Study On The Combination Of Organic Sulfur Absorbents Based On DFT Calculation

Natural gas is a significant component of the nonrenewable energy sources,and its position is self-evident.Before used,natural gas needs to be purified.At present,the technology of natural gas decarbonization has been mature and reached the technical standards.However,desulfurization,especially organic sulfur,is still a severe challenge.In this paper,the organic sulfur components(mainly mercaptan and carbonyl sulfur)in natural gas were removaled by screening from the commonly used physical and chemical absorbents in industry based on density functional theory,and the compound test was carried out.The contents and conclusions are as follows.(1)Based on DFT theory,structure optimization and single point energy calculation were performed for five physical absorbents and organic sulfur components at B3LYP/6-311+G(d,p)and M06-2X/aug-cc-pVTZ levels.The stable dimer structures were obtained by electrostatic potential,and the weak interaction analysis of the dimer structures were carried out.Finally,the corrected binding energy was calculated.The results show that the physical adsorbent NMP has the strongest absorption capacity for carbonyl sulfur and CS2,while PC has the strongest absorption capacity for methyl mercaptan,methyl sulfide and thiophene.Experiment is showed that the results of the calculation of methyl mercaptan are consistent with the experimental results in certain extent,and the calculation results of carbonyl sulfur deviate greatly from the experimental results.(2)Through the reaction mechanism of five kinds of chemical absorbents with organic sulfur,the transition state structure of the elementary reaction was speculated,and the possible transition state structures were obtained.In order to verify the correctness of the transition state structure,the intrinsic reaction coordinate was carried out for this reaction.Finally,the chemical rate constant of the reaction was calculated by the transition state theory.The calculation results show that DIPA and MDEA have high reaction absorption rate constants for methyl mercaptan and carbonyl sulfur.After that,the verification test was carried out,and the error between the calculated results and the experimental results was large.In addition,for five kinds of chemical absorbents,pKa was calculated under different basis groups.The results show that the pKa of AMP is the highest under different basis groups,which is perfect compered with experimental results.(3)According to the physical and chemical absorbents selected above,the orthogonal experiment was designed under three factors and three levels,and nine absorbents were compounded.The organic sulfur removal experiment was carried out in RPB,and the results show that the effect of compounding 7(Chemical absorbent content 40%,AMP:DIPA=1:1,PC:NMP=1:2)is better.On this foundation,the effects of temperature,rotating speed and gas-liquid ratio were researched for organic sulfur removal and KGa in RPB.The best absorption conditions were determined as follows:temperature 35?,rotating speed 1400 r/min,gas-liquid ratio 10.Under these condition,the removal rate of methyl mercaptan and carbonyl sulfur were 45.8%and 48%.