NOx removal from simulated marine exhaust gas via wet absorption using TBAB/PBS composite solution and subsequent reduction by adding Na2SO3

With the aim to develop wet denitration process for marine application, it is still challenging to simultaneously achieve high-efficiency NO x removal from flue gas and low nitrate concentration in scrubbed solution. Herein a novel two-step method was proposed to solve this issue: phosphate buffer solution (PBS) with organic additive was used to absorb NO x efficiently from flue gas, and in next step, Na 2 SO 3 as a reductant was added in the scrubbed solution to reduce NO x off-line. Five typical organic additives were chosen to compose with PBS. The tetrabutylammonium bromide and phosphate buffer solution (TBAB/PBS) composite solution exhibited superior NO x absorption performance. Furthermore, the effects of TBAB concentration, NO x oxidation degree, solution pH, temperature and O 2 concentration on NO x absorption performance of TBAB/PBS composite solution were investigated systematically, and a high NO x absorption efficiency of >90% could be achieved. It was mainly attributed to a physical complex between PBS and NO 2 , N O 3 − $$ N{O}_3^{-} $$ , N O 2 − $$ N{O}_2^{-} $$ , together with a mass transfer enhancement by TBAB. A long-run test showed that nitrate concentration was much lower than the limit value of IMO. Cyclic absorption and regeneration tests confirmed that Na 2 SO 3 could effectively regenerate the scrubbed solution in the absence of O 2 .