WO2013072228A1

WO2013072228A1 - Process for the preparation of higher alcohols

Info

Publication number: WO2013072228A1
Application number: PCT/EP2012/071990
Authority: WO
Inventors: Christian Wix
Original assignee: Haldor Topsøe A/S
Priority date: 2011-11-18
Filing date: 2012-11-07
Publication date: 2013-05-23
Also published as: CN104024193A

Abstract

Process for production of a higher alcohol product from an alcohol synthesis gas comprising hydrogen, carbon monoxide, carbon dioxide, and lower alcohols.. Use a stripper using synthesis gas as stripping gas to purify the liquid phase containing the lower and highers alcohols, in order to strip the lower alcohol from the alcohol stream. The synthesis gas used for stripping is used as starting material in the process of production of higher alcohols.

Description

Title: Process for the preparation of higher alcohols

The present invention relates to the production of higher alcohols. In particular the invention is a process for the preparation of these alcohols by conversion of carbon monoxide and hydrogen containing synthesis gas admixed with lower alcohols in presence of one or more catalysts being active in the conversion of carbon monoxide and hydrogen to higher alcohols.

It is known that higher alcohols and other oxygenates are formed as by-product in the catalytic methanol synthesis from synthesis gas. It is also known that higher alcohol products can be pro^¬ duced directly from synthesis gas.

US patent application no. 2009/0018371 discloses a method for the producing alcohols from synthesis gas. The synthe- sis gas is in a first step partially converted to methanol in presence of a first catalyst and in a second step metha^¬ nol is converted with a second amount of synthesis gas to a product comprising C2-C4 alcohols in presence of a second catalyst. The second amount of synthesis gas can include unreacted synthesis gas from the first step.

The alcohol synthesis requires a high concentration of car^¬ bon monoxide in the synthesis gas. A useful synthesis gas has a H2/CO ratio of at least 0.4 and up to 3. The synthe- sis gas for the higher alcohol synthesis is prepared by the well known steam reforming process of liquid or gaseous hy- drocarbons or by means of gasification carbonaceous mate^¬ rial, like coal, heavy oil, petroleum coke and bio mass.

Hydrogen and carbon monoxide react to produce methanol:

• Synthesis gas to methanol,

CO + 2H₂ CH₃OH

The methanol reacts with the syngas and a chain growth to higher alcohols is initiated, according to the following reaction scheme:

• Chain growth by reaction with synthesis gas,

CH3OH + CO + 2H₂ C2H5OH + H₂0 C2H5OH + CO + 2H₂^ C3H 7OH + H₂0

C3H 7OH + CO + 2H₂^ C 4H9OH + H₂0

etc .

It has been found that addition of lower alcohols to the synthesis gas results in a drastic increase in the yield of higher alcohols when compared to the conventional methanol synthesis gas. The alcohols obviously couple together and form higher alcohols: · Aldol coupling,

CH3OH + C2H5OH τ± C₃H₇OH + H₂0

C2H5OH + C3H 7OH τ± C₅H OH + H₂0

etc . As used hereinbefore and in the following description and the claims, the term "lower alcohols" refers to alcohols present in alcohol synthesis gas for use in the higher al^¬ cohol synthesis and the term "higher alcohols" refers to alcohols higher than the alcohols in the alcohol synthesis gas .

Pursuant to the above findings and observations, the gen^¬ eral embodiment of this invention is a process for produc- tion of a higher alcohol product, comprising the steps of

(a) providing an alcohol synthesis gas comprising hydro^¬ gen, carbon monoxide and lower alcohols; (b) converting the alcohol synthesis gas into a crude al^¬ cohol product stream comprising higher alcohols and unconverted alcohol synthesis gas in presence of one or more catalysts active in converting the alcohol synthesis gas to higher alcohols;

(c) cooling and separating the crude alcohol product stream withdrawn from step (b) into a gaseous phase com^¬ prising hydrogen, carbon monoxide and carbon dioxide and into a liquid product comprising the lower alcohols from the unconverted alcohol synthesis gas and the higher alco^¬ hols formed in the conversion of the alcohol synthesis gas;

(d) recycling the liquid product obtained from step (c) to a stripping treatment and stripping the liquid product with fresh synthesis gas; (e) after having stripped the liquid product in step (d) withdrawing the synthesis gas from the stripping treatment comprising hydrogen, carbon monoxide and the lower alcohols having been stripped off from the liquid phase to provide the alcohol synthesis gas of step (a) ;

(f) subsequent the stripping treatment of the liquid phase in step (d) withdrawing the stripped liquid phase being de^¬ pleted in the lower alcohols and subjecting the thus treated liquid phase to a separation treatment; and

(g) recovering the higher alcohol product from the separa^¬ tion treatment in step (f ) . Fresh synthesis gas to for use in the stripping treatment to provide the alcohol synthesis gas may be generated by steam reforming of hydrocarbons or gasification of a carbon-based feedstock. The H₂/CO ratio may be adjusted by conventional membrane technology, sweet and/or sour shift reaction, carbon dioxide recycle or other means known in the art. Sulphur (if any) is removed in a sulphur guard or by a chemical or physical wash known in the art.

Catalysts being active in the conversion of synthesis gas to higher alcohols are per se known in the art, e.g. from

US 5096688, US 4956392, US 4675343 and US 4943551. For use in the present invention a preferred catalyst consists of copper, zinc oxide and aluminium oxide, optionally promoted with one or more metals selected from alkali metals, basic oxides of earth alkali metals and lanthanides. The alcohol synthesis can be performed in an adiabatic op^¬ erated reactor with quench cooling or interbed cooling, a gas cooled reactor or preferably in a cooled tubular boil^¬ ing water reactor preferably with boiling water on tube side of the reactor tubes and thereby producing high pres^¬ sure steam. Other reactors cooled with different cooling agent will also be suitable for use in the invention.

The synthesis of higher alcohols is preferably carried out at a pressure of at least 2 MPa, typically between 2 and 15 MPa and a temperature above 220°C, preferably between 270 and 400°C.

As mentioned hereinbefore, alcohols like methanol and etha- nol participate in the synthesis of higher alcohol result^¬ ing in a large increase of the rate of formation of higher alcohols .

It has proven that increased concentrations of lower alco- hols in the alcohol synthesis gas result in an increased yield of higher alcohols.

Thus, in an embodiment of the invention, the lower and higher alcohol containing liquid phase obtained in step (c) is admixed with a stream of lower alcohols being separated from the higher alcohol product in the separation step (f) before being introduced into the stripping treatment or during the stripping treatment in step (d) . In a particular advantageous embodiment of the invention, the gaseous phase separated from the liquid phase in step (c) containing hydrogen and carbon oxides is subjected to catalytic methanation according to the reactions:

CO + 3H₂ = CH₄ + H₂0; and

C0₂ + 4H₂ = CH₄ + 2H₂0

Thereby allowing combined production of higher alcohols and substitute natural gas (SNG). During the synthesis of higher alcohols minor amounts of alkanes are formed as by-product. These are together with the hydrogen and carbon oxides in the gas phase passed to the methanation reaction and increase the yield of SNG. In still an embodiment of the invention, the production of higher alcohols is boosted by addition of a stream of lower alcohols from an external source into the alcohol synthesis gas, such as a stream of bioethanol or crude methanol prod^¬ uct and the like.

In the synthesis of higher alcohols small amounts of alde^¬ hydes, ketons and esters together with other oxo-compounds may be formed as by-products. These by-products may form azeotropic mixtures with the higher alcohols or have boil- ing points close to the alcohols and leave the purification of the product difficult.

In further an embodiment of the invention, the crude alco^¬ hol product being withdrawn from the alcohol synthesis step (b) is subjected to a hydrogenation step in presence of a hydrogenation catalyst, wherein the oxo-compounds conatin- ing by-products are hydrogenated to their corresponding al- cohols. Thereby, the final distillation of the product is much improved.

For the purpose of the product hydrogenation, the crude al- cohol product is cooled in e.g. a feed effluent heat ex^¬ changer to a temperature between 100 and 220°C and intro^¬ duced into a hydrogenation reactor containing a bed of hy- drogenation catalyst. Useful hydrogenation catalysts are catalysts containing noble metals including platinum and palladium or a copper/zinc oxide/alumina catalyst being also employed in the alcohol synthesis.

The alcohol synthesis gas can further be admixed with ke^¬ tones and/or aldehydes from an external source. These com- pounds are then partly hydrogenated in alcohol synthesis step and in the hydrogenation step to their corresponding alcohols, which further boosts the production yield of higher alcohols. The ketones and/or aldehydes are advantageously introduced into the synthesis gas by means of the recycle stream by admixing a stream of ketones and/or aldehydes during the stripping of the liquid phase in step (d) . When using an oxidic alcohol formation catalyst together with a synthesis gas with a high content of carbon monox^¬ ide, the catalyst has a reduced operation time. The cata^¬ lyst bed will after a time on stream be clogged with waxy material and has to be removed.

This problem arises during preparation of the synthesis gas under conditions to provide a relatively high content of carbon monoxide. Carbon monoxide reacts with the steel equipment used in the synthesis gas preparation and forms i.a. iron carbonyl compounds. When transferred to the alco^¬ hol synthesis catalyst, these compounds catalyse the

Fischer-Tropsch reaction and the waxy material is formed on the catalyst.

By removing the carbonyl compounds from the fresh synthesis gas upstream of the alcohol synthesis, the operation time of the alcohol synthesis catalyst can be much improved.

A particular useful metal carbonyl sorbent for use in the inventive process comprises copper aluminium spinel being modified by calcination at elevated temperature in an oxi- dizing atmosphere followed by a reduction in a reducing at^¬ mosphere, such as synthesis gas or synthesis gas diluted with an inert gas, prior to being contacted with metal car^¬ bonyl contaminated synthesis gas. Preferably, the particulate sorbent further comprises cop^¬ per oxide in excess to the amount being present in the cop^¬ per aluminum spinel prior to modification.

These sorbents remove carbonyl compounds from the synthesis gas to the low ppb range, preferably below 1 ppb.

The invention is described in more detail in the following description with reference to the drawings, in which Fig. 1 is a simplified flow sheet of a process for the preparation of higher alcohols and SNG according to a specific embodiment of the invention. Referring to Fig.l, alcohol synthesis gas 2 is formed by the overhead product from a stripper 13, wherein a crude alcohol product containing lower alcohols and higher alco^¬ hols produced in the process is stripped with fresh synthe- sis gas 1 as stripping agent and is withdrawn as the over^¬ head product to provide the alcohol synthesis gas 2, as de^¬ scribed in more detail below.

The thus provided alcohol synthesis gas 2 is introduced into higher alcohol synthesis reactor 4.

Crude alcohol product 5 from synthesis reactor 4 contains methanol, ethanol, propanol and higher alcohols together with traces of water and reaction by-products, including ketones, aldehydes, methyl acetate and methyl formate. Fur^¬ thermore, it contains gaseous compounds including hydrogen carbon monoxide and carbon dioxide.

For the removal or reduction of the amounts of aldehydes, ketons and esters, the crude alcohol product 5 is cooled

(not shown) and passed into hydrogenation reactor 6. These and other oxo-compounds optionally contained in the crude product are hydrogenated with hydrogen contained in the un^¬ converted synthesis gas from reactor 4 in presence of a hy- drogenation catalyst.

The hydrogenated crude alcohol product 7 is cooled (not shown) . The cooled product is the separated in separator 8 into gaseous and liquid phase, 9 and 17, respectively. At least a part of gaseous phase 9 is then passed through line 10 to methanator 11 for the preparation of SNG withdrawn in line 12. The hydrogen content in gaseous phase 9 may be increased by admixing hydrogen rich gas in line 21 from e.g. a synthesis gas purification step into gaseous phase 9.

Liquid phase 17 withdrawn from separator 8 is passed through line 14 to stripper 13.

Stripper 13 is operated in such manner that the less vola^¬ tile higher alcohols leave the stripper as bottom product 15 together with residual amounts of lower alcohols having not been stripped off into alcohol synthesis gas 2. A part of the amount of the lower alcohols leaves the stripper as overhead together with the fresh synthesis gas 1 and form the alcohol synthesis gas 2. The amount of lower alcohols in stripper effluent stream 15 is lower than the amount of lower alcohols in the stripper feed line 14.

Liquid stream 14 being stripped with the fresh synthesis gas is a mixture of three separated streams preheated in a heater (not shown) . A first of these streams is a split fraction 16 of stripper liquid effluent 15. The remainder of liquid effluent 15 is passed to separation treatment in distillation section 19.

A second stream is liquid phase 17 from separator 8 and a third is the overhead fraction 18 from distillation section 19 containing the lower alcohols separated from the higher alcohols in distillation section 19. The less volatile higher alcohols leave the distillation section with the bottom product.

As mentioned hereinbefore, small amounts of alkane by- products are formed during synthesis of higher alcohols.

The alkane by-product is dissolved in the liquid effluent 17 together with minor amounts of carbon dioxide. In order to prevent the amount of alkanes and carbon dioxide to build up in the synthesis loop, effluent 17 may be passed through a flash drum(not shown) wherein the alkane byproduct and carbon dioxide are separated as gas phase prior to liquid effluent 17 is passed to stripper 13. The gas phase from the flush drum is then passed to methanator 11.

Claims

CLAIMS :

1. Process for production of a higher alcohol product, comprising the steps of

(a) providing an alcohol synthesis gas comprising hydro^¬ gen, carbon monoxide and lower alcohols;

(b) converting the alcohol synthesis gas into a crude al^¬ cohol product stream comprising higher alcohols and unconverted alcohol synthesis gas in presence of one or more catalysts active in converting the alcohol synthesis gas to higher alcohols; (c) cooling and separating the crude alcohol product stream withdrawn from step (b) into a gas phase comprising hydrogen, carbon monoxide and carbon dioxide and into a liquid product comprising the lower alcohols from the un^¬ converted alcohol synthesis gas and the higher alcohols formed in the conversion of the alcohol synthesis gas;

(d) recycling the liquid product obtained from step (c) to a stripping treatment and stripping the liquid product with fresh synthesis gas;

(e) after having stripped the liquid product in step (d) withdrawing the synthesis gas from the stripping treatment comprising hydrogen, carbon monoxide and the lower alcohols having been stripped off from the liquid phase to provide the alcohol synthesis gas of step (a) ; (f) subsequent the stripping treatment of the liquid phase in step (d) withdrawing the stripped liquid phase being de^¬ pleted in the lower alcohols and subjecting the thus treated liquid phase to a separation treatment; and

(g) recovering the higher alcohol product from the separa^¬ tion treatment in step (f ) .

2. Process of claim 1, wherein the one or more catalysts in step (b) comprise copper, zinc oxide and aluminium oxide and are optionally promoted with one or more metals se^¬ lected from alkali metals, basic oxides of earth alkali metals and lanthanides.

3. Process of claim 1 or 2, comprising the further step of introducing a stream comprising lower alcohols being separated from the stripped liquid phase in the separation treatment of step (f) into the stripping treatment of step (d) .

4. Process of anyone of claims 1 to 3, comprising the further steps of

cooling the crude alcohol product from step (b) ; and contacting the cooled product with a hydrogenation catalyst in presence of a hydrogenation catalyst prior to introduc^¬ tion into step (c) .

5. Process of anyone of claims 1 to 4, wherein amounts of carbonyl compounds being present in the fresh synthesis gas are reduced by contacting the fresh synthesis gas with a sorbent comprising copper aluminium spinel being modified by reduction in a reducing atmosphere at a temperature of between 200°C and 500°C prior to being contacted with the synthesis gas.

6. Process of claim 5, wherein the sorbent comprises cop- per in excess to the amount of copper contained in the cop^¬ per aluminum spinel.

7. Process of anyone of claims 1 to 6, wherein the con^¬ version of the alcohol synthesis gas is performed at a pressure of between 2 and 15 MPa and a temperature of above 220°C.

8. Process of claim 4, wherein the hydrogenation catalyst comprises copper, zinc oxide and aluminium oxide.

9. Process of claim 4, wherein the hydrogenation catalyst comprises platinum and/or palladium.

10. Process of anyone of the preceding claims, wherein a further external stream of lower alcohols is introduced into the alcohol synthesis gas upstream the step (b) .

11. Process of claim 4, wherein a further stream with ketones and/or aldehydes is introduced into the alcohol syn- thesis gas upstream of step (b) .

12. Process of claim 11, wherein the further stream of ketones and/or aldehydes is introduced during the stripping treatment in step (d) .

13. Process of anyone of the preceding claims, wherein at least part of the gas phase separated from the crude alco- hoi product in step (c) is converted to substitute natural gas by subjecting the at least part of the gas phase to catalytic methanation.