Solids formation following expansion

Reality is often quite different. When a supercritical fluid mixture expands into pressures as high as ambient conditions, the resultant expansion plume can be a complex mixture it is a high velocity gas stream that entrains precipitated particles of extracted materials and often frozen carbon dioxide. Much adjustment needs to take place in the collection zone in order to achieve something close to 100 % recoveries of solutes with concentration ranges from parts per billion (PCBs) up to 50 % (total fat in a chocolate candy). Besides the flow dynamics of the expansion, several physicochemical parameters cause the deviation from the initial simple model. They include, but are not limited to, volatility of the solute, degree of co-precipitation of solid carbon dioxide (followed almost immediately with uncontrolled subhmation of the solid), aerosol formation, surface tension, occlusion in solid carbon dioxide, rebound from impinging surface, and many other interacting phenomena. 

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