Gas recycle loops in process for converting municipal solid waste into ethanol

1. A method for converting organic materials into ethanol comprising:

creating a primary syngas stream;

in a syngas compressor, raising the pressure of a compressor inlet stream comprising at least a portion of the primary syngas stream to a predefined level, thereby outputting a compressed gas stream;

recycling gas within a main gas recycle loop, comprising the steps of:

providing a gas recycle compressor of sufficient power to circulate gas through the main gas recycle loop;

within an alcohol synthesis reactor comprising a catalyst, in fluid communication with the syngas compressor, taking a reactor inlet stream comprising at least a portion of a combined recycle gas stream as an input and producing an effluent comprising unconverted syngas and a mixture of reaction products including alcohols and water;

in a recycle separator, separating the effluent into a first mixed-alcohol stream rich in water and alcohols, and a gas recycle stream rich in unconverted syngas;

at a mixing point, mixing at least a portion of the gas recycle stream with at least a portion of the compressed syngas to create the combined recycle gas stream; and

separating at least a portion of the first mixed-alcohol stream into a number of streams comprising:

an ethanol stream comprising primarily ethanol;

a water stream comprising primarily water;

a methanol stream comprising primarily methanol; and

a heavy alcohol stream comprising primarily propanol and heavier alcohols.

2. The method of claim 1 , further comprising transferring heat from the effluent to a stream within the main gas recycle loop downstream of the mixing point and upstream of the alcohol synthesis reactor.

3. The method of claim 1 , further comprising controlling the power of the gas recycle compressor to maintain the pressure of the reactor inlet stream near a predetermined value within the range of about 95 bar and about 155 bar.

4. The method of claim 1 , further comprising separate carbon dioxide from the recycle loop stream at a location downstream of the mixing point and upstream of the alcohol synthesis reactor.

5. The method of claim 1 , wherein the catalyst is a sulfidized catalyst, further comprising:

continuously injecting a sulfiding agent at a location downstream of the mixing point and upstream of the alcohol synthesis reactor; and

controlling the rate of injection of the sulfiding agent to keep the amount of sulfur within the syngas entering the alcohol synthesis reactor at approximately a predetermined level.

6. The method of claim 5 , wherein said predetermined level is between about 25 to about 150 ppm on a volumetric basis.

7. The method of claim 1 , further comprising:

conveying a minor portion of the gas within the main gas recycle loop to a combustion turbine, to be burned in the combustion turbine;

generating electricity from the mechanical energy of the combustion turbine.

8. The method of claim 1 , wherein the recycle separator comprises an outlet, further comprising:

decreasing the pressure of at least a portion of the first mixed-alcohol stream to a lower pressure than the pressure of the recycle separator; and

separating said portion of the first mixed-alcohol stream into a low-pressure gas recycle stream rich in unconverted syngas, and a second mixed-alcohol stream rich in water and alcohols.

9. The method of claim 8 , wherein the lower pressure is at least half the pressure of the pressure within the recycle separator.

10. The method of claim 9 , wherein the lower pressure is less than about 2 bar absolute pressure.

11. The method of claim 8 , further comprising conveying at least a portion of the low-pressure gas recycle stream to a second mixing point upstream of the syngas compressor, thereby recycling the low-pressure gas recycle stream.

12. The method of claim 8 , further comprising:

transferring heat from said portion of the first mixed-alcohol stream to a stream comprising at least a first portion of the water stream;

wherein said step of separating said portion of the first mixed-alcohol stream comprises using at least a portion of said first portion of the water stream to absorb mixed alcohols from said portion of the first mixed-alcohol stream.

13. The method of claim 1 , wherein the recycle separator comprises a water absorption column, wherein the water used for absorption comprises at least a portion of the water stream.