WO1997016506A2 - Single stage oil refining process - Google Patents

Abstract

A single stage process for completely refining a heavy hydrocarbon feedstock wherein the feedstock is monotonously heated to a final temperature of about 520-580 °C at an average heating rate of at least about 5 °C/minute at atmospheric pressure, and bubbling a non-condensing, non-oxidizing gas through the feedstock at an average flow rate of at least 0.3 wt.% per minute while the feedstock is being heated, and recovering refined liquid and gaseous hydrocarbon products and coke.

Description

SINGLE STAGE OIL REFINING PROCESS

Field of The Invention

This invention relates to the refining of liquid and solid hydrocarbon feedstocks, especially those containing components boiling at 360 °C or more, to produce higher value products such as hydrocarbon fuels and products for use in the chemical industry. More particularly, this invention relates to a single-stage process for refining heavy hydrocarbon feedstocks such as crude petroleum, residual oils, tar, bitumen, gas condensate, and the like, while enabling a high recovery of light hydrocarbon products.

Background of the Invention Industrial processes for refining hydrocarbon mixtures (e.g., crude oil) are known. Such refining is typically conducted in a number of step-by-step stages, for example:

1 ) atmospheric distillation of crude oil followed by recovery of light fractions, e.g., gasoline, kerosene, and diesel fuel; and yielding a residual oil boiling at 350 °C or higher.

2) vacuum distillation of the residual oil, followed by recovery of vacuum distillate, e.g., gas oil boiling at from about 350 °C to about 500 °C; and yielding a heavy residual oil or tar boiling at higher than about 500 °C.

Methods of refining the gas oil (vacuum distillate) include, e.g., catalytic cracking wherein a finely-devel- oped catalyst is introduced into a high-velocity stream of gas oil vapors at a temperature of 520-550 °C, and the oil-catalyst contact time ranges from 2-10 sec. The products include light hydrocarbons boiling at under 350 °C, e.g., gasoline, kerosene, diesel fuel, C1-C4 gases; and coke which deposits onto the catalyst. Regener- ation of the catalyst is provided via burning the coke from the catalyst.

The residual oil of atmosphere distillation is refined to produce boiler fuel via processes such as: - visbreaking (i.e., reducing the viscosity via partial pyrolysis of the residual oil); hydrocracking (i.e., catalytic hydrogenation employing hydrogen and partial cracking of heavy components at high pressure (above 150 atm) and a tempera- ture of about 400-425 °C); hydrorefining (i.e., subjecting the oil to hydrogenation of sulfurous, nitrogenous and oxygen- containing compounds and of nonsaturated hydrocarbons ) . The process employs a pressure of about 5 atm and a tem- perature of about 380-420 ^βC.

Methods of refining the tar include: - thermocatalytic cracking at atmospheric pressure and a temperature of about 500-550 °C. In this technique the tar is fed to a reactor as a vapor or liquid droplets. The reactor is partially filled by catalyst. Coke may be used as the catalyst. The products are: C1-C4 hydrocarbon gases (9-14 %), gasoline (10-14 %), kerosene and diesel fuel (boiling at under 350 °C) (15-20 %), gas oil (boiling at 350-500 °C) (20-40 %), and coke (10-23 %). The above products yields (shown in percent by weight) depend on the composition of the tar. Produced coke, as a rule, is burned as a fuel, e.g., to provide the needed heating of the reactor or gasified into fuel gas containing carbon monoxide and hydrogen. - delayed coking at a temperature of 370-480 °C and a pressure of 2-6 atm. The coke yield is up to 70 %. Ad¬ ditionally, some amounts of diesel or boiler fuel are also produced. Duration of the process (which runs in a closed reactor) ranges from 2-12 hours; and - oxidation of tar at a temperature of 180-400 °C and a pressure of 4-4.5 atm via bubbling air or oxygen through the tar for 2-12 hours, and yielding up to 70 % bitumen. Shortcomings of these known methods of refining include:

1) They constitute multi-stage processing. This makes it very expensive (because of investment costs and power costs) to improve the yields of valuable hydrocarbon products;

2) The productivity of each stage is low, i.e., the volumetric rate for each stage is- low;

3 ) Incomplete use is made of hydrocarbons from the raw material; and 4) Formation during each stage of heavy residue; which worsens the ecological aspects of the process.

These shortcomings result in an average level of oil refining effectiveness of about 80 % in developed countries, and this varies from 48-75 % in other countries. Only in a very few refineries is the refining effectiveness as high as 92-95 %, and the cost of refining is very high there.

It is known to stimulate the distillation of hydrocarbon mixtures via injecting into a reactor (still) various gases which do not form oxidation products and do not interact with the processed raw material. Such methods are known for atmospheric distillation of crude oil or other hydrocarbon mixtures and for vacuum distillation carried out at a constant temperature below the cracking temperature of hydrocarbons. Supply of the gas stimulates the distillation, and both the temperature and process duration are reduced for related hydrocarbons. The gases are supplied via either injecting the gases into the still or through perforations in the still's wall, bubbling the gases through the bottom of a still or via feeding the gas upwardly through a jet nozzle placed in the bottom toward the liquid mixture fed from the top of the still, and wherein a special cylinder is inserted into the still to provide a narrow gap between the cylinder and the still's wall in order to provide good mixing and uniform tempera¬ ture distribution.

It is also known to feed into the oil being treated liquid hydrocarbons with boiling temperatures lower than the distillation temperature so as to use the resulting produced vapors to stimulate the distillation.

It is also known to use slow-rate heating of the processed mixture to provide a consistent evaporation of hydrocarbons with different boiling temperatures.

Other known methods of stimulating the distillation include feeding inert gases into the hydrocarbon mixture during distillation of heavier hydrocarbons to extract lighter oils from a mixture of these oils with heavier ones without implementation of hydrocarbon cracking, but via use of hydrocarbon gases as an antisolvent. Many processes are known for refining mixtures of heavy hydrocarbons, e.g., residues from atmospheric-vacuum distillation and cracking processes, or resins or tar or solid hydrocarboncontaining materials (e.g., coal, shales, etc. ) wherein the process is stimulated via feeding gases into the feedstock.

Watson (US Patent 1,673,854) suggested a process for refining the heavy residue of oil distillation or cracking via circulation of water vapor or gas flowed through perforations in the bottom of a reactor containing the residue. The gas flow prevents the deposition of a solid fraction onto the reactor bottom, and stimulates the evaporation of light fractions. The heavy liquid fractions flow out of the reactor through holes in the bottom of the reactor. The residue is withdrawn and used as a fuel for heating the reactor, and another part of the liquid residue is enriched by fuel and injected back into the reactor through the wall thereof. The temperature of the residue is maintained as high as needed to avoid the plugging the holes for its circulation. No data on the method's effectivity are provided.

Bywater (US Patent 1,844,741) and Miller (US Patent Nos. 1,893,145 and 1,924,163) suggested the use in tar refining of hot gases of coal gasifying, carbonizing or distillation via arranging contact between such gases and treated tar or other heavy residue. The process is continued until cessation of the production of condensing hydrocarbons vapors and a pitch. -No data are reported on the product composition or refining effectiveness.

Freeman (US Patent 2,095,863) suggested to produce low-boiling-hydrocarbons from high-boiling ones or solid materials containing hydrocarbon components (e.g., coal, shales, etc. ) via passing such materials through a train of heated chambers. Each chamber has its own temperature and the temperature increases from one chamber to another. In each chamber contact is arranged between the processed materials and hydrocarbon gases or vapors obtained either as a product in earlier chambers or from separate source. It was suggested to produce some preliminary activation of these gases by passing them through special vessels over heated alkaline materials before feeding them into the refining chambers. No quantitative characteristics of the processes are reported.

Such prior art processes do not solve the problem of improving the level of oil refining, and it is unlikely that they have any advantages over the method of tar refining via the thermocatalytic technique.

In US Patent 2,700,016, Naumann suggested a refining process for distilling high-boiling hydrocarbons having a boiling temperature greater than 200 °C to provide higher yields of distillates and production of new products: i.e., black wax. The idea of the method is to heat the high-boiling hydrocarbons fed into a stationary reactor by continuously circulating a neutral gas, which does not contain an oxidant (nitrogen is preferred, but combustion products may be used) and which is heated up to 800-1400 °C. Heating of the high-boiling hydrocarbons in the reactor is provided wholly by heat exchange with the hot gas, and the temperature of the withdrawn product does not exceed 250-360 °C. Circulation of the gas is maintained until the content of hydrocarbons in the outlet gases drops down to a few percent. The remaining mass is outgassed and then air or vapor of heated residue is passed through the mass at a temperature of 900-1000 °C. As a result, black wax is produced, which possesses unusual properties, and also hydrocarbon gases and carbon monoxide. The yield of distillates can be as high as 50- 70 % depending on the procesε parameters and composition of the stock. Process duration is up to 12 hours.

The main shortcomings of the foregoing process are: it is multistage; it is a cyclic process; the productivity is low; and it requires a high power consumption. Besides, heating the feed by hot gases results in local overheating of liquid hydrocarbons, inevitably causing an increased conversion of the hydrocarbons into coke or pyrocarbon which may constitute up to 30 % by weight of the feedstock.

Summary of the Invention

The present invention provides an improved process for the refining of oil and other hydrocarbons containing heavy fractions, which employs either a batch or continuous type reactor, and differs from prior art processes by the following:

- it is conducted in one stage at atmospheric pressure, producing final gases, solid, (i.e., dry coke) products, and liquid hydrocarbons containing no coking components;

- it implements a monotonic increase in the tem¬ perature of a feedstock, i.e., the temperature of the feedstock does not decease during operation of the process, from a lower temperature, e.g. 80-375 ^CC, depending upon feedstock composition, to 525 °C or more;

- the average heating rate during the processing is much higher (i.e., more than 5 °C per minute); - it implements bubbling of a non-oxidizing gas, i.e., non-condensing hydrocarbon or other gases which do not oxidize the feedstock components, through the feedstock at temperatures including the temperature range within which the cracking of hydrocarbons and chemical interaction between hydrocarbons of the stock material and bubbling gases take place; and

- the specific average flow rate of the bubbling gas during the processing is more than 0.3 % by weight of the feedstock in the reaction zone per minute. (Averaging is over the processing time).

The combination of the above features within one process results in: the complete refining of oil hydrocarbons or heavy residuals during a single processing stage conducted at atmospheric pressure without any intermediate cooling of the stock, producing gases, solids (in the form of dry coke) and liquid hydrocarbons (and such liquid hydrocarbons contain substantially no coking components) as final products; - faster refining procedure compared to existing industrial or known practices; and

- higher aggregate yield of gaseous and liquid products due to reduction of both coke yield and losses inherent to multistage processes. It is a primary object of the present invention to provide a simplified process for refining liquid and solid hydrocarbon feedstocks, including heavy oils containing components boiling above 360 °C, e.g., crude oil, residual oil, tar, gas-condensates, shale oil and the like, which process overcomes the problems of the prior art processes.

Additional objects of the present invention are to provide a process which:

- enables single-stage complete refining of any hydrocarbon mixture at atmospheric pressure into final products (i.e., gasoline, kerosene, diesel fuel, gas oil, hydrocarbon gases or coke) without any added catalysts; achieves process stimulation by bubbling hydrocarbon or other non-condensing and non-oxidizing gases through the hydrocarbon feedstock, which gases chemically interact with components of the feedstock and wherein such interaction is facilitated catalytically by natural admixtures of transition metals, such as Fe, Ni and V in the feedstock, and wherein the average gas feeding rate is more than 0.3 % of initial feedstock weight in the reaction zone per minute;

- achieves process stimulation and speeding up of the processing via monotonic (i.e., continuous or stepwise) heating of the stock at an average heating rate of more than 5 °C per minute.

Still a further object of the present invention is an oil refining process which permits faster refining of heavy oil feedstocks, increased yields of light hydro¬ carbon products, and reduced yields of coke. Additional objects and advantages of the invention will appear in the following description, and other objects and advantages will be apparent from that description, or may be learned by practice of the inven¬ tion. The stated objects and advantages of the invention may be realized and attained by the process steps and their interaction, and operational features particularly pointed out in the appended claims.

To achieve the foregoing objects and in accordance with the purpose of the invention, as embodied and broadly described herein, there is provided a process for refining a liquid hydrocarbon feedstock, which comprises introducing the feedstock into a reaction zone; heating the feedstock in the reaction zone from an initial tem¬ perature in the range of about 80-375 °C (depending on feedstock composition) to a final temperature in the range of from about 520 °C to about 580 °C at an average heating rate of about 5 °C/minute or greater, while maintaining the pressure in the reaction zone at atmospheric pressure; introducing a heated non-condensing and non-oxidizing gas into the reaction zone at an average flow rate of at least 0.3 % of feedstock weight in the reaction zone per minute; and recovering from the reaction zone refined liquid and gaseous hydrocarbon products and coke.

Feedstocks well suited for use in the invention are heavy oil feedstocks, such as crude oils, residual oils, gas condensates, tars, bitumens, shale oil and coal- derived liquids, or fractions of any of the above. Such feedstocks typically contain substantial quantities of hydrocarbons boiling above about 360 °C. As used herein the term "non-condensing and non- oxidizing gas" refers to hydrocarbon gases which are gaseous at standard conditions and contain no compounds which could oxidize the hydrocarbon feedstock, and preferred such gases are C1-C4 hydrocarbons, especially methane, ethane, propane and butane and their mixtures, gaseous products of oil refining and coal processing, and nitrogen, and hydrogen and rare gases etc.

In one embodiment of the invention, the liquid and gaseous hydrocarbon products are withdrawn at a tempera- ture not higher than about 330 °C from a first portion of the reaction zone wherein the feedstock is heated to a temperature of about 360-430 °C, and the remaining portion of the feedstock is passed to a second portion of the reaction zone wherein it is heated to a higher tempera- ture, e.g., from about 520 °C to about 580 °C, while a heated non- condensing and non-oxidizing gas is bubbled through it, completing the process and forming dry coke, which is recovered from the second portion of the reaction zone. The accompanying drawings, which are incorporated in and constitute a part of this specification illustrate preferred embodiments of the invention, and together with the description, serve to explain the principles of the invention. Brief description of the Drawings

Figure 1 illustrates laboratory scale apparatus for the batch-type operation of the process of the present in¬ vention;

Figure 2 is a schematic flow diagram of the continuous-type operation of the process of the present invention;

Figure 3 is a plot of the total time required for refining a crude oil feedstock versus the average rate of heating the feedstock, employing the process of the present invention;

Figure 4 is a plot of the amounts of gas, liquid and solid products obtained versus the average heating rate when processing a crude oil feedstock in accordance with the present invention; Figure 5 is a plot of the amounts of coke and pyrocarbon produced when refining a crude oil feedstock in accordance with the present invention at varying average gas flow rates and average feedstock heating rates; and

Figure 6 is a plot of the output of light hydro- carbons, coke plus pyrocarbon and energy consumption obtained when processing crude oil and residual oil feedstocks in accordance with the present invention. Description of Preferred Embodiments

An object of the present process of oil refining is to reduce the duration of thermal processing of liquid- phase raw material (also referred to herein as feedstock or stock) at atmospheric pressure by stimulation of both evaporation processes and chemical reactions due to bubbling the hydrocarbon gases (e.g., natural gas, petro- chemical gases, propane-butane mixture, etc. ) through the feedstock (raw material ) .

The gas flow removes the evaporating fractions faster, and permits a reduction in the working tempera¬ tures needed for extraction of that fractions. It also shortens the processing time and increases the degree of evaporation.

The gas bubbling stimulates the chemical reactions due to appropriate turbulent gas flow, which results in easier access of raw material to metals which are in admixture with the raw material and which posses catalytic properties, (i.e., homogeneous catalysis by natural ad¬ mixtures in the raw material is stimulated), in that the hydrocarbon gases start to enter into chemical reactions so as to increase the yield of light products. Moreover, the bubbling of the gas changes both the characteristics of the process of coking and the texture of the produced coke. The produced coke is a highly porous powder which can be removed easily from the reactor where any type of liquid hydrocarbons may be refined ( starting from crude oil to tars and remains of deasphalting) . The flow rate of bubbled gas may be adjusted for the desired intensity of gas evolution or rate of chemical reactions. The type of bubbled gas is selected in dependence on the composition of products or coke texture desired and taking into account the economics of the processing. The complete refining of raw material (up to 97- 99 %) is provided via a single stage operation at atmospheric pressure. The duration of such refining is more than 2-3 times faster than that of the standard practices. The present process results in reducing the yields of coke and other heavy products, and it excludes the formation of heavy residues such as the oil residue formed during crude oil refining, tar formed during oil or oil residue refining, and the like. Instead of these heavy residues, light fractions, such as gases, light liquids and some amount of heavy liquids are formed. The heavy oil produced by the present process is a mixture of low- volatility hydrocarbons with boiling temperatures of 500 °C and higher and which does not contain heavy products contributing to coke or soot formation during further processing or use. For example, gas oil produced by the present process may be used instead of residual oil as a fuel for boilers.

The coke produced by the present process is also a valuable product. For example, it may be used in metallurgy, since it concentrates 100 % of the iron, about 50 % of the nickel and about 50 % of the vanadium contained in the parent raw material. This coke can be easily removed from reactor. During refining by the present process more than

30 % of the sulphur, and more than 80 % of the nitrogen and oxygen, combined with hydrocarbons in the raw material, are extracted as gases.

Various heavy oil feedstocks were refined using laboratory equipment in accordance with the present inven¬ tion, as described herein below.

Description of Laboratory Set-up

Experiments were conducted using a special laboratory set-up employing a batch-operated reactor. The reactor's charge of raw material varied from 50 to 100 gms. The reactor was equipped with apparatus which enabled the gas to be passed by a bubbler through the raw material. The reactor was placed vertically into an electric oven, which provided heating of the reactor up to 1000 °C at a controllable temperature rate. Withdrawal of products was provided in the upper part of reactor. The products, in gaseous and vaporized forms, were passed into a condenser, cooled by water at a temperature of 20 °C. Condensed products were collected in a gauging tank. The flow of gases and non-condensed vapors were fed through a flowmeter to a burner for complete combustion thereof.

After termination of liquid products extraction (and coke formation) the heating was switched off. After the reactor was cooled, the coke was poured out of the reactor and its weight was measured.

During operation of the process the following para¬ meters were controlled: temperature in the oven outside the reactor; temperature of the raw material in the vicinity of the bubbler; temperature of gases and vapors near the outlet from reactor; flow rates and temperature of gas at the inlet to the reactor; and flow rate of outgoing gas and vapors. The composition of the gas after the condenser was analyzed by gas chromatography. The liquid products were analyzed using atmospheric distillation wherein such products were heated to a tem¬ perature of 190 °C at atmospheric pressure, and after that, heated to a temperature of 240 °C at a pressure of 100 Torr, followed by heating to a temperature of 300 °C at a pressure of 5 Torr, and lastly, heating to 300 °C at a pressure of 1 Torr.

The fractional composition was obtained via weighing the liquid products and their fractions. The elemental composition (i.e., H, N, C, S, and metals) of the raw material, liquid and solid products was analyzed by standard methods. Other methods of analysis were also used: e.g., differential thermochemical analysis (DTA), mass-spectro- metry, gas-liquid chromatography, and determination of molecular weight distributions for both the raw material and liquid products, phase X- ray analysis of coke.

Results of all these analyses were used to obtain the balance of products distribution in the liquid, gaseous and solid phases.

Referring to Fig. 1, the experimental batch- operated reactor and related equipment, and the operation thereof, are described hereinbelow.

A cylindrical reactor (1) was used. The reactor had an inner diameter of 45 mm, a length of 270 mm, and working space of 0.43 1 between its ends. A pipe (2) through the cylinder head was used to feed the hot gas into a collector (3 ) . The gas passed upwardly through holes in perforated diaphragm (4) into the working space of the reactor and was bubbled through the stock ( 5 ) being refined. The holes were 0.5 mm in diameter and they numbered 256. Uniformity of the bubbling was provided by uniform distribution of the holes across the diaphragm and by having the total area of the holes be several times less than cross-section area of the collector. The tem¬ perature of the bubbling gas was equal to the temperature of the feedstock in the area of the gas. In the top part of the reactor a sleeve (6) was placed for withdrawing the products of refining, which were carried away by the bubbling gas. The sleeve was covered on its outside by heatinsulating material down to the branch pipe (7) provided for withdrawing low boiling components. The branch pipe (7) provided for these outgoing gases led to a water cooled refrigerator (8 ) from which the condensed vapors and liquid products were drained into the receiving tank (19). Products which were not condensed in this first refrigerator passed into a trap (9) cooled by liquid nitrogen or by a mixture of "dry ice" (frozen carbon dioxide) and acetone ( 10) . After the trap the gas passed through a pipe (11) equipped with a gas sampler (12) (used for carrying out the gas chromatographic analyses of the outgas composition) and flow meter (13) and was combusted then in the burner ( 1 ) .

The reactor was made of high-temperature steel. Some of the branching sleeves and the trap were made of glass. Tight connections between the metal and glass parts were provided by oil and heat resistant rubber placed over the joints.

The bubbling gas was delivered to the reactor through flow meter (15), and then heated to a temperature approximately equal to the temperature of the feedstock in the reactor zone wherein said gas was introduced in a heat exchanger (17). Gas feeding tube (2) was input into reactor (1) through tight asbestos isolation (16). The temperature of the supplied gas near the inlet was measured by thermocouple (18), and the temperature of the stock by thermocouple (20). The temperature of gases and vapors in the zone of products withdrawal was measured by thermocouple (21). The process was conducted as follows: stock was loaded into the reactor at room temperature. For each run the weight of the stock varied from 50-100 gms. After loading, the reactor was placed vertically into the electric oven (22). Heating was controlled via the appropriate variation of the voltage supplied to the oven. The average heating rate was varied in different runs from 2-30 °C per minute.

At a liquid stock temperature of 80-375 °C, depending on feedstock composition, the bubbling was started. The average gas flow rate was varied from 0-1.5 % of the weight of the feedstock per minute.

Continuous measurements of the following parameters were carried out during the refining: temperature of the stock, temperature of the products, flow rate of the input gas and the output gas (after the second refrigerator) , amount of liquid products in tanks (19) and (9). The process was stopped by turning off the heater when the remaining feedstock achieved a final processing tempera- ture of 450-1000 °C.

After cooling down the reactor and the products, the reactor was opened and the produced coke was allowed to pour out. When optimal regimes were selected, the coke was a fine powder. Weighing of the reactor was carried out to estimate the amount of pyrocarbon deposited on the wall (the empty reactor was weighed also). No resin and pyrocarbon formation was observed on the reactor wall or pipes during any process conducted within the range of optimal regimes (and for any stock material ranging from crude oil to heavy asphaltenes ) .

Fractional composition of liquid products was determined via standard fractionation and weighing of every separated fraction with different boiling tempera¬ tures. The amount of produced coke also was determined by appropriate weighing.

The elemental composition of the parent stock material and liquid and solid products was determined via standard methods of elementary analysis (C, H, N, S and metals Fe, Ni, V). The coke structure was identified via X-ray analysis. The group composition of parent hydrocarbons and liquid products was investigated by mass- spectrometry, differential thermal analysis, highly efficient gasliquid chromatography and measuring the heat effects at condensation. Outgas composition was controlled on a time to time basis by gas-chromatography via sampling the gas through the sleeve (12).

After the completion of every experiment and all appropriate measurements the products balance was derived.

During some regimes (e.g., at low heating rate and flow rate of bubbling gas or at no bubbling) the formation of coke or pyrocarbon film was observed on the reactor wall and even on the wall of the bubbler which could not be removed by shaking. In the products balance such deposited product was accounted for as pyrocarbon.

When refining the heavy stock material the deposition of thick products was observed in the end of sleeve (6) which guides the products to the tank (19). These products appeared because the temperature at that point was not more than 150 ^CC. After minor heating of the pipe wall these products drained easily down into the tank (19). However, if optimal bubbling regimes were used no such effect was observed because of shorter residence time in the cold zone and the "washing" of them down by lighter liquid products. The thick products were also examined as well as other liquid products.

When calculating the balance, the amount of non- hydrocarbon gaseous products (i.e., hydrogen sulfide, oxygen, and nitrogen) which were released during refining was subtracted from the stock weight.

The above-described apparatus and methods were used in the refining of a crude oil, an asphaltite and a residual oil by the process of the present invention, as described below in Examples 1, 2 and 3. Boiling tempera¬ tures are indicated hereinbelow as "T boil." Example 1. Refining of crude oil

Characterization of crude oil feedstock: a) Fractional composition:

T boil, °C Weight %

Light products: gasoline <190 16.3 kerosene 190-240 5.9 fuel oil 240-350 20.7 light gas oil 350-500 22.2 tar >500 34.9

Total 100

b) elemental composition (wt %):

C - 85.8 H - 12.25, C/H = 0.58 (atomic ratio)

S - 2.05

N - 1.0

Fe - 3.1 x 10-3

Ni - 2.55 x 10-3 V - 9.1 x 10-3

Results of refining crude oil

Experimental data has shown that higher methane flow rates and/or higher heating rates of the feedstock result in faster refining, lower yields of coke, and higher yields of liquid products.

In the optimal regime wherein methane was fed at a flow rate of 0.5 % by weight of the feedstock per minute, the output of products began at a temperature of 90-105 °C and terminated in 29 min. at a temperature of 470 °C. The coking terminated after 34 min. at a temperature of 525 °C so the average heating rate was 12.5 °C per minute. The temperature of the gaseous and vaporized products withdrawing was less than 330 °C. The composition of the products is shown in Table 1. More than 89 % of the crude oil was refined into liquid products. This included 86 % light petroleum products and light gasoil which are useful either as fuel for car engines or boilers, or as raw material for further refining into more valuable petrochemicaL products.

There was also produced some amount of heavy gasoil (i.e., about 3.3 wt %, boiling at >500 °C), a mixture of cycloalkanes (n<33) and both normal and iso-alkanes CnH(2n+2) (n<37). This heavy product differs principally from tars, which are produced via standard technology. If the products boiling at > 350 °C are used as fuel for boilers, then they will improve- greatly the combustion processes and reduce the emission of such ecologically harmful compounds as polyaromatic compounds or soot. When the present process is used, the coke produced at a final feedstock temperature of T > 520 °C is a porous small-grain powder which is easily removable from the reactor. However, if no gas bubbling is provided, then the amount of produced coke increases abruptly (i.e., by two times in the experimental reactor) and it is produced mainly as pyrocarbon, which deposits on the reactor walls.

Typical composition of produced coke is as follows

(in % by weight): °C - 90.5; H - 2.8; S - 3.6; N - 2.1

(these values can be varied via changing the gas rate). The produced coke is suitable for various applications, such as metallurgy - since the coke accumulates the heavy metals which are used as dopants. If the parent crude oil contains metals in large concentrations, then the produced coke may be used as a raw material for producing such metals. It has been observed that 100 % of the iron, 35- 40 % of the nickel and 38-45 % of the vanadium are accumulated in the produced coke.

The present method of oil refining has been found to have the following effects with respect to sulfur contained in the feedstock. 1-1.5 % of the sulfur transfers into gas (i.e., hydrogen sulfide), some small amount is accumulated in the coke and the rest of the sulfur remained in liquid products (mainly as mercaptans). The concentration of other polar compounds (O- and N- containing) is reduced by about 80 %.

As shown in Table 1, comparison of the performance of the present process with those resulting from existing technologies (which are calculated from the composition of the feedstock and characteristics of the appropriate processes) indicates that the single stage of present process supersedes the 3 stages of standard refining (i.e., atmospheric distillation (I), vacuum distillation (II) and thermocatalytic cracking of tar (III). If an additional stage (i.e., catalytic cracking of light gasoil (IV) is used, then the total yield of light liquid products and gas was found to be 8 % higher than the standard practice of four-stage crude oil refining ( see Table 1 ) .

Use of the present process eliminates the need for repeated heating of the stock, which is required in standard refining practice (stages II and III).

The total consumption of methane during the present process (in the optimal regime) was found to be about 10 % of weight of the feedstock. The use of nitrogen (i.e., an inert or non-reacting gas) instead of methane causes lower yields of liquid products (at the same conditions) and higher yields of gases (C1-C4) and coke.

The temperature range used in the present process (200-530 °C) coincides with the temperature range which is used in standard four-staged refining; however, the duration of the present process is more than 2 times shorter. TABLE 1

Composition of products (% by weight) of oil refining

Comparison of effectiveness of the present process and existing technologies

Existing

Products Present Process Technology change of (single stage) (stage I+II) yield, % by weight

Conversion into 99 65 +34 useful products, including:

Gases (C1-C4) 7.6 1.0 +6.6

Light products 55 42.5 +12.5 Tboil <350 °C

Light gasoil 31 21.5 +9.5

350 °C < Tboil <500

Heavy gasoil 2.4 0 +2.4 Tboil >500 °C

Coke 3.0 - +3.0

Residues: tar, - 34 -34

Tboil > 500 °C

Losses 1.0 1.0 0

Existing

Products Present Process Technology change of

(single stage) (stage I+II+ yield, %

III) by weight

Conversion into 99 98 +1.0 useful products, including:

Gases (C1-C4) 7.6 4.7 +2.9

Light products 55 50.7 +4.3 Tboil <350 °C

Light gasoil 31 30 +1.0

350 °C < Tboil <500 °C

Heavy gasoil 2.4 7.0 -4.6 Tboil >500 C

Coke 3.0 5.6 ^■2.6

Losses 1.0 2.0 •1.0

Existing

Products Present Process Technology change of

+ stage IV (stage I+II+ yield, %

III+IV) by weight

Conversion into 98 97 +1.0 useful products, including:

Gases (C1-C4) 15.1 10.7 +4.4

Light products 75.5 71.7 +3.8

Tboil <350 °C

Light gasoil 2.0 2.0 0

350 °C < Tboil <500 °C

Heavy gasoil 2.4 7.0 -4.6

Tboil >500 "C

Coke 3.0 5.6 -2.6

Losses 2.0 3.0 -1.0

Example 2. Refining of residues produced by stan¬ dard oil refining practices

Asphaltite produced by deasphalting (i.e., one of the heaviest products) was used as heavy residue feedstock for refining.

Characterization of feedstock used: a) mean molecular weight: 1400 amu (atomic mass unit) ; b) melting temperature: 150 °C; c) composition (by groups), % by weight:

- paraffinic and naphthenic compounds < 0.1

- heavy asphaltenes (not soluble in hexane) 26.4

- aromatic hydrocarbons 43.6 - aromatic hydrocarbons with polar groups containing 0, N, S 30.0

d) elemental composition, % by weight C - 83-84; H - 10-9;

N - 0.65;

S - 3.5;

Fe - 7x10-3;

Ni - 9.2x10-3; V - 2.5x10-2

Ash - 2.40

Results of refining heavy residues

Experimental data have shown that bubbling the gas in the present process causes an increase in the yield of liquid products. This is so mainly due to higher total yield of light products (the yield of gasoils decreases a little). At the same time, the yield of gas products is also reduced. The amount of produced coke depends on process duration.

The chemical composition of the bubbling gas affects the composition of the products mixture noticeably. Thus, if bubbling is performed with a mixture of propane/butane, then the total yield of products exceeds the weight of the parent sample. This confirms the participation of the hydrocarbon gases in reactions converting the raw material.

The physico-chemical properties of the produced coke will depend on the refining practice used. If no bubbling gas is used, then an increased content of naphthalene (and, possibly, of other polyaromatic compounds) in the coke is observed. Such coke is difficult to remove from the reactor walls. However, if gas bubbling is provided during coking, then no polyaromatic compounds are found in coke and the elemental composition of coke is as follows: atomic ratio of C/H = 8-10; sulfur content does not exceed 2 %, nitrogen content < 1-1.5 %. 100 % of the iron, 65 % of the nickel and 30 % of the vanadium contained in the parent raw material are accumulated in the coke. Due to accumulated metals, such coke possesses catalytic activity with respect to hydrocarbon gases. The produced coke is a highly porous fine-grain freeflowing powder, which easily pours out the reactor.

Data obtained at the optimum average heating rate (15 °C per minute), the optimum average gas flow rate (0.5 % of initial feedstock weight) and at a temperature at the gaseous and vaporized products outlet of less than 330 ^βC is shown in Table 2. Comparative analysis of asphaltite refining by the present process with the results of standard refining (i.e., thermocatalytic cracking (TCC) of asphaltite of similar composition (M = 1500)) (see Table 2.) indicates the higher effectiveness of the present process, in that the yields of coke and tar are greatly reduced. Some amount of heavy gasoil (about 6 %) is produced instead of such products; and the yields of light products and light gasoil (Tboil <500 °C) (which are the most valuable products) are increased by 9.5 % and 12.6 %, respectively. TABLE 2

Comparison of asphaltite refining via present process and standard thermocatalytic cracking (TCC)

Weight, % Products Present Process TCC change of

(bubbling gas - CH4) yield, % by weight

Conversion into 99 86.1 +13.9 useful products, including:

Gases (C1-C4) 14.5 11.5 +3.0

Light products 28.5 19.0 +9.5 Tboil < 350 ^βC

Light gasoil 24.5 11.9 +12.6

350 °C < Tboil <500 ^βC

Heavy gasoil 6.1 0 +6.1 Tboil >500 °C

Coke 25.3 43.7 -18.4

Residues: (asphaltite 0 13.9 -12.9 or tar) and losses 1.0

Example 3. Refining of a residual oil

Characterization of residual oil feedstock used: a) fractional composition:

Tboil, °C % by weight

240-350 26

350-500 28

>500 46

Total 100 b) elemental composition, % by weight: C - 85.8; H - 11.5 S - 2.88 N - 0.35.

c) composition (by groups), % by weight:

- paraffinic and naphthenic compounds <0.1

- heavy asphaltenes (not soluble in hexane) 0.8 - aromatic hydrocarbons 57.4

- aromatic hydrocarbons with polar groups containing -0, N, S 41.8

Results Experimental data show that bubbling hydrocarbon gas and a faster rate of heating the raw material result in a higher yield of liquid products (including light liquids) and gas, and lower yield of coke.

On the other hand, the use of nitrogen as a working gas (nitrogen does not react with the feedstock) resulted in reducing the yield of liquid and light products, and increasing the yield of gases C1-C4.

When the optimal regime of refining was used (average heating rate of 15 ^βC/min and an average gas flow rate of 0.5 % of initial weight per minute), then the liquid products were produced starting at a temperature of 320 °C and that process proceeded until a temperature of 480 °C was reached. The coking terminated at a temperature of 530-540 °C. Duration of refining was about 30 min. Total consumption of the bubbling gas (methane) was less than 15 % of raw material weight. The temperature at the gaseous and vaporized products outlet was less than 330 °C. Comparative data on product yields for vacuum distillation (VD) and the present process are reported in Table 3. TABLE 3

Product yields during refining the residual oil

Comparison of the present process and vacuum distillation

(VD)

Weight, %

Products Present VD change of

Process yield, % by weight

Conversion into 99 53 +46 useful products, including:

Gases (C1-C4) 0 +4

Light products 34 26 +8 Tboil <350 ^βC

Light gasoil 49.5 27 +22.5

350 °C < Tboil <500 °C

Heavy gasoil 2.5 +2.5 Tboil >500 ^βC

Coke +9

Residues: tar, Tboil >500 ^βC 46 -46

Losses: 1.0 1.0 0

Continuous Process

A preferred embodiment of a reactor and related apparatus for use of the present process in a continuous operation is shown in Fig. 2. The reactor consists of three sections 101, 102 and

103, which are thermally isolated one from another by insulation 130 and are heated separately by heaters 106,

107 and 108 (furnaces or heat exchangers) . The reactor is situated vertically.

Feedstock heated in heat exchanger 109 to a beginning temperature, e.g., 80-375 ^βC (depending on its composition), is introduced continuously to reactor section 101, wherein the feedstock temperature is further Increased due to furnace heater 107 during the feedstocks flowing downwardly. A portion of the bubbling gas (Ggl) is passed though flowmeter 113 ^~and heater 110 (heat exchanger) to collector 115 provided with multiple small holes into the lower portion of the section 101. The gas temperature measured by thermocouple 118 should be approximately equal to the temperature of the feedstock in the bottom of section 101. It is not so low as to cool the feedstock below its temperature in zone, where gas is introduced and is not so high as to increase coke output due to local overheating of feedstock in input zone. The feedstock temperature is measured by thermocouple 122 and is preferably equal to about 430 'C in the bottom of this section.

In the section 101 selection of volatile products intensified by the bubbling gas takes place, and vaporized products are withdrawn with the bubbling gas and pass upwardly through the section 102. The temperature in the top portion of section 102 is maintained with heater or heat exchanger 106 at 330 °C or lower, which is the tem- perature of the products outlet.

As a result of the bubbling all gaseous and vaporized products are withdrawn from the top of section 102, including products boiling at about 330 °C. Some part of the heavier products is condensed on the walls of section 102 and flows downwardly to the section 101, and some part, depending on bubbling gas flow rate, is withdrawn with gaseous and light products to a standard system for fractionating, condensing and cleaning of products 24. In this system noncondensed gaseous products and the bubbling gas are separated and cleaned of hydrosulfur with any existing technique, for example, a gas scrubber 126.

Then a part of the noncondensed gases is compressed by compressor 128 and used for bubbling gas (Ggl-Gg2). The remaining part of the gas is recovered as gaseous product (C1-C4) through line 127. Liquid fractions are withdrawn through line 129 and separated into liquid products, and a nonconditioned part (particularly the fraction Tboil> 500 °C) may be returned into section 101 through line 125 for reprocessing. Liquid products are withdrawn by line 129, they may be cooled in heat exchangers 106, 109, 110 and/or 111.

Feedstock remaining after processing in section 101 flows down to the reactor section 103, where it is heated by furnace heater 108 up to the final temperature of processing, about 520-580 ^βC. The feedstock is bubbled by gas Gg2 introduced through the holes in collector 116 arranged in the lower part of section 103.

Parameters of this flow (Gg2) are measured with flowmeter 114 and thermocouple 119, and the gas is heated in heater or heat exchanger 111.

During heating and bubbling of the feedstock remainder in section 103 destruction of heavy fractions and coke formation take place. Volatiles produced in section 103, together with bubbling gases, pass upwardlY to section 101 where they are processed additionally and withdrawn as a mixture of vapors and gases through section 102 to separation system 124.

The feedstock flow rate is measured with flowmeter regulator 112, and the flow rate is controlled so as to maintain an approximately constant level of liquid feedstock in the section 101. The ratio of bubbling gas flow rates Ggl/Gg2 - is in accordance with the ratio of the feedstock treated in the section 101 to the feedstock remainder in section 103. The total average bubbling gas flow rate Ggl+Gg2 is more than 0.3 wt. % per minute of the feedstock weight in the reactor.

Thermal regimes of processing in all parts of the reactor are measured with thermocouples 120, 121, 122 and 123 each appropriately arranged in sections 101, 102 and 103, the temperature of which can be controlled by regulation of heaters 107, 108 and 109.

Solid product (coke) is accumulated at the bottom of the section 103 and after a certain level therein is reached, the coke is periodically passed to tank 105 through a controlled valve 104 by the action of weight or by any other suitable way (mechanically, pneumatically etc. ) .

The geometry of the reactor section 101 is such that an approximately constant velocity of the feedstock will be achieved in spite of changes in the feedstock mass due to the loss of gaseous and vapor products.

The geometry and temperature distribution in section 103 are arranged to provide coke formation in a zone higher than the maximum level of coke accumulation therein. These parameters will depend on the initial composition and flow rate of the feedstock in accordance with obtained experimental data (see examples) . The average heating rate of the feedstock (from the inlet to section 101 to the bottom of section 103) should be more than about 5 ^βC per minute and preferably should be in the range of 15 °C per minute to about 25 ^βC per minute.

If all the above mentioned conditions and relations are fulfilled, the results of refining any feedstock with such a continuous reactor system will not significantly differ from the results obtained with a batch reactor system of the type described above.

The criticality of the refining result to the stock heating rate and bubbling gas flow rate is illustrated in the Figs. 3-5 for the refining of crude oil.

Referring to Fig. 3, it may be seen that maintaining the average heating rate of the feedstock in the reactor at least about 5 "C/min while it is heated from the initial to the final temperature results in a significantly reduced processing time. It should also be noted that the use of a feedstock heating rate greater than about 15 °C/min does not- provide a significant further reduction in processing time, and so is generally not warranted because of associated increase in energy requirements.

Referring to Fig. 4, it may be seen that use of a feedstock average heating rate of at least about 5 °C/min results in a significant increase in the output of liquid and gas products and a decrease in the production of coke. Fig. 5 is a plot of the coke/pyrocarbon product output versus hydrocarbon average gas flow rate when refining a crude oil using average feedstock heating rates of 12 + 2 C/min, 3.8 C/min, and 2.4 /min. The data plotted therein demonstrate the desirability of maintaining the average flow rate of the bubbling gas at a high value, while at the same time maintaining a high average high heating rate of the feedstock, in order to attain the objects of the present invention.

Fig. 6 is plot of the amounts of coke/pyrocarbon, gases and light liquid products produced and energy consumption for processing at different feedstock average heating rates for each of crude oil and mazute (residual oil) feedstocks. As seen from the data plotted therein the optimal feedstock average heating rate ranges from 5 "C/min up to about 15-20 "C/min. The experimental data obtained related to the investigation of the present process shows that all increases of the average heating rate above the minimum value (5 °C/min) leads to further decreasing of the coke and pyrocarbon output and overall treatment time. But significant such decrease is observed only to the value 15-20 ^βC/min. An increase of the heating rate to 30 ^βC/min does not lead to further a decrease of treatment time and coke output. On the other hand, an increase of the heating rate to 30 ^βC/min leads to an increases of the maximum treatment temperature, which corresponds to the end of liquid and gaseous products output.

For example treatment of mazute in accordance with present process at 13 "C/min and 30 "C/min and other same conditions leads to the same treatment times (34 min). But the maximum feedstock temperature is increased from 530 "C at 13 "C/min to 900 °C at 30 "C/min heating rate.

Moreover, at a heating rate of 30 "C/min the light liquid hydrocarbons output is decreased by at least 5 % and the output of heavier products is increased correspondingly.

Hence a average heating rate above 25-30 C/min is generally not preferred. It leads to an increase in the maximum feedstock temperature and increases the heating energy by 1.7 times.

Also, increasing the average bubbling gas flow rate above the minimum value (0.3 weight % per minute) leads to a decrease of the coke and gas output and to an increase in the output of the most valuable liquid products involved, light hydrocarbons. But the rate of coke and gas output decrease is stepwise diminished and the liquid outputs are substantially constant at 1.20 weight % per minute and greater flow rates. At the same time, an increase of the average gas flow rate demands increased energy and gas flow, which are necessary to the process. Hence increases of gas flow rate above 1.2 weight % per minute is not preferred. The optimal gas flow rate range is 0.3-1.2 weight % per minute.

So, optimal ranges exist for both of the above parameters, limiting the bottom and top values of each.

It is preferred that the bubbling gas be heated to a temperature approximately equal to the temperature of the feedstock at the location in the reactor when the gas is introduced; however, the temperature of the heated gas may be varied as long as it does not adversely affect the refining operation. It should be not so low as to cool the feedstock in zone where gas in introduced but it should be not so high to lead to local overheating of feedstock accompanied by increased coke formation.

The change of the non-condensing (at normal conditions) hydrocarbon gases to another non-condensing gas (nitrogen) was found to result (other conditions being equal, i.e., a heating rate of 5 "C/min., flow rate of 0.5 weight % per minute) in an abrupt reduction of the liquid products yields (down to 75 % against 83 % in the case of methane) because of the increased yields of gaseous products C1-C4 (up to 20 % by weight against 12 % by weight in the case of bubbling the methane).

The difference in product yields can be explained by the interaction of hydrocarbon gases with heavy fractions of the hydrocarbon stock material containing heavy metals which work as catalysts for chemical reactions at the cracking stage (i.e., at T = 400-530 °C). If nitrogen is bubbled, these reactions do not take place, resulting in a higher yield of saturated gaseous products C1-C4. These results also in remain respects should be better as compared with know practice. The experiments above described to determine conditions of optimal realization of the present invention were carried out at atmospheric pressure, which was most prefferable from the point of view of simplicity and minimal investment for refining. But the pressure can be varied as long asit does not adversely effects the refining. Particulary higher pressure could increase coke formation, what limits possible increasing of working pressure. From the other hand pressure decreasing lower than atmospheric one could decrease the refining productivity what is not desirable from economics point of view.

Finally, increasing the liquid and gaseous products withdrawing temperature more than 330 °C leads to variation of the product composition, including decrease of light products output. Hence it is not desirable, if obtaining more heavy fractions does not prefferable.

Having described the preferred embodiments of the present invention, it is to be understood that variations and modifications thereof falling within the spirit of the invention may become apparent to those skilled in the art, and the scope of the present invention is to be determined by the appended claims and their equivalents.

Claims

WHAT IS CLAIMED IS:

1. A process for refining a liquid and solid hydro¬ carbon feedstock, which comprises: (a) introducing said feedstock into a reaction zone;

(b) monotonic heating of said feedstock in said reaction zone from an initial lower to a final higher tem¬ perature in the range of from about 520 "C to about 580 "C at an average heating rate of at least about 5 "C/minute, while the pressure in the said reaction zone being atmospheric pressure;

(c) introducing a non-condensing, non-oxidizing gas into said reaction zone during step (a) above at average flow rate of at least 0.3 % by weight per minute with respect to the weigh of said feedstock in said reaction zone so as to intimately contact the feedstock therein; and

(d) recovering from said reaction zone refined liquid and gaseous hydrocarbon products and coke.

2. The process of claim 1, wherein said feedstock contains hydrocarbon components boiling at a temperature of 360 °C or greater.

3. The process of claim 1, wherein said feedstock is selected from the group consisting of crude oils, gas condensates, residual oils, tars, bitumens, shale oil and coal-derived liquids, liquid fractions of any of the above and mixtures of any of the above.

4. The process of claim 1, wherein said average heating rate is in the range of from about 5 to about

30 "C/minute.

5. The process of claim 1, wherein said average heating rate is in the range of from about 15 to about 25 "C/minute.

6. The process of claim 1, wherein said gas is a C1-C4 hydrocarbon gas.

7. The process of claim 1 wherein said gas is selected from the group of non-hydrocarbon gases which do not oxidize the feedstock components namely nitrogen, hydrogen, rare gases.

8. The process of claim 1, wherein said gas is selected from the group consisting of natural gas, gases derived from petroleum, coal, oil shale, tar and mixtures thereof.

9. The process of claim 1, wherein at least a portion of said non-condensing hydrocarbon gas introduced into the reaction zone is gas recovered in step (d) of claim 1.

10. The process of claim 1, wherein the temperature of the non-condensing, non-oxidizing gas introduced into the reaction zone is approximatly equal to temperature of feedstock in said zone.

11. The process of claim 1, wherein said liquid and gaseous hydrocarbon products are withdrawn from said reactor at a temperature not higher than about 330 "C.

12. The process of claim 1, wherein said refined liquid and gaseous hydrocarbon products are withdrawn from a first portion of said reaction zone; and a remaining portion of said feedstock is passed to a second portion of said reaction zone and heated therein to a temperature greater than that in said first portion of said reaction zone, and a non-condensing, non-oxidizing gas is introduced into said second portion of said reaction zone at an average flow rate of at least 0.3 % by weight per minute with respect to the weight of the said remaining portion of the feedstock therein; and a coke product is recovered from said second portion of said reaction zone.

13. The process of claim 12, wherein said liquid and gaseous hydrocarbon products are withdrawn from said reactor at a feedstock temperature not higher than about 360 "C, and said coke product is withdrawn from said second portion of said reaction zone at a temperature in the range of from about 520 "C to about 580 "C.

14. The process of claim 12, wherein sai liquid and gaseous hydrocarbon products are withdrawn from said reactor having feedstock temperature not higher than 430 "C and said coke product withdrawn from said second portion said reaction zone having temperature in the range of from about 520 "C to about 580 "C.