Process, method, and system for removing heavy metals from fluids

Abstract

Trace amount levels of heavy metals such as arsenic in crude oil are reduced by contacting the crude oil with an oxidizing agent, extracting heavy metals into a water phase for subsequent separation from the crude oil. In one embodiment, the oxidizing agent is selected from the group of hydroperoxides, organic peroxides, inorganic peracids and salts thereof, organic peracids and salts thereof, halogens such as iodine (I 2 ), bromine (Br 2 ), and ozone. In one embodiment, at least a complexing agent selected from the group of metal m halides and/or sulfur compounds can be added to facilitate the removal of arsenic from crude oil by forming soluble heavy metal complexes in the water phase.

1 . A method for reducing a trace amount of arsenic in a crude oil, comprising:
 mixing into the crude oil an effective amount of at least an oxidizing agent selected from the group of oxyhalites, hydroperoxides, organic peroxides, inorganic peracids and salts thereof, organic peracids and salts thereof, molecular halogens, ozone and combinations thereof to extract at least a portion of arsenic into a water-oil emulsion as arsenic cations, forming a mixture;   adding an effective amount of a complexing agent to the water-oil emulsion mixture to convert the extracted arsenic cations to water-soluble arsenic compounds in a water phase; and   separating the water phase containing the water-soluble arsenic compounds from the crude oil to obtain a treated crude oil having a reduced concentration of arsenic.   
     
     
         2 . The method of  claim 1 , further comprising adding a sufficient amount of acid to the water-oil emulsion for a pH of 5.5 or less. 
     
     
         3 . The method of  claim 2 , wherein the acid is added to the crude oil at any time: prior to the addition of the oxidizing agent, concurrent with the addition of the oxidizing agent, prior to the addition of the complexing agent, or concurrent with the addition of the complexing agent. 
     
     
         4 . The method of  claim 1 , wherein adding an effective amount of a complexing agent comprises adding a complexing agent selected from metal halides, sulfur compounds, and mixtures thereof. 
     
     
         5 . The method of  claim 4 , wherein adding an effective amount of a complexing agent comprises adding at least a metal halide. 
     
     
         6 . The method of  claim 5 , wherein adding an effective amount of a complexing agent comprises adding at least a metal halide selected from halides of Li, Na, K, Ca, Co, Ni, Fe, Zn, Ba, Sr, Ag, and combinations thereof. 
     
     
         7 . The method of  claim 6 , wherein adding an effective amount of a complexing agent comprises adding ferric chloride or zinc chloride. 
     
     
         8 . The method of  claim 4 , wherein adding an effective amount of a complexing agent comprises adding at least a sulfur compound selected from the group of sulfides, thiosulfates, dithionites, and mixtures thereof. 
     
     
         9 . The method of  claim 8 , wherein adding an effective amount of a complexing agent comprises adding at least a complexing agent selected from the group of sodium polysulfide, alkali metal sulfide, ammonium thiosulfate, alkali metal thiosulfates, alkaline earth metal thiosulfates, iron thiosulfates, alkali metal dithionites, alkaline earth metal dithionites, and mixtures thereof. 
     
     
         10 . The method of  claim 9 , wherein adding an effective amount of a complexing agent comprises adding at least a complexing agent selected from the group of potassium sulfide, sodium polysulfide, sodium sulfide, sodium hydrosulfide, sodium thiosulfate, and mixtures thereof. 
     
     
         12 . The method of  claim 1 , wherein mixing into the crude oil an effective amount of at least an oxidizing agent comprises adding at least an oxidizing agent selected from the group of molecular halogens, oxyhalites, hypochlorites, and mixtures thereof. 
     
     
         13 . The method of  claim 1 , wherein the addition of the complexing agent occurs either before, simultaneously with, or after the addition of the oxidizing agent to the crude oil. 
     
     
         14 . The method of  claim 1 , wherein the addition of the complexing agent results in at least 50 mole % of the arsenic cations being converted to water-soluble arsenic compounds. 
     
     
         15 . The method of  claim 1 , wherein the addition of the complexing agent results in at least 80% of the arsenic cations being converted to water-soluble arsenic compounds. 
     
     
         16 . The method of  claim 1 , wherein the crude oil feed is mixed with the oxidizing agent in a contact zone comprising at least one of a packed tower, a bubble tray column, a stirred mixing tank, a fiber contactor, and a rotating disc contactor. 
     
     
         17 . The method of  claim 1 , wherein the treated crude oil contains less than 50 ppb arsenic. 
     
     
         18 . The method of  claim 1 , wherein the formation of a water phase containing soluble arsenic compounds occurs within 15 minutes of the addition of the oxidizing agent to the crude oil. 
     
     
         19 . A method for reducing a trace amount of arsenic in a crude oil, comprising:
 mixing into the crude oil an effective amount of at least an oxidizing agent selected from the group of oxyhalites, hydroperoxides, organic peroxides, inorganic peracids and salts thereof, organic peracids and salts thereof, ozone and combinations thereof to extract at least a portion of arsenic into a water-oil emulsion as arsenic cations, forming a mixture;   adding a sufficient amount of acid for the water-oil emulsion mixture to have a pH of 5.5 or less;   adding an effective amount of a complexing agent selected from the group of metal halides and sulfur compounds to the water-oil emulsion mixture to convert the extracted arsenic cations as As 5+  and As 3+  to soluble arsenic compounds in a water phase; and   separating the water phase containing the soluble arsenic compounds from the crude oil to obtain a treated crude oil having a reduced concentration of arsenic.   
     
     
         20 . A method for reducing a trace amount of arsenic in a crude oil, comprising:
 contacting the crude oil with a treatment solution containing an oxidizing agent to form a water-oil emulsion, the treatment solution has a pH of 6 or less;   adding an effective amount of a complexing agent to the water-oil emulsion to form soluble arsenic compounds in a water phase; and   separating the water phase containing the soluble arsenic compounds from the crude oil to obtain a treated crude oil having a reduced concentration of arsenic.   
     
     
         21 . The method of  claim 20 , wherein the crude oil is contacted with the treatment solution in a contact zone comprising fibers and wherein the contact of the crude oil with the treatment solution forms an admixture containing a crude oil and water that flows over and along the fibers.