Process for the catalytic conversion of methane or natural...

Details Process for the catalytic conversion of methane or natural... Process for the catalytic conversion of methane or natural...

1998-02-06

2001-09-25

Tran, Hien (Department: 1764)

Gas: heating and illuminating

Processes

Manufacture from methane

C048S127700, C423S654000, C423S653000, C423S651000

Reexamination Certificate

active

06293979

ABSTRACT:

This invention relates to a process for the catalytic conversion of methane or natural gas to syngas (i.e. a mixture of carbon monoxide and hydrogen). The process is an energy efficient one using an improved supported catalyst containing oxides of nickel and cobalt, with or without noble metals. This invention particularly relates to a process for the catalytic conversion of methane or natural gas to syngas in an energy efficient manner using an improved supported catalyst containing oxides of nickel and cobalt, with or without noble metals, deposited on a sintered low surface area porous catalyst carrier (i.e. support) precoated with MgO, CaO or mixture thereof, wherein the exothermic oxidative conversion with oxygen of methane or natural gas to syngas is coupled with the endothermic steam and CO
2
reforming of methane or natural gas to syngas by carrying out these reactions simultaneously over the catalyst so that the heat produced in the exothermic reaction is used instantly for the endothermic steam and CO
2
reforming reactions thereby making the process most energy efficient and safe and also making the process operably by a simple fixed bed reactor operated adiabatically or non-adiabatically. The improved process of this invention can be used for the production of carbon monoxide and hydrogen (i.e. syngas or synthesis gas) which is a versatile feedstock for the methanol synthesis, ammonia synthesis, ammonia based fertilizers, various industrial carbonylation and hydrogenation processes and for Fischer-Tropsch synthesis of lower olefins, higher alcohols, aldehydes and liquid hydrocarbon fuels etc. The process of this invention could be used by the producers of carbon monoxide, hydrogen, and synthesis gas (or syngas) as well as their users, for examples those produce methanol and methanol-based products, ammonia and ammonia-based chemicals and fertilizers, Fischer-Tropsch synthesis products such as lower olefins, alcohols, aldehydes and liquid hydrocarbon fuels, oxo-synthesis products, reducing gases, town gas, hydrogenation and carbonylation products and reduction gas for production of sponge iron, etc.
BACKGROUND OF THE INVENTION
In the prior art, it is well known that syngas (i.e. CO and H
2
) can be produced from methane (or natural gas) by following different catalytic processes.
Steam reforming of methane: It is a highly endothermic process and involves following reactions:
Main reaction
CH
4
+H
2
O═CO+3H
2
−54.2 Kcal per mole of CH
4
at 800°-900° C.
Side reaction
CO+H
2
O═CO
2
+H
2
+8.0 kcal per mole of CO at 800° C.-900° C.
CO
2
reforming of methane: It is also a highly endothermic process and involves the following reactions:
Main reaction
CH+CO═2CO+2H
2
−62.2 kcal per mole of CH
4
at 800°-900° C.
Side reaction: Reverse water gas shift reaction
CO
2
+H
2
═CO+H
2
O−8.0 kcal per mole of CO
2
at 800°-900° C.
Partial oxidation (i.e. Oxidative conversion) of methane: It is an exothermic process and involves following reactions:
Main reaction
CH
4
+0.5 O
2
→CO+2H
2
+5.2 kcal per mole of CH
4
at 500°-800° C.
Side reaction
CH
4
+2O
2
→CO
2
+2H
2
O+191.5 kcal per mole of CH
4
at 500°-800° C.
CO+H
2
O═CO
2
+H
2
Use of nickel containing catalysts, particularly nickel (with or without other elements) supported on alumina or other refractory materials, in the above catalytic processes for conversion of methane (or natural gas) to syngas is also well known in the prior art. Kirk and Othmer, Encyclopedia of Chemical Technology, 3rd Ed., 1990, vol. 12, p. 951; Ullmann's Encyclopedia of Industrial Chemistry, 5th Ed., 1989, vol. A12, pp. 186 and 202; U.S. Pat. No. 2,942,958 (1960); U.S. Pat. No. 4,877,550 (1989); U.S. Pat. No. 4,888,131 (1989); EP 0 084 273 A2 (1983); EP 0 303 438 A2 (1989); and Dissanayske et al., Journal of Catalysis, vol. 132, p. 117 (1991).
The catalytic steam reforming of methane or natural gas to syngas is a well established technology practiced for commercial production of hydrogen, carbon monoxide and syngas (i.e., a mixture of hydrogen and carbon monoxide). In this process, hydrocarbon feed is converted to a mixture of H
2
, CO and CO
2
by reacting hydrocarbons with steam over a supported nickel catalyst such as NiO supported on alumina at elevated temperature (850° C.-1000° C.) and pressure (10-40 atm) and at steam to carbon mole ratio of 2-5 and gas hourly space velocity of about 5000-8000 per hour.
This process is highly endothermic and hence it is carried out in a number of parallel tubes packed with a catalyst and externally heated by flue gas to a temperature of 980°-1040° C. (Kirk and Othmer, Encyclopedia of chemical Technology, 3rd, Ed., 1990, vol. 12, p. 951, Ullmann's Encyclopedia of Industrial Chemistry, 5th Ed., 1989, vol. A12, p. 186).
The main drawbacks of this process are as follows: It is highly endothermic and operated at high temperature. Hence, it is highly energy intensive. Further, the water gas reaction occurring in the process leads to formation of CO
2
and H
2
from CO and water, thus increasing H
2
/CO ratio. Since lower H
2
/CO ratio than that obtained by the steam reforming is required for certain applications of syngas, secondary reformer using CO
2
or O
2
oxidants are frequently required to reduce the hydrogen content of syngas produced by the steam reforming. Also, there is a carbon deposition on the catalyst during the steam reforming.
Autothermal catalytic reforming of methane or natural gas with air or oxygen to hydrogen, carbon monoxide and carbon dioxide is also an established technology. In this process, a feed gas mixture containing hydrocarbon, steam and oxygen (or air) is passed through a burner and then the combustion gases are passed over a catalyst, nickel supported on alumina, in a fixed bed reactor at 850°-1000° C. and 20-40 atm. (Ullmann's Encyclopedia of Industrial Chemistry, 5th Ed., 1989, vol. A12, p. 202). This process has following drawbacks: There are large temperature and space velocity variations during start-up and shut-down which leads to abrasion and catalyst disintegration, requiring frequent refilling and removal of the catalyst. This process operates at high temperature and pressure and there is a formation of carbon or coke in the reactor.
U.S. Pat. No. 2,942,958 (1960), disclosed a process for the conversion of a normally gaseous hydrocarbon to carbon monoxide and hydrogen, which comprises preheating of normally gaseous hydrocarbon and steam to a temperature between 538° and 760° C., admixing the preheated gaseous hydrocarbon and steam with oxygen and contacting the resulting admixture with a catalyst which comprises a nickel oxide supported on a refractory material such as zirconia or other refractory metal oxide support in a fixed bed reactor at a reaction temperature between 1800° F. (i.e. 982° C.) and 2200° F. (i.e. 1204° C.) and pressure between 150 and 350 psig, maintaining the mole ratio of oxygen and steam to methane in the feed between 0.3 and 0.7 and between 1 and 2, respectively. The main drawback of this process is that the process operates at very high temperature (i.e., above 982° C.). Another drawback of this process is that it is hazardous to mix oxygen with the preheated mixture of gaseous hydrocarbon and steam.
In U.S. Pat. No. 4,877,550 (1989) and U.S. Pat. No. 4,888,131 (1989), Goetsch et. al. have disclosed a fluid bed process for the production of syngas which comprises reacting a light hydrocarbon feed with steam and oxygen at least about 1750° F. (i.e. 954.4° C.) and about 1700° F. (i.e. 926.7° C.), respectively, in the presence of a supported nickel catalyst, nickel supported on a alumina having particle size in the range of 30-150 microns, in a fluid bed (i.e., fluidized bed) reactor. The main drawbacks of this process are as follows: The process operates at very high temperature. Further, this process involves a use of a fluid bed reactor which is extremely difficult to scale-up, design and operate for the

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