WO2013144735A1

WO2013144735A1 - Conversion of a mixture of c2 - and c3 -olefins to butanol

Info

Publication number: WO2013144735A1
Application number: PCT/IB2013/051497
Authority: WO
Inventors: Stefanus Otto; Cayle Jon SHARROCK; Gerrit Richard JULIUS
Original assignee: Sasol Technology (Proprietary) Limited
Priority date: 2012-03-26
Filing date: 2013-02-25
Publication date: 2013-10-03

Abstract

A process (10) to convert a feedstream (20) which includes at least C₂ and C₃ olefins to butanol includes, in a hydroformylation stage (12), contacting the feedstream (20) with a hydroformylation catalyst (26) in the presence of synthesis gas (24) to form an intermediate product stream (22) which includes at least C₃ and C₄ alcohols. The intermediate product stream (22), or a C₃ and C₄ -alcohol-containing stream (32) derived from the intermediate product stream, is subjected to a separation operation (16) to provide a predominantly C₃-alcohol stream (38) and a predominantly C₄ -alcoholstream (36). At least a portion of the predominantly C₃-alcohol stream (38) isdehydrated in a dehydration stage (18) to form a propylene-enriched stream (46) which is recycled to the hydroformylation stage (12).

Description

CONVERSION OF A MIXTURE OF C2 -AND C3 - OLEFINS TO BUTANOL

THIS INVENTION relates to the conversion of olefins to alcohols. In particular, the invention relates to a process to convert a feedstream which includes at least C₂ and C₃ olefins to butanol.

It is known to convert propylene to a mixture of butanols. Known processes take an essentially pure stream of propylene and contact it with synthesis gas over a rhodium catalyst to form butyraldehyde (butanal). The butyraldehyde is subsequently hydrogenated to butanol. Examples of such processes are disclosed by US 4,210,608 and US 4,777,320. It is also known to use a cobalt-based catalyst, so that the conversion reaction proceeds directly to butanol, as taught by US 3,440,291 and US 7, 858,787.

US 6,049,01 1 discloses a process in which a dilute ethylene stream, e.g. one produced by steam cracking, is oxonated or hydroformylated to yield propanal, without the need to separate other lower paraffinic hydrocarbons. A rhodium-containing catalyst is used and the propanal produced can be hydrogenated to propanol.

US 5,1 05,01 8 discloses a process for hydroformylation of an olefin, using a rhodium catalyst with a trivalent organic phosphorus compound and a 2-stage reactor system with the reactors having different mixing characteristics, to form an aldehyde. A mixture of olefins may be used.

US 2006/0173223 and WO 03/024910 disclose a method of increasing the carbon chain length of olefinic compounds. A starting olefinic compound is hydroformylated in the presence of synthesis gas, preferably with a suitable cobalt catalyst, to produce an aldehyde and/or alcohol with an increased carbon chain link compared to the starting olefinic compound. The aldehyde that may form is optionally hydrogenated to convert it to an alcohol which has an increased carbon chain length compared to the starting olefinic compound. The alcohol with increased carbon chain length is subjected to dehydration to produce an olefinic compound with an increased carbon chain length compared to the starting olefinic compound. The olefinic compound with the increased carbon chain length is a desired product of the process. Thus, for example, the process is used to convert 1 -pentene to 1 -hexene. When a mixture of starting olefins is used, a mixture of olefinic compounds each with an increased chain length is produced.

The production of propylene occurs primarily in steam crackers using paraffinic feedstocks or in methanol/propanol dehydration plants (also referred to as "Methanol to Olefins" (MTO) plants). The major product in steam crackers is ethylene, which must be separated from the propylene and other cracked products before the propylene can be used in hydroformylation for the production of butanol. Separation equipment to effect such a separation is capital intensive and can account for up to 80% of a gas plant's capital investment. It is difficult to separate paraffins from the equivalent olefins and C₂ and C₃ splitters are particularly expensive pieces of equipment. In addition, operating costs are also very high as a result of the high energy requirements to effect these separations.

It is thus anticipated that a mixture of C₂ and C₃ olefins and paraffins, e.g. exiting a primary separation step in a gas processing plant, will be available at a substantial discount to the corresponding chemical or polymer grade olefins post- separation that can be produced, for example, by such gas processing plants. A process which can take advantage of a lower cost feedstock comprising a mixture of C₂ and C₃ olefins and paraffins, and which can provide, if desired, a single alcohol product would be desirable.

According to the invention, there is provided a process to convert a feedstream which includes at least C₂ and C₃ olefins to butanol, the process including in a hydroformylation stage, contacting said feedstream which includes at least C₂ and C₃ olefins with a hydroformylation catalyst in the presence of synthesis gas to form an intermediate product stream which includes at least C₃ and C alcohols; subjecting the intermediate product stream, or a C₃ and C₄ -alcohol-containing stream derived from the intermediate product stream, to a separation operation to provide a predominantly C₃-alcohol stream and a predominantly C -alcohol stream; in a dehydration stage, dehydrating at least a portion of the predominantly C₃- alcohol stream to form a propylene-enriched stream; and

recycling at least a portion of the propylene-enriched stream to the hydroformylation stage.

Advantageously, the process of the invention can produce, if desired, an alcohol product which includes substantially only C alcohol, from a feedstream which includes both C₂ and C₃ olefins. A valuable butanol product, preferably predominantly n-butanol, can thus be produced from a comparatively less expensive impure feedstock which includes C₂ and C₃ olefins and possibly also the corresponding paraffins. The feedstream may thus include C₂ and C₃ paraffins. Typically, the C₂ and C₃ paraffins pass unreacted through the hydroformylation stage.

The feedstream may be obtained from an MTO plant or a steam cracker, in particular from a gas processing section of a steam cracker.

The hydroformylation catalyst may be in the form of a catalyst system comprising a mixture or combination of a metal, M, where M is cobalt (Co), rhodium (Rh), ruthenium (Ru) or palladium (Pd); carbon monoxide; and a bicyclic tertiary phosphine having a ligating phosphorus atom.

Preferably the ligating phosphorus atom is neither in a bridgehead position nor a member of a bridge linkage.

In particular, the bicyclic tertiary phosphine of the hydroformylation catalyst or catalyst system may be a [3.3.1 ]phosphabicyclononane represented by formula (I) : Ri

I

Ri is an alkyl, branched alkyl, cycloalkyl, or aryl group, optionally substituted; R₂ is an alkyl group; and

R₃ is an alkyl group.

More particularly, Ri of the [3.3.1 ]phosphabicyclononane of formula (I) may be a linear C₂ to C₂o hydrocarbon chain; and R₂ = R₃. Still more particularly, R₂ and R₃ may each be methyl.

The hydroformylation stage may include more than one hydroformylation reactor. The hydroformylation reactors may be arranged in series or in parallel.

The synthesis gas is a gas which includes at least CO and H₂. Typically, the synthesis gas also includes C0₂. The synthesis gas may include CO and H₂ in a molar ratio of between about 1 :1 0 and about 10:1 .

The hydroformylation stage may be operated at a reaction temperature of between about 1 20°C and about 220°C and a reaction pressure of between about 25 bar(a) and about 100 bar(a).

Depending on the selectivity of the hydroformylation catalyst used, the intermediate product stream may include C₃ and C₄ aldehydes, in addition to the C₃ and C alcohols. If necessary or desirable, e.g. if there is sufficient aldehyde present in the intermediate product to justify processing the aldehyde, the process may include subjecting the intermediate product stream to a hydrogenation stage to convert said aldehydes to their corresponding alcohols. The process may thus include feeding hydrogen to said hydrogenation stage to hydrogenate the aldehydes.

Heavy boiling components, including esters and/or formates and/or acetals and/or condensation products may also be formed in the hydroformylation stage.

When the hydrogenation stage is present, an alcohol-containing stream from the hydrogenation stage may form or define said C₃ and C -alcohol-containing stream derived from the intermediate product stream.

Typically, in the hydroformylation stage, liquid and gaseous products are formed at the operating temperature and pressure of the hydroformylation stage. The process may include separating liquid products or components and gaseous products or components to form a hydroformylation stage gaseous product stream, which typically includes synthesis gas and any paraffins that may have been fed to, or formed during hydroformylation in the hydroformylation stage, and a hydroformylation stage liquid stream which includes at least C₃ and C alcohols. At least a portion of the hydroformylation stage gaseous product stream may be recycled to the hydroformylation stage. Typically however, a portion of the hydroformylation stage gaseous product stream is purged to maintain C₂ and C₃ paraffin concentrations in the hydroformylation stage at acceptable limits. Typically, the process includes separating said hydroformylation stage liquid stream which includes at least C₃ and C₄ alcohols into said intermediate product stream which includes at least C₃ and C₄ alcohols, and a liquid catalyst system stream which includes all components of a catalyst system providing said hydroformylation catalyst. The liquid catalyst system stream is typically recycled to the hydroformylation stage. A portion of the liquid catalyst system stream may be purged to maintain heavy boiling component concentrations at acceptable limits and to allow for the addition of fresh catalyst or catalyst system components.

The process may include, in the separation operation downstream of the hydroformylation stage, producing a volatiles stream which includes at least CO and H₂. Preferably, the volatiles stream is recycled to the hydroformylation stage.

The volatiles stream may also include C₂ and/or C₃ olefins and paraffins.

Typically, said separation operation is refrigeration free.

The process may include, in the separation operation downstream of the hydroformylation stage, separating out a heavy boiling materials stream. The heavy boiling materials stream, or a portion thereof, may be recycled to the hydroformylation stage. Instead, the heavy boiling materials stream, or a portion thereof, may be purged, e.g. with the purge portion of the liquid catalyst system stream.

The invention will now be described, by way of example, with reference to the single accompanying diagrammatic drawing which shows one embodiment of a process in accordance with the invention to convert a feedstream which includes at least C₂ and C₃ olefins to butanol.

Referring to the drawing, reference numeral 10 generally indicates one embodiment of a process in accordance with the invention to convert a feedstream which includes at least C₂ and C₃ olefins to butanol. The process 10 includes, broadly, a hydroformylation stage 12, a hydrogenation stage 14, a separation operation 1 6 and a dehydration stage 18.

A feedstream line 20 leads from a steam cracker (not shown) into the hydroformylation stage 12. An intermediate product stream line 22 leads from the hydroformylation stage 1 2 to the hydrogenation stage 14. The hydroformylation stage 12 is further provided with a synthesis gas feed line 24 and a liquid catalyst system recycle line 26. Furthermore, a gaseous product recycle line 28 leaves from the hydroformylation stage 12 and returns to the hydroformylation stage 12.

The hydrogenation stage 14 is provided with a hydrogen feed line 30. An alcohol line 32 runs between the hydrogenation stage 14 and the separation stage 1 6.

The separation stage 1 6 is provided with a volatiles stream line 34, which joins the gaseous product recycle line 28, a C₄-alcohol stream line 36, a C₃-alcohol stream line 38 and a heavy boiling materials stream line 40. The heavy boiling materials stream line 40 joins the liquid catalyst system recycle line 26 and a catalyst purge line 42.

The C₃-alcohol stream line 38 feeds into the dehydration stage 18 which is provided with a water removal line 44 and a propylene-enriched stream line 46 which returns to the hydroformylation stage 1 2.

A gaseous purge line 48 branches off from the gaseous product recycle line 28. The process 10 is used to convert olefins in a feed stream which includes at least C₂ and C₃ olefins, i.e. ethylene and propylene, and their corresponding paraffins, to butanol. Thus, a feed stream which is a mixture of ethylene, propylene and paraffins (i.e. typically at least ethane and propane) exiting a primary separation step in a gas processing plant (not shown), i.e. typically before the C₂/C₃ splitter of such a gas processing plant, is fed by means of the feed stream line 20 to the hydroformylation stage 12. In the hydroformylation stage 12, the feed stream is reacted with synthesis gas fed by means of the synthesis gas feed line 24, in the presence of a liquid catalyst system, forming an intermediate product stream which includes at least propanol and butanol and some of the paraffins fed to the hydroformylation stage and formed in the hydroformylation stage. The intermediate product stream is withdrawn by means of the intermediate product stream line 22. The hydroformylation stage 1 2 may be any conventional hydroformylation stage, e.g. that described in WO 03/02491 0, operating at elevated temperature and pressure (e.g. between 120 °C and 220 °C and between 25 bar(a) and 1 00 bar(a)). Any suitable hydroformylation catalyst or catalyst system may be employed, and a number of reactors arranges in series and/or in parallel may be used. It is however envisaged that the process 1 0 will typically make use of a cobalt-based catalyst system made up of a cobalt catalyst precursor and a tertiary phosphine thereby to promote alcohol production over the production of aldehydes.

As will be appreciated, in the hydroformylation stage 12, the ethylene is hydroformylated in conventional fashion to form n-propanol and possibly propanal, as well as some ethane, and the propylene is hydroformylated in conventional fashion to form n-butanol and iso-butanol and possibly butanal, as well as some propane. The extent to which the aldehydes are formed in the hydroformylation stage 12 depends at least on the catalyst system used. The paraffins fed to the hydroformylation stage 12 pass unreacted through the hydroformylation stage 12.

Hydroformylation of olefinic compounds to produce alcohols and possibly aldehydes with an increased carbon chain length is well-known and can be carried out in many different and known ways. The design and operation of a hydroformylation stage such as the stage 12 are thus known to those skilled in the art and the hydroformylation stage 12 is accordingly not discussed in any more detail.

The hydroformylation stage 12 also incorporates a separation section (not shown specifically) in order for products and unreacted components and the catalyst system of the hydroformylation stage 1 2 to be separated. Any suitable conventional separation technique, e.g. trayed distillation columns may be employed in the separation section of the hydroformylation stage 1 2 to separate gas phase from liquid phase and to split the liquid phase into a Cs/C enriched liquid stream consisting predominantly of aldehydes and alcohols (i.e. the intermediate product stream), and a liquid stream containing all of the components of the catalyst system. The hydroformylation stage 1 2 thus produces a gaseous product which is withdrawn and recycled by means of the gaseous product recycle line 28. Typically, the gaseous product in the gaseous product recycle line 28 includes C₂ and C₃ paraffins, carbon monoxide and hydrogen. A portion of the gaseous product is purged (typically flared) by means of the gaseous purge line 48 to maintain the C₂ and C₃ paraffin concentrations in the hydroformylation stage 12 at acceptable limits.

The hydroformylation stage 12 further produces said liquid catalyst system stream which is recycled by means of the liquid catalyst system recycle line 26. The liquid catalyst system stream includes all of the components of the liquid catalyst system. Typically, a portion of the liquid catalyst system stream is purged by means of the catalyst purge line 42 in order to maintain heavy boiling component concentrations in the hydroformylation stage 12 at acceptable limits and also to allow for the addition of fresh catalysts or catalyst system components (not shown) to the hydroformylation stage 12.

The hydrogenation stage 14 is an optional stage of the process 1 0 in accordance with the invention. Whether or not the hydrogenation stage 14 will be present will depend on the selectivity of the catalyst system used and in particular on the amount of aldehyde produced by the catalyst system in the hydroformylation stage 12. If sufficient aldehyde is formed to justify the capital and operating costs of a hydrogenation stage, the hydrogenation stage 14 may be employed, in which case hydrogen fed by means of the hydrogen feed line 30 is used to hydrogenate the different aldehydes to form their corresponding alcohols. Thus, if the hydrogenation stage 14 is present, propanal will be converted to propanol and butanal will be converted to butanol.

If the hydrogenation stage 14 is not present, the intermediate product produced by the hydroformylation stage 12 is fed by means of the intermediate product stream line 22 directly to the separation operation 1 6, as indicated by the broken line portion of the intermediate product stream line 22. As will be appreciated, the intermediate product in the intermediate product stream line 22 includes C₃ and C alcohols, i.e. propanol and butanol. If however the hydrogenation stage 14 is present, the intermediate product stream in the intermediate product stream line 22 is fed to the hydrogenation stage 14 and hydrogenated, and a C₃ and C alcohol-containing stream derived from the intermediate product stream in the intermediate product stream line 22 is fed to the separation operation 16 by means of the alcohol line 32.

In the separation operation 1 6, conventional separation technology is used to separate the feed to the separation operation 16 into a volatiles stream (typically at least ethane, propane, ethylene, propylene, CO and H₂) withdrawn by means of the volatiles stream line 34 and recycled to the hydroformylation stage 12, a C₄-alcohol stream (butanol) withdrawn by means of the C₄-alcohol stream line 36, a C₃-alcohol stream (propanol) withdrawn by means of the C₃-alcohol stream line 38 and a heavy boiling materials stream (C + compounds and esters, formates, acetals and condensation products) withdrawn by means of the heavy boiling material stream line 40. Separation of these different streams in the separation operation 1 6 is easily effected, e.g. by means of distillation, bearing in mind that the normal boiling point of propanol and butanol are quite different (97°C and 1 18°C respectively). In fact, the boiling points of key components required to be separated in the separation operation 1 6 are all quite different, as set out in the table below. Table 1 - Boiling Points of Key Components

The separation operation 1 6 advantageously does not require the use of refrigeration. The C₄-alcohol stream withdrawn by means of the C₄-alcohol stream line 36 represents the product of the process 10 and typically is in the form of a mixture of butanols. It is however preferred that the production of n-butanol is maximised by selecting an appropriate catalyst system.

Advantageously, at least some of the C₃-alcohol stream withdrawn by means of the C₃-alcohol stream line 38 is dehydrated in the dehydration stage 1 8 to form water, which is withdrawn by means of the water removal line 44, and a propylene- enriched stream which is recycled by means of the propylene-enriched stream line 46 back to the hydroformylation stage 12. Any suitable dehydration catalyst can be used in the dehydration stage 18 to dehydrate the propanol. Preferably however, the dehydration is carried out under low acidity conditions and a low acidity catalysts support such as Al₂0₃, Si0₂, Ti0₂, or Zr0₂ may be employed to afford a dehydration reaction at temperatures from about 20 °C to about 350 °C and at pressures from about 0 bar(g) to about 5 bar(g). The catalyst may comprise a gamma alumina catalyst or a promoted alumina catalyst, for example CaO.AI₂0₃ or Ca₂0₃. Al₂0₃. As a result of the presence of the dehydration stage 18, the process 10 thus produces an alcohol product with a single carbon number (i.e. a mixture of butanols).

The heavy boiling materials stream withdrawn by means of the heavy boiling material stream line 40 is returned to the liquid catalyst system recycle line 26. The heavy boiling material stream is returned in such a manner that the heavy boiling materials can either be recycled to the hydroformylation stage 1 2 by means of the liquid catalyst system recycle line 26, or the heavy boiling material stream can be purged by means of the catalyst purge line 42.

The process 10, as illustrated, can advantageously convert a gas mixture comprising ethylene, propylene, propane and ethane, as would typically be available from a steam cracker or other gas processing plant at a reduced cost compared to more pure streams, into a primarily butanol product without the need for refrigeration. It is however to be appreciated that, if desired, a portion of the propanol produced by the separation operation 1 6, i.e. a portion of the propanol in the C₃-alcohol stream line 38, can be retained as such and provided as a product of the process 1 0. In other words, the process 10 can provide the option of not recycling all of the propanol back to the hydroformylation stage 12, via the dehydration stage 18, as indicated by the optional flow line 50.

Claims

CLAIMS:

1 . A process to convert a feedstream which includes at least C₂ and C₃ olefins to butanol, the process including

in a hydroformylation stage, contacting said feedstream which includes at least C₂ and C₃ olefins with a hydroformylation catalyst in the presence of synthesis gas to form an intermediate product stream which includes at least C₃ and C₄ alcohols;

subjecting the intermediate product stream, or a C₃ and C₄ -alcohol-containing stream derived from the intermediate product stream, to a separation operation to provide a predominantly C₃-alcohol stream and a predominantly C -alcohol stream; in a dehydration stage, dehydrating at least a portion of the predominantly C₃- alcohol stream to form a propylene-enriched stream; and

2. The process as claimed in claim 1 , in which the feedstream includes C₂ and C₃ paraffins.

3. The process as claimed in claim 1 or claim 2, in which the intermediate product stream includes C₃ and C₄ aldehydes, in addition to the C₃ and C₄ alcohols, the process including subjecting the intermediate product stream to a hydrogenation stage to convert said aldehydes to their corresponding alcohols.

4. The process as claimed in claim 3, in which an alcohol-containing stream from the hydrogenation stage forms said C₃ and C₄ -alcohol-containing stream derived from the intermediate product stream.

5. The process as claimed in any of claims 1 to 4, in which, in the hydroformylation stage, liquid and gaseous products are formed at the operating temperature and pressure of the hydroformylation stage, the process including separating liquid products or components and gaseous products or components to form a hydroformylation stage gaseous product stream, which includes synthesis gas and any paraffins fed to, or formed during hydroformylation in the hydroformylation stage, and a hydroformylation stage liquid stream which includes at least C₃ and C₄ alcohols.

6. The process as claimed in claim 5, in which a portion of the hydroformylation stage gaseous product stream is recycled to the hydroformylation stage and in which a portion of the hydroformylation stage gaseous product stream is purged to maintain C₂ and C₃ paraffin concentrations in the hydroformylation stage at acceptable limits.

7. The process as claimed in claim 5 or claim 6, which includes separating said hydroformylation stage liquid stream which includes at least C₃ and C alcohols into said intermediate product stream which includes at least C₃ and C₄ alcohols, and a liquid catalyst system stream which includes all components of a catalyst system providing said hydroformylation catalyst, the liquid catalyst system stream being recycled to the hydroformylation stage.

8. The process as claimed in any of claims 1 to 7, which includes, in the separation operation downstream of the hydroformylation stage, producing a volatiles stream which includes at least CO and H₂ and recycling the volatiles stream to the hydroformylation stage.

9. The process as claimed in claim 8, in which the volatiles stream includes C₂ and/or C₃ olefins and paraffins.

10. The process as claimed in any of claims 1 to 9, in which said separation operation is refrigeration free.