Example of VOCs waste gas treatment in a pharmaceutical enterprise

This paper introduces the volatile organic waste gas pollution characteristics and the treatment status of chemical pharmaceuticals companies. According to the characteristics of volatile organic waste gas of a pharmaceutical enterprise, after comparing various treatment processes of volatile organic waste gas, the treatment process of alkali washing spray + high efficiency mist eliminator + activated carbon adsorption + nitrogen desorption + condensation was finally adopted. Waste gas treatment scale of 60000m3/h, after stable operation of the equipment. Each emission index reaches the air pollution emission limit stipulated in the “Emission standard of air pollutant for pharmaceutical industry” (GB37823-2019).


1.1.Classification and pollution of pharmaceutical industry
The pharmaceutical industry is mainly divided into six categories: fermentation pharmaceutical industry, chemical synthesis pharmaceutical industry, traditional Chinese medicine pharmaceutical industry, extraction pharmaceutical industry, biological engineering pharmaceutical industry and mixed packing pharmaceutical industry.Among them, fermentation and chemical synthesis pharmaceutical industry is a major VOCs emissions.China is a big producer of chemical bulk drug, especially the production capacity of fermented pharmaceutical products ranks first in the world.Bulk drug as the upstream products of the whole pharmaceutical industry chain, VOCs pollution is particularly serious [1].
The source of VOCs in the pharmaceutical industry is mainly in the production process, the organic solvent in the raw materials with the production process volatilization and lead to VOCs pollution. For example, in the process of chemical synthesis industrial pharmaceutical production, raw material separation and filtration, fermentation extraction, distillation recovery, purification and drying will emit a large number of solvent evaporative VOCs, and soon spread to the surrounding environment causing harm. At present, the pharmaceutical industry VOCs management level is not high [2].

2.The selection of VOCs waste gas treatment technology for a bulk drug enterprise
This Enterprise is a large-scale chemical bulk drug enterprise in the domestic pharmaceutical industry, with advanced equipment and many varieties. This enterprise produces a large number of VOCs containing waste gas in the process of the production of bulk drug, the components are complex, the types are various, the main waste gas production process equipment is reaction Kettle, vacuum pump, waste liquid pool, etc. . If not treated, it will cause serious environmental pollution [3].In response to the National Environmental Protection Policy and to reduce the impact on the surrounding environment, the Enterprise has made great efforts to request the professional and technical team to analyze the characteristics of the exhaust gas at each production site and select the best treatment process, in order to improve the environmental air quality around the plant, reduce the emission of air pollutants.

2.1.The pollution of VOCs in this enterprise
The enterprise production exhaust gas emission is normal temperature and pressure (pressure ≤200Pa, temperature ≤40℃), the concentration of VOCs in the production workshop exhaust gas is about 80mg/m3 for a long time, the concentration peak when feeding and unloading, up to 1500mg/m3, the average concentration is 250mg/m 3 .The main components of waste gas are: pyridine, dichloromethane, methanol, hydrogen chloride, ethyl acetate, tetrahydrofuran, n-propanol, N-methylpiperazine, ethanol, n-heptane, acetic acid, isopropyl alcohol, diisopropyl ethylamine, sulfoxide chloride, methyl tert-butyl ether.

2.2.Exhaust gas parameters
Samples were taken and tested at the exhaust gas outlet, and the detection data of VOCs concentration in the exhaust gas were shown in Figure 1.  Figure 1, the concentration of exhaust gas produced by this enterprise fluctuates greatly in a day. Every morning from 9:00 to 9:40 and in the afternoon from 16:00 to 16:30 for discharging, the concentration of VOCs in the waste gas will appear peak, with the peak concentration of 1500mg/m 3 .Usually the concentration is low, the average concentration is about 250mg/m 3 .
The concentration detection values of the main components in the exhaust gas produced by this enterprise are shown in Table 1. In summary, the characteristics of exhaust gas from the bulk drug production line of this enterprise are as follows: exhaust gas composition is complex, emission concentration fluctuates greatly, and contains more chlorinated hydrocarbon substances and acidic substances.

A description of the VOCs waste gas treatment process of this enterprise
According to the characteristics of the waste gas of the enterprise, the treatment of organic waste gas needs a variety of technology combinations, so as to achieve the effect of both improving the purification rate and economic and practical. This project combines the adsorption method and the condensation method, adopts the multi-tank circulation condensation and reverse purge adsorption to achieve the standard emission of waste gas treatment [4] [5].
The whole waste gas treatment process is divided into three steps：

2.3.3.The cooling process：
The exhaust gas at each discharge point of the workshop, under the suction action of the blower, the exhaust gas first enters the alkali washing tower for washing treatment, and the acid gas and watersoluble substances in the exhaust gas are removed. After further defogging, the exhaust gas enters the adsorption bed, and the porous structure of activated carbon is used to adsorb VOCs compounds. After saturated, the activated carbon was regenerated with hot nitrogen. The high concentration organic gas after desorption entered the condenser to get condensation, and the condensate was recovered by stratification. After desorption and regeneration, the adsorption bed was cooled and waited for the next adsorption process. Nitrogen is used as the desorption gas to regenerate the activated carbon in the adsorption device, which improves the desorption efficiency and the safety of the desorption system, and less waste water is produced by desorption and condensation with steam.The interlocking automation of desorption process is realized by setting multiple temperature sensors, pressure sensors, oxygen content sensors and other high-precision monitoring instruments to ensure the desorption and condensation effect.
(c) Automatic control systems Model No. : Non-standard; Explosion-proof requirements: placed in a non-explosion-proof area; Automatic control requirements: Siemens PLC+10 inch touch screen; Electrical components: Schneider; Box material: SUS304; Unit: 1 set.

Economic and technical index
The total investment of the project is 5 million yuan, and the operating cost is 1 million yuan/year.After the treatment, each emission index have reached the limits of air pollution emission stipulated in the "standards for air pollutants emission in pharmaceutical industry" (GB37823-2019) .