CA1072986A - Liquid phase process for the manufacture of methyl tertiary ethers - Google Patents

Abstract

(4790) LIQUID PHASE PROCESS FOR THE
MANUFACTURE OF METHYL TERTIARY ETHERS

ABSTRACT OF THE DISCLOSURE
The present invention is a liquid phase process for the preparation of methyl-t-butyl ether by reacting isobutylene and methanol in the presence of a heteropoly acid of molybdenum, tungsten or vanadium. Other tertiary ethers may be obtained by substituting a different tertiary olefin for isobutylene, e.g. t-amyl methyl ether from 2-methylbutene-2 and methanol.

Description

BACKGROUND OF THE INVENTION
The ether Or the lnventlon has been tradltlonally prepared by the use Or a strong mlneral acld, e.g. sulfurlc scld. Such strong aclds under the process conaitions are very corrosive ~nd cause ~lgnlricant problems when applled on a commerclal scale. A~ a result, there has been a contlnuous search for an lmproved proces6 Or hlgh erflciency that avolds these corroslon problems.
Acidlc lon exchange reslns, whlch 8180 ha~e been used ~8 catalysts ~or the preparatlon Or the etherso~ the lnventlon, cannot be used at temperatures hlgher than 70_~5GC.
due to thelr poor thenm~l stabillty. Thl8 llmltatlon results ln long reactlon times and low throu~hput per unlt volume Or a reactlon ves~el.
j Another problem assoclated wlth the known processe~
18 the rormatlon Or undeslrably ~ large quantities Or dimethyl 25 1 ether The present lnventlon also deals wlth thls probl-m and l substantlally reduees the amount Or thls undeslrable by-product.

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SUMMARY OF Tn~ lNVENTION
The present inventlon 18 a process for the preparation of methyl-t-alkyl ethers comprising reacting a mixture of a tertiary olefin Or the formula RHC = C~ wherein R is H
or alkyl and Rl i8 alkyl and methanol ln the liquld phase ln the presence of ~ homogeneQu :--free heteropoly acid catalyst having the formulaHn Aa Dc Oy XH20 wherein A 18 P, B, Sl, Ge, Sn, As, Sb, U, Mn, Re, Cu, Nl, Co, Fe, Ce, Th, Cr or mlxture thereor; and D is Mo, W, ~ or mlxture thereof;
and whereln a ~ O.l - lO;
c = 6 - 18;
n 18 the number of acldic hydrogens ln the cataly~t;
y 18 the number of oxygens in the catalyst; and x 18 the moles of water of crystallization.
Using the process of the invention, high yields of methyl-t-butyl ether and other t-alkyl methyl ethers are obtalned wlth very desirable low concentrations of by-product dimethyl ether.
The central aspect of the present lnvention is the use Or the partlcular catalysts noted ln the formula above in the liquid phase reaction of lsobutylene or of a tertlary olefln and methanol to g~Ye methyl-t-alkyl ether. The tertiary olefin has the formula RHC = CRl wherein R ifi H or an alkyl and Rl 1~ alkyl. The catalysts are suitably any of tho6e catalyst~ delimlted by the formula above. In a preferred embodiment, the molybdenum, tungsten and vanadium are employed separately. Thi8 18 conven~ently accom}~ hed ln the fo~nula ::

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lV7Z~G (4 by settlng D separately e~ual to molybdenum~ tungsten or ~anadium. 0~ speclal interest ln the present lnvention are tho~e catalyst~ that contaln phosphorus, ~lllcon and germanlum.
mi8 iB accomplished by settlng A equal to phosphorus, slllcon or gormanlum.
The number Or H20 molecules contained ln the cat~lyst as water of crystalllzatlon can vary wldely, dependlng on the method o~ preparation and on the aftertreatment of the catalyst. Thus ln each catalyst X mQy range from zero to about 40 Furthermore, an lnteractlon between the "acldlc"
hydrogens and the water Or crystalllzatlon may occur such that the value o~ n 1B changed. This may occur e.g. upon partlal reductlon of a catalyst of the abo~e formula, The catalysts Or the lnventlon are p repared by known tech~lques. Speclflc preparatlons o~ these catalysts are shown in the worklng examples of thl~ speclricatlon.
~roadly, however, the cat~lysts of the lnventlon may be prepared by any of the technlques known ln the art.
The catalyst employed ln the reactlon 18 BUltably employed elther as a dlssolved component o~ the llquld mlxture or as a heterogeneous cataly~t. Either form glves the very desirable results of the present inventlon with the homogeneous liquld mlxture being preferred because of the substantlally greater contactlng efficlency.
A glven heteropoly acld may be used as a heterogeneous catalyst ir lt is lnsoluble ln the reactlon medium. In ~uch a c~se lt may be used alone, or supported on carrier materials, ~uch as ~illca, alumlna, kieselguhr, bentonite clay~ and otherR.

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The concentratlon Or the cataly~t ln the llquid phase reactlon mlxture may vary wldely. For the homogeneou6 cataly~ts, it i8 moBt convenient to state the catalyst concentratlon in terms of weight percent. The welght percent of the catalyste may vary wlthln very broad limlts, but lt ha~ been found that weight percentageB of about 0.1 to about 5~ are preferred. For the heterogeneous catalyst eystem6 lt 18 most common to have a flxed-bed of the cataly~t through whlch the reactant feed 1B pasned. Thus, there 18 no slgnlflcant relatlonshtp between the amount Or catalyst and the amount o~
( the reactlon mlxture.
m e proce6s condition~ for the llquid pha~e reactlon may vary wldely, but ln normal practlce, the temperature range~ from about lO to 200 C. and the reactlon 1~ normally conducted under atmospherlc or ~uperatmo~pherlc pre~sure, Of special lnterest in the procen~ of the lnventlon are reaction~ conducted at temperatures o~ 70 to 150 C. u~lng superatmo~pherlc pressure. m e contact tlme of the~e reaction ~onditlons will vary substantially. The contact tlme may range ~rom as low as a few seconds to a number of hours depending upon the state of the catalyst employed, the reaction temperature and the pre~sure. The molar ratio of the tertlary ole~in to methanol may vary widely ~o long as the predomlnant product i6 the tertlary alkyl methyl ether.
Sultably, the molar ratlo~ are about 0.3 to about 10 moles of methanol per mole o~ olefin.
In addition to the~e process variables, other modi~ication~ of the reaction may be used. For example, a ~uitable solvent may be employed that will not deleteriously (479) lO~Z~6 arfect the reaction and that 18 conveniently removed from the reactlon product. m e reactlon 1B 6ultably conducted ln any reactor that can accommodate a llquld pha~e reaction.
Thu~, a ~t~rred and heated pressure vessel contalning the reactants with the catalyst dlssolved ln them may be used ~or a commerclal batch operatlon. In a contlnuous operatlon, the reactants wlth the cataly~t dlssolved may be pa~sed through a heated tubular reac,tor (packed with lnert materlal for improved heat trans~er), such that the product, and any unreacted materlal, are contlnuou~ly removed. In a heterogeneous reactlon, the lnsoluble catalyst may constltute the whole or part Or the reactor packlng.

SPECIFIC EMBODDMENTS
Exam~le~ 1-18 _ Preparatlon Or methyl_t-butyl ether uelng varlous catalyst6.
The h~teropoly acids used as catalysts of thls lnventlon were prepared by mlxlng solutlons of theoretical amounts of a soluble~molybdate or tungstate with a salt solutlon contalnlng the hetero atom ~ollowed by acldlfylng~
heatlng~ extractlng the heteropoly acld with ether, then crystalllzlng rrom the ether soltuion H4GeW12040 XH20 used in Example 12 was prepared as rollowB:
A ~olution A wa6 prepared by stirring and heatlng 3.9 g. powdered GeO2 (37 mlllimoles) and 14.2 g. Or 50 ~-l aqueous NaOH (178 milliequivalent~) in 100 ml. water.
-~ A solutlon B was made by dissolving 159 g.
Na2W04.2H20 (482 mlllimoles) ln 400 ml. cold water, and addlng (4790) ~V7~g8~

approxlmately 80 ml. Or 15% hydrochlorlc acld, wlth ~tlrrlng, untll the pH value o~ the solution became 6.8~.7.o.
Solutlons A and B were comblned, stlrred ~nd heated.
The pH value was adJusted to about 3 with 65 ml. addltlonal 15% ~1, then 20 ml. 30~ HCl was added in portions. The solutlon was bolled ~or two hour~ and allowed to evaporate to about 400 ml. resldu~l volume. The mlxture was then cooled ln an lce-bath to 18C., ml~ed with 50 ml. concentrated HCl, and poured through a fllte~ lnto a separating ~unnel, followed by addltion o~ 250 ml. ether ~n portlons, wlth lntermlttent shaklng. Another 50 ml. concentrated HCl was added, the mlxture shaken, then allowe~ to separate. m ree llquld layers separated, the lowest layer conta'ned the product heteropoly acld dlssolved in ether. It was separated, ~lltered and the ether evaporated ln a water bath at 50C.
m e resldual ~olld was dlssolved ln 80 ml. water9 filtered~
mlxed wlth 20 ml. concentrated HCl, and the extractlon with ether was repeated as above. m e ether extract was mixed wlth 50 ml. water, the ether removed by evaporatlon, and the concentrated solutlon ~lowly evaporated to dryness ln a vacuum dessiccator. The whlte, crystalllne solld thus obtalned welghed 77 g. The other c&taly~ts of the Table were prepared in essentially the same manner.
The catalysts were u~ed to prepare methyl-t-butyl ~ther ln a one-llter laboratory pres~ure reactlon vessel equlpped wlth a stlrrer, charging ports, a thermocouple, a pressure gage and a blowout dlsc.
me procedure used in Example 1 o~ the Table was as ~ollows:

`` ` 107Z~86 The catalyst H4SiMol2O40 XH2O(0.9 g.) was char~ed to the pressure vessel, the vessel was closed and evacuated.
A mixture of 56 g. isobutylene ~1 mole) and 128 g. methanol (4 moles), confined under its own vapor pressure in a small steel bomb, was charged to the reaction vessel by suction, through one of th~ charging ports. The reaction vessel was then heated with agitation at 135C. for one hour. The pressure in the vessel rose initially to 220 p.s.i., then decreased to 150 p.s.i. The catalyst was completely soluble in the reaction mixture. After the reaction, the reaction vessel was cooled to 0C. and the reaction mixture was analyzed by gas chromatography. The catalysts, catalyst concentrations, molar ratios of reactants and results are shown in the following Table.
The results of these reactions are given in the Table where the conversion and selectivity are defined as follows:

moles of reactant reacted x 100 % conversin = moles of reactant charged moles of methyl-t-butyl ether obtained % selectivity = moleS of isobutylene reacted Also included as a part of the results is the amount of by-product dimethyl ether that is formed. This result is expressed in terms of the percent of charged methanol that is converted to dimethyl ether.

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It ls seen ~ro~ the above data that the productlon Or methyl-t-butyl ether uslng the catalysts Or the ln~entlon gives hlgh converslon of the l~obutylene at ~ery hlgh selectlvlty. It 1~ al80 ~een from the data that the yleld Or dlmethyl ether 18 maintaln~d withln a ~ery deslrable low range.

- Preparation of t-amyl methyl ether.
Using the procedure of Example 1, 100 g.

2-methylbutene-2 (1.43 mole) and 46 g. methanol (1,43 ~ole) were reacted for 90 minutes ~t 135C, ln the presence of 0.5 wt,% (0.73 g,) of ~4SlM012040~XH20 as catalyst. The catalyst was soluble ln the reaction mixture. Ihe converaion of the olefln was 34.4%, that of methanol was 28.4~. ffle product contalned 28.2 wt,% o~ t-amyl methyl ether; athe selectivity ba~ed on converted 2-methylbutene-2 WAS 80.2%.
- Preparation of t-amyl methyl ether.
U8ing the procedure of Example 1, 70 g.
2-methylbutene-2 (1.0 mole) was reacted with 96 g. methanol t3.0 moles) for 90 minute~ at 135C, ln the pre~ence of 1-0 wt-% (1-7 g.) of H4SlM012040 XH20. m e converslon o~
the ole~ln was 46.o~, that of methanol 14.6~. The product contained 28 wt.~ of t-amyl methyl ether; the selectivity ba~ed on converted 2-methylbutene-2was 95~.

Claims (10)

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

1. A process for the preparation of methyl-t-alkyl ethers comprising reacting a mixture of a tertiary olefin of the formula RHC=CR? wherein R is H or alkyl and R1 is alkyl and methanol in the liquid phase in the presence of a homogeneous-free heteropoly acid catalyst having the formula Hn Aa Dc Oy ? XH2O

wherein A is P, B, Si, Ge, Sn, As, Sb, U, Mn, Re, Cu, Ni, Co, Fe, Ce, Th, Cr or mixture thereof; and D is Mo, W, V or mixture thereof; and wherein a = 0.1 - 10;

c = 6 - 18;
n is the number of acidic hydrogens in the catalyst;
y is the number of oxygens in the catalyst, and x is the moles of water of crystallization.

2. The process of Claim 1 wherein D is Mo.

3. The process of Claim 1 wherein D is W.

4. The process of Claim 1 wherein D is V.

5. The process of Claim 1 wherein A is P.

6. The process of Claim 1 wherein A is Si.

7. The process of Claim 1 wherein A is Ge.

8. The process of Claim 1 wherein the catalyst is H4SiMo12040?XH2O.

9. The process of Claim 1 wherein the reaction is conducted at a temperature of 10-200°C.

10. The process of Claim 1 wherein isobutylene is reacted.