GB2071133A

GB2071133A - Cracking process

Info

Publication number: GB2071133A
Application number: GB8007298A
Authority: GB
Original assignee: Coal Industry Patents Ltd
Current assignee: Coal Industry Patents Ltd
Priority date: 1980-03-04
Filing date: 1980-03-04
Publication date: 1981-09-16
Also published as: GB2071133B

Abstract

Single ring aromatics and ethylene can be produced by passing a partially-hydrogenated coal-derived oil into a space reactor in the presence of free hydrogen at approximately atmospheric pressure and thermally cracking the fluid. Yields of total BTX are about 10%.

Description

SPECIFICATION Cracking process This invention concerns a novel cracking process, and more especially concerns the cracking of coalderived materials.

Many of the basic feedstocks for chemical industry, especially aromatic hydrocarbons, were originally obtained on byproducts from the carbonisation of coal. Currently, most such feedstocks are obtained from petroleum, although it has become increasingly obvious that petroleum will be unable to supply all the requirements of chemical industry because of the declining world reserves of petroleum. We believe that important feedstocks which can be made from coal include benzene, toluene and xylenes, hereinaftercollectivelytermed BTX, and ethylene.

We have proposed, in Patent Application No.

7938835, that BTX and olefins can be produced by thermal or steam cracking a substantially fully hydrogenated coal oil fraction. Such a cracking process gives high BTX and ethylene yields, generally in excess of 20% each. However, to achieve the substantially complete hydrogenation necessary to give such yields requires a catalytic hydrogenation step.

The aim of the present invention is to provide an alternative process in which lower product yields are accepted and balanced against less costly processing.

The present invention provides a method of producing BTX and ethylene which comprises feeding a partially-hydrogenated coal-derived fluid comprising a mixture of aromatics, hydroaromatics and naphthenes and having a hydrogen to carbon atomic ratio of 1.4to 1.6, into a space reactoratatempera- ture of 1100 to 1300K and at approximately atmospheric pressure, in the presence of free hydrogen, and thermally cracking said fluid to form BTX and ethylene.

We are not aware of any prior proposal to thermally crack coal-derived hydrocarbons in the presence of hydrogen, and the present process is distinct from hydrocracking. The widely-known hydrocracking processes use hydrogen under pressure over a hydrocracking catalyst, some of which catalysts are very sophisticated and expensive. Known hydrocracking processes are very efficient and the inventors assume that conventional chemical engineering thinking would not consider "non-catalytic hydrocracking" which would be expected to be less efficient.

The coal-derived fluids used as starting materials in the process of the invention are suitably partially hydrogenated coal oils. The oils may be a product from the pyrolysis or hydropyrolysis of coal, or a fraction thereof or may be an oil product or byproduct stream or fraction from a coal conversion process. The oil may also be a coal extract or solution prepared by the extraction of coal using a liquid or gaseous solvent; such extraction methods are known in the art. The coal may be a bituminous or brown coal or lignite. If the oil does not have, by virtue of its previous processing, a hydrogen to carbon atomic ratio within the specified range, hydrogenation should be carried out in known manner.

Since full saturation of the oil is not required, the hydrogenation can be simply carried out in known manner without catalyst although a catalyst may be used if desired. A preferred hydrogen to carbon atomic ratio is 1.45 to 1.55.

The reaction conditions are not especially critical provided they are within the general limits set out above. Preferred temperatures may vary according to the feedstock but are generally within the range 1200 to 1250K. The reaction pressures are approximately atmospheric but this is to be understood as including pressures of Q.5 to 10 bar, preferred pressures are 1 to 5 bar.

The free hydrogen may be the only component, other than the feedstock and reaction products, in the reactor, but it need not be pure and may be in admixture with gases such as CO2, CO, N2, CH4 and steam.

The mean residence time of hydrogen and feedstock is suitably of the order of 0.1 to 10 seconds, preferably 0.2 to 5 seconds.

The products emerging from the reactor are suitably cooled and the desired products separated in known manner. The unreacted feedstock can, of course, be recycled to increase the overall conversion yield.

The invention will now be described by way of Example: EXAMPLE A partially-hydrogenated anthracene oil (coal tar fraction) of boiling range IBP-503K, having a hydrogen to carbon atomic ratio of 1.46, and containing 2% paraffins, 21% naphthenes and 64% polynuclear aromatics and hydroaromatics was fed into a tubular reactor with pure hydrogen, and in another series of tests, with nitrogen, at a rate to give a mean residence time of 0.2 seconds. The tubular reactor was heated by an external resistance heater and was maintained at pre-selected desired temperatures in the range 1023-1273 K. The products were quenched and analysed in known manner; yield graphs are shown in the accompanying Figure.

A study of the yield graphs show that the presence of hydrogen has increased the BTX yields by 3-4% points without significantly affecting ethylene yield.

The yields of saturates (methane, ethane and propane) were increased at the expense of the C3-C6 unsaturates. The differential between the yields in hydrogen and nitrogen altered little over the 200 K cracking range used, suggesting that hydrogen affected the formation of benzene and saturated hydrocarbons.

1. A method of producing BTX and ethylene which comprises feeding a partially-hydrogenated coal-derived fluid comprising a mixture of aromatics, hydroaromatics and naphthenes and having a hydrogen to carbon atomic ratio of 1.4 to 1.6, into a space reactor at a temperature of 1100 to 1300 K and approximately atmospheric pressure, in the presence of free hydrogen and thermally cracking said fluid to form BTX and ethylene.

2. A method according to claim 1, wherein the

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Cracking process This invention concerns a novel cracking process, and more especially concerns the cracking of coalderived materials. Many of the basic feedstocks for chemical industry, especially aromatic hydrocarbons, were originally obtained on byproducts from the carbonisation of coal. Currently, most such feedstocks are obtained from petroleum, although it has become increasingly obvious that petroleum will be unable to supply all the requirements of chemical industry because of the declining world reserves of petroleum. We believe that important feedstocks which can be made from coal include benzene, toluene and xylenes, hereinaftercollectivelytermed BTX, and ethylene. We have proposed, in Patent Application No. 7938835, that BTX and olefins can be produced by thermal or steam cracking a substantially fully hydrogenated coal oil fraction. Such a cracking process gives high BTX and ethylene yields, generally in excess of 20% each. However, to achieve the substantially complete hydrogenation necessary to give such yields requires a catalytic hydrogenation step. The aim of the present invention is to provide an alternative process in which lower product yields are accepted and balanced against less costly processing. The present invention provides a method of producing BTX and ethylene which comprises feeding a partially-hydrogenated coal-derived fluid comprising a mixture of aromatics, hydroaromatics and naphthenes and having a hydrogen to carbon atomic ratio of 1.4to 1.6, into a space reactoratatempera- ture of 1100 to 1300K and at approximately atmospheric pressure, in the presence of free hydrogen, and thermally cracking said fluid to form BTX and ethylene. We are not aware of any prior proposal to thermally crack coal-derived hydrocarbons in the presence of hydrogen, and the present process is distinct from hydrocracking. The widely-known hydrocracking processes use hydrogen under pressure over a hydrocracking catalyst, some of which catalysts are very sophisticated and expensive. Known hydrocracking processes are very efficient and the inventors assume that conventional chemical engineering thinking would not consider "non-catalytic hydrocracking" which would be expected to be less efficient. The coal-derived fluids used as starting materials in the process of the invention are suitably partially hydrogenated coal oils. The oils may be a product from the pyrolysis or hydropyrolysis of coal, or a fraction thereof or may be an oil product or byproduct stream or fraction from a coal conversion process. The oil may also be a coal extract or solution prepared by the extraction of coal using a liquid or gaseous solvent; such extraction methods are known in the art. The coal may be a bituminous or brown coal or lignite. If the oil does not have, by virtue of its previous processing, a hydrogen to carbon atomic ratio within the specified range, hydrogenation should be carried out in known manner. Since full saturation of the oil is not required, the hydrogenation can be simply carried out in known manner without catalyst although a catalyst may be used if desired. A preferred hydrogen to carbon atomic ratio is 1.45 to 1.55. The reaction conditions are not especially critical provided they are within the general limits set out above. Preferred temperatures may vary according to the feedstock but are generally within the range 1200 to 1250K. The reaction pressures are approximately atmospheric but this is to be understood as including pressures of Q.5 to 10 bar, preferred pressures are 1 to 5 bar. The free hydrogen may be the only component, other than the feedstock and reaction products, in the reactor, but it need not be pure and may be in admixture with gases such as CO2, CO, N2, CH4 and steam. The mean residence time of hydrogen and feedstock is suitably of the order of 0.1 to 10 seconds, preferably 0.2 to 5 seconds. The products emerging from the reactor are suitably cooled and the desired products separated in known manner. The unreacted feedstock can, of course, be recycled to increase the overall conversion yield. The invention will now be described by way of Example: EXAMPLE A partially-hydrogenated anthracene oil (coal tar fraction) of boiling range IBP-503K, having a hydrogen to carbon atomic ratio of 1.46, and containing 2% paraffins, 21% naphthenes and 64% polynuclear aromatics and hydroaromatics was fed into a tubular reactor with pure hydrogen, and in another series of tests, with nitrogen, at a rate to give a mean residence time of 0.2 seconds. The tubular reactor was heated by an external resistance heater and was maintained at pre-selected desired temperatures in the range 1023-1273 K. The products were quenched and analysed in known manner; yield graphs are shown in the accompanying Figure. A study of the yield graphs show that the presence of hydrogen has increased the BTX yields by 3-4% points without significantly affecting ethylene yield. The yields of saturates (methane, ethane and propane) were increased at the expense of the C3-C6 unsaturates. The differential between the yields in hydrogen and nitrogen altered little over the 200 K cracking range used, suggesting that hydrogen affected the formation of benzene and saturated hydrocarbons. CLAIMS

2. A method according to claim 1, wherein the coal-derived fluid is a partially hydrogenated coal oii.

3. A method according to claim 2, wherein the coal oil is a product of the pyrolysis or hydropyrolysis of coal.

4. A method according to any one of claims 1 to 3, wherein the hydrogen to carbon ratio of the fluid is from 1.45 to 1.55.

5. A method according to any one of the preceding claims, wherein the reaction temperature is from 1200 to 1250 K.

6. A method according to any one of the preceding claims, wherein the pressure is from 1 to 5 bar.

7. A method according to any one of the preceding claims, wherein the residence time in the space reactor of the fluid is from 0.2 to 5 seconds.

8. A method according to claim 1, substantially as hereinbefore described.

9. BTX or ethylene whenever produced by a method as claimed in any one of the preceding claims.