SU1745285A1 - Method of purification of organic solvents - Google Patents

Description

The known method of purification of water and aqueous working solutions is based on filtering the working solution through an absorber layer (adsorbent) and using soluble carbon or ion exchange resins as an absorber.

The disadvantages of this method are the following: filtering a contaminated working solution using flammable liquids is extremely dangerous under production conditions; according to safety conditions, this operation requires the creation of additional special devices and specially equipped workplaces; Absorbents - activated carbons and ion exchange resins used for the purification of water and aqueous solutions were ineffective in the purification of organic solvents, activated carbon does not remove residues of rosin fluxes from the solvent, and the resins are not resistant to solvents.

The purpose of the proposed method is to improve the quality of cleaning the working solution containing organic solvent-xylene or a mixture of organic solvents for washing printed circuit boards, printed wiring units, other electronic products after soldering from the active rosin flux residues contaminating the working solution during the washing process. , saving the working solution and improving the environment, simplifying the method.

This goal is achieved by the fact that in a known method of cleaning a working solution by adsorbing contaminants, cleaning is carried out with the introduction of the adsorbent into the working solution during its operation and using silica gel as the adsorbent.

The cleaning of the working solution occurs due to the constant diffusion of the dissolved residues of rosin fluxes to the surface of the particles of the granular absorber and the adsorption of these contaminants by the surface of the adsorbent. This solution eliminates the filtration of the working solution through the absorber and makes both the filtering device and the filtering operation itself unnecessary.

The proposed method makes it possible to carry out cleaning practically on any radioelectronic product washing bath existing in the production, for which purpose it is necessary to place an absorber in the mesh in the non-working areas of the washing bath

containers (metal, fabric, etc.). The method greatly simplifies instrumentation and the process itself of cleaning the working solution. Allows

It is also very simple to solve the instrumentation of cleaning the working solution using highly flammable liquids due to the absence of a filtering operation, the ease of sealing the working solution in the rinsing bath volume, the possibility of eliminating sparking and removing static electricity, etc.

The proposed method of cleaning the working solution makes it generally accessible for each enterprise to purify organic solvents used for washing electronic products after soldering, which makes it possible not only noticeably

0 to reduce the overall consumption of solvents and improve the quality of manufactured electronic products, but also inevitably improve the environment. The main most acceptable working solution at

5 washing the radioelectronic products from the active rosin flux residues is xylene, due to the highest dissolution rate of rosin flux residues, chemical inertness with respect to various structural materials, both metallic and organic, and also due to high flash point and some other characteristics.

5 Silica gel quantitatively extracts rosin and other flux components from contaminated xylene, due to which fine cleaning of the working solution is carried out, its full regeneration in the process

0 operation of the bath. The activated carbons, widely known as sorbents, proved to be ineffective and do not absorb the remains of rosin fluxes from xylene media. The total consumption of solvents used for washing printed circuit boards, printed wiring units and other electronic products after soldering can be reduced several times, the main losses of the working solution are due to

0 by the natural entrainment of the solution with washed products.

Example 1. Cleaning the working solution is carried out by washing the printed wiring units after soldering with the use of FKET flux based on purified OK-5 rosin in an ortho-xylene bath. The temperature of the working solution is 18 ° C, the duration of washing with a single loading of blocks into the working solution is 1-2 minutes. An adsorbent — granular silica gel — is introduced into a bath in a mesh container. In parallel, under the same conditions, a control bath without an absorber is operated. After 15 days of work, 2.1% rosin was detected in the control bath, and no rosin was present in the bath with the absorber. The electrical conductivity of xylene in the control bath without an absorber is C / m, in a bath with an absorber 1, C / m, i.e. corresponds to pure xylene (when measured by an alcohol-xylene mixture).

Example 2. The working solution is cleaned by washing the electronic products after soldering using activated LTI-120 activated rosin flux in a xylene bath. An adsorbent, granulated silica gel, is introduced into a bath in a tissue package. In parallel, under the same conditions, a control bath without an absorber is operated. After three days of operation, 0.4% of rosin is detected in the control bath and the sharp electrical conductivity of xylene rises to 200 S / m, there is no rosin in the bath with absorber, and the specific electrical conductivity of xylene is 1.8 / C, m. e. does not exceed the level of pure xylene (when measured by an alcohol-xylene mixture).

EXAMPLE 3 The working solution was cleaned by washing the printed circuit boards after the tin-lead coating had been melted using an activated rosin flux PCT sequentially in three xylene baths. In the baths in the tissue packaging, the adsorbent is introduced — granulated silica gel. In parallel, under the same conditions, control three baths without an absorber are used. After three days of work, 0.1% rosin is detected in the control third (finishing) bath, and no rosin is present in the baths with the absorber.

Experimental data on the absorption of rosin by granular silica gel from various solvents and their mixtures most widely used in the radioelectronic industry and instrument-making industry are given in the table.

For comparison, data on the absorption of rosin from the same solvents by carbon spherical adsorbents are given. The research is subjected to working solutions (solvents and their mixtures), both specially prepared and taken out of production after washing the printed wiring units with different rosin contents. Cleaning of the working solutions is carried out under stationary conditions. In determining the degree of extraction of rosin from the working solutions, the residence time of the absorber in them was not limited

(according to the working conditions of the washing baths, the absorber may be constantly in the working solution).

It has been established that silica gel does not completely remove rosin from ethyl

alcohol, acetone, ethyl acetate, alcohol-gasoline mixture in a 1: 1 ratio, freon 113, alcohol-freon mixture in a 1:19 ratio, alcohol-xylene mixture in a 1: 1 ratio. In these solvents (blends)

the rosin is partially extracted (at most about 1/2 of the amount present in the working solution), after which a dynamic balance of the process is established.

Rosin is absorbed from xylene by silica gel completely, which is apparently due to the chemical nature of xylene and rosin. The completeness of the extraction of rosin from xylene was confirmed by microanalytical methods with a detection depth of 0.001 mg, as well as measurement data of electrical conductivity and pH of aqueous extracts of working solutions. The values of both parameters after cleaning workers

The solutions of silica gel corresponded to their values for pure xylene;

In addition to xylene, silica gel completely extracts rosin from trichlorethylene, but

this solvent refers to environmentally harmful chlorinated organic solvents. The amount of silica gel to ensure complete cleaning of the working solution from rosin fluxes during

operation of the washing bath for a month is 50 g per liter of solution (xylene).

Using the proposed method of cleaning the working solution, including from rosin flux residues, improves the quality of cleaning the working solution in the product washing process, significantly improves the quality of washing and, thus, the reliability and durability of the CEA due to the constant implementation of the cleaning process. Permanent cleaning of the working solution directly in the product washing bath drastically reduces the total solvent consumption required for high-quality washing of printed wiring units and other products from residues of rosin fluxes. Repeated use of the same portion of the working solution reduces many times

non-recyclable waste of solvents that pollute the environment in one way or another gives a positive ecological effect. Permanent cleaning of the working solution without its filtration greatly simplifies the instrumentation of the proposed method, does not require special pumps, columns with absorbers, pipelines, etc., makes this method accessible to any industrial enterprise.

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Claims (1)

Claims The method of purification of organic solvents from pollutants, including treatment with an adsorbent, characterized in that, in order to simplify the process and increase the degree of purification of the working solution containing xylene and used for washing printed circuit boards and electronic products from rosin fluxes, as an adsorbent use silica gel.