GB2157308A

GB2157308A - Process for the removal of carbonyl sulphide from liquid hydrocarbon feedstocks

Info

Publication number: GB2157308A
Application number: GB08506748A
Authority: GB
Inventors: Jacques F J Grootjans
Original assignee: Labofina SA
Current assignee: Labofina SA
Priority date: 1984-04-13
Filing date: 1985-03-15
Publication date: 1985-10-23
Also published as: GB8506748D0; DE3512352A1; IT1183533B; DE3512352C2; FR2562905A1; BE902181A; FR2562905B1; NL8500790A; IT8520164A0; LU85309A1

Abstract

A process for lowering the carbonyl sulphide content of a liquid hydrocarbon feedstock, e.g. which contains 99% propene and from 1 to 70 ppm carbonyl sulphide, comprising passing the feedstock over an absorbent material which is an anionic ion exchange resin having an amine function, at 20-60 DEG C, at a pressure sufficient to maintain the feedstock in the liquid phase and at a LHSV of from 0.1 to 5.

Description

SPECIFICATION Process for the removal of carbonyl sulphide from liquid hydrocarbon feedstocks The present invention relates to a process for the removal of sulphur, which is present in the form of carbon oxysuiphide also called carbonyl sulphide, from liquid hydrocarbons, particularly from hydrocarbons which contain propene and other olefins.

In refineries, the treatment of liquid hydrocarbons for removing or converting impurities, needs costly and complex processes.

Various sulphur compounds such as hydrogen sulphide, mercaptans and particularly carbonyl sulphide are common impurities which one tries to eliminate.

Generally, in the refining industry, the sulphur content of hydrocarbons is reduced by treating the hydrocarbons in the gas phase. In a typical method the sulphided compounds are removed from the hydrocarbons in the gaseous state by treating them with diethanolamine, diisopropanolamine, monoethanolamine or tetraethylene glycol. It is also known that these solvents may be used to treat the hydrocarbons in the liquid state.

However, when these solvents are used for the extraction of the impurities from liquid hydrocarbons, the amount of carbonyl sulphide (hereinafter referred to as COS) cannot be reduced to less than 5 ppm.

It is also known that new polymerization processes of propene use catalysts which give more and more outstanding performances.

However, these catalysts are extremely sensitive to any polar impurities such as carbonyl sulphide, the dipole moment of which is of 0.736 Debye. When these polymerization processes are used, it is thus important to purify the feed in order that the residual content of impurities, typically carbonyl sulphide, is extremely low.

When feeds which initially contain from 30 to 70 ppm COS are purified with known conventional purification processes, the COS residual content which can be obtained after purification is of the order of from 10 to 20 ppm.

It has already been proposed to treat liquid hydrocarbon feedstocks which contain propene with 2-(2-aminoethoxy) ethanol (known as diglycolamine) in order to remove COS.

However, the residual content of carbonyl sulphide, while low since it is of the ppm order is not sufficiently low to fulfil the operating conditions required for a polymerization carried out with very active Ziegler type catalysts.

Besides the purification treatment using liquid-liquid contacts, purification using liquidsolid contacts has also been employed. This type of treatment has the advantage of limiting the risks of contamination of the propene which has to be polymerized further, and thus needing the use of a second absorber.

It has already been proposed to use zinc oxide or mixtures of zinc oxide and calcium carbonate, over which the liquefied feedstock is passed at a temperature from 20 to 60"C, in order to convert the oxides into sulphides; however, the COS residual content of the feed always remained higher than 1 ppm.

It has also been proposed to use absorbants comprising iron oxide, copper oxide or a mixture of copper oxide and chromium oxide, deposited on a support having a high specific surface area such as alumina or activated carbon black, in order to reduce the COS content of liquid hydrocarbons, from a level of 50-60 ppm in the initial feed to a level of about 0.5 ppm.

While this COS content is very low, it is not yet sufficient to send the so-purified propene to a polymerization unit which uses the highly active Ziegler type catalysts.

It has already been proposed to treat these feeds by passing them over basic ion exchange resins, at room temperature. However, the obtained residual COS content is also of the ppm order; such a content is too high to carry out the polymerization in the presence of polymerization catalysts of the last generation.

According to the present invention there is provided a process for the purification of liquid hydrocarbon feedstocks typically comprising propene and from 1 to 70 ppm of COS, by removal of carbonyl sulphide therefrom which process comprises passing the feedstock over an absorbent material which is an anionic ion exchange resin having an amine function, at a temperature of from 20 to 60"C, at a pressure sufficient to maintain the feedstock in the liquid phase, and at an LHSV of from 0.1 to 5.

The present process enables liquid hydrocarbon feedstocks which typically contain propene and other olefins to be purified by removal of carbonyl sulphide therefrom so that the residual carbonyi sulphide content of the feedstock does not exceed 30 ppb. This gives the advantage that the polymerization catalysts of propene are not poisoned too quickly when contacted with such purified feedstocks.

We have found that by passing a liquid hydrocarbon feedstock, particularly a propene feedstock which has to be polymerized, over the absorbent material of the present invention, a purified feedstock is obtained, said purified feedstock fulfillling the purity conditions which are required for a polymerization in the presence of a Ziegler catalyst of the last generation.

The absorbent material is an anionic ion exchange resin, having an amine function, usually a tertiary amine function. These resins are most often obtained from sulfonated poiy- styrene beads which are reacted with a suit able amine.

Examples of absorbent materials which may be used in the present invention, are ion exchange resins of the Dowex type or of the Amerlite type.

Examples of feedstocks which may be treated are liquid hydrocarbon feedstocks containing more than 75% propene, and more particularly feedstocks containing from 85% to 99% propene, the COS content being from 1 to 70 ppm.

If the feed has a higher COS content, e.g.

about 500 ppm, the feed is first submitted to a treatment with an amine solvent, such as monoethanolamine, in order to reduce the COS content to an acceptable value, i.e. a value lower than 70 ppm.

The liquid hydrocarbon feedstock which contains propene is passed over the absorbent material of the present invention at a temperature generally of from 20 to 60"C and at a pressure sufficient to maintain the medium in the liquid phase.

The liquid hourly space velocity (LHSV) at which the feed is passed over the absorbent material is generally from 0.1 to 5, and preferably from 0.2 to 3.

It has been noted that the use of an anionic ion exchange resin having an amine function, is of great importance for the purification process of the present invention, typically to reach the very low COS residual content.

The following Examples are given to illustrate, but not to limit, the process of the present invention.

Example 1 A liquid hydrocarbon feedstock containing 99% propene and having a COS content of 52 ppm was passed over an absorbent material which was an anionic ion exchange resin having a tertiary amine function, of the A-21 Amberlite type.

The operation was carried out at room temperature,while the pressure was adjusted to maintain the feed in the liquid phase.

The feed was passed over the resin at a liquid hourly space velocity of 0.3.

A sample of the purified feed was taken and its COS content was determined. It was 28 ppb.

Example 2 A liquid hydrocarbon feed containing 99% propene and having a COS content of 62 ppm was passed over the absorbent material described in Example 1.

The operation was carried out at room temperature and the pressure was adjusted to maintain the feed in the liquid phase.

This feed was passed over the ion exchange resin at a LHSV of 0.1.

A sample of the purified feed was taken and its COS content was determined. It was 21 ppb.

Claims

1. Process for the purification of liquid hydrocarbon feedstocks typically comprising propene and from 1 to 70 ppm of carbonyl sulphide, by removal of carbonyl sulphide therefrom, which process comprises passing the feedstock over an absorbent material which is an anionic ion exchange resin having an amine function, at a temperature of from 20 to 60on, at a pressure sufficient to maintain the feedstock in the liquid phase and at a LHSV of from 0.1 to 5.

2. Process according to Claim 1, wherein the amine function of the anionic ion exchange resin is a tertiary amine function.

3. Process according to Claim 1 or 2, wherein the LHSV is from 0.2 to 3.

4. Process according to Claim 1, 2 or 3, wherein the liquid hydrocarbon feedstock used contains more than 75% propene.

5. Process for the purification of liquid hydrocarbon feedstocks by removal of carbonyl sulphide therefrom substantially as hereinbefore described in Example 1 or Example 2.

6. Purified hydrocarbon feedstocks having a low carbonyl sulphide content whenever obtained by a process as claimed in any one of the preceding claims.