with respect to the total weight of mesophase pitch.
In an embodiment of the present disclosure, the amount of carbon fibers directly influences the density of the graphite plates. The desired density of the graphite plates is not achieved if the amount of carbon fibers exceeds 10 wt% with respect to the total weight of mesophase pitch.
In an embodiment of the present disclosure, the concentration of nitric acid is in the range of 25% to 45%. In an exemplary embodiment of the present disclosure, the concentration of nitric acid is 30%. In another exemplary embodiment of the present disclosure, the concentration of nitric acid is 40%. In still another exemplary embodiment of the present disclosure, the concentration of nitric acid is 28%. In yet another exemplary embodiment of the present disclosure, the concentration of nitric acid is 42%. In another exemplary embodiment of the present disclosure, the concentration of nitric acid is 45%.
In an embodiment of the present disclosure, the second predetermined temperature is in the range of 20°C to 55°C. In an exemplary embodiment of the present disclosure, the second predetermined temperature is 25°C. In another exemplary embodiment of the present disclosure, the second predetermined temperature is 50°C.
In an embodiment of the present disclosure, the second predetermined time period is in the range of 30 minutes to 120 minutes. In an exemplary embodiment of the present disclosure, the second predetermined time period is 60 minutes. In an exemplary embodiment of the present disclosure, the second predetermined time period is 45 minutes.
In an embodiment of the present disclosure, it is desirable to have the acid concentration in the range of 28% to 45% for the formation of compact plates. A concentration lower than 28% fails to generate sufficient amounts of functional groups in mesophase pitch and hence, its binding (or cross-linking) efficiency becomes low due to which it could not form compact plates. Alternatively, if the acid concentration exceeds 45%, it generates an ample number of functional groups in the mesophase pitch and hence, during heat treatment, it results in the decomposition of the aromatic structures present in the mesophase pitch. Therefore, resulting in excessive swelling and breaking of the part. Acid treatment with 28% to 45% acid concentration produces an optimum number of functional groups due to which the binding (or cross-linking) efficiency is maximum in treated mesophase pitch and hence compact plates can be successfully prepared at preferred acid concentrations of 28% to 45%.
In an embodiment of the present disclosure, the mesophase pitch functionalized by using nitric acid concentration at 30% to 40%, which corresponds to C/N and C/O weight ratios of 25 to 50 and 7 to 14 respectively.
The likely reaction pathway to generate functional groups after chemical treatment of the mesophase pitch with nitric acid to form cross-linked green plate is depicted in Figure 6.
In a third step, the mesophase pitch slurry is filtered followed by drying at a third predetermined temperature for a third predetermined time period to obtain a modified mesophase pitch.
In an embodiment of the present disclosure, the third predetermined temperature is in the range of 70°C to 130°C. In an exemplary embodiment of the present disclosure, the third predetermined temperature is 110°C.
In an embodiment of the present disclosure, the third predetermined time period is in the range of 100 minutes to 200 minutes. In an exemplary embodiment of the present disclosure, the third predetermined time period is 120 minutes.
In an embodiment of the present disclosure, the mesophase pitch slurry is separated by filtration followed by washing the residue with excess water, and then subjected to drying to obtain a modified mesophase pitch.
In a fourth step, the modified mesophase pitch is moulded at a fourth predetermined temperature for a fourth predetermined time period at a predetermined pressure to obtain a green plate.
In an embodiment of the present disclosure, the fourth predetermined temperature is in the range of 200°C to 350°C. In an exemplary embodiment of the present disclosure, the fourth predetermined temperature is 330°C.
In an embodiment of the present disclosure, the moulding is done by using a method selected from hand-pressed moulding, compression moulding, and channel flow pattern moulding. In an exemplary embodiment of the present disclosure, the moulding is done using hand-pressed moulding. In another exemplary embodiment of the present disclosure, the moulding is done using compression moulding. In yet another exemplary embodiment of the present disclosure, the moulding is done using channel flow pattern moulding.
In an embodiment of the present disclosure, the channel flow pattern moulding provides green plates with flow channels. The green plates with flow channels after carbonization provide channel carbon plates similar to the bipolar plates used in fuel cells.
In an embodiment of the present disclosure, the fourth predetermined time period is in the range of 20 minutes to 60 minutes. In an exemplary embodiment of the present disclosure, the fourth predetermined time period is 30 minutes.
In an embodiment of the present disclosure, the predetermined pressure is in the range of 0.1 tonne per sq.cm to 1 tonne per sq.cm. In an exemplary embodiment of the present disclosure, the predetermined pressure is 0.5 tonne per sq.cm.
In an embodiment of the present disclosure, the compression mould is used to hot-press the modified mesophase pitch to produce a green plate.
In a fifth step, the green plate is carbonized in an inert atmosphere at a first predetermined heating rate till a temperature reaches to 1200°C using a dwell time in the range of 3 minutes to 10 minutes to obtain the carbon plate.
In an embodiment of the present disclosure, the first predetermined heating rate is in the range of 5°C/min to 15°C/min. In an exemplary embodiment of the present disclosure, the first predetermined heating rate is 10°C/min.
In an embodiment of the present disclosure, the inert atmosphere is selected from nitrogen and argon. In an exemplary embodiment, the inert atmosphere is nitrogen.
In an embodiment of the present disclosure, the density of the carbon plates is in the range of 1.4 g/cm3 to 1.8 g/cm3. In an exemplary embodiment of the present disclosure, the density of the carbon plate is 1.4 g/cm3. In an exemplary embodiment of the present disclosure, the density of the carbon plate is 1.6 g/cm3.
In a final step the carbon plates are graphitized in a graphitization furnace in an inert atmosphere at a second predetermined heating rate till a temperature reaches to 2800°C using a dwell time in the range of 1 hour to 3 hours to obtain the graphite plates.
In an embodiment of the present disclosure, the second predetermined heating rate is in the range of 5°C/min to 15°C/min. In an exemplary embodiment of the present disclosure, the second predetermined heating rate is 10°C/min.
In an embodiment of the present disclosure, the inert atmosphere is selected from nitrogen and argon. In an exemplary embodiment, the inert atmosphere is argon.
In an embodiment of the present disclosure, the density of the graphite plates is in the range of 1.4 g/cm3 to 1.8 g/cm3. In an exemplary embodiment of the present disclosure, the density of the graphite plate is 1.4 g/cm3. In an exemplary embodiment of the present disclosure, the density of the graphite plate is 1.6 g/cm3.The process of the present disclosure provides graphite plates by a simple compression moulding technique. The process of the present disclosure produces a carbon/graphite plate with no swelling or shape change after the carbonization/graphitization process.
In an embodiment of the present disclosure, graphite plates are used as bipolar plates in fuel cells.
The foregoing description of the embodiments has been provided for purposes of illustration and is not intended to limit the scope of the present disclosure. Individual components of a particular embodiment are generally not limited to that particular embodiment, but, are interchangeable. Such variations are not to be regarded as a departure from the present disclosure, and all such modifications are considered to be within the scope of the present disclosure.
The present disclosure is further described in light of the following experiments which are set forth for illustration purposes 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 I: Preparation of the graphite plate in accordance with the present disclosure
Step 1 - Preparation of the mesophase pitch:
1000 gm of petroleum pitch (softening point of 90oC, toluene insoluble content of 5%, and quinoline insoluble content of less than 0.5%) was charged into a three-neck flask connected with a gas inlet for continuous nitrogen purging, and a Liebig condenser with a collection flask, to collect low molecular weight species distilled out during the process. The petroleum pitch was distilled at 420oC and maintained at the reaction temperature (380oC to 420oC) for 5 hours to remove the low molecular weight pitch during the heating process. The nitrogen gas was continuously purged during the heating process. On completion of the reaction, the pitch was cooled to room temperature under nitrogen purging to avoid oxidation of the synthesized mesophase pitch. The so obtained mesophase pitch was brittle, which was removed from the three-neck flask by breaking it into small pieces. The small pieces of mesophase pitch were milled to obtain a mesophase pitch in the form of granules (softening point of 220oC, toluene insoluble content of 58%, and quinoline insoluble content of 33%). The average particle size of the granules was less than 25 µm.
Step 2 – Chemical treatment of mesophase pitch:
The mesophase pitch (in the form of granules) obtained in step 1 was dispersed in nitric acid of various concentrations (10%, 20%, 30%, 40%, 50%, and 70%), under constant stirring for 60 minutes at 25°C to obtain a mesophase pitch slurry. The mesophase pitch slurry was filtered and washed with excess water followed by air drying at 110°C for 2 hours to obtain the modified mesophase pitch.
Step 3 – Preparation of the green plate:
1 gm of the modified mesophase pitch obtained in step 2 was hand-pressed into a small coupon mould with a 15 mm diameter followed by heating at 330oC for 30 min to produce a green plate (15 mm diameter x 5 mm thick). The process was repeated for each of the modified pitches that are chemically treated using various concentrations of nitric acid. The details of the formation of plates with various acid concentrations are provided below in Table 1.
Table 1: Formation of carbon plates with the variation in acid concentrations.
Sl. No. Acid concentration (%) Reaction time (h) Plate formation
(digital photo) Remarks Density of carbon plate (g/cm3)
1 10 1 Refer Figure 2a Did not form a plate NA
2 20 1 Refer Figure 2b Did not form a plate NA
3 25 1 Refer Figure 2c Did not form a plate.
Sample swelled. NA
4 28 1 Refer Figure 2d Formed plate 1.64
5 30 1 Refer Figure 2e Formed plate 1.63
6 40 1 Refer Figure 2f Formed plate 1.73
7 42 1 Refer Figure 2g Formed plate 1.70
8 45 1 Refer Figure 2h Plate formed but with significant porosity Less than 1.2
9 50 1 Refer Figure 2i Did not form a plate NA
10 70
(Commercial grade) 1 Refer Figure 2j Did not form a plate NA

Thus it is evident from the above results that the mesophase pitch treated with nitric acid having a concentration of 28% and 42% were able to form the green plate of desired thickness, whereas the mesophase pitches with other concentrations of nitric acid were not able to form the green plate. The carbon plate is illustrated in Figure 1a.
The functionalization using acid with a lower concentration (less than 28%) produces mesophase pitch with insufficient functionalization while excess concentration cause degradation of the aromatic content in mesophase pitch leading to failure in making compact carbon plates. The results confirm that the chemical modification of the mesophase pitch powder effectively provides a green plate without the need for an air-stabilization process. Thus the carbonization process successfully produced compact carbon plates without any swelling or shape change. The digital photograph of a large-sized plate is illustrated in Figure 3.
Step 4 - Preparation of the carbon plates:
The green plates obtained in step 3 (prepared by using 30% nitric acid) were subjected to carbonization under a continuous flow of nitrogen gas under a slow heating rate of 10°C/min till 1200°C and a dwell time of 5 min at 1200°C to obtain the carbon plate. The density of the carbon plate is 1.4 g/cm3. The list of densities of the carbon plates obtained by carbonization of green plates is shown in Table 1.
Experiment IIa: Chemical treatment of mesophase pitch
The mesophase pitch (in the form of granules) obtained in step 1 of experiment I was dispersed in nitric acid at 25% concentration, under constant stirring at 50°C for 60 minutes to obtain a mesophase pitch slurry. The mesophase pitch slurry was filtered and washed with excess water followed by air drying at 110°C for 2 hours to obtain the modified mesophase pitch.
Experiment IIb: Chemical treatment of mesophase pitch
The mesophase pitch (in the form of granules) obtained in step 1 of experiment I was dispersed in nitric acid at 45% concentration, under constant stirring at 25°C for 45 minutes (0.75 hr) to obtain a mesophase pitch slurry. The mesophase pitch slurry was filtered and washed with excess water followed by air drying at 110°C for 2 hours to obtain the modified mesophase pitch.
The modified mesophase pitch obtained in Experiment IIa and IIb was used to prepare green plate and carbon plate as disclosed in step 3 and step 4 of Experiment 1.
The details of the formation of plates with varying acid concentration and time period are provided below in Table 2.
Table 2: Formation of carbon plates with the varying acid concentration and time period.
Sl. No. Acid concentration (%) Reaction time (h) Temperature (°C) Plate formation
(digital photo) Remarks Density of carbon plate (g/cm3)
1 25 1
(60 min) 50 Refer Figure 4a Formed plate 1.70
2 45 0.75
(45 min) 25 Refer Figure 4b Formed plate 1.55

Thus, it is evident from the above results that by altering the parameters of the chemical treatment of the mesophase pitch such as reaction time and temperature the so obtained dried mesophase pitch forms the green plate with a desired thickness as per requirement.
The functionalization using nitric acid with a concentration of 25% and heating at 50°C for 1 hour and nitric acid with a concentration of 45% and heating at 25°C for 0.75 hour (45 minutes) provides the carbon plates without any swelling or shape change. Thus, it is evident that, even altering the parameters of the chemical treatment of the mesophase pitch, the plates formed with a desired thickness.
Experiment III: Preparation of carbon plate using compression press
50 gm of modified mesophase pitch obtained in step 2 of Experiment I was subjected to compression moulding using hot-press at 300°C with a load of 0.5 tonne per sq.cm for 15 minutes to obtain a green plate (10 cm x 10 cm x 3 mm thick). The so obtained green plate was subjected to carbonization under a slow heating rate of 10°C/min till 1200°C and a dwell time of 5 min at 1200°C under a continuous flow of nitrogen gas to obtain the carbon plate. The density of the carbon plate is 1.6 g/cm3.
Experiment IV: Preparation of carbon plate with flow channels using compression press
40 gm of modified mesophase pitch obtained in step 2 of Experiment I was subjected to compression moulding using channel flow pattern mould by hot-press at 300°C with a load of 0.5 tonne per sq.cm for 15 minutes to obtain a green plate (10 cm x 10 cm x 3 mm thick). The so obtained green plate was subjected to carbonization under a continuous flow of nitrogen gas at a slow heating rate of 10°C/min till 1200°C and a dwell time of 5 min at 1200°C to obtain the carbon plate. The density of the carbon plate was 1.6 g/cm3.
Experiment V: Preparation of carbon plate with carbon fibers
40 gm of mesophase pitch (in the form of granules) obtained in step 1 of Experiment I was mixed with 2 gm of carbon fibers followed by dispersing in 30% nitric acid under constant stirring for 60 minutes at 30°C to obtain a mesophase pitch slurry. The mesophase pitch slurry was filtered and washed with excess water followed by air drying at 110°C for 2 hours to obtain the modified mesophase pitch.
The modified mesophase pitch was subjected to hand-pressed into a small coupon mould with 15 mm diameter followed by heating at 330oC for 30 min to produce a green plate (15 mm diameter x 5 mm thick). The so obtained green plate was subjected to carbonization under a slow heating rate of 10°C/min till 1200°C and a dwell time of 5 min at 1200°C under a continuous flow of nitrogen gas to obtain the carbon plate. The density of the carbon plate with carbon fibers is 1.4 g/cm3.
Experiment VI: Preparation of the carbon plate using thermally treated mesophase pitch (Comparative)
The mesophase pitch (in the form of granules) obtained in step 1 of Experiment I was air-stabilized by a stepwise increase in the stabilization temperature up to 330oC, wherein the mesophase pitch was kept for 3 hours at each temperature i.e. 200oC, 220oC, 250oC, 270oC, 300oC, and 330oC to obtain a thermally treated mesophase pitch. The thermally treated mesophase pitch was used for the preparation of carbon plates using similar process conditions as employed in Experiment I. It is observed that the thermally stabilized mesophase pitch powder could not be compression moulded into a green plate due to the infusibility of the powder. Therefore, the air/thermally stabilized mesophase pitch powder failed to provide a green plate.
Experiment VII: Preparation of the carbon plate using mesophase pitch (Comparative)
1 gm of mesophase pitch (in the form of granules) obtained in step 1 of Experiment I was hand-pressed into a small coupon mould (15 mm diameter x 15 mm thick) followed by heating at 330oC for 30 min to obtain a green plate (without any chemical or thermal treatment). The green plate was air-stabilized for 18 hours in a stepwise increase in the stabilization temperature as mentioned in Experiment V to obtain a thermally treated mesophase pitch plate. The thermally treated mesophase pitch plate was used for the preparation of carbon plates using similar process conditions as employed in step 4 of Experiment I. The so obtained carbon plates from the mesophase pitch (in the form of granules) (without any chemical or thermal treatment) showed excessive swelling as illustrated in Figure 1b. These carbon plates failed to retain their shape and compactness after the carbonization step. The thermally treated mesophase pitch plate failed to form the carbon plates due to incomplete stabilization of the green plates even after stabilization for more than 18 hours. The un-stabilized mesophase pitch plate decomposed at a higher temperature of the carbonization process leading to the release of volatile components and breaking of the green plate into small pieces as illustrated in Figure 1b.
Experiment VIII: CHNSO analysis
The elemental analysis of the modified mesophase pitch (MP) obtained in Experiment I and un-treated mesophase pitch were evaluated by using CHNSO analysis. The results are provided below in Table 3.
Table 3: CHNSO analysis of the modified mesophase pitch at different (20, 30, 40, and 50%) nitric acid concentrations and un-treated mesophase pitch.
Samples C H N S O C/N C/O
Un-treated mesophase pitch (Experiment I, step-1) 93.82 4.77 0.00 1.41 0.00 Indeterminable Indeterminable
Nitric acid treated MP 20% acid 92.71 4.34 0.33 1.00 1.62 280.93 57.22
Nitric acid treated MP 30% acid 87.31 3.82 1.71 0.94 6.22 51.05 14.03
Nitric acid treated MP 40% acid 81.66 3.58 3.25 0.83 10.68 25.12 7.64
Nitric acid treated MP 50% acid 76.27 3.38 4.73 0.82 14.80 16.12 5.15
It is evident from the above results that the thermally stabilized mesophase pitch lacks -CO and -NO bonds necessary to form the cross-linking for the formation of a thick carbon plate.
The presence of functional groups in the nitric acid (30% acid concentration) treated mesophase pitch and the thermally modified mesophase pitch was further evaluated by FTIR analysis, the results are illustrated in Figure 5a. In Figure 5a that the presence of -NO and -CO stretching frequencies in nitric acid treated mesophase pitch are observed. This also confirms the formation of –NO2 and aldehyde/ketone moieties in mesophase pitch after nitric acid treatment. The insertion of -NO2 groups in mesophase pitch was also confirmed by CHNSO analysis as illustrated in Table 2 by the decrease in C/N and C/O in the chemically-treated mesophase pitch as compared to the thermally modified mesophase pitch. The replacement of the aromatic hydrogen in the mesophase pitch by -NO2 group can be confirmed by the decrease in band intensity as illustrated in Figure 5a. The C/N weight ratio in the range of 25 to 50 and C/O weight ratio in the range of 7 to 14 is required in the nitric acid treated mesophase pitch for the formation of the carbon plates.
The FTIR analysis was performed for the carbon plates prepared by using the nitric acid (30% acid concentration) treated mesophase pitch and the thermally modified mesophase pitch, the results are illustrated in Figure 5b. It is evident from Figure 5b that the intensities of the functional groups are reduced in the carbon plate and hence, these groups helped in the formation of cross-linking between asphaltene and aromatic molecules in the mesophase pitch. The cross-linking in the mesophase pitch helped in retaining the product shape without any swelling or melting. Overall, nitric acid treatment has a significant contribution to the formation of carbon plates. On compression moulding, -NO2 groups were converted into amine type groups by cross-linking between various aromatic moieties in the mesophase pitch.
Experiment IX: Preparation of the graphite plates:
The carbon plates produced from modified mesophase pitch (using 30% nitric acid) were subjected to graphitization in a graphitization furnace under continuous flow of argon gas with a slow heating rate of 10°C/min till 2800°C and a dwell time of 2 hrs at 2800°C to obtain the graphite plates. The density of the graphite plate was 1.6 g/cm3.
Experiment X: Density of the carbon plates and the graphite plates prepared in accordance with the present disclosure
The apparent density of the carbon plates and the graphite plates of the present disclosure was evaluated by the Archimedes principle in water at room temperature. It was found that the average apparent densities of carbonized plates remained in the range of 1.4 g/cm3 to 1.8 g/cm3 after the carbonization process. The graphite plates produced from carbon plates have the similar range of density i.e. in the range of 1.4 g/cm3 to 1.8 g/cm3 after the graphitization process.
It was observed that the value was comparable to the known commercially available graphite plates prepared using natural graphite and pitch material. The graphite plates prepared using the natural graphite and pitch material are available in the range of 1.64 g/cm3 to 1.82 g/cm3. The details of some of the commercially available graphite plate details are provided below.
S. No Source/Manufacturer Material Density (g/cm3)
1 Schunk Kohlenstofftechnik GmbH# SP10165 1.68
2 Schunk Kohlenstofftechnik GmbH# SP10190 1.64
3 Schunk Kohlenstofftechnik GmbH# SP10191 1.68
4 American elements
MDL Number: MFCD00144065 EC No.: 231-955-3^ Graphite plate 1.8
5 FLAG ADVERTISING (BEIJING) LIMITED*
Model NO. DC-1.85 Graphite mold 1.82
#https://backend.schunk-group.com/Schunk/BU-Industry/Documents/Brochures/Bipolar-Plates-for-Fuel-Cell-Redox-Flow-Battery/Schunk-Industry-Bipolarplatten-EN.pdf
^ https://www.americanelements.com/graphite-plate-7782-42-5
* https://flagadvertising.en.made-in-china.com/product/vSZQCGhHLKYW/China-Density-1-75-1-78-1-85-1-91g-cm3-Artificial-Graphite-for-EDM.html
TECHNICAL ADVANCEMENTS
The present disclosure described hereinabove has several technical advantages including, but not limited to, the realization of a process for the preparation of graphite plates, that:
• uses a low-cost pitch material;
• uses simple compression moulding and melt processing;
• avoids the use of graphite and binder;
• avoids repeated impregnation and calcination;
• is devoid of air-stabilization process;
• is able to fabricate bipolar plates from the pitch;
• is free of melting/swelling during carbonization and graphitization; and
• is simple, and cost-efficient.
The embodiments herein and the various features and advantageous details thereof are explained with reference to the non-limiting embodiments in the following description. Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein.
The foregoing description of the specific embodiments so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein.
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 disclosure to achieve one or more of the desired objects or results.
Any discussion of documents, acts, materials, devices, articles or the like that has been included in this specification is solely for the purpose of providing a context for the disclosure. It is not to be taken as an admission that any or all of these matters form a part of the prior art base or were common general knowledge in the field relevant to the disclosure as it existed anywhere before the priority date of this application.
The numerical values mentioned for the various physical parameters, dimensions or quantities are only approximations and it is envisaged that the values higher/lower than the numerical values assigned to the parameters, dimensions or quantities fall within the scope of the disclosure, unless there is a statement in the specification specific to the contrary.
While considerable emphasis has been placed herein on the components and component parts of the preferred embodiments, it will be appreciated that many embodiments can be made and that many changes can be made in the preferred embodiments without departing from the principles of the disclosure. These and other changes in the preferred embodiment as well as other embodiments 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 the preparation of graphite plates, said process comprising the following steps:
a) distilling petroleum pitch at a first predetermined temperature for a first predetermined time period in an inert atmosphere to obtain a mesophase pitch;
b) treating said mesophase pitch with nitric acid under stirring at a second predetermined temperature for a second predetermined time period to obtain a mesophase pitch slurry;
c) filtering said mesophase pitch slurry followed by drying at a third predetermined temperature for a third predetermined time period to obtain a modified mesophase pitch;
d) moulding said modified mesophase pitch at a fourth predetermined temperature for a fourth predetermined time period at a predetermined pressure to obtain a green plate;
e) carbonizing said green plate in an inert atmosphere at a first predetermined heating rate till a temperature reaches to 1200°C using a dwell time in the range of 3 minutes to 10 minutes to obtain said carbon plates; and
f) graphitizing said carbon plates in a graphitization furnace in an inert atmosphere at a second predetermined heating rate till a temperature reaches to 2800°C using a dwell time in the range of 1 hour to 3 hours to obtain said graphite plates
2. The process as claimed in claim 1, wherein said mesophase pitch obtained in step a) is milled to obtain a mesophase pitch in the form of granules.
3. The process as claimed in claim 2, wherein the particle size of said granules is in the range of 1 µm to 45 µm.
4. The process as claimed in claim 1, wherein said mesophase pitch is characterized by having
a) a softening point in the range of 150°C to 300°C;
b) toluene insoluble in the range of 30% to 90%; and
c) quinoline insoluble in the range of 15% to 70%.
5. The process as claimed in claim 1, wherein said mesophase pitch obtained in step a) is reinforced with a predetermined amount of carbon fibers prior to treating with nitric acid.
6. The process as claimed in claim 5, wherein said predetermined amount of carbon fibers is in the range of 0.1 wt% to 10 wt% with respect to the total weight of mesophase pitch.
7. The process as claimed in claim 1, wherein said first predetermined temperature is in the range of 300°C to 450°C.
8. The process as claimed in claim 1, wherein said first predetermined time period is in the range of 2 hours to 30 hours.
9. The process as claimed in claim 1, wherein said inert atmosphere is selected from nitrogen and argon.
10. The process as claimed in claim 1, wherein said second predetermined time period is in the range of 30 minutes to 120 minutes.
11. The process as claimed in claim 1, wherein said second predetermined temperature is in the range of 20°C to 55°C.
12. The process as claimed in claim 1, wherein said nitric acid has a concentration in the range of 25% to 45%.
13. The process as claimed in claim 1, wherein said predetermined third time period is in the range of 100 minutes to 200 minutes.
14. The process as claimed in claim 1, wherein said third predetermined temperature is in the range of 70°C to 130°C.
15. The process as claimed in claim 1, wherein said moulding is done by using a method selected from hand pressed moulding, compression moulding, and channel flow pattern moulding.
16. The process as claimed in claim 1, wherein said fourth predetermined temperature is in the range of 200°C to 350°C.
17. The process as claimed in claim 1, wherein said fourth predetermine time period is in the range of 20 minutes to 60 minutes.
18. The process as claimed in claim 1, wherein said predetermined pressure is in the range of 0.1 tonne per sq.cm to 1 tonne per sq.cm.
19. The process as claimed in claim 1, wherein said first predetermined heating rate and said second predetermined heating rate are independently in the range of 5°C/min to 15°C/min.
20. The process as claimed in claim 1, wherein said mesophase pitch contains C/N and C/O weight ratios in the range of 20 to 55 and 5 to 15 respectively.
21. The process as claimed in claim 1, wherein a density of said graphite plates is in the range of 1.4 g/cm3 to 1.8 g/cm3.
22. The process as claimed in claim 1, wherein said graphite plates are used as bipolar plates in fuel cells.

Dated this 18th day of January, 2024

_______________________________
MOHAN RAJKUMAR DEWAN, IN/PA – 25
OF R.K.DEWAN & CO.
AUTHORIZED AGENT OF APPLICANT