Article pubs.acs.org/IECR
Simulation and Operation Cost Estimate for Phenol Extraction and Solvent Recovery Process of Coal-Gasification Wastewater Chufen Yang,†,‡,* Shiying Yang,‡ Yu Qian,‡ Jianwei Guo,† and Yun Chen‡ †
Faculty of Chemical Engineering & Light Industry, Guangdong University of Technology, Guangzhou 510006, PR China School of Chemistry and Chemical Engineering, South China University of Technology, Guangzhou 510640, PR China
‡
S Supporting Information *
ABSTRACT: To further reduce the total phenols of coal-gasification wastewater which comes from the Lurgi pressurized coalgasification process, methyl isobutyl ketone (MIBK) instead of diisopropyl ether (DIPE) is used as the extraction solvent in the process to remove the phenols. To obtain process parameters for an industrial trial, process simulations with a treatment capacity of 100 ton/h wastewater are carried out. The simulation results show that with the use of MIBK as an extraction solvent, the total phenol concentration of coal-gasification wastewater can be reduced from 5410 ppm to less than 200 ppm. The operation cost estimate shows that using MIBK as an extraction solvent to extract and remove phenols from coal-gasification wastewater has good economic feasibility. With the process parameters obtained from the simulation, an industrial trial is implemented and satisfactory agreement is found. With the total phenol concentration reduced to below 200 ppm in the pretreatment, the coalgasification wastewater can be decontaminated in the subsequent biological treatment. Fortunately, in our previous work,6,7 we have developed a new process to remove ammonia and sour gas before phenol extraction, which can lower the pH value of the wastewater from 10 to around 7. With this new process, the total phenol concentration after extraction can be reduced to about 400− 500 ppm.6 It is still too high for the subsequent biological treatment process, so the wastewater cannot be decontaminated as the total phenol concentration after biological treatment is more than 0.5 ppm. It seems that the total phenol concentration must be further reduced in the extraction process. However, further research shows that, no matter the extraction stages added or the amount of solvent added, the total phenol concentration cannot be effectively reduced with the use of DIPE as the extraction solvent because of its poor extraction ability on nonvolatile (dihydric and trihydric) phenols.8 To further reduce the total phenol concentration, other extraction solvents are investigated for their extraction efficiency for the coal-gasification wastewater. It is found that methyl isobutyl ketone (MIBK) is a better extraction solvent than DIPE, as its extraction distribution coefficients for nonvolatile phenols are much higher than that of DIPE.8 However, compared with that of DIPE, the boiling point of MIBK (115.9 °C) is much higher, which will cause much more energy consumption during the solvent recovery process. It will increase operation cost of the wastewater treatment. In this paper, we use MIBK as an extraction solvent to remove phenols from the coal-gasification wastewater based on the new developed process mentioned in the previous paragraphs. As NH3, CO2, H2S and other contaminations have been removed
1. INTRODUCTION Coal-gasification wastewater comes from the Lurgi pressurized coal-gasification process which is a clean technology for highly effective utilization of coal resources. It is a notorious toxic industrial effluent in urgent need of treatment because of its high concentration of pollution components, such as phenols, ammonia (NH3), carbon dioxide (CO2), hydrogen sulfide (H2S), fatty acid, and tar, etc.1,2 Among these pollutants the phenols are considered priority pollutants3 with a total concentration of more than 5000 ppm, which includes volatile phenols at about 3000 ppm and nonvolatile (dihydric and trihydric) phenols at about 2000 ppm.4 All of these phenols are difficult to biologically degrade because of their toxicity and high concentration.5 Therefore, to relieve the biological treatment burden and make the coal-wastewater purification possible, a pretreatment to remove phenols from the wastewater is required. Solvent extraction, a process for separating components in solution according to their distribution in two almost immiscible liquid phases, is adopted to deal with this effluent.2 In China, most coal-gasification plants use diisopropyl ether (DIPE), a low boiling point solvent (boiling point 67 °C), as extraction solvent to remove most phenols from their effluents. Then a biological treatment follows to clean the effluents. However, it is not a easy job. Since the pH value of the typical coal-gasification wastewater is nearly 10, the actual extraction distribution coefficient of the phenols is very low, making the total phenol concentration in the outlet flow still high, up to 1000 ppm, after solvent extraction.4 For example, in the China Harbin Coal-Chemicals Inc. plant, the total phenol concentration after the extraction process is about 1200 ppm using DIPE as extraction solvent. After the following biological treatment, the total phenol concentration is finally about 50 ppm, which is far away from the restriction of the Integrated Wastewater Discharge Standard of China (
