CA1159475A

CA1159475A - Production of hydrocarbons

Info

Publication number: CA1159475A
Application number: CA000363473A
Authority: CA
Inventors: Thomas V. Whittam; Michael S. Spencer
Original assignee: Imperial Chemical Industries Ltd
Current assignee: Imperial Chemical Industries Ltd
Priority date: 1979-11-02
Filing date: 1980-10-29
Publication date: 1983-12-27
Also published as: ZW24380A1; AU6341280A; DE3041174A1; ZA806441B; IN155133B

Abstract

Abstract A process for producing hydrocarbons containing 6 or fewer carbon atoms in the molecule by reacting a feedstock comprising a hydrocarbon different from the intended product and containing 2 or more carbon atoms in the molecule and/or a hydrocarbon derivative, for example an oxygenated derivative such as methanol or dimethyl ether, over a catalyst comprising zeolite MCH.
Preferred reactions include cracking of higher hydrocarbons to produce olefins and the conversion of methanol and/or dimethylether to olefins, especially ethylene and propylene.

Description

115~475 1 H.31030 Production of hydrocarbons THIS INVENTION relates to the production of hydrocarbons, in particular by cracking higher hydrocarbons or by reaction of small molecular compounds, in the presence of zeolite MCH as catalyst.
Reactions leading to hydrocarbon products have been described using as catalyst a zeolite of the large-pore type such as X or Y or of the medium-pore type such as the ZSM-5 family. The latter reactions, whether they start from hydrocarbons having relatively long chains which are to be cleaved or from hydrocarbons and their derivatives having single carbon atoms or short chains up to (for example C4) which are to be polymerised, usually lead to the formation of aromatic hydrocarbons unless special measures such as low pass conversion or modified catalysts are adopted.
We have now found that our recently discovered zeolite MCH can catalyse the conversion of such feedstocks to hydrocarbons containing 6 or fewer carbon atoms.
The invention provides a process of making a hydrocarbon containing 6 or fewer carbon atoms in the molecule by reacting a feedstock comprising a hydrocarbon different from the intended product and containing 2 or more carbon atoms in the molecule and/or a hydrocarbon derivative containing hydrogen-carbon links over a catalyst comprising zeolite MCH as hereinafter defined.
Zeolite MCH has the typical chemical composition

2 2 3 . 4 to 7 SiO2 . O to 8H20 where R is a monovalent cation or n of a cation of valency n. It has a characteristic X-ray diffraction pattern similar to herschelite but with all lines broadened as a result of the small crystal size. The characteristic lines have a half peak height breadth greater than 1 degree in degrees 2 theta units at the diffraction angles shown in Table 1~

, ~ _ ~5947S
2 H.31030 Table 1 . _ , --2~ ¦d (A)Intensity I/Io x 100 , I
9.3 9.5 33 16.3 5.4 12 20.9 4.25 66 27.5 *3.24 23 30.5 *2.9~ 100 34.0 *2.64 13 __ .

(*These lines were incompletely resolved).
The half peak height breadths are more typically in the range 1,5 to 3.5 degrees 2 theta units. These correspond to a crystallite size under 200, especially under 100 Angstrom units.
Zeolite MCH in preferred forms is characterised further by the capacity to exchange at least 25% of its sodium ions with magnesium ions and substantially all its sodium ions with ammonium or rare earth ions.
It is characterisçd yet further by having a sorptive capacity, when in the sodium form, of at least 1.5% of n-hexane and 1% of para xylene, measured by weight at 25C at half the saturation vapour pressure.
For a fuller description of zeolite MCH and its preparation reference is made to our UK patent Specification No.
2,061,900A, published ~1~y 20, 1981. The zeolite MCH to be used in the process of the invention should be sufficiently pure to exert the required level of catalytic activity.
Conveniently it is material synthesised ir conditions leading to simultaneous formation of gmelinite, typically up to 30, especially 5 to 20% by weight.
In order to be useful to a preferred extent in the process of the invention, MCH is converted from the form in which it is hydrothermally produced, in which form it

3 H.31030 contains alkali metal oxide, to an active form by ion exchange. The alkali metal compounds content of MCH as used in the process of the invention is preferably less than 3, especially less than 2% W/w, calculated as equivalent Na20. Useful activity is observed even when that alkali content is 0.5% W/w or over. Preferably the MCH is activ-ated by heating at 400 to 600C in air or oxygen-free gas before beginning the reaction; such treatment is also suitable for reactivating used catalyst. The water content of freshly activated or reactivated catalyst is preferably O to 2 mols in the above chemical composition formula.
In the active form the alkali metal ions have been replaced at least partly by hydrogen or ions of polyvalent metals. Replacement by hydrogen can be effected by exchange with acid or with ions of ammonium or non-quaternary amine, since such ions decompose on calcination to leave hydrogen ions. me polyvalent metal is preferably selected from those having little or no catalytic activity for hydrogenation, except when synthesis is to accompany conversion, as described below. Suitable metals are from Group II or the rare earth group of the Periodic Table as set out in "Abridgments of Specifications" published by the UK
Patent Office. Preferably hydrogen ions and polyvalent ions are both present. Calcium-hydrogen MCH appears to be especially selective for producing ethylene and propylene.
MCH may be used at full strength or in mixtures with diluent material such as inert silica, alumina or clay , a suitable proportion of diluent being in the range 10 to 40% by weight. The diluent may facilitate forming MCH
into shapes (such as 1 to 10 mm cylinders or spheres for use in a fixed bed or into fine particles for use in a fluidised bed) and also enables the rates of the wanted and unwanted reactions over it to be controlled. The diluent can, if desired, be a zeolite; a convenient com-bination is a mixture of MCH with a zeolite such as gmelinite,as synthesised together by suitable choice of conditions.

115~

4 H.31030 The feedstock can be for example a normally gaseous (up to C4) hydrocarbon or mixture such as LPG or a readily vaporisable hydrocarbon or mixture (C5 to C12) such as natural gas liquids or naphtha or higher volatilis-able hydrocarbons such as kerosene or gas oil. If it isa hydrocarbon derivative it is suitably one having at least 2 hydrogen atoms linked to at least some of its carbon atoms. Oxygenated hydrocarbons such as alcohols, ethers, carboxylic acids, esters, aldehydes and ketones and their acetals are very suitable feedstocks. An especially useful application of the process is the production of olefins from methanol and/or dimethyl ether, since MCH, unlike for example the ZSM-5 family of zeolites, appears to be selective for the production of normally gaseous hydrocarbons and against the production of aromatic hydrocarbons. Crude feed and/or waste streams containing organic sulphur or nitrogen compounds can be upgraded to useful products by the process of the invention.
The products of reaction over MCH may include unwanted hydrocarbon derivatives and possibly also unconverted feedstock. The crude product is separated by condensation of the normally liquid compounds in it and the gaseous fraction is resolved by distillative fraction-ation or by adsorption. Unwanted and unreacted materials, after recovery of the required products and separation of other products such as methane, carbon oxides, water and (when appropriate) hydrogen, can be subject to further stages of conversion over MCH or recycled for further conversion with the main feedstock.
The reaction temperature is suitably in the range 300 to 450, especially 350 to 400C when the product olefin is to contain 4 to 6 carbon atoms, but 400 to 550 especially 425 to 525C when ethylene and/or propylene are to be the main products.
The pressure at which the process is carried out is suitably in the range 1 to 50 atm. abs., especially 1 to 15 atm. abs. but higher pressures for example to 47~

H.31030 300 atm. abs. can be used if convenient, for example when methanol or a like synthesis is combined with the process of the invention.
The space velocity should be controlled so as to give the required product distribution. Thus, for example, when the feedstock is methanol, reaction at a liquid hourly space velocity of about 1.0 produces a higher proportion of dimethyl ether than when the space velocity is 0.2.
The dimethyl ether can be recycled or reacted in a separate bed of MCH or other catalyst. It appears that the conversion of methanol is preferably incomplete, for example in the range 75 to 98~.
The catalyst maintains its activity for substantial period, but can be regenerated by heating in the conditions preferably used for activating it. Very suitably it is used in the form of a fluidised bed and catalyst is continuously withdrawn, passed through a regeneration zone and returned to the olefin-forming reaction.
The process of the invention can be used in combination with a process of synthesis of hydrocarbons and/or oxygenated hydrocarbons by catalytic reaction of carbon oxides with hydrogen. Synthesis products can be separated before the reaction over MCH but, if desired, the MCH catalyst can be disposed so as to act on the synthesis products in advance of any product separation step, for example in a bed downstream of the synthesis catalyst, or by using a mixture of discrete pieces of synthesis catalyst and MCH catalyst, or by using discrete pieces made by shaping a mixture of powdered MCH and synthe-sis catalysts or by applying to MCH by impregnation orion-exchange one or more compounds of metals or oxides having such synthesis activity. Suitable synthesis catalysts contain for example one or more of copper, zinc oxide, chromium oxide and the non-noble or noble metals from Group VIII of the Periodic Table. The pressure of the reaction over MCH can be chosen to suit the conditions of the synthesis reaction.

11~71~

6 H.31030 As Example 2 shows, MCH is relatively inactive for cracking hydrocarbons having a large "CSA" ~ diameter, that is, width of the molecule in the plane in which its cross-sectional area is a minimum. Consequently the invention provides processes in which molecules of small CSA diameter are selectively cracked. One such process is the de-waxing of a hydrocarbon feedstock, by cracking alkanes and leaving a product enriched in aromatic hydrocarbons, especially polynuclear hydrocarbons, such as may be used as a lube oil base stock or a source of intermediates for chemical processing.

Hexadecane crackin~
Samples (0.26 ml) of MCH as described below were charged to a pulse microreactor and activated by heating at 450C for 1 hour in a current of air at 3 litres per hour, 4.4 atm. abs., pressure. Then the air was replaced by an equal nitrogen stream and at 450C a 1 microlitre sample of hexadecane was injected upstream of the catalyst. ~he gas leauing the catalyst was analysed by gas chromatography. For each sample the hydrocarbon product distribution showed that hydrocarbons containing less than 6 carbon atoms were the only products. The catalyst details and percentage conversions are shown in Table 2.
Table 2 __ Catalyst and composition % conversion A RE-MCH 99.1 B H-MCH 99.9 C RE-MCH 99.9 EX~MPLE 2 (a) Example 1 was repeated with 1 microlitre samples of decalin (52% cis, 48% trans). The product distribution, percentage conversion and percentage yields are shown 11~9~7e~
7 H.31030 in Table 3. It is to be noted that as a consequence of the analytical technique used, the C8-C10 fraction includes some C7 aromatics and the C11-,C15 fraction includes! some C10 aromatics. Residual coke on the

5 catalyst is not included.
(b) Example 1 was repeated with 1 microlitre samples of 1-methylnaphthalene. The results are shown in Table 4.
The C11+ fraction reported does not include unconverted feed.
It is evident that the activity of MCH, especially H-MCH, is much lower for cracking polynuclear hydrocarbons than for hexadecane, and thus that it would be effective in removing alkanes from a mixture with polynuclear hydrocarbons.
Table 3 , Catalyst ~ A ~ C
Products (%) under C6 10.6 4.0 11.0 C6 + C717.1 2.7 13.6 C8 ~ C1014.3 1.6 12.9 decalin37.5 45.2 39.4 cis-decalin 20.5 46.5 23.0 .
Conversion (%) 42.0 8.3 137.6 Yields (%) l l under C6 25.2 ¦48.2 29.4 C6 + C7 40.7 32.5 36.1 C8 ~ C10 34 1 19 3 34.4 3'a7~

8 H.~1030 Table 4 ~ . _ Catalyst ¦ A ~ B ~ C
.
Products (~0) ~C6 . O O O
C6 + C7 0 0 0 naphthalene 19.1 2.7 19.7 1-methylnaphthalene 64.8 97.3 66.9 .
C11+ 16.1 0 13.4 , _ Conversion (%) 35.2 2.7 33.1 _ Yields (%) ~6 0 0 0 ` C6 + C7 0 0 0 naphthalene 54.3 100 59.5 C11+ 45 7 0 40.5 Cracking of a mixturQ (gas oil) Example 1 was repeated with 1 microlitre samples of 20 an Ekofisk light gas oil (initial b.p. 205C, final b.p. 390C, mean average b.p. 300C). The results are shown in Table 5.~ _ ~59'1~
g H.31030 Catalyst A B ¦ C
Products (%) ~
~6 44.6 43.9 42.3 C6 + C7 11.2 1.5 11.7 C8 ~ C10 17.4 5.5 20.3 C11+ 26.9 49.1 25.7 Conversion (%) 73.1 50.9 74.3 Yields (%) <i~6 61.0 86.2 56.9 C6 + C7 15.2 3.o 15.8 - C8 ~ C10 23.B 10.8 27.3 Crackin~ of a mixture (li~ht cYcle oil) Example 4 was repeated with 1 microlitre samples of a light cycle oil from a catalytic cracking plant. The results are shown in Table 6.

--H.31030 Table_6 Catalyst A B ¦ C
Products (%) ~C611.1 19.5 5.6 C6 + C7 2.3 <0.1 0.7 C8 ~ C1010.6 3.2 9.1 C11+76.077.~ 84.6 Conversion (%)24.022.715,4.

Yields (%) ~C646.2 85.9 36.4 C6 + C7 9.6 0.2 4.6 C8 ~ C1044.2 14.1 59.1 Formation of gaseous hydrocarbons from n-hexane or methanol A micro-reactor set up to analyse C1 - C4 hydrocarbons was operated first with a fresh sample of catalyst A, then with a different preparation of rare earth MCH (catalyst F). Each catalyst test consisted of a run using n-hexane, a run using methanol, an injection of 100 20microlitres of methanol to simulate ageing and then a second n-hexane run and methanol run. The runs each used 0.6 microlitre of starting material but otherwise experimental conditions were essentially as in Example 1. The product gas compositions are shown m Table 7 //

~,/

1~15~47 Ir~
11 H.31030 _ ~ ~ ~ ~ ~ ~ o ~
a) ~ o o . . . . o . o o hO ~ ~ U~ C~ o 0 ~ ~ ~ ~
I C~ o U~ ~o 0 Q~ X a) u~
bO ~ ~ ~ ~ ~ 0 C~ ~ O ~ O
~ ~ ~a ~ u~
_ _ ~ a~ ~ o J 0 a' ~ o o o El ~ ~ ~ C\i 0 ~ l ~ o E~ a~ X a~ u~
~ ~ ~ ~ ~ ~ 0 ~D ~ ~
C\l ~ 0 ~ 0 b~ +~ O ~ ~ ~ ~ ~i ~ O ~ O
~ ~ ~ . ~ ~
o ~ ~ ~ 0 U~
~1 ~ X a~ u~
a) s~ ~ ~ ~ o ~ o ta ~ ~ ~d ~ . ~ ~
E~ _ ~ ~ ~ ~ o u~
cl ~ ~ o O . . . ~ ~ o O
h O ~ ~ ~ ~ 0 L~ O O
~; ~a ;~
_ U~
cC a~ X a~ u~ ~ O O O O
0 ~

_ _ _ _ ~0 ~ ~ ~ 0 ~ ~ 0 0 0 U~ ~1 ~ ~X X ~C X ~:: X ~ X
~.~ ~ ~ ~ V~ ~V~C~
~ ~ a~ ~) u~ ,1 ~ ~ ~1 ~
C~O ~ E~ _ ~5~9~ 7 5 12 H.31030 Conversion of methanol over ion-exchanged MCH samPles In the conditions of Example 5 the following catalysts were tested:
B H-MCH
D Ba-MCH
E Ca-MCH
The results are shown in Table 8.

Table 8 Catalyst B B D D E E
condition fresh aged fresh aged fresh aged Gas % V/v CH4 3.6 2.1 4.1 2.8 4.7 4.7 C2H6 0.2 0.9 0.2 1.0 0.2 o.3 C2H416.6 16.2 15.1 18.2 16.2 21.5 C3H822.4 33.2 24.7 29.7 26.5 30.2 C3H641.2 18.4 32.5 39.7 42.1 28.3 i C4H10 O O O O O O
n C4H104.9 23.4 10.5 4.0 6.2 13.7 1 C4H8 2.7 0.8 2.0 1.1 0.7 0 i C4H8 2.0 0.6 1.0 0.3 0.6 ~0.1 2-C4Ha 4.9 3.2 6.3 3.2 2.7 <0.1 DLM/JH

Claims

H.31030/UK

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A process for producing a hydrocarbon con-taining 6 or fewer carbon atoms in the molecule which comprises reacting a feedstock comprising a hydrocarbon different from the intended product and containing 2 or more carbon atoms in the molecule and/or a hydrocarbon derivative containing hydrogen-carbon links over a catalyst comprising zeolite MCH.

2. A process as claimed in Claim 1 in which the catalyst comprises zeolite MCH which has been synthesised in conditions leading to simultaneous formation of up to 30% by weight gmelinite.

3. A process as claimed in Claim 1 or 2 in which the catalyst comprises zeolite MCH having an alkali metal content of less than 2% W/W, calculated as equivalent Na2O.

4. A process as claimed in Claim 1 in which the catalyst comprises zeolite MCH in which alkali metal ions have been replaced at least partly by hydrogen ions and/or by ions of polyvalent metals Group II or the rare earth group of the Periodic Table.

5. A process as claimed in Claim 1 in which the catalyst comprises zeolite MCH mixed with 10 to 40% by weight of a diluent.

6. A process as claimed in Claim 1 in which the feedstock comprises a normally gaseous hydrocarbon or hydrocarbon mixture or a readily vaporisable hydrocarbon or hydrocarbon mixture.

7. A process as claimed in Claim 1 in which the process comprises selective cracking of a hydrocarbon having molecules of small CSA diameter where the width of the molecule in the plane in which its cross-sectional area is not at a minimum.

8. A process as claimed in Claim 7 which comprises dewaxing of a hydrocarbon feedstock in which alkanes are cracked and a product enriched in aromatic hydrocarbons is obtained.

9. A process as claimed in Claim 1 in which the feedstock comprises an oxygenated hydrocarbon selected from alcohols, ethers, carboxylic acids, esters, aldehydes and ketones and their acetals.

10. A process as claimed in Claim 9 in which the feedstock comprises methanol and/or dimethyl ether.

11. A process as claimed in Claims 1, 9 or 10, in which the reaction temperature is in the range 300 to 450°C.

12. A process as claimed in Claims 1, 9 or 10 in which the reaction temperature is in the range 400 to 550°C.

13. A process as claimed in Claim 1 in which the reaction pressure is in the range 1 to 50 atmospheres absolute.

14. A process as claimed in Claim 1 in which the process is used in combination with a process of synthesis of hydrocarbons and/or oxygenated hydrocarbons by catalytic reaction of carbon oxides with hydrogen.