GB2151256A - Olefins - Google Patents

Abstract

A process for the production of an olefin by reacting over a catalyst a feedstock comprising an alcohol and/or an ether and recovering the olefin from the product of the reaction characterised in that the catalyst comprises zeolite Nu-23.

Description

SPECIFICATION Olefins This invention relates to olefins and in particular to a process for making them by conversion of a feedstock comprising an alcohol and/or an ether.

Olefins, especially ethylene and propylene, are used on a large scale as intermediates for the manufacture of staple products such as olefin polymers, ethylene oxide, non-ionic detergents, glycols and fibre-forming polyesters. Processes for producing olefins usually involve non-catalytic pyrolysis of volatile hydrocarbons such as natural gas liquids or petroleum distillates. Catalytic pyrolysis processes have been proposed but do not appear to have reached industrial use. It has also been proposed to produce olefines from synthesis gas by converting the synthesis gas to methanol orto hydrocarbons and/or their oxygenated derivatives and reacting such products over a zeolite of the ZSM-5 family.The reaction over such a zeolite is not entirely satisfactory because the olefins tend to react further to produce aromatic hydrocarbons, including polymethylated benzenes of limited usefulness. Better conversions to olefins can apparently be achieved using a modified catalyst and/or by careful temperature control, but such measures increase the complexity and cost of the process.

We have found that our recently discovered novel zeolite Nu-23 can catalyse the conversion of such feedstocks to olefins with only low formation of aromatic compounds.

Accordingly the present invention provides a process for the production of an olefin by reacting over a catalyst a feedstock comprising an alochol and/or an ether and recovering the olefin from the product of the reaction characterised in that the catalyst comprises zeolite Nu-23 as hereinafter defined.

Zeolite Nu-23 and its preparation are described in our copending European patent application No.

83304723.6, now published as European Patent Application No 103981. The crystalline zeolite material Nu-23 has a composition (in terms of mole ratios of oxides and on a calcined basis) expressed by the formula: 0.5 to 1.5 M21nO : X203: at least 5 YO2 wherein M is hydrogen, an alkali metal cation or alkaline earth metal cation, n is the valency of M, Y is silicon and/or germanium, and Xis one or more of aluminium, gallium or boron and has an X-ray powder diffraction patter substantially as set out in Table 1 (as determined by standard technique using copper K a radiation). Table 1 shows X-ray data for zeolite Nu-23 as prepared and for the calcined sodium-hydrogen form of zeolite Nu-23.

TABLE 1 Nu-23 Sodium-hydrogen as made form of Nu-23 d(A) llIo d(A) Illo 11.3 5 9.4 53 9.4 79 7.00 21 6.96 45 6.89 13 6.89 34 6.58 12 6.55 26 5.73 12 5.70 14 5.65 16 5.35 1 4.94 6 4.92 2 4.72 3 4.70 4 4.25 1 4.24 2 3.966 66 3.951 72 3.931 39 3.906 51 3.822 35 3.814 37 3.771 49 3.755 57 3.638 24 3.633 29 3.535 100 3.517 100 3.467 75 3.454 80 3.355 21 3.342 27 3.317 28 3.294 23 3.246 4 3.127 27 3.116 38 3.038 18 3.030 22 2.939 8 2.931 12 2.887 8 2.878 11 2.818 4 2.819 6 2.702 5 2.692 7 2.645 8 2.632 8 2.575 5 2.562 5 2.530 2 2.523 2 2.471 6 2.461 6 2.399 6 2.392 7 2.332 5 2.336 7 2.285 3 2.297 4 2.244 4 2.232 4 2.177 1 2.142 3 2.132 4 2.109 3 2.100 4 2.019 8 2.021 14 1.992 9 1.987 16 1.949 4 1.939 6 1.923 11 1.915 13 1.865 7 1.858 8 Results of sorption experiments on the hydrogen forms of zeolite Nu-23 suggest that it is hydrophilic, an unusual property for such a siliceous zeolite and one which may affect its catalytic properties. While there are ports at about 6.3A, most of the voidage in the zeolite is available only to molecules smaller than about 5.9 .

Within the above definition of chemical composition, the number of moles of YO2 is typically in the range 5 to 5,000 and zeolite Nu-23 appears to be most readily formed in a state of high purity when the number of moles of YO2 is in the range 25 to 1000.

This definition includes both freshly prepared zeolite Nu-23 ("freshly prepared" means the product of synthesis and washing, with optional drying, as hereinbefore described) and also forms of it resulting from dehydration, and/or calcination, and/or ion exchange. In freshly prepared zeolite Nu-23, M may include an alkali metal cation, especially sodium, and/or ammonium, and always includes nitrogen-containing organic bases, such as cyclohexane derivatives or cationic degradation products thereof, or precursors thereof, or mixtures of such compounds. These bases are hereinafter referred to as Q.Thus a zeolite Nu-23 as made typically has the following molar composition: 0.5 to 1.5 M21nO 0.2 to 130 : X203: 10 to 5,000 YO2: 0to 20,000 H2 The H2O content of freshly prepared zeolite Nu-23 depends on the conditions in which it has been dried after synthesis.

In calcined forms of zeolite Nu-23, M may be alkali metal or alkaline earth metal but includes less or no base-containing organic compounds, since these are burnt out in the presence of air, leaving hydrogen as the other balancing cation.

Among the ion-exchanged forms of zeolite Nu-23 the ammonium (NH4+) form is of importance since it can be readily converted to the hydrogen form by calcination. The hydrogen form can also be prepared directly by exchange with an acid. Other forms may also be prepared by partial or complete ion-exchange of the appropriate metal ion.

Our co-pending European patent application No.83304723.6 (EPA No 103981) also describes and claims a method of making zeolite Nu-23 which comprises reacting an aqueous mixture containing at least one oxide YO2, at least one oxide X203, and at least one organic compound selected from cyclohexylamine and derivatives thereof, the organic compound(s) having the formula:

where R1 to Re which can be the same or different are selected from hydrogen, hydroxyl, C1 to C4 alkyl, and are preferably hydrogen or methyl and Re is selected from hydrogen and C1 to C4 alkyl, and is preferably hydrogen or methyl.

To prepare zeolite Nu-23 for use as a catalyst, it can be incorporated in an inorganic matrix, with other materiais which can be either inert or catalytically active. The matrix may be present simply as a binding agent to hold the small zeolite particles together, or it may be added as a diluent to control the amount of conversion in a process. Typical inorganic diluents which may be used with zeolite Nu-23 in the process of this invention include catalyst support materials such as aluminia, silica and kaolinic clays. Other modifications to the properties of H-Nu-23 may be made by appropriate degrees of ion-exchange of H+ with other cationic species.

The feedstockfor use in the process of this invention comprises an alcohol and/or an ether, preferably a lower (C1 to C4) alcohol or ether. An especially useful embodiment of the process is the production of olefins from methanol and/or dimethylether.

The reaction temperature is suitably in the range 250 to 6000C, for example in the range 350 to 450 C.

The reaction pressure is suitably in the range 1 to 50 ats absolute, especially in the range 1 to 15 ats absolute, but higher pressures for example to 300 ats absolute can be used if convenient.

The space velocity used in the process should be controlled so as to give the desired product distribution but it is likely that the weight hourly space velocity will be in the range 0.5 to 50 hr-, preferably 1 to 10 hr-'.

The following examples further illustrate the process of this invention.

Example I A sample of zeolite Nu-23 was prepared as described in our co-pending European patent application No.

83304723.6 (EPA No 103981) and after calcination and ion-exchange it was analysed as 23.7 SiO2 : Awl203: 0.01 Na2O. The zeolite material was pressed into a pellet without any binder or diluent. The pellet was subsequently broken up and sieved to give aggregates of size 700 to 1000cm.

A gaseous feed of 50 vol% methanol in nitrogen was fed over a bed of these Nu-23 aggregates at a temperature of 450"C and a WHSV 1 g methanol/g zeolite/hr.

The analysis of the hydrocarbon fraction of the product stream after 10 minutes and after 40 minutes was: Time on Methanol Products (Hydrocarbon FractionJ stream Conversion C2= C3= C4= CrC4= C1-C4- CsC9 Arom (minus) 10 99.5 13 19 14 46 37 7 10 40 100 9 13 13 35 55 2 7 The analysis of the aromaticsfraction after 10 minutes on stream was C6 : C7: C8 10 = 0.2:1:2.6.

Example 2 Example 1 was repeated except that the feed stream was 50 vol% methanol in 21 vol% steam/29 vol% nitrogen. After 10 minutes the methanol conversion was 99.6% and the analysis of the hydrocarbon product fraction was C2= C3 C4 CrC4 C-C4- C5-C9 Arom 10 15 11 36 53 4 6 The analysis of the aromatics fraction after 10 minutes on stream was C6 : C7 : C8 10 = 0.15: : 2.4.

Claims (6)

1. A process for the production of an olefin by reacting over a catalyst a feedstock comprising an alcohol and/or an ether and recovering the olefin from the product of the reaction characterised in that the catalyst comprises zeolite Nu-23 as hereinbefore defined.

2. A process as claimed in claim 1 wherein the feedstock comprises methanol and/or dimethylether.

3. A process as claimed in claim 1 or 2 wherein the catalyst comprises zeolite Nu-23 in the hydrogen form.

4. A process as claimed in any one of the preceding claims wherein the process is carried out at a temperature in the range 250 to 600 C.

5. A process as claimed in any one of the preceding claims wherein the process is carried out at a reaction presure in the range 1 to 50 ats absolute.

6. A process as claimed in any one of the preceding claims wherein the process is carried out at a weight hourly space velocity in the range 0.5 to 50 hr-'.