Molecular sieve abstract
The present invention provides a process which is adapted for cyclodimerization
of 13-butadiene to 4-vinylcyclohexene under Diels-Alder conditions
in the presence of a large-pore carbon molecular sieve.
Molecular sieve claims
What is claimed is:
1. A process for cyclodimerization of a conjugated alkadiene which
comprises contacting a conjugated alkadiene-containing feedstock
with a large-pore carbon molecular sieve.
2. A process in accordance with claim 1 wherein the carbon molecular
sieve has an average pore size in the range between about 8-100
angstroms.
3. A process in accordance with claim 1 wherein the reaction is
conducted at a temperature between about 150.degree.-300+ C.
4. A process in accordance with claim 1 wherein the conjugated
alkadiene is 13-butadiene, and the cyclodimerized product is 4-vinylcyclohexene.
Molecular sieve description
BACKGROUND OF THE INVENTION
This invention relates to a catalytic process for the cyclization
of alkene compounds, as exemplified by the cyclodimerization of
13-butadiene to 4-vinylcyclohexene.
U.S. Pat. No. 3444253 discloses and claims a process for the
dimerization of 13-butadiene to produce 4-vinylcyclohexene-1 using
copper(I) zeolite X, or copper(I) zeolite Y. The present invention
represents an effective alternative to the process of said patent.
DESCRIPTION OF THE INVENTION
It has been found that a high Diels-Alder conversion can be obtained
by utilizing a large-pore carbon molecular sieve catalyst for cyclodimerization
of a conjugated alkadiene-containing feedstock.
The term "large-pore" refers to a non-crystalline carbon
form of a molecular sieve having an average pore size in a range
between about 8-100 angstroms.
A suitable type of molecular sieve for utilization in the invention
process is exemplified by a commercial product such as Carbosphere.RTM.
(Alltech Associates). This type of spherical carbon molecular sieve
has a surface area of about 1000 m.sup.2 /gm, and has a pore size
of about 13 angstroms. The mesh size of the carbon molecular sieve
can be obtained in ranges varying between about 60-80 mesh and 120-140
mesh. The packed density of a carbon molecular sieve in the form
of hard dense beads is about 0.6 g/cc.
The invention process is particularly advantageous for cyclodimerization
of 13-butadiene. The cyclodimerization of 13-butadiene proceeds
as follows to yield 4-vinylcyclohexene: ##STR1##
Other alkadienes which can be cyclodimerized are illustrated by
isoprene, chloroprene, 13-pentadiene, cyclopentadiene, and the
like. The cyclodimerization also can be effected between different
conjugated dienes, dienes and monoalkenes, dienes and acetylenes,
and the like. For example, maleic anhydride can be reacted with
cyclopentadiene. Conjugated alkadienes can also be co-cyclized with
alkynes such as dimethylacetylene.
An important advantage of the invention process is that high conversions
are obtained with a copper-free catalyst, as opposed to the prior
art methods of carrying out said reaction in the manner previously
described. The invention process can be conducted in several ways,
such as a continuous process or a batch process. The 13-butadiene
dimerization, for example, can be accomplished at temperatures in
the range of about room temperature to temperatures as high as 400.degree.
C. or 500.degree. C. However, the preferred temperature range is
about 150.degree. to 300.degree. C. The reaction preferably is conducted
at a pressure between about 1-1000 psi, and the product is recovered
from the reaction mixture by standard procedures such as fractional
distillation or the like.
It was unexpected that a Diels-Alder reaction such as the cyclodimerization
of 13-butadiene to 4-vinylcyclohexene could be significantly catalyzed
by a molecular sieve not containing copper in the plus one valence
state as has heretofore been the case with prior art zeolites (e.g.,
as described in U.S. Pat. No. 3444253).
It is an important aspect of the invention process that the cyclization
product resulting from the catalyzed Diels-Alder reaction must have
sufficiently small molecular dimensions to permit the diffusion
of the said product out of the large-pore structure of the carbon
molecular sieve catalyst. |