LU85148A1 - PROCESS FOR PURIFYING CHARGES OF C4 HYDROCARBONS - Google Patents

Description

(ο PROCESS OF. PURIFICATION OF C, HYDROCARBON CHARGES.

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The present invention relates to a process for purifying a C 4 hydrocarbon feedstock. In particular, the present invention relates to a process for the purification of C 4 hydrocarbon charges depleted in isobutylene following their passage through the tertiary-butyl methyl ether preparation unit.

The C ^ hydrocarbon feedstocks are generally intended to be polymerized in order to manufacture in particular polymers such as poly n-butenes which have advantageous uses in the field of lubricating oils, or even when one limits oneself to oligomerization, oligomers can be used directly as gasoline already having a very good octane number. More recently, it has been found that it is advantageous to extract the isobutylene from this hydrocarbon charge in order to transform it in a separate unit into methyl tertiary butyl ether, hereinafter called MTBE. It can be recalled that MTBE is a very interesting additive to essences. It is obtained by reacting a charge of hydrocarbons containing isobutylene with methanol in the presence of a suitable catalyst.

The Applicant has observed that the activity of the catalyst used during the polymerization or the oligomerization of the hydrocarbon feedstock t - 2 - depleted in isobutylene following its passage through the MTBE preparation unit, is considerably reduced after a short time. In fact, this reduction reaches values of the order of 60%, which is extremely unfavorable from the point of view of the yield of the polymerization reaction, thus resulting in high costs for replacing the catalyst.

The object of the present invention is to remedy this drawback. The subject of the present invention is a process for the efficient purification of C 4 hydrocarbon feedstocks, in particular those depleted in isobutylene as a result of their passage through an MTBE preparation unit, with a view to considerably improving and even avoiding any deactivation of the polymerization catalyst for these charges.

The process of the present invention for purifying the C 4 hydrocarbon feedstocks, in particular those depleted in isobutylene, originating from the manufacture of MTBE, is characterized in that it consists in passing the charge leaving the MTBE unit on absorbent material

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bant of the molecular sieve type having a pore opening of about 10A.

The Applicant has in fact unexpectedly found that by passing the charge of hydrocarbons depleted in isobutylene following its passage through the MTBE preparation unit, over a molecular sieve having pore opening characteristics.

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about 10A, before sending it to the polymerization reactor, the activity of the polymerization catalyst was maintained at a very high level, generally greater than 90%, for a very long period of time.

In fact, the feed, which was purified by passage through a molecular sieve of the 13X type, was subsequently polymerized, without any reduction in the activity of the catalyst being observed.

The molecular sieve used, of the 13X type, has pore opening characteristics of the order of 10A, that is to say that it can absorb

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all polar molecules having a diameter of less than about 10A.

Although we speak of molecular sieves, it is obvious that zeolites having a sufficient pore opening can also be used in the process of the invention.

Without being bound by the advanced theory, it seems that this type of absorbent considerably reduces the dimethyl ether content of the feed, which seems to be a poison for poly- catalysts. merit used later. The charge thus freed from the quantity of dimethyl ether which it contained is polymerized normally thereafter, generally in the presence of a usual catalyst of the phosphoric acid type on Kieselguhr, at temperatures of the order of 150 to 200 ° C. and under a pressure of the order of 30 to 60 kg / cm.

The purification process of the present invention is generally carried out at room temperature and under a pressure sufficient to work in the liquid phase. The pressures generally used are 2 between 3 and 60 kg / cm.

The Applicant has also found that the time at which the purification of the charges mentioned in the present invention is carried out is very important.

Thus, it has been found that it is imperative to carry out the purification of the hydrocarbon charges on leaving the MTBE preparation unit, and in any case before entering the polymerization reactor, in order to have maximum efficiency of the purification step, this r effectiveness being zero when the purification is carried out before the charges pass through the MTBE preparation unit.

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The following examples are given to illustrate the process of the present invention, but without limiting its scope.

Example 1

A charge of hydrocarbons was passed from the MTBE preparation unit, the composition of which was 7% by weight propane 1.1 * propylene 0.2 isabutane 42.8 n-butane 11.6 1-butene 19.5 trans-2-butene 15.1 cis-2 -butene 9.4 butadiene 0.3 on a molecular sieve, of the 13X type, at room temperature, around 25 ° C.,. and under a pressure of 5 kg / cm ^, at an hourly space velocity of liquid of 0.5 h \ before entering the polymerization reactor.

This charge, thus purified, was subjected to a polymerization in the presence of 100 ml of a phosphoric acid catalyst deposited on Kieselguhr under the following conditions:

- temperature: 175 ° C

- hourly space velocity of liquid: 1.5 hours ^ / - - 5 - - pressure: 45 kg / cm ^

Under these conditions, the conversion rate of butenes present in the feed was 93% at the start.

R After 150 hours of operation, the conversion rate, calculated on the same basis, was 92%.

For comparison, the same charge was passed directly into the polymerization reactor, thereby omitting passage through the molecular sieve.

The polymerization was carried out according to the conditions described above, and the degree of conversion of the butenes present in the feed was measured.

At the start we had 92% conversion whereas after 120 hours, it was already only 25%.

This example clearly shows the importance of the purification treatment of the present invention.

By way of comparison, a fresh charge of C ^ hydrocarbons was passed through, coming directly from the catalytic cracking unit over a molecular sieve of the 13X type before being sent successively to the MTBE preparation unit and in the polymerization reactor.

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The charge composition was f% by weight propane 0.7 'propylene 0.1 isobutane 35.2 n-butane 9.6 1-butene 13.0 isobutylene 17.5 trans 2-butene 12.9 cis 2-butene 8.9 _ butadiene 0.3 C4 + 1.8 At the outlet of the unit preparation of MTBE, the charge depleted in isobutylene was sent directly to the polymerization reactor.

The polymerization was carried out under the conditions described in Example 1.

The butene conversion rate of the feed was measured and 92% was determined at the start and after 100 hours the conversion rate was not. more than 30%.

Example 2

A fresh charge of C 4 hydrocarbons was passed through, coming directly from the catalytic cracking unit and before sending it to the MTBE preparation unit, over a molecular sieve as defined in Example 1 The charge had the following composition: - 7 -% by weight propane 0.7 propylene 0.1 * iso-butene iC, 35.2 4 n-butane nC, 9.6 4 1-butene 1-C. 13.0 4 isobutylene i-C ^ 17.5 trans-2-butene 12.9 cis-2-butene 8.9

Cl 0.3 and 1.8 4

The charge thus purified was passed over the polymerization catalyst under the same operating conditions as those described in Example 1. The polymerization was carried out according to the conditions described in Example 1 and the conversion rate of the butenes present in the charge. Initially, we had 92% conversion and after 150 hours of operation, the conversion rate, calculated on the same basis, was still 92%.

For comparison, the same charge was passed directly into the polymerization reactor, thereby omitting passage * over the molecular sieve. The polymerization was carried out under the same operating conditions described in Example 1 and the conversion rate of the butenes present in the feed was measured. At the start, we had 92% and after 150 hours of operation, the conversion rate, calculated on the same basis, was still 92%. This example clearly shows

Claims (5)

1. Process for purifying hydrocarbon charges depleted in isobutylene originating from the manufacture of MTBE obtained from a hydrocarbon charge in and inethanol, characterized in that the charge leaving the unit of MTBE on an absorbent material of the molecular sieve type having a pore opening of about 10A. 2. Process for the purification of C ^ hydrocarbon charges, depleted in isobutylene originating from the manufacture of MTBE obtained from a hydrocarbon charge of methanol, characterized in that it consists in passing the charge from the MTBE unit on an absorbent material of the molecular sieve type having an O pore opening of approximately 10 A and before sending it to a polymerization reactor. 3. Purification process according to any one of claims 1 and 4. characterized in that it is carried out at room temperature and at a pressure sufficient to operate in the liquid phase. 4. Purification process according to claim 3 characterized in that r it is carried out at a pressure between 3 and 60 kg / cm ^. 5. Charges of hydrocarbons in purified form according to the process described in any one of claims 1 to 4.