Resource Recovery From Oily Sludge Through Thermal Treatment Technology

Oily sludge is one of the main solid waste generated from the petroleum extraction,transportation,storage and processing.It contains large quantities of petroleum hydrocarbons,benzene,phenol,polycyclic aromatic hydrocarbons(PAHs),heavy metals and other toxic substance,solid particles,various chemical agents,microorganism,pathogens and so on.Thus,oily sludge has been defined as hazardous waste in many countries.In general,petroleum hydrocarbons account for 30-70%in oily sludge,which leads to extensive attention on resource recovery of oily sludge.In oily sludge,the emulsion composed of water,oil and solid particles is in stable state,so this results in inefficiency of centrifugation.Besides,the application of chemical agents increases the cost of treatment and are toxic to environment.The resource recovery methods based on heat treatment could get specific products and reduce solid residue significantly.The primary aim of this paper is to study the influcence of operation conditions during treatment process,to improve the efficiency of resource recovery treatment.Besides,new methods were proposed to utilize the heavy components(asphaltenes and resins)contained in oily sludge.The heavy components were used as raw materials for acitve carbon production.Firstly,two-stage catalytic pyrolysis was applied for the generation of hydrogen enriched syngas.Alkaline dolomite was chosen to be catalyst,and the main products were H2 and CH4.The results showed that the gas yield of catalytical pyrolysis was 13 times higher than that generated without catalyst,and the concentration of H2 was 38.9%.The performance of dolomite was enhanced by higher catalytic temperature.Mechanical impurities contained in oily sludge were dominant for gas products.After the removal of solid particles,the yield of hydrogen increased to 280 L/kg,and the concentration reached up to 70.7%.Temperature-programmed pyrolysis was adopted for production of aromatic compounds.Low heating rate favored the production of liquid product and inhibited the formation of gaseous products simultaneously.The reaction kinetics of the pyrolysis accords with Doyle equation.ZSM-5 zeolite molecular sieve which is an acid catalyst was applied.The catalytic pyrolysis was conducted on a two-stage fixed bed reactor.The ZSM-5 zeolites showed strong catalytic activity,and the aromatics yield reached up to 93.37%.The main component of the pyrolysis oil is naphthalenes,which accounted for 75.4%.The Si/Al ratio of zeolites,dosage of catalyst and residence time would affect the yield and composition of aromatic products.High Si/Al ratio means weak acidity,and this would result in lower aromatics yield.Higher dosage of catalyst and longer residence time promoted the aromatization reaction,and led to higher aromatics yield.In addition,more bicyclic aromatic hydrocarbons were generated.Carbon deposition,which can be removed by calcination in oxygen,is the main reason of catalyst deactivation.The deactivated zeolites can be regenerated and no framework demage or change was caused by regeneration process.Moreover,the regenerated zeolites showed comparable catalytic activity for aromatization.To produce activated carbon materials from oily sludge needs adjusted method.De-oiling procedure was applied as pretreatment process to concentrated the asphaltene.Then activated carbons were obtained after carbonization and activation by KOH.The highest specific surface area of AC products was 3292 m2/g which is nearly three times of AC product derived without de-oiling procedure.The pore size distribution of ACs was rather narrow,and the microporosity is higher than 80%,representing a microporous material.The AC products showed excellent adsorption capability,the methylene blue adsorption capacities reached up to 949 mg/g,and this is much higher than that of commercial wooden based AC.In addition,there were abundant oxygen-containign functional groups adhered at the surface of ACs.The results showed the feasibility of activated carbon preparation from oily sludge.Rice husk was mixed with oily sludge to improve the yield and quality of activated carbons.It is supposed to combine the advantages of these two raw materials via mixing fossil material and biomass.The results showed that the AC products possed large specific surface area of 2575 m2/g and a complex structure.The highest MB adsorption capability was 757.58 mg/g,and the adsorption isotherm can be described by Langmuir model.The microporosity decreased to 65%,proximately,demonstrating a micro-mesoporous carbon material.Moreover,the yield of ACs from the mixture was observably increased.The conclusion is significant for activated carbon preparation from oily sludge.