Processes for removing hydrazine from hydroxylamine solutions

Abstract

The present invention relates to processes for reducing or eliminating the amount of hydrazine from a hydroxylamine-free base containing hydrazine by treating said hydroxylamine-free base with a scavenger agent, and to the hydroxylamine-free base thereby obtained, as well as to its use for producing microdispersions containing a hydroxamated polymer for use as a flocculant in the Bayer process.

1 . A process for reducing the amount of hydrazine from a hydroxylamine-free base containing hydrazine, the method comprising treating said hydroxylamine-free base with a scavenger agent selected from compounds of formula I and/or II 
       
         
           
           
               
               
           
         
       
       wherein
 each of X 1  and X 2  is individually chosen from: H, OH, NR″ 2 , OR′″, SH, halide or an optionally substituted hydrocarbyl group, with the proviso that not both of X 1  and X 2  are OH groups, wherein each R″ is independently chosen from: H or an optionally substituted hydrocarbyl group; R′″ is an optionally substituted hydrocarbyl group wherein two R′″ groups can also form an optionally substituted ring system; or R′″ is an alkali metal or NR V   4 , wherein each R V  is independently chosen from: H or an optionally substituted hydrocarbyl group; 
 X 3  is chosen from: O, NR′, S, or PR′, wherein R′ is chosen from: H, OH, alkali metal, NR IV   2  or alkyl, wherein each R IV  is independently chosen from: H or an optionally substituted hydrocarbyl group; 
 R is chosen from:
 CR 1 R 2  where each of R 1  and R 2  is independently chosen from: H or an optionally substituted hydrocarbyl group, wherein R 1  and R 2  together can also form an optionally substituted ring; 
 R 3 C═CR 4  where R 3  and R 4  together form an optionally substituted ring; and 
 R 5 R 6 C—CR 7 R 8  where R 5  and R 7  together form an optionally substituted ring, and wherein each of R 6  and R 8  is independently chosen from: H, or an optionally substituted hydrocarbyl group, 
 
 
       with the proviso that R 1  can form a ring system with X 1 . 
     
     
         2 . The process according to  claim 1 , wherein the scavenging agent is selected from a member of the group consisting of:
 a) compounds of formula I, wherein each of X 1  and X 2  is independently chosen from: an alkyl group comprising from 1 to 6 carbon atoms; OR′″ wherein R′″ is an alkyl group comprising from 1 to 6 carbon atoms, or wherein two R′″ groups can be connected to form a ring; and NR″ 2  wherein each R″ is independently chosen from: H, or an alkyl group comprising from 1 to 6 carbon groups; and   b) compounds of formula II, wherein X 3  is O, NH or N—OH.   
     
     
         3 . The process according to  claim 1 , wherein the scavenging agent is selected from compounds of formula I and/or II, wherein R is a) CR 1 R 2  where each of R 1  and R 2  is independently chosen from: H, or an alkyl group; or b) R 3 C═CR 4  where R 3  and R 4  together form an optionally substituted aromatic ring system. 
     
     
         4 . The process according to  claim 1 , wherein the scavenging agent is chosen from at least one member selected from the group consisting of: phthalimide; substituted phthalimides bearing one or more electron donating groups on the aromatic ring; N-substituted phthalimides; 1,3 diketones with alkyl substitution on the 2 carbon; and
 pyromellitic diimide.   
     
     
         5 . The process according to  claim 1 , wherein the treatment of the hydroxylamine-free base with the scavenger agent is conducted at a temperature from 5° C. to 90° C. 
     
     
         6 . The process according to  claim 1 , wherein the amount of scavenger agent used is from 0.5 to 200 mole per mole hydrazine present in the hydroxylamine-free base. 
     
     
         7 . A hydroxylamine-free base solution containing less than 500 ppm of hydrazine based on hydroxylamine-free base and which contains less than 1 equivalent weight of by-product salt per equivalent of hydroxylamine. 
     
     
         8 . A method of producing a microdispersion containing at least one hydroxamated polymer, said method comprising: reacting a) a water-in-oil microdispersion comprising a continuous phase of an oil and an emulsifier and a discontinuous aqueous phase comprising a vinyl polymer containing one or more pendant functional groups which will react with hydroxylamine, with b) a hydroxylamine-free base solution according to  claim 7 . 
     
     
         9 . The method according to  claim 8 , wherein the vinyl polymer is chosen from at least one member selected from the group consisting of: (co)polymers of acrylamide; acrylic acid; and acrylic esters. 
     
     
         10 . The method according to  claim 8 , wherein the hydroxylamine-free base is used in conjunction with an excess of base selected from potassium hydroxide, sodium hydroxide, ammonia, or mixtures thereof. 
     
     
         11 . A hydroxamated vinyl polymer water-in-oil microdispersion obtained by the method according to  claim 8 . 
     
     
         12 . A hydroxamated vinyl polymer water-in-oil microdispersion comprising at least one hydroxamated vinyl polymer and less than 1 equivalent of by-product salt per equivalent of hydroxamate group present on the polymer. 
     
     
         13 . A hydroxamated vinyl polymer water-in-oil microdispersion comprising at least 18% by weight of polymer calculated on the basis of the vinyl polymer before hydroxamation. 
     
     
         14 . The hydroxamated vinyl polymer water-in-oil microdispersion according to  claim 11  having a solution viscosity of at least 10 mPa·s. 
     
     
         15 . The hydroxamated vinyl polymer water-in-oil microdispersion according to  claim 11 , wherein the hydroxamated vinyl polymer is a hydroxamated (co)polymer of acrylamide having a hydroxamate group content of at least 5 mole % based on monomer units in the polymer. 
     
     
         16 . A process for flocculation and separation of suspended solids from an industrial process stream comprising suspended solids, the method comprising adding a hydroxamated polymer microdispersion according to  claim 11  to the industrial process stream.