RU2355465C2 - Method of waste gases purification of methyl chloride - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention refers to the process chemistry of organic synthesis. The methyl chloride absorption from the waste gases is performed by the contraflow of reacting phases at temperature range -20 °C to -25 °C with using of kerosene with boiling points range 180-300 °C as absorbent. The methyl chloride desorption is carried out by absorbent heating at atmospheric pressure to temperature 20-30 °C. Heated and methyl chloride free absorbent is cooled and returned to absorption stage, the concentrated vapours of methyl chloride separated from the saturated absorbent are directed for condensation.

EFFECT: method allows to extract the methyl chloride from waste gases with its low content (10-17 mole %) with the yield 89% and substantially decrease the process cost.

4 cl, 1 tbl, 2 ex

Description

The invention relates to chemical technology for organic synthesis, in particular to methods for purification of exhaust gases containing methyl chloride.

In the production of methyl chloride from methanol and hydrogen chloride with exhaust gases, a significant amount of methyl chloride is lost, in addition, its emissions together with hydrogen chloride significantly pollute the environment.

A known method of utilization of methyl chloride from gas mixtures by condensation, freezing and fractionation at temperatures of 4-66 ° C and a pressure of 690-1380 kPa [US 3988383, 10.26.1976; US 4039597, 08/02/1977]. For cooling, liquid nitrogen is used.

The disadvantages of this method are the technological complexity and economic costs, its use is advisable in the utilization of methyl chloride from small volumes of highly concentrated process gases circulating in a closed loop "technological equipment - capacitor".

There is also known a method for the recovery of methyl chloride and methylene chloride by adsorption on a solid sorbent - activated carbon, silica gel, alumina, zeolites, etc. [US 4020117, 04/26/1977]. Adsorption is carried out at temperatures minus 50-20 ° C, desorption of chloromethanes at 100-400 ° C.

The disadvantage of this method is the low degree of capture of halogenated hydrocarbons, in addition, the use of a solid sorbent requires high desorption temperatures, which leads to wear and loss of both the sorbent and halogenated hydrocarbon. A disadvantage of coal sorbents is also their increased fire hazard due to the inevitability of the use of a large one-time loading of activated carbon.

Methyl chloride is effectively extracted from gas mixtures that also contain water and hydrogen chloride by absorption by a liquid aromatic halocarbon [US 3148041, 09/08/1964]. To capture hydrogen chloride, the gas mixture is preliminarily passed through an alkaline solution. Mono-, di- and trihalobenzenes, naphthalenes and biphenyls are available as absorbents. The absorption process is carried out in packed countercurrent columns at a temperature of 25 ° C. Desorption is carried out by distillation at 34-122 ° C.

The disadvantage of this method is the use of highly toxic aromatic hydrocarbons, in addition, desorption at high temperatures and reduced pressure leads to loss of methyl chloride and absorbent.

The known method [US 4193944, 03/18/1980] purification of gas emissions of methane chlorination by absorption of mono-and polychlorination products with chloroform, carbon tetrachloride or a mixture thereof. The disadvantage of this method is that the losses of volatile absorbent due to entrainment are large, in addition, in this case, the regeneration of methyl chloride and other products is not provided.

Closest to the proposed invention is a method for the disposal of methyl chloride [US 5954861, 09.21.1999] (prototype), in which liquid hydrocarbons having a molecular weight of 142 to 422, for example, partially branched hydrogenated 1-decene dimer (a mixture of various amounts of unbranched and branched isomers with a density of 0.798 at 16 ° C and a boiling point of 329 ° C), it absorbs 80.6-99.9% of methyl chloride from the gas mixture. For contact of the gas mixture with the absorbent, countercurrent columns with a filler are used, the absorption temperature is minus 30-10 ° C, the pressure is 138-345 kPa. The mass ratio of liquid / gas (L / G) varies from 10/1 to 30/1. So, at (L / G) = 30, 35 mol.% From a gas mixture with a high methyl chloride content, at a pressure of 207 kPa, 99.9% is removed. Of the saturated absorbent, methyl chloride is desorbed in a dish column at a temperature of 90-115 ° C and a pressure of 241-310 kPa (2.4-3 atm).

The disadvantage of this method is the low sorption ability of the hydrocarbon used and, as a consequence, the possibility of using an absorbent only for highly concentrated gas mixtures of methyl chloride. High pressure and elevated desorption temperatures contribute to increased energy consumption, as well as losses of both methyl chloride and absorbent.

The objective of the invention is the development of a simple and economical method of purification of gas emissions with a low content of methyl chloride, allowing for a further reduction in the content of methyl chloride in gases to established sanitary standards (not more than 3 g / s) and at the same time to obtain trapped methyl chloride, using an accessible and effective absorbent .

Known methods for purification of exhaust gas from the production of vinyl chloride from organochlorine compounds (mainly from dichloroethane) by absorption followed by desorption. As absorbents, kerosene is used, containing over 90% of aromatic compounds C ₁₀ -C ₁₁ and boiling in the range 185-215 ° C [Industrial organochlorine products / Handbook / Under. ed. L.A. Oshina. - M .: Chemistry, 1978. P.65-68], a vacuum distillate obtained in the process of oil distillation and having a boiling range of 350-420 ° C [RU 2129906 C1, 05/10/1999] and aircraft fuel grade TS-1 ( GOST 10227) [RU 2187358, 08/20/2002], the process is conducted at 14-20 ° C. Desorption is carried out by vacuum distillation [Industrial organochlorine products / Reference / Under. ed. L.A. Oshina. - M .: Chemistry, 1978, S.65-68] and azeotropic steam distillation [RU 2129906 C1, 05/10/1999].

In a real technological process for the production of methyl chloride (OJSC "Caustic", Volgograd), the volume of gases emitted into the atmosphere is 200 m ³ / h on average, of the following content (vol.%): Methyl chloride 10-15; hydrogen chloride 0.4-3.5; nitrogen 13.8-23.3; oxygen 1.7; hydrogen 49.5-68.5; carbon dioxide 0.3. Thus, the concentration of methyl chloride is 10-17 mol.% At a flow rate of 15-18 g / s.

We propose to use kerosene as an adsorbent of methyl chloride, used for washing cracked gas in the production of ethylene and acetylene (OJSC "Caustic", Volgograd).

The essence of the invention is a fairly high efficiency of absorption and desorption of methyl chloride using an available absorbent - kerosene, boiling off at a temperature of 180-300 ° C.

The technical result is achieved by the fact that in the method of purifying gas emissions from methyl chloride, including the absorption of methyl chloride from the exhaust gas stream in the process of its contact with the absorbent and the separation of methyl chloride from the saturated absorbent, the absorption is carried out under a countercurrent of contacting phases and contact conditions that ensure the complete removal of methyl chloride from exhaust gases, while at the same time full saturation of the absorbent removed for regeneration, kerosene is used as the absorbent (fraction with boiling point 180-300 ° С ), the selection of methyl chloride is carried out by heating the absorbent at atmospheric pressure, while the methyl chloride is isolated in the form of concentrated vapors followed by their condensation, and the absorbent freed from methyl chloride is cooled and returned to the absorption.

The absorption is carried out at a temperature of from -25 to -20 ° C, desorption is carried out at temperatures of 20-30 ° C.

It was also found that the fraction with so Kip. 180-300 ° C can be separated from spent kerosene from waste intended for burning as fuel. An experiment (Example 2) showed that the use of an absorbent isolated from spent kerosene is also effective.

Example 1

Sorption - desorption of methyl chloride in the laboratory

In laboratory conditions, we obtained methyl chloride according to the procedure of [RU 2152920 C2, 07.20.2000] by treating methanol with hydrogen chloride in the liquid phase at elevated temperature. This method allows to reduce the content of dimethyl ether in the target product by treating the resulting methyl chloride with hydrochloric acid with a concentration of 35-40 wt.% At a temperature of from -10 to -15 ° C. The resulting methyl chloride was condensed into a trap at a temperature of from -40 to -50 ° C. Then, methyl chloride (2.5 g) evaporated at a temperature of -18 ° С was passed (sparging) through kerosene (fraction with boiling point 180-300 ° С, melting point - 30 ° С, d ₄ ²⁰ 0.84) in an amount 12.67 g, cooled to a temperature of -20 ° C. After 45 minutes, 14.69 g of a 13.75% methyl chloride solution were obtained.

Methyl chloride was desorbed at a temperature increase of up to 50 ° С and holding at 50 ° С for 60 min. Chromatographic analysis showed methyl chloride in the absorbent after desorption 0.2%.

Example 2

Pilot tests of the efficiency of the absorption of methyl chloride from exhaust gases produced by JSC "Caustic" (Volgograd)

The flue gases from the production workshop with a methyl chloride concentration of 263.3-286.4 g / m ^{3 were} passed at a rate of 0.1 l / min through an installation consisting of two Drexel bottles connected in series, cooled to -20 ° C ÷ -25 ° C. The flasks were filled with a nozzle - miniature Rashig rings and absorbent (fraction with boiling point 180-300 ° C, extracted from spent kerosene) in the amount of 45 and 40 ml. Samples for determining the content of methyl chloride were taken before and after installation at regular intervals. The results of the experiment are shown in table 1.

Table 1 The results of pilot tests for the purification of gas emissions from methyl chloride No. p / p Unit operation time, min The concentration of methyl chloride in the exhaust gas before purification The concentration of methyl chloride in the exhaust gas after purification The amount of captured methyl chloride in volume% in g / m ³ in volume% in g / m ³ mg % one fifteen 11,4 263.34 0.36 · 10 ^-4 8.32 · 10 ^-4 395.01 99,99 2 fifty 12,4 286.44 0.6 13.86 1362.9 95.16 3 60 11.7 270.27 1.4 32.34 1427.4 88.03 four 60 11,4 263.34 3,1 71.61 1150.38 72.81 Total 185 11.7 (average) 270.27 1.27 29.45 4335.69 88,99

After heating the saturated absorbent for 0.5 h at a temperature of 20 ° С-30 ° С, effective desorption occurs to a methyl chloride content of 0.46%.

Thus, with a mass ratio of liquid / gas (L / G) = 14.3, extraction of about 89% of methyl chloride from exhaust gases is achieved, the concentration of methyl chloride in the saturated absorbent is 0.06 kg / kg, and with an exhaust gas flow rate of 200 m ³ / h, the emissions of methyl chloride into the atmosphere after cleaning will be about 2 g / s.

Implementation of the developed sorption method will solve the environmental problems of utilization of both methyl chloride and spent kerosene, as well as additionally receive about 48 kg / h of methyl chloride, which is currently released into the environment. In this case, the absorbent repeatedly returns to the cycle with the exception of the use of vacuum and high desorption temperatures, which significantly reduces economic costs.

Claims (4)

1. A method of purifying gas emissions from methyl chloride, including the absorption of methyl chloride from the exhaust gas stream in the process of its contact with the absorbent and the separation of methyl chloride from the saturated absorbent, the absorption being carried out under a countercurrent of contacting phases and contact conditions that ensure extremely complete removal of methyl chloride from the exhaust gases under at the same time complete saturation of the absorbent removed for regeneration, characterized in that the exhaust gases contain 10-17 mol. % methyl chloride, kerosene is used as an absorbent (fraction with boiling point 180-300 ° С), methyl chloride is extracted by heating the absorbent at atmospheric pressure, while methyl chloride is isolated in the form of concentrated vapors followed by their condensation, and freed from the methyl chloride absorbent is cooled and returned to absorption. 2. The method according to claim 1, characterized in that the used kerosene from waste (fraction with boiling point 180-300 ° C) is used as absorbent. 3. The method according to claim 1 or 2, characterized in that the absorption is carried out at a temperature of from -20 to -25 ° C. 4. The method according to any one of claims 1 to 3, characterized in that the desorption is carried out at a temperature of 20-30 ° C.