Performance Study Of CO₂ Intelligent Responsive SDS/C₁₂A Compound Foam Drainage Agent

In the process of foam dewatering gas recovery,it is difficult to defoam after the excess foam reaches the ground,which brings inconvenience to the subsequent gas-water separation process.The use of CO₂-responsive surfactants,which can artificially control the presence or absence of its surface activity,has become the first choice for solving this problem.In this paper,a combination of experimental and molecular dynamics simulations was used to study the foam properties,CO₂ response properties and mechanism of SDS/C₁₂A compound foam drainage agent which was prepared by equimolar blending the CO₂-responsive surfactant N-dodecyl-N,N-dimethyl tertiary amine(C₁₂A)and sodium dodecyl sulfate（SDS）.First,we studied the foam properties and CO₂ response of SDS/C₁₂A compound foam drainage agent by experiment.It is found that the foam formed by the compound foam drainage agent have good stability and liquid carrying capacity.The foam can be completely destroyed when the CO₂ was continuously introduced into the foam for about 1600 s.Then,when the foaming liquid was heated and N₂ was introduced,it still has foaming ability and CO₂ responsiveness,and the process can be cycled five times or more.By analyzing the surface tension of the foaming liquid before and after the response,it is speculated that the reason of the CO₂ responsiveness may be that the protonated C₁₂A and SDS form an ion pair by electrostatic action,which greatly reduces the surface activity of the foaming liquid.In addition,Na Cl,Mg Cl₂ and Ca Cl₂ have different effects on the CO₂ response of SDS/C₁₂A compound foam drainage agent.The defoaming time was prolonged due to the introduce of Na Cl and Mg Cl₂.But Ca Cl₂ has no effect on defoaming time.n-Heptane,n-Dodecane and condensate have little effect on the CO₂ response performance of the compound foam drainage agent.Second,we constructed a series liquid film models of SDS/C₁₂A compound foam and studied the dynamics process of these models.In the models before response,SDS and C₁₂A molecules are adsorbed at the air-water interface after dynamics calculation,which acts to stabilize the foam liquid film.In the model after response,SDS and C₁₂A are agglomerated in the liquid phase due to the electrostatic attraction between SDS and protonated C₁₂A and the increase of the hydrophilicity as well as the decrease of diffusion rate of the surfactants.So only a small amount of surfactants adsorbs at the air-water interface,and it is difficult to stabilize the foam liquid film.In the model containing inorganic salts,the presence of Mg Cl₂ weakens the electrostatic attraction between SDS and C₁₂A in the model after the response and increases the diffusion rate of the surfactant molecules,which affects the performance of CO₂ response of SDS/C₁₂A compound foams.So the response time was extended.The presence of Ca Cl₂doesn’t affect the interaction between molecules in the model after the response,so the response performance is not affected.In the model containing oil droplet,after the molecular dynamics simulation process,the surfactant molecules in the model before the response are distributed at the gas-liquid interface together with the oil droplet.In the model after response,the surfactant molecules encapsulate the oil droplet in the liquid phase to form micelle,so the presence of the oil phase has little effect on the CO₂response of the SDS/C₁₂A compound foam drainage agent.