Cross-Reference to Related Applications

This application claims the benefit of United States Provisional Application No.

62/580,577, filed November 2, 2017, which is incorporated herein by reference.

Field of the Invention

The invention pertains to the upgrading of heavy hydrocarbons, especially heavy crude oil.

Background of the Invention

Crude oil contains many different chemical components. In general terms, it consists primarily of hydrocarbon compounds, with varying amounts of impurities such as metals, chlorine, sulphur, nitrogen, asphaltenes and coke. Heavy crude oil has a lower hydrogen-to-carbon ratio than lighter crude oil, so the density (or specific gravity) of heavy crude oil is greater than that of a lighter crude oil. High specific gravity (low API), high viscosity and high gum formation are properties of heavy oil that cause major production and handling problems, especially in pipelines and refineries.

Heavy oil is generally any crude oil with an API gravity ranging from about 11 ° to 20° at standard conditions and with a gas-free viscosity ranging from about 100 to 10,000 centipoises (cp) at original reservoir temperature. Ultra-heavy oil, such as tar sand oil, also known as bitumen, is any crude oil with an API gravity less than about 11 ° and a gas-free viscosity greater than 10,000 cp. Pipeline-able oil such as synthetic crude oil (SCO) typically requires an API gravity of 19° and a viscosity at room temperature below 350 centipoises with insoluble gum contents below 1000 mg/100 g of SCO.

The prior art pertaining to heavy oil upgrading describes, inter alia, attempts to minimize coke formation, use of pressurized or un-pressurized heavy crude oil cracking, at elevated temperature with sequential or simultaneous venting, and the distillation of cracked heavy crude oil to separate cracked and un-cracked volatiles from cracked and un-cracked non-volatiles. Canadian patent application CA 2,764,676 (Corscadden et al.) describes sequential venting of cracked distilled oil (CDO) in "mild controlled cracking" of heavy crude oil in the presence of an inert sweep gas such as nitrogen in which "After the mild cracking process, a light top fraction 32 (distillate containing condensable and non-condensable volatiles) can be routed from the reactor 30 to a gas liquid condensing separator process 40" (page 15, lines 25-26). Although this cracking process can meet density and viscosity pipeline specifications for synthetic crude oil, it is unable to meet insoluble gum limits of 1000mg/100 g SCO without the use of an expensive hydro- treater.

Canadian Patent No. 2,897,871 to Oehr describes simultaneous venting of CDO in the absence of an inert sweep gas. It also describes mixing tetrahydrofurfuryl alcohol (THFA) with the crude oil prior to or during thermal cracking. The THFA is vented together with the thermal cracking components from the cracker and requires subsequent separation from the thermal cracking components by distillation or solvent extraction.

US Patent No. 4,274,934 to Compton describes the use of oxygen for reducing the nitrogen content of shale oil by producing insoluble pyrrole polymers that are insoluble in the shale oil. This technique is not commercially viable ahead of a thermal cracking apparatus, because the insolubles (i.e., gum) would foul the apparatus (e.g. the piping), ahead of the cracker, analogous to fouling in a pipeline. Accordingly, there exists a need for an improved means of upgrading heavy hydrocarbons, especially those using thermal cracking technology, which eliminate or reduce concerns associated with insoluble gum formation, e.g., in pipelines or refineries. Summary of the Invention

According to one aspect of the invention, there is provided a method of treating a heavy crude oil (HCO) prior to thermal cracking. First, the HCO is oxygenated (aerated) in a pre-cracking vessel, for example using air or oxygen, in the presence of a polar organic solvent, at a temperature below the boiling point of the polar solvent. This step oxidizes gum precursors in the HCO to solvent-soluble or emulsifiable polar products. Then the polar organic solvent is removed from the aerated HCO, for example by means of distillation. Optionally, the recovered polar organic solvent can be recycled to the process. The aerated HCO, having been stripped of the solvent, is then ready for thermal cracking.

According to another aspect of the invention, there is provided a method of upgrading an HCO. First, the HCO is oxygenated (aerated) in a pre-cracking vessel, for example using air or oxygen, in the presence of a polar organic solvent, at a temperature below the boiling point of the polar solvent. Then the polar organic solvent is removed from the aerated HCO, for example by means of distillation. Optionally, the recovered polar organic solvent can be recycled to the process. The aerated HCO, having been stripped of the solvent, is then fed to a thermal cracker and is thermally cracked to produce cracked distilled oil (CDO), or synthetic crude oil (SCO). According to another aspect of the invention, there is provided a method of treating a heavy crude oil prior to thermal cracking, comprising the steps of aerating the heavy crude oil in the presence of a polar organic solvent, and separating the polar organic solvent from the aerated heavy crude oil. According to another aspect of the invention, there is provided a method of reducing formation of insoluble gums in a process of thermal cracking of heavy crude oil. The method comprises, prior to thermal cracking, the steps of aerating the heavy crude oil in the presence of a polar organic solvent, and separating the polar organic solvent from the aerated heavy crude oil.

According to another aspect of the invention, there is provided a method of upgrading a heavy crude oil, comprising the steps of: (a) aerating the heavy crude oil in the presence of a polar organic solvent to form a mixture of aerated heavy crude oil and the polar organic solvent; (b) removing the polar solvent from the mixture by distillation to form aerated heavy crude oil; and (c) thermally cracking the aerated heavy crude oil.

According to another aspect of the invention, there is provided a process for reducing the gum formation properties of cracked distilled crude oil by aeration of cracker heavy oil feedstock in the presence of a distillable polar organic solvent, at a temperature below the boiling point of the distillable polar solvent, ahead of a heavy oil thermal cracker. Further aspects and example embodiments are illustrated in the accompanying drawing and described in the following description. Brief Description of the Drawing

Figure 1 is a schematic diagram of an upgrading process according to one embodiment of the invention. Detailed Description

As used herein, " heavy crude oil" (sometimes abbreviated as HCO) means heavy hydrocarbons and includes heavy oil, ultra heavy oil, bitumen, sour crude oil and oil refinery heavy hydrocarbon residues. "Lighter oils," include cracked heavy crude oil distillates, e.g. cracked-distilled oil (CDO) and synthetic crude oils made by blending cracked-distilled oil and solvent extracts of cracking residue, such extracts being referred to herein as "cracking residue extracts" (CRX). "Synthetic crude oil" (SCO) means a pipeline-able lighter crude oil which is either a cracked-distilled oil or a blend of cracked-distilled oil and cracking residue extracts.

Referring to Figure 1 , the heavy crude oil 10 is fed to an aeration vessel 12, which is supplied with oxygen gas 14. The oxygen gas may be provided in the form of air or as a mixture of nitrogen and oxygen, or carbon dioxide and oxygen, or any practical gas mixture containing oxygen. In this disclosure, "aeration" includes the provision of oxygen either as a pure gas or in the form of any suitable gas mixture. The aeration vessel 12 is also supplied with the polar organic solvent 16. The aeration step is carried out for a suitable time period, e.g., two hours, with agitation, at atmospheric pressure, and at an elevated temperature that is less than the boiling point of the polar organic solvent.

The mixture 18 of aerated heavy crude oil and the polar organic solvent is fed into a distillation apparatus 20, where the polar organic solvent is separated out by distillation, forming a solvent stream 22. This solvent steam 22 is recycled to the process. The aerated heavy crude oil 24, now stripped of the polar organic solvent, is fed into a thermal cracking vessel 26, where it is processed to produce CDO 28.

The thermal cracking can be carried out by methods well known in the art, for example, as disclosed in CA 2,764,676, CA 2,897,871 and WO 2014/124517, incorporated herein by reference in their entirety. Optionally, the thermal cracking process may include venting the volatile components either simultaneously with or sequentially to the cracking. Optionally it may include mixing the CDO with solvent-extracted cracker distillation residue. Optionally, it may include the use of a sweep gas in the thermal cracker.

This method of the invention has several advantages. It reduces or avoids

contamination of the polar solvent with condensed cracker volatiles, such as cracked naphtha, that have a boiling point similar to the polar organic solvent. This eliminates the need to attempt difficult distillation separation or solvent extraction of the polar solvent from the CDO components. Furthermore, removal of the polar organic solvent from the aerated HCO ahead of the thermal cracker prevents the polar organic solvent itself from being thermally cracked, thus increasing its recyclability. The method of the invention also reduces or prevents undesirable fouling of the pre- cracker or the thermal cracker apparatus by nitrogen-containing gums. The gums generated in the pre-cracker aerator are maintained either dissolved or emulsified in the polar organic solvent (prior to its being distilled off), or dissolved or emulsified by the non-gum polar components of the aerated HCO itself, once the HCO is heated to a temperature equal to or above the boiling point of the polar organic solvent, ahead of or in the thermal cracker. In other words, the polar organic solvent keeps the gums dissolved or emulsified in the HCO until the HCO is heated sufficiently to do that itself. The gums subsequently become a component of the thermal cracker residue in whole or in part thereby reducing subsequent levels in thermally cracked CDO or SCO.

Polar organic solvents suitable for use in the invention are those that are distillable, resistant to oxidation up to their boiling points, and able to dissolve or emulsify nitrogen-containing gums. Examples of suitable solvents include dimethylformamide, tetrahydrofurfurylalcohol (THFA), propylene glycol, ethylene glycol, diethylene glycol, and triethylene glycol. Their boiling points and dielectric constants are set forth in the following Table 1. Table 1

Examples

Example 1 (control) - Thermal cracking without pre-aeration, using nitrogen sweep gas during cracking

Athabasca Mackay River bitumen (300 grams) was thermally cracked between 400°C and 435°C in a 500 ml_ PAAR reactor cylinder equipped with a stirrer operated at 200 rpm. The PAAR cracker vessel was flooded with nitrogen and nitrogen sweep gas was introduced at 106 standard mL/min. Cracking time was 17 minutes at an equivalent temperature of 427°C. CDO was collected simultaneously to cracking. Resulting CDO properties are shown in the following Table 2:

Table 2

^* ASTM D2274 "Standard Test Method for Oxidation Stability of Distillate Fuel Oil" These results indicate that this CDO does not meet pipeline specifications for gum formation of 1000 mg per 100g of CDO. Example 2 Thermal cracking with pre-aeration in the presence of THFA solvent using air sweep gas during cracking

Athabasca Mackay River bitumen (300 grams) was heated together with 3wt% THFA for 2 hours at 150°C with 3 volume% oxygen in nitrogen at 106 standard mL/min with stirring at 200 rpm and then thermally cracked between 400 to 436°C at an equivalent temperature of 427°C for 17 minutes in a 500 mL PAAR reactor cylinder equipped with a stirrer operated at 200 rpm. The PAAR cracker vessel was flooded with nitrogen and 3 volume% oxygen in nitrogen gas was introduced at 106 standard mL/min. CDO was collected simultaneously to cracking. Resulting CDO properties are shown in the following Table 3:

Table 3

^* ASTM D2274 "Standard Test Method for Oxidation Stability of Distillate Fuel Oil"

These results indicate that this CDO does meet pipeline specifications for gum formation. Use of pre-aeration in the presence of the polar solvent in Example 2 has reduced gum formation by 67% vs. Example 1 , to a level that easily meets pipeline gum

specifications. This occurred even though the CDO nitrogen levels were higher in the lower gum-generating CDO. As will be apparent to those skilled in the art in the light of the foregoing disclosure, many alterations and modifications are possible in the practice of this invention without departing from the scope thereof. Accordingly, the scope of the invention is to be construed in accordance with the following claims.