Pseudoboehmitic alumina and process for making same

Claim 2

Process according to claim 1, wherein the recycle to feed ratio is between about 1.5 and 3.0 to produce a pseudoboehmitic alumina having an average pore volume in the 120-800 A pore size range of about 0.3 to about 0.5 cc./g.

Claim 3

Process according to claim 1, wherein the pH in the second reactor is between about 6 and 7.

Claim 4

Process according to claim 1, wherein the average residence time of the slurry in the second reactor is about 40 to about 120 minutes.

Claim 5

A process for producing alumina of substantially pseudoboehmitic structure and low soda content which comprises a. introducing into a first reactor an aqueous sodium aluminate solution having an A/C ratio from about 0.7 to about 0.9, a total caustic concentration from about 350 to about 650 grams per liter calculated as Na2CO3 and an aqueous nitric acid solution having an HNO3 concentration from about 50 to about 200 grams per liter while maintaining the temperature of the reaction mixture between about 30* and about 75* C., the quantity of nitric acid introduced being about the stoichiometric amount required to react with the sodium aluminate; b. removing the reaction mixture from the first reactor and introducing it into a second reactor where it is maintained under agitation at a temperature from about 30* to about 75* C. for an average residence time from about 10 to about 300 minutes at a pH of about 7 to form a slurry containing alumina hydrate of substantially pseudoboehmitic structure; c. recycling a portion of the slurry from the second reactor to the first reactor in a ratio of from about 0.1 to about 3 volumes of slurry to 1 volume of combined sodium aluminate solution and nitric acid solution feed; d. removing another portion of the slurry from the second reactor and filtering the slurry to a solids content from about 8 to about 20 percent be weight; e. repulping the formed filter cake with water to obtain a solids content of from about 4 to about 8 percent by weight and adding a compound selected from the group consisting of NH3 and NH4OH in an amount equivalent to from about 1.5 to about 3.0 by weight of NH4OH on the weight basis of Al2O3 of the pulp and maintaining the pulp under agitation at a temperature at about 60* C. or below for a time period of less than about 30 minutes; and f. filtering the pulp, washing the filter cake and recovering the alumina of substantially pseudoboehmitic structure.

Claim 6

Process according to claim 6, wherein the recycle to feed ratio is between about 0.1 and 1.5 to produce a pseudoboehmitic alumina having an average pore volume in the 120-800 A pore size range of about 0.1 to about 0.3 cc./g.

Claim 7

Process according to claim 6, wherein the recycle to feed ratio is between about 1.5 and 3.0 to produce a pseudoboehmitic alumina having an average pore volume in the 120-800 A pore size range of about 0.3 to about 0.5 cc./g.

Claim 8

Process according to claim 6, wherein the pH in the second reactor is between about 6 and 7.

Claim 9

Process according to claim 6 wherein the average residence time of the slurry in the second reactor is from about 40 to about 120 minutes.