(14)--12、机械压榨法和超临界流体萃取法制取油脂.ppt
Chapter 4 Vegetable 0ils Processing and Refinement知识点知识点1 机械压榨法和超临界流体萃取机械压榨法和超临界流体萃取法制取油脂法制取油脂2Hard pressing,or，Mechanical pressing(Hard Screw Pressing)（螺旋压榨）（螺旋压榨）The oldest oil recovery method is hard pressing（压（压榨）榨）,where the seed is pressed,usually after various pretreatments to enhance oil recovery,to squeeze（榨取）（榨取）the oil from the solids known as cake.Hard pressingHard pressing3FIGURE4 Depiction of hard screw pressing.定量料仓定量料仓锤式磨或辊式磨锤式磨或辊式磨蒸炒干燥器蒸炒干燥器螺旋榨油机螺旋榨油机过剩料储料罐过剩料储料罐热交换器热交换器澄油罐澄油罐oilseeds4If proper cooking methods are employed,in conjunction with a well-maintained,modern,screw press,a slow as 3%4%residual oil content can be achieved.Many screw press plants are quite small and do not optimally,if at all,flake,cook,and dry before screw pressing;so as much as 6%10%oil often remains with the cake.Hard pressingHard pressing5A screw press（螺旋压榨机）（螺旋压榨机）(Figure 6)is basically a continuous screw auger（螺杆）（螺杆）designed to accept feed material and subject it to gradually increasing pressure,as it is conveyed through the barrel cage（榨膛）（榨膛）.The barrel（桶）（桶）is composed of bars（齿）（齿）surrounding the screw（螺杆）（螺杆）and oriented parallel to the screw axis.The bars are separated by spacers decreasing in size toward the solids discharge end,which allow the oil to drain.A plug（拴）（拴）of compressed oil-lean solids,the cake,forms at the discharge end（排出端）（排出端）.Hard pressingHard pressing6FIGURE 6 Screw press principles,practice,and machinery.(压)滤饼加料斗进给蜗杆蜗杆轴7Supercritical Fluid ExtractionSupercritical Fluid ExtractionWhen carbon dioxide is compressed at a temperature(31.1)and pressure(72.9 atm)above its critical point,it does not liquify but attains a dense gaseous state that behaves like a solvent.Thus,it is called supercritical CO2(SC-CO2).Use of SC-CO2 for lipid extraction significantly reduces the use of organic solvents,avoids waste disposal problems,eliminates the use of potentially toxic and flammable solvents,and reduces the extraction time.89Supercritical Fluid ExtractionSupercritical Fluid ExtractionExtraction using SC-CO2 yields a good recovery of nonpolar lipids including esterified fatty acids,acylglycerols（甘油酯）（甘油酯）,and unsaponifiable matter.Complex polar lipids are only sparingly soluble in SC-CO2.The polarity of SC-CO2 can be varied by using an entrainer（夹带剂）（夹带剂）or modifier such as methanol,ethanol,or even water to improve the extraction of polar lipids.10Supercritical Fluid ExtractionSupercritical Fluid ExtractionThe SC-CO2 extraction is able to recover 97%100%of lipids when compared with the conventional solvent extraction methods.For canola（加拿大油菜）（加拿大油菜）and flaxseed（亚麻子）（亚麻子）a modifier ethanol(15%,v/v)and multiple extractions are needed to obtain similar values of oil content on exhaustive solvent extraction（极限溶剂提取）（极限溶剂提取）with petroleum ether.The main drawback of SC-CO2 is equipment cost and the extraction of nonfat materials,such as water.
