Patent Application
20060272982
The present invention relates to a process for the conversion of heavy charge stocks, among which heavy crude oils, bitumens from oil sands and distillation residues, by means of at least three process units: deasphalting, hydroconversion of the charge stock using phase-dispersed catalysts and distillation.
The conversion of heavy crude oils, bitumens from oil sands and petroleum residues into liquid products can be substantially effected in two ways: an exclusively thermal one and the other by means of hydrogenating treatment.
Current studies are mainly directed towards hydrogenating treatment, as thermal processes create problems relating to the disposal of the by-products, such as, in particular, coke (obtained in amounts even higher than 30% by weight with respect to the charge stock) and to the poor quality of the conversion products.
Hydrogenating processes consist of treating the charge stock in the presence of hydrogen and suitable catalysts.
The hydroconversion technologies which are at present on the market, use fixed or ebullated bed reactors and make use of catalysts generally consisting of one or more transition metals (Mo, W, Ni, Co, etc.) supported on silica/alumina (or equivalent material).
Fixed bed technologies have several problems in treating particularly heavy charge stocks, containing high percentages of hetero-atoms, metals and asphaltenes, as these contaminants lead to a fast deactivation of the catalyst.
Ebullated bed technologies have been developed and commercialized for treating these charge stocks, which give interesting performances but are complex and costly.
Hydrotreating technologies using dispersed phase catalysts can represent an interesting solution to the drawbacks of the fixed and ebullated bed technologies. Slurry processes, in fact, combine the advantage of a high flexibility on the charge stock with high performances in terms of conversion and upgrading, proving, at least in principle, to be simpler from a technological point of view.
Slurry technologies are characterized by the presence of catalyst particles having very small average dimensions and suitably dispersed in the medium: for this reason the hydrogenation processes are easier and immediate in all parts of the reactor. The formation of coke is considerably reduced and the upgrading of the charge stock is high.
The catalyst can be introduced as powder with sufficiently reduced dimensions (U.S. Pat. No. 4,303,634) or as an oil-soluble precursor (U.S. Pat. No. 5,288,681). In this latter case, the active form of the catalyst (generally the metal sulphide) is formed in situ by thermal decomposition of the compound used, during the reaction itself or after suitable pretreatment (U.S. Pat. No. 4,470,295).
The metal components of the dispersed catalysts are normally one or more transition metals (preferably Mo, W, Ni, Co or Ru). Molybdenum and tungsten have much more satisfactory performances with respect to nickel, cobalt or ruthenium, and even more with respect to vanadium and iron (N. Panariti et al., Appl. Ctal. A: Gen. 2000, 204, 203).
Even if the use of dispersed catalysts solves most of the problems of the technologies described above, it has drawbacks mainly due to the catalyst life and to the quality of the products obtained.
The way these catalysts are used (type of precursors, concentrations, etc.) are extremely important both from an economical and environmental point of view.
The catalyst can be used at a low concentration (a few hundred ppm) in the “once-through” mode, but in this case the upgrading of the reaction products is generally unsatisfactory (N. Pnariti et al., Appl. Ctal. A: Gen., 2000, 204, 203 and 215). If very active catalysts are used (for example, molybdenum) and with higher catalyst concentrations (thousands of ppm of metal), the quality of the product obtained is certainly higher, but it is necessary to effect the recycling of the catalyst.
The catalyst at the reactor outlet can be recovered by separation of the product obtained from the hydrotreating (preferably from the bottom of the distillation column downstream of the reactor) through conventional methods such as, for example, decanting, centrifugation or filtration (U.S. Pat. No. 3,240,718; U.S. Pat. No. 4,762,812) which are, however, extremely complex if applied to heavy charge stocks rich in poisoning substances.
As far as the chemical description of the conversion processes is concerned, it is very useful to introduce the stability concept which, for a crude oil or an oil residue, expresses its tendency to precipitate the asphaltene component due to a change in the operative conditions or in the chemical composition of oil and/or asphaltenes (incompatibility) following dilution with hydrocarbon cuts or chemical transformation induced by cracking processes, hydrogenation, etc. . . .
Conventionally, asphaltenes are hydrocarbons which can be precipitated from a crude oil or an oil residue, by treatment with a paraffinic hydrocarbon with a number of carbon atoms ranging from 3 to 7, for example n-heptane under the standard conditions provided for by the regulation IP-143.
From a quality point of view, it can be asserted that incompatibility phenomena occur when products having very different characteristics with respect to the nature of the malthene component, i.e. the non-asphaltene component, are mixed, as in the case of the mixing of paraffinic crude oils with aromatic oils, or the dilution of oil residues with cutter stocks of a paraffinic nature (a typical case is the fluxing of tars from visbreaking with low aromatic gas oils).
In conversion processes of oil residues, bitumens from oil sands and heavy crude oils to distillates, the maximum conversion level is limited by the stability of the residue produced. These processes, in fact, modify the chemical nature of oils and asphaltenes causing a progressive decrease in stability with an increase in the severity level. Over a certain limit, the asphaltenes present in the charge can give rise to a phase separation (i.e. precipitate) and therefore trigger coke formation processes.
From a physico-chemical point of view, the phase separation phenomenon can be explained by the fact that the asphaltene phase becomes more and more aromatic with the advancing of the conversion reactions, due to the effect of the dealkylation and condensation reactions.
Consequently, beyond a certain level, the asphaltenes are no longer soluble in the malthene phase, also because, in the meantime, the latter has become more “paraffinic”.
The control of the loss of stability of a heavy charge stock during a thermal and/or catalytic conversion, is therefore fundamental for obtaining the maximum conversion degree without creating problems due to the formation of coke or fouling.
In “once-through” processes, the optimum operative conditions (mainly reaction temperature and residence time) are simply determined on the basis of the stability of the reactor effluent through direct measurements on the non-converted residue (P value, Hot Filtration Test, Spot Test, etc.).
All these processes allow more or less high conversion levels to be reached, according to the charge stock and the technology used, in any case generating a non-converted residue at the stability limit, which we will call tar, which, from case to case, can vary from 30 to 85% of the initial charge stock. This product is used for producing combustible oil, bitumens or it can be used as charge stock in gasification processes.
Schemes have been proposed for increasing the overall conversion level of cracking processes, which include the recycling of more or less significant amounts of tar in the cracking unit.
In the case of hydroconversion processes with dispersed catalysts in slurry phase, the recycling of tar also allows the recovery of the catalyst, to the extent that the same Applicants have described, in patent application IT-95A001095, a process which allows the recycling of the catalyst recovered to the hydrotreatment reactor, without the necessity of a further regeneration step, obtaining, at the same time, a good-quality product without the production of residue (“zero residue refinery”).
This process comprises the following steps:
The same Applicants describe in the subsequent patent application IT-MI2001A001438 different process configurations with respect to that described above.
The process claimed therein by the combined use of the following three process units: hydroconversion with catalysts in slurry phase (HT), distillation or flash (D), deasphalting (SDA), is characterized in that the three units operate on mixed streams consisting of fresh charge stock and recycled streams, using the following steps:
With said configurations, the following advantages can be obtained:
The treatment of a heavy hydrocarbon charge stock by means of Solvent Deasphalting allows the separation of two pseudo-components conventionally defined DeAsphalted Oil (DAO) and asphaltenes Cn (wherein n represents the number of carbon atoms of the paraffin used in the deasphalting operation (normally from 3 to 6).
We have surprisingly found that if the DAO is subjected to a hydrotreatment section and the asphaltenes to a gasification section, the catalyst make-up is reduced, following the significant decrease in the purging quantity necessary for removing the heavy metals (Ni, V, Fe, ect.) present in the feeding stream to the hydrotreatment itself.
The process, object of the present invention, for the conversion of heavy and extra-heavy charge stocks by the combined use of at least the three following process units: solvent deasphalting (SDA), hydroconversion with catalysts in slurry phase (HT), distillation or flash (D), is characterized in that it comprises the following steps:
The heavy charge stocks treated can be of a varying nature: they can be selected from heavy crude oils, distillation residues, heavy oils coming from catalytic treatments, for example “unconverted oils” from fixed or ebullated bed hydrotreatment, “heavy cycle oils” from catalytic cracking treatment, “thermal tars” (coming, for example from visbreaking or similar thermal processes), bitumens from “oil sands”, different kinds of coals and any other high boiling charge stock of a hydrocarbon origin, normally known in the art as “black oils”.
The stream containing asphaltenes obtained in the deasphalting section (SDA) can be optionally mixed with the remaining part of the distillation residue (tar), or the liquid coming from the flash unit, not recycled to the hydrotreatment section (HT).
Said stream containing asphaltenes, mixed or not mixed with part of the distillation residue (tar) or of the liquid coming from the flash unit, can be:
It is advisable for at least part of the distillation residue (tar) or liquid coming from the flash unit, preferably at least 80% by weight, more preferably at least 90% by weight, even more preferably at least 99% by weight, to be recycled to the hydrotreatment section (HT), whereas the possible remaining part is sent to the gasification section POx). The gasification can be effected by feeding to the gasification unit, in addition to the charge stock, oxygen and vapour which react under exothermic conditions at a temperature of over 1300° C. and a pressure ranging from 30 to 80 bar, to produce mainly H2 and CO.
A stream of syngas, or a mix of H2 and CO, can be obtained from the gasification section, which can be further used as fuel by means of combustion with combined cycles (IGCC) or transformed into paraffinic hydrocarbons by means of Fisher-Tropsch synthesis or converted into methanol, dimethyl ether, formaldehyde and, more generally, into the whole series of products deriving from Cl chemistry.
The same paraffinic hydrocarbons obtained via Fisher-Tropsch can be mixed with the various cuts obtained from the distillation or flash step, improving their composition characteristics.
The catalyst precursors used can be selected from those obtained from easily decomposable oil-soluble precursors (metal naphthenates, metal derivatives of phosphonic acids, metal-carbonyls, etc.) or from preformed compounds based on one or more transition metals such as Ni, Co, Ru, W and Mo: the latter is preferred thanks to its higher catalytic activity.
The catalyst concentration, defined on the basis of the concentration of the metal or metals present in the hydroconversion reactor, ranges from 350 to 30,000 ppm, preferably from 3,000 to 20,000 ppm, more preferably from 5,000 to 15,000 ppm.
The hydrotreatment step (HT) is preferably carried out at a temperature ranging from 360 to 450° C., more preferably from 380 to 440° C., and at a pressure ranging from 3 to 30 MPa, preferably from 10 to 20 MPa.
Hydrogen is fed to the reactor, which can operate in both a down-flow mode and, preferably, up-flow. Said gas can be fed to several sections of the reactor.
The distillation steps are preferably effected under reduced pressure, ranging from 0.001 to 0.5 MPa, preferably from 0.1 to 0.3 MPa.
The hydrotreatment step (HT) can consist of one or more reactors operating within the condition range mentioned above. Part of the distillates produced in the first reactor can be recycled to the subsequent reactors of the same step.
The deasphalting step (SDA), effected by means of an extraction with solvent, either a hydrocarbon solvent or not, is normally carried out at temperatures ranging from 40 to 200° C. and a pressure of 0.1 to 7 MPa.
It can also consist of one or more sections operating with the same solvent or different solvents; the solvent recovery can be effected under sub-critical or supercritical multi-step conditions, thus allowing a further fractionation between the deasphalted oil and resins.
It is advisable for the solvent of this deasphalting step to be selected from light paraffins having from 3 to 6 carbon atoms, preferably from 4 to 5 carbon atoms, more preferably having 5 carbon atoms.
With the use of the gasification step (POx), in addition to obtaining a significant reduction in the purging quantity of the entire complex, there is the production of hydrogen, of which a portion can be adopted for the hydrotreatment reaction (HT).
In the process according to the invention a further secondary section can be optionally present for the hydrogenation post-treatment of the C2-500° C. fraction, preferably the C5-350° C. fraction, coming from the section of high pressure separators envisaged upstream of the distillation.
In this case, before being sent to one or more distillation or flash steps, the stream containing the hydrotreatment reaction product and the catalyst in dispersed phase, is subjected to a separation pre-step, effected at high pressure, so as to obtain a light fraction and a heavy fraction, this heavy fraction alone being sent to said distillation (D) step(s).
The light fraction obtained from the high pressure separation step, can be sent to a hydrotreatment section, producing a lighter fraction containing C1-C4 and H2S gas and a less light fraction containing hydrotreated naphtha and gas oil.
The possible insertion of the secondary post-treatment hydrogenation section of the C2-500° C. fraction, preferably of the C5-350° C. fraction, exploits the availability of this fraction together with hydrogen at a relatively high pressure, which is that of the hydrotreatment reactor, allowing the following advantages to be obtained:
The post-treatment hydrogenation on a fixed bed consists of the preliminary separation of the reaction effluent of the hydrotreatment reactor (HT) by means of one or more separators operating at high pressure and high temperature.
Whereas the heavy part, extracted from the bottom, is sent to the main distillation unit, the aliquot which is extracted from the head, a C5-350° C. fraction, is sent to a secondary treatment section in the presence of hydrogen, available at high pressure, where the reactor is of the fixed bed type and contains a typical desulphurisation/dearomatisation catalyst, in order to obtain a product which having a considerably lowered sulphur content and also lower nitrogen contents, a lower total density and, at the same time, increased cetane numbers as far as the gas oil fraction is concerned.
The hydrotreatment section normally consists of one or more reactors in series, the product of this system can be subsequently further fractionated by distillation to obtain a thoroughly desulphurated naphtha and a diesel gas oil within specification as fuel.
The fixed-bed hydrodesulphurisation step, normally uses typical fixed-bed catalysts for gas oil hydrodesulphurisation; said catalyst, or possibly a mix of catalysts or a series of reactors with various catalysts having different properties, causes a deep refining of the light fraction, significantly reducing the sulphur and nitrogen content, increasing the hydrogenation degree of the charge stock, thus diminishing the density and increasing the cetane number of the gas oil fraction, at the same time reducing the formation of coke.
The catalyst normally consists of an amorphous part based on alumina, silica, silico-alumina and blends of different mineral oxides, on which a hydrodesulphurizing component in association with a hydrogenating product, is deposited (with several methods). Catalysts based on molybdenum or tungsten with the addition of nickel and/or cobalt, deposited on a mineral amorphous carrier, are typical catalysts for this type of operation.
The post-treatment hydrogenation reaction is effected at an absolute pressure slightly lower than that of the primary hydrotreatment step, normally ranging from 7 to 14 MPa, preferably from 9 to 12 MPa; the hydrodesulphurizing temperature ranges from 250 to 500° C., preferably from 280 to 420° C.; the temperature normally depends on the desulphuration level required. The space velocity is another important variable in controlling the quality of the product obtained: it can range from 0.1 to 5 h−1, preferably from 0.2 to 2 h−1.
The quantity of hydrogen mixed with the charge stock is fed at a flow-rate ranging from 100 to 5,000 Nm3/m3, preferably from 300 to 1,000 Nm3/m3.
An embodiment of the present invention is now provided with the help of the enclosed
In
Two streams are obtained from the deasphalting unit (SDA): one stream (2) consisting of deasphalted oil (DAO), the other stream containing asphaltenes (3).
The stream containing asphaltenes (3) is sent to a gasification section (POx) in order to obtain syngas, i.e. a gaseous mix of H2 and CO (4).
The stream consisting of deasphalted oil (2) is mixed with the fresh make-up catalyst (5) (necessary for reintegrating that lost with the stream (15) described hereunder) and with the stream (14) (described hereunder) coming from the bottom of the distillation or flash column (D) to form the stream (6) which is fed to the hydrotreatment reactor (HT) into which hydrogen (or a mix containing hydrogen and H2S) (7) is fed.
The hydrogen fed can be part of the hydrogen coming from the gasification step (POx) (not schematised in the figure)
A stream (8) leaves the reactor (HT), containing the hydrogenation product and the catalyst in dispersed phase, which is fractionated in a distillation or flash column (D) from which the lighter fraction (9) separates together with the distillable products (10), (11) and (12) from the distillation residue (13) containing the dispersed catalyst and coke.
This stream (13) (called tar) is mostly recycled (14) to the hydrotreatment unit (HT), the remaining part (15) being sent to the gasification section (POx).
An example is provided for a better understanding of the invention, it being understood that the invention should not be considered as being limited thereto or thereby.
Following the scheme represented in
Deasphalting Step (SDA)
The yield obtained by the procedure described is equal to 82% by weight of deasphalted oil with respect to the starting vacuum residue.
The properties of the RV Ural and deasphalted oil (DAO C5) are shown in table 1.
DAO Hydrotreatment Step
Catalytic tests were carried out using a stirred micro-autoclave of 30 cm3, in accordance with the following general operative procedure:
Hydrotreatment tests were effected using the DAO produced in the deasphalting step, according to the following procedure. The reactor was charged with DAO and the molybdenum compound and pressurized with hydrogen. The reaction was carried out under the operative conditions shown in table 2, which indicates the data relating to the distribution of products and quality.
The following experimentation was carried out following the scheme represented in
Deasphalting Step (SDA)
Effected according to what is described in example 1.
Hydrotreatment Step
Using the DAO produced in the deasphalting step, hydrotreatment tests were performed according to the procedure described below. The reactor was charged with DAO and the molybdenum compound and pressurized with hydrogen. The reaction was carried out under the operative conditions described. Quenching was effected once the test had been completed; the autoclave was depressurised and the gas collected in a sampling bag for gas-chromatographic analysis. The liquid product present in the reactor was recovered and subjected to distillation in order to separate the 500° C.+residue from the other distillation cuts. The distillation residue (500° C.+) containing the catalyst, was charged again into the reactor and mixed with a suitable amount of DAO C5 previously prepared, in order to keep the quantity of the total charge stock constant. This procedure was repeated until stabilization of the quantity of the residue obtained, i.e. until stationary conditions were reached.
Distillation Step
The data relating the outlet streams after the last recycling (% weight with respect to the charge) are provided hereunder:
Vacuum residue (500° C.+): 30%
| Number | Date | Country | Kind |
|---|---|---|---|
| MI2004A 002446 | Dec 2004 | IT | national |
