Mechanism analysis of hydroxypropyl guar gum degradation in fracture flowback fluid by homogeneous sono-Fenton process

An effective hybrid system was applied as the first report for the successful treatment of key pollutants (hydroxypropyl guar gum, HPG) in fracturing flowback fluid, and the synergistic index of the hybrid system was 20.45. In this regard, chemical oxygen demand (COD) removal ratio was evaluated with various influencing operating factors including reaction time, H₂O₂ concentration, Fe²⁺ concentration, ultrasonic power, initial pH, and temperature. The optimal operating parameters by single-factor analysis method were: the pH of 3.0, the H₂O₂ concentration of 80 mM, the Fe²⁺ concentration of 5 mM, the ultrasonic power of 180 W, the ultrasonic frequency of 20–25 kHz, the temperature of 39 ℃, the reaction time of 30 min, and the COD removal rate reached 81.15 %, which was permissible to discharge surface water sources based on the environmental standards. A possible mechanism for HPG degradation and the generation of reactive species was proposed. Results of quenching tests showed that various impacts of the decomposition rate by addition of scavengers had followed the order of EDTA-2Na < BQ < t-BuOH, therefore OH radicals had a dominant role in destructing the HPG. Based on the kinetic study, it was concluded that Chan Kinetic Model was more appropriate to describe the degradation of HPG. Identification of intermediates by GC–MS showed that a wide range of recalcitrant compounds was removed and/or degraded into small molecular compounds effectively after treatment. Under the optimal conditions, the sono-Fenton system was used to treat the fracturing flowback fluid with the initial COD value of 675.21 mg/L, and the COD value decreased to 80.83 mg/L after 60 min treatment, which was in line with the marine sewage discharge standard. In conclusion, sono-Fenton system can be introduced as a successful advanced treatment process for the efficient remediation of fracture flowback fluid.     

天然杜仲胶乳的制备及表征

采用溶液乳化法制备了杜仲胶乳，考察了乳化配方及乳化工艺对乳化效果的影响，确定了如下制备条件：以杜仲胶的环己烷溶液（杜仲胶的质量分数为6%）为油相胶液，采用1% Brij-52、0.5% Tween-20、0.5%十二烷基苯磺酸钠的三相复配乳化剂体系，油水体积比为1：1.5，乳化方式为高速搅拌（8 000 r/min，10 min），除溶剂方式为旋转蒸发（-0.09 MPa，40℃），浓缩方式为离心浓缩（10 000 r/min，10 min）。在优化条件下制备的杜仲胶乳的固含量可达54%，粒径约为330 nm，Zeta电位的绝对值可达57 mV。采用X射线衍射法（XRD）、差示扫描量热法（DSC）、傅里叶变换红外光谱法（FT-IR）、扫描电子显微镜（SEM）和偏光显微镜（POM）对制备的杜仲胶乳进行了表征，结果表明：乳化没有破坏杜仲胶的结晶性能，杜仲胶乳中仍存在大量的微结晶，杜仲胶乳的晶型中以β晶型为主。