DE3325166C2 - Use of a cleaning agent to remove polymer coatings from containers - Google Patents

Abstract

Polymerization containers can be freed from polymer coatings very well with a cleaning agent made from 100 parts by weight of water, 0-150 parts by weight of water-soluble organic solvents, 10-200 parts by weight of non-homogeneously water-miscible organic solvents, 0-20 parts by weight of emulsifiers and 5-30 parts by weight of alkali and / or alkaline earth metal hydroxides , especially of those copolymers containing vinyl chloride.

Description

for removing wall coverings from copolymers made of vinyl chloride, ethylenically unsaturated Esters and, if appropriate, further comonomers, of SBR and / or SAN polymers from polymerization reactors.

2. embodiment of the use according to claim 1, characterized in that the cleaning agent per 100 parts by weight of water

0-50 parts by weight of water-soluble organic solvents

30 to 10 parts by weight of organic solvents which are not homogeneously water-miscible
0.5-5 parts by weight of emulsifiers

and

15 - 30 parts by weight of alkali and / or alkaline earth hydroxides

are included.

In the production and handling of aqueous polymer dispersions, be it those from suspension, Emulsion or microsuspension processes, difficulties arise again and again due to the formation of deposits on the container walls. The formation of these deposits in polymerization tanks is particularly critical, as this increases the heat transfer and thus the operational safety of the reactors, but also the product quality can affect.

A large number of methods and means for removing such wall coverings have therefore already been proposed been. Particular difficulties arise in particular when removing wall coverings of copolymers made from vinyl chloride and ethylenically unsaturated esters and / or other comonomers, z. B. ethylene, especially by the emulsion polymerization process, and / or crosslinked Polymers.

Wall coverings made from polymers made from ethylenically unsaturated esters, in particular vinyl esters, have been used so far dissolved by alcoholic solutions with alkali hydroxides with saponification and rinsed out with water, whereby the hydrolysis products often fail again. In many cases, therefore, several rinse cycles have to be switched one after the other will. If the copolymers also contain vinyl chloride units (VC), they increase in size the difficulties, since with the increase in the VC content the saponification stability rises and the

The solubility of the saponification products decreases

If one therefore moves from the alcoholic-aqueous system to purely organic solvent systems (see e.g. US-A-34 75 218), in which z. B. Polyvinyl chloride dissolves so, apart from occupational and environmental hygiene as well as safety problems (fire hazard), new difficulties arise because of polymer solutions Achieve high viscosities even with low solids contents and are difficult to handle and work up will.

The present invention was therefore based on the object of providing a way of removing wall coverings to find from polymerization reactors that largely overcome the difficulties of the prior art, preferably even completely avoided

The cleaning agent used for this should remove polymer coatings from the container walls and absorb without the liquid becoming highly viscous or even less fluid despite the high polymer content loses Furthermore, the drained liquid should be easy to work up.

In particular, the cleaning agent should also make it possible Containers of residues or wall coverings of copolymers made of vinyl chloride and ethylenic to purify unsaturated esters. Particular mention should be made of wall coverings that are used during polymerization have arisen in the polymerization reactor.

These objects are achieved in a surprisingly advantageous manner through the use of a cleaning agent, the

100 parts by weight of water,

0-150, preferably 0-50, parts by weight more water soluble organic solvent,

10-200, preferably 30-100 parts by weight not homogeneous water-miscible organic solvents,

0-20, preferably 0.5-5, parts by weight of emulsifiers and

5-30, preferably 15-30, parts by weight of alkali and / or alkaline earth metal hydroxides

contains.

Those organic solvents which are liquid at room temperature and have boiling points in the range of 50 to 17O ⁰ C, preferably 50 to have 15O ⁰ C are preferred. The water-soluble and non-homogeneously water-miscible solvents can each be used individually or as mixtures.

The preferred water-soluble organic solvents are alcohols, ketones, dialkyl sulfoxides and / or to call ethers. Particularly preferred are Ci to C3 alkanols, in particular methanol, ethanol, iso- and n-propanol; C3 to Cs ketones, especially acetone and methyl ethyl ketone, water-soluble ethers, e.g. B. (1,4) -Dioxane, as well as dimethyl sulfoxide.

Preferred examples of non-homogeneously water-miscible organic solvents are ethers, halogenated non-arid hydrocarbons, aromatics and liquid, optionally halogenated, paraffinic hydrocarbons.

Particularly preferred are ethers such as dialkyl and / or alkylbenzyl ethers which are liquid at room temperature and have C 1 to about C ₆ alkyl groups, provided their boiling points at normal pressure are in the boiling range mentioned, e.g. B. those with CH ₃ -, C ₂ H ₅ -, C ₃ H ₇ -, C ₄ H ₉ -, C ₅ H _n - and C ₆ Hi ₃ -alkyl groups, as well as dibenzyl ethers, especially

re tetrahydrofuran (THF); halogenated hydrocarbons, which are also liquid at room temperature and boil in the range mentioned, but not acidic Have hydrogen atoms. Carbon tetrachloride should be mentioned in particular and is particularly preferred Perchlorethylene. Aromatics such as benzene, toluene and xylenes and paraffinic hydrocarbons are also preferred.

Essential for the selection of the non-homogeneously water-miscible solvents is their ability to organisehe To dissolve, dissolve or at least swell polymers.

If necessary, emulsifiers are added to the cleaning agent used according to the invention This is always preferred when in the production of the polymers to be detached from the container walls Little or no emulsifier has been used or has become ineffective due to chemical reaction have been done. The need to add emulsifier can easily be broken down into a few Determine preliminary tests. The detergent should either be in use or when Let use emulsify slightly. If necessary, commercially available emulsifiers, preferably alkyl sulfonates, are used and / or alkylbenzenesulfonates.

The cleaning agent used according to the invention also contains alkali and / or alkaline earth hydroxides, preferably hydroxides of lithium, sodium, potassium, cesium, rubidium, calcium, strontium and / or barium. Calcium hydroxide and in particular sodium and / or potassium hydroxide are particularly preferred.

When selecting the components contained in the detergent, these components should be preferred do not react to each other, e.g. B. the emulsifiers to water-insoluble lime soaps or the hydroxides with the halogenated hydrocarbons to alkali and / or alkaline earth halides. The organic solvents should therefore not noticeably at least for the duration of the application (usually less than 2 hours) Extensions to be hydrolyzed.

As particularly advantageous, especially for the removal of wall coverings made from copolymers of vinyl chloride with comonomers such as ethylene, vinyl esters and / or (meth) acrylic acid esters, in particular with Ethylene, vinyl acetate and / or Ci to Ce alkyl (meth) acrylates, a mixture of water, especially of those with a high vinyl chloride content, Acetone, perchlorethylene and sodium hydroxide and / or potassium hydroxide and, if necessary, commercially available Sodium alkyl sulfonates and / or in particular -alkylbenzenesulfonates proved, the densities of the organic and aqueous phases are preferably approximately the same. The density of the lighter phase For example, if possible, it should not deviate by more than 10% from that of the heavier phase in order to achieve optimal results to achieve.

Surprisingly, even stubborn copolymer coverings dissolve after a short treatment time of e.g. B. 30 min to z. B. 2 hours, possibly with heating up to about 100 ^c C from practically residue-free and the emulsions containing the detached wall coverings are characterized by the fact that they have high solids contents of z. B. 30 wt .-%, based on total weight, can absorb and still without problems from the container largely residue-free, z. B. with gentle rinsing with water or a small amount (esp. 5-20% of the reactor volume) of water-soluble organic solvents, e.g. B. the alcohols mentioned, if necessary with brief heating, remove. The used agent can also be worked up without any problems.

It is also surprising that according to the invention there are also other sparingly soluble polymers which are even partially crosslinked can be removed without difficulty. Examples are the so-called SBR and SAN polymers and PVC-containing mixtures mentioned These wall coverings also go well with the above Remove the above-mentioned mixtures of acetone, perchlorethylene and sodium hydroxide and, if necessary, emulsifier.

The work-up of the drained and loaded cleaning emulsion can, as already mentioned, be very easy easy to design. Thus, the mixture is preferably first subjected to a fractional distillation at normal pressure subject. The residue is then further purified, preferably by steam distillation until the solvent content has fallen below a desired limit. For example, the Perchlorethylene content below 100 ppm, particularly preferably below 30 ppm. The distillates can be worked up in the usual way and the solvents reused. The bottom product essentially only contains a mostly water-liquid mixture of hydroxide, possibly emulsifier, Polymer residues and water. For example, it can be particularly advantageous in (also biological) wastewater treatment can be used to neutralize acidic residues. In addition, the polymer residues have the advantageous property of flocculating and so as a flocculant and in many cases even act as a precipitant for heavy metals, which can be removed from the wastewater in this way.

Claims (1)

Patent claims: 1. Use a cleaning agent for removal before: polymer coverings from containers containing lOOGew.tle of water, 0-150 parts by weight of water-soluble organic solvents,
10-200 parts by weight not homogeneously water-miscible organic solvent,
0-20 parts by weight of emulsifiers and 5-30 parts by weight of alkali and / or alkaline earth metal hydroxides,