Process for recovering gaseous hf from gaseous effluents

Claim 2

The process of claim 1 wherein gas is conducted through support material comprised of about 5 to 15 parts of NaOH per 100 parts of alumina.

Claim 3

The process of claim 3 wherein the gas is at a temperature of about 15* to 70*C. and the support material is a bed of particles from about 1 to 8 inches in depth.

Claim 4

The process of claim 4 wherei n the gas contacts the support material at a superficial velocity from about 0.1 to 5 feet per second.

Claim 5

The process of claim 5 wherein the gas contains particulates and is preliminarily processed through particulate removing means to remove particulates.

Claim 6

A process for removing gaseous HF from gas containing it comprising passing the gas evolved from the manufacture of aluminum by the electrolytic process and containing HF, in contact with a solid material consisting essentially of alumina particles containing about 4 to 30 parts of a member selected from the group consisting of NaOH, KOH and their mixtures, per 100 parts of alumina.

Claim 7

A process for removing gaseous HF from gas containing it comprising contacting the gas containing HF with a support material consisting essentially of alumina particles surface coated with from about 4 to 30 parts of a component per 100 parts of alumina, said component being selected from the group consisting of NaOH, KOH and their mixtures, said HF-containing gas being evolved from the manufacture of aluminum by the electrolytic process, and introducing the support material, when spent, into the electrolytic bath of said electroytic process.

Claim 8

The process of claim 8 wherein the support material contains about 5 to 15 parts of NaOH per 100 parts of alumina.

Claim 9

The process of claim 9 wherein the support material contains a statistical monomolecular layer of NaOH.

Claim 10

The process of claim 9 wherein the HF-containing gas is at a temperature of about 15* to 70*C., the gas is passed through the support material at a superficial velocity of about 0.1 to 5 feet per second, and the support material is a bed of particles from about 0.5 to 8 inches in depth.

Claim 11

The process of claim 11 wherein the support material contains a statistical monomolecular layer of NaOH.

Claim 12

The process of claim 8 wherein the gas contains particulates and is preliminarily processed through particulate removing means to remove particulates.

Claim 13

The process of claim 13 wherein the particulates include particulates of alumina, cryolite, aluminum fluoride, and sodium fluoride, and the reusable particles are introduced into the molten electrolytic bath.

Claim 14

A process for removing gaseous HF from gas containing it comprising contacting the gas containing HF with a material consistiNg essentially of alumina and about 4 to 30 parts per 100 parts of alumina, of a component selected from the group consisting of NaOH, KOH and their mixtures.

Claim 15

The process of claim 15 in which the alumina has about 4 to 30 parts of NaOH per 100 parts of alumina.

Claim 16

The process of claim 15 in which the alumina has about 5 to 15 parts of NaOH per 100 parts of alumina.

Claim 17

The process of claim 15 in which the alumina contains a statistical monomolecular layer of NaOH.

Claim 18

The process of claim 17 in which the HF-containing gas is at a temperature of about 15* to 70*C., the gas is passed through said material at a superficial velocity of about 0.1 to 5 feet per second, and said material is a bed of particles from about 0.5 to 8 inches in depth.

Claim 19

The process of claim 19 in which the alumina contains a statistical monomolecular layer of NaOH.

Claim 20

The process of claim 16 wherein the support material is produced from an agglomerate of pot line alumina particles selected from the group consisting of activated alumina, low alpha-alumina and calcined alumina by mixing the alumina particles with the NaOH solution to coat the particles with the solution; heating the mix in a sealed vessel at a temperature and for a time sufficient to cohere the particles; unsealing the vessel to recover the agglomerate; and sizing the agglomerate into discrete NaOH treated alumina particles.

Claim 21

The process of claim 21 wherein the pot line alumina particles are of a size ranging from less than about 100 to 500 mesh; the mix is heated at a temperature from about 120* to 200*C. under autogeneous pressure; the agglomerate is recovered from the unsealed vessel, heated to remove free water and sized.

Claim 22

The process of claim 22 wherein the pot alumina is low alpha-alumina.