Method of making methylamines using chabazite catalysts

Details Method of making methylamines using chabazite catalysts Method of making methylamines using chabazite catalysts

2000-03-24

2001-05-15

Richter, Johann (Department: 1621)

Organic compounds -- part of the class 532-570 series

Organic compounds

Amino nitrogen containing

C564S479000, C564S480000

Reexamination Certificate

active

06232502

ABSTRACT:

FIELD OF THE INVENTION
This invention generally relates to a process for the manufacture of monomethylamine, dimethylamine and trimethylamine in which methanol and/or dimethylether and ammonia are contacted in the presence of an acidic zeolite chabazite catalyst. In particular, the reactants are contacted in the presence of an acidic zeolite chabazite catalyst, wherein the ratio of silicon to aluminum (Si:Al) in said catalyst is at least about 5:1.
BACKGROUND OF THE INVENTION
Methylamines are generally prepared commercially by continuous reaction of methanol and ammonia in the presence of a dehydration catalyst such as silica-alumina. The reactants are typically combined in the vapor phase, at temperatures in the range of 300° C. to 500° C., and at elevated pressures. Trimethylamine is the principal component of the resulting product stream accompanied by lesser amounts of monomethylamine and dimethylamine. The methylamines are used in processes for pesticides, solvents and water treatment. From a commercial perspective, the most valued product of the reaction is dimethylamine in view of its widespread industrial use as a chemical intermediate (e.g., for the production of dimethylformamide). Thus, a major objective of those seeking to enhance the commercial efficiency of this process has been to improve overall yields of dimethylamine and monomethylamine, relative to trimethylamine. Among the approaches taken to meet this goal are recycling of trimethylamine, adjustment of the ratio of methanol to ammonia reactants and use of selected dehydrating or aminating catalyst species. Many patents and technical contributions are available because of the commercial importance of the process. A summary of some of the relevant art for methylamine synthesis using zeolite catalysts is disclosed in U.S. Pat. No. 5,344,989 (Corbin et al.).
Zeolites chabazite, where the zeolite is derived from mineral sources and the silicon to aluminum ratios in said zeolites is less than about 2:1, as well as zeolites rho are known to be useful as catalysts for methylamines. See U.S. Pat. No. 5,569,785 (Kourtakis et al.) and references cited therein. The use of natural, H-exchanged and M-exchanged chabazites, where M is one or more alkali metal cations selected from the group consisting of Na, K, Rb and Cs is disclosed in U.S. Pat. No. 4,737,592 (Abrams et al.).
U.S. Pat. No. 5,399,769 (Wilhelm et al.) discloses an improved methylamines process using synthetic chabazites as catalysts. Runs 3-5 in Table 5 show the methylamines distribution for different synthetic chabazites with a Si:Al ratio of about 2.5:1. The molar ratio of ammonia to methanol was 3.5: 1; such an excess of ammonia is known to decrease trimethylamine formation. The percentage of dimethylamine shown for each run was 26, 48.7 and 51.5, respectively.
What are needed and are of significant interest to the chemical industry are process improvements which suppress production of trimethylamine and optimize dimethylamine and monomethylamine yields. Other objects and advantages of the present invention will become apparent to those skilled in the art upon reference to the detailed description which follows hereinafter.
SUMMARY OF THE INVENTION
The invention provides a method for the production of dimethylamine (i.e., (CH
3
)
2
NH or DMA), monomethylamine (i.e., CH
3
NH
2
or MMA) and trimethylamine (i.e., (CH
3
)
3
N or TMA), comprising contacting methanol and/or dimethylether and ammonia in amounts sufficient to provide a carbon
itrogen (C/N) ratio from about 0.2 to about 1.5, at a reaction temperature from about 250° C. to about 450° C., in the presence of a catalytic amount of an acidic zeolite which has a chabazite crystalline structure, and wherein the ratio of silicon to aluminum (Si:Al) in said zeolite is at least about 5:1.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
For a general description of zeolites, see U.S. Pat. No. 4,737,592 (Abrams et al.), which description is incorporated herein by reference. Chabazite, a mineral zeolite, has a structure consisting of identical, near-spherical “chabazite cages,” each composed of two 6-rings at top and bottom, six 8-rings in rhombohedral positions, and six pairs of adjacent 4-rings. Each cage is interconnected to six adjacent units by near-planar, chair-shaped 8-rings. Mineral and synthetic chabazites prepared from inorganic materials can be characterized by the formula:
M
a
n
Al
12
Si
24
O
72
.40H
2
O
In this formula, the product of a and n is 12, and M generally refers to a cation preferably selected from Ca, Mg, Na and K. The cations can be exchanged for H
+
using mineral acids, by ion exchange or by conversion to an ammoniated form which can then be converted to the acid form by calcination at elevated temperatures, generally ranging from about 400 to about 600° C.
Acidic zeolites which have the chabazite crystal structure, and wherein the ratio of silicon to aluminum in said zeolites is at least about 5:1 can be prepared by heating an aqueous mixture containing an organic nitrogen-containing compound, a silicon oxide source and an aluminum oxide source to a temperature of at least 100° C. The heating is continued until crystals of the desired chabazite structure zeolite are formed and then recovering the crystals. Preferably, the organic nitrogen-containing cations are derived from 1-adamantine, 3-quinuclidinol and 2-exo-aminonorbornane.
The preparation of acidic zeolites having the chabazite crystal structure is described in U.S. Pat. No. 4,544,538 (Zones), which is incorporated hereby in its entirety by reference.
If desired, the silica alumina ratio of both natural and synthetic chabazites can be increased by procedures known in the art such as leaching with chelating agents, e.g., EDTA, or dilute acids.
The process of the present invention comprises reacting methanol and/or dimethylether (DME) and ammonia, in amounts sufficient to provide a carbon
itrogen (C/N) ratio from about 0.2 to about 1.5, in the presence of a catalytic amount of an acidic zeolite chabazite, wherein the acidic zeolite chabazite has a ratio of silicon to aluminum of at least about 5:1, at a temperature from about 250° C. to about 450° C. Reaction pressures can be varied from about 1-1000 psig (7-7000 kPa) with a methanol/DME space time of 0.01 to 80 hours. The resulting conversion of methanol and/or DME to methylamines is generally in excess of 85% (on a carbon basis) and selectivity (on a carbon basis) to dimethylamine is generally greater than 60%. In addition, selectivity to and yield of trimethylamine is suppressed. Thus, carbon yields of dimethylamine generally exceed 60% and carbon yields of trimethylamine are generally less than 10% under the process conditions of the present invention.
The molar equilibrium conversion of methanol and ammonia to a mixture of the Methylamines at 400° C. and a C/N ratio of 1.0 is 17:21:62 (MMA:DMA:TMA).
The process variables to be monitored in practicing the process of the present invention include C/N ratio, temperature, pressure, and methanol/DME space time. The latter variable is calculated as the mass of catalyst divided by the mass flow rate of methanol and DME introduced to a process reactor (mass catalyst/mass methanol+DME fed per hour.)
Generally, if process temperatures are too low, low conversion of reactants to dimethylamine and monomethylamine will result. Increases in process temperatures will ordinarily increase catalytic activity, however, if temperatures are excessively high, equilibrium conversions and catalyst deactivation can occur. Preferably, reaction temperatures are maintained between 270° C. and 370° C. more preferably 290° C. to 350° C. with lower temperatures within the ranges essentially preferred in order to minimize catalyst deactivation. At relatively low pressures, products must be refrigerated to condense them for further purification adding cost to the overall process. However, excessively high pressures require costly thick-walled reaction vessels. Preferably, pressures are maintained at 10-500 psig (70-3000 kPa). Short metha

Affiliated with

Also associated with

Rating

Method of making methylamines using chabazite catalysts does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Method of making methylamines using chabazite catalysts, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method of making methylamines using chabazite catalysts will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2459326