Catalyst and process using the catalyst

Abstract

A new chromium-containing fluorination catalyst is described. The catalyst comprises an amount of zinc that promotes activity. The zinc is contained in aggregates which have a size across their largest dimension of up to 1 micron. The aggregates are distributed throughout at least the surface region of the catalyst and greater than 40 weight % of the aggregates contain a concentration of zinc that is within ±1 weight % of the modal concentration of zinc in those aggregates.

1 . A process for preparing a chromium-containing fluorination catalyst comprising zinc, said method comprising the steps of:
 providing a tank;   introducing an aqueous solution comprising a mixture of zinc and chromium nitrates into the tank using a jet mixer;   introducing an aqueous hydroxide compound into the tank;   collecting a mixed-hydroxide product comprising zinc hydroxide and chromium (III) hydroxide from the tank;   drying the mixed hydroxide product collected from the tank;   crushing the dried product to produce a powder;   calcining the mixed-hydroxide product to convert the zinc hydroxide and chromium (III) hydroxide to their oxides; and   mixing the powder with graphite and compacting the mixture to form pellets.   
     
     
         2 . The process of  claim 1 , wherein the tank comprises a rotating stirrer blade. 
     
     
         3 . The process of  claim 2 , wherein the aqueous solution comprising the mixture of zinc and chromium nitrates is introduced into the tank close to the stirrer blade. 
     
     
         4 . The process of  claim 2 , wherein the aqueous hydroxide compound is introduced into the tank close to the stirrer blade. 
     
     
         5 . The process of  claim 1 , wherein the mixed hydroxide product collected from the tank is filtered and washed prior to being dried. 
     
     
         6 . The process of  claim 1 , wherein the aqueous hydroxide compound introduced into the tank is ammonium hydroxide. 
     
     
         7 . The process of  claim 6 , wherein the rate at which the ammonium hydroxide is introduced into the tank is adjusted to maintain a pH in the tank of from 7 to 8.5. 
     
     
         8 . The process of  claim 1 , further comprising the step of fluorinating the pellets. 
     
     
         9 . The process of  claim 8 , wherein the pellets are fluorinated using HF. 
     
     
         10 . The process of  claim 8 , wherein the catalyst that is produced comprises one or more chromium (III) compounds selected from the group consisting of chromia, chromium (III) fluoride, fluorinated chromia and chromium (III) oxyfluorides. 
     
     
         11 . The process of  claim 10 , which produces a catalyst comprising from 0.5 to 25% by weight of zinc based on the total weight of the catalyst, said zinc being contained in aggregates which have a size across their largest dimension of up to 1 micron and which are distributed throughout at least the surface region of the catalyst and wherein greater than 40 weight % of the zinc-containing aggregates contain a concentration of zinc that is within ±1 weight % of the modal concentration of zinc in the zinc-containing aggregates. 
     
     
         12 . The process of  claim 11 , which produces a catalyst in which greater than 60 weight % of the zinc-containing aggregates contain a concentration of zinc that is within ±1 weight % of the modal concentration of zinc in the zinc-containing aggregates. 
     
     
         13 . The process of  claim 11 , which produces a catalyst in which greater than 80 weight % of the zinc-containing aggregates contain a concentration of zinc that is within ±2 weight % of the modal concentration of zinc in the zinc-containing aggregates. 
     
     
         14 . The process of  claim 11 , which produces a catalyst in which greater than 90 weight % of the zinc-containing aggregates contain a concentration of zinc that is within ±2 weight % of the modal concentration of zinc in the zinc-containing aggregates. 
     
     
         15 . The process of  claim 11 , which produces a catalyst in which the number of zinc-containing aggregates in each square millimetre of the catalyst surface or in each square millimetre of the catalyst bulk is within ±2% of the mean number of zinc-containing aggregates per square millimetre of the catalyst surface or catalyst bulk. 
     
     
         16 . The process of  claim 11 , which produces a catalyst in which the zinc-containing aggregates have a size in the range of from 20 nm to 1 micron. 
     
     
         17 . The process of  claim 11 , which produces a catalyst in which from 92.0 to 100% by weight of the chromium in the catalyst based on the total weight of said chromium is present as chromium (III). 
     
     
         18 . The process of  claim 11 , wherein the catalyst that is produced comprises one or more chromium (VI) compounds and wherein from 0.5 to 4.0% by weight of the chromium in the catalyst based on the total weight of said chromium is present as chromium (VI). 
     
     
         19 . The process of  claim 18 , which produces a catalyst in which from 96.0 to 99.5% by weight of the chromium in the catalyst based on the total weight of said chromium is present as chromium (III). 
     
     
         20 . The process of  claim 11 , wherein the catalyst that is produced comprises zinc in an amount of from 1.0 to 6.0% by weight based on the total weight of the catalyst. 
     
     
         21 . The process of  claim 11 , wherein the catalyst that is produced is amorphous or partially crystalline containing from 0.4 to 5% by weight of one or more crystalline compounds of chromium and/or one or more crystalline compounds of zinc. 
     
     
         22 . The process of  claim 11 , wherein the catalyst that is produced has a surface area in the range of from 20 to 300 m 2 /g. 
     
     
         23 . The process of  claim 22 , wherein the catalyst that is produced has a surface area in the range of from 100 to 250 m 2 /g.