Organic compounds -- part of the class 532-570 series – Organic compounds – Oxygen containing
Patent
1994-09-16
1997-06-10
Geist, Gary
Organic compounds -- part of the class 532-570 series
Organic compounds
Oxygen containing
203DIG6, 203DIG16, 203DIG19, 203 29, 203 34, 203 94, 203 98, 203 99, C07C 4142, C07C 4300
Patent
active
056377770
DESCRIPTION:
BRIEF SUMMARY
This application is a 371 of PCT/FI93/00097, filed Mar. 18, 1993.
The present invention concerns a process in accordance with the preamble of claim 1 for preparing tertiary ethers.
According to such a process C.sub.4 to C.sub.6 isoolefins and possible heavier isoolefins or mixtures of said isoolefin contained in the feedstock are reacted with lower aliphatic alcohols, in particular methanol or ethanol, in a catalytic distillation reactor system in order to produce the corresponding ethers.
The invention also relates to an apparatus in accordance with the preamble of claim 15 for preparing tertiary ethers.
Catalytic (i.e. reactive) distillation is used for preparing, e.g., tert-methyl and tert-ethyl butyl ethers (in the following called MTBE and ETBE, respectively) and tert-amyl methyl ether and tert-amyl ethyl ether (in the following called TAME and TAEE, respectively). In the apparatus, the reaction takes place at the same time as the separation of the products from the feed. As far as the reaction kinetics of the system is concerned this is highly advantageous, because etherification is an equilibrium reaction in which the maximum conversion depends on the thermodynamic equilibrium of the reaction system. Thus, when MTBE is being prepared by a conventional fixed bed reactor/product separation distillation system, a isobutene conversion in the range from about 90 to about 95% is achieved, whereas reactive distillation will reach conversion rates in the range from 98 to 99%.
There are known in the art attempts to improve the conversion of the fixed bed reactor process by combining the product separation distillation with a postreactor. Thus, U.S. Pat. No. 4,503,265 (EC Erdolchemie GmbH) discloses a process for preparing MTBE, which comprises withdrawal of a side-stream from the distillation column, and circulating the side-stream via a postreactor. The MTBE yield is indicated as being in the range from 98 to 99%. In this case rather large amounts of the catalyst will have to be used in the fixed bed reactors in order to achieve the desired conversion, because the process fails to provide the same advantageous equilibrium as the catalytic distillation.
Although catalytic distillation for the time being is the most preferred way of preparing tertiary ethers, it is still hampered by some problems.
In the MTBE/ETBE/TAME/TAEE processes a catalyst comprising sulfonated poly-styrene/divinyl-benzene based cation resin is used, with particle sizes from about 0.1 to 1 mm, normally. Due to channeling of the liquid flows this kind of particles work poorly hydraulically in large industrial sized distillation columns, which increases the amount of catalyst needed. Large amounts of catalyst, however, worsen the channelling problem. Therefore, different kinds of bag/sack based processes have been developed and attempts have been made to shape the catalyst particles in the form of packings.
Another significant problem relating to catalytic distillation is the difficult replacement of the catalyst. Being arranged within the column, the catalyst is much more difficult to replace than the catalyst of a conventional fixed bed reactor. Moreover, catalyst replacement cannot be carried out as long as the unit is in operation. The prior art has often sought to reduce this problem by the use of, e.g., a prereactor which takes up the catalyst poisons.
U.S. Pat. No. 3,629,478 anticipates a catalytic distillation reactor used for separation of linear pentenes from tertiary olefines. The catalyst is placed in the downcomers of the column trays. Alternatively, instead of placing the catalyst in the downcomers, the patent suggests that the catalyst be put into small reaction vessels which would be connected to the distillation column by means of pipes. There would be one reaction vessel at each distillation tray. This alternative is not described in further detail in the specification, but it is clear that by placing the catalyst in external reactors of the suggested kind the replacement of the catalyst would be facilitated.
The use of t
REFERENCES:
patent: 3629478 (1971-12-01), Haunschild
patent: 4503265 (1985-03-01), Schleppinghoff et al.
patent: 5130102 (1992-07-01), Jones, Jr.
patent: 5177283 (1993-01-01), Ward
patent: 5235102 (1993-08-01), Palmer et al.
Aittamaa Juhani
Eilos Isto
Jakkula Juha
Lindqvist Petri
Geist Gary
Neste Oy
Williams Rosalynd A.
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