SIMULTANEOUS REMOVAL OF ALKYLPHENOLS AND OILS IN SIMULATED PRODUCED WATER BY UV/MW/FENTON-LIKE PROCESS USING A NOVEL SURFACE FUNCTIONALISED HETEROGENEOUS PAN CATALYST

Owing to post treatment challenges of managing Fe(OH)3 sludge associated with classical Fenton catalysis, this research applies a heterogeneous Fenton-like catalysis for the treatment of produced water from oil mining. The catalyst is a surface functionalized fibrous heterogeneous polyacrylonitrile (PAN) catalyst developed at De Montfort University. This catalyst has been used in the decontamination of simulated produced water (PW) for the oxidative degradation of alkylphenols and oils. In addition to being endocrinal disruptors, alkylphenols (AP) constitute the most toxic component of PW. They are primarily of petroleum origin and are thought to partition into the water phase during petroleum mining. Out of about 116 million m3 of PW discharged into the Norwegian sector of the North Sea, APs account for 323 tons of which 90% are C1 to C3 short chain alkylphenols (SCAPs). These SCAPs are amongst the most stable constituents of PW and are responsible for PW toxicity. Batch and continuous flow experiments using the PAN catalyst in a hydrogen peroxide system, PAN catalyst assisted by ultraviolet (UV) radiation, PAN catalyst assisted by microwave (MW) and PAN catalyst assisted by both UV and MW in a Fenton-like system was used for the oxidative decomposition of synthetic PW. Parameters monitored were; loss of 3,5-dimethyl phenol (DMP) which is a model alkylated phenolic compound, COD removal, and oil-in-water removal. A catalytic oxidative reaction of 200 mL simulated PW was carried out in batch mode, while 900 mL was used in a rotating disc flow reactor for the continuous flow experiments, where the influence of initial H2O2 concentration, catalyst concentration, bubbling air flow rate, variation in UV flux density, effect of competing inorganic anions, etc. were investigated. Results for the unassisted Fenton-like catalysis of PW in batch mode at optimum conditions showed 94% AP removal and up to 30% COD removal after 4 h, while oil- in- water concentration was reduced by 85.8%, although 50.3% of the lost oil was absorbed onto the catalyst. The UV- assisted catalytic oxidation (irradiance of 2.66 mW/cm2) resulted in > 99% AP degradation after 40 min, and 59% COD removal after 4 h, while the oil- in- water concentration was reduced down to non-detectable levels, with 8.78 mg/L oil (which constitutes 5.67% of initial concentration) adsorbed on the catalyst. The results of the unassisted Fenton-like continuous flow experiments at optimum conditions showed ~ 10% COD removal, ~ 90% average DMP degradation, and about 50% average OIW removal in 4 h retention time. The UV/MW/Fenton-like assisted continuous flow process at optimum experimental conditions, recorded an average of 31% COD removal, >99% OIW removal and >99% DMP degradation. Thus, assisting the reaction with UV/MW resulted in a more extensive as well as a quicker decontamination of produced water. Intermediate oxidation products tentatively determined from the catalytic oxidation of DMP include benzoquinones, hydroquinones, benzaldehydes, formic and acetic acids. The cause of catalyst deactivation after about 30 days of reaction was suspected to be due to loss of Fe through leaching and catalyst poisoning. The reaction is thought to be 87% heterogeneous route (including adsorbed component), as leached Fe contributed about 13% to the loss of DMP through a homogeneous route.