Study On Reaction And Separation Coupling Intensification For Oxidation Regeneration Process Of Spent Caustic By Higee

Alkaline washing process is usually carried out for the removal of mercaptan from liquefied petroleum gas in refineries,and the spent caustic produced after alkaline washing is difficult in storage,transportation,and disposal.Regeneration of the spent caustic can not only save resources,but also reduce waste emissions,which is conducive to green chemistry and sustainable development.The classical regeneration technology is usually realized by a reactor and a separator in series,but the regeneration performance is not high and the area is large.It is urgent to reduce the operation unit and shrink the device volume through the process intensification technology of chemical process.HiGee technology,with the core device of a rotating packed bed(RPB),is considered as one of the typical process intensification technologies.The high-speed rotating porous packing uses the shear force to cut the liquid into small droplets,liquid ligaments,and liquid films,making gas-liquid and liquid-liquid mass transfer effectively enhanced.To analyze the above regeneration process of spent caustic,matching the transfer rate with the reaction rate is the key scientific problem.Based on the characteristics of HiGee technology,the reaction and separation coupling in one rotating packed bed for process intensification was proposed to improve the regeneration performance of spent caustic.In this work,the reaction sequence was firstly determined by means of spectroscopy analysis and quantitative calculation,and the reaction mechanism was speculated by density functional theory(DFT)calculation.A kinetic experiment was designed to determine the kinetic important parameter.The scientific law of spent caustic regeneration process in the HiGee environment was studied and revealed.A coupling mathematical model of reaction and separation by HiGee was constructed to guide the amplification of the reactor.The effect of packing surface characteristics on the reaction and separation performance of spent caustic regeneration process was investigated,and the reactor optimization was realized.The main research results are as follows:1.UV-visible absorption spectroscopy analysis and DFT calculation were employed to determine the reaction sequence,and the mercaptide ion was superior to oxygen molecule adsorbed on the catalyst sulfonated cobalt phthalocyanine.Calculated by DFT,the reaction mechanism of the two-layer adsorption structure was proposed.Kinetic experiments were carried out to obtain the kinetic important parameters.The activation energy was 29.584 kJ/mol and the pre-exponential factor of the reaction was 6.84×1010 L/(mol·s).Two-sample F test was adopted to statistically test the kinetics,which confirmed that the kinetic data were highly reliable.2.The better operating parameters were determined through the oxidation regeneration process of spent caustic in the HiGee environment:N=1400 r/min,G=2.5 m3/h,L=20 L/h,T=55℃,NaOH concentration=10 wt.%,NaSR concentration=0.3 wt.%,catalyst concentration=0.01 wt.%.Under these conditions,the conversion efficiency of reactant sodium mercaptan was up to 100%,and the separation efficiency of product disulfide was up to 89.9%.An artificial neural network model was proposed for quick-prediction and parameter analysis of regeneration performance,having a deviation within±4%,and shows the superiority of RPB technology in the regeneration process of spent caustic.3.A coupling mathematical model of reaction and separation in the rotating packed bed was constructed to guide the industrial amplification of the rotating packed bed.The errors between the predicted values and pilot experimental values were within ±5%,and the model was reasonable.Compared with the traditional regeneration technology,one rotating packed bed can simultaneously realize the reaction of sodium mercaptide and the separation of disulfide.It not only realized the half of the number of the operating unit,but also achieved higher regeneration efficiency,which strongly illustrates the advantages of the oxidation regeneration process by HiGee.Based on the model,the molar concentration for each component was calculated changing with the rotating packed bed rotor radial thickness(ri),and the coupling mechanism of the reaction and separation by HiGee during the regeneration process of spent caustic were revealed.Taking a group of pilot data as the reference,it can be obtained that:at ri=0.098 m,the degree of reaction was equal to that of separation;at ri=0.14 m,almost no reaction occurred,and the only separation process of product disulfide remained.4.The effect of packing surface characteristics of the rotating packed bed on the oxidation regeneration process of the spent caustic was investigated,and the hydrophilic micro-nano structure of the packing surface has obvious advantages of regeneration.The regeneration performance of a packing with a radial thickness of 45 mm hydrophilic micro-nano structure can reach that of 50 mm un-modified packing.By changing the wettability of the packing surface,the packing thickness and the rotor size can be reduced,thereby shrinking the rotating packed bed volume,and achieving the purpose of reactor optimization.