5. Bleaching
Bleaching or decolorizing applications can be applied using clay. Bleaching process is physical adsorption by weak bonds between the dark coloured compounds in oil and the clay adsorbent . Bleaching by clays can be used for some oils and chemicals industries such as :
- Mineral oils for special applications such as transformer oils, turbine oils and medicinal white oils;
- Paraffin and waxes using in the food industry;
- Regeneration waste oils for re-refined lubricating oils;
- Rolling oils used as lubricants;
- Removal of bituminous substances from mined crude sulfur in a refining process;
- Removal of olefin hydrocarbons from aromatic hydrocarbons such as benzene, toluene, and xylene.
Used oil bleaching can be occurred using raw bleaching clay, activated bleaching clay, amorphous silicates and activated carbon. Bentonite clay has a high bleaching potential, it is mostly used to remove the color and smell of the product. Clay is recovered and can be used as filler in asphalt, bituminous mixture and cement industry. Bleaching capacity of different types of clays can be enhanced by many methods in an efficient and economical way. Thermal activation can be used to activate bauxites, bentonite and palygorskite-sepiolite clays.
Acid activation of clays was reported by several researchers. Acid activation can be affect the physicochemical properties of bentonites and galuconite. It was concluded that acid bentonite clays are usually used as oil bleaches, which can favor the adsorption of aromatic color compounds and decrease the adsorption of others compound, mainly naphthenic acids and sulfur compounds.
Karim et al., compared various types of clays for decolorizing dark lubricant oils. They concluded that the local clays (yellow bentonite, brown bentonite) need acid activation treatment to improve their decolorizing ability, because their decolorizing efficiency was lower than activated China clay and Iranian clay. On the other hand, Kaolin was efficient for bleaching lubricating oils, according to its decolorizing power and can be considered as good bleaching clay. The surface area of smectites or bentonites increased several times larger after the acid activation, for about 200 to 300 m2/g, resulting that the acid-activated clays is used to adsorb the coloring matter dissolved in oil. Aziz et al., characterized and used different types of clays as bleaching earth for the decolourization of acid treated and untreated used lubricating oil. Best results of decolourization obtained using local acid activated clay. Freundlich isotherm was more applicable than Langmuir isotherm by the different clays for the decolourizing of used lubricating oil.
6. Heavy Metal Removal
Catalyst deactivation and adverse effects on the economy of crude oil refining can be occurred in the presence of heavy metals in crude oil. Clay adsorption can be played significant role in the elimination of heavy metals. It was found that several modified as well as unmodified clays give the highest removal efficiency of Ni and V from crude oil. Kukwa et al., studied the kinetics of adsorption removal of Ni and V from crude oil using NH4Cl modified primitive clay. The removal percentage of metals increased with the increasing of adsorbent dosage and contact time. The result fitted the Lagergren’s pseudo second order kinetics model higher than the Lagergren’s pseudo first-order model. Modified primitive clay is therefore competitive among low cost adsorbents that can be used for Ni and V elimination from crude oil. Oduola and kwonna studied the removal of heavy metals and trace elements from waste lubricating oil by acid activated Ukpor clay as an adsorbent. The best adsorption removal of metals obtained using 2 mol/L concentrations of sulfuric acid to activate the clay. The initial concentrations of Ca, Pb, Zn and Ba were 804, 398, 222 and 0.1 mg/L and reduced to 3.6, 5.6, 0.01 and 0.01 mg/L, respectively.
7. Corrosion Reduction
Naphthenic acids (NA) contribute to the acidity of crude oils and one of the main aggressive compounds present. NA are the major sources of corrosion in the oil refinery equipments such as pipelines and distillation units. Additionally, the higher concentrations of NA in crude oils reduce the quality and market at a lower price. Silva et al. studied the reducing of corrosion by removing NA from a light petroleum fraction using two commercial adsorbents (clay and activated alumina). Both adsorbents proved a high reduction of the total acid number (TAN) in the residual oils. It was observed that the adsorption of acid composites of the oil significantly influenced by the thermal pre-treatment of clay. Additionally, the pre-treatment by adsorption affected the reduction in corrosion yields and the corrosion rate of the mild steel cupons decreased in the residual oils originated from the adsorption processes for both adsorbents. Xiaohui et al., studied the adsorption of NA from dewaxed vacuum gas oil during lube base oil refining using a commercial grade activated clay. The results show that the Dubinin-Radushkevich isotherm fitted a better experimental data than other isotherms and the kinetics of adsorption followed the pseudo-first order kinetic equation. The thermodynamic data evidences that the adsorption process was possible as an endothermic process. The results could explain that the NA adsorption can be occurred during lube base oil processing at refineries by activated clay. NA separation from sour crude oil was studied through adsorption of the acid using local activated clays. Results show that the ability of Muscovite clay to reduce TAN of sour crude oil and to remove NA was higher than the Ziolite clay. Clay activation by alkali was recommended to reduce the cost of activation process, because the price of NaOH is much less than that of H2SO4.
"to be continued in the next part"