World petroleum residue processing capacity has reached about 810 MMTPA. In the present petroleum refining scenario, the viability of a petroleum refinery strongly depends on the flexibility of processing heavy crudes and, in turn, heavy residues. Visbreaking is one of the major residue upgrading processes and constitutes about 33% of the total residue processing capacity. In the present communication, the published literature pertaining to the visbreaking process has been extensively analyzed and a state-of-the-art review has been written that includes the following: (i) the effect of feed properties on fuel oil stability; (ii) reaction pathways, mechanism, and kinetics; (iii) parametric sensitivity of the operating variables such as temperature, pressure, and residence time; (iv) different visbreaker designs, viz. coil visbreaker, coil-soaker visbreaker, soaker with internals, and high conversion soaker; (v) coking and fouling; (vi) estimation of design parameters, viz. gas holdup in high-pressure bubble column (soaker), gas holdup in sectionalized bubble column (soaker with internals), liquid-phase mixing and axial mixing in high-pressure bubble column, liquid-phase mixing and axial mixing in sectionalized bubble column, and weeping; and (vii) mathematical modeling of visbreaker, which mainly includes the coil and the soaker. An attempt has been made to get the aforementioned aspects together in a coherent manner so that the information is available at a glance and is expected to be useful to researchers and practicing refiners.

Thermal cracking of vacuum residues and asphalts obtained from operating Indian refineries were studied in a batch reactor. The temperature was varied in the range 400−430 °C, and the batch time was varied from 0 to 15 min. The pressure was kept at a constant value of 1.2 MPa through out the experiment. The variation in the composition of the cracked gas fraction for each feed was studied by gas chromatography. The resulting visbroken products were further characterized in terms of its different industrially important boiling cuts. A five lump kinetic model, comprising of gas (C1−C5), gasoline (IBP-150), LGO (150−350), VGO (350−500), and VR (500+) has been developed. The variation in the kinetic parameters with change in the feed properties has been discussed. Also, an attempt has been made to seek a relationship between the feed properties with the kinetic rate parameters and the activation energies.