Thermal Cracking of Athabasca Bitumen:  Influence of Steam on Reaction Chemistry

Abstract

Thermal cracking of Athabasca bitumen at various reaction conditions with and without the presence of steam was investigated to determine if steam has a chemical influence on coking. The reactions were done in 15 mL microautoclave reactors and a 3" diameter fluidized bed coking pilot unit over a range of reaction severity (350-530 °C, 10-60 min reaction time). The differences between reactions with and without steam were investigated by comparing elemental composition of the products and coke yield. The presence of steam decreased coke yield and decreased sulfur removal, and reduced the H/C ratio of the liquid products. Hydrogen exchange from steam to thermally cracked bitumen molecules was tested by doping water with deuterium oxide (D 2 O) and analyzing liquid and coke products by NMR and stable isotope mass spectrometry, respectively. Preferential deuteration of benzylic carbons was observed along with a trend of increasing deuterium transfer to liquids and coke as reaction severity increased. Free-radical, ionic, and physical mechanisms that can account for these experimental results are discussed.

A Review of Laboratory-Scale Research on Upgrading Heavy Oil in Supercritical Water

“…Vostrikov et al [72] reported the pyrolysis of eicosane in SCW and showed that water accelerated pyrolysis and reacted with a large amount of reaction intermediates. Dutta et al [73] tested the hydrogen exchange from steam to thermally cracked bitumen molecules by doping water with D2O in a temperature range of 623-803 K. They measured the exchanging degrees of three types hydrogen (α-, β-, γ-) in bitumen and found that the α-H were prone to be exchanged with the H of water. Gao et al [74] used D2O as a tracer to study the hydroconversion of Tahe residue in SCW.…”

“…The formation of large amounts of coke, through the propagation reactions of radicals, the aggregation of asphaltene, and the addition between activated asphaltene precursors and low molecular radicals or olefins [50,79], not only affects the efficient exploitation of heavy oil, but also brings a series of problems, such as the deactivation of catalysts. Fortunately, the introduction of SCW into heavy oil can effectively reduce the yield of coke [11,[73][74][75]80,81]. To further suppress the formation of coke, many novel SCW processes have been successfully developed.…”

Heavy Oil Upgrading in the Presence of Water

“…Помимо каталитической функции, вода непосредственно участвует в химических реакциях. В [17] показана возможность переноса дейтерия из молекул тяжелой воды в продукты превращения битума при температурах от 350 до 530 ºС, что может свидетельствовать о протекании реакции ингибирования углеводородных радикалов образующихся в ходе термического гомолитического разрыва связей С-С (1)-(3), что также обсуждается в [18,19]:…”

“…При неката-литическом паровом крекинге присутствие воды по сравнению с термокрекингом практически не сказывается на таких показателях процесса, как выходы кокса и жидких продуктов, глубина обессеривания и др. При этом значительного повышения концентрации оксидов углерода (СО, СО 2 ) в составе газообразных продуктов, что свидетельствовало бы об интенсификации про-текания процессов взаимодействия воды и углеводородов по НТППР либо по другим механиз-мам, не было обнаружено даже при температурах до 480 ºС [17,[93][94][95].…”

Anthracene aquacracking using NiMo/SiO2 catalysts in supercritical water conditions

“…The use of H 2 O instead of H 2 in the so called steam cracking has been proposed by several groups as a potential way to upgrade heavy and unconventional oils [4][5][6][7][8]. Hydrothermal heavy oil upgrading has shown important improvements compared to thermal upgrading methods as higher yields to lighter liquid product fractions are obtained at the expense of a reduction in the amount of coke produced [9,10].…”