Development Of A Wet Scrubbing Process For Methyl Mercaptan Treatment With Peroxides

Methyl mercaptan (CH₃SH_G) is considered to be an important contributor toodors. It is a toxic, corrosive and acid gas. The absorption of CH₃SH_Gin alkalinesolution remains one of the most widely used processes，but the remained solutionshould be further treated.A wet scrubbing process for methyl mercaptan treatment with peroxides wasdeveloped in this study. It means that CH₃SH_Gis absorbed in alkaline solution andoxidated by peroxides oxidation. Peroxides include hydrogen peroxide（H₂O₂）,peroxo-monosulfate（PMS） and persulfate（PS）. CH₃SH_Gis absorbed in alkalinesolution and oxidated by peroxides oxidation using a recycling continuous systemfor absorption and degradation. The stability of peroxides under alkaline conditionsis discussed. The influence of different reaction conditions on the absorption rate anddegradation rate is also studied. This study compares the influence of differentperoxides on absorption and degradation of CH₃SH_Gunder alkaline solution. Theobjective of this study is to optimize the system of degradation CH₃SH_G. Theprocess is carried out under atmospheric pressure and at ambient temperature. Therewas no sewage generated in the recycling continuous system of the absorption anddegradation of CH₃SH_Gover a period of time and it has potential development inthe field of odor treatment. Specific studies and results are as follows:（1） CH₃SH_Gcan be effectively absored by alkaline solution and the absorptionof the CH₃SH_Gincreased with the increasing of pH. These results show that theabsorption of CH₃SH_Gis68.5%,82.9%, and88%at pH12,12.5, and13,respectively. The absorption of CH₃SH_Gfollowed a first-order kinetics behavior.Dissolved oxygen has an important influence in the absorption of CH₃SH_G. It canimprove the absorption of CH₃SH_Gand oxidate the dissolved CH₃S^-. Thedegradation of dissolved CH₃S^-by dissolved oxygen followed a first-order kineticsbehavior. （2） The stability of H₂O₂under alkaline conditions is discussed. The influence ofdifferent reaction conditions on the absorption rate and degradation rate is also studied.It is observed that H₂O₂is relatively instability under alkaline conditions and in theconditions of pH>11.7, more than95%of H₂O₂was decomposed in110min. H₂O₂can effectively improve the absorption of CH₃SH_Gand oxidate the dissolved CH₃S^-.In the conditions of pH=12, the absorption of CH₃S^-H increased from62.9%to79.2%in the presence of H₂O₂. It was also observed that the decomposition of H₂O₂was increased with the increasing of pH and the degradation of dissolved CH₃S^-byH₂O₂was worse. The degradation of dissolved CH₃S^-by H₂O₂followed a first-orderkinetics behavior.（3） The stability of PS under alkaline conditions is discussed. It also studied theinfluence of different reaction conditions on the absorption rate and degradation rate.PS is relatively stability under alkaline conditions. PS can effectively oxidate thedissolved CH₃S^-. The absorption rate of CH₃SH_Gfirst increased and then decreasedwith the increasing the concentration of PS. Along with the increasing of PS, thedegradation rate of CH₃S^-increases. It was also observed that the efficiency betweenabsorption and degradation had been significantly increased with the increasing of pH.In the conditions of pH=12,1.4g·L^-1PS,90%of the dissolved CH₃S^-can beoxidated. The degradation of dissolved CH₃S^-by PS followed a first-order kineticsbehavior. By comparison, the ability of H₂O₂was greater than that of PS. But the rateof CH₃S^-oxidation by H₂O₂decreased quickly with the increasing of pH from12to13, whereas it was fixed for PS.（4） It is observed that stability of PMS is comparatively complexity underalkaline conditions. In the conditions of pH=12,12.5,13, the decomposition of PMSwas33.1%,39.9%,80.8%respectively. PMS can greatly improve the absorption ofCH₃SH_Gand effectively oxidate the dissolved CH₃S^-. It can’t detect the existence ofdissolved CH₃S^-and the absorption of CH₃SH_Gis always more than95%with thepresence of PMS. The absorption of CH₃SH_Gis rapidly reducing and theconcentration of dissolved CH₃S^-is increasing rapidly after running out of PMS. Itwas found that PMS had the best efficiency of CH₃SH_Gremoval. The capacity of methyl mercaptan ion （CH₃S^-） oxidized by PMS was strongest and it can not beeffected by PMS concentration and initial pH.（5） PMS could effectively promote the absorption of CH₃SH_Gand it is the bestof peroxides. PS and H₂O₂are second only to PMS. The absorption of CH₃SH_GwithPS and H₂O₂has small difference. The ability of degradation CH₃SH_Gare PMS>H₂O₂> PS. PMS could accelerate mass transfer of CH₃SH_Gdirectly, but H₂O₂andPS could only react with CH₃S^-. Methanesulfonic acid （CH₃S^-O3H） was detected asthe product of CH₃S^-H removal by peroxides, and for PMS it was the main product.Compared with H₂O₂, it contained much SO₄^2-in the wet scrubbing process with PSand PMS.