CA2694853A1 - Solvent extraction process to stabilize, desulphurize and dry wide range diesels - Google Patents

Abstract

A process allowing the removal of contaminants from an unstable oil produced by thermal or catalytic cracking, wherein, in at least one step of the process, mixing of the unstable oil with an impure solvent having a dipole moment greater than 2 is performed.

Description

SOLVENT EXTRACTION PROCESS TO STABILIZE, DESULFURIZE AND DRY
CRACKED WIDE RANGE DIESELS

FIELD OF THE INVENTION

The invention relates to an extraction process using a polarized solvent having a dipole moment greater than 2, to stabilize wide range diesels, produced by the thermal or catalytic cracking of used oils, heavy oils, vacuum gasoils or bunkers. The new process markedly improves colour, odour and storage stability of thermally cracked gasoils so they can meet market specifications. The extraction process also removes water and sulphur from the wide range diesels, and reduces their total acid numbers.

BACKGROUND OF THE INVENTION

Gasoils or diesels produced from thermal or catalytic cracking processes are known to be unstable. While in storage, they form gums and polymers that can plug burner tips in furnaces or filters in engines. Further, new environmental constraints demand that these fuels reduce their sulphur, nitrogen, water and chlorides contents. Hydrotreating is commonly used in refineries to stabilize gasoils and to remove some of their contaminants.
However, hydrotreating processes require high pressures and temperatures and the reactors must either be made of, or clad with, high alloy steels to resist hydrogen permeation in the metal walls.
There must also be a hydrogen plant or pipeline close by. Because of the high costs of such units, they are only viable as part of refineries or large plants. Also, the hydrotreated oils must be dried to meet water content and appearance specifications.

Used lubricating oils are classified as hazardous products in many countries, mostly because of the additives that they contain. Of all the by-products from the oil industry, used oils pose the greatest danger to the fresh water supply. The EPA states that: "One gallon of used oil can pollute one million gallons of water". Among the processes to treat used oils for their reuse as fuel, thermal cracking is a viable option for smaller facilities. More precisely, the additives in t the used oil must be destroyed and removed. The main product is a wide range diesel or heating fuel. It tends to darken as soon as it comes into contact with air: it is unstable. Also, the wide range diesel has a high sulphur content, 3 or 4 times the 0.1% wt sulphur specification for heating oils in Europe, and has a bad odour.

Processes to stabilize and/or de-sulphurize diesel fuels produced by cracking heavier oils are well known. In refineries, hydrocracking and hydrotreating processes use hydrogen in catalytic reactors at high temperatures and pressures to achieve clear, stable diesel fuels with good burning characteristics and with sulphur contents as low as 15 ppm that meet ultra-low sulphur specifications. These processes not only require large, heavy reactors made of metals that resist hydrogen penetration, and corrosion, but also require hydrogen production plants or pipelines near-by. They are not suited for small or isolated refineries or used oil applications.

In used oil applications, the UOP Hylube process, US Patent 5,904,838, uses hydrogen at high temperatures and pressures to recycle the feed oil into lubricating oils.
Others hydrotreat only the lube oil products, obtained by successive distillations of used oils.

Ikura et al. CA 2,245,025 mentions that gasoil produced by thermal cracking of used oils can be stabilized using methanol extraction.

There are also processes to remove sulphur and/or water from naphtha and other light oils but these are not applicable to diesel fuels. In the solutizer process, CA 456448 and CA 456599, Bell et Al. mention that mercaptans and other weak acids contained in sour hydrocarbon distillates, and more particularly in gasoline distillates, would be extracted with solutizer solution, i.e. aqueous solutions of alkali metal hydroxides containing solutizers.

Hassan et Al. (journal of Applied Sciences Research, 5(5); pp. 515-521, 2009, mentions that sulphur could be removed from straight run diesel fuel with a mixture of NMP
(normal methyl pyridine), ethylene glycol, DMF (dimethyl formamide) and furfural.
Toteva, Topalova, and Manolova (Journal of the University of Chemical Technology and Metallurgy, 42, I, 2007, pp.17-20) mention that two-stage extraction of diesel fuel with DMF could reduce the aromatics and sulphur (from 2%wt to 0.33%wt) in a non-hydrotreated diesel fuel. This is not enough to meet heating fuel specifications for sulphur of less than 0.1%wt.

Sherman et Al. (US 6,320,090) mentions that DMF could be used as a solvent to remove mostly poly aromatic hydrocarbons (PAH) as well as sulphur and nitrogen compounds from used oils that have been subjected to successive vacuum distillations.

Others have tried solvent extraction processes to remove sulphur compounds from fuel oils.

Funakoshi et Al. (US 5,753,102) use a mixture of acetone, water and iodine as the preferred solvent to remove sulphur from various straight run oils. They also tested more polarized solvents including DMF, acetonitrile, trimethyl phosphate, nitromethane, methanol, hexamethyl phosphoramide, acetic acid, pyridine, and N-methylperolidinone with less success.

Horii et Al. (US 5,494,572) complete the sulphur removal from an oil that has been hydrotreated using an organic solvent containing nitrogen, specifically pyridinium salts, with another solvent containing hydroxyl groups, specifically one or more of water, methanol, ethanol, propanol, butanol, ethylene glycol, and glycerol. Hydrotreating is the more costly process. In the process described by Taylor et Al. (US 5,059,303) oils produced via cracking processes, ranging from cracked naphtha, gasoil and vacuum residue, are contacted with an extraction solvent to reduce their sulphur and nitrogen content prior to hydrotreating. The solvents used are polarized and in an aqueous solution. They include N-methyl pyrrolidone, furfural, DMF, and phenol.

Googin et Al. (US 4,405,448) mention a polar solvent, specifically DMF and water, intended to remove polychlorinated biphenyls (PCB) from transformer oil. A second extraction using a non-polar solvent, chosen from normal pentane to normal octane, is intended to remove the PCB from the polar solvent.

For the past ten years, several oil desulfurization processes use an oxidizing agent and a catalyst to oxidize mercaptans and thiols in the oil. In a second step, polarized solvents are used to extract the sulphur oxides from the oil. Gore (US 6,274,785) uses dimethylsulfoxide as the extraction solvent. Kittrel et Al. (Canada 1,287,007) suggests using solvents having a dipole moment greater than 2, mixed with water, to extract the sulphur and nitrogen oxides from the oil. Reid (US 5,154,817) mentions that cracked oils can be stabilized with additive injection.
However, additives do not remove mercaptans and thiols from the oil.

The complete solvent regeneration is difficult because the solvents and the oils to treat have similar boiling points and gravities. Solvent losses render these processes impractical.

There was therefore a need for a process able to stabilize, desulphurize, neutralize and dry wide range diesel, which process being free of at least one of the drawbacks of the prior processes.

There was therefore a need for a process able to stabilize, desulphurize, neutralize and dry the wide range diesel oil to meet the heating oil specifications, which process being free of at least one of drawbacks of the prior art processes.

There was also a need for a process able to stabilize, desulphurize, neutralize and dry the heating oil to meet the heating oil specifications.

There was a further need for a process that would also be effective in reducing the sulphur in diesel cuts produced by catalytic or thermal cracking of heavy oils in refineries.

There was particularly a need for a low cost process to stabilize and remove contaminants from wide range diesels or gasoils that can be used in smaller plants, such as used oil cracking units.

BRIEF DESCRIPRION OF THE FIGURES

Figure 1 is : a simplified flow sheet that illustrate an embodiment of a process according to the invention.

Figure II is : is a block diagram illustrating the steps performed, and the streams produced while operating in the preferred embodiment described herein.

Figures III is: a distillation curve of raw and treated gasoil, along with the distillation curves of pure and recycled solvent; of the wide range diesel obtained by the process according to the invention, as further specified in example 3 thereafter.

Figures IV is : another distillation curve of raw and treated gasoil, along with the distillation curves of pure and recycled solvent; of'the wide range diesel obtained by a process according to the invention, as further specified in example 4 thereafter.

GENERAL DEFINITION OF THE INVENTION

Preliminary definitions:

Unstable oils: any oil which colour deteriorates when exposed to heat or/and oxygen and/or other oils ; the processes of the invention are suited for stabilizing any of such unstable oils in the broader sense.

Impurities: one or more chemical compounds that may be unwanted in a mixture but that may finally assist the extraction process.

Residues: contaminant and by-products obtained by reaction and/or extraction, that are unwanted and are to be eliminated.

GOn: gasoil (wide range diesels) in different steps of the process of the invention, n is a numerical index, an integral number, each of these integer corresponding to a chronological steps of the process and represent changes in composition.

The object of the present invention is the processes allowing to remove contaminants from a unstable oil produced by thermal or catalytic cracking. These processes comprise at least one step of mixing said unstable oil with an impure solvent having a dipole moment greater than 2.

According to a preferred embodiment the processes may comprise at least one step of contacting a stream of the said unstable oil with a solvent having a dipole moment greater than 2 and, thus, obtaining two mixtures, the first mixture being of an oil-solvent type and containing impurities, and the second mixture being of a solvent-oil type and containing impurities and residues.

The impurities in the solvent-oil mixture being identical or different of the impurities present in the oil-solvent mixture.

Advantageously, at least a fraction of the said solvent having a dipole moment greater than 2, that is present in at least one of the said two mixtures, is extracted from the mixture (s) and is at least partially regenerated before being recycled in a process of the invention.

According to a preferred embodiment of the invention, the processes comprise the following steps of:

a. intimately contacting a stream of the said contaminated oil with a solvent having a dipole moment greater than 2 and, thus, obtaining two mixtures, the first mixture being of an oil-solvent type and containing impurities, and the second mixture being of a solvent-oil type and containing residues and impurities, the impurities in the solvent-oil mixture being identical or different of the impurities in the oil-solvent mixture;

b. separating the treated oil, present in the oil-solvent mixture obtained in step a), from the solvent, leaving most (preferably at least 80% weight, more preferably at least 90%
weight) of the impurities in the solvent phase;

c. separating the solvent and the oil, present in the solvent-oil mixture obtained in step a), from the residues;

d. optionally, separating the solvent and the light oil present in the oil-solvent mixture obtained in step b), and e. optionally, separating the solvent and the oil obtained in step c);

f. recycling at least one of the solvents obtained in steps b), c), d) or e), wherein each of said solvent is preferably regenerated for at least 50 %weight but for less or equal to 99 % weight before recycling, preferably by known means such as distillation, vacuum distillation, azeotropic distillation, centrifugation, and more preferably vacuum distillation and/or centrifugation.

The processes of the invention are particularly suited for treating unstable oils having a temperature range that, as measured by the ASTM method D86, ranges from 125 C
to 500 C, and preferably ranges from 175 C to 450 C.

The boiling range of the treated oil in step a) is, as measured by the method ASTM D86, preferably between 125 C to 500 C, and is more preferably between 175 C and 450 C.

The processes of the invention are particularly suited for treating: unstable oils such as contaminated oils produced by cracking used oil, heavy oils, bitumens, vacuum gasoils, vacuum residues, tars, synthetic crude oils, bunkers and as well for treating mixtures of at least two of the these oils.

The solvent used is advantageously selected among N-methyl pyrrolidone, furfural, dimethyl formamide, phenol, pyridine, dimethyl acetamide, dimethyl sulfoxide and propylene carbonate, and among mixtures of at least 2 of these.

According to another preferred embodiment of the processes of the invention, the regenerated solvent, obtained in step f), stills contains some impurities and/or reaction products.

Usual contaminants include among others: water, sulphur compounds such as mercaptans and thiols, chlorides, organic and inorganic acids, free radicals, resins, gums, sediments, reaction products and mixtures of at least two of the latter.

Advantageously, the solvent concentration in the regenerated solvent stream obtained, in step f), is between 50% wt. and 99% wt., preferably between 70% wt. and 90% wt., more preferably about 83% wt.

In a preferred embodiment, the regenerated solvent is produced, in step f), by vacuum distillation, and the distillation is preferably performed at pressures ranging from 0.5 psis to 12 psia, preferably from 0.5 psia to 4 psia, more preferably at pressures about 1.5 psia.

In another preferred embodiment for some specific applications , the regenerated solvent is produced, in step f), by an azeotropic distillation using water as the third component.

In an another preferred embodiment for some specific applications, the regenerated solvent is produced, in step d) and/or f), by centrifugation.

Advantageously, the regenerated solvent is produced, in steps b), c), d), and f), by distillation conducted at temperatures ranging from 50 C to 350 C, preferably ranging from 100 C to 150 C, and more preferably at a temperature about 130 C.

Usually, the impurities, present in the regenerated and/or recycled solvent, have a boiling temperature ranging from 120 C to 200 C, preferably ranging from 130 C to 175 C.

Surprisingly, the impurities, present in the regenerated and/or recycled solvent, have catalytic and/or solution enhancing and/or bridging properties.

According to another preferred embodiment, in step a) of the processes of the invention, solvent extraction (contacting operation) is carried out at temperatures ranging from 8 C to 100 C, preferably ranging from 10 C to 40 C, and more preferably at a temperature of about 25 C.

The processes of the invention are particularly efficient when the solvent extraction in step b) is carried out as soon as possible, preferably after less than 1 day, more preferably after less than 5 minutes after the cracked oil is produced.

Advantageously, the solvent to oil volume ratio is between 5/1 and 1/5, preferably between 2/1 and 1/2; more preferably about 1/1 when step a) of the processes is performed in a continuously stirred extraction column.

Step b) of the processes is preferably performed by using at least one of the following techniques: in a thin film evaporator, in a wiped film evaporator, azeotropic distillation and/or in a centrifuge.

Step c) of the processes is advantageously performed in a thin film evaporator, in a wiped film evaporator or in a centrifuge.

Step d) of the process is preferably performed by phase accumulation, or in a wiped film evaporator or in a centrifuge or by combination of at least two of the technologies.

Instead of being started with impure solvents having a dipole moment greater than 2, the processes of the invention may be started with a pure or nearly pure solvent having a dipole moment greater than 2. The unstable oil is thus advantageously a wide range diesel, the initial solvent is a nearly pure solvent having a dipole moment greater than 2.

Advantageously, the stable operation can, by maintaining the operating conditions unchanged, be reached in between 10 and 120 minutes, more preferably in about 45 minutes.

In a preferred embodiment, the unstable oil is a thermally cracked oil or is a thermally cracked used oil, and the initial solvent having a dipole moment greater than 2, is DMF.

The initial temperature in step a) of these processes of the invention ranges from 15 C to 100 C, most preferably 25 C, and the initial temperatures in steps b), c) and d) are between 100 C and 150 C. Advantageously, the initial pressures in steps b), c) and d) are thus between 0.5 psia (a) and atmospheric pressure.

It is preferred to determined the operating temperatures by the vacuum obtained, but to keep them below the thermal decomposition temperature of the solvent and/or the cracking or polymerization initiation temperatures of the oil.

At the equilibrium of these processes, the temperature in step a) is usually between 15 C and 100 C, and most preferably about 25 C. The solvent content in the recycled solvent stream is thus usually between 50% weight and 99% weight, and most preferably about 83%
weight.

Advantageously, the temperatures in steps b), c) and d) are thus between 10 C
and 150 C
and/or the pressures in steps b), c) and d) are between 0.5 psia (a) and the atmospheric pressure.
DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION

Pure DMF or recycled DMF is introduced at the top of a continuously stirred contactor (1), while the cracked oil to be treated is introduced at the bottom of the column.
A decanter at the top of the column (7) separates the raffinate (16) from the DMF. The decanter at the bottom of the column (8) separates the extract (17) from the oil to be treated. The column has up to 30 compartments (2), separated from each other by a disc with a hole in the middle (5). A stirrer shaft (3) equipped with paddles (4) ensures good mixing of the solvent with the oil at each level. The stirrer motor (6) is mounted at the top of the top decanter (7). It can achieve 150 rpm.
The oil level in the contacting column is held with a level controller or simply with a column of liquid (9) using the principle of communicating of vases. A jacket surrounding the extraction column (13) maintains a constant temperature in the column with steam or cooling water as required.

The raffinate (16) is routed to a vacuum distillation column (10). The solvent and some light diesel exit through the top of the column (18). They are cooled and condensed in a condenser (11), and allowed to separate in an accumulator (12). The treated diesel (19) exits from the bottom of the column, cooled, mixed with the oil recovered from the solvent (23) and the light oil phase from the accumulator (20) and sent to storage.

Another method to recover the solvent in the raffinate is to centrifuge the raffinate. However, the separation between the solvent and the oil is not as good as in the vacuum distillation diesel recovery method. The solvent losses increase.

The extract, drawn from the bottom of the lower decanter (17), is routed to another vacuum distillation column (14) to recover the solvent and oil, exiting from the top of the column (22), from the residue, exiting from the bottom of the column. The solvent (24) is recycled to the extraction column, along with the solvent (21) from the oil recovery column.
The oil (23) is routed to storage, along with streams (19) and (20). The portion of the recycled solvent boiling between 150 C and 250 C contains the solutizing components.

EXAMPLES

The invention will now be further illustrated by mean of the following non limiting examples 1 to 4. All four examples were performed using the purification unit illustrated in. Figure 1 and the reactive solvent extraction according to block diagram in Figure 2. Except for Example 1, wherein the methanol was introduced at the bottom of the extraction column and the unstable oil at the top of the extraction column.

Recycled DMF from the process, or from another source, along with make-up DMF, is measured and introduced at the top of a continuously stirred extraction column (a), 6 cm in diameter and 250 cm high. Wide range diesel produced from used oil in a thermal cracker is measured and introduced at the bottom of the same column. The column's 111 cm stirred section is divided into three parts, each part containing 10 cells. The cells are divided from one another by a horizontal, doughnut shape, baffle. The stirrer's shaft, in the middle of the column, is equipped with 2 paddles per cell. The variable speed stirrer can turn at between 50 rpm and 150 rpm. The envelope around the contactor maintains stable temperatures in the contactor with circulating water or steam. The contactor operates at atmospheric pressure and 25 C. The stirrer turns at around 100 rpm. The decanter at the top of the contactor column separates the raffinate from the solvent and the decanter at the bottom of the column separates the extract from the feed diesel. The level in the contactor is maintained with a container, attached by a tube to the contactor, and placed at variable heights. The extract and raffinate are weighted and sent off plot for solvent recovery by vacuum distillation or centrifuging at 10,000 rpm of both the extract and the raffinate.

Example 1 - Use of methanol in the process Table I, Experiment 1, illustrates the best results obtained using methanol as solvent. For this experiment, the column was heated to 50 C (122 F).

Although the oil is stabilized, its sulphur content is unchanged by the extraction process, and its flash point is reduced below the 55 C (131 F) specified for heating oil in Europe.

EXPERIMENT No 1: Solvent at 99.9% wt Methanol, Feed diesel/solvent ratio = 3/2 Method Units Feed Diesel Product Diesel Density ISO 3675 K /l 0.85 0.84 Sulphur ISO 8754 % m/m 0.366 0.366 Water ISO 10336 mg/kg 0.13 0.02 Total Acid Number mg KOH/g 4.23 0.8 Flash Point ASTM D92 C 69 26 Micro Carbon Residue ISO 10370 % m/m 0.6 0.3 Cetane Index EPCN 322 53.9 59.1 Colour after 1 day exposed to air ASTM D1500 8 3 Colour after 5 months exposed to air ASTM D1500 7 4 Table I

Example 2: Use of DMF - pure (99.9 %) Table II illustrates the results of three experiments using the polarized solvent: dimethyl formamide (DMF). In all experiments, the oil is stabilized and keeps its light yellow colour for at least 6 months. The flash point is unchanged in the extraction process. The net heating value is also unchanged. The sulphur content is reduced in all three tests. There is a 63% reduction in sulphur content when pure solvent is used.

When a solvent that is not completely regenerated is used, the sulphur removal is improved to meet the new European sulphur specifications for heating oil of less than 0.1%wt.

The water content of the oil is also reduced to below the 250 ppm specification.
EXPERIMENT No 2: Solvent at 99.9% wt DMF, Feed diesel/solvent ratio = 1/1 Method Units Feed Diesel Product Diesel Density ISO 3675 K /l 0.844 0.828 Sulphur ISO 8754 % m/m 0.322 0.119 Water ISO 10336 mg/kg 0.077 0.009 Total Acid Number m KOH/g 4.37 1.13 lash Point ASTM D92 C 69 66 Micro Carbon Residue ISO 10370 % m/m 0.53 0.047 Cetane Index EPCN 322 54.8 60.7 ASTM
Colour after 1 day exposed to air 1500 6 1 ASTM
Colour after 5 months exposed to air 1500 7 1.5 Table II

Example 3: DMF impure - Pure at 83,4 %
The same experiment as in example 1 and 2 is performed, except that the solvent is at 83.4% wt DMF, Feed diesel/solvent ratio = 1/1.

EXPERIMENT No 3: Solvent at 83.4% wt DMF, Feed diesel/solvent ratio = 1/1 Method Units Feed Diesel Product Diesel Density ISO 3675 K /l 0.844 0.834 Sulphur ISO 8754 % m/m 0.339 0.066 Water IS010336 mg/kg 0.098 0.012 Total Acid Number mg KOH/g 1.54 0.15 Flash Point ASTM D92 C 69 57 Cetane Index EPCN 322 57.1 60.2 ASTM
Colour after 1 day exposed to air D1500 6 1 Colour after 5 months exposed to ASTM
air D1500 7 1.5 Table III
Note the abnormality in the 0% to 10% cut of the treated gasoil, and the corresponding heads and tails in the recycled solvent curve. The distillation curves in Figure II
et III demonstrate that the "solutizers" in this process have boiling points between 125 C and 200 C.

Example 4: DMF impure - pure at 77,25 %

The same experiment as in example 1 and 2 is performed, except that the solvent contains 77.25% wt DMF, Feed diesel/solvent ratio = 1/1 EXPERIMENT No 4: Solvent at 77.25% wt DMF, Feed diesel/solvent ratio = 1/1 Method Units Feed Diesel Product Diesel Density ISO 3675 Kg/1 0.844 0.834 Sulphur ISO 8754 % m/m 0.315 0.086 Water ISO 10336 mg/kg 0.11 0.011 Total Acid Number mg KOH/g 4.27 0.56 Flash Point ASTM D92 C 53 60 Micro Carbon Residue ISO 10370 % m/m 0.544 0.086 Cetane Index EPCN 322 54.2 60 Colour after 1 day exposed to air ASTM D1500 5.5 1.5 Colour after 5 months exposed to air ASTM D1500 7 1.5 Table IV

These experiments show that the impurities in the incompletely regenerated solvent facilitate the mass transfer of sulphur compounds from the gasoils to the solvent, as did the solutizers for light oils in older patents.

The incompletely regenerated solvent was obtained by heating the extract to 1700C in a thin film evaporator operating at 120 mBar.

ADVANTAGES OF THE INVENTION

The extraction process described in this patent stabilizes and neutralizes wide range cracked diesel, while removing most of the sulphur and water. As in other extraction processes researched, complete regeneration of the solvent is difficult because DMF
disintegrates around 3500C. Usually azeotropic distillation is used, with water as the third component. However, in this case, complete regeneration of the DMF is not necessary, or even desirable, since the extraction process is more effective when reaction products from previous passes are present in the solvent.

This invention is a simple and low cost process to stabilize, de-sulphurize, neutralize and dry oils produced by thermal or catalytic cracking of heavier oils. It can be used as a product oil finishing process in a used oil plant, to debottleneck a hydrotreating unit in a refinery or as a diesel oil finishing step in a refinery. The extraction is performed at ambient temperatures and pressures. The solvent can be regenerated with a simple vacuum distillation or centrifuge. It does not require an azeotropic distillation to achieve near complete regeneration, since complete regeneration is not desired. Oxidation of the mercaptans, thiols, and nitrogen compounds prior to their extraction from the oil is not required. In the case of used oil plants, a gasoil meeting all European heating oil specifications can be produced without hydrotreating.

Although the present invention has been described with the aid of specific embodiments, it should be understood that several variations and modifications may be grafted onto said embodiments and that the present invention encompasses such modifications, usages or adaptations of the present invention that will become known or conventional within the field of activity to which the present invention pertains, and which may be applied to the essential elements mentioned above.

Claims (31)

1. A process to stabilize and to remove contaminants from a unstable oil produced by thermal or catalytic cracking, said process comprising at least one step of mixing said unstable oil with an impure solvent having a dipole moment greater than 2.

2. A process according to claim 1, to stabilize and to remove contaminants from a unstable oil produced by thermal or catalytic cracking, said process including at least one step of contacting a stream of the said unstable oil with a solvent having a dipole moment greater than 2 and, thus, obtaining two mixtures, the first mixture being of an oil-solvent type and containing impurities, and the second mixture being of a solvent-oil type and containing residues and impurities, the impurities in the solvent-oil mixture being identical or different of the impurities in the oil-solvent mixture.

3. A process according to claims 1 or 2, to stabilize and to remove contaminants from a unstable oil produced by thermal or catalytic cracking, wherein at least a fraction of the said solvent having a dipole moment greater than 2 that is present in at least one of the said two mixtures is extracted from the mixture (s) and is at least partially regenerated before being recycled to said process.

4. A process according to anyone of claims 1 to 3, to stabilize and to remove contaminants from an unstable oil produced by thermal or catalytic cracking, said process including the following steps of:

a) intimately contacting a stream of the said unstable oil with a solvent having a dipole moment greater than 2 and, thus, obtaining two mixtures, the first mixture being of an oil-solvent type and containing impurities, and the second mixture being of a solvent-oil type and containing residues and impurities, the impurities in the solvent-oil mixture being identical or different from the impurities in the oil-solvent mixture;

b) separating the treated oil, present in the oil-solvent mixture obtained in step a), from the solvent, leaving most (preferably at least 80% weight, more preferably at least 90%
weight) of the impurities in the solvent phase;

c) separating the solvent and the oil, present in the solvent-oil mixture obtained in step a), from the residues, leaving at least 90 % of the contaminants in the residues;

d) optionally separating the solvent and the light oil present in the oil-solvent mixture obtained in step b), and e) optionally separating the solvent and the oil obtained in step c);

f) recycling at least one of the solvents obtained in steps b), c), d) or e), wherein each of said solvent is preferably regenerated for at least 50 % weight but for less or equal to 99 % weight before recycling, preferably by known means such as distillation, vacuum distillation, azeotropic distillation, centrifugation, and more preferably vacuum distillation and/or centrifugation.

5. The process according to any claim 1 to 4, wherein the boiling range of the said unstable oil, as measured by the method ASTM D86, ranges from 125°C to 500°C, and preferably ranges from 175°C to 450°C.

6. The process according to any claim 1 to 5, wherein the boiling range of the treated oil in step a) is, as measured by the method ASTM D86, is between 125°C to 500°C, preferably between 175°C and 450°C.

7. The process according to anyone of claims 1 to 6, wherein the said unstable oil is produced by cracking used oil, heavy oil, bitumen, vacuum gasoil, vacuum residue, tar, synthetic crude oil, bunker or is produced by cracking a mixture of at least two of these solvents.

8. The process according to anyone of claims 1 to 7, wherein the solvent is chosen among N-methyl pyrrolidone, furfural, dimethyl formamide, phenol, pyridine, dimethyl acetamide, dimethyl sulfoxide and propylene carbonate, and among mixtures of at least 2 of the latter.

9. The process according to anyone of claims 1 to 8, wherein the regenerated solvent, obtained in steps b), c), d) and/or f), still contains some impurities and/or reaction products.

10. The process according to claim 9, wherein contaminants include: water, sulphur compounds such as mercaptans and thiols, organic chlorides, organic and inorganic acids, free radicals, resins, gums, sediments, reaction products and mixtures of at least two of these.

11. The process according to anyone of claims 1 to 10, wherein the solvent concentration in the regenerated solvent stream obtained, in steps b), c), d) and/or f), is between 50% wt. and 99% wt., preferably between 70% wt. and 90% wt., more preferably about 83% wt.

12. The process according to claim 11, wherein the regenerated solvent is produced, in step f), by distillation, preferably at pressures ranging from 0.5 psia to 12 psia, preferably from 0.5 psia to 4 psia, more preferably at pressures about 1.5 psia.

13. The process according to claims 11 and 12, wherein the regenerated solvent is produced, in steps b), c), d), and f), by distillation conducted at temperatures ranging from 50°C to 350°C, preferably ranging from 100°C to 175°C, and more preferably at a temperature of about 130°C.

14. The process according to anyone of claims in claims 10 to 13, wherein the impurities, present in the regenerated and/or recycled solvent, have a boiling temperature ranging from 120°C to 250°C, preferably ranging from 130°C to 200°C.

15. The process according to claim 14, wherein the impurities, present in the regenerated and/or recycled solvent, have catalytic and/or solution enhancing and/or bridging properties.

16. The process according to anyone of claim 1 to 15, wherein in step a) the solvent extraction is carried out at temperatures ranging from 8°C to 100°C, preferably ranging from 10°C to 40°C, and more preferably at a temperature of about 25°C.

17. The process according to anyone of claims 1 to 16, whereby the solvent extraction in step b) is carried out as soon as possible, preferably after less than 1 day, more preferably after less than 5 minutes after the cracked oil is produced.

18. The process according to anyone of claims 1 to 17, wherein the solvent to volume oil ratio is between 5/1 and 1/5, preferably between 2/1 and 1/2; more preferably about 1/1.

19. The process according to anyone of claims 1 to 18, wherein step a) of the process is performed in a continuously stirred extraction column.

20. The process according to claim 19, wherein step b) of the process is performed by using at least one of the following techniques: in a thin film evaporator, in a wiped film evaporator, azeotropic distillation and/or in a centrifuge.

21. The process according to anyone of claims 19 and 20, wherein step c) of the process is performed in a thin film evaporator, in a wiped film evaporator or in a centrifuge.

22. The process according to anyone of claims 17 to 20, wherein step d) of the process is performed by phase accumulation, or in a wiped film evaporator or in a centrifuge or by combination of at least two of these methods.

23. The process according to anyone of claims 1 to 22, wherein the said contaminated oil is a wide range diesel fuel, the initial solvent is a nearly pure solvent having a dipole moment greater than 2.

24. The process according to anyone of claims 16 to 23 wherein the stable operation can, with these operating conditions unchanged, be reached in between 10 and 120 minutes, more preferably in about 45 minutes.

25. The process according to anyone of claims 1 to 24, wherein the oil is thermally cracked oil or is a thermally cracked used oil, and the initial solvent having a dipole moment greater than 2, is DMF.

26. The process according to claim 25, wherein the initial temperature in step a) is between 15°C and 30°C, most preferably 25°C, and the initial temperatures in steps b), c) and d) are between 100°C and 175°C.

27. The process according to claim 25 or 26, wherein the initial pressures in steps b), c) and d) are between 0.5 psia (a.) and atmospheric pressure.

28. The process according to anyone of claims 25 to 27, wherein the temperatures are determined by the vacuum obtained, but kept below the thermal decomposition temperature of the solvent and/or the cracking or polymerization initiation temperatures of the oil.

29. The process according to anyone of claims 25 to 28, wherein the equilibrium temperature in step a) is between 15°C and 100°C, and most preferably about 25°C.

30. The process according to anyone of claims 25 to 29, wherein the solvent content in the recycled solvent stream is between 50% weight and 99% weight, preferably between 60 %
weight and 95% weight, and most preferably about 83% % weight.

31. The process according to anyone of claims 27 to 30, wherein the temperatures in steps b), c) and d) are between 10°C and 175°C.