Studies of Transport of Asphaltenes through Membranes Using Hindered Diffusion Theories for Spheres and Spheroids

Ravikumar, V.; Tsotsis, Theodore T.; Sahimi, Muhammad

doi:10.1021/ie960598c

Cited by 5 publications

(3 citation statements)

References 44 publications

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“…Asphaltene diffusion through a porous medium with a narrow pore size distribution reveals an order of magnitude difference in the diffusion rates between some asphaltene subfractions and bulk fluid. A mathematical model describing the transport of rigid nanospheres through membranes yielded diffusivities of the same order of magnitude as the experimental results for asphaltene diffusion. , Adsorptive uptake experiments conducted at 308 K with coal and petroleum asphaltenes in a NiMo/Al 2 O 3 hydrotreating catalyst with tetrohydrofuran as a solvent also show variability. Numerous models – have been proposed to estimate the effective diffusivity of asphaltenes in commercial catalysts under hydroprocessing conditions.…”

Section: Introductionsupporting

confidence: 55%

Impact of Asphaltene-Rich Aggregate Size on Coke Deposition on a Commercial Hydroprocessing Catalyst

Zhao

Shaw

2008

Energy Fuels

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Diverse coke deposition mechanisms and models, all supported by experimental data, have been proposed for catalytic hydrogenation processes related to heavy oil and bitumen refining. In this contribution, nanofiltration is used to partition Athabasca bitumen and Maya crude oil so that the potential impact of asphaltene-rich nano-aggregate size on coke deposition on a commercial NiMo/γ-Al 2 O 3 hydrotreating catalyst could be investigated without introducing artifacts related to the use of solvents. Crude samples were filtered at 473 K through 5, 10, 20, and 50 nm ceramic filters. The feeds, permeates, and retentates are characterized in detail in a companion contribution (Zhao and Shaw, Energy Fuels 2007, 21 (5), 2795-2804). Batch coking experiments were conducted at 653 K for 2 h at a 30:1 feed to catalyst ratio (weight basis), with feed stocks, permeates, retentates, and control samples. Surface area, pore volume, and pore size distribution of coked catalysts were measured. The results were found to be consistent with partial filling of catalyst pores for all cases. Pore mouth plugging was not observed. Elemental analyses performed on cross sections of coked catalyst pellets show that coke deposition within pellets was diffusion limited for all cases evaluated while vanadium deposition, arising primarily from the maltene fraction, was not diffusion limited. Asphaltene-rich nano-aggregate size and maltene composition are shown to play secondary roles in coke deposition within catalyst pellets.

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Section: Introductionsupporting

confidence: 55%

Impact of Asphaltene-Rich Aggregate Size on Coke Deposition on a Commercial Hydroprocessing Catalyst

Zhao

Shaw

2008

Energy Fuels

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“…Elsewhere 66,67 we have discussed the effect of an evolving molecular weight distribution on the transport properties of the asphalts, such as their effective diffusivity in a pore.…”

Section: Discussionmentioning

confidence: 99%

Asphalt Flocculation and Deposition. V. Phase Behavior in Miscible and Immiscible Injections

et al. 1998

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Asphalt formation and precipitation under primary oil recovery conditions as well as secondary recovery by immiscible gas injection were studied. The crude oils were from a carbonate and highly fractured reservoir. No asphalt precipitated under these conditions. Since the oil reservoir had experienced significant formation damage and plugging of its well's tubing due to asphalt formation and precipitation, the absence of asphalt precipitation in our experiments points to the important influence on asphalt formation of flow of the oil, the streaming potentials arising from the flow, and their interaction with the electrical properties of the asphalt aggregates. Also investigated was asphalt precipitation when an enriched gas was injected into the oil under dynamic (multiple contact) miscibility conditions. Only trace amounts of asphalt precipitated when the dilution ratio R was high enough. However, significant asphalt precipitation occurred in completely miscible injections. For this case, we report extensive new experimental data for the amount of the precipitated asphalt formed with various precipitation agents over wide ranges of pressure, temperature, and crude oil composition. Increasing the pressure decreases the amount of asphalt precipitation. However, depending on the crude oil, two opposite trends in the amount of the precipitated asphalt were observed when the temperature of the system was raised. A scaling equation of state is shown to provide accurate predictions for the data. The scaling equation also yields a novel analytical equation for R c , the critical dilution ratio (measured in cm 3 of the diluent or the precipitation agent per gram of crude oil) at the onset of the precipitation given by R c ) c(MT) 1/4 , where M is the (average) molecular weight of the precipitation agent, T is the temperature in °C, and c is a constant on the order of 10 -2 . The predictions of this equation are in excellent agreement with the experimental data. Thus, this equation may be used in the design of gas injection operations for enhanced oil recovery, such that precipitation of the asphalt aggregates in the reservoir can be prevented.

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“…For one set of calculations (in which the interest was in the effect of pore size distribution parameters) the layer was assumed to be polydisperse, i.e., having a pore size distribution. The hindered convective/ diffusive transport of molecules through multilayered membranes has been studied in detail elsewhere (Ravi-Kumar et al, 1997;Ravi-Kumar, 1996;Zydney, 1992, 1993;McCoy, 1995McCoy, , 1996. The analysis is straightforward, involving the solution of the hindered convection/diffusion equations in every membrane layer and accounting for the continuity of fluxes and concentrations at the interfaces between the various layers.…”

Section: Model Developmentmentioning

confidence: 99%

Models and Simulation of Liquid-Phase Membrane Reactors

Park¹,

Ravikumar²,

Tsotsis³

1998

Ind. Eng. Chem. Res.

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A model of a liquid-phase membrane reactor is presented here. The model utilizes a reaction scheme and rate data applicable to the hydrocracking of California Hondo crude derived asphaltenes. Two reactor configurations have been investigated. In the first reactor configuration (configuration A) the shell-side reactor volume is kept constant by continuously pumping into the reactor pure solvent. In the second reactor configuration (configuration B) no additional solvent is added to the reactor shell side, whose volume, as a result, decreases as the solvent and solutes diffuse across the membrane from the shell side to the tube side. The model has been utilized to identify optimal reactor and process conditions and membrane characteristics, which maximize conversion and product yields.

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Studies of Transport of Asphaltenes through Membranes Using Hindered Diffusion Theories for Spheres and Spheroids

Cited by 5 publications

References 44 publications

Impact of Asphaltene-Rich Aggregate Size on Coke Deposition on a Commercial Hydroprocessing Catalyst

Impact of Asphaltene-Rich Aggregate Size on Coke Deposition on a Commercial Hydroprocessing Catalyst

Asphalt Flocculation and Deposition. V. Phase Behavior in Miscible and Immiscible Injections

Models and Simulation of Liquid-Phase Membrane Reactors

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