Organic compounds -- part of the class 532-570 series – Organic compounds – Oxygen containing
Reexamination Certificate
1999-08-09
2001-02-13
O'Sullivan, Peter (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Oxygen containing
C568S852000, C568S868000, C549S230000
Reexamination Certificate
active
06187972
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a process for producing an alkylene glycol from an alkylene oxide. More particularly, it relates to a process for producing an alkylene glycol with especially high efficiency.
2. Discussion of Background
An alkylene glycol, particularly ethylene glycol, is used, for example, as a raw material for synthetic fibers or resins, or as an anti-freezing liquid, and is an industrially important compound.
As a way for producing an alkylene glycol, a process of hydrolyzing an alkylene carbonate, is well known. Such a reaction is usually carried out in the presence of a catalyst for hydrolysis, and it has been proposed to use a catalyst for hydrolysis such as an alkali metal carbonate (U.S. Pat. No. 4,117,250), a molybdenum compound (JP-B-55-154927) or a tungsten compound (JP-B-55-154928) in order to increase the reaction rate.
By the use of these catalysts for hydrolysis, the hydrolysis can be accelerated, but the degree of acceleration has not been adequate. If the reaction is carried out at a higher temperature to accomplish an industrially satisfactory reaction rate, there has been a problem that the quality of the product tends to deteriorate. On the other hand, if the reaction is carried out at a lower temperature to secure the quality of the product, the reaction rate will be low, and an excessive capacity of the reactor is required to attain the predetermined productivity, or an unreacted alkylene carbonate tends to remain in the product.
Whereas, if ethylene carbonate remains after the hydrolysis in the course of production of ethylene glycol which is industrially most important, it forms an azeotropic mixture together with ethylene glycol, whereby their separation or purification tends to be difficult.
Further, in the hydrolysis of an alkylene carbonate, it is common to employ a molar ratio of water to an alkylene carbonate in the charged starting materials within a range of from about 1.3:1 to about 5.0:1. If the molar ratio is less than this range, there will be a problem that as the reaction proceeds, water will be consumed, and the water concentration will decrease, whereby the reaction rate decreases, so that it takes time to complete the reaction, and the amount of impurities formed, tends to increase. On the other hand, if water is charged in a large amount beyond this range, water will be present in the system in an amount substantially exceeding the amount consumed for the reaction, whereby there will be a problem that a large quantity of heat will be required for heating the reaction solution and separating water in the purification system.
Further, the alkylene carbonate to be used as the starting material, can be obtained by reacting an alkylene oxide with carbon dioxide gas in the presence of a carbonating catalyst. However, in a case where this step and the hydrolyzing step are carried out continuously, if the carbonating catalyst is used by recycling, the carbonating catalyst activities will gradually decrease. Accordingly, it is desired to develop a process whereby the catalyst activities will not decrease.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a process for producing an alkylene glycol, which is free from the above described problems. Specifically, it is an object of the present invention to provide a process whereby the energy consumption is suppressed, the carbonating catalyst can be used repeatedly by recycling without deterioration of the activities even in a case where an alkylene carbonate obtained by reacting an alkylene oxide with carbon dioxide gas in the presence of the carbonating catalyst, is used, and the hydrolysis can be completed efficiently at a low temperature in a short period of time.
The present inventors have conducted extensive studies to solve the above problems and, as a result, have found it possible to suppress the energy consumption and to maintain the reaction rate at a high level by maintaining the water concentration in the reaction system within a certain range in a certain range of conversion of the alkylene carbonate. The present invention has been accomplished on the basis of this discovery.
That is, the object of the present invention can be accomplished by a process for producing an alkylene glycol, which is a continuous process for producing an alkylene glycol comprising the following steps (1) to (4), wherein the hydrolysis step (2) is divided into a plurality of stages, and the hydrolysis is carried out so that the water concentration in the reaction stage wherein the conversion of the alkylene carbonate is at least 60%, is from 15 to 30 wt %:
(1) a carbonating step of reacting an alkylene oxide with carbon dioxide gas in the presence of a carbonating catalyst to form a reaction solution containing an alkylene carbonate,
(2) a hydrolysis step of hydrolyzing the reaction solution obtained in step (1) while releasing carbon dioxide gas, to form an aqueous alkylene glycol solution,
(3) a distillation step of distilling the aqueous alkylene glycol solution to obtain at least a dehydrated alkylene glycol and a solution containing the carbonating catalyst, and
(4) a recycling step of supplying the solution containing the carbonating catalyst to the carbonating step (1).
DETAILED DESCRIPTION OF THE INVENTION
Now, the present invention will be described in detail.
In the present invention, firstly, an alkylene oxide is reacted with carbon dioxide gas in the presence of a catalyst to form a reaction solution containing an alkylene carbonate. Preferably, an alkylene oxide is reacted with carbon dioxide gas and water to form a reaction solution containing an alkylene carbonate and an alkylene glycol. This reaction can be carried out in accordance with a known method.
The catalyst to be employed, may, for example, be an alkali metal bromide or iodide, an alkaline earth metal bromide or iodide, an ammonium halide such as tributylmethylammonium iodide, or a phosphonium halide such as tributylmethylphosphonium iodide. Among them, a quaternary phosphonium halide is particularly preferred, and usually one represented by the following formula is employed.
In the above formula, each of R
1
to R
4
which are independent of one another, represents a group such as an alkyl group, an alkenyl group, an aryl group or an aralkyl group, which may have a substituent inert to the reaction, bonded. X is chlorine, bromine or iodine.
Specific examples of such a quaternary phosphonium halide may be those disclosed on pages 2 and 3 of JP-A-58-22448. Among them, particularly preferred is a tetraalkylphosphonium halide wherein each of R
1
to R
4
which are independent of one another, is a C
1-6
alkyl group. The quaternary phosphonium halide is usually synthesized outside the system and then added to the system. If desired, however, the corresponding tertiary phosphine and alkyl halide may be added to the reaction system, so that the quaternary phosphonium halide is formed in the reaction system. As the carbonating catalyst, the quaternary phosphonium halide may usually be used alone, but if desired, other promoter or cocatalyst component may be used in combination. For example, the quaternary phosphonium halide may be used in combination with from 0.01 to 1 molar time of an alkali metal carbonate, whereby it is possible to reduce formation of a by-product such as diethylene glycol in the carbonating step, and to promote the reaction in the hydrolytic step.
The reaction of the carbonating step is carried out usually from 70 to 200° C., preferably from 100 to 170° C., more preferably from 100 to 150° C. If the reaction temperature is low, the reaction rate tends to be low. On the other hand, if the reaction temperature is too high, side reactions will increase, and a loss due to decomposition of the catalyst will increase. The reaction pressure is usually from 5 to 50 kg/cm
2
G (0.59 to 5.0 MPa), preferably from 10 to 30 kg/cm
2
G (from 1.08 to 3.04 MPa). As the reaction pressure becomes high, the reaction rate of an alkylene oxid
Kawabe Kazuki
Nagata Kouichi
Mitsubishi Chemical Corporation
O'Sullivan Peter
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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