Process for preparing tertiary alkyl ethers

DESCRIPTION

The present invention relates to a process for the preparation of tertiary alkyl ethers from isools and aliphatic alcohols.

More particularly, the present invention relates to the preparation of tertiary methyl butyl ether or tertiary methyl amyl ether from, respectively, isobutylene or isoamylene and methanol.

Hereinafter, reference will be made only to the preparation of tertiary methyl butyl ether for the sake of simplicity, however, it is intended that the process be fully valid for the preparation as well. others

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tertiary alkyl ethers, bearing in mind that the differences in boiling bridges between components and products are of the same order of magnitude.

The preparation of tertiary roethyl butyl ether (MTBE) is carried out according to the known technique by reacting isobutyl. N, generally contained in varying percentages in a C2 hydrocarbon fraction, with methanol in the presence of a suitable catalyst generally consisting of sulfonated styrene / divinylbenzene resins, at temperatures ranging from room temperature to about 100 ° C.

Pure isobutene is not available in practice at the premises and reference will be made to the above mentioned case of the hydrocarbon fraction in which it contains isobutene.

The reaction has the character of an equilibrium reaction and with the amounts of methanol close to the stoichiometric amount the transformation of (isobutene is in the order of 90% or more at temperatures such that a reasonable reaction rate can be obtained.

If higher degrees of conversion are desired, excess methanol is present which must be separated from the reaction product and recycled, which allows, under reasonable conditions, to reach degrees of conversion slightly above 9 ° C or more. Separation of the reaction product ç passage of the residual mixture to a second reaction phase, which allows, under near stoichiometric conditions, to reach conversion rates of about 99%.

However, in this case, the problem arises that, to perform this operation, it is necessary to vaporize the hydrocarbons twice in and employ two reactors and two distillation columns with increasing investment and operating costs.

The latest technique (European patent application N² 886 (published March 19, 1980)) suggests a solution to overcome the above problems and provides precisely for the feeding of a mixture containing isobutenoecmethanol to a catalyst-filled distillation column for the preparation of MTBE, wherein the catalyst functions. also as distillation filler, obtaining at the same time the formation of MTBE and the separation of MTBE from the hydrocarbons in C Cj.

process described in said patent application!

However, there are some serious drawbacks to the fact that the catalyst functions as a filler for the distillation column and is therefore required to comply with particular requirements and, in particular, must have a small pressure drop and indeed For this reason, it is employed in the form of corset ribbons which leave large spaces for the passage of steam and liquid but, on the other hand, present difficulties in preparing and loading on the column.

The process described in said European patent application furthermore has the disadvantage that the continuous phase within the column is represented by the vapor phase while the dispersed phase is the liquid phase and this results in low MTBE yields as the reaction proceeds. performs practically in vapor phase.

This gives rise to the possibility that sensitive amounts of dimers may form as there is a lack of alcohol in the vapor phase.

The Applicant has surprisingly found that all of the above drawbacks can be overcome by performing the formation reaction and separating tertiary methyl butyl ether (MTBE) from the accompanying hydrocarbons and compounds in a single plate fractionation column where some plates contain beds. of small bead catalyst for the preparation of tertiary alkyl ether (MTBE) b. based on sulfonated styrene / divinylbenzene resins.

The process according to the present invention comprises the following operations:

feeding the isoolefin-containing hydrocarbon feedstock into a plate fractionation column in which some plates containing catalyst beds consisting of sulfonated styrene / divinylbenzene resins are separated by groups of single fractionation plates or plates;

feeding alcohol alone near the fractional column head, preferably above the last catalyst bed and some (between * + and 8) plates below the reflux feed point;

- reaction of isoolefin with alcohol on plates containing catalyst beds dipped in the liquid containing the alcohol and through which vapors bubble; and

- separating the ether produced from the other compounds in both the fractionation plates and the catalyst bed plates, giving substantially pure ether at the bottom of the column and, on the head, the hydrocarbons in the filler and, possibly, the alcohol under the mixture. -.azeotropic mixture form with the cargo hydrocarbons.

The process according to the present invention, in the case of preparing MTBE, comprises the following operations:

- feeding the isobutene-containing hydrocarbon feedstock into a plate fractionation column, where some plates, which have the catalyst bed for the formation of MTBE, consisting of resins of^: sulfonated styrene / divinylben2ene are separated by groups of fractionation plates or only by a single fractionation plate;

feeding methanol alone near the head and preferably above the last catalyst bed and between 4 and 8 plates below the reflux feed point;

reaction of isobutene with methanol in the dishes containing the catalyst beds dipped in the liquid containing methanol and through which the vapor bubbles; and

- separation of the MTBE produced from the other compounds, both in the fractionation plates and in those containing catalyst bed, obtaining substantially pure MTBE in the lower part of the column and the hydrocarbons in different iso-butene heads; methanol in the amounts corresponding to the azeotropic mixture.

The process according to the present invention is carried out at a pressure of between 500 and 1000 kPa.

The isoolefin-containing hydrocarbon feedstock is fed to the plate column according to the present invention in such a position that there are at least 2 plates with catalyst beds above said feed and at least one plate with catalyst beds. catalyst below said feed. The vapors produced in the fractionation column boiler bubble through the catalyst beds, which are preferably no less than 3, and then methanol and isobutene react in the liquid phase covering each catalyst bed.

The catalyst is in the form of spheres with a diameter of between 0.5 and 1 mm and the thickness of each catalyst bed is of the order of magnitude of one meter, liquid present in each dish containing the catalyst flows into the distillation dish which It is underneath by one or more conventional drop pipes and the catalyst is always immersed in the liquid.

The catalyst remains attached to each plate and is contained at least at the base and top of the bed by nets that prevent its exit.

The present invention will be further explained by reference to the accompanying figure which represents a non-limiting embodiment.

In it, with (1) is indicated the fractionation plates and with (2) a fractionation plate which has above it a catalyst bed (3)? which is retained by the nets (4 and 5) ../? The liquid follows the path indicated by the arrows (6), passing through the catalyst bed. The vapor follows the path to the top indicated by the arrows (7). An example of non-limiting embodiment of the process according to the following is described below. with the present invention.

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Example

A distillation column was assembled using 10 cm diameter and 100 cm long flanged trunks containing 6 capsule distillation plates (2.2 capsules per plate).

The column was assembled by alternating 1 meter trunks full of catalyst with six-plate trunks with a total of 6 trunks above feed and 2 trunks below feed. The column was fed with 2 kg / hour of hydrocarbons containing 50% isobutene.

A reflux ratio of 1 to 1 was maintained and, together with reflux, 575 grams of methanol was introduced; worked at a pressure of 800 kPa at temperatures between 60 ° and 150 ° C; 1035 grams of hydrocarbons in C em em were obtained as head products. which contain 30 grams of methanol and 5 grams of isobutene. From the bottom, 15 grams of practically pure MTBE came out.