Visbreaking Based Integrated Process for Bitumen Upgrading and Hydrogen Production

Abstract The large Alberta's heavy oil and bitumen reserves demand novel, cost effective upgrading schemes for distillates production and resids disposal. Vacuum resids (VR's 500 ° C+) in average comprise 50 % (w/w) of these reserves. This study presents a new alternative for upgrading VR's by combining three processing steps: I. Production of modified almost instable heavy molecules by mild thermal cracking (Visbreaking, VB), II. Adsorption of modified heavy molecules over inexpensive, tailor-designed porous sorbents/catalysts, III Production of hydrogen via Low temperature Catalytic Steam Gasification (CSG) of the previously adsorbed molecules. Results will be presented on the combined processing as well as using both a model molecule and real feedstock (Athabasca VR) for the adsorption and hydrogen production steps. Introduction Development of cost effective upgrading schemes for Alberta's large hydrocarbon reserves is a must due to their heavy nature. Heavy oils and bitumen typically contain 50 % (w/w), if not more, of components remaining after vacuum distillation. Upgrading technologies rely on carbon rejection schemes or hydrogen addition. For the later, generation of this expensive reagent is always an issue. So far, the most common hydrogen generation process used in the upgrading of heavy hydrocarbons is Steam Reforming (SR) of natural gas and/or naphtha. Nevertheless, both streams have better alternative uses that make the hydrogen production process to have a significant impact on the bitumen upgrading economics. An alternative cost effective way of producing hydrogen could be the selective segregation of a minimal fraction of the heaviest hydrocarbon molecules, those most instable, followed by their gasification at low temperature. This alternative for hydrogen production at the upgrading sites of northern Alberta could be of great interest for both installed and future up-graders. Such a potential application would benefit the quality of the synthetic crude being produced since heavy compounds like asphaltenes considerably contribute to its quality limitations. Additionally, the hydrogen resulting from the gasification of these heavy compounds could either be used for refining purposes or for in-situ reservoir upgrading. For this study a Thermal Cracking process, visbreaking (VB) was used for modification of heavy molecules, since it is a very simple and low cost technology (1). Under VB conditions, residues are simultaneously disproportioned into low molecular weight (MW) distillates and hydrogen deficient bottoms. Further insoluble coke is generated when the process is carried out to higher severities (2,3). VB yield is constrained by the stability of the product. Under typical visbreaking conditions, conversion of naphtenic VR's is limited to around 30 % (w/w). At this conversion level product stability reaches a minimum critical value, commonly expressed by a peptization parameter (P-value) ~ 1.1(4). Instable molecules are the result from recombination of aromatic radicals in a reaction governed by a free radical mechanism. The continuous trend toward instability conditions along a visbreaking process is derived from a couple of simultaneous effects: I. aromatic molecules loose rapidly their alkyl appendages, increasing their aromaticity and, II. the solubilizing maltene phase becomes enriched in alkyl compounds which are not properly suited for maintaining aromatic compounds in solution (4).

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