Study On The Preparation Of Methyl Mercaptan Over (CO/H₂S/H₂) Catalyzed By Supported Molybdenum-based Catalys

Methyl mecaptan also named methanethiol,which is easy to generate sulfur-containing substance due to the active chemical property,and it’s a kind of significant organic intermediates and chemical raw materials.At present,the production of methyl mercaptan mainly adopts methanol-hydrogen sulfide synthesis route,but there are some shortages including the raw material cost is high,the low efficiency of methyl mercaptan and the by-product of dimethyl sulfide will cause environment problem,etc.Compared with the CH3OH-H2S route,one-step synthesis of CH3SH through simple raw materials such as high sulfur syngas(or CO/H2/H2S mixture)will be more attractive and prospective.Reducing industrial flue gas contains a large amount of carbon oxides(CO/CO2)and sulfur species(H2S/COS),and the direct emissions will cause the environment problems such as global warming and acid rain.The utilization of carbon and sulfur species in the reducing industrial flue gas are not sufficient,mainly through separation of carbon and sulfur species firstly,then with the recycling respectively.In this paper,reducing industrial flue gas was simulated,and the synthesis of CH3SH with mixture(CO/H2/H2S)as raw material over Mo-based catalysts was investigated.Not only can eliminate the influence of reducing sulfur species to the environment and achieve the high value of utilization,but also can get the chemical products-CH3SH that in urgent needed in market and is conductive to carbon emissions.The active component MoO3 was used to prepare the catalysts through incipient wetness method on the synthesis of CH3SH in this paper.The alkali additives,second additives,supports,preparation process and the total loading were optimized;the catalysts were characterized with TEM,N2 absorption-disorption,H2-TPR and XRD to discuss structure-activity correlation;the optimum reaction conditions were explored and products distribution were analyzed to put forward the possible reaction networks;the stability of catalyst was tested.The main results summarized as follows:(1)Methyl mercaptan was synthesized when Mo-based catalysts were added alkali additives.The best alkali additive of K2CO3 and when n(K/Mo)was 2,the catalysts prepared by incipient wetness method displayed the optimum activity.H2-TPR characterization explained that the low-temperature hydrogen consumption peak splited and the octahedral molybdenum species on the surface of the SBA-15 transformed to tetrahedral with the addition of alkali.XRD characterization illustrated that with the increase of K/Mo molar ratio,the multi-molybdenum species formed with K2O and MoO3 on SBA-15 surface gradually transformed to a single species of molybdenum K2MoO4,which is in favour of the synthesis of CH3SH.(2)The second additives of transition metal(Fe,Co and Ni)nitrate was added into K-Mo/SBA-15 catalyst,the activity obviously improved,but the selectivity of CH3SH reduced.The order of transition metal added into catalysts on CH3SH selectivity was Co>Ni>Fe.And when n(K/Mo/Co)=2/1/0.35,the K-Mo-Co/SBA-15 catalyst showed the highest activity.(3)The K-Mo-Co catalysts were prepared with four kinds of supports.The order of CO conversion was SBA-15>microspheres silica gel>MSAMS-2>SiO2;the order of CH3SH selectivity was SBA-15>MSAMS-2>microspheres silica gel>SiO2.SBA-15 is the best support for the preparation of catalysts in this paper.(4)The optimum pretreatment conditions of catalysts as follows:reduction temperature is 400℃,vulcanization temperature is 280℃,vulcanization time of 6 h.The optimum reaction conditions for preparation of CH3SH with mixture(CO/H2S/H2)over Mo-based catalysts is:300℃,n(CO/H2S/H2)=1/1/2,0.2MPa,1000h-1.The main products were CH3SH,CO2,CH4,COS,and H2O,with a small amount of C2H4 and C2H6.The study of reaction network found that COS is intermediate for the synthesis of CH3SH,and also is the level of product,CH3SH and H2O were generated after the hydrogenation of COS.The main byproduct of CO2 mainly generated from water-gas transformation reaction;the decomposition of COS generated a small amount of CS2.Further reaction of CH3SH and H2 generated a trace of C2H4 and C2H6.The stability of K-Mo-Co/SBA-15 is excellent through test.