Process technology is described making possible substantial improvements in the separation and recovery of highly pure vinyl aromatic monomers, notably styrene. A number of design, construction and operational features are made available for selection and use both for new plant facilities and for upgrading existing plant facilities. One major aspect of the invention is reduction in retention or residence times in the distillation towers. In another embodiment, a startup process comprises (i) introducing a feed comprising vinylaromatic monomer, polymerization inhibitor, aromatic hydrocarbon components having boiling points above that of the vinylaromatic monomer to a packed distillation column, said column having a maximum theoretical .DELTA.P above which flooding of said column may occur, the average residence time of liquid, inhibitor-depleted vinylaromatic monomer distillate overhead inside said column being 6 minutes of less, (ii) periodically or continuously measuring the difference between the pressure at the top of the column and the pressure at the bottom of the column to thereby ascertain the actual .DELTA.P within the column, and (iii) controlling the pressure within the column so that the actual .DELTA.P within said column is substantially constant and does not exceed said maximum theoretical .DELTA.P.