Fischer-tropsch process

Abstract

The present invention relates to a method for producing hydrocarbons from a gas mixture comprising hydrogen and carbon monoxide, in at least two conversion reactors, being the first and second reactor, said reactors comprising catalysts. The reactors can be placed in series or parallel.

1 . A method for producing hydrocarbons from a gas mixture comprising hydrogen and carbon monoxide, in at least two conversion reactors, being the first and second reactor, said reactors comprising catalysts, which method comprises the steps of:
 (i) providing a gas mixture comprising hydrogen and carbon monoxide to two or more of the conversion reactors;   (ii) catalytically converting the gas mixture of step (i) at an initial temperature and an initial pressure to obtain an initial hydrocarbon product stream comprising the normally gaseous, normally liquid and optionally normally solid hydrocarbons from each conversion reactor;   (iii) obtaining from each of the at least two reactors, an initial hydrocarbon stream and an off-gas;   (iv) determining the concentration of hydrocarbons in each of the initial hydrocarbon streams obtained in step (iii) of at least one of the following hydrocarbon groups:
 hydrocarbons having a chain length of 1 to 4 carbon atoms (C1-4 fraction); 
 hydrocarbons having a chain length of 5 to 30 carbon atoms (C5-C30 fraction); and 
 hydrocarbons having a chain length of at least 31 carbon atoms (C31+ fraction); 
   (v) based on the concentration of one or more of said groups, raising or lowering the reaction temperature of at least one of the reactors;   (vi) obtaining a second hydrocarbon stream from each of the reactors;   wherein the concentration of the C5-C30 fraction of the combined second hydrocarbon streams is at least 3%, and preferably at least 5% higher than the concentration of C5-C30 fraction of the combined initial hydrocarbon stream; or   wherein the concentration of the C31+ fraction of the combined second hydrocarbon streams is at least 3% and preferably at least 5% higher than the concentration of the C31+ fraction of the combined initial hydrocarbon streams.   
     
     
         2 . A method according to  claim 1 , wherein the reaction temperature in at least one reactor is lowered and the reaction temperature in another reactor is raised. 
     
     
         3 . A method according to  claim 1 , wherein the two or more reactors each have a reactor operating point and the reactor operating point of at least one of the reactors is raised by:
 increasing the amount of synthesis gas provided to the reactor;   raising the temperature of the cooling water provided to said reactor;   providing a nitrogen containing compound, to the reactor, preferably by adding the nitrogen containing compound to the gas mixture prior to step i), preferably the nitrogen containing compound is selected from the group of ammonia, HCN, NO, an amine and combinations or two or more thereof.   
     
     
         4 . A method according to  claim 1 , wherein the two or more reactors each have a reactor operating point and the reactor operating point of at least one of the reactors is lowered by:
 decreasing the amount of synthesis gas provided to the reactor;   lowering the temperature of the cooling water provided to the reactor; and/or   providing a nitrogen containing compound, to the reactor, preferably by adding the nitrogen containing compound to the gas mixture prior to step i), preferably the nitrogen containing compound is selected from the group of ammonia, HCN, NO, an amine and combinations or two or more thereof.   
     
     
         5 . A method according to  claim 1 , wherein the conversion reactors are operated at an initial temperature in the range of 200 to 230° C. and preferably from 205 to 220° C. 
     
     
         6 . A method according to  claim 1 , wherein the reaction temperature is raised in order to reduce the concentration of the C31+ fraction. 
     
     
         7 . A method according to  claim 1 , wherein the catalyst of one of the reactors has a higher activity than the catalyst in the other reactor. 
     
     
         8 . A method according to  claim 4 , wherein the method further comprises one of the following steps:
 providing a nitrogen containing compound, to the first reactor in case the first reactor comprises the least active catalyst;   providing a nitrogen containing compound, to the second reactor in case the second reactor comprises the least active catalyst.   
     
     
         9 . A method according to  claim 1 , wherein the catalyst comprises cobalt as a catalytically active ingredient and wherein the catalyst is preferably present in the reactor as a fixed bed catalyst. 
     
     
         10 . A method according to  claim 1 , wherein the gas mixture comprising hydrogen and carbon monoxide is synthesis gas, off gas from a conversion reactor or a combination thereof. 
     
     
         11 . A method according to  claim 10 , wherein a first reactor is provided with a synthesis gas as the gas mixture comprising hydrogen and carbon monoxide and a second reactor is provided with the off gas obtained in step (iii) from the first reactor as the gas mixture comprising hydrogen and carbon monoxide. 
     
     
         12 . A method according to  claim 1 , wherein a first and second reactor are each provided with synthesis gas as the gas mixture comprising hydrogen and carbon monoxide. 
     
     
         13 . A method according to  claim 1 , wherein the reactors are operated at a pressure ranging from 10 to 100 bar absolute. 
     
     
         14 . A method according to  claim 1 , further comprising the step of:
 (vii) determining the concentration of hydrocarbons in each of the second hydrocarbon streams obtained in step (vi) of at least one of the hydrocarbon groups.