Trichloromethane Waste Gas Treatment and Recovery Technology

Trichloromethane is a colorless, transparent, heavier than water, and volatile liquid at room temperature. It is slightly soluble in water and miscible with most commonly used organic solvents. It has a pungent odor similar to ether. Due to its strong solubility, low boiling point, relatively low toxicity, and reaction inertness, it has long been a solvent for various applications.

Trichloromethane has a low boiling point and is prone to volatilization during industrial production and application, causing environmental pollution. The commonly used processes for treating trichloromethane waste gas include low-temperature condensation, solvent absorption, and activated carbon adsorption.

Low temperature condensation method is a process that utilizes the relationship between the decrease in saturated vapor pressure of trichloromethane with decreasing temperature, lowering the temperature below the boiling point of trichloromethane, and transforming it from a gaseous state to a liquid state. This process has a good recovery effect on high concentration trichloromethane waste gas, but incomplete condensation will still result in high concentration waste gas being discharged.

The solvent absorption method is a process that utilizes the high solubility of trichloromethane, selects other high boiling organic solvents to absorb trichloromethane waste gas, and then distills and recovers trichloromethane. The processing efficiency of this process is low, the solvent absorption is insufficient, and the absorbent itself will also evaporate, resulting in secondary pollution.

Activated carbon adsorption method is a process that utilizes the adsorption properties of activated carbon to adsorb trichloromethane in exhaust gas, and then recovers trichloromethane through steam blowing. The adsorption effect of activated carbon in this process is greatly affected by moisture, and the adsorption performance decreases significantly after multiple blow off regenerations; And trichloromethane is easily catalyzed and decomposed by impurities in activated carbon, producing hydrogen chloride gas. When it comes into contact with water, it turns into hydrochloric acid and corrodes equipment severely, shortening the service life of pipeline equipment.

In response to the current problems in the treatment of trichloromethane waste gas, Jiangsu Haipu Functional Materials Co., Ltd. has developed HDV type polymer nanoadsorbent, which can adsorb and remove trichloromethane from waste gas. After adsorption saturation, the nano adsorbent is desorbed and regenerated using steam, and trichloromethane vapor can be condensed and recovered. The specific process is as follows:

The specific process is as follows: the trichloromethane waste gas in the workshop is first extracted by a vacuum pump and then subjected to secondary condensation. The temperature of the primary condensation is around 10 ℃, and the temperature of the secondary condensation is around -10 ℃. The condensed and liquefied trichloromethane is received in a storage tank, and the uncondensed trichloromethane waste gas is connected to an adsorption tower containing nano adsorbents for adsorption enrichment (adsorption temperature at room temperature, adsorption pressure at~6kpa). After adsorption, the waste gas can be discharged in compliance with standards. After the adsorbent is saturated, low-pressure steam is introduced into the adsorption tower for stripping (at a temperature of around 80 ℃). The mixture of trichloromethane and water vapor blown out can be separated and recovered by condensation liquefaction, settling and layering. The temperature of the nano adsorbent after steam desorption is relatively high. After cooling to room temperature with clean air, it can be reused for adsorption. The adsorption tower is usually equipped with two units, one for adsorption and one for desorption as a backup. For high concentration exhaust gases, two or more units can also be configured.

This process can achieve a removal rate of over 99% for trichloromethane in exhaust gas and has been validated on multiple project sites.

Advantages of HDV type nano adsorbent:

(1) Controllable pore structure and high pore volume;

(2) Has good physical and chemical stability, is resistant to acid, alkali, and organic solvents, has high thermal stability and mechanical strength, and is wear-resistant;

(3) The surface exhibits high hydrophobicity, and humidity has no effect on adsorption performance;

(4) Easy to regenerate and stable adsorption performance;

(5) No hazardous waste is generated without the need for replacement.