METHOD FOR MINIMIZING CARBON FORMATION ON METHANATION CATALYSTS

Deposition is controlled by (a) measurement of compsn., temp. and pressure of the inlet stream, (b) determination of compsn., temp. and pressure of the equilibrium prod. stream, based on the simultaneous equilibrium of the reactions (i) CO + 3H2 right arrow left arrow CH4+'IO, (ii) CO+H2O right arrow left arrow CO2 + H2, and (iii) CO2+4H2 right arrow left arrow CH4+2H2O. (c) calculation of reaction equilibrium constant (K1) for the reaction of CO right arrow left arrow C+CO2, given by K1=W/P1X2, (in which W is molar fraction of CO2, P1 the pressure and X the molar fraction of CO, as obtained in (b)). (d) calculation of reaction equilibrium constant (K2) for the reaction CH4 right arrow left arrow C+2H2, given by K2=Y2.P1/Z, (in which Y is molar fraction of H2, and Z molar fraction of CH4, as obtd, in (b)), (e) measurement of temp. (T1) of the product stream. (f) calculation of carbon deposition potential (C1), given by CU=Tk1-T1, (in which Tk1 is equilibrium temp. corresp. to K1), (g) calculation of carbon deposition potential (C2) given by C2=T1-Tk2, (in which Tk2 is equilibrium temp. corresp. to K2), (h) addn. of C1 and C2 to give total deposition potential, and (i) control of compsn., temp. and pressure of the inlet stream to keep the total potential 22.2 degrees (5.6 degrees) C. Life of the catalyst bed before it becomes blocked with carbon is extended. Carbon already deposited can be removed by adjusting the inlet conditions to give total potential below 0 degree C.