RU2258694C1 - Method of inhibiting metallic surfaces of methyl methacrylate production equipment - Google Patents

Abstract

FIELD: chemical engineering.

SUBSTANCE: task of invention resides in prevention of monomeric methyl methacrylate from polymerization via inhibition of inner surface of the process equipment and thereby prevention of polymeric scale formation thereon, which would lead to heavy cleaning operation involving dismounting of equipment to fragments and burning out of polymeric scale. To that end, inner surface of equipment is treated with inhibitory solution containing sodium liquid glass solution, sodium silicofluoride as hardened in amount 25% of the weight of liquid glass, and water-soluble nigrozin at concentration in hardened liquid glass layer not exceeding 1% of the weight of liquid glass. Method may be used in production of other ethylenically-unsaturated monomers.

EFFECT: eliminated scale cleaning operation.

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Description

The present invention relates to the chemical industry, namely the production of (meth) acrylic monomers. The method can also be used in the manufacture of other vinyl monomers containing double unsaturated bonds.

In the production of such monomers, there is a problem of polymerization of the monomer on the inner walls of the equipment with the formation of polymer growths, which leads to a decrease in productivity and, ultimately, to the conclusion from the working state of the equipment.

In order to prevent the polymerization of vinyl monomers on the inner surface of the equipment, various methods of surface inhibition are used.

A known method of inhibiting [1] in contact with the monomer of the surfaces of the reactor during the polymerization of vinyl monomers, in which the surface of the reactor is treated with a mixture of silicic acid compounds (colloidal solution of H ₂ SiO ₃ ) and phosphoric acid compounds.

To inhibit the internal surfaces of the equipment, solutions containing organic dyes or pigments [2] (azo-, nitro-, nitro-, anthraquinone, indigo, etc.) as well as inorganic components (silicic acids, silicates, metals and their salts, inorganic colloids).

However, these compounds have poor adhesion to metal surfaces, which leads to a violation of the integrity of the inhibitory coating and a decrease in the time of trouble-free operation of the equipment.

To protect the walls of the reactor from the formation of polymer growths during suspension polymerization of vinyl chloride, a method for coating the surface with alcohol-soluble nigrosin has been widely used [3]. With respect to the production of methyl methacrylate, the method cannot be applied due to the good solubility of alcohol-soluble nigrosin in the environment of methyl methacrylate and other organic solvents contained in the reaction mass (acetone, methanol, etc.).

The closest in technical essence and the achieved technical result, selected as a prototype is a method [4] to protect the surface of the equipment during the polymerization of unsaturated monomers (vinyl chloride) by applying to the equipment walls a composition consisting of polyvinyl alcohol (PVA) and liquid glass dissolved in water .

The composition has good adhesion to metal surfaces, however, its inhibitory ability, in relation to the production of methyl methacrylate, is insufficient, since the inhibition time on the vinyl chloride polymerization system is 10 cycles of 12 hours, i.e. 120 hours of operation. On the methyl methacrylate-metal surface system, the proposed method showed even shorter effective inhibition times. In order to increase the time and effectiveness of the inhibition of metal surfaces in the production of methyl methacrylate, we propose to cover the inner surface of the equipment with an inhibitory solution, which includes water-soluble nigrosin, liquid sodium glass and a hardener. The hardened coating has very good adhesion to metal surfaces after its preliminary treatment. The good solubility of liquid sodium glass and nigrosine in water makes them mutually soluble. On the other hand, liquid sodium glass and water-soluble nigrosine are practically insoluble in methyl methacrylate. The optimal concentration of nigrosine in the mixture, found experimentally, does not exceed 1 wt.% In relation to liquid glass.

The authors are not aware of technical solutions containing signs similar to those distinguishing the proposed technical solution from the prototype, namely, there are no known methods of protecting equipment by applying a mixture that would include water-soluble nigrosin.

This allows us to conclude that the proposed method is new. The use of nigrosine, hardener and liquid sodium glass in the composition of the proposed method with a certain ratio of all components allows to obtain a mixture with good inhibitory and adhesive properties. In this regard, the authors suggest that their proposed technical solution meets the criterion of "Inventive step".

An inhibitory solution is prepared as follows.

With stirring at room temperature, hardener is introduced into liquid sodium glass in small portions until it is completely dissolved in an amount of 25% by weight of liquid glass. A 5% aqueous solution of nigrosin is immediately added to the prepared mixture with stirring in such an amount that the total concentration of nigrosin is not more than 1% by weight of liquid glass.

The resulting composition is applied to the metal surface in one of the ways: by spraying with a nozzle, a brush or by immersing a metal part in the composition. After coating, the metal part is dried until the composition turns into a solid film. Film thickness not more than 10.0 microns. Drying is carried out both at ordinary temperature for at least 2 days, and at elevated temperature (up to 80 ° C) for 3-4 hours.

The essence of the invention is illustrated by the following examples.

Example 1. In a round-bottom glass flask with a capacity of 0.25 liters, equipped with a reflux condenser, plates of various metals (copper, steel, aluminum, etc.) with a size of 20 × 40 × 1 mm are suspended.

The metal plates are treated with a mixture of liquid sodium glass, liquid glass hardener and water-soluble nigrosin as an inhibitor of the polymerization of methyl methacrylate and other double bond monomers. The mixture is prepared as follows. Liquid sodium glass is mixed with a hardener in an amount of 25% by weight of liquid glass. Sodium silicofluoride is taken as a hardener. Water-soluble nigrosin is added to the mixture with stirring in an amount of not more than 1 wt.% With respect to liquid glass. The mixture is applied to a metal plate. Curing of the mixture begins at room temperature and lasts up to 5 days. To accelerate curing, an elevated temperature can be used. So, at a temperature of 100 ° C, the composition hardens within 2 hours.

Treated metal plates are tested as follows. Methyl methacrylate or a reaction mixture containing up to 75 wt.% Methyl methacrylate and solvents (acetone, methanol, water) is poured into the flask and brought to a boil. Methyl methacrylate vapors wash the plate, enter the reflux condenser and condense. Condensate, draining into the flask, washes the plate again. After certain periods of time, the heating is stopped, the plate is removed from the flask, dried and weighed. By the gain of the plate (and visually), the formation of polymer growths of polymethyl methacrylate on the surface of the plate is observed.

To assess the inhibitory activity of water-soluble nigrosin during the polymerization of methyl methacrylate on the metal surface, experiments were carried out with control samples of the mixture. One mixture was prepared without water-soluble nigrosin, and nigrosin was added to the other in an amount of 1% by weight of liquid glass. A small amount of water-soluble peroxide compounds, the initiators of polymerization, was introduced into both mixtures. On plates placed in methyl methacrylate pairs coated with a mixture without water-soluble nigrosin, the formation of polymer growths was observed after 4-5 hours.

The plates coated with the mixture, which included water-soluble nigrosin, worked without the formation of polymer growths of polymethyl methacrylate for 400 hours.

Example 2. In the workshop, on one of the four systems for the synthesis of methyl methacrylate (MMA), whose capacity is 1300 tons per month, with exhaust gases after the refrigerator, a pipeline was installed, coated on the inside with the proposed solution of the polymerization inhibitor.

The pipeline includes:

- tee (length of each branch of ~ 250 mm) from a copper pipe with a diameter of 57 mm;

- tap (~ 300 mm long) from a copper pipe with a diameter of 57 mm;

- three pieces of aluminum pipe (each piece ~ 1500 mm long) with a diameter of 57 mm.

The pipeline was coated by the gulf method. After application to the surface of the pipeline, the composition was dried at room temperature for five days.

The exhaust gas pipelines after the second, third, and fourth MMA synthesis systems were not coated with a polymerization inhibitor and were control with respect to the first system. Technological control over the operation of the exhaust gas piping systems was carried out according to their temperature regime.

Observations showed:

- the system pipeline, the inner surface of which is coated with the proposed solution of the polymerization inhibitor, works without the formation of 6120 hours on the polymer metal surface;

- exhaust gas pipelines of three (control) systems for the synthesis of MMA periodically, after 7-12 days, are clogged with polymer, opened for cleaning or replaced.

Sources of information

1. Japanese application No. 62-20509, IPC C 08 F 14/06, 2/10, publ. 01/29/1987.

2. US Patent No. 4758639, IPC C 08 F 2/18, C 08 F 2/22, publ. 07/09/1988.

3. Popov V. A., Shvarev E. P. et al. "Physico-chemical aspects of polymer deposition on the surface of a reactor during the polymerization of vinyl chloride", Plastics, 1989, No. 12, pp. 12-15.

4. US Patent No. 4622245, IPC C 08 F 2/00, publ. 11/11/1986.

Claims (1)

A method of inhibiting the metal surface of methyl methacrylate production equipment by treating the internal surface of the equipment with an inhibitory solution, characterized in that the treatment is carried out with an inhibitory solution that contains sodium liquid glass solution, the hardener is sodium silicofluoride in an amount of 25% by weight of liquid glass and water-soluble nigrosin, the concentration of which is the cured liquid glass layer does not exceed 1 wt.% with respect to the liquid glass.