Synthesis Of Amide Fluorocarbon Foaming Agent For CBM Fracturing And Study On Its Aggregation Behavior

Foam fracturing fluid is widely used in CBM fracturing because of its low filtration,easy flow-back and low damage,in which the foaming agents play an extremely important role.Fluorocarbon surfactant has superior surface activity and has great potential when used as foaming agents.So in this paper we decide to synthesize amide fluorocarbon surfactant and investigate its aggregation behavior in aqueous solution and on coal surface,based on survey and investigation on status of fluorocarbon surfactant synthesis and surfactant aggregation behavior.In the laboratory amide fluorocarbon surfactant(HPA4)is synthezed from perfluoro caprylic acid and diglycolamine through fatty acid process.The optimal ratio of reagents,catalyst content,time and temperature for first reaction step,time and temperature for second reaction step during fatty acid process are optimized as 1:1.2,0.6%,5h,130?,5h,90? through single factor optimization method,respectivley.Foam volume and half-life period for the optimal synthesized product are 600 mL and 620 s,respectively.In addition,the product is characterized by Fourier transform infrared spectroscopy and nuclear magnetic resonance,the results show that amide fluorocarbon surfactant is the purpose product.Self-aggregation behavior of synthesized product HPA4 is investigated.The results show that the HPA4 has superior surface activity over hydrocarbon surfactants and fluororcarbon surfactants of the same type in aqueous solution.The micellization process for HPA4 is spontaneous and exothermic,which is driven by entropy.Obvious enthalpy-entropy compensation phenomenon is observed during micellization process of HPA4.Effects of coal rank on the adsorption desnsity of HPA4 are demonstrated through ultraviolet spectrophotometry.The results show that nonionic fluorocarbon surfactant HAP4 is adsorbed on coal through hydrogen bonds.Adsorption desity of HPA4 onto low-rank coal is the largest,the adsorption density on medium-rank coal takes the second place and the one onto high-rank coal is the minimum.The adsorption pattern of HPA4 on coals complies with the Langmuir monolayer adsorption law.The adsorptipn process is spontaneous and endothermic,during which higher temperature is a positive factor.Adsorption density of HPA4 onto low-medium-rank coal first decrease and then increase over the electrolytes concentration,however for high-rank coal it always goes up.Adsorption density on coals all goes down with pH value then reaches a plateau.Effect of HPA4 adsorption on CBM desorption is investigated through CBM adsorption-desorption experiments.The resuls shows that the Langmuir pressure and volume during CBM desorption process all increase after HPA4's adsorption,indicating that fracturing fluid manily composed of HPA4 can accelerate CBM desoption after fracturing treatment,which has a broad application prospect.