The Treatment Of Wastewater With High Concentration Of Aniline Using Membrane Extraction

Membrane extraction is one kind of new separation technology which combinesmembrane process with liquid-liquid extraction. During last several years, PDMS membranetechnologies such as membrane solvent extraction and so on have attracted great attention forremoval of volatile organic compounds(VOCs) from wastewaters. Polydimethylsiloxane(PDMS), a kind of non-porous polymeric material, exhibits high permeability to aniline andcan be used as membrane material for the extraction of these compounds from one phase intoanother.In this process, anline is extracted through non-porous membrane and concentrated intoan HCl solution as hydrochloride salts. Anilinium is a charged ion that cannot cross backthrough the hydrophobic membrane into the wastewater, so the driving force for mass transferthrough the membrane is maintained. MARS process uses HCl as the stripping solution,which not only saves organic solvent but also avoids contamination. It exploits the basicity ofaniline to produce a driving force based on the chemical energy contained in HCl and can becarried out under conditions of pressure and temperature that are near ambient throughout allitems of equipment.In this study, the effects of the aniline initial concentration, hydrodynamic condition,temperature, pH value and ionic strength on removal efficiency and mass transfer coefficentwere investigated. Recovery efficiency of the stripping solution, the HCl concentration andpH values in the stripping solution at steady state were analysed. This process was used totreat wastewater from a pharmaceutical industry Lynchem Dalian. Ratio of phase, theconcentration of aniline in the stripping solution and the driving force with time wereinvestigated. The experimental results showed that the overall mass transfer resistance wasdominated by membrane resistance. The relationship between temperature and thepermeability of aniline agreed with the Arrhenius equation. The ionic strength influenced thepartition coefficients in aqueous-membrane-aqueous systems, and improved the mass transfer.The aniline mass balance of the whole system showed that the recovery efficiency of theaniline is up to 93％. The HCl concentration is the key parameter that links the two steps ofthe process. In the removal step, it controls the concentration of total aniline in the strippingsolution. In the recovery step, the higher the concentration of aniliniurn submitted toneutralization, the higher the recovery efficiency. The aniline removal efficiency is up to 97％ for industrial wastewater on conditions that flow rote 3.05L/d, temperature 50℃, pH valuel,membrane length 18m and the initial aniline concentration 33081mg/L.The concentration ofaniline in the stripping solution increases with time and the driving force for mass transferthrough membrane is maintained when pH value≈1. Findings show that this system isstable in a continuous configuration.On the basis of trail results, the pilot project of utilizing PDMS to treat wastewater fromLynchem Dalian was designed. This process was suitable for the treatment of high strengthwastewater with anline. The economic benefit was obvious.The net benefit was 103.84￥perton when initial concentration was 33081 mg/L for design. It is calculated that the paybackperiod of investment is about 1.6 years.