CA1322766C - Etherification process - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
A liquid phase process for oligomerization of C4 and C5 isoolefins or the etherification thereof with C1 to C6 alcohols wherein the reactants are contacted in a reactor with a fixed bed acid cation exchange resin catalyst at an LHSV of 5 to 20, pressure of 0 to 400 psig and temperature of 120 to 300° F. wherein the improvement is the operation of the reactor at a pressure to maintain the reaction mixture at its boiling point whereby at least a portion but less than all of the reaction mixture is vaporized. By operating at the boiling point and allowing a portion of the reaction mixture to vaporize, the exothermic heat of reaction is dissipated by the formation of more boil up and the temperature in the reactor is controlled.

Description

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Docket 938 CAN
ETHERJ~LcA~ON ~ ES~

The Government of the United S~ates o America has certain rights in this invention pursuant to Contract No.
DOE-FC07-800CS40454 awarded by the US Department of Energy.
B~CKGROUND OF THE INvENTIoN
Field of khe Inventlon The pres~nt lnvention relates to an improv~d process ~or carrying out liquid phase oligomerizations and etheriisations in a fixed catalyst bed.

Related Art Recently a new me~hod o~ conducting certain catalytic reactions has been devised. Two particular r~action~ or which this method has been particularly use~ul are oligomerization and etherification of C4 and C5 isoolefin~. The method involved i~ briefly described as one where concurrent reaction and di~tillation occur in a combination reac~or~distillation column with the distillation structure serving a5 the catalyst. These process and catalytic distillation structures are described , )n~

in several U. S~ Patents, namely U. SO Pat. No's. 4,2429530;
4,250,052; 4,232,177; 4,302,356; 4,307,254; and 4,336,407 This new system has been commercially applied to the production of methyl tertiary butyl ether (MTBE) produced by the r~action of isobutene contained in C4 refinery streams and methanol.
It is well known that primary alcohols will react preferentially with thP tertiary alkenes in the presence of an acid catalyst, for example, as taught in U~S. Patent No's. 3,121,124; 3,6~9,478; 3,634,534; 3,825,603; 3,846,088;
4,,071,567; and 4,198,530.
The catalytic distillation process differs from these older processes in that a catalyst system was disclosed ~U. S. Patent No's. 4,215,011 and 4,302,356~ which provided for both reaction ancl distillation concurrently in the same reactor, at least in part within the catalyst system. For example r in this system and procedure, methanol and an isobutene containing C4 ~tream are continuously fed to the reactor/distillation column where they are contacted in the catalytic distillation struature. The methanol pre~erentially reacts with isobutene, ~orming MTBE, which is heavier than ~he C4 components o~ the feed and the methanol ? hence it drops in the column to form the bottoms. Concurrently, the unreacted C4'S ~e~g.
n~butane, n~butenes) are lighter and form an overhead.
The reaction just described is reversible, which means that it is normally e~uilibrium limited, howeYer~ by ~ 32 9J~

removing the ether (M~BE) from contact with the catalyst (as a bottoms), the reaction is forced to completion (Le Chatelier Principle). Hence it can be run to obtain a very high conYer~ion of the isobutene present (95%~). As a result, a great deal of control over the rate of reaction and distribution of products can be achieved by regulating the system pressure. The boiling point in the reactor is determined by the boiling point of the lowest boiling material (which ~ould be an aæeotrope) therein at any given pressure. Thus at a constant pressure a change in the temperature at a point within the column indicates change in the composition of the material at that point. Thus to change the temperature in the column the pressure is changed or any given composition.
Since oligomeriæation and etherification are ~xothermic there is excess heat in the reactor. In the liquid phase system, methods were devised to remove this heat, since in the case of resin type catalysts excessive temperature ~hot spots) can damage the catalyst. In the catalytic distillation the excess hea~ merely causes more boil up in the column.
In an unrelated area the volatilization of a portion of the feed in a catalytic C3 hydrogenation to provide a quasi-isothermAl reactor is discussed in Chemi~l ~n3i~n~lnl Pro~ress , Vol 70, No. 1~ January~ 1974, pages In addition to the catalytic distillation system, ~3~2~'~;3 there are several other etherification systems in commer~ial u~e or available which are liquid phase systems~ That is, these systems are operated under conditions of pressure to maintain the contents of the reactor in liquid phase. One of the principal problems encountered in these systems is the exothermic heat of reactionO ~eat is sometimes removed by using heat exchangers in the reactor, such as tubular reactors having a heat exchange medium contacting the tubPs, other systems employ feed diluents to maintain a low concentration of reactive isobutene. In other words, the ..
temperature in the catalyst bed has to be controlled by the removal of excess heat in somle manner.
The present invention which relates to the liquid phase type of reaction also provides a means for removing heat from the fixed continuou'3 catalyst bedO It is a further advantage that the present type of liquid phase reaction may be used in conjunction with a cat~lytic distillation column reactor to obtain very high conversions of iso C4 and C5 alkenes in the feed stream/
~ hese and other advantages will become apparent from the following descriptionsO
~ RY ~F ~ nz_~T~
The present invention is an improvement in the exothermic, liquid phase reaction of C4 and C5 isoolefins with themselves to form oligomers, preferably dimers, and with C~ to C~ alcohol to form ethers by contact in a fixed bed catalyst of acidic cation exchange resin, wherein the improvement i5 the operation of the reactor at a pressure to maintain the reaction mixture at its boiling point within the range of 120 degrees F. to 300 de~rees F. whereby at least a portion but less than all of said reaction mixture is in the vapor phase.
This is a substantial departure from the prior art for this type of reactor, where sufficient pressure was employed to maintain the reaction mixture in liquid phaseO
A given composition, the reaction mixture, will have a different boiling point at diferent pressures, hence the temperature in khe reactor is controlled by adjusting the pressure to the desired temperature within the recited range. The boiling point of reaction mixture thus is the temperature of the reaction and the exothermic heat of reaction is dissipat~d by vaporization of the reaction mixture. The maximum tempera'ture of any hPated liquid composition will be the boiling point of the composition at a given pressure~ with additional heat merely causing more boil up. The same principal op~rates in tha present invention to control the tempera~ure. There must be liquid present, however~ to provide ~he boil up, otherwise the temperature in the reactor will continue to rise until the catalyst is damaged. In order to avoid exotherms which will vaporize all of the reaction mixture, it is necessary to limit the amount of isoolefin in the feed to the reactor to abouk 60 wt.~ of the total feed.
The prasent reaction can be used on streams 3 2 r~J ~ ~3 containing small amounts of the isoolefin, however, feed to the reaction will need to be preheated to near the boiling point of the reaction mixture, since low concentrations of isoolefin ~1 to 8 wt. %) do not provide a very great exotherm (i~e., as noted above the prior art used diluents to control the temperature in the liquid phase reaction).
In any event it may be necescary to preheat the feed to the reaction such that temperature of the reaction, i.e., the boiling point of the reaction mixture (feed temperature plu~
exother~) is in the range of 120 degrees F. to 300 degrees F., wh:ich represents the desirable range for ~he equili~rium reactions at a pressure in the range of 0 to 400 psig.
The catalyst bed may be described as a fixed continuous bed, that is, the catalyst is loaded into the reac~or in its particulate ~orm to fill the reactor or reaction zone, although there may be one or more such continuous beds in a reactor, separated by spac s devoid of catalyst.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a simple reactor operated in a quasi-isothermal manner.

Fig. 2 is a modi~ication where the heat of the reaction is recovered to preheat the feed to the reactor, i.
e.~ operated quasi-isothermally and adiabatically.
ETAI:IJED DESCRIPTIQN OF THE INVE~NTION

~L 2 2 ~
The temperature in the reactor is thus controlled by the pressure u~ed. The temp~rature in the reactor and catalyst bed is limited to the boiling point of the mixture pre~ent at the pressure applied, notwithstanding the magnitude of the exotherm. A small exotherm may cause only a few percent of the liquid in the reactor to vapori~e whereas a large exotherm may cause 30-90% of the liquids to vaporize. The temperature, however, is not dependent on the amount of material vaporized but the composition of the material being vaporized at a given pressure. That "excess"
heat of reaction merely causes a greater boil up (vaporization) o the material present.
Although th~ reaction is exothermic, it is necessary to initiate the reaction, e.g., by heating the feed to the reactor. In prior reactors such as the tubular rea~tors the temperature of the reaction (bed) may be controlled with the heat exchange medium; i.e., either adding or removing heat as re~uired. In any event once the reaction is initiated an exotherm d~velops and must be controll~d to prevent a runaway reaction or damage to the cakalyst.
The reaction product ~ethers, dimers, unreacted fePd) in the present invention is at a higher temperature than the feed into the reactor with a portion being vapor and a portion liquid~ The reactor is operated at a high uid hourly space velocit~ (5-20 LHSV, preferably 10-20 to avoid the reverse reaction and polymerization of the olefins present in the feed)~ IJnder these conditions high ~ 7~

conversion of feeds, containing 5 to 3G weight percent isoolefins are obtained, e.g., 80-90% conversion and somewhat lower conversions for stream containing higher concentrations of the isoolefinsO
Thus, it may be desirable to have two and possibly more of the present reactors in series to obtain higher conversions of the isoolefins~ In ~uch a case the product from the flrst reartor will normally be cooled, by heat exchan~e to obtain the desired temperature in the second reactor.
Conveniently the feed to the first reactor is used to cool the product from the first reactor prior to its entry into the second reactor, hence the heat o~ reaction supplies some of the heat necessary to initiate the reaction in the first reactor. This method of recoverin~ the heat of reaction can also be used where a single reactor is employed~ ~ence the reactor or reactors can be operated in a substantially adiabatic manner.
The product ~rom either a single reactor or a sPries o~ reactors operated quasi-isothermally a~ taught here may be separated by conventional distillation/ by recovering oligomer or the ether as a bottom product and unreacted feed components as overheads, with ap~ropriate water washing to remove or recover any alcohol (methanol and ethanol form azeotropes with the unreacted C~ and C5 feed stream components3.
However, 2 further embodiment of the present invention is the combination of the present reaction operated in fixed bed in partial liquid phase tas described) with a catalytic distillation using an acidic cation exchange resin as the distillation structure~ This has the advantage of further reacting the residual isoolefins while fractionating the reaction product concurrently to produce even higher conversion of the isoolefins. This combination has a further advantage in that both catalyst beds, i.e~, the fi~ed partial liquid phase reactor and the catalytic distillation reactor can be relatively small compared to the use of either bed alone when used to obtain the same level of isoolefin conversion obtained by the combination.
Ano~her advantage of the combination is that the small partial liquid phase bed can serve as a guard bed for the distillation column reactor bed~ since catalyst poisons (metal ions and amines) even iLf present in parts per billion will deactivate the acidic cation exchange resin in time.
The small guard bed can be easily and less expensively replaced as it is deactivated while ~he life o~ the ca~alytic distillation bed may be extended several yearsO
Catalysts suitable for the present process are cation exchangers, which contain sulfonic acid yroups, and which have been obtained by polymerization or copol~merization of aromatic vinyl compounds followed by sul~onation. Examples o aromatic vinyl compounds suitable for preparing polymers or copolymers are~ styrene~ vinyl toluene, vin~l naphthalene, vinyl ethylbenzene~ methyl ~3~7~

styrene, vinyl chloroben2ene and vinyl xyleneO A large variety o methods may be used for preparing these polymers;
for examplel polymerization alone or in admixture with other monovinyl compounds, or by crosslinking with polyvinyl compounds, for example~ with divinyl ben~ene, divinyl toluene, divinylphenylether and others. The polymers may be prepared in the presence or absence of solvents or dispersing agents, and various polymerization initiators may be used, e.g., inorganic or organic peroxides, persulfates, etc.
The sulfonic acid group may be introduced into these vinyl aromatic polymers by various known methods; for exampler by sulfating the polymers with concentrated sulfuric acid or chlorosulfonic acid, or by copolymerizing aromatic compounds which contain sulfonic acid groups ~see e.gO, US Pat. No. 2,366,007). Further sulfonic acid group may be introduced into these polymers which already contain sulfonic acid groups, for example, by treatment with fuming ~ulfuric acid, i.e., sulfuric acid which contains sulfur trioxide. The treatment with fuming sulfuric acid is preferably carried out at 0 to 150 degrees C and the sulfuric acid ~hould contain sufficient sulfur trioxide after the reaction so that it still contains 10 to 50% free sulfur trioxide, The resulting products preferably contain an av~rage of 1~3 to 108 sul~onic acid groups per aromatic nucleus.
Par~icularly, suitable polymers which contain sulfonic acid ~3~766 groups are copolymers of aromatic monovinyl compounds with aromatic polyvinyl compounds, particularly, divinyl compounds, in which the polyvinyl benzene content is preferably 1 to 20~ by weight of the copolymer (see~ or examplel German Patent Specification 908,247).
The ion exchange resin is preferably used in a granular size of about 0.25 to 1 mm, although particles from 0.15 mm up to about 1 mm may be employed. The finer catalysts provide high surface area, but also result in high pressure drops through the reactor. The macroreticular form of these catalysts is preferred because of the much larger surface area exposed and the limited swelling which all of these resins und~rgo in a non-aqueous hydrocarbon medium.
Similarly, other acid resins are suitable, such as perfluorosulfonic acid resins which are copolymers of sulfonyl ~luorovinyl ethyl and fluorocarbon and described in grea~er detail in Du~ont "Innovation", Volume 4, No. 3, Spring 1973 or the modified forms thereof as described in US
Patent No.'s 3,784,399; 3,770,567 and 3,849,243.
The resin catalyst is loaded into a reactor as a ~ixad bed of the granules, The feed to the reaction is fed to the bed in liquid phase. The bed may be horiæontal~
vertical or angled~ Preferably bed is vertical with the feed passing downward through the bed and exiting, after r~action, through the lower end of the reactor.
For the present oligomeri~ation and etheriication reactions~ the feed may be a C4 or C5 containing ~ ~2~7S6 .

~tream, for example, a C4 or C5 refinery cut, although a mixed stream could be employed. In addition to C4 ~ such a C4 stream may contain small amounts of C3 and C5 and a C5 will contain small amounts of C4 and C6, depending on the precision of the refinery fractionation~
Isobutene is the C4 isoolefin and it dimerizes to praduce diisobutene. Some higher oligomers are produced as wel~ as some codimers with n-butene~ that are normally present in a C4. The dimerization is the preferential reaction because the two most rea¢tive molecules are combining. Higher polymers result ~rom the continued co~tact of the dimer with isobutene in the presence of the catalyst, At the high LHSV (iow residence time) employed for the present reaction, little polymer is formed.
Isoamylene has two isomers, i.e., 2-methyl butene-l and 2 methyl butene 2, both of which are normally present in a C5 stream. Both are highly reactive and the dimer product is a mi~ture of the three possible dimers.
Both the isobutene and isoamylene preferentially react with alcohols in the presence of an acid catalyst, he~ce only small amounts of dimer or other oli~omerization p~-oducts are produced when the atherification is carried 4uto ~ he Cl to C6 alcohol~or the etherification may he fed to the reactor with the hydrocarbon stream or by a separate feed. The methanol is preferably fed at the ~l~2~

upstream end of the reactor to inhibit oligomerization of the ole~ins and to preferentially react with more reactive isoole~ins to form ethersO
The alcohol, e.g., methanol may be and is preferably present in a stoichiometric amount of the isoolefin present although an excess of up to 10%, may be dPsirable. In addition, slightly less than a stoichiometric amount may be employed. It should be appreci~ted that the skilled chemist will optimize the proportions and precise conditions for each particular piece of equipment and variation in catalyst, once the basic invIention is comprehended~ The alcohols employed are those Ihaving 1 to 6 carbon atoms.
Preferred are thosP having one hydroxyl group, Preferred alcohols include methanol, ethanol, propanol, n-butanol, terkiary butanol, l-pentanol, 2-pentanol, 3-pentanol, 1 hexanol, 2-hexanol, 3-hexanol~ cyclopent nol and hexanol~
A preferred grouping of alcohols are those having 1 to 4 carbon atoms and one hydroxyl groupv The alcohols may be used alone or in mixtures of any proportion to produce highly complex ether products having unique proper~ies as octane improver~ for gasoline or as solvents.
The reaction in the ixed bed is primarily a liquid phase reaction, but unlike all other known liquid oligomexizations and etherifications reaction~ carried out in this manner, no attempt is made in the presen~ process ~o maintain a completely liquid phase. Since the reaction is ~322766 exothermic, the pressure in the reactor is adjusted to maintain the desired temperature which allows some portion of the material to be vaporized. The reactor may be said to run in a quasi-i60thermal manner.
EXA~PLEI
Referring to Fig. 1, a simple reactor 10, packed with acidic cation exchange resin catalyst 12 is shown~ The reactcr was pilot plant size and contained a 10 foot by inch diameter bed of Amberlyst 15 Beads.
The feed was of refinery C4 cut admixed with methanol and entered the reactor via line 14. The feed had been preheated to 138 degrees ~'., and flowed through ~he resin bid and exited via line 16. The feed entering the reactor was in liquid phase and the product exiting was par~ially vaporized. The conditions and resu]ts of this run are summarized in TABLE I. Con~ersion o~ isobutene 89.7%.
The recovered ~tream 16 would normally be subjected to further treatment, by way of fractionation to separate the unreacted C4 from the ether and to recover the unreacted methanol~ The product stream 16 can go directly into a distillation column (not shown) where the heat of the reaction is utilized in the distillation.
EXA~PhES 2 ~ND ~
In Fig. 2 modifiGation of the simple procedure of Fig. 1 is illustrated. The ~eed, a refinery C4 stream, enters heat exchangers 50 via line 60 where it indirectly contacts product from reactor 52 which enters the heat 1~
~ T~ r~

~3227~

exchanger via 54~ Once the reaction is started the product exiting the reactor is at a higher temperature than the feed and is used to heat feed entering the reactor via line 56.
As in Fig. 1, the feed is a mixture of the C4's and methanol. After the indirect contact of the reaction product and ~eed in the heat exchange 50 the cooled product exits via line 58.
Operated in this manner the feed to reactor is a~ a temperature near the exotherm, hence the reactor is operating under near adiabatic conditions.
The net heat of reaction of the system is the difference between the temperature of the feed into the system and the product out o the system, i~e., 45 degrees F., which is about the same as for the simple system illustrated in Fig~ 1 (since the ~eeds are similar). The conditions and results o~ the two runs with two dif~erent C4 feeds are illustrated in Table II using the system of Fig.2. It should bQ noted that the ~eed o Example 3 contained a higher isobutene content than Example 1. Since the pressure was the same ~or both examples, the exotherm for Example 3 was higher. In order to haYe reduced the temperature in Example 3, the pressure would have needed to have b~en reduced, since the composi~ion in the reactor had changedO
~ n either embodiment ~FigO 1 or Fig. 2) the product stream may be pas~ed to a second or subsequent quasi-isoth~rmal reactor and the process repe2ted. This ~322766 would be expedient when the isoalkene is greater than about 30% of the feed9 since conversion would be low on a per pass basis. Also, as sho~n in Fig. 2, the product ~tream 58 may be fed to a distillation tower 62 where the ether product is recovered as a bottoms 64 and unreacted feed stream components and methanol recovered as overhead 66 Alternatively, tower 62 may be catalytic distillation tower where the residual isoalkene is reacted with residual methanol (or added methanol to produce extremely high conversions of the isoalkene in a single pass through the system ~e.g. 95%+). The packing in a catalytic distillation column is described in the above noted patents, but briefly, it has been found that placing the resin beads into a plurality of pockets in a cloth belt, which is supported in the distillation column reactor by open mesh knitted stainless steel wir~ b~ twisting the two together, allows the requisite flows, prevents loss of catalyst, allows for the normal swelling of the beads ~nd prevents the breakage of the beads through mechanical attrition.
The cloth may be of any material which is no~
attacked by the hydrocarbon eed or products under the conditions of the reaction. Cotton or linen are useful, but fiber glass cloth or "Teflon~ cloth are preferred. A
pre~erred catalyst system comprises a plurality of closed cloth pockets arranged and supported in said distillation column reactor and supported in said distillation column reactor by wire mesh intimately associated therewith, y ~

~32276~

The particular catalytic material may be a powder, small irregular fragments or chunks, small beads and the like. The particular form of the cat~lytic material in the cloth pocket~ is not critical, so long as suf~icient ~urface area is provided to allow a reasonable reaction rate. This si~ing of catalyst particles can be best determined for each catalytic material ~since the porosity or available internal surface area will vary for dif~erent materials, and, of course, affects the activity of the catalytic material).
For the present oligomerizations and etherifications, the catalyst is the same type, an acidic cation exchanged resin, used in the continuous bed reactors.
It should be appreciated that the same mechanism of allowing excess heat of reaction to merely create boil up has been employed in both the continuous bed rectors and in the catalytic dis~illation. Although as noted above, continuous bed reactors have been disclosed to operate for different process in a quasi~isothermal manner the operation of a liquid phase etherification in this manner is in direct conflict with all of art on the subject.
In the three examples o~ the present invention given here, approxirnately 30% of the feed in the continuous bed quasi-i~othermal reactor was vaporiæed. In Examples 2 and 3 the product 54 leaving the heat exchanger was all liquid t however, in some operations according to the present invention, depending on the temperature and composition of stream 54, a portion may still be in the vapor sta~e.

~7 :~3227~
The heat exchanger 62 should be si~ed, such that an amount of heat e~ual to the heat of reaction in reactor 52 is allowed to pass through, otherwise the heat in the reactor will build up. An alternative means is to provide a by pass~ shown by dashed line 55 whereby a portion of the effluent from the reactor is by passed around the heat exchanger to obtain the same result.
In the oligomerization, just as in the etherification, the tertiary olefins are more reactive and tend to form oligomers, primarily dimers, e.g., diisobutene, some higher oligomers and some codimers with normal olefins.
The oligomerizations are run under the same general conditions as the etherifications with the oligomer products being the heavier component of the product stream~ In fact, it may be desirable in some operations to switch between the two reactions, by adding or withholding the alcohol as desired.

13~2~6 TABLE I

Conditions Line 14 Line 16 Temp., F, 138 185 Press., psig -- 150 LHSV 11.9 Composition lbs/hr wt ~ lbs/hr wt Isohutene 15 . 6 14 . 6 1. 6 1. 5 O~he~ C4's 79.474.2 79~4 74.2 Methanol 12.,0 1102~1A,O 3O7 MTBE, -- - 22.0 20.,6 Conver~ion of isobutene 8!3o79~i .1 ~32~
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Claims (26)

1. An improvement in the process of the exothermic, liquid phase reaction of:
(a) C4 or C5 isoolefins with themselves to form oligomers thereof by contacting a stream containing up to 60 weight percent of said isoolefins with an acid cation exchange resin at a temperature in the range of 120° F. to 300° F. in a reactor to form a reaction mixture containing oligomers, or (b) C4 or C5 isoolefins with C1 to C6 alcohol to form ethers thereof by contacting a stream containing up to 60 weight percent of said isoolefins and alcohol with an acid cation exchange resin at a temperature in the range of 120° F. to 300° F. in a reactor to form a reaction mixture containing ether wherein the improvement is the operation of said reactor at a pressure to maintain said reaction mixture in said reactor at its boiling point within the range of 120° F. to 300° F. whereby at least a portion but less than all of said reaction mixture is vaporized.

2. The process according to claim 1 wherein C4 or C5 isoolefins are reacted with themselves to form oligomers thereof.

3. The process according to claim 2 wherein a predominantly C4 hydrocarbon stream containing from 1 to 60 weight percent isobutene is contacted with said fixed bed catalyst.

4. The process according to claim 3 wherein the pressure in the reactor is in the range of 0 to 400 psig and the LHSV of said stream is in the range of 5 to 20.

5. The process according to claim 4 wherein the reaction mixture contains unreacted C4 hydrocarbon and a predominant amount of diisobutene.

6. The process according to claim 5 wherein said stream is preheated by indirect heat exchange contact with the reaction mixture from said reactor,

7. The process according to claim 2 wherein a predominantly C5 hydrocarbon stream containing from 1 to 60 weight percent isoamylene is contacted with said fixed bed catalyst.

8. The process according to claim 7 wherein the pressure in the reactor is in the range of 0 to 400 psig and the LHSV of said stream is in the range of 5 to 20.

9. The process according to claim 8 wherein the reaction mixture contains unreacted C5 hydrocarbon and a predominant amount of dimers of isoamylene.

10. The process according to claim 9 wherein said stream is preheated by indirect heat exchange contact with the reaction mixture from said reactor.

11. The process according to claim 1 wherein C4 or C5 isoolefins are reacted with C1 to C6 alcohols to form ethers thereof.

12. The process according to claim 11 wherein a predominantly C4 hydrocarbon stream containing 1 to 60 weight percent isobutene is contacted with said fixed bed catalyst.

13. The process according to claim 12 wherein the alcohol is methanol.

14. The process according to claim 12 wherein the pressure in the reactor is in the range of 0 to 400 psig and the LHSV of said stream is in the range of 10 to 20.

15. The process according to claim 14 wherein said stream is preheated by indirect heat exchange contact with the reaction mixture from said reactor.

16. The process according to claim 11 wherein a predominantly C5 hydrocarbon stream containing 1 to 60 weight isoamylene is contacted with said fixed bed catalyst.

17. The process according to claim 16 wherein the pressure in the reactor is in the range of 0 to 400 psig and the LHSV of said stream is in the range of 10 to 20.

18. The process according to claim 17 wherein said stream is preheated by indirect heat exchange contact with the reaction mixture from said reactor.

19. The process according to claim 1 wherein said stream is preheated prior to contact with said catalyst.

20. The process according to claim 1 wherein said reaction mixture is recovered and fractionated to recover a bottom product of (a) oligomer or (b) ether

21. The process according to claim 11 wherein from slightly less to up to 10% excess of the stoichiometric amount of methanol is present.

22. The process according to claim 13 wherein from slightly less to up to 10% excess of the stoichiometric amount of methanol is present.

23. The process according to claim 22 wherein said reaction mixture is passed to a distillation column reactor containing acid cation exchange resin in a plurality of pockets in a cloth belt, supported in said distillation column reactor by open mesh knitted stainless steel wire to react residual isobutene and methanol therein.

24. The process according to claim 21 wherein the isoolefin comprise over 30% of said stream and the reaction mixture is passed to a second reactor containing a fixed bed cation exchange resin operated at a pressure to maintain said reaction mixture therein at its boiling point in the temperature range of 120° F. to 300° F. whereby at least a portion but less than all of the said reaction mixture is vaporized.

25. An improvement in the process of the exothermic, liquid phase reaction of:
C4 or C5 isoolefins with C1 to C6 alcohol to form ethers thereof by contacting a downflow stream containing up to 60 weight percent of said iso-olefins and alcohol with an acid cation exchange resin in a vertical fixed bed at a temperature in the range of 120°F. to 300°F. in a reactor to form a reaction mixture containing ether wherein the improvement is the operation of said reactor at a pressure to maintain said reaction mixture in said reactor at its boiling point within the temperature range of 120°F. to 300°F. whereby at least a portion but less than all of said reaction mixture is vaporized and recovered as a single stream exiting through the lower end of the reactor.

26