Viscosity Breaking (Vis-breaking)

  Viscosity breaking aims to thermally crack long-chain feed molecules to shorter ones, thus reducing the viscosity and the pour point of the product. In this process, the feed is usually a high viscosity, high pour point fuel oil that cannot be used or transported, especially in cold climates, due to the presence of waxy materials. Wax is a complex mixture of long-chain paraffins mixed with aromatic compounds having long paraffinic side chains. Vis-breaking is a mild cracking process that operates at approximately 450°C using short residence times. Long paraffinic chains break to shorter ones, and dealkylation of the aromatic side chains occurs. Table 1-1 shows the analysis of feed and products from a vis-breaking unit.

Table 1-1: Analysis of feed and products from viscosity breaking