CA1056853A - Process for converting high-boiling byproducts of isoprene production into isoprene, isobutylene and formaldehyde - Google Patents

Abstract

ABSTRACT
A method of processing high-boiling byproducts of isoprene production obtained at the first stage of isoprene production by the dioxane method into isoprene, isobuty?lene and formal-dehyde comprises catalytic splitting of said products in the vapour phase in the presence of water with a weight ratio there-between of 1-1+2, respectively, at 250-290°C over aluminium oxide as catalyst. The resulting vapour mixture is catalytical-ly split at 315-360°C over calcium-phosphate catalyst with the formation of a reaction mixture containing isoprene, isobutyle-ne and formaldehyde.

Description

~5~53 MBq'EOD 0~ PRODUCI~IG HIG~ 13OILIN~
BYPRODUC~S O:F ISOP~E PRODUC~ION

~ e pre3ent i~ventio~ relates to methods of processing high-boiling byproducts of isopre~e production into isoprene, isobut~lene a~d formaldehyde, and more specifically it co~cerns a method of proc~ssing hig~boiling byproducts o:~ isoprene pro-duction obtained at the first stage o~ isoprene production by the dio~ane method.
Isopre~e, isobutylene a~d formalde4yde are widaly used : -in the manu~acture oî s~nthetio xubbers a~d other chemical pro-ducts, ~ t t~e first stage o~ i~opre~le productlo~ by the dioxa~e ~:
method a reaction mi~ture is obtai~:led which contai~ dimoth~l-dioxa~, as well as high~boiling byproducts distributed amo~g ~he organic and aqueous la;yer~ o:e t;he reactio~ mixture.
~ here are known a ~umber of methods o~ proce~sing high boiling b;srproducts o:~ isoprene! produc ~io~ ~hus, it is knowcl to ~ubJeot these products ~o h;ydroli~ in the pre~0nce o~ i~orga~ic acids. EIeaYy pxoblems~ however9 arise in dsvelop-i~; th~ produ¢tion method ~or æuch proce~eæ associa~ed with 1:
e~requireme~ts o~ oo~ti~uous operatio~ o~ a pla~t a~d bLrni~g . , ~:: t~ r~sinous residu~3 or wa~tss co~tainin~s a~ i~orga~ic acid~ 1 ;.

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~ 8 ~ 3 It is also known to process high-boiling byproducts o~
isoprene production on the basls .af their catalytic split-ti~g in the vapour phase over solid catalysts a-t elevated temperature O~e of these methods involves the processi~g of high-boil-ing byproducts o~ isoprene production over a oatalyst o~ the aluminosilicate type. By this method, high boiling byproducts contained in the aqueous layer o~ the reaction mixtuxe o~ di-methyldioxa~e synthesis (the ~irst stage o~ isopre~e production by t~e dio~ane method) are fed for splitting ~ithout preliminary isolatio~ from water9 the orga~ic layer of high-boiling bypro-ducts being also ~ed ~or split-ti~g. ~his method ~eatures a ver~
low yield o~ isopre~e which is only about 12~o ~rom theory.
It is also know~ to process high-boiling byproduotis~ their components or mi~tures th~reo~ with dimethyldio~ane over cal- ~
cium-phosphate catal~t~ ~he process is conducted at about ~50C .
with a ratio of high-boiling byproducts to water of 1:3. The mai~ disadva~tage o~ this method c:onsists in a rapid coking of calcium-phosphate ca-talyst havi.~g a ve~ developed surface .
and a large void volume. A long-term burning out of coke is required for recovery o~ the cataly~t sur~ace so that this me-` thod i~ rather i~ef~icient. ~he yield of isopre~e by this me-thod is comparatively low.
It i~ a~ obaect o~ the invention to provide a method o~
processing hi~-boiling byproducts o~ isoprene produotion ob-- . : ,, : , , , ~ . .

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, tained at the first sta~e of isoprene production by the dioxane method which permits to achieve an improved yield of isoprene.
With this and other objects in view9 the invention con-sists in the provision of a method of processing high~boiling byproducts of soprene production, wherein said high-boiling byproducts are catalytically split in the vapour phase in the presence of water with a ratio therebetween of 1:1~29 respec-tively, over a solid catalyst~ and wherein, according to the invention, the catalytic splitting of said high-boiling byproducts is conducted over aluminium oxide as catalyst at 250~290C to -~
obtain a vapour mixture which is subsequently subjected to a catalytic splitting at 315-360C over calcium-phosphate cata-lyst with the formation of a reaction mixture containing iso-prene, isobutylene and formaldehyde.
As mentioned above? high-boiling byproducts formed at the first stage of the process in preparing dimethyldioxane in isoprene production from formaldehyde and isobutylene com-prise~a complex mixture of various compounds exhibi~ing dif-ferent chemical properties and reacti~ity. This includes three isomers of dioxane alcohols, pyran compounds, numerous ethers~
as well as various formals of cyclic and linear structure and unidentified compounds ~specially including numerous heavy Eractions boiling above the boiling poi~t of dioxane alcohols, .`~ ,.
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~5~D5~ii853 Our studies show that at the present state of the art no ~atisfactory result can be obtained usi~g any single cata-lyst in any single-stage proce~s.
~ husg the catalytic splitting o~ high-boili~g b~products over aluminium oxide results in obtaini~g a negligible qua~ti-ty of isoprene, isobutyle~s and a high yield o~ the total o~
unsaturated alcohols, formaldehyde, pyran compou~d~ etc~
(see ~ables 1 a~d 2).
~onditions o~ processing high-boiling ~able 1 ~yproducts over aluminium oxide ~mperature in High-boil- R~te o~ feed~
tho Ga~aly~t ao-ing bypro- i~g of high-Cataly~y~_0 _ duat3/wat~r boiling pro-top middl~ bottom rat per g o~ ca-talyst Alumi~ium o~ids 266 254 254 1:22~0 ' .:

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T~e basic part of the mixture obtained after the splitt i~g may be directly used ~without separation) for the produc~
tion o~ isoprene. I~ separating such mi~ture~ e.g. by re~ining a re~orming of some starti~g compounds present in the high-boiling byproduct~ may take place, mainl~ due to water and ~or-mald~hyde addition at double bonds (Prince reaction).
The employmen-t of calcium-phosphate catalyst for direot splitting high-boiling byproducts also cannot give desired re-sult~ (see ~ables 3 an~
~able 3 Conditions of processing high-boiling byproducts over calcium-phosphabs ca--taly~

~empcrature~ High-boiling ~fedhiig~ bail-Catalyst C wa~sr ratio /hg byproduct~, ` of cataly~t Calcium-p~o~
phate catal~t 32Q-325 1:2 1.0 :-~
i ~ hile isopr~ne yield is her0 high~er than in the case o~ using aluminium oxid~, bhe yields of other valuable pro-ducts, suGh a~ isobutylene and ~ormaldebyde are rath3r i~8uf-ficient~ Bu~ a~ importa~t thing i~ t~at with t~e direc~ process, ing o~ high-boiling byproducts over calcium p~osphate catalys~

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-~ 8-~ ~6~ 3 having a fine~porous structure the coke formation is materially i~creased. ~he yield o~ coke and losses attai~s 16%. ~his ~act itsel~ does not permit to u~e this cataly~3t ~or decompos~tlo~
o:~ b;yproduct~ .
H~waver, it has bee~ fou~d that the successive operation with t~e two catalysts allowed to eliminate the di~ficulties encountered where they are used separately. As a result of splitti~g o~ high-boiling byproducts over alumi~ium o~ide ~ a vapour mi~ture wit~ a low content of isoprene is obtained.~his permits to co~duct a rather deep conversion process wit~out an~ risk o~ occurrence o~ s~condary reactions. The splitti~g of the resulting vapoul~ mixture which thus co~tai~s a negli-gible guantity of high-molecular compounds over calcium-phos-phate ca-talgst parmits to eliminate a rap~d coking of t~e ca~
talyst and results in the formati.on of a reaction mi~-ture con-taining isoprene, isobutylene and ~ormaldehyde so that the re-fining o~ this mixture i~3 ~ot associated wit~ losses o~ valu-able products i~ the course o~ c~amical reactio~s~
~ hus, bg co~ducting a suGcessi~e splitti~ o~ high-boil-~ byproducts over alumi~ium o~ida and calcium-phQsp~ate ca-taly~ts isoprene, as well a~ isobu~le~e and ~ormaldehyde oa~ ~
b~ obtai~ed ~rom ~igh-bolling byproduots at a comparatively hiæh yield, A yleld of isoprene i~ ¢o~erting high-boiling ' -.. ....

_9_ ~ 3 byproducts is from 22 to 2~o~ formaldehyde - 25% and isobuty-le~e - 7%. ~he me-thod according -to the invention permits to completely process hig~-boiling byproducts without dischargi~g a~y fraction thereof for recycling of unconverted heavy compo-nents contained i~ the starting produot~ and heavy reaction productsO ~e method may be ef~ected using sta~dard egùipme~t employed in i~oprena production from formaldebyde and isobuty-le~eO
~he proce~s may be co~ductçd in the continuous manner.
~ha method according to the i~vention is e~fected a5 .
foLlow~.
For splitting hi~h-boiling byproducts the use was made of an installation ¢omprisi~g an evaporator, two reactor~, co~-ventional condensation apparatu~ cooli~g apparatus, apparatus ~or catching light ~ractions, for xeceivi~g gas and liquid products~
For the conduct of the process t~e temperature and rate of deliver~ of startin~ products are selected to ensure a suf-ficient rate of th0 process so a~ to make it mora economical a~d, o~ ~he other hand, 50 as to elimi~ate the development of ~nd~sired seco~dary co~versions. I~ additiong the seGo~dary co~varsions are hindered by diluting t~e reactio~ mixture wit~
~team so that a~ excessive amou~t o~ water should be fed i~to the i~stallation for ~ormal ope~atio~ o~ the b~th reac~ors.
Starting high-boilin~ byproduct~ and water i~ a selected .

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~56~353 waight ratio are fed by means o~ a meteri~g pump into a heat-ed evaporator. T~en t~e resulti~g vapours are ~ed i~to a re-ac~tor co~taini~g aluminium oxide, wherein the mixture i9 Ca-talytically split at a preselected temperatureO The resulting vapour mixture is then admitted into a reactor c~arged with calcium-phosphate catalyst ~or ~urther catalytic co~versio~
and then into the condensation and receiving apparatus9 As a result, a reaction mixture is obtained which contains isopxene, isobutylene and formaldehyde. ~he liquid and gaseous products thu~ obtained are measur~d, separated and anal~ed~ :
With conti~uou3 operation o~ the installation t~o reactor .~ys-tsms are used which are alter~ately switchedover for pro-cessi~ tbs starti~g products and ~or recov~ry o~ th0 cata~
l~sts. ~he de~ red products ~re iso;latod from the reaction mi~ture b~ known method~, such as rls~i~ing, and the residue is reoycled for seoondar~ processing of the mixture with the starting high-boiling bypxoducts~
The pre~ent inventio~ will be better u~der~tood from t~
: ~oll~wi~g speci~ic e~ample8 E~ample 1 30 g oP alumi~ium o~ide were chaxged into the first reac-tor. 60 g o~ calcium~phosp~ate cataly~t were charged i~o the ' -second reactoru ~he conditions o~ splitting high-boili~g by-.

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~56~513 products ar~ Kiven in Table 5.It is clear ~rom -the above-given da-ta thati only 402 g o~
u~saturated alcohols or ~~q~- 100 = 0.78 w.~0 are pxesent in the reaction mix-ture (organic layer)~ Thi~ quantity ca~-not have a~y appreciable e~ect on the results of re~ini~g eYen if all u~saturated alcohols react with formaldehyde.
At the ~ame time, the results give~ above show that by ~he method accordi~g to the invention about 90~0 o~ high-boil-i~ byproducts are converted with the following yield~ o~ de-sired products: ~
isoprene - 22.4 % of co~verted high-boiling byproducts9 ~ormaldehyde - 2501% o~ converted high-boiling byproduct~
i~obutylene ~ 7.5% of converted high-boiling byproduct~a In additio~, the following products are obtai~ed which may be used ~or conversion into de~ired product~ at isoprene p1ant~s metihylhydropyran - 7. l~o dimetihyldio~anq - 3.8%
~mstha~ol - 7.9%
trimethyl~arbinol - l~9~o~
so tha-t additiio~al yield o~ isoprene, formaldePyd~ a~d iso-~ . I
butyle~à is obtai~ed which wa~ not taken ~to acoou~ in thLs~
Example~

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~561353 Table 5 Reactor Temperature in HighDboiling Rate of feed-in the ~low the catalyst co byproducts/ ing high boil-direction o~ lumn water r-atio i~g byproducts high~-boiling - weight g/h per 1 g byproducts top mlddle bottom of catalyst vapours o~ ~
~___.____..__________________________________________________ __~
l~t r~actor with alumi~ium o~ide

2~3 2~3 280 1:2 2.0 ::

2~d reactor v~ith calcium-phosphate cataly~t 317 324 340 1:2 1.0 ~ ' '.

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~ample 2~
30 g o~ aluminium oxide were charged into t~e first reactor, 60 ~ o~ calcium-phosphate catalyst were charged into the second reactor. The conditions of proce~sing high-boiling byproducts are given i~ '~able 7 ~ he co~te~t o~ unsaturated alcohols i~ the ~inal mixtur~
is al~o negli~ible - ~ 100 = ~.52% which ¢annot appre-ciably lower the yield of is~opr0ne in refini~g liquid reac-tio~ products due to chemical reactions.
~ he de~r~e of conversion of high-bolli~g byproducts is more than 80~.
~ he yield3 o~ the desired products are as follows:
i~oprone - 23.3% of co~var~ed high-boiling byproducts, formald~yde - 25.1% o~ convertad high-boiling bypro ducts~
isobutyle~e - 7-9% of co~verted high-boilin~ byprodu¢t~.
In addit~o~, the products which are processed at iso-pre~o plant~ i~to de~ired products are obtained:
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m~th~ldihydropyra~ - 8.0~
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dimethyldioxa~ 3.4%
metha~ol - 4~8%
trimethylcarbinol - 2~6%
All remai~i~g products ma~ al30 be recyclsd for further p~oo~s~ing into isoprene, formald~hyde a~d isobutyleneO

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Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:-

1. A method of processing high-boiling byproducts which are obtained during a first stage of isoprene production by the dioxane method, to give isoprene, isobutylene and formaldehyde, comprising catalytically splitting said byproducts in the vapour phase in the presence of water with a weight ratio therebetween of 1:1-2, respectively, at 250-290°C over aluminium oxide as catalyst to obtain a vapour mixture; catalytically splitting said vapour mixture over calcium-phosphate catalyst at 315-360°C
to obtain a reaction mixture containing isoprene, isobutylene and formaldehyde.