Design, Preparation And Performance Evaluation Of Medium-chain Branched Nonionic Surfactants For Cleaning Oily Soi

Oily soil is oil-containing solid waste generated during crude oil mining,transportation,refining,and oil-containing wastewater treatment,which poses a serious threat to the ecological environment and human health.Because the surfactant cleaning method has strong pertinence,simple process and good cleaning effect,it has become the most important method for oil contaminated soil treatment in major oil fields in China.Non-ionic and branched surfactants usually have higher surface/interface activity,lower CMC,and good salt tolerance,are especially suitable for the field of oily soil cleaning.Based on this article,a series of medium-chain branched nonionic surfactants were designed and synthesized.Their basic properties such as surface/interface properties and soil adsorption were measured,their cleaning performance was evaluated,and their role in cleaning oily soil was discussed mechanism.The paper first uses L-phenylalanine,long-chain alkyl acid chloride(C12/C14/C16/C18)and polyethylene glycol monomethyl ether(MPEG,Mn=350,550,750,1000 g/mol)as raw materials,Through amidation reaction and esterification reaction,a series of new non-ionic surfactants N-long-chain carbonyl-L-phenylalanine monomethyl polyethylene glycol ester(Rn-L-MPEG)were synthesized,and the product was characterized by infrared spectroscopy and nuclear magnetic hydrogen spectroscopy.From the results of the reaction yield,as the carbon number of the long-chain acid chloride in the reactant increases or the molecular weight of MPEG increases,the reaction activity decreases and the yield decreases,but overall the reaction yield is higher,among which amidation and the yields of the esterification reaction are all above 90%.The paper then systematically studied the surface and interface properties of Rn-L-MPEG and the relationship between them and their structure.The results show that:Rn-L-MPEG has excellent surface/interface activity and good salt tolerance;as the molecular weight of MPEG increases,the surface tension of Rn-L-MPEG gradually decreases.With the growth of the alkyl chain in the acid chloride,the surface tension of Rn-L-MPEG shows an increasing trend.Among the series of surfactants,R12-L-MPEG1000 has a minimum surface tension of 28.11 mN/m;Interfacial tension of Rn-L-MPEG changes with molecular structure and surface tension,the oil-water interfacial tension of R12-L-MPEG1000 is as low as 1.46 mN/m;the adsorption of Rn-L-MPEG on the soil surface is a spontaneous and exothermic multi-molecular layer physical adsorption,and its adsorption amount has four stages with the increase of concentration,the second stage is the main stage,as the molecular weight of MPEG increases,the adsorption amount of Rn-L-MPEG gradually increases,while as the alkyl chain in the acid chloride grows,the adsorption amount of Rn-L-MPEG shows a downward trend.Finally,the paper evaluates the cleaning performance of Rn-L-MPEG on oily soil and briefly explores its cleaning mechanism.Through the pre-evaluation experiment of cleaning effect,R12-L-MPEG1000 with the best performance was selected;The optimization of its thermochemical cleaning conditions is as follows:the amount of cleaning agent added is 2.5%,the solid-liquid ratio is 4:1,and it is cleaned at 50℃water bath with a stirring speed of 400 r/min for 40 minutes;After using R12-L-MPEG1000 to stir and wash the simulated oily soil,the oil removal rate can reach 92.29%,and the residual oil rate is 1.57%.By comparing the study of the soil’s adsorption of heavy oil and R12-L-MPEG1000 and the emulsification performance of R12-L-MPEG1000 to crude oil,it is inferred that the cleaning mechanism of R12-L-MPEG1000 is the roll-off-emulsion and the adsorption-displacement mechanism.