Organic compounds -- part of the class 532-570 series – Organic compounds – Oxygen containing
Reexamination Certificate
2000-07-03
2001-09-11
Shippen, Michael L. (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Oxygen containing
C568S727000
Reexamination Certificate
active
06288284
ABSTRACT:
The present invention relates to a process for the production of bis(4-hydroxyaryl)alkanes by an acid-catalysed reaction between aromatic hydroxy compounds and ketones, in which the temperature, ketone content and water content of a liquid reaction mixture are adjusted by means of a suitably composed gas phase.
It is known to synthesise bis(4-hydroxyaryl)alkanes by an acid-catalysed reaction between aromatic hydroxy compounds and ketones. U.S. Pat. Nos. 3,634,341 and 3,760,006 describe the influence exerted by the water content of the reaction mixture on catalyst efficiency, and a water content of 2-3 wt. % is indicated as the critical limit for the reaction in a fixed-bed reactor. WO 94/19079 and EP-A 770 590 disclose the continuous removal of water formed in the reaction, by passing a dry inert gas, for example nitrogen, through the reactor in countercurrent. It is shown in U.S. Pat. No. 4,400,555 (EP-A 342 758) and EP-A 754 666 that the selectivity of bis(4-hydroxyaryl)alkane formation in a production process having a plurality of reactors connected in series can be increased if the ketone is distributed among the different reactors; it is proposed in WO 94/19079 that for bis(4-hydroxyaryl)alkane production in a (stripper) column the ketone be supplied in gaseous or liquid form by way of a plurality of dispensing points throughout the length of the column. A disadvantage of the latter process is the major capital investment and control engineering involved in thus proportioning the ketone supply over a plurality of reactors or a plurality of supply points of a stripper. The rate of reaction of bis(4-hydroxyaryl)alkane formation is furthermore reduced by proportioning the ketone supply. The lower reaction rate is accepted in order to increase the selectivity.
A method is required in which simultaneously the reaction is not only more selective, but also proceeds at a faster rate, in order thus to maximise the space-time yield.
It has now been found that bis(4-hydroxyaryl)alkanes can be produced at high selectivity and simultaneously at a high space-time yield if the temperature, ketone content and water content of a liquid reaction mixture are adjusted by means of a suitably composed gas phase. The present invention provides a process for the production of bis(4-hydroxyaryl)alkanes by an acid-catalysed reaction between aromatic hydroxy compounds and ketones, in which there are guided through a reactor a liquid phase which contains aromatic hydroxy compound, ketone and optionally water, and a gas phase which contains aromatic hydroxy compound, ketone and optionally water, at concentrations such that in the reactor water passes over from the liquid phase into the gas phase and ketone from the gas phase into the liquid phase.
The gas phase and the liquid phase may be guided through the reactor either in co-current or in countercurrent. Countercurrent is the preferred modus operandi.
Freely selectable, approximately constant concentrations of ketone and water can be adjusted throughout the length of the reactor at simultaneously approximately constant, freely selectable temperatures, as a result of the process according to the invention. According to the invention it is likewise possible to carry out a method in which, instead of conditions being approximately constant, it is possible to select conditions under which the temperature and/or the concentration of aromatic hydroxy compound, ketone and water in the liquid phase are not constant throughout the length of the reactor. Thus, for example, temperature gradients and/or ketone and/or water concentration gradients can be impressed in the liquid phase. The underlying concept of the process according to the invention is the adjustment of the temperature, the ketone content and the water content in the liquid reaction mixture by means of a suitably composed gas phase.
In the process according to the invention the molar ratio of aromatic hydroxy compound to ketone in the liquid phase supplied to the reactor is generally from 3.5:1 to 125:1, preferably 5:1 to 60:1, particularly preferably 10:1 to 30:1. The liquid phase supplied to the reactor may contain small quantities of water. The water content is preferably from 0 to 2 wt. %.
The molar ratio of aromatic hydroxy compound to ketone in the gas phase supplied to the reactor results from the condition that ketone should pass over from the gas phase into the liquid phase in the reactor at the reaction temperature and reaction pressure. In order to adjust approximately constant ketone concentrations in the liquid phase, the ketone concentration in the gas phase entering the reactor should accordingly be selected to be approximately as high as the concentration which would adjust in the gas phase by way of the dispensed-in liquid phase at the reaction temperature and reaction pressure under conditions of thermodynamic equilibrium. If a ketone concentration gradient is to be adjusted in the reactor, the ketone concentration in the gas phase supplied to the reactor should be selected to be higher or lower than the concentration which would adjust under conditions of thermodynamic equilibrium.
The water concentration in the dispensed gas phase results from the water concentration in the dispensed liquid phase, on the same principle. It must be selected such that in the reactor at the reaction temperature and reaction pressure water passes over from the liquid phase into the gas phase. The water concentration in the gas phase should accordingly be selected to be approximately as high as the concentration which would adjust in the gas phase by way of the dispensed liquid phase at the reaction temperature and reaction pressure under conditions of thermodynamic equilibrium, in order to adjust a constant water concentration in the liquid phase. If a water concentration gradient is to be adjusted in the reactor, the water concentration in the gas phase supplied to the reactor should be selected to be higher or lower than the concentration which would adjust under conditions of thermodynamic equilibrium.
As a result of suitable adjustment of the concentrations in the gas phase and the liquid phase in the reactor, water is removed from, and ketone supplied to, the liquid reaction mixture in continuous manner by the gas phase. The consumption of ketone or the arising of water as a result of reaction are consequently balanced by the phase transition between the gas phase and the liquid phase. In this manner the concentrations of ketone and water in the liquid phase and the temperature in the reactor can be held approximately constant, or a concentration gradient or temperature gradient can be impressed.
This operating characteristic is highly advantageous, because a continuous making-up of spent ketone and the simultaneous continuous removal of water from the liquid phase hold the reaction rate high throughout the length of the reactor. The regulatable, optionally approximately constant reaction conditions in the reactor, and the approximately isothermic operating characteristic enable selectivity to be improved simultaneously.
The temperature in the reactor is between the temperature of crystallisation of the reaction mixture and 130° C. It is adjusted by selecting the pressure in the reactor. If the ketone concentration and the water concentration are held constant throughout the length of the reactor, a highly uniform temperature regime can be achieved. The removal and supply of heat take place, by contrast with the process described in WO 94/19079, not as a result of heating an inert gas stream, but far more effectively principally as a result of local evaporation and condensation. By contrast with the prior art process, the temperature can in this way be held approximately constant throughout the reaction zone.
The pressure to be adjusted for the desired temperature and the desired ketone and water concentrations can be calculated by way of the thermodynamic equilibrium; under operating characteristics without inert gas, it is generally from 5 to 1000 mbar, preferably 15 to 200 mbar. In orde
Eek Rob
Fennhoff Gerhard
Hallenberger Kaspar
Mendoza-Frohn Christine
Ronge Georg
Bayer Aktiengesellschaft
Gil Joseph C.
Preis Aron
Shippen Michael L.
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