RU2084404C1 - Method for treating waste water - Google Patents

Abstract

FIELD: waste water purification. SUBSTANCE: invention relates to removing formaldehyde and methanol from waste water, in particular, to treating waste water originated from urea-formaldehyde resin production including preliminary removal of formaldehyde on acidic granulated clayey adsorbent and ammonium carbonate followed by two-step column distillation of methanol and formaldehyde to produce still residue containing residual amounts of the two pollutants. Distillation is conducted at pH 9.0-10.0 with first-step still temperature up to 80 C and first-step temperature in upper sections of column 64 C and in lower section 75 C, and in the second step, respectively, 120-125, 98, and 105 C. EFFECT: enhanced efficiency of process. 4 tbl

Description

 The invention of the industry as environmental measures aimed at the treatment of wastewater from formaldehyde and methanol.

A method for purification from methanol and formaldehyde described in [1] is described, which consists in the distillation of methanol from purified tar resins formed in the process of producing urea-formaldehyde resins without preliminary purification from formaldehyde. The scheme includes the accumulation of water, distillation in two steps. In the first stage, the methanol fraction with a methanol content of over 90% is distilled off. In the second stage, a condonate containing formaldehyde 5 of 10% methanol is distilled off to 5%
The distillation cube contains up to 100 mg / l of methanol, up to 50 mg / l of formaldehyde. The cube is purified from formaldehyde in a complex chemical way. There is also a method of wastewater treatment with obtaining a methanol fraction when the formaldehyde content is significantly higher than the MPC [2]
The disadvantages of these methods include:
the impossibility of obtaining a methanol fraction from suprasmal waters with a formaldehyde content below the MPC;
the condensate of the second distillation stage contains a significant amount of methanol and formaldehyde, which narrows the scope of this fraction;
distillation cubes contain a significant amount of methanol up to 100 mg / l and formaldehyde up to 50 mg / l, which requires additional purification. Moreover, the cleaning method proposed in [1] is rather complicated.

The prototype of the claimed method, the selected method according to the source of information [1]
Both the known and the claimed method involves the treatment of wastewater from methanol and formaldehyde due to column distillation.

 The main task posed and resolved in this invention is to develop a method for wastewater treatment from methanol and formaldehyde to obtain each of them as an individual substance. The technical result of the invention is to increase the yield of methanol and formaldehyde and reduce the concentration of the components of the cube to the MPC level.

 To solve this problem, wastewater containing formaldehyde resins is sedimented until they are separated into tar and tar resin, followed by the introduction of acid granular adsorbent and ammonium carbonate into tar water. The formaldehyde content in wastewater without preliminary treatment can be in the concentration range from 1000 to 30000 mg / l, and methanol from 3000 to 60,000 mg / l.

The distillation in the first stage takes place at a pH of 9.0 to 10.0 and the column is heated with a cubic temperature of up to 80 ^o C and a heating temperature in the column sections from 64 ^o C in the upper section to 75 ^o C in the lower, in the second stage, distillation is carried out at the temperature in the cube is 120 125 ^o C and the temperature in the sections of the column from 98 ^o C in the upper section to 105 ^o C in the lower.

 The method is as follows.

Wastewater is sedimented for two hours, the resin portion is removed, and 40 kg of acidic granular clay sorbent is introduced into 1 m ^{3 of} tar resin, the mixture is kept for 20 minutes, then 16 kg of crystalline ammonium carbonate is added to 1 m ^{3 of} treated wastewater and reused incubated for 5 minutes, the liquid fraction is separated and distillation is carried out. For this, a two-stage scheme is used, consisting of two distillation column caps (in the first stage) and slot type (in the second stage). Distillation of purified suprasmol water is carried out at a pH of 9 - 10, which ensures the stability of urotropine under distillation conditions. The columns operate in the following temperature conditions:
1. The first stage uses a column with three-section heating. The temperature in the cube is maintained up to 80 ^o C and the heating temperature of the sections of the column in the range from 64 ^o C in the upper section to 75 ^o C in the lower section.

2. In the second stage, the column has a three-section heating column. In this case, the temperature in the cube is maintained within 120 125 ^o C, and the temperature in the sections of the column from 98 ^o C in the upper section to 105 ^o in the lower.

This allows you to use all fractions of the distillation of the treated tar water and implement a scheme with a closed cycle of used water, excluding their discharge. From the upper part of the first purification step, a methanol fraction with a methanol concentration higher than 95% and formaldehyde no more than MPC (0.5 mg / l) is isolated. This fraction can be used in the synthesis of urea-formaldehyde resins, as well as in the form of raw materials for the production of pure methanol. Water condensate is released from the upper part of the second stage, which is then sent for additional purification from urotropin and used in the synthesis of urea-formaldehyde resins. The condensate is characterized by a pH of 9 10, a content of urotropine not exceeding 80 mg / l, methanol 20 mg / l, formaldehyde 0.5 mg / l, which is significantly lower than the figures given in [1]
A cube of the second stage of purification containing ammonium sulfate with a concentration of 40% can be used as raw material for the production of commercial ammonium sulfate.

 The proposed scheme makes it possible to obtain fractions with a lower concentration of toxic substances, to use the formed products more fully, and to exclude additional chemical treatment of distilled suprasmol waters. This scheme provides an opportunity to implement a technological cycle without water discharge. It is more perfect in the totality of the listed parameters from the point of view of ecology.

Example 1
The effect of pH on the stability of urotropine is shown in table. one.

 Optimal from the point of view of stability of urotropin for the operation of the technological scheme is a pH in the range of 9.0 to 10.0.

Example 2
The temperature of the cube of the first stage of distillation (the possibility of sublimation of urotropine) is given in table. 2.

The optimum temperature for a cube of 80 ^o C. At 70 ^o C there is a poor completeness of distillation, because there is methanol in the cube. At 85 ^° C. traces were found at the top of the column.

Example 3
The temperature of the cube of the second stage is given in table. 3.

The optimum temperature of the cube of the second stage is 120 125 ^o C. A temperature above 125 ^o C leads to additional energy costs.

Example 4
The formation of crystals of ammonium sulfate in the resulting solution (see table. 4).

 The concentration of 40% is optimal. At a concentration of 35%, we have a smaller amount of the returned production cycle. At 45%, crystals of ammonium sulfate precipitate, causing clogging of the equipment.

Thus, for the treatment of wastewater containing urea-formaldehyde resins from methanol, a two-stage scheme is used, consisting of distillation columns with cap and slotted modifications. As a result of the distillation of suprasmal water, fractions are formed that can be used as individual substances. Moreover, the methanol fraction contains at least 95% methanol. The aqueous condensate contains three components, where urotropine 80 mg / l, methanol 20 mg / l, formaldehyde 0.5 mg / l. The cube of the second stage contains the fourth individual component of ammonium sulfate in an amount of up to 40%
Literature
1. Anokhin A.E. Collection and disposal of formaldehyde-containing liquid effluents: Obzn. inform. issue 6, M. VNIPIEIlesprom, 1992, p.12.13.

 2. Artsukevich I.M. Oparin D.A. Gulyai I.E. Stepuro I.I. Pikul L.Ya. Wastewater treatment containing formaldehyde and methanol. Abstracts of the XVth Mendeleev Congress on General and Applied Chemistry, 1993, p. 18.

Claims (1)

A method of treating wastewater generated in the production of urea-formaldehyde resins, including a two-stage column distillation of methanol and formaldehyde with the formation of a cube containing residual amounts of methanol and formaldehyde, characterized in that the wastewater is purified from formaldehyde with an acid granular clay adsorbent and ammonium carbonate, then distilling at pH 9.0 10.0, wherein the first stage is maintained cube temperature to 80 ^o C and the column sections 64 ^o C in the upper sections to 75 ^o C at the bottom, and in the second stage the temperature is maintained cube 120 125 ^o C and the column sections 98 ^o C in the upper section to 105 ^o C at the bottom.

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