Method of Upgrading Heavy Crude Oil

FIELD

The present method relates to the field of upgrading heavy hydrocarbons, especially heavy crude oil (HCO), such as high sulphur containing heavy oil (i.e. "sour heavy crude oil"), to a light crude oil (LCO).

BACKGROUND OF THE INVENTION

Crude oil contains a number of different chemical components. In general terms, it consists primarily of hydrocarbon compounds, with varying amounts of impurities such as sulphur, nitrogen and oxygen. Heavy crude oil has a lower hydrogen-to-carbon ratio than lighter crude oil, therefore the density (or specific gravity) of heavy crude oil is greater than that of light crude oil.

High specific gravity and viscosity are properties of heavy oil that cause major production and handling problems. Viscosity is the resistance of fluid to flow.

Heavy oil is generally any crude oil with an API gravity ranging from about 10° to 20° at standard conditions and with a gas-free viscosity ranging from about 100 to 10,000 centipoises 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 10° and a gas- free viscosity greater than 10,000 centipoises.

A significant problem with heavy oil is the difficulty and expense entailed in increasing the volume of light hydrocarbons distilled from a heavy oil feedstock. Typically, this is done by increasing the hydrogen-to-carbon ratio. This can be accomplished by either removing carbon or by adding hydrogen. Carbon is typically removed by coking, solvent deasphalting, or catalytic cracking. Hydrogen is typically added by hydrotreating or hydrocracking.

Hydrocracking processes are known which utilize a catalyst in a hydrogen environment to convert heavy distillates into lighter distillates such as gasoline or jet fuels. Such processes typically include adding to heavy oil feedstock or distillate a source of donor hydrogen such as hydrogen gas. Unfortunately, typical heavy-oil feedstocks have relatively high metal content (100 parts per million or higher) thus limiting the application of hydrocracking because the metals contaminate the catalyst.

Prior art systems for upgrading crude oil, including bitumen, through hydrodesulphurization suffer from the following disadvantages:

• high temperature processing with expensive catalysts susceptible to heavy metal fouling; and

• huge demands for expensive hydrogen gas input.

Accordingly, there exists a need for means of upgrading heavy hydrocarbons, including heavy and crude oils, which transcends prior art systems by combining the following desirable features:

• scalability;

• portability;

• simplified processing;

• elimination or reduction of heavy metals in the products; and

• reduction of sulphur content ahead of hydrotreaters.

Use of tetrahydrofurfuryl alcohol (THFA) in treating heavy oil to reduce viscosity is described in U.S. patent 4,877,513, issued to Haire et al. The process of Haire et al. involves the addition of small amounts of THFA to heavy oil (i.e. 1-3 wt%) followed by heating at elevated temperature (e.g. 398°C) in the presence of iron-containing surfaces or particles for periods of between 600 to 6000 seconds, to reduce the viscosity and

specific gravity of the heavy oil. The methods of Haire et al. suffer from the following significant drawbacks:

• the reactor is highly susceptible to "spray flow regime issues"; • the product of the Haire et al. invention is highly contaminated with heavy metals, and actually concentrates contained heavy metals, making it extremely difficult to hydrotreat to further reduce viscosity and/or sulphur content;

• heavy metals are concentrated in the degassed liquid product since only gas is vented from the product oil; • the process operates only at sub-atmospheric pressure (e.g. 0.2 atmospheres);

• the process requires a tubular reactor, the inner walls of which must include ferrous metal;

• the process requires removal of water and gas prior to processing through the tubular reactor; and • reaction time in the tubular reactor is excessive (e.g. 83 minutes or 4980 seconds).

U.S. Patent No. 4,360,420, issued to Fletcher et al., discloses a method of re-refining used oil by low pressure evaporation or distillation, followed by solvent extraction of the distillate with THFA (see col. 2, lines 18-27 of Fletcher et al.). U.S. Patent No.

7,094,331 , issued to Kiser, discloses the use of 0.5 to 5 % by weight dihydric alcohols as non-distillation additives to reduce heavy hydrocarbon viscosity. Neither of these patents describe methods for upgrading a heavy or crude oil to a light crude oil compatible with hydrotreaters.

SUMMARY OF THE INVENTION

The present invention is a method of upgrading heavy crude oil, especially high sulphur HCO, via the addition of THFA. Correspondingly, the present invention relates to the use of THFA as a cracking additive, the use of THFA as a distillation additive, and to hydrocarbon distillates and light crude oils produced by distillation of HCO in the

presence of THFA. As used herein, HCO refers to heavy hydrocarbons and includes heavy oil, ultra heavy oil, bitumen, sour crude oil and oil refinery heavy hydrocarbon residues. In contrast to the prior art, in the present invention the THFA is used as a combination distillation and cracking additive.

THFA is a monohydric alcohol-ether, which in the present invention is added to HCO to form an HCO-THFA mixture. The HCO-THFA mixture is heated and distilled to form a lower density, lower acidity, ash-free distillate called light gas oil (LGO), containing less sulphur and having lower viscosity than the feed HCO. Subsequent distillation of the LGO residue can be performed under vacuum to produce a vacuum gas oil (VGO). The distillate is essentially a light crude oil (LCO) containing THFA. LCO is used herein to refer to light crude oil and includes light gas oil (LGO) and vacuum gas oil (VGO). The distillate is an ash-free LCO that has a lower olefin content than conventional distillates.

The distillate of the present invention has higher value than its HCO feed and can be used, for example, as a fuel in a gas-turbine for producing electricity, steam, or electricity plus steam, (with or without all or a portion of its THFA removed). Furthermore, the distillate of the present invention (with or without all or a portion of its THFA removed) can be easily upgraded (e.g. with hydrotreaters) to reduce its sulphur content and to further increase its API gravity, since it is heavy metal-free and therefore will not foul hydrotreater catalysts.

DETAILED DESCRIPTION OF THE INVENTION

The following examples illustrate non-limiting applications of the current invention:

Example 1

Two samples of HCO from Lloydminster, Alberta, Canada, were heated for 2 hours at 150 ⁰ C followed by atmospheric pressure distillation, Sample 1 having 10 parts by weight THFA per 90 parts by weight HCO, and Sample 2 having no THFA. Sample 1

was aerated and stirred with a magnetic Teflon®-coated stirrer bar during the heating step prior to distillation, and the THFA-HCO mixture was stirred during distillation. The samples were heated until excessive foaming occurred in the distillation apparatus. Distillation was carried out using the apparatus described in the American Society of Testing Materials (ASTM) method D86. The initial and final boiling points for atmospheric pressure distillate of Sample 2 were 143°C and 342°C, respectively. The initial and final boiling points for the atmospheric pressure distillate of Sample 1 were 158 ⁰ C and 320 ⁰ C, respectively.

It is known that THFA is able to form small amounts of organoperoxide (THFAP) under aeration, especially at elevated temperatures. Organoperoxides are able to decompose under heat to create free radicals which are believed to enhance thermal cracking of molecules such as those in HCO. It is believed that a functionality of THFA is to generate HCO free radicals conducive to enhanced thermal cracking before or during distillation when the THFA is exposed to oxygen alone or in combination with HCO. This is indicated by lower maximum boiling point of the Sample 1 distillate than of the Sample 2 distillate (i.e. 320 ⁰ C vs. 342°C).

It will be readily apparent to persons skilled in the art that aeration may be carried out in a number of different ways, although the results may vary. For example, the THFA- HCO mixture can be aerated prior to distillation as described above, the THFA-HCO mixture can be aerated during the distillation, the distillate (containing THFA) can be aerated, THFA can be aerated prior to mixing with HCO, etc.

Table 1 below compares results obtained by distillation of Samples 1 and 2:

1 HCO input = 90 21 grams (includes water)

Therefore, the distillation of THFA-HCO mixture achieved the following results:

• 45% increase in yield of distillate by weight using THFA additive (Sample 1) vs. no additive (Sample 2).

• 53% reduction in acid content of the Sample 1 distillate (as measured by total acid number "TAN") vs. the Sample 2 distillate.

In addition, the Sample 1 distillate had the following characteristics, relative to the undistilled HCO feed:

• 14% reduction in the olefin content of the Sample 1 distillate, as measured by nuclear magnetic resonance (NMR) vs. the undistilled HCO feed.

• 88% reduction in acid content of the Sample 1 distillate, (as measured by total acid number "TAN") vs. the undistilled HCO.

• 44% reduction in sulphur content of the Sample 1 distillate, having THFA added to the HCO feed vs. the undistilled HCO feed (i.e. 2.1 % and 3.8% sulphur by weight in Sample 1 distillate and undistilled HCO feed, respectively).

Addition of THFA to the HCO feed clearly enhanced the value of the distillate while producing an inorganic ash free product. Such a product would be clearly suitable for use as a fuel in, for example, gas turbines or other combustion devices producing steam, electricity, or steam plus electricity. The product may also be used as a higher value oil-refinery or upgrader feedstock.

Example 2

Sample 3, having the same HCO used in Example 1 , was distilled in similar fashion to Example 1 above, to determine the effect of THFA on distillate density (e.g. American Petroleum Institute "API" gravity") and viscosity. Sample 3, consisting of a THFA-HCO mixture having 10 parts by weight THFA per 90 parts by weight HCO, was heated for 2 hours at 150 ⁰ C with aeration and stirring, followed by atmospheric pressure distillation. The results are as follows:

• 201 % increase in API gravity of Sample 3 distillate vs. undistilled HCO feed (i.e. API gravity of 9.3 for undistilled HCO feed vs. API gravity of 27.0 for Sample 3).

• 99.9% reduction in viscosity of Sample 3 distillate vs. undistilled HCO feed (i.e. viscosity of 93 centipoises for Sample 3 vs. 82200 centipoises for undistilled HCO feed).

These results clearly show the value of adding high boiling point THFA alcohol-ether to HCO, especially high-sulphur HCO, (i.e. sour heavy crude oil).

Example 3 Two samples (Samples 4 and 5) of HCO (this time bitumen from Athabasca, Alberta, Canada), were distilled via atmospheric pressure distillation (760 mm mercury pressure) followed by vacuum distillation (0.67 mm mercury pressure) in which distilled gases during the atmospheric pressure distillation were collected in a Tedlar® bag. Samples 4 and 5 were not subjected to 2 hour aeration, stirring or heating at 150 ⁰ C. Sample 4 had 10 parts by weight THFA per 90 parts by weight HCO, and Sample 5 had no THFA. Distillations were carried out using the apparatus described in the American Society of Testing Materials (ASTM) method D86. Sample 4 was stirred with a magnetic Teflon®- coated stirrer bar, during the atmospheric distillation. Atmospheric pressure distillation time for Sample 4 was 528 seconds (time from start of producing distillate to the end of producing distillate). The initial and final boiling points for atmospheric pressure distillate of Sample 5 were 296°C and 374°C, respectively. The initial and final boiling points for atmospheric pressure distillate of Sample 4 were 176°C and 38O ⁰ C, respectively.

The HCO feed had the following properties: viscosity 350,000 cP at 20 ⁰ C, olefins 0.334, TAN = 3.22, API -8.5, density ~1.017, sulphur 4.98 wt%.

The addition of THFA to the HCO achieved the following results:

• 10.1% increase in yield of atmospheric pressure distillate (47.7% vs. 42.9 wt% of bitumen feed using the THFA additive (Sample 4) vs. no additive (Sample 5);

• 13.6% reduction in the yield of atmospheric pressure non-distillable residue (47.8% vs. 54.3%) using the THFA additive (Sample 4) vs. no additive (Sample

5);

• 4.6% increase in the combined yield of atmospheric pressure distillate and vacuum distillate (61.4% vs. 58.3 wt%) using the THFA additive (Sample 4) vs. no additive (Sample 5);

• 37.6% reduction in acid content of the atmospheric pressure distillate ("TAN" 0.90 vs. 1.36) using the THFA additive (Sample 4) vs. no additive (Sample 5);

• 46.0% reduction in olefins content (millimoles H/gram 0.830 vs. 1.537) of the atmospheric pressure distillate using the THFA additive (Sample 4) vs. no additive (Sample 5); and

• 37.6% reduction in viscosity at 20 ⁰ C of the atmospheric pressure distillate (centipoises 11.3 vs. 18.1) using the THFA additive (Sample 4) vs. no additive

(Sample 5).

In addition, the Sample 4 distillate had the following characteristics, relative to the undistilled HCO feed:

• 177% increase in API gravity of the atmospheric pressure distillate using the THFA additive (Sample 4) vs. the undistilled HCO feed (API 23.6 vs. -8.5);

• 34.5% reduction in sulphur content of the atmospheric pressure distillate using the THFA additive (Sample 4) vs. the undistilled HCO feed (sulphur wt% 3.26 vs.

4.98);

• 72.0% reduction in acid content of the atmospheric pressure distillate using the THFA additive (Sample 4) vs. the undistilled HCO feed (TAN 0.90 vs. 3.22); and

• >99.9% reduction in viscosity of the atmospheric pressure distillate using the THFA additive (Sample 4) vs. the undistilled HCO feed (centipoises 11.3 vs. 350,000).

THFA can be removed from the distillate, as from LCO, by distillation since its boiling point of 178 ⁰ C is lower than that of the majority of LCO components. Most of the LCO

components have boiling points higher than THFA. With respect to the distillate of Sample 4, it is estimated that less than about 5% of the distillate boils below the THFA boiling point, and that about 95% of the distillate boils above the THFA boiling point. Therefore it is possible to obtain high THFA recovery by distillation alone.

Distillation units with multiple theoretical plates (e.g. packed commercial hydrocarbon distillation columns typical in oil refineries for LCO from crude oil) could easily separate THFA from the distillate in one distillation. This was not possible in the above examples, which used a low efficiency glass laboratory distillation apparatus.

THFA is also water soluble, therefore an alternative for removing THFA from the distillate would be to remove the THFA by water extraction.

However, it is not always necessary to remove all of the THFA from the LCO.

It is believed that another functionality of THFA is to reduce heavy hydrocarbon viscosity during first stage distillation to produce LGO and or LCO, and resulting in better fluid mechanics necessary for enhanced HCO cracking to distillable products. It is expected that distillation feedstock having THFA content that is higher or lower than the 10 wt% specifically discussed herein would result in similar enhancements in LCO or LCO quality including yield, sulphur content, olefin content, etc., although quantitatively the results are expected to be sensitive to THFA dose. In addition, it is expected that as the present invention is scaled up to industrial scale, and as the present invention is optimized for various applications (e.g. depending on the type or quality of HCO feed stock, the type or quality of distillate desired, financial considerations, energy efficiency considerations, etc.), parameters of the invention, including the dose of THFA, will be adjusted without departing from the scope of the invention. Therefore, based on the description of the invention provided herein, it will be readily apparent to persons skilled in the art that the present invention is not limited to doses of 10 wt%, and that the scope of the invention includes THFA doses higher and lower than 10 wt%.

It is important to note that the distillates produced from Samples 1 , 3 and 4 above are free of heavy metals. Therefore they can be upgraded (with or without the THFA contained therein) to reduce sulphur content and to further increase API gravity, since they will not foul hydrotreater catalysts.

In the Examples described above, the THFA and HCO were mixed and then added to the distillation vessel together. However, the invention need not necessarily be carried out in this manner. It is also possible to add the THFA and HCO to the distillation vessel separately. For example, pump THFA and HCO separately into the distillation vessel.