Increased consumption of crude oil and its derivatives has resulted in reduction of high quality petroleum sources. In addition, refining crude oil gives heavy cuts, which can only be used as fuel if not upgraded. Therefore, different processes have been developed for appropriate applications of such heavy residues as tar. One of the processes for upgrading tar is reduction of viscosity (visbreaking). This is performed by soaker and coil methods. In this work, the effect of increased pressure on coke yield by a new hypothesis has been introduced. Increasing pressure reduces carbon to hydrogen ratio and coke formation by preventing the release of light gaseous products and hydrogen transfer between the other components. Furthermore, the effect of time on the amount of production and viscosity variations as well as the relation between temperature and time at temperatures below viscosity conversion process temperature has been investigated.
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