Supercritical Fluid Extraction Process and Change of Quality of Recovered Chemicals

Analytical testing (85-89) Supercritical fluid extraction process and quality changes of recovered chemicals Lu Ziyang, Wu Xiao, Xu Baoquan, Gao Jianli (Institute of Environmental Protection of Gansu Province, Lanzhou, Gansu 730030, China) Phenylene (PCE) O-chlorophenol (OCP), Chemicals such as o-nitrophenol (ONP), which are difficult to decompose organochlorine pollutants and Simazine (CAT), have undergone adsorption and supercritical fluid extraction processes. Chemicals have been identified by UV and IR spectroscopy. Chemical changes occur qualitatively, and the recovered material is of a very high purity, with economic value of recycling. :Adsorption and trapping; Supercritical fluids; Extraction and recovery; Material change engineer, Visiting researcher at universities and research institutions in Japan from 1987 to 1994, currently serving as deputy director of the Gansu Provincial Environmental Protection Research Institute, mainly engaged in the use of supercritical In the process of CO2 extraction to treat wastewater, there is no qualitative change in the chemical substances recovered, and the degree of purity needs to be confirmed by research. Therefore, the authors separately studied trichloroethylene (TCE) tetrachloroethylene (PCE) o-chlorophenol (O CP), o-nitrophenol (ONP) Simazine (CAT, 2 chloro-4,6-diethylamine). Triazine) was extracted and recovered with supercritical carbon dioxide from adsorbed and trapped soil activated carbon and aqueous solution, and the resulting material was identified by UV and infrared spectroscopy. Through the analysis of spectral data, it was confirmed that the molecular structure of these substances did not change during the recovery of such substances by supercritical carbon dioxide extraction; and the purity of these recovered substances is generally still high.

1 is a supercritical fluid extraction device, extraction capacity is 03L, extraction pressure and extraction temperature can be automatically controlled. Carbon dioxide is first purified by a drier, and then dry ice ethanol is used to cool the pump head. The flow rate is regulated by the plunger pump stroke and the gas flow meter.

The test ultrasonic oscillator was a CST-1A ultrasonic generator.

-300 UV spectrophotometer, FTIR230 infrared spectrometer.

2 The supercritical fluid extraction device extracts and recovers the adsorbed TCEPCEOCRONP from activated carbon and soil samples, respectively. The activated carbon and soil samples are put into a cloth bag, accurately weighed, and added to the extraction dish. The extraction conditions of supercritical carbon dioxide were as follows: a temperature of 0.45 MRa flow rate of 10 L/mn, and an aqueous solution of the pesticide CAT for 30 min was placed in an extraction dish for direct supercritical fluid extraction. The resulting chemical extracted is collected in a separator. The collected sample and the original sample used for the adsorption experiment were diluted with absolute ethanol (spectrally pure), and the ultraviolet and infrared absorption spectra of these chemicals were determined. The solutions before and after the pesticide CAT treatment were directly measured by UV spectroscopy.

3 EXPERIMENTAL RESULTS AND DISCUSSION 1 Ultraviolet absorption spectra of OCR and ONR recovered from the supercritical extraction of soil The extracted OCR liquid from the soil is darker in color than the original sample OCP liquid and is in a dark brown color, which is extracted at the same time as the ultra-mass. The reason.

The UV spectra of the OCPs before and after the extraction were analyzed. The results can confirm the following two problems: 1 Comparison of the absorbance at the characteristic absorption wavelength, examining the changes in the content of OCP after extraction, to confirm the purity of the recovered OCP and before extraction Compared with whether or not there is a drop; 2 whether there is any change in the characteristic absorption wavelength of the OCP before and after extraction to determine whether the molecular structure of the OCP has changed in the extraction process.

The UV spectrum of the OCP before and after the supercritical extraction shows that the absorbance of the extracted OCP is slightly lower than that of the OCP before extraction (Table 1). The data listed in Table 1 can be used to determine the UV spectra of OCPs before and after the treatment of supercritical fluids in Table 1. Sample Category Characteristic Absorption Wavelength/nm Characteristic Absorbance Original sample OCP treatment Recovery OCP see, two absorption peaks almost overlapped. Although the extracted OCP after the extraction contained some pigment material from the soil, its content was still as high as 998%. It indicated that supercritical CO2 was used to extract and recover the OCP adsorbed by the soil. The content of impurities such as pigments from the soil was extremely low. The quality score is only about 02%.

In addition, from the data listed in Table 1, it can be seen that the difference between the characteristic UV absorption wavelength of the original sample OCP used for the supercritical extraction and the characteristic UV absorption wavelength of the OCP obtained by the supercritical extraction in the soil is in the ultraviolet spectrum analysis instrument. The wavelength tolerance is within 2nm. From this it can be concluded that the OCP's molecular structure has not changed after the supercritical carbon dioxide was recovered at 45°C and 100MPa.

The ONP's situation is similar to the above. No changes in the properties of the ONP were observed after the soil adsorption and supercritical CO2 extraction and recovery. The maximum characteristic absorption wavelength of the ONP before and after the supercritical extraction process was 273 and the purity was still higher than 990%. The appearance of the two types of ONP before and after is yellow and the ONP crystals after supercritical fluid withdrawal are fine. This is due to the crystallization conditions at the time when the ONP precipitates from the rapidly expanding carbon dioxide gas stream in the separator in the supercritical fluid extraction process. According to the general principle of the crystallization process, the rapid precipitation process is not conducive to the formation and growth of crystals. In addition, a small amount of other extracted components from the soil are mixed with the recovered ONP, so that the color of the ONP is somewhat dark and not as bright as the original sample ONP that is not used for soil adsorption.

2 Infrared absorption spectrum of TCE extracted and recovered from activated carbon by supercritical fluids After three different methods were used to make TCE adsorbed on activated carbon, supercritical carbon dioxide extraction was performed on these three types of activated carbon respectively to recover the TCEs in three types. The infrared spectrum of the recovered TCE in the case is shown in Figure solids, which is not: the same as the original sample grain larger leutetropy is caused by carbon dioxide removal of this part not to be bookmark2 200th2500 33 extracted from activated carbon using supercritical fluid Infrared Absorption Spectra of the Recovered PCE The activated carbon sample in which PCE was adsorbed from the aqueous solution, and A and B2 parts were prepared at the same time. One part (C) was prepared from the sample of activated carbon adsorbed directly from the PCE liquid. The infrared spectra of these 3 PCEs are shown separately. Gas chromatographic analysis was performed on the treated waters treated with A and B activated carbons. The results are shown in the vicinity of 600 cm. The absorption spectra are different. As described in the previous section, this is Caused by the effect of moisture. However, sample B in the 1 100 34 supercritical fluid extraction of pesticides directly from the water UV absorption spectrum of CAT supercritical carbon dioxide directly into the aqueous solution containing herbicide CAT direct extraction, when the temperature is 35 °C, pressure is At 200 MPa, CAT with a recoverable water content of 34% was initially obtained. With the changes of temperature, pressure, flow rate and time, the treatment removal rate showed a further increase. The problem of whether the processed CAT is decomposed under such harsh conditions needs to be confirmed.

The UV absorption spectrum of CAT aqueous solution was analyzed. The absorption spectrum of the original sample aqueous solution and the absorption spectrum of the recovered material aqueous solution had the same peak shape, and their characteristic absorption wavelengths were all at 222 nm. From this, it can be seen that the molecular structure of CAT did not change under the above experimental conditions.

4 Conclusions OCPs and ONPs extracted and recovered from soils using supercritical fluids have not undergone chemical changes and are still the original substances.

The activated carbon sample obtained by the aqueous solution adsorption TCE directly adsorbed by the aqueous solution aeration and the TCE adsorbed to the liquid TCE directly adsorbed by the supercritical fluid did not undergo any chemical change, but was still the original substance.

The PCE directly adsorbed on activated charcoal did not undergo chemical changes after being recovered by supercritical fluid extraction. For activated carbon with PCE adsorbed by aqueous solution, the recovered PCE did not undergo chemical change after regeneration by supercritical carbon dioxide. However, because dechlorination occurred during the adsorption of activated carbon packed column, the generated TCE could be separated from PCE.

The aqueous solution of pesticide simazine (CAT) was directly treated with a supercritical fluid. The recovered material was still simazine and no chemical change occurred.