Circulation Utilization Of Spent Bleaching Clay From Bleaching Of Oil

In this paper, we studied the circulation utilization of spent bleaching clay frombleaching of oil. Firstly, the condition of removing residual soap in soybean oil alkali refiningprocess was studied with spent bleaching clay as adsorbent. Secondly, the method andcondition of regeneration of spent bleaching clay detailedly researched in this experiment,and the bleaching conditions of oil by regenerated clay was also studied. Finally, according tothe analysis of adsorption isotherm and structure of regenerated clay, we make a tentativediscussion on the adsorption mechanism of regenerated clay in the edible oil bleachingsystem.The result of removing residual soap in soybean oil alkali refining process indicated thatshort time saved spent bleaching clay has a strong ability to remove residual soap. Based onthe single-factor experiment, the orthogonal test determined the optimum conditions were asfollows: temperature80℃, spent bleaching clay0.5%, time20min. Under these conditionsthe content of residual soap in alkali refined soybean oil can be decreased from355.12mg/Kg to29.09mg/Kg, and the rate of removing soap from oil could reach91.81%, betterthan that by traditional method.The regeneration methods of spent bleaching clay was researched, and the method ofcalcine-acidification was determined as better regeneration method of spent bleaching claycompared with calcination, and the optimum temperature was detemined as500℃. Based onthis temperature, the process conditions of acid activation were optimized by response surfacemethodology, and a mathematical mode of a second order quadratic equation was developed,and the optimum conditions were as follows: sulfuric acid volume fraction6.70%,acidification temperature55℃, liquid-solid ratio3.2:1, acidification time60min. Underconditions above, the bleaching efficiency of the regenerated clay was94.82%, higher thanactivated clay (92.19%).Experiments on the bleaching of oil using the regenerated clay were performed, and theresult showed that regenerated clay has strong adsorbability. The bleaching conditions of oilwere optimized by the response surface methodology, and a mathematical mode of a second order quadratic equation was developed，then the optimized technological parameters were asfollows: bleaching temperature95℃, regenerated clay5.9%, bleaching time21min. Underthese conditions, the bleaching efficiency of the regenerated clay was95.28%, higher thanactivated clay (94.83%). In addition，the solvent extraction combined with HG-AAS wasdeveloped to determine the content of arsenic in oil and clay, and results indicated that thecontent of arsenic in regenerated clay was0.191mg/Kg，which is distinctly lower than that ofactivated clay(0.222mg/Kg), and the content of arsenic of oil bleached by regenerated claywas only11.48μg/kg, which is similarly lower than that by activated clay(12.06μg/kg).The study of adsorption mechanism of regenerated clay in the edible oil bleachingsystem indicated that the adsorption of Pigment composition by regenerated clay of oilbleaching tests showed an adsorption curve fit to the Freundlich isotherm, and the Freundlichisotherm equation was: y=0.498x+0.1859. What’s more, this adsorption belonged to themonolayer adsorption, and existed competitive adsorption of other adsorption properties.Based upon, we also analysised the structure of regenerated clay, and combined with theadsorption mechanism of activated clay, then results indicated that the whole absorptionprocess includes physical adsorption and chemical adsorption. The physical adsorption wasmainly caused by the adsorption of macromolecular organic matter by porous structure, andthe chemical adsorption was mainly caused by charge neutralization and catalyzed oxidationreaction of oil on the surface of regenerated clay.