3042
Ind. Eng. Chem. Res. 2002, 41, 3042-3043
Adsorption of Oxygenates from Used Transformer Oil Using Surfactant- and Microemulsion-Impregnated Clays A. Cristina M. Silva,† Tereza N. Castro Dantas,† and Eduardo L. Barros Neto† Programa de Po´ s-Graduac¸ a˜ o em Engenharia Quı´mica, Universidade Federal do Rio Grande do Norte (UFRN), Avenida Senador Salgado Filho s/n, Campus Universitario, Lagoa Nova, 59.072-970 Natal, RN, Brazil
Ce´ lio L. Cavalcante, Jr.*,‡ Grupo de Pesquisas em Separac¸ o˜ es por Adsorc¸ a˜ o (GPSA), Departamento de Engenharia Quı´mica, Universidade Federal do Ceara´ (UFC), Campus do Pici, Bl. 709, 60.455-760 Fortaleza, CE, Brazil
This paper presents batch adsorption experimental results for oxygenate removal from used transformer oil using surfactant- and microemulsion-impregnated diatomite as adsorbents. The efficiency of the removal is evaluated by total acidity number (TAN) analysis (ASTM method D-974). TAN results decreased from 0.17 mg of KOH/g to as low as 0.07-0.09 mg of KOH/g for some of the impregnated diatomite samples. Introduction
Table 1. TAN for Used Oil Treated with Surfactant-Impregnated Diatomite
The regeneration of used oil has been done commercially using clays (Fuller’s Earth, Bentonite, and Bauxite) to remove the oxygenates formed with aging of the oil.1-6 Several studies using other adsorbents (e.g., silica gel,7 zeolites,8 and activated carbon9) have not proved to be more efficient than activated clays for oxygenate removal from used spent oil. In a previous study,10,11 we have shown the capacity of Filtrol-24 to effectively remove oxygenates from used transformer oil, bringing the oil sample practically to the same original condition of the fresh oil. Diatomite, largely available in Brazil, is a hydrous form of silica or opal composed of depositional, consolidated skeletal remains of unicellular aquatic plankton. The mineral composition is primarily biogenic silica, detritus, and shale.12 Unfortunately, batch adsorption runs with pure diatomite did not present the same effectiveness of Filtrol-24 for oxygenate removal from used oil.13 Surfactants have been largely studied for selective removal of several metallic cations, such as Cd, Cu, and Cr.14 Microemulsions are thermodynamically stable, isotropic fluid mixtures of water, oil, surfactant, and, in many cases, also a cosurfactant.15,16 In the past few decades, the use of microemulsions in several fields has been the focus of researchers because of their variety of technological applications (e.g., cosmetics, agriculture, food, biomedical applications, metal recovery, enhanced oil recovery, combustion, organic reactions, etc.).17,18 In this paper, we present batch adsorption results for samples of pure diatomite and for diatomite impregnated with surfactants or microemulsions in order to evaluate its effect on their capacity for oxygenate removal from used insulating oil from transformer. * To whom correspondence should be addressed. Tel: (55)(85)288-9611. Fax: (55)(85)288-9601. E-mail:
[email protected]. † Universidade Federal do Rio Grande do Norte. ‡ Universidade Federal do Ceara ´.
adsorbent
surfactant
diatomite diatomite diatomite diatomite diatomite diatomite diatomite diatomite diatomite
ammonia diquaternary alkyl chloride Amide-60a Tween-80a Tween-20a lauryl ether sodium sulfate polyethoxylated nonylphenol N-101a
a
type of TAN surfactant (mg of KOH/g) cationic cationic cationic nonionic nonionic nonionic nonionic nonionic
0.16 0.16 0.11 0.07 0.35 0.26 0.21 0.20 0.14
Commercial brand names.
Experimental Section The original adsorbent employed in this study was crude diatomite, from Ceara´-Mirim, RN, Brazil, calcinated at 980 °C and then ground in a ball mill. Its chemical composition was 1.90% Al2O3, 72.70% SiO2, 0.48% Fe2O3, 0.08% TiO2, 0.32% CaO, 0.15% MgO, 2.00% Na2O, 0.11% K2O,
