EP0244277A1 - Process for deasphalting a hydrocarbon oil - Google Patents

Abstract

Method for deasphalting a hydrocarbon oil (1) containing asphaltenes using a hydrocarbon solvent (4) having 3 to 8 carbon atoms. An asphalt phase and a solution of deasphalted oil in the solvent are formed. To separate the solvent from the deasphalted oil, the solution is circulated along an inorganic membrane (7) with a pore radius chosen between 2 and 15 nanometers: the filtrate is enriched in solvent and can be recycled. The deasphalted oil is selectively retained on the upstream side of the membrane.

Description

The present invention relates to a process for deasphalting a hydrocarbon oil and separation by ultrafiltration, in liquid phase, of the deasphalted hydrocarbon oil and of the deasphalting solvent.

A large number of hydrocarbon feedstocks used in the petroleum industry, such as certain crude oils, residues from atmospheric distillation or vacuum distillation, shale or oil sands oils, or coal liquefies, are characterized by a content high in asphaltenes as well as in metals such as nickel and vanadium; therefore, they cannot be subjected directly to conventional refining treatments such as catalytic cracking, hydrocracking or hydrodesulfurization for example.

Indeed, the metals and a fraction of the asphaltenic carbon remain fixed on the catalyst, clogging the pores, destroying the activity of the active centers and creating pressure drops. This results in the need to renew the catalyst charge at a rate which is all the more frequent the higher the metal and asphaltene contents. It is then advisable to separate the asphaltic load into two fractions: a fraction composed essentially of asphaltenes and containing the major part of the metals and the complementary fraction consisting of deasphalted oil. The separation operation most commonly described in the prior art is the precipitation of asphaltenes by adding to the asphaltene oil adequate quantities of light hydrocarbons under suitable conditions. When targeting a selective precipitation of asphaltenes, the solvents used consist of light, paraffinic or olefinic hydrocarbons, preferably containing 3 to 8 carbon atoms, which are used pure or preferably as a mixture.

This deasphalting operation must be carried out as selectively as possible so as to obtain a maximum yield of deasphalted oil. The yield of deasphalted oil obviously depends on the asphaltene content of the treated feed and the nature of these asphaltenes; the selectivity of the operation depends on the operating conditions, temperature, pressure, residence time in the separation container but it depends above all on the nature of the precipitation solvent and the solvent / charge ratio used. To be effective, this operation involves the use of a large volume of solvent, since the volume ratios of the solvent to the charge are generally between 2/1 and 15/1, and most often between 3/1 and 8 / 1.

The devices most used for this operation consist of:
- either in an extractor-settler; by the bottom of this extractor-settler, the coagulated asphalts are collected as well as a small fraction, generally of the order of 5-15%, of the solvent used.

At the head of the extractor-decanter, a mixture of hydrocarbon oil, freed from its asphalts, is collected which will subsequently be called "deasphalted oil", as well as the major part - usually around 85-95% solvent used for the operation.

- either in a multi-stage column: the charge is introduced into the upper half of the column, the solvent is sent against the current at the bottom of the column; by the bottom we recover the asphalt; by the heated head, the deasphalted solvent oil mixture is recovered.

Depending on the nature of the solvent used, this mixture is collected at a temperature usually between 60 and 220 ° C, under a pressure such that the mixture of solvent and deasphalted oil is in the liquid state. The content of deasphalted oil in this mixture extracted at the top obviously depends on the nature of the filler and the amount of solvent used relative to the filler, as well as on the operating conditions. Generally, the weight percentage of the deasphalted oil in this top fraction is between 10% and 40% and, most often between 20 and 38%.

The treatment of this fraction, consisting in separating the solvent from the deasphalted oil is a theoretically simple operation, given the differences in the respective volatilities of the constituents; indeed the deasphalted oil has a boiling range, under normal pressure, well above 350 ° C; however, the evaporation of the solvent requires, because of the large quantities of solvent used, considerable energy expenditure.

Also, very many solvent evaporation methods, tending to reduce energy costs, have been described in the prior art; we can, for example, cite the patent US 2,943,050 which describes a process successively using two flash evaporators, the French patent FR 2,425,472 describing a process using three continuous flash distillation zones operating under constant temperature and pressure conditions , French patent FR 2,490,103 claiming a solvent recovery process in several stages, in falling film evaporators also allowing nucleated boiling. Some of these processes would reduce the cost of spending by about 50% of the operation, which however remains high.

Another method of reducing these energy costs is to bring the mixture of deasphalted oil and solvent to a temperature above the critical temperature of the solvent. Under these conditions of supercritical state, the solubility of the deasphalted oil in the solvent decreases and there is a demixing of the two phases. This technique has been described in numerous patents and publications, such as US patents 2,940,920, 4,239,616, 4,290,880 and 4,305,814.

However, if it is true that this process makes it possible to achieve significant energy savings in terms of the recovery of the deasphalting solvent, it has the disadvantages of being able to be used only under conditions of temperature and pressure higher than those employed in conventional solvent recovery, and to require a thorough heat exchange between the deasphalted oil-deasphalting solvent mixture on the one hand and the separated deasphalting solvent on the other hand.

The aim of the present invention is to propose a new deasphalting process comprising a step of separation of deasphalted oil and deasphalting solvent, by ultrafiltration, in the liquid phase, without change of state, this separation being carried out at high temperature, and allowing significant energy savings compared to existing processes.

The use of organic semi-permeable membranes in processes for the separation of various compounds is well known; such processes are often called "reverse osmosis" or "ultrafiltration". These membranes are generally made up of polymer materials such as cellulose esters, regenerated celluloses, polyamides, polyvinyl chloride or crosslinked polyethylene, polyacrylonitrile and polysulfone.

Their use is considerable in the petrochemical sector ment limited due to their poor resistance to hydrocarbon solvents on the one hand and their very low thermal stability on the other hand.

As regards ultrafiltration processes using mineral membranes intended to separate hydrocarbon products in the liquid state by operating at a temperature above 80 ° C., mention may be made of patent FR 2,482,975. This patent uses mineral ultrafiltration barriers coated with a sensitive layer of at least one metal oxide having a radius of permeametry between 50 and 250 A; it is intended for the regeneration of used oils by elimination of their impurities which are retained by the barriers used and can also be used to reduce the level of asphaltenes in hydrocarbon feedstocks. For this latter application, the process turns out to be unsatisfactory since the rate of elimination of asphaltenes remains low, as shown in Example 2 of the French patent.

The object of the invention is to propose a deasphalting process which overcomes the drawbacks of the known processes. It is both energy efficient, since it avoids distillation, in whole or in part, in selective.

According to this process, the separation of deasphalted oil and deasphalting solvent is carried out in the liquid phase, without change of state, at a temperature generally greater than 80 ° C., allowing significant energy savings compared to existing processes.

According to this process, the purified oil is selectively retained by an inorganic porous ultrafiltration membrane, and the solvent passes through this membrane.

• a) - on traite l'huile par au moins un solvant hydrocarbure ayant de 3 à 8 atomes de carbone, dans des conditions de désasphaltage permettant la formation de deux phases, une première phase constituée d'un mélange d'huile désasphaltée et de solvant et une seconde phase riche en asphaltènes, et on sépare ces deux phases.
• b) on fait circuler la première phase d'huile désasphaltée et de sol­vant, en phase liquide, le long d'au moins une membrane inorganique d'ultrafiltration dont le rayon de pores est choisi entre 2 et 15 nanomètres (20 et 150 Å) à une température d'au moins 80 °C, par exemple 80-400°C, dans des conditions d'ultrafiltration, et on recueille séparément l'ultrafiltrat, enrichi en solvant, et une phase non-filtrée résiduelle, le retentat, enrichie en huile désasphaltée et constituant le produit principal du procédé, et
• c) on renvoie l'ultrafiltrat à l'étape (a) pour y constituer au moins une partie du solvant hydrocarbure ayant de 3 à 8 atomes de carbone.

More precisely, this process is characterized in that:

• a) - the oil is treated with at least one hydrocarbon solvent having 3 to 8 carbon atoms, under deasphalting conditions allowing the formation of two phases, a first phase consisting of a mixture of deasphalted oil and solvent and a second phase rich in asphaltenes, and these two phases are separated.
• b) circulating the first phase of deasphalted oil and solvent, in liquid phase, along at least one inorganic ultrafiltration membrane whose pore radius is chosen between 2 and 15 nanometers (20 and 150 Å) at a temperature of at least 80 ° C., for example 80-400 ° C., under ultrafiltration conditions, and the ultrafiltrate, enriched in solvent, and a residual unfiltered phase, the retentate, enriched, are collected separately in deasphalted oil and constituting the main product of the process, and
• c) the ultrafiltrate is returned to step (a) to constitute therein at least a portion of the hydrocarbon solvent having 3 to 8 carbon atoms.

Preferably, an inorganic membrane with a pore radius of 4 to 9 nanometers is used.

The porous ultrafiltration membrane may be any of those described in the prior art, and for example in US patents - 4,060,488 or 4,411,790, or FR-2,550,953.

In particular, the membrane may include a porous support of carbon, metal, ceramic or equivalent, on which a fine mineral material has been deposited, for example one of the oxides of the following elements: titanium, zirconium, magnesium, silicon, aluminum , yttrium, hafnium, boron, mixed oxides of several of these elements, or an alkali or alkaline earth metal fluoride, silicon carbide, silicon nitride, etc.

The inorganic membranes used according to the invention can work up to temperatures of 350 to 400 ° C. without losing their separation efficiency because their porous texture is stable in these thermal conditions. In addition, in this temperature range these same inorganic membranes are capable of operating at upstream-downstream pressure differences which can easily range up to 25 bars.

The speed of circulation along the membrane is, for example, 0.5 to 20 m / s, preferably 1 to 10 m / s, in order to further improve the selectivity, an improvement attributed to the formation of a layer of concentration polarization formed of the heaviest molecules on the ultrafiltration layer.

The ultrafiltration stage (b) is preferably continued until the solvent content of the mixture of deasphalted oil and of solvent having circulated along the membrane, in contact with it, but having resisted filtration and therefore remaining on the upstream side of the membrane, represents only 1 to 50%, preferably 2 to 30%, of the solvent content of said mixture of deasphalted oil and solvent having filtration, and then subjected said mixture, depleted in solvent, to a distillation to separate at least a portion of the residual solvent.

When steps (a) and (b) are carried out under the same pressure or under slightly different pressures, the ultrafiltration treatment is advantageously carried out at a temperature of 2 to 50 ° C. lower than the temperature that the first phase had deasphalted oil and solvent at the end of step (a). Regardless of this indication, the temperature can be, for example, from 80 to 220 ° C; the temperature and the pressure are usefully chosen so as to maintain the first phase of deasphalted oil and of solvent in completely liquid phase, at least on the upstream side of the membrane. The pressure must obviously be chosen higher upstream side than downstream side of the membrane.

Depending on the application of the process, the membranes can be grouped in variable numbers in ultrafiltration modules, these modules can be arranged in series or in parallel. The number of these modules obviously depends on the selectivity of the ultrafiltration membranes, the nature of the charge, and the degrees of enrichment desired for the two fractions.

The fillers capable of being treated by the process of the invention are those which are collected at the top of the extractors of the conventional solvent deasphalting units. Are subjected to the deasphalting operation all the hydrocarbon feedstocks of various origins, having an asphaltene content (determined by precipitation with n.heptane) greater than 0.2% by weight; these fillers may have optionally undergone thermal pretreatments such as, for example, visbreaking or visbreaking.

The deasphalting solvents used in these operations are light, paraffinic or olefinic hydrocarbons, preferably comprising from 3 to 8 carbon atoms, which are used pure or as a mixture. More specifically, for economic reasons, use is made of hydrocarbon cuts such as propane cut, butane cut, butane cut mixture, propane cut, penetrating cut and possibly the so-called "light gasoline" cut consisting mainly of mixtures of aliphatic C en hydrocarbons. and C₆.

The mixture of deasphalted oil and deasphalting solvent collected at the outlet of a conventional deasphalting unit is most often, depending on the nature of the solvent, at a temperature of 60 to 220 ° C. and at a pressure of 30 to 45 bars; for example for cuts C₅ and C₅-C₆, the temperature of the mixture is generally between 170 and 220 ° C, and the pressure of the order of 30 to 40 bars. Such a mixture can therefore, under these same temperature and pressure conditions, be sent to the ultrafiltration modules, which constitutes an advantage of the process.

The membranes, when they have the porous texture defined above, can function for a long time without annoying loss of filtering power. It is however possible to periodically apply a higher pressure on the downstream side than on the upstream side, which has the effect of cleaning the filter. The filters of patents US-4,411,790 and FR-2,550,953 have the advantage of being able to undergo this operation.

The appended figure represents a particular mode of implementation of the method. This figure shows, for convenience, the ultrafiltration modules by the ultrafiltration assembly (6) in which the ultrafiltration membranes are represented by (7).

The charge to be deasphalted is introduced into the extractor continuously (2) through line (1), the fresh deasphalting solvent being introduced into the extractor through line (4) and the solvent recycled through line (3).

At the head of the extractor, the mixture (d) of deasphalted oil and deasphalting solvent is collected via line (5); this mixture is introduced into the ultrafiltration assembly (6) from which come out:
- by line (8) the ultrafiltrate, consisting of a mixture rich in solvent which is recycled by line (3) to the extractor-deasphalter (2);
- Via line (9), the unfiltered fraction, the retentate, consisting of a mixture rich in deasphalted oil which is brought to an evaporator (flash) (10) where the elimination of the remaining solvent takes place. The deasphalted oil, freed of solvent, is collected by the line (11) at the outlet of the evaporator (10).

The vaporized solvent leaves the evaporator (10) via the line (12) and is recycled to the extractor (2).

At the bottom of the extractor (2), the coagulated asphalts and a small part of the deasphalting solvent are collected via the line (13).

This asphalt fraction can be treated by conventional means not shown in the figure; this fraction can for example be subjected to evaporation in the evaporator (14), which will make it possible to remove most of the solvent, then to stripping with steam, not shown intended to remove the last fractions of the solvent. The solvent removed during these operations will be recovered and recycled to the deasphalter (2) via line (15). The asphalt is drawn off via line (16).

EXAMPLE

A residue from Safaniya is asphalted by the addition of pentane. The operation is carried out with a solvent / oil volume ratio of approximately 3/1 to 4/1 at 180 ° C. under 4 MPa. Two phases separate. The asphaltic phase is evacuated. The oily phase which contains about 23% by weight of solvent is circulated along aluminum oxide membranes with a pore radius of 4.5 nm (tangential ultrafiltration). The pressure is 40 bars upstream and 32 bars downstream of the membranes, and the temperature of 180 ° C. The circulation speed along the membrane is 3.5 m / s.

The fraction which has not passed through the filters is collected, consisting of deasphalted oil still containing 10% of solvent. This solvent is separated by evaporation in a falling film evaporator and the desired deasphalted oil is thus obtained. The filtrate, formed of solvent and a little oil (less than 5%) is returned to the deasphalting zone; the supply of fresh solvent is reduced accordingly, to maintain the ratio of 3/1 to 4/1 between the solvent and the oil to be deasphalted.

The yield of deasphalted oil is 68%.

The characteristics of the charge and of the oil obtained are given below:

Claims (9)

1) - Process for deasphalting a hydrocarbon oil containing asphaltenes, characterized in that: a) - the oil is treated with at least one hydrocarbon solvent having 3 to 8 carbon atoms, under deasphalting conditions allowing the formation of two phases, a first phase consisting of a mixture of deasphalted oil and solvent and a second phase rich in asphaltenes, and these two phases are separated. b) - circulating the first phase of deasphalted oil and solvent, in the liquid phase, along at least one inorganic ultrafiltration membrane whose pore radius is chosen between 2 and 15 nanometers (20 and 150 Å ) at a temperature of at least 80 ° C., under tangential ultrafiltration conditions, and the ultrafiltrate, enriched in solvent, and a residual unfiltered phase, the retentate, enriched in deasphalted oil and constituting the main product of the process, and c) - the ultrafiltrate is returned to step (a) to constitute therein at least a portion of the hydrocarbon solvent having 3 to 8 carbon atoms. 2) - Method according to claim 1, wherein the pore radius is 4 to 9 nanometers. 3) - A method according to claim 1 or 2, wherein the ultrafiltration treatment of step (b) is continued until the solvent content of the residual unfiltered phase is no more than 1 to 50% of the solvent content of the first phase of deasphalted oil and of solvent collected in step (a) and subjected to ultrafiltration, and said distillation is then carried out resulting residual unfiltered phase to separate at least a portion of the residual solvent. 4) - Method according to one of claims 1 to 3, wherein the ultrafiltration treatment is carried out at a temperature of 2 to 50 ° C lower than the temperature that had the phase deasphalted oil and solvent at the end of the deasphalting operation of step (a). 5) - Method according to one of claims 1 to 4, wherein the pressure and the temperature under which the ultrafiltration is carried out are chosen to maintain the phase of deasphalted oil and solvent in fully liquid phase, at least on the side upstream of the membrane. 6) - Process according to claim 3, in which the ultrafiltration treatment of step (b) is continued until the solvent content of the residual unfiltered phase only represents 2 to 30% of the solvent content of the first phase of deasphalted oil and of solvent. 7) - Method according to one of claims 1 to 6, wherein the temperature of step (b) is 80 to 400 ° C. 8) - Method according to one of claims 1 to 7, wherein the circulation speed along the membrane is 0.5 to 20m / s. 9) - Method according to one of claims 1 to 8, wherein the membrane is made of aluminum oxide.

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