8. Waste Oil Recovery
Waste oil is considered a valuable and an important resource of energy. Waste oil is recovered using several techniques including chemical technique (acid/clay), physical technique such as distillation, thin film evaporation and solvent extraction. One of the important technique for refining and recovery waste oil is adsorption using several adsorbents.
The re-refining of waste lubricating oil using acid activated Ukpor clay as an adsorbent was investigated. The best performance of adsorption on the waste lubricating oil was achieved with activated clay using 2 mol/L concentrations of sulfuric acid. The performance improvement of the acid activated clay may be according to the increasing of their surface area and large pore volume. The results indicate that adsorption using acid activated clay improved the physico-chemical properties of the lubricating oil by enhancement density, viscosity, pour point, flash point, and decrease TAN, moisture and sulfur content. The best kinetic data was fitted by the Pseudo-second order kinetic model. On the other hand, adsorption treatment using sm400 activated clay as an adsorbent was studied to restore the physico-chemical parameters of the used transformer oil. Results show that the used transformer oil was purified, but its quantity decreased during adsorption. Additionally, treated oil was eco-friendly and had green chemistry uses.
Many studies investigated the recovery of waste oils using acid/clay treatment. In this technique waste oil is treated with strong acid and followed by clay adsorption. Abu-Elella et al., studied the treatment of waste engine oils using four different acids (sulfuric acid, phosphoric acid, acetic acid and formic acid) followed by clay earth adsorption treatment. The results show that the formic acid followed by clay treatment improve the flash point of the treated oil. Additionally, the kinematic viscosity improvement of the oil was achieved by comparing with fresh engine oil using the sulfuric acid, acetic acid and formic acid followed by clay treatment. On the other hand, the phosphoric acid-clay treatment has no significant action on the kinematic viscosity and flash point of the treated oil. Josiah and Ikiensikimama studied the effect of the acid desludging and the activated clay adsorption ratio from the recovery of waste engine oil. The recovery increased by increasing the ratio with a maximum recovery of about 83%.
Other studies investigated to recover waste oils by comparing between various techniques. The most re-refining techniques of waste oil used as the following: firstly, pre-treatment using filtration or heat, then i) either vacuum distillation followed by hydrogen finishing or clay treatment, ii) solvent extraction followed by clay treatment and iii) chemical treatment followed by hydro-heating. Udonne compared different recovery techniques of used lubrication oils: acid-clay, distillation-clay, acid treatment and activated charcoal-clay, and concluded that the viscosity improved from about 25.5 cs for used lubrication oil to about 86 cs, 89 cs and 81 cs of treated oil for distillation, acid/clay treatment and activated/clay treatment, respectively. Ahmad et al., reported about the obtaining of useful fuel-like products through the conversion of spent lubricating oil using prebaked clay as adsorbent followed by pyrolysis over coal ash as catalyst. The results show that the using of coal ash in low concentration evidenced good activity and selectivity toward the liquid pyrolysates formation having fuel value comparable with diesel fuel.
Solvent extraction followed by adsorption treatment was found to be one of the competitive techniques for the recovery of waste oil. Emam and Shoaib compared two techniques for recovery of waste oils collected from different sources. First technique was solvent extraction followed by clay treatment and the second technique was acid treatment followed by clay-percolation. Also, treated oil characteristics were compared with virgin base oil. The results show that a best characteristics quality of the treated oil was obtained using acid/clay-percolation and a higher yield of about 83% was achieved using solvent extraction/clay treatment. Mohammed et al., evaluated the performance of six extracting solvents, followed by adsorption treatment using different adsorbent materials (such as almond shell, walnut shell, eggshell and acid activated clay) to treat waste lubricants. Acid activated clay treatment provided the best results of treated oil. The properties of waste oil were changed by acid activated clay treatment as the following: the increasing of viscosity and flash point were from 38.3 cst and 178°C to 85 cst and 238°C, respectively, whereas, the decreasing of density, pour point and colour were from 912 kg/m3, -6°C and 0.53 to 896 kg/m3, -13.2°C and 0.12, respectively. Daham et al., reported the specifications of the two types of base oil recovered using solvent extraction (MEK and 1-butanol) followed by activated bentonite clay adsorption as the following: viscosity at 100°C 8.3, 9.2 cSt, flash point 210, 223°C, pour point -17.4, -22.2°C, TAN 0.25, nil, color 3.0, 2.5 and ash 0.03, 0.002, respectively.
9. Conclusions
Clays are played an important role in petroleum refining industry. Clays are very efficient and economical sorbents according to their properties. Different types of clay such as bentonite, attapulgite, hectorite, kaolin and sepiolite are obtainable and used in different applications. Adsorption is very important process in petroleum industry. Clay adsorption plays an important role in the treatment and finishing of crude oils and petroleum fractions through desulfurization, deasphalting, bleaching, corrosion reduction, heavy metals removal, waste oil recovery and other. Additionally, clay modifications through metals impregnation, acid and thermal activations, etc. can be enhanced the adsorption treatment and finishing of crude oils and petroleum fractions.