SK281664B6 - Method for reducing viscosity of dense oil residuals - Google Patents

Abstract

A method for reducing the viscosity of dense oil residues (1), comprising a first step of lightly cracking (I) the dense oil residue (1) and a second step of thermally cracking (II) the dense gas oil (3) formed during the light cracking, said thermal cracking producing a thermal residue (7) and lighter products, wherein a) the thermal residue (7) obtained in the second thermal cracking step is mostly completely isolated and b) a composition comprising fresh, dense oil residues (1) diluted with heat the residue (7) isolated in step a) is repeatedly introduced into the light cracking step

Description

The invention relates to a process for reducing the viscosity of dense oil residues.

BACKGROUND OF THE INVENTION

In order to obtain less viscous oil products from starting, extremely viscous, oil residues, methods of lowering the viscosity by mild thermal cracking (light cracking) are widely used, as described, for example, in the article by Beuther et al. and entitled "Thermal Visbreaking of Heavy Residues", The Oil and Gas Joumal, 57:46, November 9, 1959, p. 151-175 or "Visbreaking: A Flexible Process" by Rhoe et al., Published in Hydrocarbon Processing, January 1979, p. 131-136.

Said processes can be applied to various refinery fractions, such as atmospheric and vacuum distillation residues, fiirfural extracts, asphalted tars, catalytic cracking bottoms.

Light cracking processes are thermal processes carried out under milder conditions, resulting in lighter hydrocarbon fractions. Light cracking processes typically produce gases, liquid fuel gas (LPG), naphtha, gas oil and thick distillates.

Light cracking processes are often accompanied by thermal cracking processes in which the thick gas oil from the vacuum distillation coming from light cracking is subjected to thermal cracking under much more drastic conditions than in the previous light cracking step. In this way, other lighter fractions are isolated.

However, a disadvantage of these combined processes (light cracking and thermal cracking) is the production of a considerable amount of residues which, due to their physicochemical properties (e.g. density, viscosity and distillation curve), can only be used as heating oil after dilution with gaseous oil.

Therefore, it was necessary to find new thermal processes which were effective while producing a small amount of said residues.

It has now been found a process that reduces the viscosity of dense oil residues and which no longer suffers from the drawbacks of the described combined processes, since it not only reduces the amount of thermal cracking residues formed, but mostly eliminates them completely.

SUMMARY OF THE INVENTION

As already mentioned, the invention relates to a method for reducing the viscosity of dense oil residues, which comprises a first step in which light cracking (I) of dense oil residues occurs and a second step in which thermal cracking (II) of dense gaseous oil formed during light wherein said thermal cracking produces a thermal residue and lighter products. This method is characterized by:

(a) the thermal residue obtained in the second thermal cracking step is usually isolated; and

b) a composition comprising fresh thick oil residues ordered by the thermal residue isolated in step a) is repeatedly introduced into the light cracking step.

The term "light cracking" refers to a well-known process in the art for reducing the viscosity of dense oil fractions. Said light cracking processes can be carried out, as is known, on a dense oil residue, optionally in the presence of hydrogen (hydrovisbreaking) or in the presence of so-called hydrogen donor solvents (see, for example, US-A-2 953 513), or in the presence of hydrogen; a donor solvent (see US-A-4,292,168) and also in the presence of a catalyst (see, for example, US-A-5,057,204).

In a preferred embodiment, the light cracking (I) processes are carried out without hydrogen, catalysts and hydrogen donor solvents. The method comprises introducing a dense oil residue into a furnace heated to the desired temperature during a preset time.

Since in most petrochemical processes there is a correlation between the reaction temperature and the residence time of the reactants, one light cracking process can be more drastic than others if a longer residence time is used at the same temperature.

The light cracking process can usually be carried out using one or more furnaces, but in all cases the temperature of the cracking furnace or furnaces is in the range of 350 ° C to 525 ° C, preferably in the range of 380 ° C to 500 ° C, and time a retention time of between 2 and 20 minutes, preferably between 3 and 10 minutes.

As already mentioned, the dense oil residues to be subjected to the easy cracking step (I) can come from different refinery streams.

Light cracking processes can therefore be applied to various dense oil fractions, such as atmospheric and vacuum distillation residues, furfural extracts, asphalted tars, catalytic cracking fractions taken from the bottom and asphalts. Typically, at least 75 wt. The components of the dense oil residue have a boiling point greater than 370 ° C. Said dense oil residues may also contain an admixture of heteroatoms, for example nitrogen or sulfur, and metals, especially vanadium.

In a preferred embodiment, the dense oil residue introduced into the light cracking step (I) is essentially composed of the remainder of the atmospheric distillation. Atmospheric distillation residues typically have the following properties: density between 0.940 g / m ³ and 1,000 g / m ³ : initial distillation temperature (according to ASTM D 1160 method) between 180 ° C and 220 ° C; a temperature at which 5% of the volume is distilled from 330 ° C to 370 ° C; a temperature at which 10% of the volume is distilled from 380 ° C to 410 ° C: and a temperature at which 50% of the volume distills, from 490 ° C to 520 ° C.

The light cracking step (I) produces a number of hydrocarbon fractions. Typically, the following fractions are recovered: a) gases and liquid fuel gas, b) naphtha, c) gas oil, d) thick vacuum distillate, e) vacuum distillation residue + fuel oil and / or tar.

Separation of light cracking products from said fractions is irrelevant for the implementation of the process of the invention. However, it is preferred to isolate fractions of high addition value such as, for example, naphtha and gas oil.

On the other hand, it is essential to isolate all or at least a portion of the thick gas oil from the vacuum distillation, otherwise known as HVGO (high vacuum gas oil). This is a hydrocarbon fraction having a density at 15 ° C of 0.880 g / cm ³ to 0.980 g / cm ³ , an initial distillation temperature (ASTM D 1160) ranging from 240 ° C to 290 ° C and a final distillation temperature ranging from 530 ° C to 590 ° C.

This thick gas oil from the vacuum distillation is usually, m.p. j. in most cases, it is isolated by vacuum distillation, usually at about 2666.4 Pa to 5332.8 Pa.

Further thick gaseous oil from the vacuum distillation can be isolated at 2 bottoms of the distillation column at atmospheric pressure, typically at pressures of 0.2 MPa to 0.4 MPa. The properties of this fraction (i.e., the residue obtained from the bottom of the distillation chamber at atmospheric pressure) are within the range of properties of the thick vacuum distillation gas oil. Thus, the thick vacuum distillation gas oil obtained after the light cracking step refers to both the oil isolated by distillation under reduced pressure and the remainder isolated at atmospheric pressure.

Some or all of the thick gas oil isolated from the vacuum distillation is introduced into the thermal cracking step (II).

If only a portion of said dense gas oil is introduced into the thermal cracking step, then any other oil fraction having the same physicochemical properties as said dense vacuum oil distillation gas may form the remainder. The vacuum residue from the top is a typical fraction that can be used to supply thermal cracking (II) together with the thick vacuum distillation gaseous oil isolated after the light cracking step.

However, for the thermal cracking step, it is preferred that the entire fraction of the thick gas oil from the vacuum distillation is isolated after light cracking.

Obviously, since other oil fractions having the properties of a thick gas oil from vacuum distillation are also added to said gas oil, it will be necessary that the dimensions of the thermal cracking furnace be larger than those corresponding to the processing of the amount of thick gas oil from the vacuum. vacuum distillation, which comes from light cracking.

On the other hand, if the thermal cracking furnace had dimensions smaller than those necessary to process the amounts of thick gaseous oil from the vacuum distillation, isolated after the light cracking step, then it would be necessary to remove some of the oil or isolate only the required amount.

The thermal cracking step (II) is carried out under much more drastic conditions than the light cracking step (I), either at elevated temperature at the same residence time or at the same temperature and extended residence time.

The temperature of the thermal cracking step (II) is usually between 450 ° C and 510 ° C and the residence time is between 20 minutes and 60 minutes.

At the end of the thermal cracking step, a fraction referred to as a thermal residue, which represents the resulting thermal cracking product after removal of the light fractions (350 ° C), is isolated.

The stream leaving the thermal cracking is usually fed to a separator in which the lighter fractions (350 ° C) are isolated. The remaining product is a thermal residue having a density at 15 ° C of 1.00 to 1.07 and a P value (determined by Shell method No. 1600 of 1983) between 1.4 and 2.3, an initial distillation temperature (according to ASTM D 1160 of the method) between 180 ° C and 220 ° C, a temperature at which 50% by weight distills off, between 440 ° C and 490 ° C and a temperature at which 90% by weight distills off, between 570 ° C and 610 C.

The thermal residue thus obtained is mixed with another dense oil residue equal to or different from the initial charge, and the mixture thus obtained is reintroduced into the light cracking step (I).

The mixture of the dense oil residue and the thermal residue preferably comprises 5 wt. % to 50 wt.%, more preferably 10 wt. % to 40 wt.%, and even more preferably 20 wt. % to 30 wt.%, a thermal residue and a supplement of up to 100 wt. to form a thick oil fraction.

In general, the process according to the invention makes it possible to eliminate all the thermal residue in a combined apparatus in which light cracking and thermal cracking take place.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows the process diagram of the process of the invention and Figure 2 shows the process diagram of the conventional process of the prior art in which the thermal residue at the end of the thermal cracking step is not recycled.

DETAILED DESCRIPTION OF THE INVENTION

As already mentioned, Figure 1 shows a light cracking apparatus A filled with a thick oil residue

1. A thin stream is obtained from this apparatus A, which is sent to the atmospheric distillation unit D and a dense stream, which is sent to the vacuum distillation unit B. From this unit, the light gas oil fraction 2 is fed to the atmospheric distillation unit. D together with the thick gas oil fraction 3 and the light cracking residue to be used as a fuel oil component. The thick gas oil fraction 3 forms a charge for the thermal cracking unit C together with the thick gas oil recovered as residue 6 recycled from the atmospheric distillation unit D and together with possible batches of a similar composition of other origin. The thermal cracker C yields a light fraction which is fed into the atmospheric distillation unit D and the thermal residue 7 which is recycled to the light cracker A.

The following examples are illustrative only and are not to be construed as limiting the scope of the invention as set forth in the appended claims.

Two runs were carried out in the refinery, the refinery being filled in both cases with the remainder of atmospheric distillation having the following characteristics:

Density at 15 ° C 0,981 P value 2.10 Conradson's carbon residue 9.70 wt. Viscosity at 50 ° C 49.3 .10 ' ³ Pa.s Overall Sir 2.82 wt. Distillation ASTM D160 Initial distillation temperature 197 ° C 5% evaporated volume 343 ° C 10% evaporated volume 393 ° C 20% evaporated volume 429 ° C 30% evaporated volume 455 ° C 40% evaporated volume 480 ° C 50% evaporated volume 512 ° C 60% evaporated volume 552 ° C 70% evaporated volume 609 ° C 80% evaporated volume 655 ° C 90% evaporated volume 711 ° C 95% evaporated volume 822 ° C Final distillation temperature 850 ° C Current supplied to thermal cracker with: had the following characteristics: Density at 15 ° C 0,975 Conradson's carbon residue 1.04 wt. Distillation ASTM D160 Initial distillation temperature 275 ° C 5% evaporated volume 325 ° C

SK 281664 Β6

10% evaporated volume 348 ° C 20% evaporated volume 375 ° C 30% evaporated volume 398 ° C 40% evaporated volume 414 ° C 50% evaporated volume 436 ° C 60% evaporated volume 448 ° C 70% evaporated volume 468 ° C 80% evaporated volume 485 [deg.] C 90% evaporated volume 510 ° C 95% evaporated volume 535 ° C Final distillation temperature 587 ° C

Referring to Figure 1, a 60% by weight stream is fed to the thermal cracking step (II) in both test runs (1 and 2). % Of HVGO from vacuum distillation unit B, 30 wt. % fraction from the bottom of atmospheric distillation unit D and its remaining 10 wt. it forms a dense, gaseous oil from the top of the vacuum vessel that is fed from other parts of the refinery.

The thermal residue after separation of the light products had the following characteristics:

Density at 15 ° C 1,053 P value 2.00 Total sulfur 3.68% by weight. Distillation ASTM D160 Initial distillation temperature 205 ° C 5% evaporated volume 383 ° C 10% evaporated volume 408 ° C 20% evaporated volume 426 ° C 30% evaporated volume 442 ° C 40% evaporated volume 456 ° C 50% evaporated volume 474 ° C 60% evaporated volume 490 ° C 70% evaporated volume 520 ° C 80% evaporated volume 544 ° C 90% evaporated volume 594 ° C 95% evaporated volume 618 ° C Final distillation temperature Mp> 750 ° C

In Comparative Run 2, the thermal residue was quenched with gaseous oil to provide fuel oil, and the subsequent light cracking step was filled with another fresh thick oil residue.

In Run 1, the thermal residue was mixed with another thick oil residue, and this mixture was introduced as a whole into a light cracking step (I). The composition was 25 wt. and the remaining 75 wt. fresh, thick oil residue.

The two test runs were carried out according to Schemes 1 and 2, i. j. test 1 was carried out in recycling almost all of the thermal residue leaving the thermal cracking step, and comparative test 2 was performed according to the operating scheme shown in Figure 2, i. j. without recycling the thermal residue obtained from the thermal cracking step.

In the experiment, the bottom temperature of the light cracking unit was 485 ° C, while the temperature of the thermal cracking furnace was 495 ° C.

The results of the 20-day test runs are shown in Table 1.

Table 1

faction Yield% w / w Test 1 Test 2 gas 3.8 2.1 LPG 3.7 2.9 C5 / C6 2.5 2.1 C7 - 140 ° C 8.6 5.8 Gas oils 45.2 35.9 Thermal residue 0.2 16.5 Rest of light cracking 36 34.7

The yield data given, which indicates average values, shows that the process according to the invention undeniably increases the yield of gaseous oils (about 9% by weight) and reduces the yield of C7 - 140 ° C of distillates to a very small extent (about 2% by weight). Increasing the yield of other distillates is less substantial.

A very important result is a reduction of the residues (light cracking + thermal cracking) by more than 10% by weight, and thus a proportionally higher quality of the gaseous oil used as flux.

Claims (2)

A method for reducing the viscosity of dense oil residues (1), comprising a first step of lightly cracking (I) thick oil residues (1) and a second step of thermal cracking (II) of thick gas oil (3) produced during light cracking, wherein the above thermal cracking produces a thermal residue (7) and lighter products, characterized in that a) the thermal residue (7) obtained in the second step of thermal cracking is completely isolated and b) the composition comprising fresh, thick oil residues (1) diluted with the thermal residue (7) isolated in step a) is repeatedly introduced into the light cracking step. The process according to claim 1, characterized in that the light cracking is carried out under hydrogen-free conditions, catalysts and solvents providing hydrogen. Method according to claim 1, characterized in that the dense oil residue (1) is formed by the remainder of the atmospheric distillation. Method according to claim 1, characterized in that the mixture of fresh, dense oil residue (1) and thermal residue (7), which is reintroduced into a light cracking step, comprises 5 wt.% To 50 wt.%. thermal residue (7) and fresh, dense oil residue (1) make up the remainder to 100% by weight. Method according to claim 4, characterized in that the composition reintroduced into the light cracking step comprises 10% by weight, up to 40% by weight, of the thermal residue (7). The method of claim 5, wherein the composition reintroduced into the light cracking step comprises 20 wt% to 30 wt%. thermal residue (7). 2 drawings Fig. SK 281664 Β6 CM u. Λ ABOUT