WO1995006023A1

WO1995006023A1 - Hydrogenation process

Info

Publication number: WO1995006023A1
Application number: PCT/EP1994/002792
Authority: WO
Inventors: Jean Alexandre André HANIN; Jan Martin De Rijke
Original assignee: Exxon Chemical Patents Inc.
Priority date: 1993-08-25
Filing date: 1994-08-22
Publication date: 1995-03-02
Also published as: GB9317639D0

Abstract

A two-stage catalytic hydrogenation of aldehyde-containing feedstocks, especially oxo product containing sulphur compounds, employs a sulphur-sensitive catalyst in the first stage and a sulphur-tolerant catalyst in the second stage.

Description

"Hydroqenation Process"

This invention relates to a process for hydrogenating an organic compound, for example, an aldehyde, and more especially to a catalyst for such a hydrogenation reaction.

Such a reaction provides a commercially important route from an aldehyde, for example one obtained from an olefinic feedstock by the oxo process, to the correspond¬ ing alcohol. The reaction is normally carried out in the presence of a catalyst, and numerous processes employing different catalyst systems have been proposed for the purpose.

These include a process using a copper-chromium catalyst, with the aldehyde in the liquid phase, at medium pressure. This has the advantages of good selectivity and relatively low capital investment. The disadvantages are that the catalyst is relatively expensive and very sensitive to sulphur poisoning. Most feedstocks originating from petroleum contain some sulphur, and even small proportions, e.g., in the range of 1 to 3 ppm sulphur, cause a reduction of 70% in the activity of the catalyst within a matter of days, after which there is a more gradual decline in activity. When, as is common, a number of reactors are linked in series, and the initial activity reduction has occurred in the first reactor, sulphur breaks through to the next reactor, where a similar rapid decline takes place. The overall result is a rapid decline in activity of the whole reactor train, necessitating either a lower production rate or a frequent catalyst change.

Catalysts more tolerant to the presence of sulphur are known. These are generally supported sulphided metal catalysts, especially cobalt, nickel, molybdenum, tungsten, or combinations of such metals with each other, e.g. , Co/Mo or Ni/Mo. If a Co/Mo catalyst is used, with a liquid phase feed at high pressure, the operating cost is low, but a large capital investment is required and selectivity is poor. With a Ni/Mo catalyst, a liquid phase feed, and medium pressure, both capital and operating costs are low. The disadvantage is, however, that a significant proportion of the aldehyde feed is converted to acids and to heavy by-products, especially dimers, thereby reducing yields. Because purchasers' specifications for the alcohol product often include a maximum acid content, the production of by-product acid represents not only a yield disadvantage but also a product quality problem.

There have been numerous proposals for combinations and modifications of catalyst to overcome problems of individual catalyst types. For example, in GB-A-441096, the undesired simultaneous hydrogenation of double bonds and carbonyl groups in unsaturated acids, when it is desired to reduce only the acid groups, is avoided by adding a sulphided quinoline to a copper/chromium catalyst. Partially sulphided nickel catalysts are used in hydrogenation reactions in GB-A-646408 and 1563690.

Two different catalysts in series are disclosed in U.S. Patent No. 4902404, where hydrocarbons are hydrogenated in two zones, one with, e.g., a Co/Mo catalyst and the other with, e.g., a metal amine molybdate-derived catalyst, in either order. GB-A- 2142010 describes hydrogenation of aldehydes to alcohols, first over a sulphided catalyst and then over a metallic nickel catalyst.

The present invention provides a process for converting an aldehyde to an alcohol, which comprises hydrogenating an aldehyde-containing feedstock in the _N presence of a sulphur-sensitive hydrogenation catalyst, ; whereby an intermediate product of lower carbonyl number is produced, and hydrogenating the intermediate product in contact with a sulphur-tolerant hydrogenation catalyst.

As the sulphur-sensitive catalyst, typically but not exclusively one which loses at least 50% of its initial activity when 50 g of sulphur has passed over 1 kg of catalyst, there may be mentioned copper chromite, reduced copper/zinc oxide, palladium, or nickel catalysts. Some such catalysts may lose 50% of their initial activity when as little as 5 g of sulphur have contacted 1 kg of catalyst.

Spent catalysts of the types mentioned above from other hydrogenation reactions, which have been discarded because of low activity as a result of sulphur poisoning, may be suitable for re-use as catalysts in the first, sulphur-sensitive, zone for aldehyde hydrogenation. The catalyst may be supported or unsupported; if supported a preferred support is carbon, alumina, silica, a silica/alumina mixture, clay, or a zeolite. Many such catalysts are known in the art or described in the literature. A copper chromite catalyst is preferred.

As the sulphur-tolerant catalyst, there may be mentioned primarily sulphided metal catalysts, for example a catalyst based on one or, preferably, two metals selected from cobalt, molybdenum, nickel, and tungsten, especially Co/Mo, Ni/W, or Ni/Mo, advantageously on a support of, for example, carbon, alumina, silica, silica/alumina mixtures, clays, and zeolites. Preparation of these catalysts is described in, for example, O. Wiessen et a_l, Sulfide Catalysts, Their Properties and Applications, Pergamon Press, 1973. Many suitable catalysts, and their preparation, are known in the art or described in the literature.

As indicated above, the process of the present invention is applicable to conversion of aldehydes resulting from the oxo process to the corresponding alcohols. The crude oxo product typically comprises a mixture of aldehydes, alcohols and other products, with aldehydes representing, for example, up to 90 weight %, typically from 30 to 60 wt%, and alcohols up to 60 wt%, typically from 5 to 40 wt%, of the feed. Typically the feedstock will contain sulphur compounds, generally present in a proportion of up to 500 ppm, more usually from 1 to 50 ppm, calculated as elemental sulphur and based on the total weight of the feedstock. The feedstock may also contain water, advantageously in a proportion of up to 3%, preferably within the range of from 1 to 3%, based on the total weight of the feedstock.

The oxo aldehydes generally comprise a mixture of straight and branched chain aliphatic aldehydes, normally largely saturated, with from, for example, 6 to 20 carbon atoms depending on the carbon number of the feed olefin. As examples of such aldehydes, there may be mentioned j hexanal, heptanal, octanal, nonanal, decanal, undecanal, dodedecal, tridecanal, tetradecanal, pentadecanal, hexadecanal, and octadecanal, in their various isomeric forms, from which may be formed by the process of the invention the corresponding alcohols in various isomeric forms, normally in admixture.

Advantageously, according to the invention, hydrogenation by the sulphur-sensitive catalyst, referred to below as the first stage of the reaction, reduces the aldehyde content of the feed to an extent such that the carbonyl number is reduced to at most 150 mg KOH/g, advantageously to a value in the range of from 5 to 60 mg KOH/g.

A method to determine carbonyl numbers is discussed by S. A. Bartkiewicz and L. C. Kenyon in "Automated Determination of Trace Carbonyls", Analytical Chemistry, Vol. 35, No. 3, pp. 1122-1123 (March 1963). The carbonyl number may be converted into mmol aldehyde/g by division by the molecular weight of KOH (56.1 g/mol) . If the molecular weight of the aldehyde is known, mmol aldehyde/g may be converted further into wt% through muliplication by its molecular weight in g/mol and multiplication by the factor 10 to arrive at wt% aldehyde.

It has surprisingly been found that although the activity of the first stage catalyst may be reduced by any sulphur compounds present in a crude oxo product or other petroleum-based feedstock being hydrogenated, since a relatively low residence time is sufficient to reduce the carbonyl number of the feedstock to below the level at which unacceptable by-product, especially acid and heavy by-product, results in the second stage, the overall efficiency of the reactor system is greatly improved.

Accordingly, the invention also provides the use of two catalysts in series in the hydrogenation of an aldehyde-containing feedstock to form an alcohol, the first catalyst being sulphur-sensitive and the second catalyst being sulphur-tolerant, to reduce acid and/or heavy by-product make.

The use is especially valuable when the feedstock contains sulphur compounds, and also when the same catalyst unit is being used to process different feedstocks covering a wide range of carbonyl numbers, e.g. , from 50 to 400 mg KOH/g, some of which contain sulphur and others do not or are substantially sulphur- free.

The conditions in the two stages will depend to some extent on the molecular weight of the feedstock and its aldehyde content. Advantageously the organic feed in both stages is in the liquid phase. In the first stage, using as an example a C₉ feedstock, the temperature is advantageously within the range of from 140 to 200°C, preferably about 180°C, the pressure is advantageously within the range of from 50 to 70, preferably about 55, bar (1 bar = 10^s Pa) and the liquid hourly space velocity is advantageously from 2.0 to 10.0 v/v/h, preferably about 4 v/v/h. A hydrogen partial pressure of from 30 to 50 bar is advantageously employed, preferably about 40 bar. Similar conditions apply in the second stage except that, since a longer residence time is generally required in the second stage, the space velocity is advantageously from 0.3 to 4.0, preferably about 1.5, v/v/h.

If desired, each stage may be carried out in more than one reactor. At least when operating under the conditions described above, a residence time in the first stage of from 0.1 to 0.25 hr suffices to bring the carbonyl number of the majority of feedstocks to below 150 mg KOH/g, even when using a Cu/Cr catalyst with less than 30% of its initial activity. A residence time in the second stage of 0.7 to 0.9 hr is sufficient to reduce the final product's carbonyl number to 1 mg KOH/g or below when using, for example, a sulphided Ni/Mo catalyst, with low by-product formation.

Advantageously, at least the first stage is carried out in a reactor system capable of operating isothermally at an elevated temperature on a high aldehyde feedstock. A preferred reactor is a heat-exchanger type reactor with the catalyst loaded in multiple small diameter (internal diameter of, for example, from 0.03 to 0.10 m) tubes with cooling water on the shell side. By this means, even with a low residual activity catalyst, the required carbonyl reduction may be effected at elevated temperatures but in isothermal conditions.

The following Examples illustrate the invention. Example 1 (Comparative)

The feed was a C₉ linear oxo product, with a carbonyl number of 294 mg KOH/g, corresponding to an aldehyde content of about 74%, an acid number of 1.4 mg KOH/g, a heavy oxo fraction (HOF) of 4.7% and a light oxo fraction (LOF) of 1.7%, the remainder being C₉ alcohols and formate esters. The HOF comprises dimer- type products, e.g., ethers, esters and ether alcohols, while the LOF consists essentially of olefins and paraffins.

The feed was applied to the first of a series of four fixed bed reactors containing a sulphided Ni/Mo catalyst, at a pressure of 55 bar,' a temperature of 180°C and WH of 3.7, together with hydrogen at a partial pressure of 50 bar and 2.1 wt% water.

The intermediate product from the first reactor was sampled, and found to have a carbonyl number of 6.4 mg KOH/g, acid number of 16.4 mg KOH/g, HOF of 14.5 and LOF of 2.4% by weight.

This was then fed to the other sulphided Ni/Mo catalyst-containing reactors, under the same conditions, but with a combined WH of 1.2, yielding a final product i with a carbonyl number of 0.87 mg KOH/g, and an acid

I number of 9.7 mg KOH/g, HOF of 16.6 and LOF of 3.0% by weight.

It is apparent that a significant HOF and acid make occurs under these conditions.

Example 2

Example 1 was repeated, using the same feed and the same reaction conditions, but with the first of the four fixed bed reactors charged with a copper chromite catalyst instead of sulphided Ni/Mo catalyst.

The intermediate product from the first reactor was sampled after a period of operation and found to have a carbonyl number of 59 mg KOH/g, an acid number of 1.6 mg KOH/g, HOF of 6.2 wt% and LOF of 1.3 wt%.

The product from the fourth reactor was sampled, with the following results: carbonyl number 0.41 mg KOH/g, acid number 1.7 mg KOH/g, HOF 6.6 wt%, LOF 3.0 wt%.

By the process according to the invention, a significant reduction in HOF and acid make is achieved, while still obtaining a final product of carbonyl number below 1 mg KOH/g.

Example 3 The procedure of Example 2 was continued until 1200 litres of feedstock had been treated per litre of CuCr catalyst and the activity of the first stage catalyst had fallen to about 30% of its initial value, and further samples were then taken.

The intermediate product from the first CuCr catalysed reactor was found to have a carbonyl number of 155 mg KOH/g, an acid number of 2.4 mg KOH/g, a HOF of 5.4 wt% and LOF of 2.2 wt%.

The product from the last Ni/Mo reactor was found to have a carbonyl number of 0.40 mg KOH/g, an acid number of 3.9 mg KOH/g, a HOF of 8.4 wt% and LOF of 2.3 wt%.

It is apparent from these results that as the CuCr catalyst is deactivated and the carbonyl number of the feed to the Ni/Mo catalysed reactors exceeds 150 mg KOH/g, HOF make increases to a value that is becoming unacceptable.

Claims

CLAIMS :

1. A process for converting an aldehyde to an alcohol, which comprises hydrogenating an aldehyde- containing feedstock in the presence of a sulphur- sensitive hydrogenation catalyst, whereby an intermediate product of lower carbonyl number is produced, and hydrogenating the intermediate product in contact with a sulphur-tolerant hydrogenation catalyst.

2. A process as claimed in claim 1, wherein the sulphur-sensitive catalyst is one which loses at least 50% of its initial activity when 50 g of sulphur has contacted 1 kg of catalyst.

3. A process as claimed in claim 1, wherein the sulphur-sensitive catalyst is a reduced copper/zinc oxide catalyst or a metallic nickel catalyst.

4. A process as claimed in claim 1, wherein the ! sulphur-sensitive catalyst is copper chromite.

5. A process as claimed in any one of claims 1 to 4, wherein the sulphur-tolerant catalyst is a sulphided metal catalyst.

6. A process as claimed in claim 5, wherein the catalyst is at least one metal selected from cobalt, molybdenum, nickel and tungsten.

7. A process as claimed in any one of claims 1 to 4, wherein the sulphur-tolerant catalyst is a sulphided cobalt/molybdenum or a sulphided nickel/molybdenum catalyst.

8. A process as claimed in any one of claims 1 to 7, wherein the aldehyde-containing feedstock is the product of an oxonation reaction.

9. A process as claimed in claim 8, wherein the feedstock to the sulphur-sensitive catalyst contains up to 90% by weight aldehyde.

10. A process as claimed in claim 9, wherein the feedstock contains from 30 to 60 % by weight aldehyde.

11. A process as claimed in any one of claims 1 to 10, wherein the aldehyde is a saturated aliphatic aldehyde.

12. A process as claimed in claim 11, wherein the aldehyde is a C₆ to C₂o aldehyde.

13. A process as claimed in any one of claims 1 to 12, wherein the feedstock to the first stage of the reaction contains up to 500 ppm by weight sulphur.

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14. A process as claimed in any one of claims 1 i to 13, wherein the feedstock to the first stage of the reaction contains up to 3% by weight water.

15. A process as claimed in any one of claims 1 to 14, wherein the first stage of the reaction reduces the carbonyl number of the feedstock to at most 150 mg KOH/g.

16. Use of two catalysts in series in the hydrogenation of an aldehyde-containing feedstock to form an alcohol, the first catalyst being sulphur-sensitive and the second catalyst being sulphur-tolerant, to reduce acid or heavy by-product make.

17. Use as claimed in claim 16, wherein the feedstock is a sulphur-containing feedstock.

18. Use as claimed in claim 16, in which different feedstocks are processed sequentially in the same unit, at least one of the feedstocks being sulphur- containing and at least another one of the feedstocks being substantially sulphur-free.

19. Any new feature hereindescribed or any new combination of hereindescribed features.