Abstract
The thermal degradation profile for any type of oil-based sample under thermogravimetric analysis (TGA) conditions exhibits three distinct stages, namely, vaporization from room temperature to 340–350 °C, cracking from 340–350 °C to 480–500 °C, and char oxidation from 500 °C to 570 °C. The former two stages occur in both inert (nitrogen) and oxidative (air) environments, whereas the latter only occurs in the presence of oxygen. Deconvoluting thermogravimetric data allows one to estimate the composition of oil derivatives with a view to expeditiously obtaining useful information from a refining process. To this end, thermal degradation of crude oil and its main refining cuts were modeled here by using the smallest possible number of representative pseudo-components. In order to ensure accurate fitting of thermogravimetric results, mass losses were interpreted in terms of autocatalytic kinetics. Fitting to an nth-order kinetics was useful below 350 °C (vaporization), but not above this temperature, because of cracking with fast mass losses in the vicinity of certain temperatures. This modeling scheme for thermogravimetric results afforded the following conclusions: (i) atmospheric gas-oil typically contains 10% residual kerosene fraction; (ii) atmospheric residue still contains 35–45% distillable compounds; (iii) the main component of visbreaking feed (nearly 66%) degrades at a similar temperature as asphaltenes; (iv) visbreaking residue is similar to feed at high temperatures but contains light components similar to naphtha or gas-oil, which vaporize at low temperatures; and (v) simulating crude oil allowed us to estimate the potential production of distillates (62.93% from heavy crudes and 79.61% from light crudes). Such useful information can be used by process engineers to assess the performance of equipment such as distillation columns or visbreaking units, and also to estimate the quality of some streams, such as atmospheric gas-oil or visbreaking feed.
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