Separation of Hydrogen Sulfide from Wastewater by Emulsion Liquid Membranes

Abstract

Hydrogen sulfide was separated from highly saline wastewater by emulsion liquid membranes (ELMs). Such membranes consist of polyalkenyl succinimide as emulsifying agent, diethanolamine as carrier, kerosene as membrane, and sodium hydroxide as stripping solution. The effect of four surfactants on the stability of ELMs was investigated and every operational parameter was tested. The highest achievable separation efficiency was 99.73 % for a 100 mg L -1 solution. Obviously, the salinity of the external phase has a negligible effect on the separation of H 2 S using ELMs. IntroductionHydrogen sulfide (H 2 S) is a detrimental material in some industry processes. Because of its volatility, it harms the operator's health when inhaled and also causes environmental pollution even at very low concentrations [1,2]. It can be deadly depending on concentration and duration of exposure. Eye irritation starts to occur at 10-20 ppm, and a concentration over 1000 ppm might lead to death [3]. The corrosion of H 2 S in wastewater also causes serious failures of casting tubes and other metal equipment. Therefore, the control of H 2 S became a major concern in industrial wastewaters [4]. Several methods have been used to treat H 2 S, such as biofilters and biotrickling filters [5,6], adsorbents [7,8], and catalytic oxidations [9,10]. These methods all provide satisfactory removal efficiency, however, the process flows are complicated and the treatment cost is higher. For wastewaters with high salinity in the oil field, the above-mentioned methods have some shortcomings.The emulsion liquid membrane (ELM) technique was invented first by Li in 1968 [11, 12]. Typically, a stable emulsion with two immiscible phases is formed which subsequently is dispersed into wastewater as the external phase [13]. Normally, the internal phase is a stripped agent aqueous solution, the external phase contains the target substance, and the membrane phase is the oil phase containing a surfactant to remove the external and internal phases. The internal and external phases are usually miscible. The target substance is removed from the feed phase through the membrane phase and recovered from the internal aqueous phase by finally breaking the emulsion.The ELM technique has four advantages: (i) large mass transfer area, (ii) high diffusion rate, (iii) separation and stripping in one system, and (iv) wide adaptability and high separation efficiency [14][15][16]. Therefore, ELM processes have been frequently used in purification or separations, such as for hydrocarbons [17], organic acids and amines [18,19], wastewater treatment [20,21], metal ions [22][23][24][25], and so on. The experimental results demonstrated that the ELM was a successful technique and the extraction efficiency was above 90 %. However, there was no available information in the literature on the separation of H 2 S in wastewater using ELMs. Therefore, a new attempt was carried out.Here, separation of H 2 S from wastewater with high salinity using the ELM technique was performed. The wastewater...