Recent Approaches, Catalysts and Formulations for Enhanced Recovery of Heavy Crude Oils

Crude oil deposits as light/heavy form all over the world. With the continued depletion of the conventional crude and reserves trending heavier, the interest to maximise heavy oil recovery continues to emerge in importance. Ordinarily, the traditional oil recovery stages leave behind a large amount of heavy oil trapped in porous reservoir structure, making the imperative of additional or enhanced oil recovery (EOR) technologies. Besides, the integration of downhole in-situ upgrading along with oil recovery techniques not only improves the efficiency of production but also the quality of the produced oil, avoiding several surface handling costs and processing challenges. In this review, we present an outline of chemical agents underpinning these enabling technologies with a focus on the current approaches, new formulations and future directions

Zinc Oxide-Catalysed Photo-Oxidative Degradation of Chlorophenols

Chlorophenols are priority pollutants that must be eradicated from the environment owing to the severity of their toxicity and resistance to traditional treatment. Photocatalytic oxidation is an advanced oxidation method which has proven reliability to eliminate persistent pollutants from air and water. The activity of zinc oxide for pollutant removal by photocatalytic oxidation has been well established. In this work the photocatalytic transformation of 4-chlorophenol, 2,4-dichlorophenol and 2,4,6-trichlorophenol in irradiated ZnO suspensions at 299 K was studied. The effect of operating parameters such as catalyst and concentration doses on the decomposition rate of these para-chlorinated compounds has been investigated and optimised. It was discovered that the optimum feed concentration for the phenolic compounds is 50 mg L-1. The optimum amount of ZnO was determined for the degradation of 4-chlorophenol, 2,4-dichlorophenol and 2,4,6-trichlorophenol which decreased as with increasing of chlorine substituent. For 4-chlorophenol degradation the first clearer description of the effect of doses using response surface was reported. Kinetic profiles on the decomposition of chlorophenols over ZnO were consistent with pseudo-zeroeth order rate scheme. For 2,4-dichlorophenol and 2,4,6- trichlorophenol the decomposition was slow at the short irradiation time. It was found that the degradability of chlorophenols increased as the number of ringchlorine increased. The effect of pH on the destruction rate was found to be influenced by chlorophenol adsorption and dissociation equilibrium. The effect of different anions on the rate of chlorophenol degradation was evaluated by utilising sodium salts as additives. Except for 4-chlorophenol it was found that, inorganic anion additives such as SO4 2-, S2O8 2- and Cl- demonstrated inhibition to the decomposition rate of chlorophenol. HPO4 2- was found to show strongest inhibition and could even hamper the degradation of 4-chlorophenol. The progression of intermediates during the mineralisation of chlorophenols was chromatographed on high performance liquid chromatograph (HPLC). The structure elucidation of pathway products en route to mineralisation of chlorophenols was performed by the combined gas chromatography-mass spectrometry (GC-MS) and HPLC methods. The study disclosed some hitherto unreported intermediates of photocatalytic decomposition of 4-chlorophenol and 2,4-dichlorophenol. Catechol was detected as new intermediate of 4-chlorophenol degradation. Similarly, 4- hydroxybenzaldehyde, benzoquinone and 4-chlorophenol are for the first time reported for 2,4-dichlorophenol degradation. The work also revealed the intermediates of 2,4,6-trichlorophenol which have not been in literature. It is highlighted herein the mechanism of formation of all pathway intermediates

Comparative analysis of ZnO-catalyzed photo-oxidation of p-chlorophenols

The present study compares for the first time the photocatalytic oxidation of three p-chlorophenols (4-chlorophenol, 2,4-dichlorophenol and 2,4,6-trichlorophenol) in irradiated ZnO suspensions. The effect of operating parameters such as catalyst and concentration doses on the decomposition rate of these p-chlorinated compounds has been studied and optimized. The optimal feed concentration for each of the chlorinated phenolic compounds is 50 mg/L whereas the ZnO doses decreased as the number of chlorine substituent is increased. Kinetic profiles on the decomposition of chlorophenols over ZnO agreed with the pseudo-zeroeth order rate scheme with rate constants following the order 2,4,6-trichlorophenol > 2,4-dichlorophenol > 4-chlorophenol. The validity of the pseudo zero order model could be linked to the initial doses of the chlorophenols used vis-à-vis the catalyst. The study revealed stable intermediates of photocatalytic chlorophenol transformation by high performance liquid chromatography (HPLC) and gas chromatography-mass spectrometry (GC-MS) technique. A combined mechanism is given to account for the photocatalytic destruction of the chlorophenols

Optimised Photocatalytic Degradation of Crystal Violet Over 1wt% MgO-ZnO Composite Catalyst

Crystal violet is a member of toxic, environmentally ubiquitous basic dyes that must be eliminated. In this paper, the performance of 1wt % MgO-ZnO suspensions in the photocatalytic degradation of this dye is reported. The catalyst was characterized by x-ray diffraction (XRD) and scanning electron microscopy (SEM). The degradation and mineralization of crystal violet were monitored UV-Visible spectrophotometer and total organic carbon analyzer. The XRD analysis of the catalyst revealed a hexagonal wurtzite structure. The effect of operating variables such as initial crystal violet concentration, catalyst concentration and pH of the solution was optimized using the Box-Behnken design and response surface methodology. The degradation model was statistically remarkable with p<0.0001%. The maximum degradation efficiency of prepared catalyst was found to be 95 %. The degradation kinetics agreed with the Langmuir-Hinshelwood model. However, only 60% of total crystal violet-based organic carbon was removed from the solution due to recalcitrance of this environmentally important compound

Heterogeneous photocatalytic degradation of organic contaminants over titanium dioxide: A review of fundamentals, progress and problems

Even though heterogeneous photocatalysis appeared in many forms, photodegradation of organic pollutants has recently been the most widely investigated. By far, titania has played a much larger role in this scenario compared to other semiconductor photocatalysts due to its cost effectiveness, inert nature and photostability. Extensive literature analysis has shown many possibilities of improving the efficiency of photodecomposition over titania by combining the photoprocess with either physical or chemical operations. The resulting combined processes revealed a flexible line of action for wastewater treatment technologies. The choice of treatment method usually depends upon the composition of the wastewater. However, a lot more is needed from engineering design and modelling for successful application of the laboratory scale techniques to large-scale operation. The present review paper seeks to offer an overview of the dramatic trend in the use of the TiO2 photocatalyst for remediation and decontamination of wastewater, report the recent work done, important achievements and problems

Adsorption of Aqueous Using Granular Adsorbents from Accanthospermum hispendum DC

Granular activated carbons have been important adsorbents for the decontamination of aqueous environmental contaminants. Acanthospermum hispidum weed represents a ready available source of low-cost adsorbents in sub-Saharan Africa that has barely been paid attention. The effects of pH, contact time, concentration, adsorbent dosage, particle size and temperature on the adsorptive removal of Pb (II) from aqueous solutions over activated carbon granules from the thorns of Accanthospermum hispindum (AC-T) were for the first time investigated and compared with those of the leaves (L), the sodium hydroxide modified thorns (NaOH-T) and regular thorns (T) of this plant. These adsorbents were characterised by the surface charge analysis, scanning electron microscopy (SEM) and the Attenuated Total Reflectance Fourier Transform infrared (ATR FTIR) spectroscopy. The SEM revealed a wafer-like appearance for the AC-T with a large distribution of open pores. The adsorption data of lead uptake onto the adsorbents were examined using two pseudo-order kinetic schemes and three isotherm models. To fully understand the adsorption capacities of the adsorbents, batch desorption recoveries were studied. The FTIR depicted the various functionalities responsible for the adsorption. Adsorption over AC-T was found to agree with pseudo second-order kinetic scheme, the Langmuir and Freundlich isotherm. This material exhibited the highest adsorption capacity. The order of reusability of the adsorbents is T < AC-T < NaOH-T

Adsorption of aqueous Cd(II) and Pb(II) on activated carbon nanopores prepared by chemical activation of doum palm shell

Non-uniformly sized activated carbons were derived from doum palm shell, a new precursor, by carbonization in air and activation using KOH, NaOH and ZnCl2. The activated carbon fibres were characterised by X-ray diffraction, N2 adsorption-desorption, scanning electron microscopy, particle size analysis and evaluated for Cd(II) and Pb(II) removal. The 40-50 nm size, less graphitic, mesoporous NaOH activated carbon yielded high adsorption efficiency, pointing largely to the influence surface area. The performance of the KOH based activated carbon was arguably explained for the first time in terms of crystallinity. The efficiencies of the mesoporous ZnCl2-formulated activated carbon diminished due to the presence of larger particles. Batch adsorption of divalent metals revealed dependence on adsorbent dose, agitation time, pH and adsorbate concentrations with high adsorption efficiencies at optimum operating parameters. The equilibrium profiles fitted Langmuir and Freundlich isotherms, and kinetics favoured pseudo-second order model. The study demonstrated the practicability of the removal of alarming levels of cadmium and lead ions from industrial effluents

Mechanochemical Synthesis and Characterization of N-doped TiO2 for Photocatalytic Degradation of Caffeine

The present study reports the synthesis of N-doped TiO2 photocatalyst for the degradation of caffeine using mechanochemical grinding method from the mixture of titania/urea followed by calcination at 400 ⁰C. The phase composition, particle size, surface area, morphology and optical properties were characterized. The XRD results revealed that anatase is dominant and the size of crystal is decreased from 35.8 to 33 nm after mechanical doping. An improved surface area of 42.9 m2g-1 is also reported. The morphology from SEM also showed a uniform yellow-like powder indicating complete dispersion of nitrogen on the TiO2 surface. The prepared sample showed visible-light absorption in the region 430 nm corresponding to band gap energy 2.88 eV, indicating its potential applications as a visible light induced photocatalyst. Photocatalytic oxidation of caffeine were investigated in 300 minutes irradiation time and N-doped TiO2 demonstrated the higher removal efficiency of 97% compared to commercial TiO2 powder with 91% efficiency at the same experimental condition

Photocatalytic degradation of 2,4-dichlorophenol in irradiated aqueous ZnO suspension.

This paper focuses on the destruction of aqueous 2,4-dichorophenol in ZnO suspension irradiated by low wattage UV light at 299 K. The operating variables studied include initial 2,4-dichlorophenol concentration, photocatalyst doses and pH. At 1.5 g l-1 feed concentration of ZnO and 50 mg l-1 initial 2,4-dichlorophenol level, a complete degradation was achieved in 180 min. The decomposition kinetics with respect to 2,4-dichlorophenol approximates pseudo zero-order with rate constant peaking at 0.38 mg l-1 min-1. High performance liquid chromatography (HPLC) and gas chromatography-mass spectrometry (GC-MS) detected benzoquinone, 2-chlorohydroquinone, 4-chlorophenol, 3,5-dichlorocatechol, hydroquinone, 4-hydroxybenzaldehyde and phenol during the ZnO-assisted photodegradation of 2,4-dichlorophenol among which some pathway products are disclosed for the first time. The reaction mechanism accounting for the degradation pathway intermediates is proposed. Inorganic anion additives such as S2O8 2-, SO4 2-, Cland HPO4 2- manifested inhibition against 2,4-dichlorophenol removal

Photocatalytic removal of 2,4,6-trichlorophenol from water exploiting commercial ZnO powder.

2,4,6-trichlorophenol is an important water pollutant owing to the severity of its toxicity. The aqueous phase photocatalytic oxidation of 2,4,6-trichlorophenol over ZnO was investigated as a potential method for the abatement of this pollutant. The effects of operating parameters such as initial ZnO doses and substrate concentration on the removal of 2,4,6-trichlorophenol were studied and optimised at 0.75 g L− 1 and 50 mg L− 1, respectively. The photocatalytic system afforded the highest degradation efficiency at neutral pH. The decomposition of 2,4,6-trichlorophenol by the photoprocess agreed satisfactorily with pseudo zero-order kinetic model. The effect of the presence of SO42−, S2O82−, HPO42− and Cl− on the 2,4,6-trichlorophenol removal rate was for the first time revealed. Some hitherto unreported pathway intermediates of ZnO-assisted 2,4,6-trichlorophenol degradation were recorded using gas chromatography–mass spectrometry (GC–MS) and high performance liquid chromatography (HPLC). A tentative reaction mechanism for the formation of these intermediates was proposed