Synthesis gas conversion process

1. A method for restarting a synthesis gas conversion process, wherein the synthesis gas conversion process comprises flowing synthesis gas into a reactor in contact with a synthesis gas conversion catalyst at a desired reaction temperature and pressure to produce a synthesis gas product and flowing effluent comprising the synthesis gas conversion product out of the reactor, the method comprising:

(A) stopping the flow of the synthesis gas into the reactor;

(B) flowing hydrogen or natural gas into the reactor to purge the reactor; and

(C) restarting the flow of synthesis gas into the reactor;

wherein during step (B) hydrogen flows into the reactor in contact with the catalyst at a temperature of up to 400° C., then air flows into the reactor in contact with the catalyst at a temperature in the range from 70° C. to 350° C. for a period of time in the range from 1 to 24 hours, then hydrogen flows into the reactor in contact with the catalyst at a temperature of up to 400° C.

2. The method of claim 1 wherein the reactor is a conventional reactor.

3. The method of claim 1 wherein the reactor is a microchannel reactor.

4. The method of claim 1 wherein prior to step (A) the pressure within the reactor is at a pre-stoppage pressure, and during step (A) the pressure within the reactor is reduced to a level lower than the pre-stoppage pressure, and prior to step (B) the pressure within the reactor is increased to the pre-stoppage pressure.

5. The method of claim 1 wherein the process is conducted in a plant comprising a plurality of reaction trains, each reaction train comprising a synthesis gas conversion reactor containing a synthesis gas conversion catalyst, the reaction trains being connected to a reactant feed stream comprising fresh synthesis gas, the method comprising:

(A) flowing the reactant feed stream at an overall process flow rate to the plurality of reaction trains in the plant;

(B) dividing the reactant feed stream into a plurality of reactant substreams;

(C) flowing each reactant substream through a separate reaction train to convert the reactants in the reactant substream to a synthesis gas conversion product;

(D) stopping the flow of a reactant substream to one of the reaction trains; and

(E) continuing to flow the reactant feed stream to the remainder of reaction trains in the plant to provide a flow rate of fresh synthesis gas that is the same or substantially the same as the flow rate of fresh synthesis gas used in step (A).

6. The method of claim 1 wherein the synthesis gas conversion process comprises a process for converting synthesis gas to methane, methanol or dimethyl ether.

7. The method of claim 1 wherein the synthesis gas conversion process is a Fischer-Tropsch process.

8. The method of claim 7 wherein the catalyst comprises cobalt.

9. The method of claim 1 wherein the catalyst is in the form of a fixed bed of particulate solids.

10. The method of claim 1 wherein a tail gas is produced in the reactor, at least part of the tail gas being combined with the synthesis gas to form a reactant mixture, the volumetric ratio of the synthesis gas to tail gas being in the range from 1:1 to 10:1.

11. The method of claim 1 wherein the synthesis gas conversion process is a Fischer-Tropsch process and the synthesis gas comprises H 2 and CO, the mole ratio of H 2 to CO being in the range from 1.4:1 to 2.1:1.

12. The method of claim 1 wherein the temperature in the reactor is at a pre-stoppage temperature prior to stopping the flow of synthesis gas into the reactor, and the temperature of the reactor during the step of restarting the flow of synthesis gas into the reactor is at the pre-stoppage temperature or below the pre-stoppage temperature by up to about 20° C.

13. A method for restarting a synthesis gas conversion process, wherein the synthesis gas conversion process comprises flowing synthesis gas into a reactor in contact with a synthesis gas conversion catalyst at a desired reaction temperature and pressure to produce a synthesis gas product and flowing effluent comprising the synthesis gas conversion product out of the reactor, the method comprising:

(A) stopping the flow of the synthesis gas into the reactor;

(B) flowing hydrogen or natural gas into the reactor to purge the reactor; and

(C) restarting the flow of synthesis gas into the reactor;

wherein the reactor includes a heat transfer surface, and the ratio of the surface area of the heat transfer surface to the volume of catalyst in the reactor is at least about 300 m 2 of heat transfer surface area per m 3 of catalyst.