CA1079307A - Dehydration of alpha-methylbenzyl alcohols to form monovinylidene aromatic monomers - Google Patents

Abstract

Abstract of the Disclosure .alpha.-Alkylbenzyl alcohol and substituted .alpha.-alkyl-benzyl alcohols are converted in high yield and purity to styrene and substituted styrenes by contacting the alcohol in vapor phase with silica gel and steam.

Description

io~,g3~

This invention comprises a process for the vapor phase dehydra-tion of ~-alkylbenzyl alcohols and substituted analogues thereof to form styrene and sub-stituted styrenes.
Dehydration of alcoh~ls to their corresponding unsaturated structural compounds is well known in the art.
; Dehydration techniques are not generally employed in the manufacture of styrene and many homoloyues thereof because standard dehydrogenation of ethyl benzene is considered to be a more economic route. In addition, styrenes produced by conventional dehydration techniques o~ten contain enough ethyl benzene and other impurities to require extensive purification.
It is characteristic of standard dehydrogenation techniques employed in the production of styrene that fairly large quantities of unreacted ethyl benzene be present in the styrene fraction~ Such quantities of ethyl benzene in the styrene fraction are substantial enough to cause loss of properties in polymers of such styrenè fractions. Fur- ~:
thermore, due to the closeness of the boiling points of styrene and ethyl benzene, removal of ethyl benzene by distillation is expensive.
Moreover~ normal dehydrogenation of many substi-tuted ethyl benzenes, particularly the tertiary alkyl sub~
~` 25 stituted ethyI benzenes, destroys or alters the substituted : :
group. For example, dehydrogenation of ar-~t-alkyl)-ethyl benzene to form;thelr corresponding styrenes usually results in nlpture~and/or loss of the t-alkyl group as well az dehydrogenation of the athyl group.

:
:: :: . :
~., : : ~ :
~ 14,774A-F

;: :: : :

~0'~3~'Y

Attempts to prepare ar-(t~alkyl)styrenes by con-ventional dehydration of the corresponding ar-(t-alkyl)-a--methylbenzyl alcohols have not been satisfactory due to the formation of other byproducts and the rupture of the t-alkyl group which frequently accompanies dehydration.
As a result of this ruptl~e, appreciable quantities of ethyl benzene and under certain conditions, diole~inically unsaturated aromatic monomers are foxmed in addition to the desired ar-(t-alkyl)styrene. These diolefinically unsatu-rated aromatic monomers, e.g., ar-(i-propenyl)styrene in dehydration of ar-(t-butyl)-~-methylbenzyl alcohol, are very difficult to separate from the de~ired ar-(t-alkyl)styrene.
During polymerization of the ar-(t alkyl)styrene monomer, the diolefinically unsaturated aromatic monomer acts as a crosslinking agent thereby producing a substantially cross~
linked styrene polymer which is insoluble in many organic solvents such as toluene and benzene. Thi~ lack of solu-bility is undesirable in many applications employing such styrene polymers.
Conventional dehydration techniques for preparing sty~ene and substituted styrenes are not completely satis factory in that substantial amounts of ethyl benzene and othçr~difficult to separate impurities often remain or are produced~ Such difficulties ha~e been pointed out in U.S.
,.
Patent No. 2,399,395 and U.S~ Patent No~ 3,442,963, ~or ; example.~ ~
Therefore, it would be highly desixable to pro- -vide a new, improved technique for produ¢ing styrene and substltutéd styrenes in high yield which contain little or no ethyl benzene and other impurities, particularly diole-finicalIy unsaturated aromatic monomers.

: ~ : ,. .. .
~ 14,774A-F ~ -2-; ~ `"^''"''"'' 10~930~

Accordingly -the present invention is an improved process for dehydrating ~-alkylbenzyl alcohols and to form the corresponding styrene monomer in high yield and purity.
The present invention resides in a process for preparing a monovinylidene aromatic monomer by dehydrating an a-alkylbenzyl alcohol represented by the general formula R R OH
R ~ fH2 R R Rl H : :.
wherei.n R is hydrogen, alkyl having from 1 to 12 carbon atom3 or halogen and Rl is hydrogen or alkyl having 1 to 4 carbon atoms, comprising the step of contacting the a alkylbenzyl alcohol in vapor phase with a dehydration catalyst con-sisting essentially of silica gel in the presence of from 0.03 to 25 parts by weiyht of added watsr per part by weight of alcohol, said dehydration step being carried out at temperatures from 200 to 510~C.
: Prior art teachings indicate that water produced during dehydration of an alcohol should be removed from the reaction mixture ln order to move the reversible dehydra- -tion reaction to the right and thereby increa~e the yield ;:
: of the unsaturated productO In the process of this in vention, a siIica gel of a type which has hereto~ore 25~ often been employed as a support for another catalyst , ~ . .
is used as the dehydration catalystO Surprisingly, in the practice of this process, it is found that the presence .
of water, (p:referably aceomplished by addition of from 0.03 to 25 weight parts per weight part of alcohol ~ to;the al~cohol~prior to dehydration and/or during -,, .
~ ~'4,77-A-F ~ _3_ .

~ 3~

dehydration)~ efEectively increases the yield of the desired styrene and substantially reduces, and under optimum conditions, almost completely eliminates the formation of ethyl benzene and other impurities which are difficult to separate, In general, the desired monovinylidene aromatic monomer is produced in purity greater than about 99 mole percent and contains less than about 1, preferably less than about 0O5 mole percent of alkyl benzene impurity, so-called ethyl benzene impurity.
As a result, styrene monomers produced by this method require little or no further purification to remove impurities having boiling points nearly the same as the monomer; thus expensive dis~illation procedures are elim- ;
inated. Styrene polymers produced from these styrene monomers are found to have improved properties as a result of the increased purity. As a result of low concentrations, i.e., less than 0.02 mole percent based on total monomer, of diolefinic impurity, ar-(t-alkyl)styrenes produced by this process can be polymerized directly into polymers which are soluble in toluene, benzene and other organic solventsO Such organic soluble polymers are particularly useful in various coatings~ thermoplastic moldings, reactive diluents, polyester varnishes and chemical applications that require a monomer essentially free of diolefinic species.
For the purposes of this invention, the term "a-alkylbenzyl alcohol" includes ~-alkylbenzyl alcohols, .. ~ . - , .-:
especially ~-methylbenzyl alcohol and substituted analogues ` thereof. Such aIcohols are represented by the general ~ : ~.,~
formula-14,774A-F -4-~ 30'~

R R OH
R ~ C - CH2 wherein R is hydrogen, alkyl having from 1 to 12 carbon atoms, e.g., for example, methyl, t-butyl, t-amyl and other t-alkyl; halogen, e.g., for example, bromo, chloro, and fluoro; and Rl is hydrogen or alkyl having from l to 4 carbon atoms.
Exemplary a~alkylbenzyl alcohols include, for example, a-methylbenzyl alcohol, ar chloro-a-methylbenæyl alcohol, ar-bromo-~-methylbenzyl alcohol, ar-fluoro-a--methylbenzyl alcohol, ar-dichloro-a-methylbenzyl alcohol, ar-dibromo-ar-chloro-~-methylbenzyl alcohol, ar-chloro--~-ethylbenzyl alcohol, 4-chloro-2,5-difluoro-~-methyl-benzyl alochol, ar-(t~butyl) a-methylbenzyl alcohol, ar-chloro-ar-(t-butyl)-~-methylbenzyl alcohol, ar-bromo--ar-~t-butyl) a-methylbenzyl alcohol, ar-(t-amyl)-a--methylbenzyl alcohol, ar,~-dimethylbenzyl alcohol, -ethyl-2-isopropyl-5-methylbenzyl alcohol, or a-iso- ~ -::
butyl-2,4,5-trimethylbenzyl al~ohol.
Preferred ~ alkyl benzyl alcohols are -methyl-benzyl alcohol, ar-halo-~-methylbenzyl alcohol such as ar-chloro and ar-bromo u-methylbenzyl alcohol and ar--(t-alkyl)~-m~thylbenzyl alcohols such as p-(t-butyl)-~;25~ -methylbenzyl alcohol, p-(t-amyl)-~-methylbenzyl alcohol and sl~ilar a]cohols ~herein t-alkyl has 4 to 8 carbon :
atoms. The abo~e alcohols are known compounds and can be prepared by synthasis obvious to those skilled in the art. ~IllustraLtively, ar-alkyl-~-methylbenzyl alcohols :

~ 14,774A-F~ -5-:
~ ~ , ~07~3~J

can be prepared by the stepwise synthesis of (l) alkylating ethyl benzene with olefin in the presence of sulfuric acid in accordance with the me1:hod of Ipatieff et al., J~CS, Vol. 58, 9l9 (1936)J

. .

~ 14,774A-F -Sa- .

~0~3a~

(2) oxidizing the alkylated ethyl ben~ene to the corres-ponding acetophenone-alcohol mixture as described by H. J~
Sanders et al., I 6 E Chem, Vo] 45, 2(1953), and (3) reduc-ing the mixture by catalytic hydrogenation to the desired alcohol.
The silica gel employed in this invention may be in any of the several forms of silica gel which will permit intimate contact between the silica gel and alcohol vapor during the dehydration. It is desirable that the silica gel be in the form of a divided solid, pre-ferably in the form of particles not measuring more than about an inch in any dimension. Further the silica gel should be of a type that is not decJraded or des~royed when contacted with large quantities of water. Although good results are obtained with a number o grades of particulate silica gel, bes~ results are obtained with the silica gel in the form of a particulate solid having a mesh size ranging from 2 to 400 and a surface area of at least about 300 square meters per gram, preferably from 300 to 900 m2/g. Of special preference are the commercial grades of silica gel that have here~ofore been employed as sup ports for other catalysts. In these preferred ~mbodiments~
the possibility of complete contact be~ween the silica gel and the alcohol is maximized. It is especially pre-ferred that the sLlica gel be inely divided porous particles having an average pore diameter ranging from 2 to 200 Angstrom UnitsO Methods for preparing silica gel are well known to skilled artisans. Also any of several com-mercial grades of silica gel fitting the above general description may be employed.

14,774A-F -6-~ .

~ 3~

In the practice o~ this invention the u-alkyl-benzyl alcohol in vapor phase ls contacted with the silica gel in the presence of from 0.03 to 25 parts by weight of water per part by weight of alcohol~ preferably from 0.5 to 20 weight parts, especially from 1 to 2 parts of water per weight part of alcohol. It is generally pre-ferable that the alcohol be inl:imately mixed with specified amounts of water in the form of steam prior to dehydration.
This is easily accomplished by passing liquid or vaporous mixtures of the alcohol and water over or through a bed or column of an effective heat transfer material such as silicon carbide, fused ceramic packing or non-corrosive metal packing. In such embodiments, a column having a lower portion of a bed of silica gel and an upper portion of the heat transfer agent can be made and the alcohol containing water is then passed dow~ward into the column through the heat transfer agent and then through the silica gel bed. It is often desired to employ an organic carrier liquid which is a solvent for the alcohol, e.g. t toluene or benzene, but which can be easily removed by simple distillation. In such embodi~ents, the alcohol and ~ carrier liquid are mixed together prior to vaporization ; ~ of the alcohol mixture. It is understood that the addition of water to the reaction may be made after the alcohol has passed through the heat transfer agent. Also the ; water need not be added in the form of steam or super-heated steam although it is preferred to do so.
Generally, the desirable temperatures of opera- -.
~ ~ ~ tion of the process of this invention are in the range of .: , ~ 3Q ~ 200'C to 510"C, preferably from 260QC to 500C, especially ~, : :

~ 14,77~A-F ~ ~7~

~ 30'~

from 300 to ~00C. In the dehydration of ar-(t-alkyl)--~-methylbenzyl alcohols, it is desirable to employ dehydration temperatures above 260C, preferably from 325C to 425C, in order to insure contact between the silica gel and the alcohol in the vapor state. It is generally desirable to carry out dehydration at atmospheric pressure, although it is possible to achieve dehyclration with relatively good purity and yield at subatmospheric to superatmospheric pressure, e.g., from 0.2 to 5 atmospheres. Vaporization of the alcohol, however, may be advan~ageously achieved by using reduced pressure. Vaporiæation may also be achieved by contacting the alcohol with steam or super-heated steam substantially prior to dehydration~
The quantity of silica gel which effectively dehydrates the alcohol depends in part upon the rate at which the vaporous alcohol is to be passed through the silica gel bed or column, upon the surface area of the gel per unit of weight, upon the amount of water to be employed.
Generally higher vapor flow rates and larger quantities of water require more silica gel to achieve effective dehy-dration.
Practice of the present invention as described hereinbefore yields the desired monovinylidene aromatic monomer, particularly the ar-(t-alkyl)styrene, in purity greater than 99 mole percent based on total product after simple distillation which removes unreacted ketones and alcohols. Accordingly, the alkyl benzene impurity is held below about 1, preferably below about 0.5 mole percent.
In the dehydration of the ar-(t-alkyl)~-methylbenzyl alcohols by the method of this invention, diolefinic and .
'~

14,774A-F -8-~0~93~

other polyolefinic impurity is held below 0.02 mole percent based on total procluct after simple distillation.
The invention is urt:her illustrated by the Eollowing examples which shoulcl not be construed as limit-ing the scope of the invention. ~11 parts and percentages are by weight unless otherwise indicated.
Example l A first mixture of 50 parts of ~-methylbenzyl alcohol and 50 parts of toluena is preheated to 300C and mixed with 100 parts of steam at 300C. The resulting steam/alcohol mixture is passed downward at a rate equi-valent to that employed in Example 2 through a glass coL~In (l" outside di~meter x 27" length) e(~ui~ped with an electric furnace and containin~ a 14-incll upper layer of silicon carbide (8 mesh) preheated to 350C and a 6-inch lower layer (20 g) of silica gel (on 10 mesh, 300 m2 of surface area/g and having a pore volume of 1 cc/g, sold as a catalyst support under the trade name Davison Silica Gel Grade 57 by Davison Chemical). Water and dehydrated organic product are condensed in the lower part of the column, collected and separated4 The organic product is dried and distilled. The distilled product is determined by inrared spectroscopy and vapor phase chromatography .:: -.
to be 99~ mole percent styrene containing less than 0.5 mole percent of ethyl benzene. Overall yield on the basis of starting alcohol is greater than 95 percent.
Example 2 ~ ~
A~mixture of 50 parts of 4-(t-butyl)-~-methyl- - ~;
benzyl alcohol and 50 parts of toluene is prepared. A
reaction col~n (l" outside diameter x 27i' length) is filled to a bed height of 8-9 inches with silica ~el (8-10 ~: ' ,' ' 14,774A-F ~ -9-~O~9307 mesh, 340 m2 of sur~acc area/g, 140~ average L)ore cliameter and sold as a catalys-t support under the trade name D~vison Silica Gel Grade 70 by Davison Chemical) and sufficient amount of silicon carbide (6 mesh) is added to the tube to increase total bed height to 16 inches. The reaction column is heated to 300C. Water preheated to 300C and the mixture are added simultaneously into the feed end of the column at rates of 9~ m:L~hr and 45 ml/hr re-spectively. An intimate admixture of steam and the alcohol mixture in vapor phase i~ formed and passes down-ward through the silicon carbide preheated to 350C which acts as a preheat section for the vapor and then through the silica gel to effect dehydration~ Following passage through the silica gel, water and organic product are con-densed in the column, and collected. The dehydrated organic product is decanted, dried a~d distilled. The distilled product is determined by infrared spectroscopy and vapor phase chromatography to be 4-(t-butyl)styrene at 99 percent or greater purity. Overall yield on basis of amount of starting alcohol is ~reater than 90 percent.
Polymerization of the 4-(t-butyl)styrene by heat-ing in the presence of benzoyl peroxide yields a polymer which is soluble in toluene at 20C.
Example 3 Several sample runs are carried out generally -~-according to the procedure of Example 2. In these runs, mixtures of 50 parts of 4-(t-butyl)-~-methylbenzyl alcohol --~-and 50 parts of toluene are prepared and mixed with varying ~-amounts of steam. The vaporous steam-alcohol mixture is ~ 30 passed downwaxd into a glass column (1" OD x 27" length) :: : . :~ 14,774A-F -10- -~ ' ,'.

: :- . . ~. :~. .

~J930~

having a 14" upper bed of silicon carbide (10 mesh) pre-heated to varying temperatures and a 6" lower bed of silica gel (same as in Example 2). ~ater and dehydrated organic product are condensed, collected and separated as in Example .
2. The results are recorded i:n Table I.
To show the ~articulax advantage of employing added water in this system, a control run (Cl) is made under conditions similar to the above runs with the ex-ception that no water is added to the alcohol at any point prior to or during dehydration, the results of this control run are also recorded in Table I~ To indicate upper limits :
as to temperature during dehydration, two control runs (C2 and C3) employing varying amounts of ~water are also carried out in accordance with the procedures employed in the above sample runs. The results are recorded in Table I.

... .:
: '"'- :"' : :

~ ~ , :, . . .

, .

~ 14,774A-F -11-~: ;

930'~

a) a .,, a~ a) a) O a) a) R R
e ~ R .4 Q Q .R .4 R R ,LI R ~1 --I ~
~ ~:1 ~ 1 0 0 0 oo o o o o o o o o o o a a u~ 1 H H

O~
,1 -I e ~
~a) ooooooooooo~1~1 N
_, ~ ~
U~ ~ ~q O
r~
O dP
h ~ ~1 H ~ 0 H a) ` N ~ ~ ~I CO
Q, O o o _I ~1 ~1 :.
~1 O
1 h O O O O O O O O O O O O O O :
h V V ~ A
~¢ O ~ ' E~ u~ O
U~ ' .. .
. , ~1 o ~
o ~ ~ O co ~ O O O
) ~ o o ~ a~ ~r o o ~ o o u~.
h ~ .

: , ' .

: ~ ~ : .

O h 0 ~ ~ 0 o O ~ ~ o U~ - .
f~ U)~i~0 oooooooooô' '-14, 7 7 4A--F ~ 12-- : ~

g3~q U
o ~i a a ~
U) .~
.
s: ,, ~ , a) -- .
'd I ~
Q Ql ~,) 4~ 0 o O U ~
U U~ ~ . ...
O : ,-o -1 ~ ,a U O U
,-1 ~1~G' ::1 m o ~1 .. ~ ~"1 a) o O C) S~
U~
O ~ h ,S:~
,~ G' H ,~
~:1 ~ 'o o U~~1 0 ~ ' '' oa) ~
2, 0 ~ :
S ~ ~' u ~ ~:

o ~
o . : ~a~ o ~ ~ R 40 o ~q 14 :~ ~7 7 4A--F~ 13--~ 3 Example 4 Several sample runs are carried out e6sentially according to Example 2 except that a wide range of temper-atures are employed~ In the several runs, mixtures of 50 parts of ar-(t-butyl)-~-methylbenzyl alcohol containing ~7 mole percent of ar-(t-butyl)acetophenone and 50 parts of toluene are prepared. A glass column (l" OD and l6"
length) equipped with an electric furnace is filled to a heiyht of 3.5" with silicon carbide (8 mesh, 42 grams), to a total height of 13.5" with silica gel (same as in Example 2, 50 grams), and to total height of l6.0" with s.ilicon carbide (8 mesh, 40 grams) and preheated to varying temperatures from 200 to 500C for the several runs.
Steam superheated to at least 550C and the alcohol/toluene mixture are added simultaneously into the feed end of the column at rates of l00 ml/hour (measured as condensed water) and 50 ml/hour respectively, An intimate admixture of steam and the alcohol mixture in vapor phase is formed and passes downward through the heat transfer agent and the silica gel to effect dehydration. The water and organic product are then condensed, collected and separated. The ~ ..
organic product is distilled and dried, and its constitu- :
ency is dete.rmined by infrared spectroscopy and vapor phase chromatography. The xesults are shown in Table II. .
.:
.:

' --14,774A-F

:-: :., , . ., . ~ , ! ' ' , . , . ~ , ': ', ~ 30'~

To point out the advantage of silica gel cata-lysts over conventional dehydration catalysts, several control runs (C4-C8) are made employing essentially the same procedure used above except that a titania dehydration catalyst (4-8 mesh, and 70 m2 of surface area/g) is substituted for silica gel. The dehydra~ion column has a 3.5" bottom layer of silicon carbide (8 mesh), a 10"
middle layer of titania catalyst and a 2.5" top layer of silicon carbide. The organic product is recovered and analyzed by infrared spectroscopy and vapor phase chroma-tography and the results are recorded in Table IIo :: :

:
.

~~14,774A-F 15- ~ ~
. ,~ , .: , .

~L0793~)'7 I ~o ~, ,~ o ~ t) Q Q) O
I~'1 r~IIIIII I III
~ I :~
_ ~3 N
I I
5~ ~
(~ Q

~ O
o~o ~ O
.
~1 R
~3 o ~ ~r ~r ~ ~1 ~ u~
I ~
~ h C) a) ~ ~ . .
~ I ~ , -,, .IJ r-l N
O ~ Q
O Q
1 ~1 O o O O O O O O .-1 11~ ~ ' ' H .IJ _ ,~ ~1 H 'Cl ~1 a) 1 O I~) I :.
~ ~ ~ . ' ' '.

. . ~ . . . . . . . . .
,:' -`~ ~ ~ ':

: ~ O ~ O ~ O ~ O ~ 0~ td rl .'' ' ' ~ ~ : 0: ~ rl h rl h rl1~ rl ~

O ~ o o o o o o o o o o o ~ , ::
~: o o o o o o o O O o O O
: u~ o U~ o Lt~ o u~ O u~ O In E~ X ~, :

Z ~: ~ : *~ ~ *~ *a~

14, 774A-F ~ : -l6~

: ~ :

~ 93~

AS eviclenced by Table II, signii-icantly larger quantities of ar-(t-butyl)-ethyl benzene are generally produced in dehydrations employing titania as catalyst than those employing silica geL under essentially the same conditions. The ar-(t-butyl)-ethyl benzene is dii-ficult to separate from ar-(t-butyl)styrene whereas ar~(t-butyl)-acetophenone is separated from either of the above by simple distillation, Example 5 A solution of 50 parts of ar-(t-butyl)-a-methyl-benzyl alcohol containing ~7 mole percent of ar-(t-butyl)-acetophenone in 50 parts of toluene is mixed with super-heated steam (550C) in a ratio of 2 parts of water to one part of tha mixture. The steam-alcohol mixture is passed downward through a glass column (1" OD x 21" length) con- -taining a 10" upper layer oi- silicon carbide and a 10"
lower layer of silica gel (same as in Example 2). The temperature at the top of the column is 350C and at the bottom of the column is 325C. The water and organic pro-duct i5 distilled and dried, and its constituency is deter-mined by infrared spectroscopy and vapor phase chroma-~
tography. The results are shown in Table III.
For the purposes o comparison a control run (C
is carried out by following the above process except that alumina (4-8 mesh and 210 m2g of sur~ace area/gram~ is substituted i-or~silica gel as dehydration catalyst. The organic product is distilled and dried and its constituency is de~ermined~by the means described above~ The results are also recorded in Table III.
. :

:~, :: :
~ 14,774A-F 17-.. . ~ , , " .

w ~: l O ~ R
W I
~ 1 ~0 ,1--1 0 Q~ Q
~ >1 0 "o ~) ,1 R R v c~
I I ~1 ~ ~) ~
__ N
Ll h W

a) ~
:~ N
~1 _ ~ ~ ~ ~ o ,1 ~ ~ .
~3 R R o o O _ _ F Ll Ll ~ 0 1~
H ~~ C~
H u~,.1 ~
H O~ N
U ~ h' ~~ R o oo E~ ~, I ~ o O 5~ ~
~ 0 aJ
i : .
. . .
~ ~ r' .4 )-I I~
I
o ~ 0 :~ F. H .. .
O a~ N
.4 ~ o u~
~n O
~ :

O r~lr-l ~ ~ ' 11~ ~
O ~ 0 0 0 * ~,1 , 'I ~; ~ O :

14, 774A--F -18 ~ :
.::
- , .

.. . . . ; . .

~ 93~'~

Exam~le 6 The dehydratlon process of the pre~ent invention is carried out in a continuous manner by continuously ~ee(l-ing molten ar-(t-butyl)-a-methylbenzyl alcohol at 200 lb/hr and water superheated to 550C at 400 lb/hr into a column (18" OD x 6'8" length~. The column contains a 3'4" upper bed of metallic heat transfer material preheated to 350C
and a 3'4" lower bed of silica gel (same as in Example 2).
The temperature at the lower end of the column is 325C.
The dehydrated orgarlic product is continuously collected at the lower end of the column and then recovered at 99~ percent purity by simple distillation. The de-hydrated product is determined by infrared spectroscopy to be ar-(t-butyl)styrene.
Example 7 Several samples of ar-chloro a-methylbenzyl alcohol containing small amounts of ar-chloro-acetophenone are continuously dehydrated hy mixing the liquid alcohol with varying amounts of superheated s~eam ~550C) and passed as vapor phase through the column descri~ed in Example 3. Dehydration temperatures for the various runs are also varied. The amounts of low boiling components are shown in Table IV. .:
For the purposes of comparison, similar samples of ar-chloro~ methylstyrene also containing small amounts . .
of ar-chloro~acetophenone are continuously dehydrated ln the same manner except that no water is added during the process. The amounts of low boiling components for these . .~ :
( 10 r Cll ~ Cl2) are also shown in Table IV
. ~'-' ' .

:14,774i-F : -l9 ~lO~31~

U~
a) ~ ~
.,, ~ Ul o ,1 aJ ~ o )-I h 1l1 ~1 ~ ~ ~ o E~ ~ o ~ ~ or~l H O . . . . . . . ~--1 5~ ~ r~ ;r o ~ o r~
~, O \ c~ ' c' c~ ~' N
-~ ~ ~
,~ y S~
O h Q~ ~
m ~
r~ Ei h o ~ ~~r o t~ r O
o o o O o ~ 0 0 O
U~
~) ~ ~ a~
a) ~, ~: s~ o ~: ~ ~ ~ o O ~ I N o co co Q~ ~ O ~ ~I co co ~1 oo E~ ~1~ ~1 0 O ~ ~1 O ~ ,-1 o~1 o o o ~1 ~ O
~. .~ 0~1 ..
tl~ O U~ O ~: ~ ~ :
) I -~ O
.,, ,, ~, ~1 a) ~ o d ~ I a~
,1 ~ Q.
H O a) ~ ~ . .
~4 ~; I O .
L.l ~ ~ S l .~
~4 O O O O C~ cn O r~l O
~1 ~: ~ ~I c~ cn cn ,. ~ , . . . O ~1 h I ~ ~D 1`Lt~I~ In 1~ ~P O
~1 a~
d u~
C~ ~,X :, ~: I ~ ~ ,:
O ~ --I O
~rl ~ O O O O O O O O ~ ~ ~.. .
: ~ : O O OIn L0 O O rl ~rl 0 ~ a) ::
E~ , ,~
O rl .
'0 ~ O f~

~ o~ In o ~r~ o o o

3 x a) u~ ,., . "

O ~ ~ O O .' )r~lIt) ~1 Z Z
X c~ * ~c r-l ::: : :
14, ~ 7 4~-F: ~ : ~ 2 0- . :

. .
, :,, ~. , :, , -: ;, ,; . : ~ . -~7~3~7 Examples 8-13 -In accordance with the con-tinuous dehydra-tion process of Example 3, several substituted ~-methylbenzyl alcohols are dehydrated to the corresponding substituted styrenes thereof. The results obtained are comparable to khose obtained in Example 3. The alcohols successfully dehydrated are as follows:
ar-t-butyl~ -dimethylbenzyl alcohol ar-dichloro-~-methylbenzyl alcohol ar-dibromo-a-methylbenzyl alcohol ar-di-t-butyl-a-methylbenzyl alcohol ar~tl-ethyl l-methylpentyl)-~,-methylbenzyl alcohol ar-t-butyl-ar-methyl-~-methylbenzyl alcohol.
Several dehydration runs are also carried out -~
using silica gel catalysts having different mesh sizes in the range from 2 to 400 and surface areas in the range from 300 to 900 m2/g with good results.
''.
, :, :"
~: .' ' . .

.

., ~ : :

~ 14,774A-F i -21-,

Claims (16)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A process for preparing a monovinylidene aromatic monomer by dehydrating an .alpha.-alkylbenzyl alcohol represented by the general formula wherein R is hydrogen, alkyl having from 1 to 12 carbon atoms or halogen and R1 is hydrogen or alkyl having 1 to 4 carbon atoms, comprising the step of contacting the .alpha.-alkylbenzyl alcohol in vapor phase with a dehydration catalyst consisting essentially of silica gel in the presence of from 0.03 to 25 parts by weight of added water per part by weight of alcohol, said dehydration step being carried out at tem-peratures from 200° to 510°C.

2. The process according to Claim 1, wherein the water in the form of steam is mixed with the .alpha.-alkylbenzyl alcohol prior to contacting the alcohol with silica gel.

3. The process according to Claim 1, where-in the silica gel is in the form of a divided solid having a surface area of at least about, 300 square meters/gram.

4. The process according to Claim 3, wherein the silica gel is divided, porous solid having an average pore diameter ranging from 2 to 200 Angstrom units.

5. The process according to Claim 1, wherein the alcohol is ar-chloro-.alpha.-methylbenzyl alcohol.

6. The process according to Claim 1, wherein the alcohol is .alpha.-methylbenzyl alcohol,

7. The process according to Claim 1, wherein the alcohol is an ar-(t-alkyl)-.alpha.-methylbenzyl alcohol.

8. The process according to claim 7, wherein the t-alkyl is t-butyl.

9. The process according to Claim 7, wherein the t-alkyl is -t-amyl.

10. The process according to Claim 1, wherein the proportion of added water is from 0.5 to 20 parts per weight of alcohol, the temperature of the dehydration step is preferably from 260° to 500°C, and including the step of distilling the dehydration product to obtain the mono-vinylidene aromatic monomer in purity greater than about 99 mole percent and containing less than about 1 mole percent of alkylbenzene impurity.

11. The process according to Claim 1, wherein said monovinylidene aromatic monomer is an ar-(t-alkyl)-styrene prepared by dehydrating said .alpha.-alkylbenzyl alcohol, said dehydration step being carried out at temperatures from 260° to 500°C, and distilling the dehydration product to obtain the ar-(t-alkyl)styrene in purity greater than about 99 mole percent and containing less than 0.02 mole percent of diolefinic impurity.

12. The process according to Claim 11, wherein the alcohol is ar-chloro-ar-(t-butyl)-.alpha.-methylbenzyl alcohol.

13. The process according to Claim 11, wherein the alcohol is ar-bromo-ar-(t-alkyl)-.alpha.-methylbenzyl alcohol.

14. The process of Claim 11, wherein the alcohol is ar-(t-butyl)-.alpha.-methylbenzyl alcohol consisting essen-tially of the meta and para isomers thereof, and employing from 0.5 to 20 parts by weight of water per part of alcohol and a temperature within the range from 390°C to 505°C.

15. The process according to Claim 1, wherein said contacting step comprises passing a vapor phase of an ar-(t-alkyl)-.alpha.-methylbenzyl alcohol and from 0.5 to 20 parts by weight of water in the form of superheated steam per part of the alcohol through a column containing a heat transfer agent and said dehydration catalyst in the form of a divided solid having a surface area of at least about 300 square meters per gram, said process being carried out at a dehydration temperature from 260° to 425°C such that the alcohol is dehydrated.

16. The process of Claim 15, wherein the dehy-dration temperature is in the range from 325° to 425°C.