CA2054990A1 - Process for the preparation of mtbe - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
A process is provided for etherification of essentially pure iC4= with MeOH to form MTBE in a distillation column reactor containing a mixed bed acid cation exchange resin as a catalytic distillation structure in an a distillation reaction zone. An inert C4 hydrocarbon is initially fed to the distillation column reactor to act as a diluent and a heat sink which boils at the desired temperature range for the reaction. Additionally the inert C4 diluent acts as an azeotroping agent for the MeOH in the lower end of the column carrying more of the MeOH back up into the reaction distillation zone. After start up and circulation the inert C4 hydrocarbon feed is stopped and that in the system is retained therein by total reflux of the overheads and judicious operation of the lower portion of the distillation column reactor.

\crl.pat\1227.app

Description

2 PROCESS FOR TH}3 PREPA:E~ATION OF ~lTBE

3 BAC~GROUND OF THE INVENT:CON
` 4 Field of the Inve~ i~21 The present invention relates to the production o~ methyl 6 tertiary butyl ether (MTBE) ~rom the reactlon o~ isobutylene 7 (iC4=) with methanol (MeOH). More par~$cuiarly the invention 8 relates to a process where high purity iC4~ may be used as the 9 feed while still maintaining adeguate tempexature control and ic4= selec~ivity to MTBE. Most particularly the invention 11 relates to a catalytic distillation process wherein an inert C4 12 hydrocarbon is initially fed ~o a distillation column reactor to 13 provide a heat sink and dilute the reactants. After start up the 14 initial feed of the inert C4 hydrocarbon is ceased and that ~ed is retained in the system.
16 Related Art 17 The production of MTBE from the acid catalyzed reactlon of 18 iC4= and MeOH is well known in the art. Generally the iC4- is 19 contained in a mixed hydrocarbon stream containing predominantly C4's which includes normal butenes, butanes and possibly lighter 21 C3 hydrocarbons. rrhe iC4 content of these streams is typically 22 from 10-70 mole ~. The MeOH pre~erentially reacts with the iC4-23 to form MTBE with the remainder of the materials in khe mixed 24 hydrocarbon passing through essentially as inerts.
One major difficulty with the iC4~/MeO~ reaction has been 26 temperature control due to the exothermicity of the reaction.

~crl.pat~1227.app xc ~

Several methods of temperature control have been applied 2 including indirect heat exchange ln the catalyst bed, inter-bed 3 cooling and quer~ch. One mekhod which has found wide spread acceptance is catalytic distillation wherein the heat of reaction simply causes boil up of ~che material in the catalyst bed. The 6 temperature is controlled by the pressure. This particular 7 method is exempli~ied by commonly owned U.S. Patents 4,232,177, 8 4,307,254; and 4,336,407. A variation utilizing vaporization of 9 the mixture for heat removal is disclosed in Canadian Pat.No.
929,537 wherein the vaporized portion is condensed and returned 1 to the reactor, there being no distillation or separation.
~2 Additionally IJ.S. Patent 4,540,831 discloses substantially the 13 same process as the Canadian reference wherein all of the 14 overheads are condensed and both products and unreacted materials are withdrawn as bottoms.
16 The catalytic distillation method of reaction works well 17 when there is sufficient material within the bed to act as a heat `18 sink-that is, there is sufficient material within the bed to 19 absorb all of the heat of reaction without eomplete vaporization in the bed. After complete vaporization, the heat would simply 21 be added as sensible heat and increase the temperature.
22 In U.S. Patent 4,540,831 the 3~road embodiment of ths process 23 comprises exothermally reacting a first chemical compound and 24 second chemic~l compound in a reaction zone to form a third chemical compound, vaporizing the first or second compound to 26 remove heat and condensing the vapor overhead and removing the \crl.pat~1227.app 2 1 third compound and substantially all of the unreacted first and 2 second compound in the bottoms effluent steam. The patent for 3 example describes an MTBE process uslng as a feed an admixture of 4 c4 hydrocarbons including butanes and isobutylene in a process where the MTBE formed within the catalyst bed and the remaining 6 C4 hydrocarbons descend through the catalyst bed and are removed 7 as a single combined effluent stream.
8 The use o~ concentrated iC4= as a feed stock for MTBE
g processes presents special problems because of the heat of reaction and the potential loss of selectl~ity due especially to 11 dimerization. A simple solution to this problem would be to 12 dilute the iC4= feed with inerts that boil in the reaction 13 temperature range as the more common feed streams already are.
14 The best diluents would therefore be other C4's, such as the butanes and normal butenes in the mixed hydrocarbon streams 16 available.
17 However, these other C4's have value as feedstocks to other 18 processes and while they are not appreciably consumed in the MTBE
19 process, they do become contaminated, especially with MeO~ and other oxygenated products which reduce their value as feedstoc~s 21 as, for example HF alkylation. More significantly the dilution 22 of a substantially pure isobutylene feed with sufficient inert 23 diluents, e.g., 10 to 70% isobutane based on isobutylene, results 24 in the processing of large quantities of materials to separate them from the product. Thus, by dilution, a pure reactant feed 26 is contaminated to dampen the reaction and removed to get the \c,l.pDt\1z27.~pp 3 1 product, which requires larger equipment.
2 $VMM~Y O~ IK~ Y~
3 Briefly the present is a process for etheri~icatlon of 4 substantially pure iC4= with MeOH to form MTBE in a distillation column reactor containing a fixed bed acld cation exchange resin 6 as a catalytic distillation structure in an a dlstillation 7 reaction zone. An inert C4 hydrocarbon is initially fed to the 8 distillation column reactor to act as a diluent and a heat sink 9 which boils at the desired temperature range for the reaction.
Additionally the inert C4 diluent acts as an azeotroping agent 11 for the MeOH in the lower end of the column carrying more of the 12 MeOH back up into the reaction distillation zone. After start up 13 and circulation the inert C4 hydrocarbon feed is stopped and that 14 in the system is retained therein by total reflux of the overheads and judicious operation of the lower portion of the 16 distillation column reactor. Thus forming an isobutane blanket 17 in the reactor. Very little, if any, of the inert C4 hydrocarbon 18 is taken as bottoms which primarily consists of the ~TBE product 19 and some unreacted MeOH. Some of the overheads may have to be withdrawn as a bleed stream to remove the lighter hydrocarbons 21 which may be contained in the inert stream and for pressure 22 control of the distillation column reactor. Pre~erably the mole 23 ratio of isobutylene to isobutane maintained in the catalyst zone 24 is in the range of about 1:5 to 1:100 ; preferably 1:10 to 1:50.
Make up inert C4 hydrocarbon is added only to replace the small 26 amount in the bottoms and the overhead bleed.

\crl.pat\1227.app 4 9~r3 1 BRIEF ~E~C~IPT~O~ QF T~FL_PRAwI~G
2 FIG. 1 is a flow diagram ln schematic form o~ one embodlment of 3 the present invention~
4 Fig. 2 is a flow diagram in schematic form of a second embodiment of the presen~ invention.
6 DETAILED DESCRIPTION OF TH~_PREFE~R~ EM~ODIMENTS
7 A catalytic distillation process util~zes a distillation 8 column reactor which contains one or more distillation zones and 9 one or more reaction distillation zones. The zones are distinct because the disti~lation zones contain standard distillation 11 structure such as inert packing or ~istillation trays. The 12 reaction distillation zone contains a catalytic distillation 13 structure which acts both as a catalyst for .the reaction and a 14 distillation structure for the fract$onal d~stillation of the mixture within the reaction distillatlon zone.
16 Catalyst suitable for the MeOH/iC4= reaction to produce MTBE
17 are cation exchange resins, which contain sulfonic acid groups, 18 and which have been obtained by polymerization or 19 copolymerization of aromatic vinyl compounds followed by sulfonation. Examples of aromatic vinyl compounds suitable for 21 preparing polymers or copolymers are- styrene, vinyl toluene, 22 vinyl naphthalene, vinyl ethyl benzene, methyl styrene, vinyl 23 chlorobenzene and vinyl xylene. A large variety of methods may 24 be used.for preparing these polymers; for example, polymerization alone or in admixture with other monovinyl compounds, or by 26 crosslinking with polyvinyl compounds; for example, with divinyl ~cr~.pat\1227,app 5 ~r~r_~ ~9 0 1 benzene, divinyl toluene, divinylphenyl ether and others. The 2 polymers may be prepared in the presence or absence or solvents 3 or dispersing age~ts, 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 6 aromatic polymers by various known methods; for example, by 7 sulfating the polymers with concentrated sulfuric acid or 8 chlorosulfuric acid, or by copolymerizing aromatic compounds 9 which contain sulfonic acid groups (see e.g., U.S. Pat. No.
2,366,007). Further sul~onic acid groups may be introduced into 11 these polymers which already contain sulfonic acid yroups; for 12 example, by treatment with fuming sulfuric acid, i.e., sulfuric 13 acid which contains sulfur trioxide. The treatment with fuming 14 sulfuric acid is preferably carried out at 0 to 150- C and the lS sulfuric acid should contain sufficient sulfur trioxide after the 16 reaction. The resulting products preferably contain an average 17 of 1.3 to 1.8 sulfonic acid groups per aromatic nucleus.
18 Particularly suitable polymers which contain sulfonic acid groups 19 are copolymers of aromatic monovinyl compounds with aromatic polyvinyl compounds, particularly, divinyl compounds, in which 21 the polyvinyl benzene content is preferably 1 to 20% by weight of 22 the copolymer (see, for example German Patent Specification No.
23 908,247).
24 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 26 about 1 mm may be employed. The finer catalyst provide high ~crl.pat~1227.opp 6 3~

1 surface area, but also result in high pressure drops through the 2 reactor. The macroreticular form of these catalysts is 3 preferred because of the much larger sur~ace area exposed and the 4 limited swelling which all of thes~ resins undergo in a- non-aqueous hydrocarbon medium.
6 Si~ilarly, other acid resins are ~uitable, sUch as 7 perfluorosulfonic acid resins which are copolymers of sulfonyl 8 fluorovinyl ethyl and fluorocarbon and described in greater 9 detail in DuPont "Innovation", Volume 4, No. 3, Spring 1973 or the modified forms thereof as described in U.S. Pat. No.'s 11 3,784,399; 3,770,567 and 3,849,243.
12 In the preferred form the resin catalyst beads form too 13 compact a bed and will not function adequately in a distillation, 14 since there is a very large pressure drop through the bed and free flow of internal re~lux and rising vapor is impeded. The 16 resins may be used in the shape of conventional distillations 17 structures, such as rings, saddles and the like. The particulate 18 resins may be employed by enclosing them in a porous container 19 such as cloth, screen wire or polymeric mesh. The material used to make the container must be inert to the reactants and 21 conditions in the reaction system. The cloth may be any material 22 which meets this requirement such as cotton, fiber glass, 23 polyester, nylon and the like. The screen wire may be aluminum, 24 steel, stainless steel and the like. The polymer mesh may be nylon, teflon or the like. The mesh or threads per inch of the 26 material to make the container is such that the catalyst is \~rlpDt\l227.Dpp 7 3~

1 retained therein and will not pass throu~h the openlngs in the 2 material. Particles of a~out 0.15 mm size or powders may be used 3 and particles up to a~out to about 1/4 inch diameter may be 4 employed in the containers. Containers and systems for using the particulate catalyst are variously described in commonly owned 6 U.S. Pat. No.'s 4,215,011; q,302,356 and 4,443,559 which are 7 hereby incorporated by reference.
8 Each container containing a solid catalytic material g comprises a catalyst component. ~ach catalyst component is intimately associated with a spacing component which is comprised 11 of at least 70 volume % open space up to about 95 volume % open 12 space. This component may be rigid or resilient or a combination 13 thereof. The combination of catalyst component and spacing 14 component form the catalytic distillation structurP. The total volume of open space for the catalytic distillatlon structure 16 should be at least 10 volume ~ and preferably at least 20 volume 17 % up to about 65 volume ~. Thus desirably the spacing component 18 or material should comprise about 30 volume % of the catalytic 19 distillation structure, preferably about 30 volume % to 70 volume %. Resilient materials are preferred. One suitable such 21 material is open mesh knitted stainless wire, known generally as 22 demister wire, or expanded aluminum. Other resilient components 23 may be similar open mesh knitted polymeric filament of nylon, 24 teflon or the like. Other material, eOg., reticulated polyurethane foam (rigid or resllient) may be ~ormed in place or 26 applied around the catalyst component. In the case o~ larger \crl,prt\12Z7,~pp 8 ~ 3~3 1 catalyst components such from abou~ 1/4 to 1/2 inch pellets, 2 spheres, pills and the like each such larger component may ~e 3 individually intimately associated with or surrounded by the 4 spacing component as described above. It is not essential that the spacing component e~tirely cover the catalyst component. It 6 is only necessary that the spacing component lntimately 7 associated with the catalyst component will act to space the 8 various catalyst components away ~rom one another as described 9 above. Thus, the spacing component provides in effect a matrix of substantially open space in which the catalyst components are 11 randomly but substantially evenly distributed.
12 A preferred catalytic distillation structure for use herein 13 comprises placing the cation exchange resin particles into a 14 plurality of poc~ets in a cloth belt, which is supported in the distillation column reactor by open mesh knitted stainless steel 16 wire by twisting the two together in a helical form. The allows 17 the requisite flows and prevents loss of catalys~. The cloth may 18 be any material which is inert in the reaction. Fiber glass 19 cloth or "Teflon" cloth are preferred.
In the following examples the catalyst section was packed 21 with Purolite CT-175 resin packaged in individual bags each 22 wrapped with demister wire. The wire mesh provides the support 23 for the catalyst bags and provides some degree of vapor passage 24 through the catalyst particles, which otherwise ~orm a very compact bed which has a high pressure drop. The down flowing 26 liquid is in intimate contact with the rising vapors in the \crl.p2t~1227,2pp 9 Z~ 9~3~

1 column.
2 The distillation column reactor was operated in the "froth 3 mode". That is, the column was operated at near flooding ~ conditions such that the column was ~illed with a frothing liquid caused by the rising vapors ~hrough a liquid level maintained in 6 the column~ This insures comple~e wetting o~ the catalyst while 7 still allowing for frac~ional distillation. The column is not 8 "flooded~ in the conventional sense by vapor flow, ~ut rather by 9 a downward liquid flow restricter ~o maintain a desired differential pressure which is expressed as a percent of 11 differential pressure at ~looded conditions, dP%.
12 Two embodiments are depicted in the attached ~igures in 13 which like components are given like numerals for ease of 14 reference. The figures are ~low dlagrams in ~chematic form and such conventional eguipment as rebollers, controllers, and 16 control valves are not included as they would ~e obvious to those 17 of ordinary skill in the art of distillation column design.
18 Referring first to FIG. 1 the ~irst embodiment is shown.
19 Th~ distillation column reactor 10 is shown to have the catalytic distillation structure in the upper portion of the 21 column in a reaction distillation zone 20 and standard 22 distillation structure in the lower portion o~ the column in the 23 distillation zone 30. Essentially pure iC4 and MeOH are fed via 24 line 1 and combined with the inert C4 hydrocarbon stream from line 2 into feed line 3 which enters above the reaction 26 distillation zone 30.

\crl~pat\1227.app 10 l The ~eOH and iC~- are con~acte~ in the presence of the acid 2 cation exchange resin in the reaction distillation zone 20 to 3 foL~ MTBE. The exothermic heat o~ reaction causes the resultant 4 mixture in the reaction distillatlon æone 20 to boil. ThP MTBE
being higher boiling than either the M~O~I or C4's is distilled 6 downward into distillation zone 30 where dissolved C4ls and MeOH
7 are distilled back up into ~he reaction distillation zone 20.
8 The process of the present invention is preferably carried out at 9 pressure in said distillation column reactor ~n the range of 100 to 200 psig and temperature in the range of 120 to 180-F.
ll Substantially all o~ the ic4- reacts with MeOH in the reaction 12 distillation zone 20. ~he amount of unreacted MeOH depends upon 13 the molar ratio of MeOH to iC4-, but if fed in a stoichiometric 14 amount, substantially all of the MeOH should also be reacted.
Recommended ratios of MeOH to iC4= are between 1:1 to 1.5:1.
16 The remainder of the C4's, predominantly the lnert C4 17 hydrocarbon, are carried overhead via line 4 and thence to 18 condenser 50 where all of the condensibles (C4+) are condensed l9 and collected in receiver/separator 40. Any noncondensible material, such as any C3 and lighter hydrocarbon contained in the 21 inert C4 hydrocarbon stream, are vented via line 6. A small 22 bleed stream 7 is provided in the over head vapor line 3 fox 23 pressure control. All of the condensed material in the receiver 24 40 are returned to the top of the column as reflux. Once reflux has been established make up inert C4 hydrocarbon is added only 26 as required to replenish that lost in bleed 7. Essentially pure \crl.pat\1227.app 11 h ~ ~3 ~

1 ~TBE is withdrawn from the ~istillation column reactor as bottoms 2 via line 3.
3 Essentially all of the ic4- will be consumed in the reaction 4 distillation zone 20. Therefore very little is taken in the overheads 4 or dissolved in the product MTBE leaving the reaction 6 distillation zone 20. Depending upon the molar ratio of MeOH to 7 iC4= some MeOH will be dissolved in the MTBE and carried downward 8 into the distillation zone 30. In such a case it m~ght be 9 desirable to divert some of the reflux (mostly inert C4 hydrocarbon~ to distillation zone 30 where it would act as an 11 azeotroping agent for the MeOH and insure that all of the MeOH
12 would be distilled back up into the reaction distillation zone 13 20.
14 A second embodiment of the process is shown in FIG. 2. This embodiment differs from the first in that a separate distillation 16 section 31 is provided below the distillation zone 30 which might 17 be in the form of a separate column. The liguid from . .
18 distillation zone 30 is fed~intermediate the separate section 31 19 via line 8 and a vapor containing predominantly inert C4 hydrocarbon is taken from the top tray via line 9 and combined 21 with the overheads in line 4 and condensed therewith by condenser 22 50 and collected in receiver 40. An additional feature of this 23 embodiment is that part of the liguid C4's ~rom the receiver 40 24 is diverted via line 5A to the lower distillatlon zone 30 as an azeotroping agent for the MeOH as discussed above. The remainder 26 of the C4ls are refluxed to the top of the column via line 5B.

\cr~.pat\1227.app l2 ~c~

1 While both embodiments have been directed to using 100~ iC4=
2 feed, the process should lend itself to pr~cesses which use lC4-3 streams containing hi~h enough purity ~i.e. 60-100%) to cause the 4 temperature control problems. ~rhat is, sufficient diluent in the form of inert C4 hydrocarbon may be initially added as desired to 6 control,the ~emperature and selectlvity, and that added retained 7 in the system by the method. This would reduce the amount of 8 diluent necessary and reduce the problems of removing 9 contaminants in the diluent.
EXAMPLES
11 The following examples were run using a one inch laboratory 12 column twenty feet in height. The top six feet were packed with 13 Purolite CT-175 resin contained in individual fiber glass bags, 14 and wrapped with demister wire. The weight of dry catalyst was 50 grams. The lower sixteen feet of the column was packed with 16 inert ceramic saddles. Thermocouple probes were placed in the 17 column with probes 11 through 14 (numbering fro~ the bottom up) 18 in the catalyst bed.
19 Analysis was by gas chromatography with FID detectors. The columns were capillary SE-30 with subambient temperature 21 programming, and Carbowax 20M. Samples were taken in sample 22 bombs and injected through a suitable sampling valve the gas 23 chromatograph.
24 When operating in the froth mode there is so much material in the column that a substantial amount of time is required to 26 reach a new steady state. Samples were taken every three hours \crl.pat~l227.app 13 1 until sequential samples had essentially the same analysis.
2 Example_l (çomparativeL
3 Three runs were made to determine the effect o~ iC4=
4 concentration using isobutane as a dlluent of the lc4- streamO
The iC4= concentration in the first run was 35 mole ~, 45 mole %
6 in the second and 50 mole % in the third. The results are shown 7 in Table I. The feed to the laboratory column in the ~irst two 8 runs was below the catalyst bed. A~ a feed iC4= concentration of 9 45 mole % the selectivity to MTBE fell off rapidly. It did not appear feasible to feed below the bed because insufficient MeOH
11 is carried up into the catalyst by the relatively small amount of 12 hydrocarbon present. Even with a large excess of MeOH (Run 2), 13 the selectivity decreased for the 45 mole % feed as compared to 14 the 35 mole % feed. The feed for the third run was moved to above the catalyst bed to insure that all of the MeOH contacted 16 the catalyst and the selectivity was regained.

~cr~.pat~t227.Dpp 14 9!3~) TABLE I
Run. no. 1 2 3 ic4 Feed 35% 4S% 50%
Pressure, psig 140 124 140 Cat Zone dP,~ 73 82 74 Feed Point Below cat. Below cat.~bov~ cat.
Temperature, 'F
Bottoms 313 274 227 Catalyst 157 153 129 Overhead 154 140 124 Feed Rate, g/hr 548.8 912 545 MeOH/iC4~ mole ratio1.06 1.4 1.1 Bottoms, g/hr 176 531 330 Bottoms analysis. wt~
Lt. ends 0/001 0.014 0.000 C4's 0.052 0.039 21.995 MeO~ 1.961 7.174 4.340 TBA 0.280 0.338 0.252 MTBE 97.469 82.332 73.390 Unk. 0O001 0.001 0.000 DIB-l 0.168 7.188 0.007 DIB-2 0.049 2.126 0.002 Hvys 0.020 0.798 0.000 MTBE production rate, g/hr/g cat. 3.43 - 4.37 4.84 MTBE purity, wt%
(excl lt ends and C4lS) 99.47 88.73 99.64 Conv. of IC4= to MTBE, % 68.57 63.86 74.32 \crl.p~t\1227.~pp 15 1 ~x~mple~
2 Two runs were made using a blanket of isobutane in the upper 3 portion of the column. The tower was started up to reflux with 4 isobutane and the IC4=~MeO~ was fed above the catalyst zone. The differential pressure in the froth mode was maintained (with a 6 constant heat input) by the feed rate balanced by the bottoms 7 withdrawal rate. The amount of isobutane necessary as a blanket 8 in the catalyst zone to accommoda~e the heat of reaction was g controlled by the position o~ a ~emperature break between the bottoms and the catalyst zone. The position was held constant by 11 occasional or continuous addition of the inert hydrocarbon.
12 Results are given in Table II.
13 Excellent temperature con~rol was possible using an 14 isobutane blanket in the catalyst zone to moderate the reaction of 100~ iC4= feed with 10% excess MeOX (Run 4). However, using 16 less than stoichiometric amounts of MeO~ allowed the loss of some 17 selectivity to MTBE (Run 5).
18 While there was still MeOH in the bottoms sample, the 19 bottoms contained less than 2~ total C4's. Better results should be achieved with a more efficient column. Hydrocarbon in the 21 effluent, in the case of pure iC4= ~eed, could be eliminated by 22 distillation below the catalyst bed. The use of an analytical 23 instrument to indicate MeO~ concentration continuously should 24 allow a minimum of MeOH to be withdraw~ with the MTBE by adjusting the feed of MeOX to a mlnimum. ~ higher concentration 26 of isobutane should help selectivity by increasing the a2 eotropic ~crl.pat\1227.rpp 16 1 amount of ~leOH distilling back into the cataly6t zone..
TABLE II
Run. no. ~ 5 iC4= Feed % 100 100 Pressure, psig 115 105 Cat Zone dP,~ 95 73 Feed Point Above cat. Above cat.
Temperature, F
Bottoms 251 264 Catalyst 155 155 Overhead 133 124 Feed Rate, g/hr 363 454 MeOH/iC4= mole ratio 1.1 0.95 Bottoms, g/hr 245 316 Bottoms analysis. wt%
Lt. ends 0.025 0.005 C4 ~S 1.418 1.930 MeOH 9.226 6.620 TBA 0.390 0.283 MTBE 85.332 88.536 Unk. 0.002 0.000 DIB-l 0.197 1.845 DIB-2 0.032 0.246 Hvys 0.113 0.246 MTBE production rate, g/hr/g cat. 4 .18 5 . 60 ~TBE purity, wt%
(excl lt ends andC4ls) 99. 25 96 . 82 Conv. of iC4= to MTBE, % 59.55 60.57 Effective dilution ratio in Reactor isobutene/isobutanel 2/100 10/100 esti~ate \crl.pat\12Z7.~pp 17

Claims (16)

1. A process for the production of MTBE from a substantially pure stream of isobutylene, comprising:
(a) concurrently feeding a first stream comprising substantially pure isobutylene and a second stream comprising methanol to a distillation column reactor into a feed zone;
(b) feeding a third stream comprising an inert C4 hydrocarbon to said distillation column reactor into said feed zone to maintain a mole ratio of isobutylene to C4 in the range of about 1:5 to 1:100 in said reactor; and (c) concurrently in said distillation column reactor (i) contacting said isobutylene with said methanol in a reaction distillation zone in the presence of an acid cation exchange resin in the form of a catalytic distillation structure thereby reacting a majority of said isobutylene with methanol to form MTBE, (ii) fractionating the resultant mixture in said reaction distillation zone whereby unreacted methanol, unreacted isobutylene and inert C4 hydrocarbons are maintained as overheads and MTBE, methanol and minor amounts of unreacted isobutylene and inert C4 hydrocarbon are recovered as bottoms; and (iii) condensing substantially all of said overheads and returning substantially all of said condensed overheads to said distillation column as reflux. The process according to claim 1 wherein make up inert C4 \crl.pat\1227.app hydrocarbon is added as necessary only to replace that removed.

2. The process according to claim 1 wherein make-up inert C4 hydrocarbon is added as necessary only to replace that removed.

3. The process according to claim 1 wherein a small bleed stream of said overheads is withdrawn to control the pressure in said distillation column reactor and said inert C4 hydrocarbon is added to replace that removed in said bleed stream.

4. The process according to claim 1 wherein the molar ratio of methanol to isobutylene fed to said distillation column reactor is 1:1.

5. The process according to claim 1 wherein the molar ratio of methanol to isobutylene fed to said distillation column reactor is greater than 1:1.

6. The process according to claim 5 wherein the molar ratio of methanol to isobutylene fed to said distillation column reactor is 1.1:1.

7. The process according to claim 1 wherein substantially all of said isobutylene reacts with methanol in said reaction distillation zone.

8. The process according to claim 1 wherein said feed zone is above said reaction distillation zone.

9. The process according to claim 1 wherein the combined concentration of unreacted isobutylene and inert C4 hydrocarbon in said bottoms is less than 2 wt%.

10. The process according to claim 3 wherein said inert C4 hydrocarbon stream contains small amounts of C3 and lighter hydrocarbons and substantially all of said C3 and lighter hydrocarbons are removed in said bleed stream.

11. The process according to claim 1 wherein the pressure in said distillation column reactor is in the range 100 to 200 psig.

12. The process according to claim 10 wherein the temperature in said reaction distillation zone is in the range of 120 to 180°F.

13. The process according to claim 1 wherein the rate of said make up inert C4 hydrocarbon is determined by the temperature directly below said reaction distillation zone.

14. The process according to claim 1 wherein said third stream is fed to said distillation column reactor alone until reflux is established and then said first and second streams are fed.

15. A process for the production of MTBE from a substantially pure stream of isobutylene, comprising:
(a) feeding a first stream comprising an inert C4 hydrocarbon to a distillation column reactor into a feed zone;
(b) after reflux of the first stream has been established terminating said first stream and concurrently feeding a second stream comprising substantially pure isobutylene and a third stream comprising methanol to said distillation column reactor into said feed zone;

(c) concurrently in said distillation column reactor;
(i) contacting said isobutylene with said methanol in a reaction distillation zone in the presence of an acid cation exchange resin in the form of a catalytic distillation structure thereby reacting a majority of said isobutylene with methanol to form MTBE, and (ii) fractionating the resultant mixture in said reaction distillation zone whereby unreacted methanol, unreacted isobutylene and inert C4 hydrocarbons are recovered as overheads and MTBE, methanol and minor amounts of unreacted isobutylene and inert C4 hydrocarbon are recovered as bottoms;
(d) condensing substantially all of said overheads and returning substantially all of said condensed overheads to said distillation column as reflux; and (e) adding make up inert C4 hydrocarbon from said first stream as necessary only to replace that incidentally removed.

16. The process according to claim 15 wherein a portion of said condensed overheads is diverted to a distillation zone below said reaction distillation zone.