Wang, Kunpeng (2019-11). AN EXPERIMENTAL INVESTIGATION OF HIGH DOSE RATE ELECTRON BEAM IRRADIATION OF PETROLEUM IN A CONTINUOUS FLOW SYSTEM. Doctoral Dissertation.
Thesis
High dose rate electron beam (10 MeV, 15 kW, LINAC) irradiation was investigated as a potential technology for heavy oil upgrading. The flow system allows irradiation of crude oils at constant temperature while bubbling natural gas through the oil. Experimental parameters including dose, temperature, shear rate and dose rate were allowed to change in order to find the optimal condition. Pure hydrocarbons were selected and irradiated by the same source at low temperatures. Results revealed that conversion and product yields not only depends on those irradiation conditions, but also relies on the molecular structure of irradiated compounds. Irradiation of petroleum activates hydrocarbon compounds which subsequently undergo a series of chemical reactions including radical initiation, propagation and termination. Two reaction pathways could be initiated by absorbed energy, then compete inside the irradiated compounds and eventually lead to multiple products. Cracking is due to hydrocarbon chain scission and produces products smaller than the parent molecules. Polymerization is caused by molecule recombination and produces products larger than the parent molecules. Cracking and polymerization could be enhanced or suppressed by altering irradiation conditions such as irradiation temperature and total absorbed energy. To selectively favor one of them and suppress the other one requires detailed investigation of many parameters. In general, higher dose rate and higher temperature favor cracking reactions. Fundamental studies were conducted by irradiating pure and neat hydrocarbon compounds with the same electron beam source. Responses from irradiating different compounds varied dramatically. Saturated hydrocarbons tended to produce the most products. The presence of rings on a saturated hydrocarbon greatly enhanced its tendency toward polymerized products which are commonly dimers and trimers. Unsaturated hydrocarbons were less reactive with lower yields of products. One unsaturated ring on a molecule will tremendously suppress its reactivity toward chain scission products and only produce detectable polymerized species. Stability of a hydrocarbon compound and its radiation product pattern are closely related to its molecular structure. The saturation degree of a molecule and its average bond strength could be used to characterize the stability and product yields for a compound. Crude oil is a complex mixture of thousands of hydrocarbon compounds and nonhydrocarbons. Conversion and product yields from irradiating crudes do not simply resemble those from irradiation of pure compounds due to unknown chemical composition and unknown reaction pathways. This explains why it is so challenging to predict heavy oil conversion under electron beam irradiation. Crude oils could be separated into a few fractions, e.g. saturates, aromatics, resin and asphaltene. Irradiation of each fraction may follow the same results obtained from irradiating pure and neat compounds. Saturates should have the highest conversion to light products whereas everything else either is chemically stable or polymerizes. That provides a possibility of improving the total conversion and product yields from crude oil irradiation by separating crudes into different fractions, then selectively irradiating the saturates and avoiding other fractions.
