Procedure for synthesis of crystalline microporous silico-alumin

Details Procedure for synthesis of crystalline microporous silico-alumin Procedure for synthesis of crystalline microporous silico-alumin

1994-08-25

1997-09-02

Langel, Wayne

Chemistry of hydrocarbon compounds

Unsaturated compound synthesis

From nonhydrocarbon feed

423700, 423702, 423704, 423705, 423718, 423DIG30, C07C 100, C01B 3708, C01B 3900

Patent

active

056634714

DESCRIPTION:

BRIEF SUMMARY
The application concerns a procedure for the production of crystalline microporous silico-alumino-phosphates with a controlled silicon content, a crystalline microporous silico--alumino-phosphate with improved stability to deactivation and an application of this in the production of olefins from methanol.
We are familiar from Norwegian Patent Application No. 832712 with microporous crystalline silico-alumino-phosphates and a procedure for synthesizing such products. These products have a three-dimensional space lattice built up from PO.sub.2 +, AlO.sub.2 - and SiO.sub.2 tetrahedral units, whose most important chemical composition on a water-free basis is: present in the intracrystalline pore system; "m" is the number of moles of "R" present per mole of (Si.sub.x Al.sub.y P.sub.z)O.sub.2 and m has a value between 0 and 0.3, the maximum value in each case being dependent on the molecular dimensions of the template material and the available pore volume in the silico-alumino- phosphate structure in question; "x", "y" and "z" are molar fractions of silicon, aluminium and phosphorus respectively, present as tetrahedral oxides. The minimum value of "x", "y" and "z" is 0.01, and the maximum value of "x" is 0.98, of "y" 0.6 and of "z" 0.52. The minimum value of "m" in the formula above is 0.02.
The reaction mixture is achieved by combining at least one part each of the aluminium and phosphorus sources in the absence of the silicon source. Then the resultant mixture is reacted with the remaining components to get the total reaction mixture.
The reaction mixture is placed in a pressure vessel for shaking then heating under autogenic pressure to a temperature of at least 100.degree. C., and preferably between 100.degree. and 260.degree. C., until a crystalline silico-alumino-phosphate is obtained. The product is extracted in any appropriate way, for example by centrifuging or filtering.
It is generally known that the chemical composition of the silico-alumino-phosphates is very important for their physical and chemical properties, including their properties when used as catalytic materials. It would therefore be a great advantage if one could use production methods for silico-alumino-phosphates where the chemical composition of the product can be variably controlled. This is particularly true of the silicon content. The known technique makes no allowance for this. In syntheses of SAPO-34 in NO 832712, for example, there is a poor match between the chemical composition of the synthesis gel and the synthesized silico-alumino-phosphate.
According to the examples in NO 832712, equimolar quantities of aluminium oxide and phosphorus pentoxide are used to synthesize SAPO-34. Since Si partly replaces P in the SAPO structure, a mixture is obtained where an excess of P has arisen in the form of phosphoric acid. The amount of Si which replaces P, and thus the composition of the end product, does not seem to be controllable in these syntheses.
After a period of time, all catalysts used to convert methanol to olefin (the MTO reaction) lose their active ability to convert methanol to hydrocarbons--that is, the catalyst is deactivated. With MTO catalysts of the molecular sieve type, this is because the microporous crystal structure is filled up with low-volatility carboniferous compounds which block the pore structure. This is often called deactivation by "coking". The carboniferous compounds can be removed by combustion in air. This is a familiar technique.
Deactivation can also take the form of the collapse of the space lattice, but this kind of deactivation takes place over a much longer timescale than deactivation by coking.
Stability to deactivation by coking is a very important property for an MTO catalyst, so it would be a great advantage if one could produce MTO catalysts with improved stability to deactivation by coking.
The object of the invention is thus to produce crystalline microporous silico-alumino-phosphates with controlled silicon content. Another object is to produce silico-alumino-phosphates which have an enhanc

REFERENCES:
patent: 4673559 (1987-06-01), Derouane et al.
patent: 4677242 (1987-06-01), Kaiser
patent: 5096684 (1992-03-01), Guth et al.
patent: 5158665 (1992-10-01), Miller
patent: 5475182 (1995-12-01), Janssen

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