Organic compounds -- part of the class 532-570 series – Organic compounds – Amino nitrogen containing
Reexamination Certificate
2000-04-27
2002-12-17
Davis, Brian J. (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Amino nitrogen containing
Reexamination Certificate
active
06495724
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to catalysts for producing methylamines and to method for manufacturing the catalysts. Methylamines, particularly, dimethylamine are important as starting materials for solvents represented by dimethylformamide, rubber products, pharmaceuticals and surfactants
2. Description of the Prior Art
Methylamines are produced usually from methanol and ammonia using solid acid catalysts such as silica-alumina, at a temperature around 400° C. Another known method comprises subjecting monomethylamine to a disproportionation reaction. The main product in the above methods for the production of methylamines is trimethylamine which has the least demand. However, dimethylamine is the most useful, and, therefore, methods for selectively producing dimethylamine have been demanded.
Methods for producing methylamines using zeolites which are more advantageous than conventional silica-alumina catalysts have also been proposed. For example, these methods use zeolites such as zeolite A (JP 56-69846 A), FU-1 (JP 54-148708 A), ZSM-5 (U.S.P. 4082805), ferrierite and erionite (JP 56-113747 A), ZK-5, Rho, chabazite and erionite (JP 61-254256 A), and mordenite (JP 56-46846 A, JP 58-49340 A, JP 59-210050 A, and JP 59-227841 A). In addition, there is a method for producing methylamines in an amount exceeding the thermodynamic equilibrium proportion, by using silicoaluminophosphates (JP 2-734 A).
The present inventors filed patent applications, on the basis of findings that silica-modified silicoalumino-phosphates have greater activity and selectivity for dimethylamine than known zeolite catalysts and prior art silicoaluminophosphates (JP Application Nos. 9-197232, 9-360124 and 10-025832). However, the silica-modified silicoaluminophosphate catalysts have a problem of decrease in initial activity, so that a further improvement in life is demanded from a practical point of view.
SUMMARY OF THE INVENTION
The object of the present invention is to provide catalysts for producing methylamines which have a practical catalyst life and selectivity for dimethylamine and are free from the problem of decrease in activity encountered in the silicoaluminophosphate catalysts, and also methods for manufacturing the catalysts.
The inventors have found that crystalline silicoaluminophosphates having specific properties and compositional ratios which have never been referred to, in particular, those which are replaced with specific elements or those which are coated with the elements or oxides thereof have smaller decrease of initial activity with time and are effectively improved in catalyst life. As a result, a great improvement is obtained in life of silicoaluminophosphates having excellent initial activity and selectivity for dimethylamine as catalysts for producing methylamines.
The present invention relates to crystalline silicoalumonophosphate catalysts having improved life and being useful as catalysts for producing methylamines which are mainly composed of dimethylamine and produced by a reaction of methanol with ammonia, a reaction of methanol with monomethylamine or a disproportionation reaction of methylamines. The present invention relates also to methods for manufacturing the catalysts.
In more detail, the present invention includes the following aspects.
1) The present invention relates to a catalyst for producing methylamines which comprises a crystalline silicoaluminophosphate molecular sieve having a molar ratio of silicon atom to aluminum atom in the range of 0.01-0.30.
2) The present invention further relates to a method for manufacturing a catalyst for producing methylamines. It comprises mixing an aluminum compound, a phosphorus compound, a silicon compound, an amine or ammonium salt and water so that the molar ratio of them satisfies the following formula (1) when the aluminum compound, the phosphorus compound and the silicon compound are expressed by Al
2
O
3
, P
2
O
5
and SiO
2
, respectively, and then subjecting the mixture to a hydrothermal treatment:
Al
2
O
3
.(1±0.2)P
2
O
5
.(0.5±0.45) SiO
2
. (1.5±0.45)Am.(75±25)H
2
O (1)
wherein Am denotes an amine or ammonium salt having 3 to 24 carbon atoms.
3) The present invention further relates to a method for producing methtylamines which comprises allowing methanol to react with ammonia in the presence of the crystalline silicoaluminophosphate molecular sieve mentioned in the above 1).
4) The present invention further relates to a method for producing methtylamines which comprises subjecting monomethylamine to a disproportionation reaction in the presence of the crystalline silicoaluminophosphate molecular sieve mentioned in the above 1).
DESCRIPTION OF THE PREFERRED EMBODIMENTS
For selective production of methylamines, especially, dimethylamine, preference for the molecular sieves is to have an effective micropore size ranging from 0.3 to 0.6 nm. According to the IUPAC structural code of zeolites and their analogous compounds, mention may be made of, for example, 8-membered ring-structural ABW, AEI, AFX, APC, ATN, ATT, ATV, AWW, CHA, DDR, EAB, ERI, GIS, JBW, KFI, LEV, LTA, MER, MON, PAU, PHI, RHO, RTE, RTH, and VNI; 9-membered ring-structural CHI, LOV, RSN, and VSV; 10-membered ring-structural DAC, EPI, FER, LAU, MEL, MFI, MFS, MTT, NES, TON, and WEI; and 12-membered ring-structural AFS, AFY, ATO, CAN, GME, MAZ, MEI, MTW, OFF, RON, and VET.
The present invention uses the crystalline silicoaluminophosphate molecular sieves (SAPO) having the above structures. The crystalline silicoaluminophosphate molecular sieves are products wherein a part of P or Al-P bond is replaced with Si by an isomorphic replacement, in a crystalline aluminum phosphate compound (ALPO) having a chemical composition of the following formula (2) which is represented by oxide mole ratios, excluding crystalline water and organic bases of structure directing agents (for example, JP 57-77015 A):
Al
2
O
3
.(1.0±0.2)P
2
O
5
(2).
Examples are SAPO-17, 18, 26, 31, 33, 34, 35, 37, 40, 41, 42, 44, 47 and 56, and especially preferred are SAPO-17, 18, 34, 35, 44, 47 and 56. Herein, the relationship between the SAPO numbers and their structures is mentioned, for example, in Encyclopedia of Inorganic Chemistry, Vol. 8, 4369 (1994). The IUPAC codes corresponding to SAPO-17, 18, 34, 35, 44, 47 and 56 are ERI, AEI, CHA, LEV, CHA, CHA, and AFX, respectively. The most preferred is SAPO-34 of chabazite structure.
These crystalline silicoaluminophosphate molecular sieves can be relatively readily manufactured using an aluminum compound, a phosphorus compound, a silicon compound, an amine or quaternary ammonium salt as a structure directing agent, and water.
As methods for manufacturing the crystalline silicoaluminophosphate molecular sieves, there are known methods as described in, for example, JP 59-35018 A and a method for manufacturing catalysts for producing methylamine as described in JP Application No. 9-197232 in which the sequence of addition of starting materials or the temperature range is specified. Anyone of the two methods can be employed. various products different in properties can be obtained depending on compositions or pHs of the starting mixtures, orders of addition of the starting materials, varieties of the structure directing agents, and/or conditions of hydrothermal synthesis.
However, in order to obtain those which have large activity and selectivity as catalysts for producing methylamine together with satisfactory catalyst life, it is most important that an atomic ratio of silicon to aluminum which constitute the crystalline silicoaluminophosphate molecular sieves falls within the range of 0.01-0.30. Furthermore, it is preferred that an average crystal grain size of the crystalline silicoaluminophosphate molecular sieves measured by a scanning electron microscope (SEM) is 5 &mgr;m or less, that the crystal has a cubic, rectangular parallelepipedic, spheroidal, hexagonal or prismatic form, and that both the size and the form of the crystal
Hidaka Toshio
Higuchi Katsumi
Kawai Takeshi
Davis Brian J.
Mitsubishi Gas Chemical Company Inc.
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