A PROCESS FOR THE REMOVAL OF SILOXANES FROM LANDFILL GASES

Abstract

In a process for the removal of siloxanes from biogas streams, especially a landfill gas stream or a gas stream from anaerobic digesters, the gas stream is first passed through a conventional siloxane removing unit to remove the majority of the siloxanes and subsequently passed over a selected catalyst with polishing effect, thereby removing remaining traces of siloxanes. The catalyst with polishing effect is chosen from i.a. zeolites, porous silica, titania and various metals on alumina or titania.

Claims

1. A process for the removal of siloxanes from biogas streams, especially a landfill gas stream or a gas stream from anaerobic digesters, wherein the gas stream is first passed through a conventional siloxane removing unit to remove the majority of the siloxanes and subsequently passed over a selected catalyst with polishing effect, thereby removing any remaining traces of siloxanes.

2. Process according to claim 1, wherein the catalyst with polishing effect is chosen from zeolites, porous silica, titania, nickel on alumina, manganese on alumina, molybdenum on alumina, cobalt on alumina, a combination of any or all of cobalt, molybdenum and nickel on alumina, copper and manganese on alumina, vanadia on titania, molybdenum on titania, zinc oxide, copper supported on zinc oxide, and cerium oxide.

3. Process according to claim 1, wherein the siloxane removing unit comprises an alumina-based adsorbent.

4. Process according to claim 1, wherein the siloxane removing unit and the catalyst with polishing effect are both operated at temperatures between 300 and 450 C.

5. Process according to claim 4, wherein the heat required to perform siloxane removal at temperatures between 300 and 450 C. is provided by combusting a portion of the cleaned product landfill gas from the siloxane removing unit to supply a hot flue gas that heats the process gas upstream from the siloxane removal reactor.

Description

[0017] The idea underlying the present invention is (1) to use an alumina-based sorbent operated at temperatures between 300 and 450 C. to adsorb the majority of the siloxanes present in the landfill gas and (2) to subsequently use a specially selected catalyst, also operated at temperatures between 300 and 450 C., to act as a polisher to remove any remaining trace of siloxanes from the gas. This polishing catalyst is more specifically chosen from zeolites, porous silica, titania, nickel on alumina, manganese on alumina, molybdenum on alumina, cobalt on alumina, a combination of any or all of cobalt, molybdenum and nickel on alumina, copper and manganese on alumina, vanadia on titania, molybdenum on titania, zinc oxide, copper supported on zinc oxide, and cerium oxide.

[0018] So the present invention relates to a process for the removal of siloxanes from biogas streams, especially a landfill gas stream or a gas stream from anaerobic digesters, wherein the gas stream is first passed through a conventional siloxane removing unit and then passed over a selected catalyst with polishing effect, thereby removing any remaining traces of siloxanes, and wherein the catalyst with polishing effect is selected among those cited above.

[0019] The siloxane removing unit comprising an alumina-based adsorbent is operated at temperatures between 300 and 450 C., at which temperatures the majority of the siloxanes are adsorbed. The selected catalyst with polishing effect is also operated at temperatures between 300 and 450 C.

[0020] The heat required to perform siloxane removal at temperatures between 300 and 450 C. is provided by combusting a portion of the cleaned product landfill gas from the unit to supply a hot flue gas that heats the process gas upstream from the siloxane removal reactor andin this mannerenabling the use of abundant landfill gas as a fuel and at the same time avoiding silica deposits in such a gas fired heater.