EP0235027A1 - Process of fractionating solid asphalts - Google Patents

Abstract

A process for the fractionation of solid asphalts which can be carried out under conditions of low temperature and pressure is described.

The process consists in treating a suspension of powdered asphalt in an aqueous phase containing a surface-active agent with a water-immiscible hydrocarbon solvent and in separating:
- the hydrocarbon phase which contains an asphalt with a softening point lower than the starting asphalt
- the aqueous phase which contains in suspension an asphalt with a softening point higher than the starting asphalt.

Description

The invention relates to a process for fractionating solid asphalts which can be carried out under low temperature and pressure conditions.

We are witnessing, today, an increasingly important use, in refineries, of products such as residues from atmospheric or vacuum distillation of conventional oils, heavy crude or topped oils, or even shale oils or tar sands.

These various fillers are characterized in that they contain a large amount of asphaltenes and "resins"; However, these products, which contain inter alia heteroatoms such as sulfur and nitrogen as well as complexed metals such as vanadium or nickel, make the conventional operations for refining such feeds extremely difficult.

In the field of catalytic processes, hydrotreatments see their performance decrease rapidly due to the deposition of nickel and vanadium sulphides on the catalysts which leads to their poisoning; in catalytic cracking, the high Conradson carbon content of these charges causes coke deposits on the catalysts, necessitating an increase in the regeneration temperature of the cataly zeolitic sors used; moreover, the presence of too much nickel and vanadium in the charges is detrimental for various reasons (significant formation of gas, modification of the catalysts causing a loss of their activity); in hydrocracking, only fillers containing minute proportions of asphaltenes can be used if one wishes to avoid rapid poisoning of the active sites of the catalysts.

With regard to the thermal visbreaking process, the severity of the operating conditions is linked to the content of asphaltenic products in the fillers; the coagulation of partially cracked asphaltene molecules results in the instability of the effluents, which tend to decant during storage, and to clog the filters.

All these drawbacks have prompted refiners to seek to separate the asphaltenic and resinous compounds from the oily fraction which contains them. This separation is carried out by the so-called solvent deasphalting technique, which consists in breaking the existing balance between the asphaltenes and the maltenic medium by adding to the charge a solvent which reduces the surface tension and the viscosity of the medium.

Most of the time, paraffins or light olefins comprising from 3 to 7 carbon atoms are used for this purpose, used alone or as a mixture. These products play the role of anti-solvents compared to asphaltenes and, where appropriate, to "resins".

For a given charge, the yield of deasphalted oil as well as its quality depend on the nature of the solvent, the volume ratio of the solvent to the charge, the temperature and the pressure at which the deasphalting operation is carried out.

The composition and characteristics of the phase precipitated during of the deasphalting operation, called "asphalt phase" can therefore vary widely. This asphalt phase can be roughly differentiated into two classes of compounds, one called "asphaltenes", defined as all of the products preciptified by an excess of n-heptane, according to AFNOR T60-115, the other called " resins ", defined as all products insoluble in propane but soluble in heptane. It is now well known that asphaltenes contain the majority of the metals (nickel and vanadium) contained in heavy oils.

On the other hand, the economy of the deasphalting process requires that the asphaltic fraction be as small as possible for a given quality of deasphalted oil; it is known that, all other things being equal, the yield of asphalt decreases when the molecular weight of the deasphalting solvent is increased; we are currently witnessing the increasingly frequent use of solvent such as the so-called C₅ cut, which consists essentially of pentane and isopentane. For a given charge, the transition from propane to pentane results in an increase in the yield of deasphalted oil, since this will contain part of the "resins". However, we manage to find a good compromise between the quality and the quantity of deasphalted oil thus obtained.

With regard to the asphalt phase, this evolution towards deasphalting solvents of higher molecular mass results in a reduction in the weight yield, due to the lower content of resins; qualitatively, asphalts precipitated according to this method most generally have softening points (measured according to the Ball and Ring method, AFNOR Standard T66-008) higher than 100-120 ° C, which can reach 180 ° C at 200 ° vs.

Such asphalts are difficult to use. Their softening point is too high to be able to consider in a way their use as road bitumen. In the form of fluxed fuels, they lead, without adaptation of conventional combustion plants, to emit a quantity of unburnt particles incompatible with the legislation in force; moreover their fairly high softening point implies dilution with a large amount of fluxing agent.
In solid form, their softening point, most of the time of the order of 120-160 ° C., is not high enough for easy use as fuel in installations of fluidized bed type. Also, the separation of such asphalts into two fractions, one having a softening temperature lower than that of the starting asphalt, as well as a lower metal content, and the other having a very high softening temperature, such as greater than 250 ° C, has a certain economic interest.

The object of the present invention is to carry out such a separation, by means of a process allowing the separation of solid asphalts in the form of particles in suspension in an aqueous medium in two fractions, by addition of a solvent immiscible with water, so as to obtain a first fraction of asphalts in solution in the solvent used and a second fraction of asphalts in suspension in the aqueous medium, having a viscosity such that this suspension is easily transportable and pumpable.

There are, in the prior art, a large number of documents describing the separation of heavy oils into three fractions: asphaltenes, "resins" and deasphalted oil, thanks to the action of at least one deasphalting solvent, these separations taking place in several successive stages.

The technique used is described, inter alia, in US patent 2,940,920, which uses only a deasphalting solvent; in summary, it consists in subjecting, in a first step, the charge to the action of an excess of light paraffinic or olefinic solvent, under conditions such that a lower asphaltic phase and an upper oily phase can be separated by decantation in this step. In a second step, the oily phase resulting from the first step is brought to a higher temperature and pressure, which causes the separation between a lower phase consisting of resins and an upper phase comprising the deasphalting solvent and the residual oil. ; the separation between these two constituents is carried out in a third step, under supercritical conditions which allow the separation of the solvent and the deasphalted oil.

This process, generally known as the "Pink Process", has been the subject of numerous patents describing different operating conditions, or the use of several solvents, as specified for example by US Patents 3,830 732 or US 4,125,459; many publications have also described this technique, such as one of the most recent, by S.R. NELSON and R.G. ROODMAN, in CHEMICAL ENGINEERING PROGRESS, May 1985, p.63.

This process has two major drawbacks; on the one hand, it involves, from the economic point of view, significant investment costs since the separation of the charges into their three main constituents is carried out under conditions of high temperature and pressure; on the other hand, it is hardly possible to envisage obtaining by this route asphalts having a softening temperature greater than about 200 ° C., the viscosity of these products being such that they cannot be pumped, even heated to temperatures of the order of 300 ° C.

• a) on suspend de l'asphalte solide en poudre dans une phase aqueuse renfermant au moins un agent tensio-actif,
• b) on traite la suspension d'asphalte obtenue dans l'étape (a) par un solvant hydrocarboné non-miscible à l'eau,
• c) on sépare la phase hydrocarbonée résultante de la suspension aqueuse, cette dernière renfermant en suspension un asphalte à point de ramollissement plus élevé que celui de l'asphalte de départ, et
• d) on fractionne la phase hydrocarbonée pour recueillir séparément le solvant hydocarboné et un asphalte ayant un point de ramollissement inférieur à celui de l'asphalte de départ.

The process of the present invention is characterized by the following steps:

• a) solid powdered asphalt is suspended in an aqueous phase containing at least one surfactant,
• b) the asphalt suspension obtained in step (a) is treated with a water-immiscible hydrocarbon solvent,
• c) the resulting hydrocarbon phase is separated from the aqueous suspension, the latter containing in suspension an asphalt with a softening point higher than that of the starting asphalt, and
• d) the hydrocarbon phase is fractionated to separately collect the hydrocarbon solvent and an asphalt having a softening point lower than that of the starting asphalt.

Any aqueous phase in which the asphalt is insoluble may be suitable. It could therefore be water, or water containing compounds in solution which do not appreciably modify the insolubility of it to asphalts. It will thus be possible to modify the density of the aqueous medium if necessary.

The aqueous suspension obtained in step (c) is made up of a suspension of "hard asphalt" particles with a high softening point, easily pumpable and transportable.

It is possible, if desired, to separate the hard asphalt particles from the water by known means, as indicated below. The asphalts which can be used in the context of the invention are solid asphalts which can be obtained in the form of fine particles, of dimensions between 1 and 300 μm, and preferably between 3 and 150 μm. These asphalts are in particular those obtained by deasphalting operation of heavy oil or of residue with a solvent having from 3 to 7 carbon atoms, and having a softening point higher than approximately 100 ° C.

The process of the invention can be carried out in batch operations but it can also be implemented in the form of a continuous process; it can implement the following characteristics: The suspension of the asphalt particles and in the aqueous solution containing the surfactant is carried out, according to known techniques, in a suitable mixer.

This operation is advantageously carried out in a temperature range between room temperature and the softening temperature of the asphalt, generally between 15 and 70 ° C. The weight ratio of the aqueous solution to the asphalt can vary from 27/75 to 75/25, and is preferably between 30/70 and 60/40. The duration of the suspension is generally between 10 s and 30 min, depending on the technique used. The suspension obtained is stable and can be stored without risk of sedimentation, which allows operations in discontinuous operation; moreover, this suspension is easily transportable or pumpable, its kinematic viscosity is generally between 200 and 5000 mm² / s.

The surfactant used to prepare the suspension can be anionic, cationic, nonionic or zwitterionic in nature. These agents are well known to those skilled in the art and the invention is not limited to the use of a particular category of these agents. Examples of non-ionic agents are the products obtained by reaction of ethylene oxide with, for example, an alcohol, an alkylphenol, an ester, an amide or an alkyl sulphate.

Examples of anionic agents are sulfonates such as alkyl arylsulfonates, alkyl sulfates and alkylcarboxylates of sodium, potassium or ammonium. Examples of cationic agents are the quaternary ammonium salts derived from tertiary akylamines with a long hydrocarbon chain. As an example of zwitterionic surfactants, mention may be made of alkylcarboxy-betaines or alkylsulfamidobetaines.

These surfactants can be used alone or as a mixture, within the limit of their compatibility; thickeners or stabilizers can be added to it, or any other product allowing stable suspensions to be obtained.

The concentration by weight of surfactant in the aqueous solution of this agent is, for example, between 0.03% and 5% and preferably between 0.1 and 1%.

The treatment of the aqueous asphalt suspension with a water-immiscible hydrocarbon solvent constitutes the second step of the process of the invention; its purpose is to selectively extract, using the solvent, a part of the asphalts, which is mainly constituted by the "resins" present in these asphalts. This operation therefore requires intimate contact between the solvent and the asphalt in suspension; one can use any device capable of making such a contact, such as for example, reactors provided with agitation systems such as propellers or turbines.

The solvents which can be used in the context of the invention are water-immiscible hydrocarbon solvents in which the "asphalts" are insoluble and which are solvents for the "resins". Examples of solvents which can preferably be used are paraffinic, olefinic or cyclanic hydrocarbons comprising from 5 to 8 carbon atoms, which can be used alone or as a mixture. For economic reasons, use is more specifically of hydrocarbon cuts such as the so-called "C₇" cut or "light gasoline".

Solvents are preferred whose average molecular weight is at least equal to that of the solvent which had been used during the deasphalting operation of an asphaltic oil which led to the asphalt used here as a starting product.

The weight ratio of the solvent to the asphalt in suspension can vary for example from a ratio of 5/1 to 12/1, and preferably between 6/1 and 9/1.

This extraction operation is carried out at a temperature between room temperature and the softening temperature of the asphalt; depending on the nature of the solvent used and the softening point of the treated asphalt, it can be carried out at atmospheric pressure or under pressure; it is preferably carried out at a temperature between room temperature and the boiling point of the solvent.

This solvent extraction step of the asphalt suspension can be carried out continuously or discontinuously. It can be carried out either in the same device or in a series of devices, in one or more successive operations. One can, for example, use a series of mixer-settlers operating against the current, so as to gradually extract the heavy phase, containing the asphalts in suspension, by the extraction solvent. The operation can also be carried out in the same device, by carrying out a first extraction with part of the solvent, awaiting the separation of the phases, separating the solvent phase and treating the aqueous phase containing the asphalt in suspension with a second part of the solvent. , etc. The steps of extracting the asphalt suspension with the solvent and decanting into two phases, the organic phase containing the extracted asphalt and the aqueous phase consisting of a suspension of non-extracted asphalt particles, can therefore be carried out in the same device or in different devices.

The duration of the extraction stage is variable; it depends on the nature of the filler, the solvent used and the operating conditions; it is generally between 15 and 60 min.

The step of separation into two phases can be carried out, continuously, in an apparatus of the decanter or centrifuge type; the settling time (or residence time in the decanter) is generally between 0.5 and 3 h.
The process makes it possible to separate two phases by decantation: 1) - the upper phase consists of a solution of the asphalts extracted - mainly "resins" - in the extraction solvent; the dry matter concentration by weight of this solution depends on the nature of the asphalt treated, the nature of the solvent used and its quantity as well as the operating conditions; it is, most of the time, between 3 and 12%. The removal of the solvent from this solution can be carried out by any suitable means, and a large number of devices known in the art allowing this operation; there may be mentioned, for example, "flash" evaporators or thin-film evaporators. The solvent thus removed can be reused in the extraction step (b) of the process.

The dry residue obtained consists of the part of the initial asphalt which has been extracted with the solvent; its yield and composition can therefore vary widely. However, it is mainly constituted by the "resins" fraction of the initial asphalt, and also contains a certain proportion of the "oil" fraction.

Its characteristics, compared to the original asphalt, are:
- a significantly lower softening temperature; this lowering of the softening temperature can reach or even exceed 100 ° C.
- a reduction in the content of metals (Ni and V) and sulfur.
- an increase in the atomic ratio H / C.
- A significant decrease in the level of Chalt asphaltenes, this rate generally being less than 10%.

Depending on their characteristics, the asphalt fractions thus obtained by evaporation of the solvent from the organic phase can be used in various ways; they can, for example, be used for the formation of road or industrial bitumens; after dilution with a suitable solvent, they can be used as fuel com COMBUSTIBLE ^No. 2, or ordinary, or high viscosity; they can also be used as charges for heat treatment units such as visbreaking or hydroviscoreduction, or catalytic hydrotreatments such as, for example, hydrodesulfurization; they can also be used as starting material for the preparation of mesophases making it possible to obtain carbon-carbon composite materials, these examples of use being in no way limiting.

2) - The lower phase obtained by decantation consists mainly of a suspension of asphalt particles in the aqueous solution containing the surfactant. It generally comprises a small part of the solvent used for the extraction; this can be evaporated and recycled to the extraction stage. The kinematic viscosity of this suspension is, at ambient temperature, generally between 150 and 4000 mm2 / s; such a suspension, which moreover has thixotropic properties, is easily pumpable and transportable, which represents a main characteristic of the invention. The weight ratio of the aqueous solution to the asphalt is, in this suspension, generally between 30/70 and 80/20, and most often between 35/65 and 65/35.

This asphalt fraction corresponds to the starting asphalt fraction not extracted by the solvent during the process; it is therefore enriched in "asphaltenes" and depleted in "resin" and "oil" fractions and presents, with respect to the initial asphalt, the following variations in characteristics:
- significant increase in the softening temperature measured using the "ball-ring" method, this increase possibly reaching or exceeding 100 ° C.
- increased sulfur and metal content,
- sharp increase in the content of Chalt asphaltenes.

All of these characteristics lead to reserving the use of these "hard asphalts" very rich in asphaltenes for certain uses as fuels. They can be obtained in solid form from the aqueous suspension, by any suitable separation means, a particularly advantageous method consisting in causing the suspension to break. In solid form, they can be advantageously used as fuels in fluidized bed combustion systems, thanks to their very high softening temperature. They can also be used in the form of an aqueous suspension, analogous to "coal-water" fuel oil; the content of combustible dry matter in the suspensions obtained can be easily increased by adding solid particles of various origins such as carbon or biomass, the presence of surfactant in the suspension facilitating this operation.

The attached figure illustrates an embodiment of the process of the invention in continuous operation, in which the asphalt, in the form of a suspension in aqueous solution, is subjected to two successive extractions.

The aqueous surfactant solution is introduced via line (1) into the mixer (3) provided with the stirring system (4); the asphalt, in the form of fine particles, is introduced into the mixer (3) through the line (2). The suspension of the asphalt particles, obtained by agitation, passes through the line (5) in the first extractor (6) provided with the agitation system (8). This extractor is supplied by the line (7) with solvent coming from the decanter (19) and which therefore contains the fraction of "resins" dissolved during the second extraction.

The first extraction is carried out by mixing the phases, then all of the phases are removed from the extractor (6) by the line (9) to the first decanter (10): from this decanter two phases are separated:

- The upper phase consists mainly of "resins" in solution in the extraction solvent; it is sent, by line (11), to the solvent evaporator (12). The "resins" are removed from this evaporator, by line (13), and, by line (14), the extraction solvent which is recycled (after cooling not shown in the figure) to the second extractor (15 ).

- The lower phase, containing mainly in aqueous suspension the asphalt particles having undergone a first extraction, is withdrawn from the decanter (10) by the line (17) and is conveyed to the second extractor (15).

The second extraction is carried out by stirring, using the system (16), in the extractor (15), which receives, in addition to the pre-extracted asphalt suspension, all of the fresh solvent recycled by the line (24). After extraction, all the phases pass through the line (18) in the second decanter (19) from which, after decantation, two phases are removed:

- The upper phase consists of a solution, with a low concentration of "resins" in the extraction solvent; it is recycled through the line (7) to the first extractor (6).

- The lower phase essentially contains, in aqueous suspension, asphalt particles having undergone two extractions, as well as a small amount of extraction solvent. It is transported from the decanter (19) by the line (20) to the solvent evaporation system (21), from which the "hard asphalts" or "brais" are removed by the line (22) in aqueous suspension. From the top of the evaporation system (21), a small fraction of solvent is collected by the line (23), which joins most of the solvent in the line (14), all of the solvent recovered being recycled by the line. (24) to the second extractor (15). An addition of solvent making it possible to compensate for small losses of solvent can be carried out by line (25).

Instead of the mixer-settlers described above, a multi-stage extractor can be used, for example of the rotary disc type.

The examples which follow are intended to illustrate the invention; they describe a discontinuous mode of asphalt fractionation.

EXAMPLE 1

The asphalt which represents the load to be fractionated comes from a pentane deasphalting unit from a vacuum residue of Safaniya crude oil. This asphalt, the main characteristics of which are given in Table I, was ground into fine particles using an impact crusher. The dimensions of the particles obtained vary from 3 to 130 μm, and 50% by weight of these particles have a diameter of between 20 and 60 μm.

In a 200 l reactor fitted with a propeller agitator, the following are successively introduced:
- 25 kg of an aqueous solution containing 0.5% by weight (125 g) of tall oil (anionic surfactant, commercial, from the manufacture of paper pulp) and 0.125% by weight of soda (31 , 25 g)
- 25 kg of asphalt particles.

After 30 min of stirring at 60 ° C., a homogeneous suspension of asphalt particles is obtained, the kinematic viscosity of which is 300 mm² / s. (CSt)

130 l of heptane are introduced into the reactor, and while maintaining the temperature at 60 ° C., it is vigorously stirred for 30 min, then it is left to stand for 3 h, and the upper phase formed is removed from a volume of 120 l.

A second extraction is then carried out by adding 120 l of heptane to the asphalt suspension remaining in the reactor, operating in the same way as for the first extraction.

After decantation, the aqueous asphalt suspension is withdrawn separately from the bottom of the reactor, then the heptane supernatant phase which is joined to the hydrocarbon phase obtained during the first extraction.

The hydrocarbon phase (240 l) is brought to 180 ° C in a thin layer evaporator; 225 l of heptane and 11 kg of "resins" are collected, the main characteristics of which are given in table I.

From the lower phase, 20 l of heptane are removed by distillation; the remaining aqueous suspension (39 kg) has a kinematic viscosity of 220 mm² / s (cSt). After filtration and drying at 150 ° C., 14 kg of "hard asphalt" are obtained, the characteristics of which are given in Table I.

EXAMPLES 2 to 4

By operating as in Example 1, but using other surfactants, in the same weight proportion as in Example 1,
- In Example 2, a commercial cationic surfactant is used, of fatty aliphatic monoamine type, in an acid medium
- In Example 3, a commercial surfactant of anionic type is used, from the class of alkyl aryl sulfonates
the surfactant used in Example 4 is of the nonionic type; it is a polyoxyethylated alkyl phenol.

The same results were obtained. Anionics are preferred, however, because of the greater ease of breaking the aqueous suspension by addition of an acid.

Claims (8)

1 - Process for fractionating solid asphalt containing resins, comprising the following steps: a) a suspension of solid asphalt particles containing resins is formed in an aqueous phase containing at least one surfactant. b) the solid asphalt suspension obtained in step (a) is treated with a water-immiscible hydrocarbon solvent, in which the resins are soluble and the asphalts insoluble, c) the resulting hydrocarbon phase is separated from the aqueous suspension, the latter containing in suspension an asphalt with a higher softening point and a lower resin content than the starting asphalt, and d) the hydrocarbon phase is fractionated to separately collect the hydrocarbon solvent and a resin having a softening point lower than that of the starting asphalt. 2 - Process according to claim 1, in which the size of the particles of solid asphalt is from 1 to 300 micrometers. 3 - Process according to claim 1 or 2, wherein the weight ratio of the aqueous phase to the asphalt in step (a) is from 25/75 to 75/25. 4 - Method according to any one of claims 1 to 3, wherein the weight concentration of surfactant in the aqueous phase of step (a) is 0.03 to 5%. 5 - Process according to any one of claims 1 to 4, wherein the hydrocarbon solvent of step (b) has an average molecular weight at least equal to the average molecular weight of the solvent which had been used during the operation of deasphalting of an asphalt oil having led to the asphalt of step (a). 6 - Process according to any one of claims 1 to 5, wherein the weight ratio of the solvent to the asphalt, in step (b), is from 5/1 to 12/1. 7 - Process according to any one of claims 1 to 6, in which the aqueous asphalt suspension obtained in step (c) is again treated, in a step (e), with a hydrocarbon solvent immiscible with water, and in which the resins are soluble and the asphalts insoluble, and the resulting hydrocarbon phase is separated from the aqueous suspension, said hydrocarbon phase, resulting from step (e), being sent to step ( b) to constitute therein at least part of the hydrocarbon solvent. 8 - Process according to any one of claims 1 to 7, in which the hydrocarbon solvent of step (b) is chosen from paraffinic, olefinic and cyclanic hydrocarbons having from 5 to 8 carbon atoms.

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