- Email: [email protected]
From methane to hydrogen, carbon black and water
In/ J. Hydrogen Energy Vol. 20. No. 3, pp. l’i7- 202, 19%
Pergamon
Copyright
1‘ 1995 International
for Hydrogen Energy Elsevier Science Ltd Printed m Great Britain. All rights reserved
0360-3199(94)EOO22-Q
FROM
METHANE
TO HYDROGEN.
Association
0360 719995 (9 qo i 0.0)
CARBON
BLACK
AND WATFR
L. FULCHERI and Y. SCHWOB Centre d’Energ&ique, Ecole des Mines de Paris, 06560 Sophia-Antipolis, France
(Received for publication
11 March 1994)
of the total world production of hydrogen comes from vapor cracking of methane. Even though methane is the least carbogen of all hydrocarbons, steam conversion of one ton of methane is accompanied by the emission of about four tons of CO, into the atmosphere. Simple thermolysis of methane being no more endothermic than the vapor cracking reaction. cracking methane withput any oxygen into carbon and hydrogen should. theoretically, be no more energy-expensive than existing processes.To be effective, such a thermolysis needs a very high temperature reaction which, with recent improvements in plasma technology, is now accessible. The main advantage of carrying out thermolysis at high temperature is that, while producing hydrogen, reaction conditions may also be favourable for carbon black production. From physical considerations related to existing processes,the authors present a theoretical study which could open the way to new plasma-twisted processes. More anecdotally, a certain number of natural gas resources remain unexploited due to their isolation; it is theoretically possible to transform these resources into carbon and water without any external energy supply. It would then be possible to irrigate the desert while producing a solid state product whose transport may be easfer than gas Abstract-Most
NOMENCLATURE Duration of amortization in years Annual amortization rate Cost of electrical set up, including source, plasma supply and maintenance, related to one ton of carbon black Specific heat Input temperature before cracking reaction Temperature of cracking reaction Rate of hydrogen consumed for energy cracking SUPPlY Variation of free enthalpy related to Reaction 3 Variation of enthalpy related to Reaction 2 Standard enthalpy of Reaction 2 Electrothermic efficiency Fuel cell efficiency Rate of 0, in the in the furnace process Rate of CO, in the furnace process Rate of H, in the furnace process Rate of H,O in the furnace process Rate of C in the furnace process INTRODUCTION A significant part of the hydrogen produced in the world comes from methane [l]. In most processes, steam conversion is used. A big disadvantage of such processes is that the production of hydrogen is accompanied by the emission of large quantities of CO, into the atmos-
phere, one part coming from the conversion and another as a result of the combustion of a part of the methane (the energy needed for decomposition). CH, + 2Hz0 + Energy -+ CO, + 4H,
11)
In accordance with a recent article by Muradov [Z]. we think that, while fossil fuels, and methane especially. will remain in the future an efficient way of producing hydrogen, processes will have to change in order to take into account the environmental aspects. In particular, we think that the use of water. which induces CO, production, may be avoided by using a simple thermolysis process. CH, + Energy + C + 2H.. Such a decomposition, which is nearly as endothermic as the vapor reforming one (relative to lhe hydrogen produced) may be performed at high temperatures ( z 1500-2000 K) using an energy supply. The main advantage of this approach is that, at this temperature level, it is theoretically possible to produce (at the same time) pure hydrogen and carbon black, whereby carbon black can be economically much more than a byproduct. As mentioned above, the required temperature level
involves the use of an energy supply. En particular. one solution may consist of using an electrical power supply in a plasma process.This will be discussedin the present work. 197
198
L. FULCHERI and Y. SCHWOB II,0
co,
NO* SO,
CO/CO, 1% CH, + AIR
IN2 IS
A
Fig. 1. Furnace black--reactor schematic.
WHAT IS CARBON BLACK? Total world production of carbon black is about 6 million tons per year [3]. Most of this is used in the rubber industry as a reinforcing filler. Modern tires contain about 30% (massic ratio) of carbon black. Several dozen different grades are listed by international ASTH classification, where each grade corresponds to a very specific application. While several processeshave existed in the past, the most common (80% of the total world production) is nowadays the furnace process. This is based on an incomplete combustion of a hydrocarbon, C,H,, combustion of one part of the feedstockgiving cracking energy to the other part. A typical furnace black reactor is shown in Fig. 1:
CH,-+C+2Hz is endothermic. The standard decomposition enthalpy of reaction (2) is: AH:, = + 18 kcal mole-’ = +75.3 kJ mol-‘.
(4)
When reaction (2) is performed at high temperature, &, total enthalpy of the reaction is: T
AHR2 = AH;,
+
’ (C,cs + 2C,,J
dT
s TO T 1
i V&J
dT
J=o
T being the input temperature of the reactants. Assuming that in industrial processes,the input meth+ 7H20H20 + 7,C (3) ane can be preheated for nothing by tail gases, from ambient temperature to 6OO”C,the energy supply needed While the first processesused methane, heavy aromatic for heating and decomposition at TR (temperature of the oils now represent most of the carbon black feedstock. reaction), as a function of temperature is given in Fig. 2 Typical yields of carbon black, depending on feedstock (we neglected hydrogen dissociation and other second quality, are 0.35 tons per ton of feedstock (the other part order reactions) [S]. being transformed into CO,). Prices vary with quality The variation of energy with temperature grows linearly in the range we considered (1273-2273 K). Related between $1000 and $4000 per ton [4]. to carbon mass,this energy varies approximately between 3 and 5 kWh per kg of carbon produced. DECOMPOSITION OF METHANE Cd-L
+
70~0,
+
7co 2 CO,
+
7Q-b
The plasma process Thermodynamic aspects
As mentioned, the direct decomposition of methane:
The idea of making carbon black by cracking a hydrocarbon using a plasma source is not a new idea;
FROM METHANE TO HYDROGEN, CARBON BLACK AND WATER
199
25 1600
1800
Temperature (K)
2ooo
2200
Fig. 2. Total enthalpy of the decomposition reaction
the principle was patented by the authors in 1980 [S-S]. However, because of new environmental problems and improvements in plasma technology, the idea can be updated as a good solution for simultaneously making carbon black and hydrogen without CO, emission (Fig. 3). Looking at a very specific existing thermal process,the acetylene black process [9], the authors think that, recreating by plasma the conditions resulting from the highly exothermic decomposition of acetylene, it is theoretically possible to produce structured carbon particles into a hydrogen gas Row. If we assumethat typical electrothermic efficiency, qsT, of modern plasma arc devicesis over 80% we can estimate that the electric energy supply needed for the cracking operation varies between 4 and 7 kWh per kg of carbon produced or between 1 and 1.9 kWh per normal cubic meter of hydrogen produced.
COMPARISON OF FURNACE AND PLASMA PROCESSES Becauseof the wide range of grades of catbon black, our comparison will only concern a well-defined product, whose industrial name is super abrasion furnace black (SAF). This grade corresponds to an average structured black, used essentially as reinforcing filer to improve abrasion properties. The average commercial price is about US $lOOQ-1400per ton. Production temperature of this product is about 16OO”C,so the theoretical energy supply, as defined above, may be estimated at 5000 kWh per ton of carbon produced. We present in Fig. 4 the input/output massand energy balances for the two processes (related to one ton of product). Economic comparison
We present here a very simple economic approach of comparison of the two processes(furnace and new plasma Table 1. Comparison between furnace and new plasma process. process). This comparison is made from the followPrices for 1 ton of product ing data which are related to 1993 French prices (US $1 = 5.67 FF). New plasma Super abrasion furnace process Furnace feedstock US $140 per ton Natural gas feedstock US $210 per ton Feedstock SAF us $450 US $560 per ton Hydrogen Natural gas us $84 US $280 Electrical kWh 4.41 cms per kWh Electric energy us $220 Investment related to electrical USS#@perkW Credit H, us S- 186 power set up Total (mass + energy) us $534 us $314 Amortization plasma Utilization rate 0.68 (6000 h per year) us $97 0.02 Rate of annual maintenance cost Total us $411 us $534 over total investment
200
L. FULCHERI
and Y. SCHWOB
HC kWb
Fig. 3. Plasmablack--reactor schematic.
For a n year amortization at a rate of t% a year, the cost of the electrical set up, C, including source, power supply and maintenance, related to one ton of product is:
of about 96% with a lower energy of only 2.2 kWh per kg of carbon. THE CASE OF ISOLATED SITES
c=
440 x 5000 ’ 0.68 x 8760
tx(l+c) (1 + t)” - 1 + 0.02 >
(6)
With a five year amortization at a 10% annual rate, the cost of the electrical set up, C, is US $97 per ton of carbon black. So, for a typical capacity of 100,000tons per year with a 0.68 utilization rate, total electric power of a plasma black installation will be 83 MW. From the very simple hypothesis presented before, the use of plasma for making carbon black and hydrogen from natural gas seemsto be very interesting. Indeed, the over-cost due to electric assistance is broadly compensated by: l
l l
low cost of feedstock (due to the theoretical 100% carbon yield) production of pure hydrogen removal of CO, emissions.
Moreover, other advantages resulting from this process are: the suppression of quenching (due to the absenceof oxygen); and the removal of SO, emissions [lo, 111,due to the use of methane. This result compares well with conclusions of a study presented in 1983 [12], as the authors, who were using a 15 kW r.f. plasma, obtained with methane carbon yields
In a certain number of places important resources of natural gas are located in desert areas where the absence of water and electricity is a serious problem. Becauseof their isolation and the difficulties of carrying natural gas, some of these resource are unexploited, for economic reasons. In such places, it could be interesting to convert gas in situ. Moreover, hydrogen oxidation being a very exothermic reaction H, + +O, + H,O, it is possible to use a part of the hydrogen for making electrical energy. In this case, the use of fuel cells could be an adequate solution. So, the overall process could be CH, + a0, + C + 2(1- cl)H, + 2ctH,O.
(8)
In the case of hydrogen oxidation (equation 6), useful energy is free enthalpy AC,, = 56.7 kcal mol-’ = 237.3 kJ mol-’
(9)
If we assume that typical electrochemical fuel cell efficiency, qpc’ is commonly over 60 %, [13], the rate of the hydrogen to be consumed for the overall operation, c((equation 7) is given as a function of the temperature by the expression
FROM HC (3200 kg)
METHANE
CHJl333
TO HYDROGEN,
kg-1866 Nm’)
CARBON
BLACK
AND WATER
‘01
Table 2. Total mass balance related to one imtlai ton of (‘H, T,(K) 1213 2213
‘X&4 1000 1000
1 0.54 096
400 kg 560 Nm’
CONCLUSION
Even though hydrogen may be considered as a clean energy source, the majority of industrial production comesfrom vapo-cracking of methane in a processwhich 1OOUOkg iii 3730 Nm’ 5000 Nm’ generatesabout four tons of CO, for one ton of hydrogen. Direct thermolysis of methane being no more endotherI mic than the vapo-cracking reaction, it is theoretically t possible to crack methane into carbon and hydrogen uumace &Plasma using no more energy than the existing processes.To be effective. such a decomposition needs a high temperature loo0 kg carbon black level. These temperatures are, with recent improvements of plasma technology, broadly accessible. Fig. 4 Input ‘output balance for the two processes The main advantage of this approach is. while totally removing CO, emission, it is theoretically possible to make hydrogen and carbon black, simultaneously. From simple hypotheses and physical consideration related to existing processes,the authors have presented a theoretical study whose conclusions could open the way to a new carbon black plasma assisted process. In addition to the total suppression of carbon dioxide The variation in c( is given in Fig 5. The theoretical emissions and the production of pure hydrogen, the new rate of hydrogen needed for the energy supply varies processconsidered,using methaneas feedstock.should also between 0.5 for the lower temperature reaction (1273 K) allow a significant reduction in sulphur dioxide emissions. Finally, to be effective, all these theoretical considerto 0.95 for the upper one (2273 K). The first case corresponds to a rather poorly structured product; the ations will need to be confirmed by experimental results. last one, which corresponds to a well structured product, With this objective, an important program is beginning in our center. The first experiments on a 100 kW uses nearly all of the hydrogen. Table 2 shows the total three-phase ac. current will start in Spring 199~ mass balance (related to one ton initial CH,) co,
2
0.95
Rate of hydrogen consumed
0.9 0.85 0.8 0.75 0.7 0.65 0.6 0.55 05 1400
1600
2200
1800
Fig. 5. Rate of consumed hydrogen in the plasma-fuel
cell process.
L. FULCHERI and Y. SCHWOB
202
REFERENCES 1. J. Saint-Just, J. M. Basset, J. Bousquet and G. A. Martin, Le gaz naturel, matitre premiere pour l’avenir, Lu Recherche, 21, 730 (1990). 2. N. 2. Muradov, How to produce hydrogen from fossil fuels without carbon dioxide emission, Int. J. Hydrogen Energy, 18, 211 (1993). 3. J. B. Donnet, Carbon Black, 2nd edn. Marcel Decker, New York (1993). 4. V. J. Guercio, Carbon black feedstock overview. The Global Outlook for Carbon Black, Intertech Conferences,Portland, ME (1993). 5. R. H. Perry and D. Green, Perry’s Chemical Engineers’ Hand-book, McGraw-Hill, New York. 6 Armines, Pro&de et dispositif de fabrication de noir de carbone et noir de carbone obtenu. B. F. 8000981,(1980). 7. N. A. Idonov, Y. M. Korolev, L. S. Polak and V. T. Popov, Plasma chemical production of dispersed carbon. Phase composition study, Khim. Vys. Energ. 20, 174.
8. K. Shakourzadeh and J. Amouroux, Reactor design and energy concepts for a plasma process of acetylene black production, Plasma Chem. Plasma Process. 6 335 (1986). 9. Y. Schwab, Acetylene black: manufacture, properties and applications. In Chemistry and Physics of Carbons, P. L. Walker (ed.). Vol. 15, pp. 11@227(1979). 10. J. W. Boyd, Air quality issuesfor carbon black, The Global Outlook for Carbon Black, Intertech Conferences,Portland, ME (1993). 11. Y. Schwab, Prospects for carbon black in Easten and Western Europe, The Global Outlook for Carbon Black. Intertech Conferences, Portland, ME (1993). 12. C. Cristofides and V. J. Ilberson, Processing hydrocarbons in a thermal R. F. plasma reactor, ISPC-6, Montreal, paper A-8-2, July 1983. 13. D. Linden, Handbook of Batteries and Fuel Cells, McGraw-Hill International, New York (1984).
Pergamon
Copyright
1‘ 1995 International
for Hydrogen Energy Elsevier Science Ltd Printed m Great Britain. All rights reserved
0360-3199(94)EOO22-Q
FROM
METHANE
TO HYDROGEN.
Association
0360 719995 (9 qo i 0.0)
CARBON
BLACK
AND WATFR
L. FULCHERI and Y. SCHWOB Centre d’Energ&ique, Ecole des Mines de Paris, 06560 Sophia-Antipolis, France
(Received for publication
11 March 1994)
of the total world production of hydrogen comes from vapor cracking of methane. Even though methane is the least carbogen of all hydrocarbons, steam conversion of one ton of methane is accompanied by the emission of about four tons of CO, into the atmosphere. Simple thermolysis of methane being no more endothermic than the vapor cracking reaction. cracking methane withput any oxygen into carbon and hydrogen should. theoretically, be no more energy-expensive than existing processes.To be effective, such a thermolysis needs a very high temperature reaction which, with recent improvements in plasma technology, is now accessible. The main advantage of carrying out thermolysis at high temperature is that, while producing hydrogen, reaction conditions may also be favourable for carbon black production. From physical considerations related to existing processes,the authors present a theoretical study which could open the way to new plasma-twisted processes. More anecdotally, a certain number of natural gas resources remain unexploited due to their isolation; it is theoretically possible to transform these resources into carbon and water without any external energy supply. It would then be possible to irrigate the desert while producing a solid state product whose transport may be easfer than gas Abstract-Most
NOMENCLATURE Duration of amortization in years Annual amortization rate Cost of electrical set up, including source, plasma supply and maintenance, related to one ton of carbon black Specific heat Input temperature before cracking reaction Temperature of cracking reaction Rate of hydrogen consumed for energy cracking SUPPlY Variation of free enthalpy related to Reaction 3 Variation of enthalpy related to Reaction 2 Standard enthalpy of Reaction 2 Electrothermic efficiency Fuel cell efficiency Rate of 0, in the in the furnace process Rate of CO, in the furnace process Rate of H, in the furnace process Rate of H,O in the furnace process Rate of C in the furnace process INTRODUCTION A significant part of the hydrogen produced in the world comes from methane [l]. In most processes, steam conversion is used. A big disadvantage of such processes is that the production of hydrogen is accompanied by the emission of large quantities of CO, into the atmos-
phere, one part coming from the conversion and another as a result of the combustion of a part of the methane (the energy needed for decomposition). CH, + 2Hz0 + Energy -+ CO, + 4H,
11)
In accordance with a recent article by Muradov [Z]. we think that, while fossil fuels, and methane especially. will remain in the future an efficient way of producing hydrogen, processes will have to change in order to take into account the environmental aspects. In particular, we think that the use of water. which induces CO, production, may be avoided by using a simple thermolysis process. CH, + Energy + C + 2H.. Such a decomposition, which is nearly as endothermic as the vapor reforming one (relative to lhe hydrogen produced) may be performed at high temperatures ( z 1500-2000 K) using an energy supply. The main advantage of this approach is that, at this temperature level, it is theoretically possible to produce (at the same time) pure hydrogen and carbon black, whereby carbon black can be economically much more than a byproduct. As mentioned above, the required temperature level
involves the use of an energy supply. En particular. one solution may consist of using an electrical power supply in a plasma process.This will be discussedin the present work. 197
198
L. FULCHERI and Y. SCHWOB II,0
co,
NO* SO,
CO/CO, 1% CH, + AIR
IN2 IS
A
Fig. 1. Furnace black--reactor schematic.
WHAT IS CARBON BLACK? Total world production of carbon black is about 6 million tons per year [3]. Most of this is used in the rubber industry as a reinforcing filler. Modern tires contain about 30% (massic ratio) of carbon black. Several dozen different grades are listed by international ASTH classification, where each grade corresponds to a very specific application. While several processeshave existed in the past, the most common (80% of the total world production) is nowadays the furnace process. This is based on an incomplete combustion of a hydrocarbon, C,H,, combustion of one part of the feedstockgiving cracking energy to the other part. A typical furnace black reactor is shown in Fig. 1:
CH,-+C+2Hz is endothermic. The standard decomposition enthalpy of reaction (2) is: AH:, = + 18 kcal mole-’ = +75.3 kJ mol-‘.
(4)
When reaction (2) is performed at high temperature, &, total enthalpy of the reaction is: T
AHR2 = AH;,
+
’ (C,cs + 2C,,J
dT
s TO T 1
i V&J
dT
J=o
T being the input temperature of the reactants. Assuming that in industrial processes,the input meth+ 7H20H20 + 7,C (3) ane can be preheated for nothing by tail gases, from ambient temperature to 6OO”C,the energy supply needed While the first processesused methane, heavy aromatic for heating and decomposition at TR (temperature of the oils now represent most of the carbon black feedstock. reaction), as a function of temperature is given in Fig. 2 Typical yields of carbon black, depending on feedstock (we neglected hydrogen dissociation and other second quality, are 0.35 tons per ton of feedstock (the other part order reactions) [S]. being transformed into CO,). Prices vary with quality The variation of energy with temperature grows linearly in the range we considered (1273-2273 K). Related between $1000 and $4000 per ton [4]. to carbon mass,this energy varies approximately between 3 and 5 kWh per kg of carbon produced. DECOMPOSITION OF METHANE Cd-L
+
70~0,
+
7co 2 CO,
+
7Q-b
The plasma process Thermodynamic aspects
As mentioned, the direct decomposition of methane:
The idea of making carbon black by cracking a hydrocarbon using a plasma source is not a new idea;
FROM METHANE TO HYDROGEN, CARBON BLACK AND WATER
199
25 1600
1800
Temperature (K)
2ooo
2200
Fig. 2. Total enthalpy of the decomposition reaction
the principle was patented by the authors in 1980 [S-S]. However, because of new environmental problems and improvements in plasma technology, the idea can be updated as a good solution for simultaneously making carbon black and hydrogen without CO, emission (Fig. 3). Looking at a very specific existing thermal process,the acetylene black process [9], the authors think that, recreating by plasma the conditions resulting from the highly exothermic decomposition of acetylene, it is theoretically possible to produce structured carbon particles into a hydrogen gas Row. If we assumethat typical electrothermic efficiency, qsT, of modern plasma arc devicesis over 80% we can estimate that the electric energy supply needed for the cracking operation varies between 4 and 7 kWh per kg of carbon produced or between 1 and 1.9 kWh per normal cubic meter of hydrogen produced.
COMPARISON OF FURNACE AND PLASMA PROCESSES Becauseof the wide range of grades of catbon black, our comparison will only concern a well-defined product, whose industrial name is super abrasion furnace black (SAF). This grade corresponds to an average structured black, used essentially as reinforcing filer to improve abrasion properties. The average commercial price is about US $lOOQ-1400per ton. Production temperature of this product is about 16OO”C,so the theoretical energy supply, as defined above, may be estimated at 5000 kWh per ton of carbon produced. We present in Fig. 4 the input/output massand energy balances for the two processes (related to one ton of product). Economic comparison
We present here a very simple economic approach of comparison of the two processes(furnace and new plasma Table 1. Comparison between furnace and new plasma process. process). This comparison is made from the followPrices for 1 ton of product ing data which are related to 1993 French prices (US $1 = 5.67 FF). New plasma Super abrasion furnace process Furnace feedstock US $140 per ton Natural gas feedstock US $210 per ton Feedstock SAF us $450 US $560 per ton Hydrogen Natural gas us $84 US $280 Electrical kWh 4.41 cms per kWh Electric energy us $220 Investment related to electrical USS#@perkW Credit H, us S- 186 power set up Total (mass + energy) us $534 us $314 Amortization plasma Utilization rate 0.68 (6000 h per year) us $97 0.02 Rate of annual maintenance cost Total us $411 us $534 over total investment
200
L. FULCHERI
and Y. SCHWOB
HC kWb
Fig. 3. Plasmablack--reactor schematic.
For a n year amortization at a rate of t% a year, the cost of the electrical set up, C, including source, power supply and maintenance, related to one ton of product is:
of about 96% with a lower energy of only 2.2 kWh per kg of carbon. THE CASE OF ISOLATED SITES
c=
440 x 5000 ’ 0.68 x 8760
tx(l+c) (1 + t)” - 1 + 0.02 >
(6)
With a five year amortization at a 10% annual rate, the cost of the electrical set up, C, is US $97 per ton of carbon black. So, for a typical capacity of 100,000tons per year with a 0.68 utilization rate, total electric power of a plasma black installation will be 83 MW. From the very simple hypothesis presented before, the use of plasma for making carbon black and hydrogen from natural gas seemsto be very interesting. Indeed, the over-cost due to electric assistance is broadly compensated by: l
l l
low cost of feedstock (due to the theoretical 100% carbon yield) production of pure hydrogen removal of CO, emissions.
Moreover, other advantages resulting from this process are: the suppression of quenching (due to the absenceof oxygen); and the removal of SO, emissions [lo, 111,due to the use of methane. This result compares well with conclusions of a study presented in 1983 [12], as the authors, who were using a 15 kW r.f. plasma, obtained with methane carbon yields
In a certain number of places important resources of natural gas are located in desert areas where the absence of water and electricity is a serious problem. Becauseof their isolation and the difficulties of carrying natural gas, some of these resource are unexploited, for economic reasons. In such places, it could be interesting to convert gas in situ. Moreover, hydrogen oxidation being a very exothermic reaction H, + +O, + H,O, it is possible to use a part of the hydrogen for making electrical energy. In this case, the use of fuel cells could be an adequate solution. So, the overall process could be CH, + a0, + C + 2(1- cl)H, + 2ctH,O.
(8)
In the case of hydrogen oxidation (equation 6), useful energy is free enthalpy AC,, = 56.7 kcal mol-’ = 237.3 kJ mol-’
(9)
If we assume that typical electrochemical fuel cell efficiency, qpc’ is commonly over 60 %, [13], the rate of the hydrogen to be consumed for the overall operation, c((equation 7) is given as a function of the temperature by the expression
FROM HC (3200 kg)
METHANE
CHJl333
TO HYDROGEN,
kg-1866 Nm’)
CARBON
BLACK
AND WATER
‘01
Table 2. Total mass balance related to one imtlai ton of (‘H, T,(K) 1213 2213
‘X&4 1000 1000
1 0.54 096
400 kg 560 Nm’
CONCLUSION
Even though hydrogen may be considered as a clean energy source, the majority of industrial production comesfrom vapo-cracking of methane in a processwhich 1OOUOkg iii 3730 Nm’ 5000 Nm’ generatesabout four tons of CO, for one ton of hydrogen. Direct thermolysis of methane being no more endotherI mic than the vapo-cracking reaction, it is theoretically t possible to crack methane into carbon and hydrogen uumace &Plasma using no more energy than the existing processes.To be effective. such a decomposition needs a high temperature loo0 kg carbon black level. These temperatures are, with recent improvements of plasma technology, broadly accessible. Fig. 4 Input ‘output balance for the two processes The main advantage of this approach is. while totally removing CO, emission, it is theoretically possible to make hydrogen and carbon black, simultaneously. From simple hypotheses and physical consideration related to existing processes,the authors have presented a theoretical study whose conclusions could open the way to a new carbon black plasma assisted process. In addition to the total suppression of carbon dioxide The variation in c( is given in Fig 5. The theoretical emissions and the production of pure hydrogen, the new rate of hydrogen needed for the energy supply varies processconsidered,using methaneas feedstock.should also between 0.5 for the lower temperature reaction (1273 K) allow a significant reduction in sulphur dioxide emissions. Finally, to be effective, all these theoretical considerto 0.95 for the upper one (2273 K). The first case corresponds to a rather poorly structured product; the ations will need to be confirmed by experimental results. last one, which corresponds to a well structured product, With this objective, an important program is beginning in our center. The first experiments on a 100 kW uses nearly all of the hydrogen. Table 2 shows the total three-phase ac. current will start in Spring 199~ mass balance (related to one ton initial CH,) co,
2
0.95
Rate of hydrogen consumed
0.9 0.85 0.8 0.75 0.7 0.65 0.6 0.55 05 1400
1600
2200
1800
Fig. 5. Rate of consumed hydrogen in the plasma-fuel
cell process.
L. FULCHERI and Y. SCHWOB
202
REFERENCES 1. J. Saint-Just, J. M. Basset, J. Bousquet and G. A. Martin, Le gaz naturel, matitre premiere pour l’avenir, Lu Recherche, 21, 730 (1990). 2. N. 2. Muradov, How to produce hydrogen from fossil fuels without carbon dioxide emission, Int. J. Hydrogen Energy, 18, 211 (1993). 3. J. B. Donnet, Carbon Black, 2nd edn. Marcel Decker, New York (1993). 4. V. J. Guercio, Carbon black feedstock overview. The Global Outlook for Carbon Black, Intertech Conferences,Portland, ME (1993). 5. R. H. Perry and D. Green, Perry’s Chemical Engineers’ Hand-book, McGraw-Hill, New York. 6 Armines, Pro&de et dispositif de fabrication de noir de carbone et noir de carbone obtenu. B. F. 8000981,(1980). 7. N. A. Idonov, Y. M. Korolev, L. S. Polak and V. T. Popov, Plasma chemical production of dispersed carbon. Phase composition study, Khim. Vys. Energ. 20, 174.
8. K. Shakourzadeh and J. Amouroux, Reactor design and energy concepts for a plasma process of acetylene black production, Plasma Chem. Plasma Process. 6 335 (1986). 9. Y. Schwab, Acetylene black: manufacture, properties and applications. In Chemistry and Physics of Carbons, P. L. Walker (ed.). Vol. 15, pp. 11@227(1979). 10. J. W. Boyd, Air quality issuesfor carbon black, The Global Outlook for Carbon Black, Intertech Conferences,Portland, ME (1993). 11. Y. Schwab, Prospects for carbon black in Easten and Western Europe, The Global Outlook for Carbon Black. Intertech Conferences, Portland, ME (1993). 12. C. Cristofides and V. J. Ilberson, Processing hydrocarbons in a thermal R. F. plasma reactor, ISPC-6, Montreal, paper A-8-2, July 1983. 13. D. Linden, Handbook of Batteries and Fuel Cells, McGraw-Hill International, New York (1984).