Improved Extraction Procedures for Coal Products Based on the Soxtec Apparatus

Soxtec, a medium-cost extraction apparatus, was tested against classical Soxhlet extraction applied to coal and coal-derived products. An optimization study of Soxtec operating conditions for our samples led to a reduction of 90% in the total extraction time needed by Soxhlet, with a comparable repeatability of results and similar extraction yields. As Soxtec and Soxhlet share a common set of general operating conditions, product composition is very similar, and most of the differences can be explained in terms of the increased efficiency of Soxtec, probably due to a better mass transfer. A multistep extraction procedure was also studied. Keeping most of the advantages of single-step Soxtec extraction, it also solves some of its problems (mainly the possibility of saturation) and provides some kinetic data to assess the completeness of the extraction. The enhanced speed of Soxtec also makes it possible to carry out sequential extraction of coal-derived products. Although this work was devoted to coal-derived products, these procedures should be applicable to other kinds of samples as well.