Wiped-wall molecular still

Distillations. The upgraded coal liquids were distilled with a metal-mesh-spinning-band still under the conditions shown in Figure 1 to produce cuts at 200°, 325°, and 425° C. Asphaltenes were then precipitated from each >425° C residuum dissolved in benzene by addition of 50 volumes of normal pentane (15). Further distillations on the asphaltene-free materials, at 202° C and 4 micron pressure using a wiped-wall molecular still, produced 425° to 540° C distillate cuts and residua fractions. 

As desirable products have similar molecular weights (ethyl docosahexaenoate is 356, and ethyl eicosapentaenoate is 330), it is clear that this type of fish oil product cleanup is best done at the oil stage to avoid losses at the same time as contaminant removal, which is carried out as described above. However, dimers and/or other polymeric and/or colored materials may be left behind if wiped wall equipment is used in its capacity of a simple and inefficient short-path still for the ethyl esters only. This process will produce a water-white distillate product. Regrettably, it is not an efficient way to separate ethyl-EPA from ethyl-DHA. 

A more recent test method (ASTM D-5236) is seeing increasing use and appears to be the method of choice for crude assay vacuum distillations. Wiped-wall or thin-fihn molecular stills can also be used to separate the higher-boiUng fractions under conditions that minimize cracking. In these units, however, cut points cannot be directly selected because vapor temperature in the distillation column cannot be measured accurately under... 

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