Maintaining low carbon monoxide levels in product carbon dioxide

Abstract

A process for maintaining a low carbon monoxide content in a carbon dioxide product that is made in a synthesis gas purification process is disclosed. More particularly, the invention involves an improved process in which a portion of a loaded solvent is sent through a carbon dioxide absorber instead of to a series of carbon dioxide flash drums.

1 . A process for producing a gas stream comprising carbon dioxide and less than 1000 ppm carbon monoxide, said process comprising sending a first synthesis gas stream through a first carbon dioxide absorber wherein said first synthesis gas stream comprises an unshifted or partially shifted synthesis gas and sending a second synthesis gas stream through a second carbon dioxide absorber wherein said second synthesis gas stream is a fully shifted synthesis gas stream or a synthesis gas stream from a sulfur removal section of said process, wherein within said first carbon dioxide absorber and said second carbon dioxide absorber said first synthesis gas stream and said second synthesis gas stream contact a solvent to remove carbon dioxide from said first and said second synthesis gas stream and wherein at least a portion of solvent from said first and said second carbon dioxide absorber is returned to said second carbon dioxide absorber prior to a loaded solvent being sent from said second carbon dioxide absorber to a zone for removal of carbon dioxide from said solvent. 
     
     
         2 . The process of  claim 1  wherein said synthesis gas is sent to a sulfur absorber to contact a liquid solvent to remove said sulfur compounds and produce a synthesis gas with a reduced concentration of sulfur compounds. 
     
     
         3 . The process of  claim 1  wherein said shifted synthesis gas is sent to a sulfur absorber unit to contact a liquid solvent to remove said sulfur compounds and produce a shifted synthesis gas with a reduced concentration of sulfur compounds. 
     
     
         4 . The process of  claim 1  wherein said liquid streams comprise at least one of a dimethyl ether of polyethylene glycol, a N-methyl pyrrolidone, a tetrahydro-1,4-oxazine, a methanol, and a mixture comprising diisopropanolamine and tetrahydrothiophene-1,1-dioxide. 
     
     
         5 . The process of  claim 1  wherein a loaded solvent stream from said second carbon dioxide absorber is combined with said second feed to form a third stream that is then returned to said second carbon dioxide absorber. 
     
     
         6 . The process of  claim 5  wherein a loaded solvent stream from said first carbon dioxide absorber is combined with said third stream. 
     
     
         7 . The process of  claim 1  wherein said carbon dioxide product stream contains less than about 1000 ppm carbon monoxide in addition to carbon dioxide in said carbon dioxide product stream. 
     
     
         8 . The process of  claim 1  wherein a portion of a loaded solvent is removed from said second absorber to be chilled and a second portion of a loaded solvent is removed from said second absorber to be treated in a carbon dioxide removal zone.