Heavy oil upgrading process

Details Heavy oil upgrading process Heavy oil upgrading process

2000-05-16

2003-02-25

Griffin, Walter D. (Department: 1764)

Mineral oils: processes and products

Chemical conversion of hydrocarbons

With subsequent treatment of products

C208S096000, C208S097000, C208S131000, C208S132000, C208S309000

Reexamination Certificate

active

06524469

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a method for the upgrading of heavy hydrocarbon oils and, more specifically, to a method for reducing the viscosity and metals of such oils. The heavy oil is first thermally cracked, then solvent deasphalted.
BACKGROUND
The United Nations Information Centre for Heavy Crude and Tar Sands defines bitumen as petroleum having a viscosity>10,000 cP. Petroleum with viscosity less than 10,000 cP and a density between 10° API and 20° API is defined as heavy oil, while extra heavy oil has a density<10 API. The total estimated resource in place of heavy oil and bitumen in the world is 6.2 trillion barrels. Canada is believed to have 75% of the world's supply of natural bitumen. The Alberta Energy and Utilities Board (AEUB) estimates that there are 1.7 trillion barrels of bitumen in place in Canada, with about 300-350 billion barrels ultimately recoverable. Venezuela, on the other hand, is estimated to contain 65% of the world's reserves of heavy oil. The Orinoco Heavy Oil Belt is estimated to contain 1.2 trillion barrels of extra heavy oil with about 270 billion barrels of it ultimately recoverable.
The distinguishing features of heavy oils are (1) low API gravity, (2) high levels of atmospheric residuum, (3) high viscosity, (4) high levels of sulfur, (5) moderate levels of Conradson Carbon Residue (CCR), and (6) moderate to high levels of metals (Ni and V). These properties, and especially the high viscosity, make recovery of heavy oils difficult. In Canada, subsurface heavy oils from the Cold Lake region are produced by the injection of steam into the ground to lower the viscosity sufficiently to allow the oil to flow. Traditionally, a diluent is then added to the produced oil to further reduce the viscosity of the oil sufficiently to allow it to be pipelined to market. In Venezuela the oil is already warm enough to flow but still too heavy to pipeline directly, thereby also requiring the addition of diluent in order to pipeline it to the upgrading facilities. In both of these cases, the diluent is typically a naphtha stream (21 to 76.6° C. boiling range) which can be separated from the heavy oil by distillation at the end of the pipeline, but which still must be returned to the well to be reused. This involves an additional pipeline and more expense.
The direct upgrading of heavy crudes is also difficult. Distillation typically yields low levels of distillates. The remaining residual oils cannot be added in significant amounts to fluid catalytic crackers because of the extraordinarily high levels of metals and Conradson Carbon Residue (CCR), which result in a high level of hydrogen generation and high coke on catalyst respectively. Therefore, coking, which is one of several thermal cracking processes, has traditionally been the process of choice for upgrading heavy oils. As of 1996, Syncrude Canada processed 214,000 BBL/d of Athabasca tar sands bitumen in their fluid coker (B. L. Schulman et al.; Upgrading Heavy Crude Oils and Residues to Transportation Fuels: Technology, Economics and Outlook, 1996, SFA Pacific, Inc., Mountain View, Calif.). In addition, four separate consortia have planned major upgrading projects in Venezuela; and delayed coking has been the unanimous choice for the primary upgrader in each of them (T. Chang;
Upgrading and Refining Essential Parts of Orinoco Development
, Oil and Gas J., Oct. 19, 1998, 67-72). While coking does remove a significant amount of the metals and carbon residue, the quality of the coker liquids is poor. They are high in sulfur, olefins, diolefins and heavy aromatics and, as a result, require a substantial amount of additional hydrotreating before they can be sent to fluid catalytic cracking units or blended into transportation fuels.
One alternative to coking is visbreaking, which is another widely applied thermal cracking process for the conversion of residual oils (J. F. LePage et al.; Resid and Heavy Oil Processing, Editions Technip, Paris, France, 1992). As of 1996 there was almost 4 million barrels per day visbreaking capacity installed worldwide with more than 95% of that capacity outside the United States. Visbreaking is characterized by high temperature and short residence time; so that, unlike coking, the cracking reactions are terminated before coke is made. Nevertheless, 50 to 60% conversion of 343° C.+fraction of the feed to a lower boiling range can easily be obtained in visbreaking under certain conditions. Visbreaking alone does not significantly change the heteroatom content (S, N), metals or asphaltene content of the feed. Its sole function is molecular weight (e.g. boiling range) reduction and, hence, lowering of viscosity.
Another process commonly used in the upgrading of heavy oils is solvent deasphalting. In the crude, asphaltenes are held in a colloidal solution (or “peptized”) by the polar molecules and the aromatic molecules. If an aliphatic solvent is added (as during solvent deasphalting), the nature of the liquid around the asphaltenes changes from one that favors peptization (and therefore stability) of the asphaltene colloids to one that does not favor peptization and therefore precipitates asphaltenes. Visbreaking and other mild thermal processes result in cleavage of the alkyl side chains from asphaltenes (R. C. Schucker and C. F. Keweshan,
The Reactivity of Cold Lake Asphaltenes
, Prepr. Div. Fuel Chem., Amer. Chem. Soc., 1980, 25(3), 155-165). This has two effects: (1) the aromatic cores are less able to be peptized because the side chains are gone and (2) the surrounding liquid becomes more aliphatic (more like an aliphatic deasphalting solvent) and therefore is not as good at solubilizing the asphaltenes. As a result, during visbreaking, asphaltenes will begin to precipitate and subsequently will form deposits, which, if not controlled, plug the tubes with coke. Ordinary solvent deasphalting, as practiced commercially, uses a solvent to feed ratio of 4:1 to 6:1, thus resulting in increased energy consumption for solvent removal and larger equipment sizes. Therefore, there remains a need in the art for improvements to heavy feed upgrading that will overcome the above shortcomings.
SUMMARY OF THE INVENTION
In accordance with the present invention there is provided a process for the upgrading of a heavy oil feedstock that comprises the steps of thermally cracking said feedstock at conditions that will produce a thermally cracked product stream having a lower average molecular weight and boiling point than said feedstock without significant coke formation; volatilizing from said product stream light ends including any water that might be in the stream; adding an alkane solvent to said devolatilized product stream thereby inducing the formation of asphaltene aggregates; passing said devolatilized product/solvent mixture to a first membrane permeation unit; recovering a permeate/solvent stream that is substantially reduced in asphaltenes; heating said permeate/solvent stream above the critical point of said solvent; recovering said solvent and recycling it to the discharge of said thermal cracker; recovering a substantially deasphalted oil product; mixing the retentate stream from said first membrane permeation unit, which is substantially increased in asphaltenes, with the same deasphalting solvent; passing said retentate stream/solvent mixture to a second membrane permeation unit, wherein a substantial portion of the remaining liquid in said retentate/solvent stream that is substantially reduced in asphaltenes permeates through the membrane; and recovering a high-solids retentate stream comprising predominantly asphaltenes, steam stripping said retentate and recovering the solids.
In a preferred embodiment of the invention the feed is a heavy oil stream having an API gravity of less than 10° API.
In another preferred embodiment of the invention the visbreaker is a coil visbreaker design.
In another preferred embodiment of the invention the visbreaker is operated under hydrogen at a pressure of about 100 psig to about 1200 psig.

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