Separation of water from hydrocarbons

Abstract

A method for the removal of dissolved water or water and ice from hydrocarbon liquids such as petroleum refinery fuels or natural gas liquids in a manner which enables the fuels to be readily treated by the coalescence/separation technique while reducing the potential for plugging filters and other equipment with ice crystals. Free water or water/ice is removed from the liquid hydrocarbons by contacting the hydrocarbon feed with a treating agent which as an affinity for water prior to subjecting the mixture to coalescence/separation. The treating agent is preferably a co-solvent for the water and the hydrocarbon such as an alcohol e.g. methanol. The treating agent and water are separated from the hydrocarbon component during the coalescence/separation and recirculated to the feed with the composition of the recycle aqueous phase being controlled to achieve the desired level of water removal to meet relevant product specifications. Consistent with the removal of the water during the coalescence/separation, the water concentration of the recycle loop containing the co-solvent/water blend gradually increases with removal of the water from the feed. This progressive increase in water level can be compensated by controlled addition of pure co-solvent to the recycle coupled with continuous or periodic dumping of excess mixture. Alternatively, the circulating mixture may be subjected to continuous or batch regeneration or disposed of in any other way which is convenient and economical.

1 . A method for removing water or water and ice from a liquid hydrocarbon, which comprises:
 contacting the a feed stream of the hydrocarbon with a treating agent having an affinity for water which is immiscible with the hydrocarbon,   subjecting the mixture of hydrocarbon and treating agent to coalescence/separation to coalesce the non-hydrocarbon components of the hydrocarbon/water/treating agent mixture to form larger size coalesced liquid droplets,   separating the coalesced liquid droplets comprising water and treating agent from the hydrocarbon to form a dehydrated hydrocarbon product,   recirculating water and treating agent separated from the hydrocarbon as a recycle blend to the feed stream of the hydrocarbon.   
   
   
       2 . A method according to  claim 1  in which the treating agent comprises a mixture of water and a co-solvent for water and the fuel 
   
   
       3 . A method according to  claim 2  in which the co-solvent comprises an alcohol. 
   
   
       4 . A method according to  claim 3  in which the alcohol comprises a lower monohydric alcohol or a lower dihydric alcohol. 
   
   
       5 . A method according to  claim 3  in which the alcohol comprises methanol, ethanol, propanol, ethyleneglycol, propyleneglycol or dipropyleneglycol. 
   
   
       6 . A method according to  claim 4  in which the alcohol comprises methanol. 
   
   
       7 . A method according to  claim 1  in which the mixture of hydrocarbon feed and the blend of treating agent and water is separated by a three stage separation sequence comprising filtration, coalescence of water and treating agent into droplets and separation of the coalesced liquid droplets. 
   
   
       8 . A method according to  claim 2  in which the volume ratio of the co-solvent/water blend to the hydrocarbon feed is from 0.1 to 10 volume percent. 
   
   
       9 . A method to  claim 2  in which the volume ratio of the co-solvent to the water in the blend which is mixed with the hydrocarbon feed is from 80:20 to 20:80 co-solvent:water. 
   
   
       10 . A method according to  claim 9  in which the volume ratio of the co-solvent to the water in the blend which is mixed with the hydrocarbon is from 60:40 to 40:60 co-solvent component: water. 
   
   
       11 . A method according to  claim 1  in which the water concentration of the recirculating treating agent/water blend gradually increases with removal of the water from the feed. 
   
   
       12 . A method according to  claim 1  in which the composition of the recycle blend is controlled to achieve the requisite level of water removal for the hydrocarbon product to meet relevant product specifications. 
   
   
       13 . A method according to  claim 12  in which the composition of the recycle blend is controlled by addition of treating agent to the recycle blend. 
   
   
       14 . A method according to  claim 13  in which a portion of the recycle blend is removed from the recirculation. 
   
   
       15 . A method according to  claim 1  in which the mixing of the treating agent and water blend with the hydrocarbon feed is initiated by automatic control responsive to an indication of ice crystal accumulation in the hydrocarbon. 
   
   
       16 . A method according to  claim 1  in which the hydrocarbon comprises a petroleum refinery liquid fuel product. 
   
   
       17 . A method according to  claim 16  in which the fuel product comprises a gasoline or middle distillate fuel product. 
   
   
       18 . A method according to  claim 17  in which the middle distillate fuel product comprises a road diesel fuel. 
   
   
       19 . A method according to  claim 1  in which the hydrocarbon comprises natural gas liquids. 
   
   
       20 . A method according to  claim 19  in which the natural gas liquid feed comprises natural gas liquids, water and glycol and in which the glycol is separated from the natural gas liquids with the water.