Method for preparation of alkyl-substituted butadienes

A method for forming monoolefinic alcohols and optionally alkyl-substituted conjugated dienes. A lower alcohol is oxidized to the aldehyde, and the aldehyde separated from the product mixture by reaction with a monoolefinic alcohol to form a hemialdehyde. An aliphatic isomonoolefin is reacted with a portion of the hemialdehyde stream, to form additional unsaturated monoolefinic alcohol as product, and for recycle to the aldehyde recovery step. The unsaturated monoolefinic alcohol can be dehydrated to an alkyl-substituted conjugated diene such as isoprene.

FIELD OF THE INVENTION 
The invention relates to a method to produce monoolefinic alcohols. The 
invention also relates to a method to produce alkyl-substituted conjugated 
dienes. 
BACKGROUND OF THE INVENTION 
Monoolefinic alcohols have potential value in the production of 
alkyl-substituted conjugated dienes, such as isoprene. A convenient method 
of producing monoolefinic alcohols is to react an olefin such as 
isobutylene with an aldehyde. The aldehydes are readily produced by the 
oxidative treatment of a lower alcohol with a molecular oxygen-containing 
gas such as air. 
However, a limiting factor in the feasibility of the process has been the 
difficulty in extracting the aldehyde from the reaction mixture resulting 
from the alcohol oxidation step. The oxidation step reaction product 
mixture contains unreacted alcohol, aldehyde, and water, and tends to form 
various close boiling admixtures or even azeotropic admixtures in some 
instances. Separation by conventional means, such as by fractional 
distillation, is difficult, expensive, or commercially impractical. 
Efforts to separate the aldehyde by treatment with an extraneous solvent 
have been helpful, but have necessitated the use of an additional and 
expensive material which always poses the likelihood of product 
contamination and interference in desired reactions since some of the 
extraneous solvent tends to recycle. 
SUMMARY OF THE INVENTION 
I have discovered an effective and useful scheme which recycles in part a 
monoolefinic alcohol product of the process to form a hemialdehyde with 
the aldehyde contained in the product mixture resulting from the alcohol 
oxidation step. The hemialdehyde can then be readily separated such as by 
fractional distillation means. The separated hemialdehyde is contacted 
with an aliphatic monoolefin, such as isobutylene, forming the desired 
monoolefinic alcohol. The monoolefinic alcohol is recovered in part, and 
in part recycled for formation and separation of additional hemialdehyde. 
The monoolefinic alcohol product can be utilized as an intermediate in the 
production of chemicals, or can be dehydrated to form alkyl-substituted 
butadienes, such as isoprene, for production of desirable rubbers and 
resins. 
My process provides effective separation of aldehyde from the aldehyde 
production step by utilizing as the separating agent a product formed by 
my process and thus requires no extraneous solvent or added material. The 
process is simple, yet effective, and represents an economically practical 
approach to the production of monoolefinic alcohols and isoprene or 
substituted isoprenes.

DETAILED DESCRIPTION OF THE INVENTION 
My invention provides a straightforward method for recovery of aldehyde 
after its formation from an alcohol/oxygen reaction step, utilizing for 
this important recovery step a product of the process step of reaction of 
an isobutylenic with the aldehyde. As before emphasized, my scheme is 
illustrated, in order to assist those skilled in the art by particular 
reference to 
methanol/formaldehyde/isobutylene/3-methyl-3-buten-1-ol/isoprene. However, 
my scheme is not limited solely to these basic reactants but is useful and 
effective for a reasonable range of reactants. 
My process for the production of the monoolefinic alcohols and of 
alkyl-substituted butadienes such as isoprene comprises a series of 
reaction steps alternating with recovery steps, as illustrated in the 
attached block diagram. 
An essential feature of my invention is that the unsaturated monoolefinic 
alcohol formed in the process is at least in part recycled back to the 
absorption step to react with the aldehyde to form additional 
hemialdehyde. Thus, the unsaturated monoolefinic alcohol formed by the 
process is employed as a reactant to form and recover a hemialdehyde, and 
can also be used to form by dehydration the alkyl-substituted conjugated 
diolefin. My process scheme requires no outside solvent or reactant to 
extract aldehyde formed in the oxidation of alcohol, but rather utilizes a 
product produced by the process itself. 
Lower Alcohols 
The first step in my process is a formation of the aldehyde from an 
alcohol. The alcohols employed are the lower hydrocarbyl aliphatic primary 
alcohols containing one alcohol group. These alcohols also can be 
represented by the general formula: 
##STR1## 
wherein R is hydrogen or a saturated hydrocarbyl aliphatic radical. 
Presently preferred are the lower alcohols wherein R contains 0 to 3 
carbon atoms, though higher molecular weight species are suitable, though 
less preferred because of higher cost. Of these, most preferred is 
methanol since it is cheap and because the end product is the much 
preferred isoprene. 
Exemplary monohydric alcohols include the presently preferred methanol, as 
well as ethanol, n-propanol, n-butanol, 2-methyl-propan-1-ol, n-pentanol, 
1,2-dimethylpropan-1-ol, and the like. While mixtures can be employed, 
such are less desirable as resulting in a mixed end product which usually 
is less valuable. 
Lower Aldehydes 
The lower hydrocarbyl aliphatic monoaldehyde formed in the first step of my 
process scheme can be represented by: 
##STR2## 
wherein R is as defined hereinabove. Exemplary aldehydes are those 
corresponding to the exemplary alcohols above, such as formaldehyde, 
acetaldehyde, n-propanol, n-butanal, 2-methylpropanal-1, n-pentanaldehyde, 
1,2-dimethylpropanal-1, and the like. 
The aldehyde can be made by dehydrogenation by contacting an alcoholic 
vapor with a suitable catalyst and with a molecular oxygen-containing gas, 
such as air, in an amount insufficient for combustion. Any conditions 
known to the art can be employed. Exemplary conditions include contacting 
a mixture of air and a lower alcohol with a catalyst such as a silver 
gauze catalyst at a temperature of about 1100.degree. to 1200.degree. F., 
preferably for methanol about 1150.degree. F., and at a pressure of about 
3 psig to 10 psig, preferably for methanol about 4 psig. The lower alcohol 
feed stream is dehydrogenated at least in part to the corresponding 
aldehyde, and a portion of the resultant hydrogen reacts with oxygen to 
form water. Dehydrogenation generally is incomplete so that unreacted 
alcohol remains in the product stream from the oxidation step. 
Alternative means for formation of the aldehyde include reaction of a lower 
alcohol with excess air over a molybdenum oxide catalyst at a temperature 
of about 450.degree. to 550.degree. F., and at a pressure of about 15 psia 
to 25 psia pressure. 
Aliphatic Monoolefins 
The aliphatic monoolefins are aliphatic hydrocarbyl isomonoolefins. These 
also can be termed methylene-substituted aliphatic hydrocarbons. These 
aliphatic hydrocarbyl isomonoolefin reactants contain the isobutylene 
group. These aliphatic monoolefins also can be represented by the general 
formula: 
##STR3## 
wherein each R is as defined above. Presently preferred are isomonoolefins 
wherein each R is hydrogen, such that the preferred species is isobutene 
or 2-methylpropene-1. Exemplary of the methylene-substituted aliphatic 
hydrocarbons are 2-ethylpropene-1, 2-n-propylpropene-1, 
2-n-propylbutene-1, 2-isobutylhexene-1, 2-ethylbutene-1, 
2-isopropylpentene-1, and the like. While mixtures can be employed, such 
are less desirable because of the resulting mixtures of products, usually 
less valuable, or which may require expensive resolution. 
The reaction of a lower aldehyde with an isomonoolefin is an addition 
reaction resulting in the formation of aliphatic hydrocarbyl monoolefinic 
monoalcohols. The monoolefinics also can be represented by a generic 
formula: 
##STR4## 
wherein each R is as defined above. These compounds contain a minimum of 5 
carbon atoms per molecule. Of these, 3-methyl-3-buten-1-ol is preferred 
since it is most economically produced, and since it is a ready source of 
valuable isoprene. 
In the formation of the hemialdehyde, the monoolefinic alcohol reacts with 
the lower aldehyde is a manner which can be illustrated in accordance with 
the following scheme, using formaldehyde and 3-methyl-3-buten-1-ol in 
skeletal form as typical reactants: 
##STR5## 
though the hemialdehydes are of variable composition. The hemialdehydes 
are typified by hemiformal which can be represented by C.sub.4 H.sub.9 
(CH.sub.2 O).sub.n OH wherein n ranges from about 1 to 3. 
Referring to my FIG. 2, the description is illustrated by the preferred 
reactants for exemplary purposes, but the method is of general application 
to the reactants I have described. 
Referring to my FIG. 2, formaldehyde reaction gases 1, from the 
formaldehyde reactor means (not shown), enter the formaldehyde absorber 
means 2 wherein they are contacted, preferably countercurrently, with a 
3-methyl-3-buten-1-ol recycle stream 3. The absorption process can be 
conducted at a temperature in the range of about 100.degree. to 
150.degree. F., preferably about 120.degree. to 135.degree. F., whereby 
the reaction of formaldehyde and 3-methyl-3-buten-1-ol forms a hemiformal. 
In the upper part of the absorber 2, recycle water 4 can be introduced to 
assist in the recovery of most of the remaining formaldehyde, methanol, 
and unreacted 3-methyl-3-buten-1-ol. 
The temperature can be maintained in the desired range, since the reaction 
is exothermic, by suitable cooler means system 10, or, alternatively, by 
cooling coils (not shown) within the absorber means 2. 
The fixed gases, saturated with water, are vented 5 from the top of the 
absorber column means 2, and can be flared as shown or otherwise sent to 
waste disposal. The pressure in absorber means 2 should be maintained 
slightly above atmospheric, such as about 2 psig to 20 psig, preferably 3 
psig to 8 psig. The hemiformal solution 6 is withdrawn from the bottom of 
the absorber means 2. This stream 6 contains the absorbed formaldehyde, 
effectively as a hemiformal, together with methanol, and small amounts of 
formic acid from the formaldehyde production process. 
By distillation of the hemiformal stream 6 in the hemiformal column means 
7, light components 8 are separated from the absorber product 6. The 
distillation of fractionation column means 7 can be operated with a 
bottoms temperature of about 300.degree. to 330.degree. F., preferably 
about 320.degree. F., or possibly somewhat less, so as to minimize 
decomposition of the hemiformal into formaldehyde and 
3-methyl-3-buten-1-ol. The tendency for re-formation of lower aldehyde and 
unsaturated alcohol also can be minimized by introducing minor amounts of 
additional recycle 3-methyl-3-buten-1-ol, which nonobjectionably also can 
contain some formaldehyde as the hemiformal, as a side stream 15 into the 
hemiformal column means 7. 
The hemiformal column means 7 overhead stream 8 comprises water, methanol, 
formic acid, and some unsaturated alcohol which in some cases, such as 
3-methyl-3-buten-1-ol, may tend to azeotrope with the water. After 
condensing 9 at about 15 psia to 50 psia, preferably about 20 psia to 35 
psia at approximately 100.degree. F., the resultant overhead phase 11 is 
accumulated and separated 12 and returned in part 13 as reflux to the 
hemiformal column means 7 along with a portion 15 of the water phase 14 
for suitable operation of the hemiformal column fractionator means 7. 
The bottoms 17 from the hemiformal column means 7 comprises hemialdehyde, 
3-methyl-3-buten-1-ol, pentyl formates, and water. A portion 18 is 
reboiled 20 in reboiler 19 for proper column operation, and the remainder 
21 is employed as a hemiformal concentrate stream to the alcohol reactor 
means 37. 
The remaining water phase product stream 16 from the hemiformal column 7 
overhead 11 is fed to a methanol/water splitting means 22 and subjected to 
separation such as by fractionation means into a methanol recycle stream 
overhead 23 and a bottoms water stream 24. A portion 25 of the water 
stream 24 can be reboiled 26 and returned as reboil 27 to the formaldehyde 
absorber means 22 for efficient separation, and the remainder 28 can be 
removed 29 to waste disposal 30, or in part can be recycled 4 to the 
formaldehyde absorber means 2. The methanol overhead 23 is condensed 31 
into an accumulator means 32 for recycle 33 as reflux to the formaldehyde 
absorber means 23 for efficient operation, and the remainder 34 can be 
otherwise utilized as desired, but for maximum economy in my process, the 
methanol stream 34 preferably is recycled to the initial methanol 
oxidation reaction step (not shown) to produce further formaldehyde 
reaction stream 1. If the waste water stream 30 contains any recoverable 
amounts of pentenols or other materials, it can be further treated as 
desired. 
The bottoms product stream 21 of hemialdehyde from the hemialdehyde column 
means 7 can be combined with hemialdehyde 64 recovered from subsequent 
processing to create a hemialdehyde feed stream 35. The hemialdehyde 
stream 35 together with an isobutylene stream 36 are fed to an alcohol 
reactor means 37 for production of 3-methyl-3-buten-1-ol. Isobutylene feed 
36 comprises fresh isobutylene feed 38 along with any recycle isobutylene 
such as all or part of 39, 40, and 41. 
The reaction of formaldehyde and isobutylene results in: 
##STR6## 
3-methyl-3-buten-1-ol, along with minor amounts of pentyl formate: 
##STR7## 
(3-methyl-3-buten-1-yl formate) plus some minor methanol formation also. 
The reaction of isobutene and the lower aldehyde contained in or provided 
by the hemialdehyde takes place in reactor means 37, such as a continuous 
reactor, employing reaction conditions such as about 7 to 15, preferably 9 
to 12, more preferably about 10, moles of isobutylene iC.sub.4 " per mole 
formaldehyde in the feed; utilizing a contacting temperature in the range 
of about 500.degree. to 600.degree. F., presently preferred about 
520.degree. to 560.degree. F., more preferred such as about 545.degree. 
F., under a pressure of about 1800 to 2500 psia, presently preferred about 
1900 to 2200, more preferred about 2000 psia; employing a suitable 
residence time such as about 25 to 40 minutes, presently preferred about 
25 to 35, more preferred about 30 minutes. Under these conditions 
anticipated conversion of aldehyde is about 80 percent, with about 80 
percent selectivity to 3-methyl-3-buten-1-ol. 
Feed isobutylene stream 36 and hemialdehyde stream 35 can be heat exchanged 
with any of the reactor effluent streams such as 42 with suitable heat 
exchanger means (not shown) located between reactor vessels or by heat 
exchange surfaces within the vessels or walls. 
Reactor effluent 42 is separated such as by fractionation in debutenizer 
means 43 into streams comprising recycle isobutylene 39, a methanol and 
water phase 44, and a bottoms product stream 45 containing 
3-methyl-3-buten-1-ol, some unreacted aldehydes as the hemialdehyde, and 
some by-products such as the pentyl formates. 
A portion 46 of recycle isobutylene 39 can be separated such as by 
fractionation in debutanizer means 47, if desired, to remove unreacted 
saturated C.sub.4 components 48 to flare or other disposal, while the 
overhead 40 isobutylene and the rest of the recycle isobutylene 39 is 
returned to the isobutylene feed 36 to reactor means 37. 
Bottoms product 45 from debutenizer means 43 can be split into a recycle 
stream 49 of 3-methyl-3-buten-1-ol used as extractant feed 3 for contact 2 
with aldehyde stream 1, some recycle 50 of 3-methyl-3-buten-1-ol to the 
hemiformal column 7, and the remainder 51 3-methyl-3-buten-1-ol stream 
which contains the net production of 3-methyl-3-buten-1-ol, and by-product 
pentyl formates. 
Separation 52, such as by fractionation, of 3-methyl-3-buten-1-ol stream 51 
removes pentyl formates 53 at a fractionation temperature of about 
260.degree. to 300.degree. F., preferably about 270.degree. F. to 
290.degree. F., and a pressure of about 20 psia to 40 psia, preferably 20 
psia to 25 psia, to produce a purified 3-methyl-3-buten-1-ol stream 54 for 
feed to a dehydration reactor means 55, or for other recovery as an 
olefinic alcohol product as may be preferred. 
If an alkyl-substituted conjugated diene product is desired, the 
3-methyl-3-buten-1-ol 54 can be dehydrated in reactor means 55 to form an 
isoprene product stream 56, using a temperature in the range of about 
480.degree. to 700.degree. F., presently preferred about 550.degree. to 
600.degree. F., more preferred about 570.degree. F., under a pressure of 
about 15 psia to 100 psia, presently preferred about 20 psia to 40 psia, 
more preferred about 25 psia, employing an LHSV of 1 to 30, preferably 
about 2 to 5, more preferred about 3, employing a suitable dehydration 
catalyst such as pelleted tribasic calcium phosphate as described in U.S. 
Pat. No. 3,657,376. 
Dehydration reactor means effluent 56 can be separated 57 such as by 
fractionation to remove isobutylene overhead 41 which can be returned to 
the alcohol reactor means 37, and water 58 which is removed. The bottoms 
product 59 contains isoprene, hemiformal, and heavies, and can be further 
separated such as by fractionation 60 to remove isoprene and any other 
C.sub.5 's such as piperylene overhead 61 for such further purification, 
if any, as needed for particular rubber end products. The bottoms product 
62 is mainly hemialdehyde which can be separated such as by fractionation 
means 63 into stream 64 for recycle 35 to the alcohol reactor 37, and a 
heavies reject 65 for disposal. 
The alkyl-substituted butadienes produced in accordance with my process are 
those corresponding to dehydration products, such as isoprene, of the 
monoolefinic alcohols such as 3-methyl-3-buten-1-ol as described 
hereinabove. 
The following is a typical anticipated material balance using the stream 
numbers as described hereinabove, and as correlated with my attached FIG. 
2. The balance is not exact due to roundoff of the tabulated figures. 
Components listed as formaldehyde and pentenols may exist as hemialdehyde 
as described hereinabove. 
__________________________________________________________________________ 
MATERIAL BALANCE FORMALDEHYDE 
RECOVERY STEP QUANTITIES IN MOLES 
Stream No. 1 3 4 5 6 16 21 28 29 34 50 
__________________________________________________________________________ 
Hydrogen 178 178 
Oxygen 4 4 
Nitrogen 1081 1081 
CO+CO.sub.2 +CH.sub.4 
61 61 
Water 622 613 203 1032 
1000 
32 995 382 5 
Formaldehyde (CH.sub.2 O) 
582 37 8 610 1 642 1 33 
Methanol 165 15 150 150 150 
Formic Acid 2 3 5 5 5 2 
Pentenols 257 257 486 229 
Pentyl Formates 19 19 35 16 
__________________________________________________________________________ 
Total 2694 
313 616 1550 
2073 
1156 
1195 
1000 
384 156 278 
Stream No. 35 36 38 39 41 42 46 48 58 59 64 
__________________________________________________________________________ 
Water 32 32 416 
Formaldehyde 
763 152 121 121 
Methanol 41 
Formic Acid 
Isobutylene 7600 
499 7073 
38 7073 
707 10 
N Butylenes 43 3 40 40 4 
Isobutane 200 2 200 200 20 2 
Pentenols 572 1061 86 86 
Pentyl Formates 
35 76 
Isoprene 414 
Piperylene 2 
Heavies (as C.sub.5 H.sub.10 O) 35 
__________________________________________________________________________ 
Total 1402 
7843 
504 7313 
38 8675 
731 12 416 658 207 
Stream No. 44 45 49 51 53 54 56 61 62 65 
__________________________________________________________________________ 
Water 32 416 
Formaldehyde 152 70 82 82 121 121 
Methanol 41 
Formic Acid 
Isobutylenes 38 
N Butylenes 
Isobutane 
Pentenols 1061 
486 575 575 86 86 
Pentyl Formates 76 35 41 41 
Isoprene 414 414 
Piperylene 2 2 
Heavies (as C.sub.5 H.sub.10 O) 35 35 35 
__________________________________________________________________________ 
Total 73 1289 
591 698 41 657 1112 
416 242 35 
__________________________________________________________________________ 
The material balance illustrates an application of my process which 
utilizes a portion of a monoolefinic alcohol product stream as a reactant 
to recover aldehyde. In the material balance presented above, the 
unsaturated monoolefinic alcohol product further is converted to isoprene. 
The disclosure, including data, illustrate the value and effectiveness of 
my invention. The examples, the knowledge and background of the field of 
the invention and general principles of chemistry and other applicable 
sciences, have formed the bases from which the broad descriptions of the 
invention including the ranges of conditions and generic groups of operant 
components have been developed, which have formed the bases for my claims 
here appended.