Athabasca bitumen was hydrocracked over a commercial NiMo/γ-Al2O3 catalyst in two reactors, a microbatch reactor and a 1-L continuous stirred tank reactor (CSTR). Coke deposition on catalyst was measured as a function of hydrogen pressure, time on stream, and liquid composition by measuring the carbon content of the cleaned spent catalyst. The carbon content ranged from 11.3% to 17.6% over the pressure range 6.9−15.2 MPa in CSTR experiments. Batch and CSTR experiments showed a rapid approach to a constant coke content with increasing oil/catalyst ratio. Coke deposition was independent of product composition for residue concentrations ranging from 8% to 32% by weight. Removal of the coke by tetralin at reaction conditions suggested reversible adsorption of residue components on the catalyst surface. A physical model based on clearance of coke by hydrogen in the vicinity of metal crystallites is presented for the coke deposition behavior during the first several hours of hydrocracking use. This model gives good agreement with experimental data, including the effect of reaction time, the ratio of total feed weight to catalyst weight, hydrogen pressure, and feed composition, and it agrees with general observations from industrial usage. The model implies that except at the highest coke levels, the active surfaces of the metal crystallites remain exposed. Severe mass-transfer limitations are caused by the overall narrowing of the pore structure, which in γ-Al2O3 would give very low effective diffusivity for residuum molecules in micropores.
C yclone fouling in fluid cokers can lead to untimely shutdowns for oil sand upgrading operators. This problem was described extensively by Richardson (1 997). The cyclones, located above the fluid bed, are responsible for separating solid coke particles from the vapour stream before it enters the scrubbing section of the coker. Excessive buildups of coke have been noted to form in various parts of each cyclone, as shown in Figure 1. These coke formations lead to an increased pressure drop through the coker and a reduction in the overall efficiency of the cyclones. This problem worsens with the passage of time until, eventually, the coker must be shut down so that the coke formations in the cyclones can be removed. Richardson (1997) discussed a number of mechanisms which may be responsible for the production of these coke structures. It is possible that the vapour phase rising from the fluid coke bed may continue to thermally crack, forming smaller molecular species and coke. Since coke i s a byproduct of thermal cracking, the formations observed in the cyclones would be initially formed by reactions of the vapour phase. Deposition of the coke onto surfaces within the cyclones would initiate the surface formation mechanism. The growth of the coke surface may continue as a result of interaction of vapour phase free radicals and the coke deposited on the walls of the cyclones. The purpose of this study was to determine if coke could be produced from the vapour phase derived from the thermal cracking of Athabasca bitumen and to investigate the effects of reaction time and temperature on the vapour phase coke yield.Coke is composed mostly of carbon (more than 95 percent by mass) combined with small amounts of hydrogen (Speight, 1991). Much research has been performed in the field of gas phase carbon formation.
This is an advanced student text based, in part, on a graduate course given by the author at Purdue University. The approach taken is axiomatic and draws extensively on the ideas of Caratheodory. It is heavily mathematical and quite clearly is not intended for the beginning student .Having presented the fundamental material in a concise but readable way, the author moves on to consider the elementary applications of thermodynamics in what can only be called a rambling, disorganized manner. I found the way in which he intermixed material which is always true with that which is true only for ideal systems (gas or mixture) particularly confusing. Thus, for example, the chapter headed 'Equilibrium in Ideal Systems' contains the derivation of the phase rule and the phase behaviour of real single-component systems, neither of which is discussed elsewhere in the book. However, far more serious is the way in which the author derives a result for a particular ideal system and uses this later without indicating that the constraint still holds. A student dipping into this book is at risk of picking up and using equations or information without being aware of the restrictions applying to them. The author also seems to have some odd ideas as to what constitutes an ideal gas. He asserts that the heat capacity, C,, for an ideal gas is independent of temperature, but a few pages further along he allows Cp to vary with temperature, having, in the meantime, proved that C, -C, = R.The section on real systems and, in particular, the use of standard states is one of the most opaque I have ever come across. In the preface, the author says that one of the ways that his text differs from conventional treatments of thermodynamics is in his ' detailed investigations on the uniqueness of predictions of properties of solutions, in the face of a bewildering array of standard states'. He certainly seems to have done this, but perhaps not quite in the way he intended.I suggest therefore that the reader skips chapters 2 and 3, where all this confusion is to be found, and moves on to the last third of the book, which is much more valuable and well written. The chapters here cover: (4) Properties of Electrolytes; (5) Systems in External Fields-Gravitational Fields, Adsorption, Radiation, Electrical Fields, Superconducting Materials, and (6) Irreversible Thermodynamics. These topics are rarely covered in a textbook of this type and the discussion is at just the right level to provide a knowledgeable introduction to these more specialized parts of the subject.The price can only be considered exorbitant, particularly for a book produced photographically from typescript.
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