No abstract

Over the past 29 years there have been myriad research efforts into the catalytic removal of nitrates from drinking water. In this work, 147 papers published during that period have been examined from the point of view of the ability of catalysis to produce water that is suitable for human consumption as well as amenable to industrial scale-up at reasonable working conditions of temperature and residence time. After close examination of the aforementioned articles, it is evident that this methodology has fulfilled only half its aims: it is able to reduce the nitrate concentration to guideline levels for human consumption, but it inevitably produces concentrations of ammonia and nitrites that are beyond the accepted limits for safe consumption of water. It is sometimes recommended that catalysis be combined with an ancillary technique, such as adsorption, in order to eliminate the undesirable byproducts mentioned above.However, this implies resorting to extra treatment units at the industrial scale, thus making the whole treatment process more complex and expensive. Our conclusion is

Currently, membrane gas separation systems enjoy widespread acceptance in industry As multistage systems are needed to achieve high recovery and high product purity simultaneously, many such configurations are possible. These designs rely on the process engineer's experience and therefore sub-optimal configurations are often the result. This paper proposes a systematic methodology for obtaining the optimal multistage membrane flowsheet and corresponding operating conditions. The new approach is applied to cross-flow membrane modules that separate CO 2 from CH 4 , for which the optimization of the proposed superstructure has been achieved via a MINLP model, with the gas processing cost as objective function. The novelty of this work resides in the large number of possible interconnections between each membrane module, the energy recovery from the high pressure outlet stream and allowing for non-isothermal conditions. The results presented in this work comprise the optimal flowsheet and operating conditions of two case studies.

Highlights  MILP Objective reduction method based on the maintenance of the dominance structure  Three models defined depending on the reduction grade the user wants to achieve  Method to tackle high dimensional multi-objective optimization problems  Method that quantifies the alterations in the dominance structure

No abstract