Study On Supercritical CO₂ Fluid Extraction Of Bensulfuron-Methyl In Soil

Bensulfuron-methyl(BSM) is a kind of highly efficient sulfonylurea herbicides.It's residue would do harm to following crops and bring serious pollution to environment and ecological toxicity.So it is important to study the method of analysing the residue of BSM in soil.Therefore,the pick-up of BSM in soil with supercriticai CO₂ extraction was systematically investigated in this paper.The main results were summarized as follows:1 The measuration of equilibrium solubility of BSM in the supercritical CO₂In order to validate the reliability of the equipment,the solubility of Naphthalene in the supercritical CO₂ was measured and compared with the literature.The equilibrium solubility of BSM in the supercritical CO₂ was measured by using a dynamic method at pressures between 10MPa and 35MPa,at temperatures of 308.15 K,318.15K and 328.15 K.The result showed that the molar fraction of BSM solubility was in the range of 4.13×10^-7～1.93×10^-6,and the experimental data was well correlated with the empirical density-based Chrastilmodel and the empirical improved Chrastilmodel.The former generalized the relationship between the BSM solubility and supercritical CO₂ density, which was lny=1.745151nρ-3457.74191/T+5.8819.The latter excelled the former at simulation.The AARD was 8.82%and the RMS was 11.3%.Both of them were close to each other,which showed the maneuverability of model was good.2 Study on supercritieai CO₂ fluid extraction of BSM from soil(1)Taking extraction efficiency as the inspection target,the effect of pressure, temperature,time,kinds and percent of modifier,nozzle temperature and extraction mode were studied.The single factor test showed that 15%methanol was the best modifier content for the extraction of BSM and it dispensed with static extraction. Pressure,temperature,time and nozzle temperature all had positive correlation with extraction efficiency in initial stage.(2) Five-factor and four-level orthogonal design was used to optimize the extraction conditions.Orthogonal experiment showed the influence of single factors was the pressure＞the temperature＞the percent of modifier＞the time＞the nozzle temperature.(3) On the basis of orthogonal test,three levels of factors were selected to do the central composite design experiment.The quadric regression model for the extraction rate was established.The equation of the extration content was Y=86.4233+8.0413X₁ -2.4713X₂-1.0050X₃-2.1217X₁²+4.9800X₁X₂-4.0867X₂²+0.3725X₁X₃-6.5675X₂X₃-6.7342X₃²,in which the coefficients(R²) was 0.9676.The model was significantly fit well and the three factors were all significant to the content of BSM.The optimal condition was the pressure 34.83MPa,the temperature 57℃and the percent of modifier 14.4%by response surface and ridge analysis,in which condition the predicted value was 92.69%and the verified value was 93.45%.In this method,the limit of detection(S/N=3) was 0.028mg/L,the mean fortified recoveries of BSM ranged from 81.3%to 93.6%,with relative standard deviation(RSD) in the region of 3.41%～8.63%.3 The effect of kaolinite,montorillonite and humic acid content in soil on the extraction efficiencyThe orthogonal design and the test of adding three materials to soil at different rates were used to study extraction efficiency.It was found that the effect on the extraction efficiency followed the sequence:kaolinite＞montmorillonite＞humic acid.Further linear regression analysis showed that the extraction efficiency had a negative correlation with the content of kaolinite,montmorillonite and humic acid,which also suggested a high significance of three materials content for extraction efficiency.It was also conducted that analysis on correlation between K_f and extraction efficiency.The K_f of BSM adsorbing in different soil were all significant to the content of BSM,which indicated that the adsorption played an important role on the efficiency of supercritical fluid extraction.