Process for the continuous removal of undesirable components of solid particles by a solvent applied in counterflow

Claim 1

A process for the removal of undesirable soluble contaminants from solid particles by passing a solvent for the contaminants through a bed of the contaminated solid particles, the process comprising the following sequential steps: (1) charging the contaminated solid particles into the upper end of a column of solvent by way of an upper decanter zone which has a greater diameter than that of the solvent column; (2) adding solvent to the solvent column near its lower end and causing the solvent to move at a predetermined rate upwardly, thereby causing the contaminated solid particles in the solvent column to form an expanded bed, (3) removing solvent with dissolved contaminants therein from the upper decanter zone, (4) measuring the concentration of the contaminants in the solvent in the solvent column at at least one point along the length of the solvent column, (5) stopping the charging of contaminated solid particles to the top of the solvent column and the adding of solvent to the base of the solvent column when the concentration measured in step (4) equals a predetermined level, (6) adding solvent to the solvent column near its upper end and concurrently removing a section of the bed of solid particles from the lower end of the column for a predetermined time period, (7) at the conclusion of said predetermined time period, stopping both the supply of solvent to the upper end of the solvent column and the removal of solid particles from the lower end of the solvent column, and (8) repeating steps (1)-(7).