Dual-stage synthesis of lpg from bio-based sources

Abstract

A method is provided for synthesizing bio-based LPG from renewable sources via a bio-based synthetic gas feedstock, in a dual-stage reaction system comprising an oxygenate synthesis reaction zone and an oxygenate conversion reaction zone that are configured for producing and converting a methanol intermediate for reduced CO2 selectivity. The method includes recovering LPG from either the full reaction zone effluent or from a purge stream separated from the full reaction zone effluent for LPG recovery.

1 . A method for producing bio-based LPG, comprising:
 1) reacting a blended bio-based synthesis gas comprising CO, CO 2  and H 2  in an oxygenate synthesis reaction zone containing an oxygenate synthesis catalyst and forming a first effluent containing oxygenates and unreacted bio-based synthesis gas, wherein the oxygenates in the first effluent include at least 50 mol % methanol;   2) reacting at least a portion of the first effluent in an oxygenate conversion reaction zone containing an oxygenate conversion catalyst and forming a second effluent comprising C2− hydrocarbons, bio-based LPG, and C5+ hydrocarbons,   3) separating at least a portion of the hydrocarbons, including C2−, bio-based LPG and C5+ hydrocarbons, from the second effluent to form a recycle effluent; and   4) blending at least a portion of the recycle effluent with fresh bio-based synthesis gas to perform step a).   
     
     
         2 . The method of  claim 1 , wherein the bio-based synthesis gas comprising CO, CO 2  and Hz in step 1) is prepared by contacting a biogas comprising biomethane with an oxidizing gas selected from O 2 , CO 2  and H 2 O or combinations thereof at reforming reaction conditions in a reforming reaction zone to produce. 
     
     
         3 . The method of  claim 1 , wherein the oxygenate synthesis catalyst comprises one or more methanol synthesis-active metals selected from the group consisting of Cu, Zn, Zr, Al, Pt, Pd, Rh, Ru, and Cr, wherein the oxygenate synthesis catalyst contains no molecular sieve component. 
     
     
         4 . The method of  claim 1 , wherein the oxygenate conversion catalyst contains less than 1 weight % of a water gas shift (WGS) active metal component. 
     
     
         5 . The method of  claim 4 , wherein the oxygenate conversion catalyst contains essentially no WGS active metal component. 
     
     
         6 . The method of  claim 3 , wherein the oxygenate conversion catalyst comprises a zeolite having a SiO 2 /Al 2 O 3  molar ratio of less than 90. 
     
     
         7 . The method of  claim 3 , wherein the oxygenate conversion catalyst comprises a zeolite having a SiO 2 /Al 2 O 3  molar ratio of less than 30. 
     
     
         8 . The method of  claim 1 , wherein the oxygenate conversion catalyst comprises a small pore molecular sieve selected from Chabazite, SSZ-13, SAPO-34, SSZ-39, MCM-35, EU-12, RHO, SAPO-18, SAPO-56. 
     
     
         9 . The method of  claim 1 , wherein the oxygenate conversion catalyst comprises SSZ-13. 
     
     
         10 . The method of  claim 1 , wherein the second effluent comprises greater than 40 weight % LPG, based on the total hydrocarbon content of the second effluent. 
     
     
         11 . The method of  claim 1 , wherein the second effluent comprises less than 25 weight % C5+ hydrocarbons, based on the total hydrocarbon content of the second effluent. 
     
     
         12 . The method of  claim 1 , wherein:
 1) the bio-based synthesis gas in the oxygenate synthesis reaction zone in step 1) is reacted at a reaction temperature between about 220° C. and about 350° C. and a pressure of between about 500 psi and about 1500 psi; and   2) the portion of the first effluent in the oxygenate conversion reaction zone in step 2) is reacted at a reaction temperature between about 280° C. and about 500° C. and a pressure between about 500 psi and about 1500 psi.   
     
     
         13 . The method of  claim 12 , wherein the reaction temperature in the oxygenate conversion reaction zone is at least 25° C. higher than the reaction temperature in the oxygenate synthesis reaction zone. 
     
     
         14 . The method of  claim 12 , wherein reacting the portion of the first effluent in the oxygenate conversion reaction zone is reacted at a pressure between about 750 psi and about 1500 psi. 
     
     
         15 . The method of  claim 1 , further comprising:
 a1) removing an aqueous product from the second effluent and producing a third effluent after step a);   a2) removing C3+ hydrocarbons from the third effluent by contacting at least a portion of the third effluent with a liquid absorption solvent in an absorption zone, absorbing C3+ hydrocarbons from the third effluent, and producing a hydrocarbon-enriched fraction and a hydrocarbon-depleted fourth effluent, and recovering the bio-based LPG fraction;   a3) removing light gases, including C2− hydrocarbons, CO, and CO 2 , from the fourth effluent by contacting at least a portion of the fourth effluent with a solid adsorbent for adsorbing at least a portion of the light gases, desorbing the adsorbed gas and producing a second light gas stream and returning non-adsorbed H 2  to the fourth effluent to form the recycle effluent.   
     
     
         16 . The method of  claim 15 , further comprising separating hydrocarbons from the liquid absorbent; fractionating the hydrocarbons and recovering the bio-based LPG fraction. 
     
     
         17 . The method of  claim 15 , wherein in step a2) absorbing at least a portion of hydrocarbons in the third effluent into the liquid absorption solvent in absorption zone at a temperature of less than 50° C. and at a pressure between about 500 psi and about 1500 psi. 
     
     
         18 . The method of  claim 15 , wherein the liquid absorption solvent is selected from nC16 paraffinic hydrocarbon, kerosine, and light cycle oil. 
     
     
         19 . The method of  claim 15 , further comprising:
 a4) adsorbing the light gases from the fourth effluent onto the solid adsorbent at an adsorption pressure above 400 psi;   a5) separating the adsorbed C2− hydrocarbons, CO, and CO 2  from the solid adsorbent at a pressure at least 25 psi below the adsorption pressure; and   a6) returning non-adsorbed H 2  to the fourth effluent at a pressure above 400 psi.   
     
     
         20 . The method of  claim 19 , further comprising, after step a5), passing at least a portion of the separated C2− hydrocarbons, CO, and CO 2  to the reforming reaction zone. 
     
     
         21 . The method of  claim 15 , further comprising contacting a first purge stream, comprising between about 10% and about 90% of the third effluent, with the liquid absorption solvent, absorbing C3+ hydrocarbons from the first purge stream, and recovering at least the bio-based LPG fraction. 
     
     
         22 . The method of  claim 15 , further comprising contacting a second purge stream, comprising between about 5% and about 50% of the fourth effluent, with the solid adsorbent, adsorbing C2− hydrocarbons, CO, and CO 2  from the second purge stream, and returning non-adsorbed H 2  to the recycle effluent. 
     
     
         23 . The method of  claim 15 , wherein the hydrocarbon-enriched fraction comprises 10% to 90% C3+ hydrocarbons. 
     
     
         24 . The method of  claim 15 , further comprising passing the second light gas stream to a reforming reaction zone for producing a recyclable blended bio-based synthesis gas.