LU85466A1 - PROCESS FOR THE RECOVERY OF BUTENE-1 OF QUALITY SUITABLE FOR POLYMERIZATION - Google Patents

Description

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Process for the recovery of butene-1 of a quality suitable for polymerization.

The present invention relates to a method for the recovery. butene-1 extraction of suitable quality for polymerization.

Butene-1 is contained in the hydrocarbon streams comprising in variable percentages the following constituents: butene-1, isobutane, isobutene, n-butane, butenes-2, 10 hydrocarbons in and Cg both saturated and of olefinic character * butadiene, acetylenic derivatives.

The hydrocarbon streams to be used as raw materials according to the present invention have a low content of butadiene and acetylenic derivatives, so if the starting charge comes from the cracking process. the vapor, butadiene which it contains at a high rate must be eliminated using a solvent or any other process.

The composition of the hydrocarbon flows in to be used according to the present invention is between the following ranges:

Cj 0.2 - 1.5% by weight iC ^ 1 - 30% by weight 1- C ^ - 10 - 60 I by weight n-C4 3 - 20 I by weight 25- I-C4 “10 - 40% by weight 2- C4 ”8 - 30 î by weight

Cj. 0.1 - 1.0 J by weight

Butadiene + Acetylene 0.1 - 6% by weight

The problem posed is the recovery of butene-1 while keeping the conversion of butene-1 to butene-2 as low as possible in the stage of selective hydrogenation of butadiene and acetylene derivatives.

It is known from the prior art that the selective hydrogenation of butadiene and acetylenic hydrocarbons must be carried out before the stages of separation of the various constituents from butene-1, but when operating using processes known in the art there occurs at the same time as the hydrogenation also a significant isomerization of butene-1 J to butene-2.

2 The extent of this isomerization depends on the quantity of butadiene authorized by the standards relating to butene-1. The lower the maximum level of butadiene authorized by the standards of butene-1, the lower must be the quantity

* I

5 of butadiene residual in the hydrocarbon stream after hydrogenation, and higher is the loss of butene-1 due to the isomerization to butene-2.

As a simple indication, starting from an i $ n butadiene content of approximately 2% in the stream sent to the hydro-generation stage, if the maximum content of butadiene authorized in the standards for butene-1 is of 200 ppm, the loss of butene-1 as a result of isomerization will be approximately 2% by weight, if the standards for butene-1 authorize a content. .maximum of 50 ppm of butadiene, the loss by isomerization of butene-1 is greater than 5¾ by weight.

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The authors of the present invention have now discovered quite surprisingly that it is possible to reduce the drawbacks of the technique used in the prior art, using a stage of selective hydrogenation of butadiene and acetylenic derivatives, placed at an appropriate point in the installation.

The flow of hydrocarbons is subjected thereto to conventional treatments in order to separate the isobutene by transforming it into an alkyl-teitio-butyl ether by reaction with an aliphatic alcohol, preferably with methanol, in the presence of a heterogeneous catalyst comprising functional sulfonic groups on a styrene-divinlbenzene matrix, in particular of the "Amberlyst" 15 type (registered trademark).

By means of the reactions described, practically all of the isobutene is transformed into an alkyl tertiary butyl ether which, in turn, is removed by distillation in a manner. known.

The process according to the present invention consists in distilling, in a first distillation column operating at 3> at an absolute pressure of between 5 and 20 bars, the fraction containing the constituents mentioned above, free or almost free of isobutene, by obtaining a head flow consisting essentially of isobutane, and a tail flow comprising the residual constituents which in turn are distilled in a second distillation column under an absolute pressure of between 3 and 10 bars, giving a flow head consisting of butene-1 with a purity between 80¾ and 95¾ (containing butene-1 + basically butane and butadiene + acetylenic derivatives} and a tail stream containing the compounds with high boiling point 10, n -butane and cis- and trans-butene-2.

The overhead stream from the second distillation column is sent to a unit for selective hydrogenation of butadiene and acetylenic derivatives, the concentration of these compounds being reduced to a value between 15 and 200 ppm in order to meet the standards for butene-1 of suitable quality for polymerization.

The hydrogenation unit operates under the following conditions: inlet temperature 35 to 50 ° C, absolute pressure 4 to 20 bar.

The stream from the selective hydrogenation unit, freed from diene and acetylene compounds, is sent to a distillation column operating at an absolute pressure of between 3 and 10 bars, to obtain, from a plateau near the top from the column, butene-1 of a quality suitable for polymerization and, as bottoms stream, n-butane and. butenes-2 with reduced amounts of butene-1.

The process according to the present invention retains its advantages requiring extremely mild reaction conditions even in the case where the selective hydrogenation must be carried out in the presence of inhibitors of isomerization of the bonding of butene-1 to butene-2, which have to be added to the C 4 hydrocarbon feed.

In addition, the process according to the present invention has, in all cases, the additional advantage of being able to reduce the dimensions of the equipment necessary for selective hydrogenation and therefore reduce the capital invested.

4. . As regards the types of the constituents of the various streams, reference is made to the example below, which is not intended to be a limit for the invention as regards the concentrations of the various constituents in any single stream. and with regard to the pressures under which the various stages operate.

EXAMPLE

The example was carried out according to the diagram illustrated in the single drawing attached, which does not represent a limit 10 to the present invention, drawing in which (1) is the flow of hydrocarbons including inter alia butene-1 , isobutene, butadiene and acetylene derivatives, (2) is a stream of methanol sent to the etherification unit (16) of isobutene, (3) is the stream of methyl tether ether- butyli-15 that obtained (4) is the flow that is substantially free of isobutene, (18) is the first distillation column operating at an absolute pressure of approximately 14 bars, (5) is the overhead flow essentially comprising isobutane , (6) is the tail stream which is sent to the second distillation column (19) operating under an absolute pressure of approximately 6 bars, (7) is a stream containing essentially butene (1), ( 8) is a stream containing the heavy products; the stream (7) is sent to the hydrogenation unit (17) to which hydrogen is sent via the line (9), and from which is discharged. . 25, gë the flow (11) consisting essentially of hydrogen in excess and butene-1; (10) is the hydrogenated stream which is sent I r in the fractionation column (20) operating under an absolute pressure of * .about 7 bars, from the top of which there is; iin i flow (12) consisting of non-condensed materials, - · · 30 · bl; es and butene-1, and we get out of the tenth plateau from the flax top flüx (13) containing butene-1 quali- * y%,. tee suitable for polymerization, and by the bottom we> ‘obtain the residue (14) consisting essentially of n- V '‘! butane and desbutene-2.

The stream (15) is a mixture of the streams (5), (B) and (14).

The balance of the process is indicated in the table below where the J numbers of the positions correspond to those of the drawing. 1 l · - 5 c »g- I I I I! I I I I i

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Claims (1)

1. Process for the recovery of butene-1 from qua-. lity suitable for polymerization from a fraction C 4, which contains it, free of isobutene or almost free of isobutene, which consists in distilling this fraction in a • first distillation column under an absolute pressure between 5 and 20 bars, obtaining a head stream containing essentially isobutane and a tail stream containing the residual constituents, and distilling the stream containing the 10 residual constituents in a second distillation column under an absolute pressure of between 3 and 10 bars, obtaining a head stream of butene-1 with a purity of between 80 and 95¾ and a tail stream comprising the compounds with high boiling point, n-butane and 2-butenes cis- and 15 trans-, this process being characterized in that the overhead stream coming from the second distillation column is sent to a unit for selective hydrogenation of butadiene and acetylenic derivatives, these compounds being reduced at a concentration of between 30 and 200 ppm, that the stream leaving the selective hydrogenation unit is ultimately sent to a distillation column operating at an absolute pressure of between 3 and 10 bars, to obtain from a tray near the top of the column butene-1 of suitable quality for polymerization. t ---, s a *