Characteristic changes of asphaltenes during visbreaking of North Gujarat short residue

Singh, I. D.; Kothiyal, Vimal; Ramaswamy, V.; Krishna, Rajamani

doi:10.1016/0016-2361(90)90088-8

Cited by 22 publications

(12 citation statements)

References 10 publications

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“…This is consistent with observations of the formation of a neophase at coke formation onset (Shenghua et al 1999). Pyrolysis reactions involve the cleavage of carbon bonds with carbon, hydrogen, and heteroatoms resulting in the formation of free radicals that continue scission reactions or condense into carbon-rich material (Singh et al 1990, Del Bianco et al 1993. Use of the Coking Indexes can allow distillation to proceed to the verge, but not beyond the onset of coke formation, resulting in significant increases in distillate yield while minimizing the risk of fouling.…”

Section: Introductionsupporting

confidence: 83%

Residua Upgrading Efficiency Improvement Models: Coke Formation Predictability Maps

Schabron¹,

Pauli²,

Rovani³

2002

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The dispersed particle solution model of petroleum residua structure was used to develop predictors for pyrolytic coke formation. Coking Indexes were developed in prior years that measure how near a pyrolysis system is to coke formation during the coke formation induction period. These have been demonstrated to be universally applicable for residua regardless of the source of the material. Coking onset is coincidental with the destruction of the ordered structure and the formation of a multiphase system. The amount of coke initially formed appears to be a function of the free solvent volume of the original residua. In the current work, three-dimensional coke make predictability maps were developed at 400 EC, 450 C, " and 500 EC (752 EF, 842 EF, and 932 EF). These relate residence time and free solvent volume to the amount of coke formed at a particular pyrolysis temperature. Activation energies for two apparent types of zero-order coke formation reactions were estimated. The results provide a new tool for ranking residua, gauging proximity to coke formation, and predicting initial coke make tendencies.iv

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Section: Introductionsupporting

confidence: 83%

Residua Upgrading Efficiency Improvement Models: Coke Formation Predictability Maps

Schabron¹,

Pauli²,

Rovani³

2002

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“…Higher conversion can be achieved when visbreaking deasphalted oil is compared to visbreaking oil that was not deasphalted. However, during visbreaking, new asphaltenes are formed, irrespective of whether the feed material is deasphalted or not. ,− The formation of new asphaltenes erodes the conversion advantage gained by solvent deasphalting before visbreaking and is, therefore, a detrimental side reaction.…”

Section: Introductionmentioning

confidence: 99%

Visbreaking of Vacuum Residue Deasphalted Oil: New Asphaltenes Formation

2020

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The formation of new heavier material during thermal processing has long been known, and under typical visbreaking conditions, vacuum conversion of deasphalted oil is described using a first-order kinetic reaction. Using the equivalent residence time (ERT) assumption, the residence time and reaction temperature are interchangeable variables to achieve the same conversion, where conversion is defined as the decrease of the vacuum residue through its conversion to lighter boiling fractions. With the combination of these observations about the visbreaking process, the following research question was raised: would process conditions that, in principle, lead to the same conversion also lead to the same asphaltenes content in the final product? The answer to this question was evaluated in this work, where vacuum residue deasphalted oil was submitted to visbreaking. Isoconversion conditions were obtained by the ERT concept. As expected, an increase in n-pentaneinsoluble material was obtained at all process conditions studied. The kinetics of asphaltenes formation was different to the kinetics of vacuum residue conversion because the amount of asphaltenes formed were different at the same conversion and vice versa. Subsequent analysis of the new n-pentane-insoluble material revealed that asphaltenes were participating in hydrogen transfer reactions. The amount of hydrogen transferred during conversion at 438 °C were around 20 mg of H/g of asphaltenes in the product. Free radicals were formed as a consequence of hydrogen transfer reactions, and their recombination resulted in the formation of heavier material, which was reflected in an increase in n-pentane-insoluble material during visbreaking. Further investigation revealed that the free radicals remained reactive upon storage, which resulted in a 9 wt % increase in asphaltenes after 210 days of storage under nitrogen. Results also showed that isoconversion was not achieved as predicted by the ERT definition and the differences between predicted and experimental values are discussed on the basis of the assumptions to calculate ERT.

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“…As pyrolysis progresses, the intermediate polarity material decreases during the induction period. Initial pyrolysis reactions involve the cleavage of benzylic carbon-carbon bonds and aliphatic carbon-heteroatom bonds and hydrogen-heteroatom bonds, resulting in the formation of free radicals that continue scission reactions or condense into carbon-rich material (Singh et al 1990, Schabron et al 2001a, Del Bianco et al 1993). …”

Section: Pyrolysis and Cokingmentioning

confidence: 99%

Heavy Oil Process Monitor: Automated on-Column Asphaltene Precipitation and Re-Dissolution

Schabron¹,

Rovani²,

Sanderson³

2006

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About 37-50% (w/w) of the heptane asphaltenes from unpyrolyzed residua dissolve in cyclohexane. As pyrolysis progresses, this number decrease to below 15% as coke and toluene insoluble pre-coke materials appear. This solubility measurement can be used after coke begins to form, unlike the flocculation titration, which cannot be applied to multi-phase systems. Currently, the procedure for the isolation of heptane asphaltenes and the determination of the amount of asphaltenes soluble in cyclohexane spans three days. A more rapid method to measure asphaltene solubility was explored using a novel on-column asphaltene precipitation and re-dissolution technique.This was automated using high performance liquid chromatography (HPLC) equipment with a step gradient sequence using the solvents: heptane, cyclohexane, toluene:methanol (98:2). Results for four series of original and pyrolyzed residua were compared with data from the gravimetric method. The measurement time was reduced from three days to forty minutes. The separation was expanded further with the use of four solvents: heptane, cyclohexane, toluene, and cyclohexanone or methylene chloride. This provides a fourth peak which represents the most polar components, in the oil.iv

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Characteristic changes of asphaltenes during visbreaking of North Gujarat short residue

Cited by 22 publications

References 10 publications

Residua Upgrading Efficiency Improvement Models: Coke Formation Predictability Maps

Residua Upgrading Efficiency Improvement Models: Coke Formation Predictability Maps

Visbreaking of Vacuum Residue Deasphalted Oil: New Asphaltenes Formation

Heavy Oil Process Monitor: Automated on-Column Asphaltene Precipitation and Re-Dissolution

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