Development And Application On The Removal Technology Of Emulsified Oil From Coal Chemical Wastewater

China’s energy structure,which is characterized by a shortage of oil and gas but an abundance of coal,underscores the critical role of coal in driving economic growth and ensuring energy security.However,the challenge of effectively removing emulsified oil from coal chemical wastewater poses a significant obstacle to achieving continuous and stable operations in subsequent treatment units.This issue not only hinders the clean and efficient utilization of coal in China but also has broader implications for the country’s overall sustainability goals.It is imperative to explore the mechanisms behind the stabilization of oil emulsions in coal chemical wastewater.By doing so,we can develop a cost-effective and efficient technology to remove oil from wastewater,thus addressing a common issue in the coal chemical industry.This paper provides an analysis of the composition,characteristics,and existence of emulsified oil in coal chemical wastewater firstly.It also explores the mechanism of oil-water system stability.The study reveals that emulsified oil is composed of various organic compounds,including alkanes,benzenes,olefins,ketones,and naphthalenes.The percentage of alkanes in coal chemical emulsified oil is approximately 50 wt%,significantly lower than the over 80 wt%found in petroleum wastewater.This difference is a crucial factor in the relatively small disparity in oil-water density observed in coal chemical wastewater.Furthermore,coal chemical wastewater tends to be weakly alkaline.The stability of emulsified oil in coal chemical wastewater can be attributed to the reduction in oil-water interfacial tension resulting from an increase in p H value.This reduction in tension facilitates the breakdown of oil droplets into smaller droplets.Additionally,the larger absolute value of Zeta potential enhances the stability of the oil-water system.These factors combined contribute to the stable existence of emulsified oil in coal chemical wastewater.Then,various modified fibers were prepared with PP and PE as raw materials,and PVDF and PTFE as modifiers.A new emulsified oil removal technology was proposed based on the fibers,combining with the conceptual design and cost feasibility analysis in industry.The results showed that the WCA of modified PP-PVDF-5 increased from84.80^o to 103.71^o.The oil removal efficiency of PP-PVDF-5 fiber reached 92.24%for simulated wastewater,and the oil removal efficiency reached 81.10%for real coal chemical wastewater.The oil content of the effluent reduced to～380 ppm,which could meet the requirements of the subsequent process.The treatment cost per ton of wastewater was as low as 0.204 RMB,which saved the industrial cost.It is worth mentioning that the study for the first time derived an equation to calculate the underwater oil contact angle with Young’s equation and Antonov’s rule.The underwater oil contact angle of PP-PVDF-5 decreased from 70.36^o to 34.89^oby calculating,which is consistent with the actual situation.This formula can provide quantitative guidance for material modification.In order to solve the problem of high-water content in coal tar due to low oil-water interfacial tension,a new PTM composite membrane was prepared by loading MWCNTs and Ti O₂ onto PVDF,and the membrane was used to remove water from coal tar.The result showed that PTM has near-superhydrophobicity and superlipophilicity.It has good flux for typical oil components of coal tar.The separation efficiency for a variety of oil-water mixtures was over 98%.The separation efficiency for simulated coal tar reached 85.76%,and the water content of simulated coal tar reduced from 25.00%to5.75%.This indicates that PTM had good application potential in solving the problem of high-water content coal tar dehydration.