IE43301B1 - Process for producing tertiary alkyl ethers - Google Patents

Abstract

1506312 Tertiary alkyl ethers SNAMPROGETTI SpA 13 May 1975 [21 May 1974] 20209/75 Heading C2C A tertiary alkyl ester is produced by reacting an alcohol with an olefin having a carboncarbon double bond on a tertiary carbon atom in the presence of an ion-exchange resin in atleast two stages, whereinin one stage the alcohol is present in excess and in another stage the olefin is in excess. The reaction may be carried out using two reactors; all of one reactant is fed to one reactor while all or part of the other reactant is fed to the other reactor, and reaction products are at least in part circulated from one reactor to the other. The invention is exemplified by the reaction of isobutene in a mixed olefin stream with methanol to form methyl tertiary butyl ether. A suitable apparatus is described. Reference has been directed by the Comptroller to Specification 1,176,620.

Description

This invention relates to a process for the production of tertiary alkyl ethers.

It is known that tertiary alkyl ethers can be prepared by reacting a primary alcohol with an olefin having a carbon-carbon double bond on a tertiary carbon atom; thus methanol reacts with isobutene or isoamylenes (2-methyl-pent-1 or 2-ene) to form respectively methyl tertiary butyl ether (hereinafter abbreviated to MTBE) and methyl tertiary amyl ether.

The reaction is so selective for tertiary olefins that it constitutes a useful process for their removal from olefinic stream in which they are contained together with linear unreactive olefins.

The reaction has an equilibrium v/hich is the more favourable to the synthesis of the ether the lower the reaction temperature, in accordance with its negative enthalpy.

According to the present invention, there is provided a process for producing a tertiary alkyl ether, which process comprises reacting an alcohol with an olefin having a carbon-carbon double bond on a tertiary carbon atom, in the presence of an ion exchange resin in at least two stages, wherein in one of the stages the alcohol is present in excess and wherein in another of the stages the olefin is present in excess.

, Conveniently the reaction is carried out in two stages, the first stage in a first reactor and the second stage in a -243301 second reactor.

In one embodiment of the present invention, all of the fresh alcohol feed is fed directly to the first or second reactor, all of the fresh olefin feed is fed directly to the second or first reactor respectively, part of the reaction product from the second reactor is recycled to the first reactor whereby that reagent fed directly to the second reactor is introduced indirectly into the first reactor, and at least part of the reaction product from the first reactor is fed to the second reactor.

In an alternative embodiment of the present invention, all of one of the two reagents is fed directly to the first reactor, part of the other reagent is fed directly to the first reactor, the remainder of the other reagent is fed directly to the second reactor, at least part of the reaction product from the first reactor is fed to the second reactor, and part of the reaction product from the second reactor is recycled to the first reactor.

The ion exchange resins act as catalysts, and particularly suitable to the task are the ion exchange resins in their acid form; good results are obtainable with macroreticular resins of the Amberlyst 15 type. Amberlyst 15 is a styrene-divinyl based resin have SO^ functional groups, a porosity of 32%, a surface area of about 45 square metres per gram and an ion exchange capacity of 4.7 to 4.9 milliequivalents per gram. By means of such catalysts it is possible to reach the thermodynamic equilibrium with industrially acceptable contact times, at temperatures of 5O-6O°C. At lower temperatures, although thermodynamically more favourable, the rate is not sufficiently high to permit in practice the attainment of equilibrium. -3Ϊ301 In one embodiment the tertiary olefin is fed as a mixture of that olefin with other olefins.

Preferably the reaction is carried out at a liquid hourly space velocity in the range of from 20 to 50 LHSV, to reduce the likelihood of oligomerization of the tertiary olefin.

For a better understanding of the present invention and to show how the same can be carried into effect, reference will now be made, by way of example, to the accompanying drawings in which:Figure 1 represents a plant for synthesizing methyl tertiary butyl ether starting from methanol and isobutene; and Figure 2 shows a modified plant for the same purpose as that of Figure 1.

In the plant of Figure 1, methanol is fed through a pipe 1 to a reactor Rl together with the effluent stream in a pipe 3 from the top of a column C2, this stream being constituted by an olefinic stream having a reduced content of isobutene.

The reaction mixture in reactor Rl contains an excess of methanol so that the isobutene conversion is high.

The effluent stream in a pipe 4 from reactor Rl enters a distillation column Cl from the top of which an olefinic fraction in a pipe 6 is obtained, in which the isobutene is lower than 2%, and from the bottom of which in a pipe 5 a mixture of methanol and MTBE is obtained. -443301 The bottom stream in pipe 5 and an olefinic feed in a pipe 2 are introduced into a reactor R2. The reaction mixture in R2 contains an excess of isobutene so that the methanol conversion is high.

The product in a pipe 7 leaving the reactor R2 enters the distillation column C2 from the bottom of which MTBE with a high degree of purity is discharged in a pipe 8 and from the top of which an olefinic stream with a reduced content of isobutene is discharged' and is recycled in pipe 3 to reactor Rl.

In reactor R2 there is a large excess of isobutene, and it is possible to have secondary oligomerization reactions, of isobutene and this is what effectively occurs by working at 60-70 °C and liquid hourly space velocities (LHSV) in the range 5-10. The phenomenon can be minimized by distributing the olefin feed both to reactor Rl and to reactor R2 (as described in Example 2).

It has been found however that it is possible to obtain high selectivities even in the presence of an excess of isobutene, by working at 60 °C and LHSV of 40 in reactor R2, without lowering the conversion to MTBE.

The plant shown in Figure 2 represents a variant of the plant illustrated in Figure 1, in which the fresh olefin feed is fed directly not only to reactor R2 but also to reactor Rl.

In Figure 2, Rl and R2 represent the first and second reactors, Cl and C2 represent the first and second distillation -543301 columns, 1 represents the pipe conveying methanol feed to reactor Hl, 2 the pipe carrying fresh olefin feed to the system, 3 the pipe conveying the overhead product of column 2, 4 the pipe conveying part of the olefin feed in pipe 2 to reactor Hl, 5 the pipe conveying the remainder of the olefin feed in pipe 2 to the reactor R2, 6 the pipe conveying the reaction product from reactor Rl to column Cl, the pipe conveying the bottom product from column Cl to reactor R2, 8 the pipe conveying the reaction product from reactor H2 to the column C2, 9 the pipe withdrawing the bottom product (MTBE) from the column C2, and 10 the pipe withdrawing the overhead product (olefin with low isobutene content) from the top of column Cl.

The present invention will now be illustrated by the following Examples, in which the process of Example 1 was carried out on the plant as shown in Figure 1 and in which the processes of Examples 2 and 3 were carried out on the plant as shown in Figure 2. In the Examples all parts by weight unless otherwise specified.

EXAMPLE 1 . 21.11 Parts of methanol in pipe 1 were combined with the stream in pipe 3 leaving the top of column C2, constituted by 23.38 parts of isobutene, 43.43 parts of linear olefins and 0.35 part of methanol. The resulting mixture, in which the isobutylene:methanol molar ratio was 0.62:1, was fed to reactor Rl wherein it reacted in the presence of Amberlyst 15 at a temperature of 60 °C with LHSV of 5 volumes per hour -64 33 0 and per volume of catalyst and at a pressure sufficient to maintain the system in the liquid phase.

The effluent stream in pipe 4 from reactor Rl, which was constituted by 8.46 parts of methanol, 35.76 parts of MTBE, 0.62 part of isobutene and 43,43 parts of linear butenes was fed to distillation column Cl; from the top of Cl in pipe 6 there were obtained 44.95 parts oi a fraction having the following percent by weight composition: isobutene = 1,4 methanol = 2.0 linear olefines = 96.6, From the bottom of column Cl in pipe 5 35.76 parts of MTBE and 7.56 parts of methanol were fed, together with 37.00 parts of isobutlene and 43.43 parts of linear butenes in pipe 2, to reactor R2 wherein they reacted over Amberlyst 15 at the temperature of 60 °C and with LHSV of 40.

In R2 the isobutene .'methanol molar ratio was 2.8:1.

The effluent stream in pipe 7 from reactor R2 was constituted by 55.60 parts of MTBE, 0.35 part of methanol, 23.38 parts of isobutene, 53.43 parts of linear butenes and 0.99 part of diisobutene. The reaction product in pipe 7 was fed to distillation column C2 from the top of which through pipe 3 23.38 parts of isobutene, 43.43 parts of linear butenes and 0.35 part of methanol were recycled to reactor Rl, and from the bottom of which, through pipe 8, 56.59 parts of MTBE at 98.25% purity were withdrawn.

The overall conversion of methanol was 96% with a -74 3 3 01 a selectivity with respect to MTBE of 100% while the isobutene conversion was 98% with a selectivity with respect to MTBE of 97%.

EXAMPLE 2 32.12 Parts of methanol in pipe 1 were combined with (i) the effluent stream in pipe 3 from the top of column C2, constituted by 0.98 part of methanol^ 40.73 parts of linear butenes and 23.94 parts of isobutene and (ii) a portion in pipe 4 of the feed olefins in pipe 2, this r portion being constituted by 16.44 parts of isobutene and 16.77 parts of linear butenes.

The reaction mixture, in which the isobutene: . methanol molar ratio was 0.72:1 was fed to reaction Rl with LHSV of 5; it reacted in reactor Rl over Amberlyst 15 at 60 °C and at a pressure sufficient to maintain the system in the liquid state.

The reaction product ih pipe 6 constituted by 10.67 parts of methanol, 1.11 parts of isobutene, 57.50 parts of linear butenes and 61.70 parts of MTBE, was fed to distillation column Cl from the top of which were obtained in pipe 10 59.67 parts of a fraction having the following percent by weight composition: isobutene = 1.9 methanol = 1.8 linear butenes = 96.3 From the bottom of column Cl were obtained in pipe 7 9.61 parts of methanol and 61.70 parts of MTBE. -843301 The bottom product of column Cl in pipe 7 was reacted in reactor R2 with 39.66 parts of isobutene and 40,73 parts of linear butenes fed in pipe 5 and constituting remaining portion of the olefinic feed in pipe 2; this reaction in R2 took place at 60°C and LHSV of 40. In this case the isobutene:methanol ratio was 2,35:1. The reaction product in pipe 8 constituting by 0.98 part of methanol, 85.45 parts' of MTBE, 23.94 parts of isobutene, 40.73 parts of linear butenes and 0.88 parts of diisobutene was sent to distillation column C2 from which the distilled top product constituted by 0.98 part of methanol, 23.94 parts of isobutene and 40.73 parts of linear butenes, were recycled in line 3 to reactor Rl.

From the bottom of column C2 in pipe 9 were recovered 86.33 parts of MTBE at 99% purity.

The overall conversion of methanol was 96.7% with a selectivity with respect to MTBE of 100% and the isobutene conversion was 98% with a selectivity with respect to MTBE of 98%.

EXAMPLE 3 The feed to reactor R2 of Example 2, when reacted at two different temperatures and at three different space velocities, gave the following results: -913301 Temperature LHSV 60 °C 70 °C 3 8.5 40 3 8.5 40 Total conversion 61 55 44 63 55 45.5 of isobutene Conversion of isobutene 41.5 46.5 41 43 42.5 37 to MTBE Selectivity with respect 68 84 93 68 77.5 •81 to MTBE LHSV = Liquid hourly space velocity expressed as volumes of liquid feed per volume of catalyst per hour.

Our Patent Specification No. 43300 describes and claims a process for producing an alkyl tertiary butyl ether, which process comprises feeding a primary alchol and a hydrocarbon stream comprising isobutene and buta - 1,3 - diene, wherein there is at least 4% by weight of buta - 1,3 - diene in the hydrocarbon stream, to a synthesis zone containing as catalystan acid ion exchange resin, at a temperature in the range from 60 to 12O°C, with a liquid hourly space velocity (expressed as the volume of liquid per hour and per volume of catalyst) in the range of from 5 to 35, and wherein the temperature in the synthesis zone is approximately in accordance with the following equation T = 2 (LHSV+25) where T is the temperature expressed as °C and LHSV is the liquid hourly space velocity; and separating downstream of the synthesis zone the resulting alkyl tertiary butyl ether from other compound(s) present by distillation.

Claims (11)

1. CLAIMS; 1. A process for producing a tertiary alkyl ether, which process comprises reacting an alcohol with an olefin having a. carbon-carbon double bond on a tertiary carbon atom, in the 5 | presence of anion exchange resin in at least two stages, wherein in one of the stages the alcohol is present in excess and wherein in another of the stages the olefin is present in excess.

2. A process according to claim 1, wherein the reaction is carried out in two stages, the first stage in a first -, reactor and the second stage in a second reactor.

3. A process according to claim 2, wherein all of the fresh alcohol feed is fed directly to the first or second 15 reactor, all of the fresh olefin feed is fed directly to the second or first reactor respectively, part of the reaction product from the second reactor is recycled to the first reactor whereby that reagent fed directly to the I second reactor is introduced indirectly into the first 20 reactor,and at least part of the reaction product from the first reactor is fed to the second reactor.

4. A process according to claim 2, wherein all of one of the two reagents is fed directly to the first reactor, part of the other reagent is fed directly to the first 25 reactor, the remainder of the other reagent is fed directly to the second reactor, at least part of the reaction product from -115330 1 the first reactor is fed to the second reactor, and part of the reaction product from the second reactor is recycled to the first reactor.

5. A process according to any preceding claim, wherein the tertiary olefin is fed as a mixture of that olefin with other olefins. •I !

6. A process according to any preceding claim, wherein the tertiary olefin is isobutene and the alcohol is methanol.

7. A process according to any preceding claim, wherein the tertiary olefin liquid hourly space velocity is in the range of from 20 to 50h \

8. A process according to claim 1 substantially as described with reference to Figure 1 of the accompanying drawings.

9. A process according to claim 1 substantially as described with reference to Figure 2 of the accompanying drawings.

10. A process according to claim 1 substantially as described in any one of the foregoing Examples.

11. A tertiary alkyl ether whenever produced by a process according to any preceding claim.