WO1994006739A1

WO1994006739A1 - Hydroformylation of olefins

Info

Publication number: WO1994006739A1
Application number: PCT/EP1993/002512
Authority: WO
Inventors: Philippe Louis Buess; Ronald Dean Garton; Jean Alexandre André HANIN; Nicolaas Anthony De Munck; Henricus Gerardus Maria Willems; Arie Van Vliet; Jan Martin De Rijke; Hans Oprel; Hubertus Jozeph Beckers
Original assignee: Exxon Chemical Patents Inc.
Priority date: 1992-09-18
Filing date: 1993-09-17
Publication date: 1994-03-31
Also published as: GB9219832D0

Abstract

A process for producing an alcohol from an olefinic feedstock which comprises hydroformylation of the olefin feedstock, hydrogenation of the resulting product mixture and distillation of the hydrogenated product to separate the mixture into (i) a lower boiling Light Oxo Fraction (LOF), (ii) desired alcohol and (iii) a higher boiling Heavy Oxo Fraction (HOF); the HOF then being subjected to catalytic steam cracking followed by catalytic hydrogenation, at least a portion of the resulting cracked and hydrogenated mixture then being recycled to an earlier stage of the process.

Description

"Hvdroformylation of olefins"

This invention relates to the hydroformylation of olefins to produce, inter alia, alcohols and more especially alcohols suitable for use in the manufacture of esters for use as plasticizers, for example, for poly(vinyl chloride) .

Alcohols may conveniently be made by the oxo process, which has as a major step hydroformylation. Hydroformylation in general terms is a process for the preparation of oxygenated organic compounds by the reaction of carbon monoxide and hydrogen (synthesis gas) with carbon compounds containing olefinic unsaturation.

The oxo reaction is performed under hydroformylation conditions in the presence of a carbonylation catalyst or catalyst precursor such, for example, as dicobaltoctacar- bonyl, and results in the formation of a compound, e.g., an aldehyde, which has one more carbon atom in its molecular structure than the olefin feedstock. Subsequent hydrogenation of the primary product leads to alcohols which may be used in the manufacture of esters, including esters for use as plasticizers.

Typically in alcohol production the feedstock for a hydroformylation process is a commercial C₆ to C₁₂ olefin fraction and the desired end product is the corresponding C₇ to C₁₃ saturated alcohol or derived mixed product produced by hydrogenation of the aldehyde oxonation product. By virtue of the nature of the feedstock commonly available to industry, and indeed of the catalyst and reaction conditions employed, the hydroformylation reaction inevitably yields a range of products because of the numerous secondary reactions which take place. The main products of the hydroformyla¬ tion unit are aldehydes and alcohols, with side reactions in the hydroformylation, catalyst removal and hydrogena¬ tion stages of the process usually producing some 5 to 20 wt% of high boiling materials such as aldols, esters, ethers and acetals. Such high boiling materials, which represent a serious yield loss to the alcohol producer, are collectively termed the Heavy Oxo Fraction (HOF) , and are formed in large part by condensation, esterification and dehydration reactions.

In a conventional oxo alcohol process, the feedstock as described above is fed together with synthesis gas into an oxonation unit where catalytic hydroformylation takes place, using e.g., hydrocobalt-carbonyl as the active catalyst species. The oxonation unit product passes to a unit for removing catalyst, and then to a hydrogenation unit where it is hydrogenated to form the desired alcohol. The product mixture at this stage, comprising the desired alcohol, the high boiling HOF and a low boiling fraction termed the Light Oxo Fraction (LOF) , is then passed to a distillation unit where LOF, HOF and desired alcohol product are physically separated. The LOF taken off overhead is a low value product, typically containing unreacted olefin feed and paraffins. As mentioned, the HOF usually contains dimers, for example, esters, aldols and ether-alcohols (e.g. C2₀ compounds for C^_Q alcohol production) and trimers, for example, acetals (e.g. C₃₀ compounds for C^_Q alcohol production) , and heavier; although substantially alcohol- free (apart from the heavy aldols and ether-alcohols) , it may contain a minor amount of alcohol which has not been removed in the distillation stage. Again such HOF is conventionally purged from the system at low value. It is desirable, therefore, to develop a more profitable use of HOF within the oxo process and which serves to increase the yield of more useful products of the process.

Some such uses have already been proposed.

U.S. 2,595,096 (Parker) seeks to improve the alcohol yield of the oxo process by treating the bottoms obtained following oxonation, hydrogenation and removal of, first, unreacted hydrocarbons and then alcohols from the hydrogenated product stream. Such bottoms are said to contain polymerized aldehydes and ketones, principally acetals, high molecular weight ethers and secondary alcohols and polymerized hydrocarbons. It is the acetal content of these bottoms which, in this patent, is con¬ sidered to be useful. The acetal content is hydrolysed with dilute mineral acid, with water (steam) or by catalytic means, the product then being steam distilled. The quantities of alcohols and aldehydes collected may themselves be recycled to the hydrogenation stage.

Alternatively the product from the hydrolyser may be vacuum distilled and then hydrogenated or treated with aldehyde polymerizing agents. Further distillation gives the desired alcohol product.

The relatively mild hydrolysis conditions used in the Parker process are only really useful if the acetal content of the bottoms fraction is high. A more severe cracking process, which makes use of the whole of the bottoms fraction, is described in the applicant's earlier patent application EP-A-183,545 in which hydroformylation of the feedstock is followed by catalyst separation, hydrogenation and distillation.

The HOF (Heavy Oxo Fraction) separated out by the distillation is subjected to catalytic steam cracking, at a temperature of from 260 to 380°C, using as catalyst an active metal oxide or pseudo-metal oxide to form a residue and a cracked mixture which are separated by distillation. The cracked mixture, comprising a major proportion of alcohol and aldehyde, and a minor propor¬ tion of olefin and saturated hydrocarbon, is then recycled to the hydroformylation or hydrogenation stage of the oxo process, leading to an improved overall yield of alcohol.

A different use of the HOF is described in the applicant's earlier patent application EP-A-185,477.

The process takes HOF as the starting material and produces certain ether/ether-alcohol rich compositions having useful properties, especially in solvent or surfactant precursor applications.

The process involves taking the product of a hydro¬ formylation reaction, hydrogenating it and distilling the product to separate out a mixture of ether, ether-alcohol and acetal components (HOF) from lighter ends, then catalytically hydrogenating the mixture, at a temperature of 200 to 250°C, to form an alcohol-enriched product.

The hydrogenated product is then reflux distilled to give

(i) a desired ether/ether-alcohol composition

(ii) a lighter alcohol-rich fraction, and

(iii) a heavier acetal fraction.

The ether/ether-alcohol rich fraction may then be further separated by reflux distillation into an ether- rich fraction and an ether-alcohol rich fraction.

An optional additional step in the process is to take the distilled ether/ether-alcohol and acetal mixture (HOF) and to subject it to catalytic steam cracking at a temperature from 260°C to 380°C using as a catalyst an active metal oxide or pseudo-metal oxide to form an ether enriched heavy product mixture and lighter materials. The heavy product mixture then goes on to be hydrogenated and distilled. It is said in EP-A-185,477 to be possible to combine the processes of EP-A-185,477 and EP-A-183,545 to give both improved alcohol yield and ether/ether-alcohol byproducts having value - see page 18 of EP-A-185,477.

The alcohols produced by the oxo process are often used in the manufacture of esters for use as, amongst other things, plasticizers.

The aldehyde and acid content of alcohols used for plasticizer manufacture is required to be very low as high or moderate levels of such impurities can lead to discoloration, tackiness, and reduced UV stability when the plasticizer is incorporated in a polymer.

It has been found that when recycling as discussed above with reference to EP-A-183545 is carried out with the oxo process, in time there is a build up of acid which leads to the product alcohol containing relatively high levels of acid impurities and therefore being outside the range specified by the plasticizer manu¬ facturers.

There remains a need, therefore, for a method which can improve the alcohol yield of the oxo process whilst providing an alcohol product having very low acid levels.

The present invention provides a process including a recycling loop for producing an alcohol from an olefinic feedstock which comprises (a) hydroformylating the feedstock with synthesis gas in the presence of a hydroformylation catalyst to form a product mixture, containing aldehyde, alcohol, unreacted feed and secondary products, and removing catalyst therefrom;

(b) hydrogenating the substantially catalyst-free mixture to convert aldehyde to the desired alcohol;

(c) distilling the alcohol-containing hydrogenated product mixture to separate (i) a lower boiling Light Oxo Fraction (LOF) , (ii) desired alcohol and (iii) a higher boiling Heavy Oxo Fraction (HOF) ;

(d) subjecting the HOF to catalytic steam cracking at a temperature of from 260°C to 380°C using as catalyst an active metal oxide or pseudo-metal oxide to form a cracked product mixture;

(e) subjecting the cracked product mixture to catalytic hydrogenation; and

(e) recycling at least a portion of the hydrogenated cracked product mixture to the hydroformylation (a) , hydrogenation (b) or distillation (c) stage of the process or, provided that the heavy fraction has been removed therefrom, mixing the said portion with the separated desired alcohol fraction (ii) . The hydroformylation conditions employed to produce the crude product mixture may be those which are well known in the art. For example the hydroformylation reaction (a) may be carried out at a temperature of from 125 to 175°C and a pressure of 15 to 30 MPa. The hydroformylation catalyst used may be, for example, cobalt in desired active form, preferably in a concentra¬ tion of from 0.05 to 3 wt% based on the olefinic feed. Typically the syn gas used has a H₂:CO volume ratio in the range 0.9:1 to 1.5:1.

The oxo-aldehyde hydrogenation (b) is typically carried out at a temperature of 140 to 190°C and under a pressure of 5 MPa. A copper chrome catalyst is preferred.

The HOF resulting from stage (c) of the invention typically has a composition comprising 0 to 35, more typically 25 to 35, wt.% alcohols, 15 to 25 wt.% ethers, 30 to 50 wt.% ether-alcohols, 2 to 10 wt.% esters, and 5 to 10 wt% acetals, with possibly extremely minor amount of other materials e.g., up to 2 wt.% heavies, depending on feedstock and selected process conditions. Depending on the feed to the oxo reactor, such HOF is typically the material boiling in the range 200 to 450°C at atmospheric pressure.

The temperature at which the HOF steam cracking step (d) is performed is most preferably in the relatively high range of 290 to 360°C, and preferably at pressures of from 100 to 1000 kPa, more preferably 100 to 300 kPa. It is preferred that the hydrolysis of the HOF is performed with the weight ratio of steam and HOF in the range 0.1:1 to 2:1, more preferably 0.2:1 to 1.2:1. In general, the higher the steam ratio, the better is the selectivity to aldehyde/alcohol rich cracked HOF mixture, but for economic reasons the optimum range has been found to be from 0.15:1 to 0.5:1.

The catalysts which may be employed in the cracking stage (d) in accordance with the invention are those which promote hydrolysis of the components of the HOF, which generally contains alcohols (assuming not all have been removed in the separation stage), ethers, esters, ether-alcohols and acetals. Thus the catalyst is selected such that the hydrolysis reaction takes place under the rather severe conditions defined to yield a product mixture (the cracked HOF mixture) which is relatively enriched in higher alcohols and aldehydes. The catalysed reactions performed under the specified conditions may be for example acetal hydrolysis, ester hydrolysis, or ether hydrolysis.

It has been found that the desired reactions take place in the presence of metal or pseudo-metal oxides in the active state, such as silica, alumina or titanium dioxide, or mixed silica/alumina. It is particularly preferred to employ alumina as the hydrolysis catalyst. Such catalysts, in the temperature range specified, at least partially convert the HOF components to alcohols and aldehydes.

The use of an active metal or pseudo-metal oxide hydrolysis catalyst in accordance with the invention, particularly alumina, at 260 to 380°C, yields a cracked HOF mixture which is useful to the oxo-process operator for improving alcohol yield since it contains high . proportions of aldehyde/alcohol. In particular it has been found that steam cracking of HOF using an alumina catalyst at 260 to 380°C yields HOF residue and a cracked HOF mixture which may comprise up to 90% alcohol/aldehyde and some 10% olefinic hydrocarbon based on the total alcohol/aldehyde/olefin content of the mixture. In general, for a particular catalyst, increasing steam cracking temperature has been found to give increased overall conversion of the HOF but reduced selectivity to the alcohol/aldehyde component.

A reduced selectivity to alcohol/aldehyde results, on recycle of the material to the hydrogenation stage (b) of the process, in an increased proportion of LOF. Since in the process of the invention a cracked HOF mixture having components which yield an economic benefit from increased yield of desired higher alcohol is required, the temperature at which stage (d) is carried out is important. Too low a temperature will not give conver¬ sions which make the capital expenditure associated with HOF cracking worthwhile, whereas too high a temperature will increase the proportion of olefin/paraffin and hence increase LOF, if recycle is to the hydrogenation stage, and this too will be detrimental to the economics of the process.

The steam cracking of the HOF in accordance with the invention yields, as well as the cracked HOF mixture, a HOF residue which is typically oxygenated dimers and trimers (C₂o to C₃₀+ materials for a C₁₀ alcohol) .

Both the cracked HOF mixture and the HOF residue may be passed to a hydrogenation unit after first passing through a water removal stage. The conditions for the second hydrogenation stage (e) are much more severe than those of the first hydrogenation stage (b) . The hydrogenation is preferably carried out at a temperature in the range 200 to 240°C and at a pressure in the range 4.5 to 6.5 MPa. Any suitable hydrogenation catalyst may be employed, but the preferred catalysts are the copper chrome (also termed Cu/Cr or copper/chromium oxide or copper-chromite) catalyst or supported nickel catalysts.

It has been found that hydrogenation to the desired alcohol enriched/low acid/low aldehyde product mixture proceeds satisfactorily at a space velocity of from 0.4 to 2 vol/vol/hour with the more preferred space velocity range being from 0.75 to 1.5 vol/vol/hour.

The product mixture from the hydrogenator preferably has an acid number less than 1.0 mg KOH/g and a carbonyl number less than 1.0 mg KOH/g and will typically comprise 0 to 5 wt% olefins/paraffins, 55 to 75 wt% alcohols/aldehydes, 15 to 25 wt% ethers, 5 to 15 wt% ether-alcohols, 0 to 5 wt% esters and 0 to 5 wt% acetals.

The product mixture may then be directly recycled back to the hydroformylation, hydrogenation or distilla¬ tion stages of the oxo process. In a preferred embodiment, however, the cracked hydrogenated product mixture is passed through a distillation stage where it is separated into a light fraction and a residue, only the light fraction, typically comprising up to 8 wt% LOF, 75 to 95% wt% alcohol and up to 20 wt% ether, being recycled. It is preferred that the acid number of the light fraction be less than 0.5 mg KOH/g and the carbonyl number less than 0.2 mg KOH/g. The light fraction typically boils in the temperature range 85 to 220°C (for C₆ to C₁₂ olefin feedstock) , however, the boiling range is of course very dependent on the carbon number of the alcohol, on the distillation conditions and on the composition of the mixture.

The residue may be used in further processes to produce valuable by-products.

The residue typically boils at temperatures above 200 to 300°C at atmospheric pressure although, it will be understood, the attribution of a specific boiling temperature to a complex mixture of components is not straightforward, depending amongst other things on whether distillation is on a continuous or a batch basis, the length of the distillation column and the point or phase in the column at which temperature is measured.

The proportions of the components will depend on the carbon numbers of the feedstock and the degree of separation required by the operator. The boundary between the light fraction and the residue depends to an extent on the wishes of the process operator and the economics of the particular oxo-process. It is generally the case that the residue comprises substantially the dimer and trimer and even heavier components of the organic phase.

Preferably the undistilled cracked product mixture or the light fraction from the distillation is recycled to the hydrogenation stage of the process, although it is of course possible to introduce the mixture at the hydro¬ formylation stage so as to provide some upgrade of its admittedly very low olefin content to aldehyde and ultimately alcohol. Economic considerations would usually require recycle to the hydrogenation stage, since recycle to the hydroformylation stage might result, by virtue of the major proportion of alcohol/aldehyde in the mixture, in an increased production of undesirable by¬ products and also an unnecessary increase in operating costs. However recycle to the hydroformylation stage may be elected if for some reason the cracking conditions have resulted in a cracked HOF mixture containing a proportion of olefin/paraffin approaching that of alcohol/aldehyde. If recycle is to the hydrogenation stage (b) the alcohol passes through to the distillation stage (c) unconverted, any remaining aldehyde is con¬ verted to alcohol, and any remaining olefinic hydrocarbon is either reduced or passes through unchanged. If recycle is to the hydroformylation stage (a) the alcohol and any remaining aldehyde may undergo reactions to generate undesirable by-products, or may pass through unconverted to the hydrogenation stage (b) . Olefinic hydrocarbons are oxonated and upgraded to the higher aldehyde/alcohol, which is then passed to the hydrogena¬ tion stage (b) .

In both recycle routes saturated hydrocarbons pass through the entire system unreacted, being substantially removed (together with unreacted olefins) as LOF. The recycle route selected by the operator will depend on the economics, feedstock and reaction conditions of the particular plant operation.

Preferably the mixture which is recycled after hydrogenation (e) is one which is substantially the monomer components of the cracked HOF organic phase, that is those compounds containing one more carbon atom in their molecules than the carbon number of the feedstock of the overall process. Preferably the cracked HOF mixture will contain no more than about 20 wt.% of dimers and above, whilst the residue preferably contains less than 10 wt.% of monomeric components.

Since the cracking reaction shows a progressively increasing conversion with temperature, but selectivity to alcohol/aldehyde reaches a maximum then falls off with increasing temperature, there is a maximum in alcohol/ aldehyde yield to which it is desirable to progress by control of temperature although this is affected by the hydrogenation conditions. Bearing this in mind, it is preferred that the mixture as recycled should contain alcohol/aldehyde in a proportion which corresponds to greater than about 30 or 40 wt.% of the organic material obtained following cracking of the HOF. It is particularly preferred that the amount should correspond to greater than about 75 wt.% since this helps to maximize the overall process yield of higher alcohol.

It is also possible to recycle directly to the distillation stage (c) . If this is the chosen recycle route then the recycled light fraction advantageously has an acid number of less than 0.5 mg KOH/g and a carbonyl number of less than 0.2 mg KOH/g.

The cracked and hydrogenated material produced in the process of the present invention has a sufficiently low acid content that recycling of the material does not lead to a build up of acid in the system, which as indicated above may be a major cause of the poor quality alcohol products in other systems. The alcohol product of the process of the present invention desirably has an acid number less than 0.05, and preferably less than 0.025, mg KOH/g.

A further advantage of the process of the present invention is a reduction in the carbonyl number of the alcohol product. The severe hydrogenation conditions convert the vast majority, normally 99% (but at least 95%) of any aldehydes into alcohol before recycling. Any remaining aldehyde is normally converted as it passes through the hydrogenation (b) and/or hydrofinishing stage.

The reduction in carbonyl content also leads to a higher quality final alcohol, and hence ester, product.

The process according to the invention is par¬ ticularly suitable for use with branched olefin feedstocks, preferably those with carbon numbers Cg to C^₂, more preferably Cg to C₁₀, and results in improved yields of branched alcohol, and also in by-products having higher value. In particular, the HOF residue which is the product of the process has been found to be a surprisingly useful material. The HOF residue contains substantially dimeric, trimeric and heavier compounds based on the original feedstock, and preferably contains a minor amount e.g. less than 10 wt.%, of monomeric compounds derived from the feedstock.

The invention further provides the alcohol product of a process according to the invention which has a carbonyl number of less than 0.20 mg KOH/g and preferably less than 0.10 mg KOH/g.

A further aspect of the present invention is the use in the manufacture of an alcohol from an olefin by a process comprising oxonation of the olefin to form an aldehyde and hydrogenation of the aldehyde to form the desired alcohol, separating a fraction comprising desired alcohol from a higher boiling heavy oxo fraction (HOF) and cracking the HOF, of the steps comprising catalytically hydrogenating the cracked HOF and recycling at least a portion of the hydrogenated cracked HOF to a stage in the process prior to the separation of the desired alcohol from the HOF or provided that the heavy fraction has been removed therefrom mixing it with the separated desired alcohol.

One method of carrying out the invention will now be described by way of example only by reference to the accompanying drawing in which:

The sole Figure is a flow diagram showing a preferred embodiment of the present invention.

The substantially catalyst-free oxonation product (1) is passed through a hydrogenation stage (Hydro) to give a hydrogenated product (2) . The product (2) is distilled in a first distillation column (Tl) and the Light Oxo Fraction (3) is separated out. The remaining fraction is passed to a second distillation column (T2) where the desired alcohol-rich fraction (4) is separated out, leaving a Heavy Oxo Fraction (HOF) (5) . The alcohol-rich fraction (4) is passed through a hydro- finishing stage to give the desired alcohol product (10) .

The HOF (5) undergoes catalytic cracking in the cracking unit (HCU) to give a cracked product mixture (6) which is passed to the catalytic hydrogenation unit (HHU) . The hydrogenated cracked product mixture (7) passes to a distillation unit (T3) where it is separated into a light fraction (9) , which is recycled to the first hydrogenation step (Hydro) , and a residue (8) which may be used to produce high-value by-products.

In an alternative embodiment, also shown in the Figure, the hydrogenated cracked product mixture (7) may be recycled directly (via the route shown by a dotted line) to the first hydrogenation step (Hydro) without passing through the distillation step (T3) .

Not shown in the Figure are the aspects of the present invention where the hydrogenated cracked product mixture is recycled to the distillation stage (c) of the process or where the mixture, having had the heavy fraction removed, is mixed with the desired alcohol fraction (ii) .

The following Example, in which all values relate to steady state conditions in a continuous process, illustrates the invention:

Example 1 (1) Hydroformylation stage

Hydroformylation was performed using a feed compris¬ ing syn gas containing hydrogen and carbon monoxide in a molar ratio of 1.16:1 and (ii) a commercially available stream of branched nonenes including also about 2 wt% octenes and about 8 wt% decenes. The olefin feed was delivered at a rate of 1 tonne/hr, and the syn gas at a rate of 0.27 tonnes/hr (413 Nm³/hr) giving a space velocity of 1.9 vol/vol/hr. The reaction was carried out at a pressure of 30 MPa and a temperature of 175°C, using a cobalt catalyst at 0.3 wt% based on the feed.

(2) Decobaltincf stage

The crude oxo product containing higher aldehyde resulting from stage (1) was decobalted to less than 10 ppm cobalt in conventional manner by neutralizing the cobalt hydrocarbonyl with sodium hydroxide and washing with water.

(3) Hydrogenation stage

The product of stage (2) was fed to a conventional hydrogenation train where, using Cu/Cr or Ni-containing catalysts, a hydrogen pressure of 5 MPa and a tempera¬ ture of 140 to 190°C the product containing higher aldehydes, formates and acetals was converted to a hydrogenation product mixture containing the desired higher alcohol.

(4) Separation stage

The mixture of stage (3) was then distilled under vacuum to produce three fractions, a light oxo fraction (LOF) , a heavy oxo fraction (HOF) and a desired alcohol fraction (AF) as shown below:

The yield of desired alcohol (chiefly C₁₀, with minor amounts of C₉ and C_1:L) was 102 g per 100 g of feed olefin. The alcohol fraction was then passed to a hydrofinishing process.

The HOF was analysed and was shown to comprise:

32.9 wt% C₉ to C_1;L alcohols

67.1 wt% heavies (C₁₈ to C₂ esters, ethers and ether-alcohols, C₂7 to C33 acetals, and others)

The mixture was characterized by having a carbonyl number of 22.28 and an acid number of 0.91 (both expressed in mg KOH/g) . (5) HOF Cracking Stage

The HOF product separated in stage (4) was intro¬ duced in admixture with half its mass of steam into a steam cracking reactor. The reactor was packed with an active alumina catalyst, RHONE-POULENC A2-5, and operated at 350°C, and a pressure of 300 kPa. The flow of HOF through the reactor was 0.120 tonnes/hr, corresponding to a space velocity of 0.33 v/v/hr expressed as volume of HOF per volume of catalyst per hour. After cracking, any water present in the mixture was removed and recycled. The alcohol-enriched mixture was found to comprise 1.8 wt% olefins/paraffins, 67.5 wt% alcohol/aldehyde and 30.7 wt% heavies/HOF residue. The mixture had a carbonyl number of 66.00 mg KOH/g and an acid number of 5.40 mg KOH/g.

(6) Hydrogenation Stage

The cracked product from (5) was passed through a catalytic hydrogenation reactor at a rate of 0.120 tonnes/hour corresponding to a space velocity of 1.5 v/v/hr. The pressure employed was 5.0 MPa and the hydrogenation was carried out over a copper-chromite catalyst (Girdler G22RS) at 230°C.

The alcohol-enriched product mixture was found to have the following characteristics: 3.6 wt % olefins/paraffins

67.6 wt% alcohol/aldehyde

28.8 wt% heavies/HOF residue carbonyl number (mg KOH/g) 1.20 acid number (mg KOH/g) 1.20

(7) Distillation Step

The above hydrogenated cracked product mixture was then passed to a vacuum reflux distillation at a pressure of 2 kPa and a reflux ratio of 2.

An alcohol-rich light fraction was separated out. It had the following composition and characteristics: 5.4 wt% olefins/paraffins

93.0 wt% alcohol/aldehydes 1.6 wt% heavies

Carbonyl number (mg KOH/g) 0.04

Acid number (mg KOH/g) 0.29

The remaining product, the HOF residue, comprised:

14.4 wt% alcohol/aldehyde

85.6 wt% heavies (8) Recycling Stage

The alcohol-rich light fraction of stage (7) was recycled to the hydrogenation stage (3). A flow of 0.081 tonnes/hr of light fraction was incorporated into a stream of 1.239 tonnes/hr of decobalted oxo product from stage (2) .

Analysis of alcohol product

The alcohol product from stage (4) was analysed and was found to have a carbonyl number of 0.21 and an acid number of 0.01.

Hydrofinishing brought the carbonyl number down to 0.05; the acid number remained at 0.01.

The acid number of 0.01 falls well below the maximum acid number, 0.05, allowed by plasticizer manufacturers and is characteristic of a high quality alcohol product.

Comparative Example 1

The process, reaction conditions and feedstock were as for Example 1 up to the HOF cracking stage (5) . (7) Distillation Stage

The product from the HOF cracking stage was then subjected to a vacuum reflux distillation, there being no hydrogenation stage (6) . At a pressure of 2 kPa and a reflux ratio of 2 an alcohol-rich light fraction was removed having the following composition and characteristics:

7.4 wt% olefins/paraffins

87.6 wt% alcohol/aldehyde 5.0 wt% heavies carbonyl number (mg KOH/g) 90.25 acid number (mg KOH/g) 4.38

The remaining fraction, the HOF residue, comprised: 0.1 wt % olefins/paraffins

10.5 wt% alcohol/aldehydes

89.4 wt% heavies

(8) Recycling Stage

The light fraction of the above stage was recycled to the hydrogenation stage (3) of the process by incor¬ poration at a rate of 0.095 tonnes/hr into a stream of 1.230 tonnes/hr of decobalted oxo product obtained following stage (2) .

Analysis of Alcohol Product

The alcohol product from the distillation step (4) comprised 0.2 wt% olefins and paraffins and 99.8 wt% higher alcohol. The carbonyl number of the product was 0.44 and the acid number was 0.04. After hydrofinishing the carbonyl number had dropped to 0.14 the acid number remaining at 0.04.

The acid number is very close to the maximum acid number allowed by the plasticizer manufacturers. The carbonyl number is also high (0.14) compared with a carbonyl number of 0.05 in Example 1.

Claims

CLAIMS:

1. A process for producing an alcohol from an olefinic feedstock which comprises

(a) hydroformylating the feedstock with synthesis gas in the presence of a hydroformylation catalyst to form a product mixture containing aldehyde, alcohol, unreacted feed and secondary products and removing catalyst therefrom;

(c) distilling the alcohol-containing hydrogenated product mixture to separate (i) a lower boiling Light Oxo Fraction (LOF), (ii) desired alcohol and (iii) a higher boiling Heavy Oxo Fraction (HOF);

(d) subjecting the HOF to catalytic steam cracking at a temperature within the range of from 260°C to 380°C using as catalyst an active metal oxide or pseudometal oxide to form a cracked product mixture,

(e) subjecting the cracked product mixture to catalytic hydrogenation and recycling at least a portion of the hydrogenated cracked product mixture to the hydroformylation (a), hydrogenation (b) or distillation (c) stage of the process or provided that the heavy fraction has been removed therefrom mixing it with the separated desired alcohol fraction (ii).

A process as claimed in claim 1 , wherein the hydrogenated product of step (e) is distilled to give a residue and a light fraction, comprising mostly alcohol, which fraction only is recycled to the hydroformylation (a), hydrogenation (b) or distillation (c) stage of the process.

A process as claimed in claim 1 , wherein all of the hydrogenated product formed in step (e) is recycled directly to the hydroformylation (a) or hydrogenation (b) stage without passing through a distillation stage.

4. A process as claimed in any one of claims 1 to 3, wherein the recycling is to the hydrogenation stage (b).

A process as claimed in any one of claims 1 to 3 wherein the recycling is to the hydroformylation stage (a).

A process as claimed in any one of claims 1 to 5, wherein the catalyst used in the catalytic hydrogenation (e) is a copper chrome or a supported nickel catalyst.

A process, including a recycling loop, for producing an alcohol from a Ce to C12 olefinic feedstock which comprises

(a) hydroformylating the feedstock with synthesis gas at a temperature of from 125 to 175°C and a pressure of from 15 to 30 MPa in the presence of a hydroformylation catalyst to form a product mixture containing aldehyde, alcohol, unreacted feed and secondary products and removing any catalyst therefrom;

(b) hydrogenating the substantially catalyst-free mixture to convert aldehyde to the desired alcohol having a carbon number which is one carbon number greater than the olefinic feedstock;

(c) distilling the alcohol-containing product mixture to separate a (i) lower boiling Light Oxo Fraction (LOF) and (ii) desired alcohol and (iii) a higher boiling Heavy Oxo Fraction (HOF); (d) subjecting the HOF to catalytic steam cracking at a temperature of from 260°C to 380°C and a pressure of from 100 to 1000 kPa employing steam and HOF in a weight ratio of from 0.1 :1 to 2:1 and using alumina as catalyst, to form a cracked product mixture;

(e) subjecting the cracked product mixture to catalytic hydrogenation and

(f) recycling at least a portion of the hydrogenated cracked product mixture to the hydroformylation (a), hydrogenation (b), or distillation (c) stage of the process or provided that the heavy fraction has been removed therefrom mixing a portion with the separated alcohol (ii).

8. The use of an alcohol produced by the process of any one of claims 1 to 7 in the manufacture of esters, especially esters for use as plasticizers.

9. The use, in the manufacture of an alcohol from an olefin by a process comprising oxonation of the olefin to form an aldehyde and hydrogenation of the aldehyde to form the desired alcohol, separating a fraction comprising desired alcohol from a higher boiling heavy oxo fraction (HOF) and cracking the HOF, of the steps comprising catalytically hydrogenating the cracked HOF and recycling at least a portion of the hydrogenated cracked HOF to a stage in the process prior to the separation of the desired alcohol from the HOF or provided that the heavy fraction has been removed therefrom mixing it with the separated desired alcohol.