Process for separating isobutylene from C4 hydrocarbon mixtures

Claim 2

In the process of selectively extracting isobutylene from a hydrocarbon mixture of C 4 hydrocarbons comprising olefins and paraffins in addition to said isobutylene by reacting said hydrocarbon mixture with a first aqueous solution of sulfuric acid to convert said isobutylene to tertiary butyl alcohol soluble in said first aqueous solution, separating said first aqueous solution from a raffinate comprising the remaining hydrocarbon mixture and entrained tertiary butyl alcohol and regenerating said tertiary butyl alcohol in said first aqueous solution to isobutylene, the improvement comprising: a. extracting said hydrocarbon mixture in a first stage at a temperature between about 30° and 45°C with said first aqueous solution having about 40 - 55 percent by weight sulfuric acid and separating a first raffinate and a first extract comprising tertiary butyl alcohol; and b. extracting said first raffinate after separating the entrained tertiary butyl alcohol by washing with aqueous sulfuric acid at a temperature between 20° and 40°C in a second stage at a temperature between 10° and 25°C with a second aqueous solution having about 60 - 70 percent by weight sulfuric acid and separating a second raffinate comprising remaining hydrocarbon substantially free of isobutylene and a second extract which is regenerated to recover dimers and trimers of isobutylene.

Claim 3

The process of claim 1, wherein said first aqueous solution in said first stage has about 48 - 54 percent by weight sulfuric acid and said first aqueous solution in said second stage has about 62 - 66 percent by weight sulfuric acid.

Claim 4

In the process of selectively extracting isobutylene from a hydrocarbon mixture of C 4 hydrocarbons comprising olefins and paraffins in addition to said isobutylene by reacting said hydrocarbon mixture with a first aqueous solution of sulfuric acid to convert said isobutylene to tertiary butyl alcohol soluble in said aqueous solution, separating said first aqueous solution from a raffinate comprising the remaining hydrocarbon mixture and entrained tertiary butyl alcohol and regenerating said tertiary butyl alcohol in said first aqueous solution to isobutylene, the improvement comprising: a. extracting said hydrocarbon mixture in a first stage at a temperature between about 30° and 45°C with said first aqueous solution having about 40 - 55 percent by weight sulfuric acid and separating a first raffinate and a first extract comprising tertiary butyl alcohol; b. washing said first raffinate continuously with aqueous sulfuric acid at a temperature between 20° and 40°C to remove entrained tertiary butyl alcohol in a wash extract and produce a washed first raffinate; and c. extracting said washed first raffinate in a second stage at a temperature between about 10° and 25°C with a second aqueous solution having about 60 - 70 percent by weight sulfuric acid and separating a second raffinate comprising remaining hydrocarbons substantially free of isobutylene and a second extract which is regenerated to recover dimers and trimers of isobutylene.

Claim 5

In the process of selectively extracting isobutylene from a hydrocarbon mixture of C 4 hydrocarbons comprising olefins and paraffins in addition to said isobutylene by reacting said hydrocarbon mixture with a first aqueous solution of sulfuric acid to convert said isobutylene to tertiary butyl alcohol soluble in said aqueous solution, separating said first aqueous solution from a raffinate comprising the remaining hydrocarbon mixture and entrained tertiary butyl alcohol and regenerating said tertiary butyl alcohol in said first aqueous solution to isobutylene, the improvement comprising: a. extracting said hydrocarbon mixture in a first stage at a temperature between about 30° and 45°C with said first aqueous solution having about 40 - 55 percent by weight sulfuric acid and separating a first raffinate and a first extract comprising tertiary butyl alcohol; b. washing said first raffinate continuously with aqueous sulfuric acid at a temperature between 20° and 40°C to remove entrained tertiary butyl alcohol in a wash extract and produce a washed first raffinate; and c. extracting said washed first raffinate in a second stage at a temperature between about 10° and 25°C with a second aqueous solution having about 60 - 70 percent by weight sulfuric acid and separating a second raffinate comprising remaining hydrocarbons substantially free of isobutylene and a second extract which is regenerated to recover dimers and trimers of isobutylene.

Claim 6

The process of claim 3, wherein said washing step (b) is carried out at a temperature between about 20° and 40°C with said first aqueous solution having about 40 - 55 percent by weight sulfuric acid and said wash extract is used as said aqueous solution of step (a).

Claim 7

The process of claim 4, wherein said first aqueous solution in said first stage has about 48 - 54 percent by weight sulfuric acid and said second aqueous solution in said second stage has about 62 - 66 percent by weight sulfuric acid.

Claim 8

The process of claim 2, wherein said second rafinate contains less than 0.2 percent by weight of isobutylene and said first extract yields isobutylene exceeding a purity of 99 percent by weight.

Claim 9

The process of claim 5, wherein said second raffinate contains less than 0.2 percent by weight of isobutylene and said first extract yields isobutylene exceeding a purity of 99 percent by weight.

Claim 10

The process of claim 2, wherein said second raffinate contains 0.14 percent by weight of isobutylene and said first extract yields isobutylene having a purity of 99.6 percent by weight.

Claim 11

The process of claim 5, wherein said second raffinate contains 0.14 percent by weight of isobutylene and said first extract yields isobutylene having a purity of 99.6 percent by weight.