Method for manufacturing petroleum pitch having high aromaticity

Abstract

Method of producing a pitch suitable for a binder, said method comprising bringing petroleum base residual oil into direct contact with a non-oxidative gaseous heat transfer medium to subject said oil to cracking poly-condensation.

Parent Case Text

CROSS REFERENCE TO RELATED APPLICATION

This is a continuation-in-part of Ser. No. 240,619 filed Apr. 3, 1972 now abandoned.

Description

BACKGROUND OF THE INVENTION:

This invention relates to a method for manufacturing a a highly aromatic pitch having a softening point of 130.degree.-300.degree.C, a hydrogen/carbon atomic ratio of 0.4-1.1 and 40-80 wt% fixed carbon content and, more particularly, to a highly aromatic pitch suitable for use as a coke manufacturing binder.

Blast furnace coke and foundry coke are conventionally manufactured from heavy coking coal. The heavy coking coal resource, however, is limited and such coal is not available in abundance. To compensate for this fact several attempts have been made to manufacture blast furnace coke and foundry coke from a comparatively easily available weakly coking coal by adding a binder to give an adequate caking property to the weakly coking coal. An already proposed countermeasure is to utilize a coal pitch or petroleum base residual oil as such a binder. Coal pitch, however, is not available in abundance and the petroleum base residual oil, which contains aliphatic hydrocarbons as its principle constituents, cannot be used advantageously as a binder due to its insufficient miscibility with the coal as well as its low coking value.

SUMMARY OF THE INVENTION:

It has now been discovered that a petroleum pitch, suitable for use as such a binder, can be prepared by heat-treating an aliphatic hydrocarbon-containing petroleum base residual oil for efficiently cracking, polycondensing and aromatizing same.

It is therefore a primary object of this invention to provide a petroleum pitch which can be used as a binder to give a caking property to a weakly coking coal.

Another object of this invention is to provide a heat treatment method for converting a petroleum base residual oil to such a petroleum pitch.

These and other objects of this invention will become apparent from reading the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic flow diagram representing the process of the present invention for the production of a pitch suitable for use as a binder for low coking coals, and;

FIG. 2 shows the relationship between the partial pressure and temperature of the vapor phase.

DESCRIPTION OF THE PREFERRED EMBODIMENTS:

The aliphatic hydrocarbon-containing petroleum base residual oil usable as raw materials for manufacturing the pitch of this invention include various residual oils obtained from the petroleum refinary industry (e.g., normal pressure distillation residual oil, vacuum distillation oil, thermal cracking residual oil and contact cracking slurry oil) and other various petroleum refinary residues such as Duo-sol extract, furfural extract, propane extraction residual oil, heavy crude oil, tar sand oil, shale oil and mixture of these materials. From the point of view of economics, however, those materials which contain more than 30% by weight of constituents having 350.degree.C or lower boiling points are not preferred. Desirable raw materials are residual oils such as, for example, a vacuum distillation residual oil which is in a solid or semi-solid state at normal temperatures.

However, these petroleum base residual oils have heretofore found no extensive usage other than as fuel and road-paving material. Moreover, the use of these petroleum base residual oils as fuel has been inhibited because the combustion of these oils -- which have a high sulfur concentration -- produces sulfurous acid gas and results in atmospheric pollution. On the other hand, the demand for road-paving petroleum residual oils in recent years has increased at a much slower pace as compared with the increase in production and supply of these petroleum residual oils which has accompanied the increase in production of petroleum products and petrochemical products. This is regarded as a serious problem which might impede the future development of the petroleum refinary industry.

In consideration of this problem together with the actual problem that the coking coal is in short supply for manufacturing blast furnace coke, attempts have been made to manufacture artificial coking coal from petroleum base residual oils. The primary purpose of these attempts is commonly to provide a substitute for natural coking coal. Practical difficulties encountered in these attempts are that the resulting products are expensive due to the low yield thereof, the resulting products have a considerably large sulfur content and that the raw materials for manufacturing such artificial coking coals have only a narrow selectivity.

The petroleum pitch prepared by this invention represents an advance in the art from the viewpoint of economics and the conserving of natural resources. The pitch prepared from a residual oil such as petroleum asphalt by converting the chemical structure and composition thereof has an excellent caking or binding effect and hence,

1. By adding a small quantity of the pitch to a coke manufacturing blended coal, a high quality blast furnace coke can be prepared;

2. The pitch of this invention greatly saves heavy coking coals from use, of which future availability, judging from its limited deposit, seems to be limited, and yet allows the production of high quality coke; and

3. By blending the pitch with a non-coking coal or weakly coking coal having no or a little caking property, a quality coke comparable to those prepared from heavy coking coals can be produced.

According to this invention, the pitch is prepared by treating a petroleum base residual oil with heat. The heat treatment of this invention may be conducted in such a manner that the raw material oil is brought into direct contact with a non-oxidative gas or a perfectly combusted gas containing substantially no oxygen, as a heat carrier gas, heated to 400.degree.-2000.degree.C. Suitable non-oxidative gases used in this invention include nitrogen, argon, steam, hydrogen and hydrocarbon gas.

To effect thermal cracking, aromatization and polycondensation smoothly and to prevent the production of undesirable coke by eliminating the danger that the raw material oil will be locally over-heated by the heat carrier gas, it is necessary to maintain the temperature of raw material oil within the range of 350.degree.-450.degree.C which is lower than the above-mentioned temperature of heat carrier gas. To make the heat carrier gas bring into direct contact with the raw material oil, the heat carrier gas may be distributed into a continuous phase of the raw material oil. For this purpose the heat carrier gas may be blown into the raw material oil or, alternatively, a jet scrubber may be employed advantageously for the gas/liquid contact. In either case the reaction may be effected advantageously either batchwise or in a continuous manner.

The pressure in the reaction vessel should be less then 3.0kg/cm.sup.2 (gauge) and the dwell time for the reaction should be within the range of from 0.5 to 20 hours, preferably from 0.5 to 10 hours.

The heat carrier gas used in the present invention serves as heat source and further serves greatly in stripping the oil produced by cracking. Such action of the heat carrier gas aids in producing a pitch having desirable properties as binder.

The heat treatment of this invention may be conducted as summarized above, or the raw oil may be also preheated prior to the above-described heat treatment. The preheating stage may be operated by heating the raw oil to an elevated temperature by external or internal heating means for a short time or by a combination of such means, or alternatively, by heating the raw oil in a tubular heating system for a short time. Thereafter the preheated raw oil is flashed into the reaction vessel to effect the heat treatment.

Of the above, the preheating procedure using the tubular heating system is most effective because the raw oil can be efficiently and quickly brought up to an elevated temperature. In this embodiment, the raw oil is preferably passed through the tubular furnace with a dwell time within the range from 0.5-15 minutes so that the temperature of the raw oil at outlet of the tubular furnace will be within the range from 450.degree. to 520.degree.C and the pressure at the outlet will be within the range from 0 to 150kg/cm.sup.2 (gauge). The thus preheated raw oil flashes upon entering the reaction vessel.

In the preheating stage, the decomposition of the raw oil occurs to some extent but the poly-condensation reaction to only a negligible extent. Thus, the preheating stage has no adverse influence on the subsequent heat treatment of this invention.

The technical principles of the heat treatment of this invention are as follows:

1. A certain amount of heat sufficient to complete reaction of the raw material oil is supplied to the raw material oil by bringing a high temperature gaseous heat transfer medium into direct contact with a large quantity of raw material oil;

2. That portion of the raw material oil which is unstable at high temperatures is cracked and the cracked oil is separated from the pith fraction by the stripping action of the gaseous heat transfer medium; and

3. A pitch having the desired properties is prepared from that portion of the raw material oil having comparatively good heat stability by holding said portion under not too severe temperature conditions for an extended period of time.

A thermal cracking of the raw material residual oil cannot be effected without being accompanied by thermal polycondensation. A structural model of vacuum distillation residual oil may be a cyclic structure which is aromatic and/or alicyclic carrying one or more long aliphatic side chains. When such a vacuum distillation residual oil is used as a raw material, in an early stage of the heat treatment thereof a cracking of the side chain will occur at certain temperatures but no remarkable polycondensation reaction. As the oil fraction mainly consisting of the cracked aliphatic compounds is stripped from the liquid phase by the gaseous heat transfer the ring concentration will increase and the polycondensation will become more and more conspicuous. The numerical expression of the degree of cracking may be possible by measuring the distilled oil fractions, whereas the numerical expression of the degree of polycondensation may be obtained by a solvent test, that is, by measuring the weight percentage of the portion insoluble in standard solvents such as heptane, benzene, quinoline, etc. To prepare a pitch having a softening point above 130.degree.C, for example, the polycondensation must be allowed to proceed to a considerable degree. This may readily be understood by numerically expressing the degree of reaction. The degree of reaction may be expressed in terms of a non-dimensional numerical value k.theta. , where k is a function of temperature and the reaction velocity constant (1/sec) determined on the supposition that the cracking is a reaction of the first order and .theta. is the reaction time (sec). When expressed in terms of k.theta., where k.theta. has a relatively small value, the reaction takes place mainly in the form of cracking and, under conditions where k.theta. has a larger value, the reaction takes place mainly in the form of polycondensation.

According to this invention the thermal cracking and thermal polycondensation of the raw material residual oil may be considered to be classified into two sequential steps:

First Step: Under conditions of k.theta..ltoreq..alpha.(wherein, while .alpha. varies with the temperature of heat transfer gas, it is a value of approximately 2.0 in cases where the temperature of heat transfer gas is less than 850.degree.C), the main reaction proceeds in the form of a cracking of the side chains and that cyclic portion which is cracked easily, but no marked degree of polycondensation takes place. Therefore, the manner of reaction has no special importance and the raw material oil may be heated either by use of an externally heated tube or by making the raw material oil come into direct contact with a heat carrier.

Second Step: Under conditions of k.theta.>.alpha.(wherein .alpha. has the same meaning as the above), the following two reaction conditions are essential:

A. The liquid phase should not be overheated during reaction but should preferably be maintained lower than 450.degree.C. This is because an excessively high temperature will result in a drastic polycondensation reaction and increase of the mesophase, which necessarily develops in the coking process. As a result, the liquid phase will not form a pitch suitable for use as a binder. The term mesophase as used herein means a type of liquid crystal which develops when the pitch is heated to approximately 400.degree.C. The mesophase consists of pitch-composing molecules having an aromatic structure which have through the interaction associated together through the interaction as anisotropic spherules, as is visually observable by use of a polarizing microscope. When heated to higher temperatures, the mesophase liquid crystals grow larger and combines with adjacent crystals to form a larger mesophase, which may be regarded as a precursor of coke.

B. The conditions required for stripping the oil cracked in said first step from the liquid phase (pitch phase) must be carefully selected. These stripping conditions are selected in accordance with the partial pressure and temperature of the vapor phase. The relationship between the partial pressure and temperature is as shown in FIG. 2. The partial pressure of vapor phase as used herein means the total partial pressure of the cracked gas and the oil vapor in the heat transfer gas (hereinafter, the partial pressure of vapor phase is expressed as Porg.). The critical partial pressure may be 5 mmHg at 300.degree.C, and preferably lower than 3 mmHg, because if the reaction proceeds under conditions where more volatile cracked oil remains in the liquid phase (or pitch phase), then the mesophase will grow large even at temperatures lower than 450.degree.C and coking will take place to a large extent, giving a reaction product in the form of a mixture of coke and oil but not a pitch. This suggests that the reaction need be effected at temperatures at which the liquid phase (pitch phase) has a considerable viscosity. When the liquid phase has too low a viscosity, agglomeration of mesophase will occur easily to form coke but not pitch.

The equation representing the upper curve of FIG. 2 is as follows: ##EQU1## wherein T is the temperature (.degree.C) of the liquid phase in the reaction zone.

In the second step and, especially, under conditions where k.theta. becomes large enough, the reaction will proceed mainly in the form of polycondensation. Therefore, to prepare a pitch, and especially a pitch suitable for use as a binder, adequate precautions have to be made to eliminate the danger that agglomeration of the mesophase will occur. For this reason, when the reaction has to be effected at relatively low temperatures and under normal or elevated pressures, the reaction must be conducted over a comparatively long period of time while introducing an increasingly larger amounts of steam.

By means of the present invention, the heat energy required to efficiently treat one weight unit of the raw material oil can be reduced remarkably, generally to an amount as low as 1/10 of that required by any conventional method employing a cracking furnace of the internal heating type. This is because the heat energy supplied to the reaction system by the heat transfer medium results in the thermal cracking of raw material oil and the free radicals produced by thermal cracking serve as initiators for the polycondensation and aromatization reactions of the molecules within the liquid phase. This permits the desired reaction to proceed smoothly in the liquid phase under not so severe temperature conditions and promotes the distillation of by-product oil fractions.

The preferred reaction conditions as mentioned previously were found experimentally. The lower temperature limits for the heat transfer gas and the raw material represent, for example, the lowest temperatures at which the reaction can proceed economically; whereas the upper temperature limits for the heat transfer gas and raw material oil have been established with the purpose of restraining the undesirable coking phenomenon and/or maintaining the stripping conditions above a certain level. The flow rate of the heat transfer gas is selected in accordance with the reaction temperature. If the operating parameters are properly selected, the distilled oil fraction and residual pitch fraction will have a predetermined and controlled chemical structure and composition.

The pressure of reaction system will be controlled at or near normal atmosphere. A slight increase (less than 3 kg/cm.sup.2 G) or reduction in pressure may serve to help the reaction or separation proceed smoothly. The internal temperature of the reaction system may be maintained within a predetermined range by heating it externally.

Now the process for industrially producing the pitch of this invention will be described with reference to FIG. 1. The raw material oil stored in a tank 1 is fed by a pump 2 into a preheating and cracking furnace 3, where it is preheated and subjected to a cracking process. The cracking furnace 3 may be a tubular oven or an externally heated type. To prevent coking from occuring within the heating tube and to reduce the sulfur content of the product, hydrogen or volatile hydrocarbons such as, for example, a portion of the more volatile oil distilled from the process may be introduced at 4. Valve 5 is provided to control the pressure within the preheating and cracking apparatus.

The raw material which has been preheated or cracked in the first step is then introduced into a reaction vessel 6, where the raw material is subjected to a cracking process of the second order and the cracked more volatile fractions (gas and oil fractions) and pitch are separated. A high temperature heat transfer medium is introduced through nozzle 8 into the reaction vessel as a heat source and also as a stripping medium for the distilled fractions.

The cracked gas and distilled fraction which have been stripped within the reaction vessel 6 are fed through a line 9 into a fractionator 10 and overhead drum 11 and further separated into a gas 12, more volatile oil 13, condensed water 14, and residual oil 15 according to the conventional procedure. The pitch fraction obtained in the reaction vessel 6 is fed through a line 16 onto a cooling belt 17 to form the pitch product 18.

As will be understood from the foregoing, the process of this invention is either a modified visbreaking process or a modified delayed coking process or, otherwise, a combination of these processes. The gaseous and oily byproducts are separated either by flashing or by various distillation methods.

As mentioned previously, the petroleum pitch, which is obtained by heat-treating an aliphatic hydrocarbon-containing petroleum base residual oil for cracking/polycondensation and aromatization, is characterized by the following properties:

Softening point: 130-300.degree.C Fixed carbon: 40-80 wt% H/C ratio: 0.4-1.1

Of these values the softening point measured by use of a Koka type flow tester (manufactured by Shimazu Seisakusho, Ltd., Kyoto, Japan) is the temperature at which a 1g sample started to flow through a nozzle of 1mm diameter under a pressure of 10 kg/cm.sup.2 and at a heating rate of 6.degree.C/min. The weight percentage of fixed carbon was measured in accordance with JIS-K-2421 (1966). The H/C ratio was determined by an elementary analysis.

The petroleum pitch having these properties is obtained from a petroleum base residual oil by converting the chemical structure and composition of its main constituents by heat treatment. The petroleum pitch is rich in aromatic hydrocarbons and has a remarkably improved coking value and affinity with coal. Therefore, addition of the pitch prepared by this invention to a weakly coking coal will greatly increase the cracking property of the coal, resulting in a coke having a drum index comparable with the coke obtained from a heavy coking coal.

The blending ratio of the pitch of this invention with the weakly coking coal varies depending on the type of coal. When 50 parts of pitch is blended with 50 parts of Australian weakly coking coal (Newdell), the resulting coke will have drum index (DI.sub.15.sup.30) of 91.4; when 1 part of pitch is blended with 40 parts of Australian quasi-coking coal, 40 parts of Japanese weakly coking coal and 20 parts of American heavy coking coal, the resulting coke will have a drum index of 91.5 (for detail, refer to the Examples which follow). By adding the pitch of this invention to a raw material coal having a low caking property, it is possible to obtain a coke having a high quality comparable with the coke prepared from a heavy coking coal.

At an H/C ratio above 1.1, the pitch will be insufficiently compatible with the coal; on the other hand, at an H/C ratio below 0.4, the pitch will contain increased amounts of infusible constituents and thus will have a reduced caking property. If the pitch has a lower softening point, it will be difficult to mill the pitch prior to mixing with the raw material coal or to stock the milled pitch without causing any blocking. On the contrary, if the pitch has an excessively high softening point, then the pitch will contain an increased quantity of infusible constituent and present a reduced compatibility with coal.

If the pitch has an excessively low fixed carbon content, then the pitch will evaporate excessively during the coking process and will not produce a coke having a sufficient density and strength. If the pitch has an excessively high fixed carbon content, then the pitch will contain an increased quantity of infusible constituents, presenting a reduced caking property. Moreover, oily fractions developed as by-product in the course of producing the pitch are consisted of mainly paraffin base hydrocarbons, therefore, they can be easily converted to products of high economic value such as fuel oil of low sulfur content, lubricating oil and gasoline.

The scope and applicability of this invention will be more fully illustrated by the following working examples.

EXAMPLE 1

6 kg of vacuum distillation residual oil from Khafji crude oil (having the properties listed in Table 1) was placed in a reaction tank equipped with mixer, heater and cooler. A gaseous heat transfer medium, preheated to an elevated temperature, was then injected into the oil in the liquid phase and the temperature maintained constant. Table 2 gives the operating conditions and the material balances for three runs, 101, 102, and 103, employing different heating mediums and operating conditions. The properties of the products, distilled oil and the pitch, are shown in Table 3. In these batch-type runs, the first step of the reaction (mainly cracking) occurs in the first stage and the second step of the reaction (mainly poly-condensation) in the second stage, and these steps follow in a single run.

Table 5 lists the results of can baking tests (box test) which were conducted to determine the coking strength of the pitch product, simulating its use in a blast furnace. This test was conducted using the pitch obtained from run No. 101. The term "can baking test" refers to a test method in which an 18 liter oil can is charged with sample having a granular size the same as that which would be used in an industrial coking furnace. The results shown in Table 5 reveal that the pitch obtained according to the present invention has excellent binding properties. The distilled oil from Nos. 101 to 103 were tested by elementaly analysis and by NMR and IR spectra. These latter tests revealed that the distilled oil products contain from 60 to 80% by weight aliphatic hydrocarbons. The starting material:

Table 1. ______________________________________ Vacuum distillation residual oil from Khafji crude oil ______________________________________ Specific gravity 1.032 Element analysis (wt%) Fixed carbon (wt%) 12.8 C 84.0 Softening point (.degree.C) 46 H 10.41 Ash (wt%) 0.05 N 0.66 Penetration 92 S 4.90 H/C 1.49 ______________________________________

Table 2 __________________________________________________________________________ Example 1 - Operating Conditions No. 101 102 103 __________________________________________________________________________ Operating Heat transfer gas Oxygen- Steam Nitrogen conditions hydrogen flame Heat transfer gas temperature 1500 700 500 (.degree.C) Heat transfer gas flow rate 3.2 5.0 4.2 (M.sup.3 /Hr) Liquid phase temperature 350 430 450 (.degree.C) Duration of operation (Min.) 30 210 60 k.theta. * 14.5 11.4 __________________________________________________________________________ Material H.sub.2 (wt%) 0.5 0.1 0.1 balance CH.sub.4 " 5.2 4.8 3.3 C.sub.2 H.sub.6 +C.sub.2 H.sub.4 " 8.8 4.4 1.2 C.sub.3 H.sub.8 +C.sub.3 H.sub.6 " 7.2 Trace 0 C.sub.4 Hydrocarbon + " 5.0 0 0 H.sub.2 S " 2.0 2.1 1.9 Distilled oil " 45.3 62.5 69.8 Pitch " 24.5 20.6 21.7 Loss 1.5 5.5 2.0 __________________________________________________________________________ *While the calculated value of k.theta. in No.101 is 0.2, effective k.theta. is estimated to be considerably larger than 0.2. The reason is that the temperature within the boundary layer between the bulk liquid phase and bubble phase is considerably higher than the measured value (350.degree.C) due to high temperature of heat transfer gas used.

Table 3. __________________________________________________________________________ Properties of the Distilled oil product No. 101 102 103 Specific gravity (d.sub.4.sup.15) 0.911 0.940 0.934 Flash point (.degree.C) 102 146 152 __________________________________________________________________________ *Distillation Initial Boiling Point(I.B.P.) 132 211 200 test (.degree.C) 20% distilled (.degree.C) 252 344 331 50% distilled (.degree.C) 348 474 460 80% distilled (.degree.C) 475 525 520 __________________________________________________________________________ Elementary C (wt%) 86.30 84.80 85.6 analysis H (wt%) 11.08 11.88 12.15 N (wt%) 0.52 0.43 0.36 S (wt%) 2.10 2.26 2.32 H/C (atomic ratio) 1.55 1.68 1.71 __________________________________________________________________________ *The temperatures shown above have been corrected to represent the boilin points (.degree.C) at normal pressure.

Table 4. __________________________________________________________________________ Properties of the pitch product No. 101 102 103 __________________________________________________________________________ Softening point (.degree.C) *250 *280 *263 Fixed carbon (wt%) 62.3 75.1 67.2 Ash % 0.7 0.5 0.2 __________________________________________________________________________ Element C " 86.5 87.6 87.9 analysis H " 4.62 5.49 5.76 N " 1.90 1.76 1.56 S " 6.08 6.75 6.48 H/C (atomic ratio) 0.650 0.752 0.786 Solvent extraction test Benzene insoluble matter (wt%) 65.4 74.8 58.9 Quinoline insoluble matter (wt%) 32.0 40.3 27.2 __________________________________________________________________________ *These figures were obtained with the Koka-type flowtester manufactured b Shimazu Mfg. Co., Japan.

Table 5 __________________________________________________________________________ Coking test Comparative example Present invention No. 1 2 3 4 5 __________________________________________________________________________ Proportions Coal (strongly coking coal from U.S., volatile 20 -- 10 -- -- matter 19-20 wt%) " (coking coal from Australia, volatile matter 40 50 40 45 40 20-23 wt%) " (weakly coking coal from Japan, volatile 40 50 45 45 45 matter 35-40 wt%) Pitch of the present invention (No.101)* -- -- 5 10 15 Strength of coke Drum index (DI.sub.15.sup.30), JIS, K-2151-6 92 76 93 91 93 __________________________________________________________________________ *Two additional tests were conducted, using the pitches obtained in runs Nos. 102 and 103, respectively, and mixing each the listed coals in the proportions listed in column 3. The Drum Index for each of these mixtures was 92.

EXAMPLE 2

A residual oil obtained from the distillation of Arabian light crude Oil under normal pressure (at 350.degree.C) and having the properties given in Table 6 was placed in the apparatus described in Example 1. The operating conditions and material balance are shown in Table 7.

Table 6 ______________________________________ Properties of the residue from the distillation of Arabian light crude under normal pressure ______________________________________ Specific gravity (d.sub.4.sup.15) 0.957 Fixed carbon (wt%) 6.8 Softening point (.degree.C) below room temperature Ash (wt%) 0.03 Element C (wt%) 84.9 analysis H " 11.67 N " 0.14 S " 2.89 H/C 1.65 ______________________________________

Table 7 ______________________________________ Operational conditions Material balance (wt%) ______________________________________ Heat transfer gas Nitrogen H.sub.2 0.04 Heat transfer medium 700.degree.C CH.sub.4 2.0 temperature Heat transfer medium 5.0M.sup.3 /Hr C.sub.2 H.sub.6 + C.sub.2 H.sub.4 1.8 flow rate Starting oil temp. 430.degree.C C.sub.3 H.sub.8 + C.sub.3 H.sub.6 Trace Duration of operation 120 Min C.sub.4 Hydrocarbon 0 k.theta. 8.1 H.sub.2 S 0.7 Distilled oil 80.1 Pitch 11.9 Loss 3.46 ______________________________________

The properties of the distilled oil and the pitch thus obtained are given in Table 8.

The pitch obtained in this example (Table 8) was mixed with coals of the types and in the proportions given in column No. 3 of Table 5. This mixture was then subjected to the can baking test as described in Example 1. The "coke strength," or Drum Index, was determined to be 91.

Table 8 __________________________________________________________________________ Properties of the distilled Properties of the pitch product oil product __________________________________________________________________________ Specific gravity (d.sub.4.sup.15) 0.920 Softening point (.degree.C) 159 Flash point (.degree.C) 134 Fixed carbon (wt%) 53.1 Distillation test Ash % (wt%) 0.3 I.B.P. (.degree.C) 190 Element analysis 20% distilled (.degree.C) 355 C (wt%) 85.9 50% distilled (.degree.C) 410 H 6.61 80% distilled (.degree.C) 465 N 0.49 S 6.54 Element analysis H/C 0.924 C (wt%) 85.30 Solvent extraction test H 12.44 Benzene insoluble 16.6 N 0.20 matter (wt%) S 1.80 Quinoline insoluble 1.8 H/C 1.75 matter (wt%) __________________________________________________________________________

EXAMPLE 3

Using the apparatus and system illustrated in FIG. 1, 300kg/hr of Khafji vacuum residue was subjected to preheat treatment in a tubular furnace wherein the outlet pressure was 15kg/cm.sup.2, the outlet temperature 475.degree.C and the dwelling time 1.3 minutes (at 350.degree. to 475.degree.C).

The preheated vacuum residue was flashed by injection into a reaction vessel where 90kg/hr of steam (at 710.degree.C) was injected into the bottom liquid, maintaining the bottom liquid at a temperature of from 400.degree. to 410.degree.C for 6 hours.

The cracked gas and oil produced in the heat treatment were stripped out of the reaction vessel and a highly aromatic pitch was obtained in a yield of 26.5% by weight, while the yields of gas, light oil and heavy oil were 3.9%, 10.2% and 59.5% by weight, respectively. The properties for the feed stock and the pitch product are shown in Table 1 and Table 9, respectively.

The pitch product was ground into powder and mixed with various types of coal, and the mixture was then subjected to a can baking test (box test) as described in Example 1. Table 10 gives the test results.

Table 9 ______________________________________ Properties of the pitch product Softening point 225.degree.C Fixed carbon 69 wt% Benzene insoluble matter 65 wt% Quinoline insoluble matter 38 wt% H/C (atomic ratio) 0.76 ______________________________________

Table 10 __________________________________________________________________________ Coking tests - Example 3 No 1 2 3 4 5 __________________________________________________________________________ Coal Strongly coking coal from U.S. 20 20 0 0 10 (volatile matter 19 - 18 wt%) Coking coal from 40 40 50 50 45 Australia (volatile matter 26-28) wt%) Weakly coking coal from Japan 40 40 50 50 45 (volatile matter 35-40 wt%) Pitch of the present invention 0 1 0 5 5 Coke strength, DI.sub.15.sup.30 91.2 91.8 82.2 81.1 92.3 (JIS-K2151) __________________________________________________________________________

Another series of coking strength tests were conducted, using the pitch of this example as a binder; the results thereof are given in Table 11. The results show that a mixture of the weakly coking coal from Australia (Newdell) and the pitch of the present invention provides a coking strength comparable to those of strongly coking coals.

Table 11 __________________________________________________________________________ Compositions for the Can Baking Tests - Example 3 No. 1 2 3 4 5 __________________________________________________________________________ Weakly coking coal from 100 95 90 70 50 Australia (New Deal) Pitch of the present invention 0 5 10 30 50 Coke strength DI.sub.15.sup.30 68.9 74.3 81.5 88.7 91.4 __________________________________________________________________________

In this example, the first step reaction (cracking) was principally carried out in the tubular furnace and the second step reaction (poly-condensation) occurred subsequently in the reaction vessel. This example shows that high temperature such as 475.degree.C may be employed in the first step reaction.

EXAMPLE 4

Using the apparatus and system illustrated in the flow sheet of the drawing, a residual oil starting material, the same as that used in Table 1, was processed with a feed rate within the range of 100kg/hr to 300kg/hr.

The superheated steam (from source 7) was introduced into the reactor 6 at 620.degree.C and at a flow rate of 30.4kg/hr. The test conditions were as follows: T.sub.F (temperature at the exit of pre-heating furnace) 480.degree.C; T.sub.C (liquid temperature in the reaction) 420.degree.C; P.sub.O (pressure at the entrance of the preheating cracking furnace) 32 kg/cm.sup.2 G; P.sub.1 (pressure inside the reactor) 0.1 kg/cm.sup.2 G; O.sub.1 (dwelling time in the preheating cracking furnance) 3.2 minutes, and O.sub.2 (dwelling time in the reactor) 3.5 hours.

The test yielded the following products:

By-product gas 4.6%, light oil 11.3 wt%; heavy oil 58.4 wt%; and residual pitch 25.5 wt%. Table 12 shows the properties of these products.

Table 13 gives the operating conditions for a series of tests conducted using the system and apparatus depicted in the drawing. "Case 1," as shown in Table 13, refers to the test run described above.

The pitch products obtained from each of the test runs of Table 13 were subjected to a can baking test (box test) for the determination of coking strength. The mixtures used in each of these tests consisted of 80 parts by weight of OS coal from USSR, which is a non-coking coal, and 20 parts by weight of the pitch. The results of these tests are also shown in Table 13.

Table 12 __________________________________________________________________________ Properties of products of Example 4 properties of oil Composition of gas properties of pitch light oil Heavy oil __________________________________________________________________________ H.sub.2 S 11.9 (vol.%) C 83.5 (wt.%) 83.5 (wt.%) C 87.7 (wt.%) H.sub.2 7.4 H 14.6 11.4 H 5.77 CH.sub.4 32.5 S 1.6 4.6 S 6.15 C.sub.2 H.sub.4 2.7 IBP 38.degree.C 212 H/C 0.78 S.P. 230 C.sub.2 H.sub.6 15.6 20%120 325 F.C. 67.0 (wt.%) C.sub.3 H.sub.6 7.5 80%196 505 B.I. 58/3 (wt.%) C.sub.3 H.sub.8 10.7 Q.I 27.0 (wt.%) C.sub.4 - C.sub.5 11.6 Sp.Gr. 1.25 (20.degree.C) __________________________________________________________________________

Table 13 __________________________________________________________________________ Example 4 Operating Conditions and Yields CASE 1 2 3 4 5 6 7 8 9 10 11 __________________________________________________________________________ Feed rate (Kg/H.) 101 100 102 100 103 300 300 300 300 300 300 Flow rate of superheated 30.4 50.7 25.0 18.5 5.3 120 80 80 120 120 120 steam (Kg/H.) Temperature of superheated 620 620 850 850 1600 650 750 830 630 650 680 steam (T.sub.STM .degree.C) Temperature at the exit 480 480 475 485 480 500 500 500 485 485 485 of the preheating cracking furnace (T.sub.F,.degree.C) Pressure at the entrance of 32 33 102 105 101 29 29 28 28 28 28 the preheating cracking furnace (P.sub.O, Kg/cm.sup.2 G) Pressure at the exit of the 10 11 73 72 70 3 3 3 4 4 4 preheating cracking furnace (P.sub.1, Kg/cm.sup.2 G) Dwelling time in the 3.2 2.5 3.5 3.5 3.5 2.7 2.7 2.7 3.2 3.2 3.2 preheating cracking -furnace (.theta..sub.1, min.) Temperature at the liquid 420 380 410 385 365 430 480 510 430 430 430 in the reactor (T.sub.L, .degree.C) Pressure of the liquid 0.1 0.5 0.1 -0.75 -0.90 2.2 2.2 2.2 0.3 2.9 5.8 in the reactor (P.sub.2, Kg/cm.sup.2 G) Average dwelling time 3.5 6.5 2.0 2.5 1.0 1.5 0.14 0.05 1.3 1.6 1.9 in the reactor (.theta..sub.2, Hr.) Partial pressure of 167 129 198 55 58 390 545 (545) 157 445 747 hydrocarbon vapor in the reactor (Porg, mmHg) k.theta. 13.2 2.1 3.6 2.4 ** 8.6 8.1 9.5 7.5 9.2 11.9 Product yield Gas wt % 4.6 7.2 8.4 8.0 15.8 5.2 9.5 -- 4.8 5.0 6.2 Light oil 11.3 10.5 12.1 12.0 23.0 11.5 12.8 -- 11.0 13.5 17.5 Heavy oil 58.4 45.9 55.2 54.9 36.5 57.7 53.0 -- 58.5 51.6 45.4 Pitch 25.5 36.2 24.7 25.1 24.7 25.2 24.1 -- 24.5 28.5 31.0 Properties of pitch Softening Point, 230 128 241 232 229 229 230 unmeasu- 221 225 222 .degree.C able Fixed Carbon, wt% 67.0 58.3 69.3 66.2 68.4 67.3 68.3 74.1 67.8 69.0 71.0 H/C (atomic ratio) 0.78 0.82 0.77 0.78 0.71 0.79 0.81 0.62 0.77 0.78 0.75 Benzene insoluble, 58.3 49.2 59.2 58.6 63.2 58.0 60.0 72.0 59.0 61.0 64.2 wt% Quinoline 27.0 7.4 29.1 26.1 30.3 26.5 38.0 59.0 26.3 31.0 42.5 insoluble, wt% Coke Strength (DI.sub.15.sup.30)* 92.6 92.1 91.7 93.1 92.4 93.0 90.8 72.0 92.8 92.0 90.5 __________________________________________________________________________ *The strength in case of OS coal alone was 15.1. **While the calculated value of k.theta. is 0.2, effective k.theta. is estimated to be considerably larger than 0.2. The reason is the same as that of the run No. 101 in Example 1. Note: Cases 7, 8 and 11 are comparative Examples.

In the runs of Example 4, the first step reaction (cracking) was mainly occurred in the preheating furnace and the second step reaction (poly-condensation) occurred in the bottom phase within the reactor.

In producing a pitch suitable for a binder, the second step reaction is more significant than the first step reaction.

This will be appreciated by comparing cases 6 and 8, with cases 9 and 11, respectively.

In case 8, the coking occurs to a remarkable extent due to too high a liquid temperature in the reactor (T.sub.l .degree.C), hence a stable operation can not be maintained. In addition, a material balance can not be obtained in case 8 since the operation is forced to shut down after a lapse of 30 minutes. Moreover, the use of too high a partial pressure of hydrocarbon in the reactor (Porg, mmHg) gives rise to an increase in the oil content in the pitch phase, hence a phase separation occurs, which produces heavy coking. Also, operation under such a high partial pressure (Porg, mmHG) tends to form a pitch which resembles a mixture of oil and coke, and the size of mesophase particles in the thus formed pitch become much larger.

The properties of such a pitch as binder (see case 11) are poor as compared with cases 9 and 10.

The invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The foregoing examples are, therefore, to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the claims rather than by the foregoing description, and all changes which come within the meaning and range of the equivalents of the claims are therfore intended to be embraced therein.

Claims

We claim:

1. A process for the liquid phase cracking and aromatization of a reduced crude oil residuum consisting mainly of aliphatic hydrocarbons to produce pitch having a H/C ratio of 0.4 - 1.1 and a non-pitch oil containing a major portion of aliphatic hydrocarbons, said process comprising:

providing, in a reaction zone, a vapor phase and a continuous liquid phase, which includes said residuum, at a total pressure less than 3.0 kg/cm.sup.2 G with a liquid dwell time of 0.5 to 20 hours;

feeding a non-oxidative heat transfer medium at a temperature within the range of 400.degree.C to 2000.degree.C through and in direct contact with said liquid phase in said reaction zone to maintain said liquid phase at a temperature of 350.degree.-450.degree.C, to induce a polycondensation reaction in said liquid phase, and to strip volatile components from said liquid phase;

controlling the feed rate of said heat transfer medium to maintain the partial pressure in mmHg of organics in said vapor phase at less than about: ##EQU2## wherein T is the temperature (.degree.C) of the liquid phase within the reaction zone; and

removing a non-pitch overhead from said reaction zone and recovering said pitch as the bottoms product of said reaction zone.

2. The method of claim 1 wherein said petroleum base residual oil is preheated to a temperature of 450.degree.C - 520.degree.C by passing said residual oil through a tubular system where the outlet temperature is within the range of 450.degree.C to 520.degree.C and the outlet pressure within the range of 0 to 150 kg/cm.sup.2 G, maintaining the dwell time of the residual oil in the tubular system within the range of 0.5 to 5.0 minutes.

3. The method of claim 1 wherein said non-oxidative gaseous heat transfer medium is selected from the group consisting of nitrogen, argon, steam, hydrogen and hydrocarbon gases.

4. The method of claim 1 wherein said liquid phase temperature and said partial pressure of organics are within the operating region designated "condition suitable for pitch formation" in FIG. 2.