CS219316B2 - Method of making the methylterc,butylether - 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

The present invention provides a process for the preparation of methyl tert-butyl ether.

It is known that tert-alkyl ethers can be prepared by reacting a primary alcohol with olefins bearing a double bond on the tertiary carbon atom, so methanol reacts with isobttylene or isoamylenes (Z-methylpenten-1 or -2) to form methyl t-t-butyl. ether (MTBE) or methyl t-amyl ether (MTAE).

The reaction is so selective for tertiary olefins that it constitutes a valuable process for removing them from the olefin streams in which it is present together with the linear non-active olefins.

The reaction has an equilibrium state the more favorable to ether synthesis, the lower the reaction temperature coincides with its negative enthalpy.

It is known that the reaction is' catalysed by Lewis acids (aluminum chloride, boron trifluoride), inorganic acids (sulfuric acid) and organic acids (alkylaryl-sulfonic acids, ion exchange resins).

Ion exchange resins are particularly suitable for this purpose. acidic form, and it is known that the truly best results are obtained with "Amberlyst" micro-crosslinked resins. By using such catalysts it is possible to achieve thermodynamic equilibrium in contact times which are industrially acceptable at 'temperatures' of 50 to 60 ° C. At lower temperatures, more thermodynamically more favorable, the kinetics '' are not high enough to allow in practice to achieve equilibrium.

This-. de facto limits conversions; indeed, in the case of isobutylene and methanol used at equimolecular ratios, the conversions achieved do not exceed 92%.

Increasing the conversion of the reactant can naturally be achieved by increasing the content of the second reactants in the feed, but this results in a reduction in the conversion of the excess reactant. It. it may cause certain disadvantages, as it happens, for example, in the synthesis of MTBE from methanol and isobutylene contained in olefin fractions.

The use of an excess of isobutylene results in the olefin stream after the MTBE combination still contains 5 to 100% isobutylene, and this is a disadvantage when using said fraction in the production of maleic anhydride or butadiene, on the contrary, an excess of methanol. it makes it very difficult to purify MTBE due to the formation of azeotropic mixtures.

It is an object of the present invention to provide a process which makes it possible to achieve a high conversion of both reactants, and this has not yet been achieved by any of the processes proposed to date.

The object of the present invention is to achieve a high conversion for both reactants, although they are globally maintained in stoichiometric ratios.

SUMMARY OF THE INVENTION The present invention provides a process for the preparation of methyl tert-butyl ether by reacting methanol with isobutylene in the presence of an ion exchange resin, characterized in that the reaction is carried out at a space velocity of 20 to 50 volumes per reaction volume per catalyst in two steps. the molar ratio of isobutylene to methanol in the first step being 0.4 to 0.8 and in the second step 1.5 to 4.

The process according to the invention is particularly suitable for the preparation of tert-butyl tertiates from isobutylene and alcohols, proceeding with a large excess of olefins without the side-reaction of isobutylene.

The process according to the invention is shown schematically in the drawings, in which Fig. 1 represents the synthesis of methyl tertiary butyl ether (MBTE) from methanol and isobutylene. The diagram shows the line 1 for methanol feed, line 2 for the olefinic feed mixture, line 3 for the top product of the second distillation column, line 4 for product discharge from the first reactor, line 5 for the bottom product from the first distillation column, line 6 ¹ for removal of the olefin fraction from the first distillation column, product discharge line 7 from the second reactor, and line 8 for removal of the obtained methyl tert-butyl ether from the bottom of the second distillation column.

The process is carried out by feeding methanol into the first reactor together with the product from the top of the second distillation column consisting of reduced olefin content. The reaction mixture in this reactor contains an excess of methanol so that a high isobutylene conversion is obtained. The product from the first reactor enters the first distillation column, from which an olefin fraction with an isobutylene content of less than 2% is discharged from the top and a mixture of methanol and methyl methyl ether is obtained at the bottom. This mixture, mixed with the starting olefinic mixture, is fed to a second reactor. The reaction mixture in this reactor contains an excess of isobttylene so that a high methanol conversion occurs. The product from the second reactor enters a second distillation column, from whose bottom a high degree of methyl tert-butyl ether is removed and from the upper part an olefinic mixture with a reduced isobutylene content of δ is added to the first reactor.

In the second reactor, where a large excess of isobutylene is employed, secondary isomerization reactions of isobutylene can actually occur, which actually occur at 60-70 ° C and at a space velocity of 5-10 volumes of the mixture per catalyst volume per hour.

This phenomenon can be minimized by separating the olefin mixture into both the first and second reactors (see Example 2).

However, it has been found that high selectivity can be achieved even in the presence of an excess of isobutylene when operating at 60 ° C and space velocity. 40, no conversion reduction. mttУylttrc.Uutylltttytru.

The diagram shown in Fig. 2 represents a variant of the process of Fig. 1, wherein the olefin is fed not only to the second reactor but is distributed between the first and second reactors. FIG. 2 shows the methanol feed line 1, the olefin feed line 2 divided into the line 4 and the line 5. Further, the product line 6 for the removal of the product from the first reactor, the product line 7 for the removal of the bottom product from the first reactor. the first distillation column, the product discharge line 8 from the second reactor, the product 9 discharge line from the second distillation column, the upper product discharge line 10 from the first distillation column, and the upper product discharge line 3 from the second distillation column.

Example 1

The operation was performed in accordance with Figure 1.

21.11 parts by weight of methanol were connected to the stream leaving the top of the second column and consisting of 23.38 parts of isobutylene, 43.43 parts of linear olefins and 0.35 parts of methanol. The mixture in which the isobutylene-methanol molar ratio was 0.62 was dosed. to a reactor where it was reacted in the presence of Amberlyst 15 at 60 ° C and at a space velocity of 5 volumes per hour / catalyst volume and at a pressure sufficient to keep the system in a liquid state.

The stream coming from the first reactor through line 4 consisting of 8.46 parts of methanol, 35.76 parts of MTBE, 0.62 parts of isobutylene and 43.43 parts of linear butenes was fed to the first distillation column. 44.95 parts of the following fraction were obtained from its head via line 6 ':

isobutylene (% w / w) = 1.4 methanol (% w / w) = 2.0 linear olefins (% w / w) = 96.6

35.76 parts of MTBE and 7.56 parts of methanol were withdrawn from the bottom of the column through line 3, and these, together with 37.00 parts of isobutylene and 43.43 parts of linear butenes from line 2, were fed to a second reactor where they reacted over Amberlyst 15 at 60 ° C and a space velocity of 40 vol / vol. 'h. In the second reactor, the molar ratio of isobutylene to methanol was 2.8.

The stream exiting from the second reactor through line 7 consisted of 55.60 parts of MTBE, 0.35 parts of methanol, 23.38 parts of isobutylene, 53.43 parts of linear butenes and 0.99 parts of diisobutylene. The reaction product was fed through line 7 to a second distillation column from which 23.38 parts of isobutylene, 43.43 parts of linear butenes and 0.35 parts of methanol were taken from line 3 through line 3. These materials were recycled to the first reactor and 56.59 parts of MTBE of 98.25% purity were removed from its bottom via line 8.

The total methanol conversion was 96% with a selectivity of 100% and the isobutylene conversion was 98% with a selectivity of 97%.

Example 2

This example differs from the previous one and is shown in Fig. 2.

32.12 parts by weight of methanol (line 1) were combined with the stream exiting line 3 from the top of the second distillation column, consisting of 0.98 parts of methanol, 40.73 parts of linear butenes and 23.94 parts of isobutylene, and part (line 4). of olefin feed (line 2), which part consisted of 16.44 parts of isobutylene and 16.77 parts of linear butenes.

The reaction mixture with an isobutylene to methanol ratio of 0.72 was fed to the first reactor at a space velocity of 5 v / v. b. Reacted over Amberlyst 15 at 60 ° C and at a pressure sufficient to maintain the system in a liquid state.

The reaction product leaving line 6 consisted of 10.67 parts of methanol, 1.11 parts of isobutylene, 57.50 parts of linear butenes and 61.70 parts of MTBE, and was fed to a first distillation column from which 59 was fed through line 10, 67 parts fraction with isobutylene (% by weight)> = 1.9 methanol (% by weight) - 1.8 linear bulbs (% by weight) = 96.3

From the bottom of the column, 9.61 parts of methanol and 61.70 parts of MTBE were recovered via line 7.

The bottom product from the first distillation column leaving line 7, together with 39.66 parts of isobutylene and 40.73 parts of linear butenes (line 5), constituting the remaining amount of olefin feed (line 2), reacted in the second reactor at 60 ° C and space velocity. 40% v / v In this case, the ratio of isobutylene to methanol was 2.35. The reaction product, consisting of 0.98 parts of methanol, 85.45 parts of MTBE, 23.94 parts of isobutylene, 40.73 parts of linear butenes and 0.88 parts of diisobutylein, was fed via line 8 to a second distillation column from which the capillary was fed via line 3 0.93 parts of methanol, 23.94 parts of isobutylene and 40.73 parts of linear butenes recycled to the first reactor.

From the bottom of the second distillation column, 9 86.33 parts of MTBE having a purity of 99% were obtained via line.

The total methanol conversion was 96.7% with a selectivity of 100%. The isobutylene conversion was 98% with a selectivity of 98%.

Example 3

The feed to the second reactor from the previous example was reacted at two different temperatures and three different space velocities with the following results:

temperature ° C 60 70 spatial velocity -obj./obj. h. 3 8.5 40 3 8.5 40 total isobutylene conversion 61 55 44 63 55 45.5 conversion of isobutylene to MTBE 41.5 46.5 41 43 42.5 37 selectivity 68 83 93 68 77.5 82

OBJECT OF THE INVENTION

Claims (3)

A process for the preparation of methyl tert-butyl ether by reacting methanol with isobutylene in the presence of an ion exchange resin, characterized in that the reaction is carried out at a space velocity of 20 to 50 volumes of reaction mixture per catalyst volume per hour in two steps. to methanol in the first stage 0.4 to 0.8 and in the second stage 1.5 to 4. 2. The process of claim 1 wherein in the first step the total amount of one reactant is reacted with the product of the second step obtained by reacting the total amount of the second reactant with the product of the first step. 3. A process according to claim 1, wherein the total amount of olefin feed is divided into two portions, wherein 65-75% of the total amount is used in the reaction step in the presence of an excess of olefin and the remainder is conducted. together with the product of said step to the second step.