Conversion Process of Hydrocarbons

This invention relates to a process for producing an useful and pollution-free hydrocarbon oil from a heavy oil such as the tar-sand bitumen and vacuum residues from various petroleum origins.

In more detail, this invention relates to the process for producing the pollution-free hydrocarbon oil having high utility with high efficiency by effectively combining the thermal cracking and hydrocracking processes of the said heavy oil.

At present it is very desirable to establish a method for the effective utilization of the extract oil from the tar-sand and the oil shale which exceed the estimated minimum amount of petroleum deposit in view of for the tendency of exhaustion of the high quality petroleum resources.

For example, the output of bitumen from the tar-sand is estimated to be 150,000 million tons. The tar-sand is broadly distributed in Canada, Venezuela, U.S.A., U.S.S.R. and Rumania.

The tar-sand contains 8-12 wt. percent of the heavy oil. The recovery of the heavy oil from the tar-sand is effected by blowing steam into either the tar-sand mined from the outcrop or the tar-sand buried under the ground. The oil fraction recovered from the tar-sand according to the process as mentioned above is not only the heavy oil having specific gravity of more than 1.0 but also very high viscous oil having viscosity of 70 cSt at 210.degree. F.

The oil fraction contains more than 4wt. percent of sulfur, large quantities of the nitrogen compounds, the oxygen compounds, the organic vanadium compounds (more than 150 ppm of vanadium), the organic nickel compounds (more than 70 ppm of Ni), alkali earth metal, iron and fine particles of clay having about 40.mu. diameter. The tar-sand oil contains large amount of asphaltenes and resins.

Because of the inferior quality of the heavy oil as mentioned above, it is very difficult to treat in comparison with the vacuum residues, from ordinary crude oil. The conventional treating process of the tar-sand bitumen is the coking process which gives a product comprising about 60 wt% of the distillate, about 10 wt% of the gaseous product and about 30 wt% of coke.

The gaseous product and the distillate obtained from the tar-sand bitumen are refined to hydrogenate the unsaturated compounds and to remove the sulfur compound by the hydrotreating. However, as the coke obtained from the bitumen contains a large amount of sulfur and ash comprising various kind of metals, therefore the usage of coke is limited.

The inventors have arrived at the present invention on the basis of the result of research about the process for effectively producing the useful and pollution-free hydrocarbon oil from the standpoint of the effective utilization of the bad quality heavy oil. Namely, the bitumen from the tar-sand is completely converted into the fractions comprising naphtha, kerosene and gas oil while controlling the gasification, by thermal cracking and then by hydrocracking under the certain conditions respectively.

The product obtained is useful as a fuel oil having a low sulfur content and a low metal content and also as the starting material for the secondary processing.

Giving full particulars of the thermal cracking process, the conventional thermal cracking, Visbreaking for example, is effected under the reaction conditions of 480.degree.-540.degree. C and about 20 Kg/cm.sup.2, and it aims for lowering of viscosity and pour point of the vacuum distillates.

But, by the thermal cracking, the desulfurization, the denitrogenation and the demetallization of the vacuum residues cannot be expected. The conventional thermal cracking process does not serve to completely convert the vacuum residues to the low boiling fractions.

As to the hydrocracking, it is very difficult to select the hydrocracking conditions in which the desulfurization, the denitrogenation and the demetallization of the heavy oil are effectively carried out. Even if the hydrocracking conditions capable of effecting the desulfurization, the denitrogenation and the demetallization, namely the reaction temperature, the hydrogen pressure, the liquid hourly space velocity, the gas velocity and the catalyst can be selected, it is difficult to completely convert the vacuum residues (boiling point of more than 530.degree. C) into the middle boiling point fractions comprising kerosene and gas oil.

One of the objects of this invention relates to providing a process for completely converting into the product oil of high value, the tar-sand bitumen and the vacuum residues from the various petroleum origins which are very difficult to treat because of large amount of sulfur, nitrogen, the metal compounds and asphaltenes, by the thermal cracking and hydrocracking under the certain reaction conditions respectively.

Another one of objects of this invention relates to providing the process for converting the tar-sand bitumen and the vacuum residues to the useful and pollution-free product oil comprising naphtha, kerosene and gas oil and containing less sulfur compounds.

The starting material used in this invention comprises the heavy oils having specific gravity (15/4.degree. C) of 0.90-1.10 such as tar-sand bitumen, shale oil, atmospheric and vacuum residues from petroleum origins.

The thermal cracking is effected under the certain conditions, namely at the temperature of 400.degree.-800.degree. C, preferably 450.degree.-530.degree. C, the hydrogen pressure of 1-200 Kg/cm.sup.2, preferably 20-50 Kg/cm.sup.2 and the contact time of 10-500 seconds, preferably 100-300 seconds.

The amount of asphaltenes contained in the starting material increases by the thermal cracking, and the more the conditions of the thermal cracking becomes severe, the more the amount of asphaltenes tend to increase.

The property of the thermal cracked asphaltenes is different from that of asphaltenes originally contained in the crude oil. In more detail, the asphaltenes are the most heavy component of the heavy oil and consist of the condensed polycyclic aromatic rings in the fundamental structure, and also contain naphthene and paraffin side chains. Sulfur, nitrogen and/or oxygen atoms, heavy metals such as vanadium and nickel etc. are contained in the structure of the condensed polycyclic aromatic rings.

Resins are similar to asphaltenes in the structure, but the ratio of naphthene and paraffin side chains to the condensed aromatic rings is greater than that of asphaltenes.

Under the thermal cracking conditions, asphaltenes are converted to the lower molecular compounds of the condensed polycyclic aromatic structure by the thermal dealkylation of the paraffin side chains and by the thermal cracking of the naphthene rings.

Resins are also similarly converted to the lower molecular asphaltenes by splitting the paraffin and naphthene side chains.

The more the conditions of the thermal cracking becomes severe, the more the cracking proceeds excessively, whereby the gasification is accelerated, the generation of olefin gas increases and the coking of the condensed polyaromatic compounds occurs.

In view of the said matters, it is not preferable to make the conditions of the thermal cracking too severe, when it is desired that the heavy oil is completely converted to the middle boiling point fractions.

The asphaltenes have the structure of the large micelle which is the cluster of the condensed polyaromatic compounds and contains hetroatoms. Therefore, it is very difficult to disperse the asphaltene molecules in the pores of the catalyst for the hydrocracking of the heavy oil.

Since asphaltenes become the small molecules by the thermal cracking, they are easier to close with the active sites of the catalyst in the subsequent hydrocracking, thereby making it possible to dissociate the asphaltene micelles and to hydrocrack the asphaltene molecules.

It has been found that the tar-sand bitumen and the vacuum residues are completely converted to the useful and pollution-free hydrocarbon oil comprising naphtha, kerosene and gas oil when the hydrocracking, the subsequent step of the thermal cracking, is carried out after the amount of asphaltenes contained in the tar-sand bitumen and the vacuum residues amounted to the certain extent by the thermal cracking.

Namely, although the reaction conditions of the thermal cracking depends on the kind of the starting material, it has been found that by the subsequent hydrocracking, the thermally treated tar-sand bitumen and the vacuum residues are converted to the fractions having the boiling point of less than 530.degree. C without any remaining residue, while restraining the formation of C.sub.1 - C.sub.4 gas to less than a few % when the thermal cracking condition is selected so as to increase the amount of asphaltenes contained in the thermally treated oil to 1.2 - 3.0 times of that of the starting material.

The hydrocracking of this invention is effected under the certain conditions, namely the reaction temperature of 350.degree.-500.degree. C, preferably 390.degree.-450.degree. C; the liquid hourly space velocity of 0.1-5, preferably 0.5-1.5; the hydrogen pressure of 50-300 Kg/cm.sup.2, preferably 100-200 Kg/cm.sup.2, the hydrogen feed rate of 500-3,000 l-H.sub.2 /1-oil, preferably 800-1,500 l-H.sub.2 /1-oil. The catalyst used in the hydrocracking is selected from the catalysts comprising one or more than two kinds of metals of the 6th or the 8th groups of the periodic table, for example, Mo--Co, Mo--Ni, W--Ni, Mo--Co--Ni, W--Co--Ni--or W--Co--Ni--Mo carried on .gamma.-alumina obtainable from alumina comprising substantially boehmite and boehmite gel from the stand point of the X ray diffraction spectrum diagram. The carrier used in the catalyst of the hydrocracking may be .gamma.-alumina having any physical properties. The most suitable carrier is manufactured by calcining at the two step calcining tempertures (the first step calcining temperature of 100.degree.-400.degree. C, 2-10 hrs; the second step calcining temperture of 400.degree.-700.degree. C, 1-10 hrs), the alumina gel obtained by washing alumina gel with alcohol without aging, while controlling the formation of bayerite.

Among the alumina carrier manufactured as mentioned above, the most suitable one is the alumina carrier showing the acidic colour by the benzene azodiphenyl amine indicator of pKa + 1.5. Silica may be added to the alumina carrier.

The physical properties of the alumina carrier used in the hydrocracking catalyst are the surface area of 100-450 m.sup.2 /g, preferably 150-300 m.sup.2 /g; the pore volume of 0.3-0.9 ml/g, preferably 0.4-0.6 ml/g; the bulk density of 0.3-0.9 g/ml., preferably 0.4-0.6 g/ml; the mean ppore diameter of 50-240 A, preferably 120-160 A; the crystalline form (after hydrolysis) of boehmite gel.

The methods for supporting the active metal on the alumina carrier, drying the carried catalyst, calcining and activating thereof can be accomplished according to conventional methods. The catalyst used in this invention, for example, possesses the properties of the surface area of 196-210 m.sup.2 /g, the pore volume of 0.57-0.58 ml/g, the mean pore diameter of 134-141 A, the bulk density of 0.65-0.67 g/ml and the bulk crashing strength of 5.4-6.6 Kg/cm.sup.2.

The process of this invention was carried out using the tar-sand bitumen as the starting material. The reactor was used in the thermal cracking was stainless steel pipe providing the effective reaction volume of about 28 cm.sup.3.

The reactor used in the hydrocracking was the fixed bed high pressure tubular flow type reactor of stainless steel having the inner diameter of 30 mm, and the length of 1,240 mm. And the catalyst used was the extruded catalyst of 200 ml having the diameter of 1.5 mm.

Table 1 shows the test results of the thermal cracking and the hydrocracking of the tar-sand bitumen, while table 2 shows the test result obtained by the combined processes of the thermal cracking and hydrocracking of the tar-sand bitumen.

It has been proven from the tables 1 and 2 that the tar-sand bitumen is cracked to the product oil without remaining the fractions having the boiling point of more than 530.degree. C.

The tar-sand bitumen has been treated according to the process of this invention under the same reaction condition to those of the example 1 to investigate the removal of sulfur, nitrogen, metal and asphaltenes. It has been proved from the tables 3 and 4 that the superior effects about the removal of sulfur, nitrogen, metal and asphaltenes are obtained according to the process of this invention.

The vacuum residue of Iranian Heavy crude having the following properties have been treated according to the process of this invention under the same reaction conditions to those of the example 1.

It has been proved from the tables 5-7 that the superior effects about the removal of sulfur, nitrogen, metal and asphaltenes are obtained according to the process of this invention.