Final Remarks and Recommendations

Experimental data extracted from different levels (batch reactor, pilot-plant, and industrial units) are extensive and the derived kinetic model parameters are indeed dependent on feed properties. Thus, using parameters determined for one feed to others is risky and can introduce more error in the prediction of product yields. This is one typical drawback of lumped-based models. Interestingly, only one model reported the calculation of activation energies and frequency factors as function of molecular weight of the lumps involved in the reaction scheme. The reported results 

Regarding feed characterization, there is a need to characterize the residue from commonly available information without losing its essential characteristics. Typical feed analysis consists of distillation curve, kinematic viscosity, specific gravity, and sulfur, asphaltenes, and CCR residue contents. To develop more detailed kinetic models, advanced characterization is necessary for instance, SARA (saturates, aromatics, resins, asphaltenes) composition and analysis of each component would improve the prediction capability of kinetic models. 

As for hydrodynamics, liquid-phase residence time is affected by pressure, since an increase of this variable suppresses the vaporization of low-boiling fractions, increases the liquid-phase holdup, and, conseqnently, the liqnid-phase residence time. In commercial visbreakers, the snperficial gas velocity is two to five times that of the superficial liquid velocity, and this ratio may change with residue conversion, operating pressure, and amount of steam injected in the coil, and consequently the operation regime may change. That is why for proper modeling of the hydrodynamics of visbreaking reactor, all these effects should be taken into consideration for accurate prediction of the liqnid-phase residence time. Pressure drop is also another process parameter that is vital to predict. 

It is also desirable that the visbreaking model can predict, apart from product yields, conversion and temperatnre profile, also product properties for a given feed, reaction severity, and nnit geometry. In particular, the properties that are important to know are viscosity, asphaltene content, CCR content, and stability of the visbroken residue. Other product properties are also required, such as densities, sulfur content, pour point, and distillation curve. 

Having a robust model for simulation of the visbreaking process can help predict product yields, product properties, residue conversion, and related process parameters aiming at defining the following  

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