Removal Of Cyanide And Ammonia From Acrylonitrile Wastewater By Gas Membrane Absorption Process

The gas membrane absorption process (GMAP) is a new technology for separating volatile species from liquid solution. It has bright future and has been paid much attention because it has many advantages, such as lower cost, easy to operate, not changing structure of matters, enable to recover volatile substance, no secondary pollutants produced and so on.Most acrylonitrile facilities are currently adopted Sohio method to manufacture the products and the main raw materials are propylene and ammonia. High strength of organic effluents is also produced in the production process, which include cyanide, acrylonitrile, ammonium, acetonitrile and other compounds. The wastewater is difficult to be treated with traditional physical-chemical methods and bio-technologies due to its toxicity and complexity. Hydrophobic microporous polypropylene hollow fibers membrane has been used to remove cyanide and ammonia from mixed industrial acrylonitrile wastewaters of China National Petroleum Corporation Jilin Chemical. In this study, the major influence factors about cyanide and ammonia removal have been investigated, such as velocity, pH and temperature. The infullence of composition of wastewater on removal of cyanide by gas membrane absorbtion process (GMAP), the problem existing in pilot-scale study and the corresponding solutions, the membrane fouling and the membrane cleaning after a long time of operating were also analyzed and disscussed.The results showed that the cyanide removal efficiency was in the range of 40%～70% and the ammonia removal efficiency could reach the range of 80%～93% when the initial pH of the wastewater was adjusted to 11～12. Adjusting the pH of wastewater to 5～6 the cyanide removal efficiency would increase to 82%～93% after ammonia removal, which resulted from the acetone cyanohydrin decomposed and produced HCN at strong basic conditions. In addition, adding NaOH into the wastewater not only made the colloid concentration in wastewater decrease from 0.95 mg/L to 0.20 mg/L, which was benefit for alleviating membrane fouling, but also effectively restrained migration of water vapor by osmotic distillation (OD). The membrane became hydrophilic after 74 hours continuous running. The fouling of the hollow fiber membranes was mainly due to the sedimention of iron salt and titanium salt on the membrane surface. Washing the membrane by hydrochloride solution is the best cleaning method for removing iron salt. Using gas membrane absorbtion process (GMAP) treating acrylonitrile wastewater could obtain good removal rates of cyanide and ammonia, which could decrease the load of subsequent processing effectively. The GMAP present a bright future for treating acrylonitrile wastewater.