Production of iso olefin oligomers

A tertiary alkanol such as tertiary butyl alcohol is converted in one step to an oligomer of the olefin corresponding to the alkanol by reacting a homogeneous solution of the alkanol and an acid catalyst at conditions effective to form the oligomer.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to the conversion of tertiary alkanols such 
as tertiary butyl alcohol to oligomers of the corresponding iso-olefin in 
a one-step liquid phase process using a homogeneous catalyst such as 
methane sulfonic acid. 
2. Description of the Prior Art 
The dehydration of tertiary alkanols such as tertiary butyl alcohol to the 
corresponding olefin is a well known reaction. See, for example, U.S. Pat. 
Nos. 5,475,183, 3,665,048, and the like. Catalysts such as alumina, 
methane sulfonic acid, and the like have been used. 
Further, it is known that tertiary alkanols such as tertiary butyl alcohol 
can be directly converted to oligomers of the corresponding iso-olefin in 
one step using solid heterogenous catalysts such as zeolite Beta. See U.S. 
Pat. No. 5,157,192. 
There are, however, problems associated with the heterogeneous catalyst 
systems. Product separation is a problem as is control of the reaction and 
the removal of heat in heterogeneous systems. In addition, condensation 
products tend to accumulate on the solid catalyst surfaces leading to a 
rapid decline in catalyst activity and the necessity for frequent 
reactivation. 
SUMMARY OF THE INVENTION 
In accordance with the present invention, a tertiary alkanol is contacted 
in the liquid phase with a homogeneous acid catalyst at conditions 
effective for the selective formation of dimers and trimers of the olefin 
corresponding to the tertiary alkanol. In especially preferred practice, 
tertiary butyl alcohol is converted in high yield and selectivity to 
diisobutylene and triisobutylene through practice of the invention.

DETAILED DESCRIPTION 
Tertiary alkanols which are reacted in accordance with the invention 
preferably are tertiary butyl alcohol and tertiary amyl alcohol; other 
tertiary alkanols can be reacted. 
The tertiary alcohol conversion is carried at conditions effective to 
convert at least about 50% of the tertiary alkanol, preferably 60 to 98% 
to dimers and trimers corresponding to the olefin derivative of the 
alkanol. Pressures employed are sufficient to maintain the liquid phase, 
illustrative pressures are 20 to 200 psia, preferably 40 to 100 psia. 
Reaction temperatures are effective to achieve the above indicated 
conversions of tertiary alkanol to the dimer and trimer of the 
corresponding olefin. Suitable temperatures range from 50.degree. to 
150.degree. C., preferably 60 .degree. to 90 .degree. C. 
Reaction times range from about 30 to 120 minutes, preferably 60 to 100 
minutes. 
The use of a homogeneous acid catalyst is essential to practice of the 
invention. Organic sulfonic acids are preferred. Methane sulfonic acid and 
para toluene sulfonic acid are especially useful. Other less preferred 
acid catalysts include sulfuric acid, phosphoric acid, and the like. 
The catalyst is used in amount ranging from about 10 to 60 wt % preferably 
30 to 50 wt %, based on total feed. 
Referring to the drawing, the conversion of tertiary butyl alcohol is 
illustrated. A homogeneous solution of tertiary butyl alcohol and catalyst 
is fed to reaction zone 1 via line 2. Reaction zone 1 preferably comprises 
an isothermal pipe reactor or other plug flow system. As the feed mixture 
passes through the reactor, reaction conditions are maintained to ensure 
the reaction mixture is in the liquid phase and to provide for the desired 
reaction. Tertiary butyl alcohol is converted to diisobutylene and 
triisobutylene, and the reaction mixture becomes a two phase liquid 
mixture. The reaction mixture exits reaction zone 1 via line 3 and passes 
to zone 4 wherein it is separated into an upper hydrocarbon phase 
comprised of diisobutylene and triisobutylene, and a lower polar phase 
comprised of unreacted tertiary butyl alcohol, water and catalyst. 
The hydrocarbon phase is removed via line 5, and the various components can 
be readily recovered by distillation (not shown). 
The polar phase is removed via line 6 and after purging water and other 
impurities (not shown) the tertiary butyl alcohol and catalyst values can 
be recycled to reaction zone 1. 
EXAMPLE 
A tertiary butanol feed (94% tertiary butyl alcohol) was admixed with 
methane sulfonic acid and fed to an isothermal pipe reactor. The weight 
ratio of tertiary butyl alcohol/methane sulfonic acid was 60/40. Residence 
time in the reactor was 1.6 hours and reaction conditions were 80.degree. 
C. and 60 psig. 
The reaction mixture was separated into an organic phase which contained 
less than 1% tertiary butyl alcohol and a polar phase which contained 
essentially no isobutylene or oligomers. 
Tertiary butyl alcohol conversion was 92% with 7% selectivity to 
isobutylene, 57% selectivity to diisobutylene, 33% selectivity to 
triisobutylene and 2% selectivity to tetraisobutylene. On an isobutylene 
free basis, the combined C.sub.8 plus C.sub.12 selectivity was nearly 98%.