Vapors Generation of Volatile Organic Compounds (VOCs) From Pure Liquids

Production of fixed concentration of vapors from pure liquid has many applications in laboratory and field studies of occupational health and toxicological research and also in calibration of air pollutant measurement devices of the workplaces. In this study, the advantages and disadvantages of different concentration generation methods were discussed. In addition two methods were compared and the factors that influence the concentration were identified. In order to make certain concentrations of styrene, evaporation and injection methods were used. In evaporation system air was blown in the 250 (ml) midget impinger in two modes (close to the liquid surface and the inside liquid). In injection system a syringe pump (3100 Graseby, Smiths Co) was used. Affecting factors on concentration stability like temperature, flow rate, position of nozzles have been investigated. To produce 300(ppm) of styrene vapor concentrations in RH=19%, coefficient of variation (C.V) of the concentrations generated in bubbler and syringe pump system were 2.86 and 2.01 percent respectively. Syringe pump system reach to equilibrium approximately in 60 (min), while it takes 105 (min) for the evaporative concentration system. When the nozzle of bubbler is placed close to the liquid surface, and when the nozzle is placed inside the liquid, coefficient of variation were 1.97% and 2.52% respectively. Controlling the influencing factors like temperature and flow rate are most important points for generation of constant concentration. The low coefficient of variation in the syringe pump system proved better capability and functionality of this system compared to bubbler system. One advantage of the syringe pump system is that it is not dependent on liquid level of the container.