| Visbreaking is a kind of mild thermal conversion process for heavy oil, and it is suitablefor upgrading various heavy oil feedstocks to produce fuel oil with lower viscosity. However,the specification for the stability of fuel oil and coke formation during the process restrict theprocessing depth. In order to improve the stability of upgraded oil and suppress the cokeformation during the visbreaking process, the hydrogen donors are added to the process, theycan help the visbreaking alleviate the coke formation and improve the fuel quality. As heavydistillates are in the nature of high aromatic and naphthenic rings like the tetralin structure,they could be taken as hydrogen donors for the visbreaking of heavy oils.In this paper, three kinds of distillates from Venezuelan Merey16heavy oil was chosenas hydrogen donors, A(200℃~280℃), B(280℃~350℃), C(350℃~420℃), and the hydrogentransfer ability and hydrogen-donated upgrading performance of these three distillates werestudied systematically. First, the structural composition of different distillates weredetermined, then the chemical probe method used to measure hydrogen transfer ability wasmodified, finally the hydrogen transfer ability of the three kinds of distillates was determinedby the modified chemical probe method. The results showed that the order of hydrogendonating ability was C>B>A, the order of hydrogen accepting ability was C>A>B, and theorder of hydrogen transfer index was B>C>A, respectively. The hydrogen transfer ability ofthe distillate was closely related to its structural composition. High content of α-H, aromaticsand resins contributed to hydrogen donating ability, while high content of γ-H and saturatescontributed to hydrogen accepting ability. The distillate which has high fAand CI shows highhydrogen donating ability and hydrogen accepting ability.The hydrogen transfer ability of the distillates could be influenced by reaction time andreaction temperature. When the highest hydrogen transfer index of Distillate B was obtained, the reaction time was about90min at the temperature of400℃,10min at425℃and30min at410℃.Upgrading of Venezuelan residue with three hydrogen donors was conducted,respectively. With hydrogen donating distillates, the conversion of the residue decreased andvisbreaking depth increased. And the distillates with higher hydrogen transfer index had abetter suppressive effect on the conversion of residue. The product from hydrogen-donatedvisbreaking had a lower viscosity, better stability and less coke yield than conventionalprocess. In addition, less gas and more middle distillate were obtained in hydrogen-donatedvisbreaking. The residue from hydro-donated visbreaking also had a lower asphlaltene contentand higher content of saturates, aromatics and resins. The hydrogen donating distillates couldlower the coke yield and lengthen the coke induction period of the residue in the visbreakingprocess. Distillate A, B and C could lengthen coke induction period of the residue at400℃by7min,17min and13min, and lengthen coke induction period of the residue at425℃by1min,4min and3min respectively. |
