CS259342B1 - Method of inert gas deodoration used during preparation of alkyds and undersaturated polyesters - Google Patents

Abstract

The aim of the solution is to eliminate harmful ones malodorous fractions in the inert gas, which has passed through the reaction mixture and is drained from the polycondensation apparatus. It will be reached by one-stage washing of the exiting inert gas with a concentrated solution urea, warm 25 to 80 ° C, optionally adjusted to pH 6 to 10 by addition of weak acids, especially acetic acid or by adding weak bases, especially aqueous bases ammonia solution, sodium carbonate or (potassium or very dilute solution strong bases, preferably sodium hydroxide or potassium.

Description

The invention relates to a process for purifying an inert gas used in the preparation of alkyds and unsaturated polyesters. In this way, the malodorous components contained therein are removed from the inert gas which has penetrated the reaction mixture and is removed from the polycondensation of the apparatus.

Alkyd resins are the product of polycondensation of polyhydric alcohols or their derivatives with dibasic or polybasic acids or their derivatives. For special cases, the starting alkyd resins are further modified with further components.

Unsaturated polyester resins are the product of polycondensation of divalent alcohols or derivatives thereof with divalent unsaturated and saturated acids or derivatives thereof. In special cases, monohydric alcohols or acids are also reacted. The polycondensation product, an unsaturated polyester, is further diluted with a monomer capable of copolymerizing with an unsaturated polyester component to form the final commercial product, an unsaturated polyester resin.

In the reaction of the starting components, both types of resins release water as a reaction by-product. Its exit from the reaction mixture is not associated with particular problems at the beginning of the polycondensation, but at the end of the polyesterification the reaction mixture acquires such a viscosity that the evaporation of water from the reaction mixture is associated with considerable difficulties. Acceleration of water exit from the reaction mixture is then achieved either by adding an azeotropic component to the reaction mixture or by purging the reaction mixture with inert gas, or both. The inert gas used is nitrogen, carbon dioxide, argon and possibly purified combustion gases, which is again a mixture of nitrogen and carbon dioxide. In the preparation of alkyds, the reaction mixture is purged with air, which leads to an improvement in some of the quality parameters of the alkyd resins.

The amount of inert gas introduced into the reaction mixture varies from 5 to 12 m per 1 melt of resin. With a batch of 10 tons of the reaction mixture in one reactor, 50 to 120 µl of inert gas, containing additionally water of reaction, unreacted starting reactants and waste gases of aldehyde, mainly acrolein charter, are extremely harmful and odorous even after large dilution air.

From gaseous resp. vapor phase, virtually all esterification water and all less volatile reactants or intermediates are condensed in the condenser cooler above the reactor.

However, the aldehyde strongly odorous fractions remain in the gas phase. The disposal of these shares has received special attention lately and has been solved so far in the following ways. The inert gas is mixed with air and the organic constituents contained in the inert gas are catalytically burned. Or the inert gas is mixed with air and the organic constituents contained in the inert gas are combusted directly as disclosed in Soviet author's certificate 253 752. the method is to use the deodorization of an inert gas, which is carried out in two stages, as described in U.S. Pat. AO No. 188 693, in that, in the first stage, a larger part of the odorous fraction is washed out of the inert gas with a water spray or in a column, and the remainder is absorbed on activated carbon in the second stage.

The first two methods of disposal of the odorous fractions are associated with fuel consumption for heating the mixture to the reaction temperature necessary for catalytic combustion, respectively. for direct combustion.

In the third method, two-stage deodorization, it is a problem that the activated carbon columns are bulky, and a special, gaseous charcoal, which is very expensive, is required to completely recover the odorous fractions.

Most of these drawbacks are overcome by the present invention, which relates to a process for the deodorization of an inert gas used in the preparation of alkyds and unsaturated polyesters.

It is based on the fact that the exiting inert gas is washed with a single-stage concentrated urea solution, warm 25 to 80 [deg.] C., optionally adjusted to a pH of 6 to 10 by addition of aqueous solutions of weak acids, especially acetic acid or weak bases, especially aqueous ammonia. sodium or potassium carbonate or a very dilute solution of strong bases, preferably sodium or potassium hydroxide.

The present invention takes advantage of the fact that the stinking constituents contained in the inert gas are of an aldehyde nature. The corresponding aldehydes react with the urea amino groups to form non-volatile, odorless addition or condensation products. The very low volume fraction of odorous components in the inert gas (up to 1% by volume) allows a large volume of inert gas to be deodorized with a given volume of solution, i.e. the absorption can be successfully carried out to a considerable degree of urea reaction. The resulting condensation products can be used both as a mineral liquid fertilizer with a high nitrogen content and as a precondensation product in the preparation of urea-formaldehyde or melamine-formaldehyde resins. The second way of using condensation products is that acrolein-urea condensation products have previously been used as commercial textile treatment products.

The temperature and pH of the concentrated urea solution are adjusted according to the type of inert gas, when using carbon dioxide as an inert gas, adjusting the pH of the solution to an alkaline reaction is not expedient, since carbon dioxide would convert the alkali component into a less effective bicarbonate. Dimensions, resp. the types of abrasive column are chosen according to the volume of the inert gas to be discharged. The column material and the like are selected according to the pH of the urea solution.

The process for deodorizing the inert gas of the present invention is apparent from the examples.

He did

Into a 150 L reactor equipped with electrical resistance heating, 66 wt. parts by weight of linseed oil and 0.009 5 wt. and the contents are heated to 140 ° C. At this temperature 15 wt. parts of pentaerythritol, the suspension is gradually heated up to 255 ° C and alcoholysis is allowed to proceed. After completion of the alcoholysis, the reaction mixture is cooled to 160 ° C and 24 wt. parts of phthalic anhydride. After the addition of phthalic anhydride, 160 to 200 ° C distills off the bulk of the water through the deflector and downstream condenser and at a temperature of 200 ° C a stream of 400 l / h of nitrogen containing about 2% by volume of oxygen is introduced. This stream accelerates the reaction by-products trade, returning a major portion of the volatile phthalic anhydride to the reactor through the partial deflgmator.

The inert gas exiting the apparatus is fed to the column, where virtually all odorous fractions are washed from the circulating 51% urea solution at 60-65 ° C.

The column has a diameter of 100 mm, the height of the part filled with 10 mm Raschig rings, is about 700 mm.

The column, urea solution tank and circulation pump are glass. The urea solution is maintained at 60-65 ° C by electric heating.

The urea absorption solution, after addition of the appropriate amount of formaldehyde, is worked up in a known manner into a resin suitable for gluing wood.

Example 2

To the reactor of Example 1, 30 wt. parts of 1,2-propylene glycol, 32.2 wt. % of maleic anhydride and 20.8 wt. % of phthalic anhydride. The reaction mixture is gradually heated to 150 ° C, where the actual isothermia of the reaction also applies. From 155 ° C above, water begins to distill off, at 175 ° C 2.8 wt. % of xylene and the azeotropic polyesterification is continued. After reaching a temperature of 190 ° C in the reactor, a stream of carbon dioxide containing 1.2% by volume of oxygen was introduced into the reaction mixture at 800 l / h. The xylene phase of the distillate is continuously returned to the reactor, and the carbon dioxide exiting the apparatus is fed to the column described in Example 1, where it is washed with about 53% urea solution at 50-55 ° C containing 0.8 wt. sulfuric acid.

24 liters of solution per hour are recirculated through the pump. The gradual concentration of the urea solution, due to the evaporation of water from the solution, is compensated for by the periodic addition of water to the cartridge below the column, similar to Example 1. The carbon dioxide exiting the column is virtually odorless and discharged into the atmosphere.

Claims (1)

OBJECT OF THE INVENTION Process for the deodorization of an inert gas used in the preparation of alkyds and unsaturated polyesters, characterized in that the exiting inert gas is washed in one step with a concentrated urea solution at 25 to 80 ° C, optionally adjusted to a pH of 6 to 10 by addition of weak acids, especially acetic acid or % of a base, in particular an aqueous solution of ammonia, sodium or potassium carbonate, or a very dilute solution of strong bases, preferably sodium or potassium hydroxide.