EP0372276B1 - Process for the recuperation of contaminated oils - Google Patents

Abstract

Process for the recuperation of contaminated oils by thermal treatment and distillative separation of the chlorine compounds obtained, and hydrogenative refining thereof. <IMAGE>

Description

The present invention relates to a process for working up contaminated oils by thermal treatment in a thermal or catalytic cracking stage, working up the product by distillation and then hydrogenating treatment of distillate fractions.

In the past decade, experts have increasingly dealt with the environmentally friendly reprocessing of contaminated used oils, which are also known under the term "used oils", although "contaminated used oils" is to be regarded as a superordinate term.

Although a precise definition of the term "waste oil" is missing (see, for example, Chapter 1, K. Müller "waste oil recycling", Erich Schmidt Verlag, Berlin 1982), in the broadest sense it is mostly used lubricants and functional fluids that are no longer directly reusable based on petroleum, but also those based on coal tar, vegetable, animal or synthetic. These materials can also be substances that are solid or semi-solid at normal temperature.

The new lubricants and functional fluids contain numerous additives, such as Corrosion inhibitors, oxidation inhibitors, foam inhibitors, detergents, dispersants, metal deactivators, color stabilizers, viscosity index improvers, pour point depressants, wear control additives, emulsifiers and others.

These additives give rise to numerous compounds of oxygen, sulfur, nitrogen, phosphorus, metals such as, for example, heavy metals, but also other metals, halogens, silicones Plastics and other compounds in the oils mentioned.

While using new oils as lubricants and functional fluids, physical processes such as e.g. increased temperature, abrasion, but also due to chemical processes such as Oxidation, changes in the additives so that the secondary products of these reactions and changes are also present in a used oil, such as finely divided metals, substances with an asphaltene or resin-like consistency and other secondary products due to chemical changes in the additives etc.

Often contaminated oils of very different origins are collected together at collection points, so that the mixture can also contain numerous solvents, water and solids. The content of chlorinated compounds, in particular of polychlorodiphenyls, -terphenyls, polychlorodiphenylmethanes and other chlorine-containing additives, is of particular importance in the case of waste oils or the mixtures mentioned.

Because of these chlorine compounds but also the metals or metal compounds, the combustion of the waste oils is very problematic, since the formation of toxic substances such as dioxins or polychlorodibenzofurans and their emissions into the environment cannot be completely ruled out. Due to the very large quantities of waste oils and their importance as a raw material, combustion is known as energy recycling, i.e. heat generation by burning is also not to be regarded as optimal, since hydrogen-rich substances that are used for other uses e.g. are of great importance as fuel or feedstock for olefin plants, are converted into H₂O and CO₂.

Numerous processes have therefore been developed to process used used oils into reusable oils.

The reprocessing of used oils is often referred to as secondary refining.

The classic process is the sulfuric acid process, in which waste oils are treated with 96% sulfuric acid. So-called acid resins settle here. It is then neutralized and the oil treated in this way is distilled. This treatment is usually repeated. There remain oils that still contain impurities, are dark in color and have an unpleasant smell. They are therefore difficult to recycle. In addition, the disposal of the acid resins causes great problems.

An improvement is the sulfuric acid / bleaching earth method, in which after the sulfuric acid treatment is treated with bleaching earth and then distilled in vacuo (R. Meixlsperger in W. Kumpf, K. Maas, H. Straub: Müll und Abfallbesorgung, 395, no . 4010).

In the selectropropane H₂SO₄ process, the sulfuric acid treatment is preceded by a propane extraction (R. Dutrian and D.V. Quang in Chemical Engineering 79 (1972) p.4).

A more modern process in which hydrogen is refined is the CTI process (R.F. Westerduin in: Polytechnisch tijdschrift / proces-techniek 34 (1979) p.5). In this process, vacuum distillation is carried out first, followed by high vacuum distillation. It is then treated with hydrogen at about 50 bar and 300-350 ° C.

It is obvious that despite these processes, both for environmental reasons and for economic reasons, solutions are urgently required according to which the large amounts of waste oil can be processed in a technically simple manner while protecting the environment.

For the direct processing of used oils together with crude oil in Refineries are stated in: K. Müller, Waste Oil Recycling, Verlag Erich Schmidt, Berlin 1982 on page 101: "Due to the original properties of the substance, the possibility of adding waste oils to crude oils prior to their processing in refineries to increase the proportion of lubricant may be due to the existing ones in waste oils typical impurities and the associated negative effects on catalysts and process stirring when processing crude oils are completely excluded.

For these reasons, special secondary refining processes are required to process used oils into high-quality base oils.

Contrary to this prejudice, the applicant has surprisingly succeeded in developing a process that is already used on a large industrial scale with great success in a refinery and that allows waste oils to be processed with excellent results within the framework of conventional refinery technology, characterized in that a thermal treatment of the contaminated Oil consisting of a thermal or catalytic cracking stage is carried out, that the distillative separation of chlorine-containing distillates and that a hydrogenative refining of the chlorine-containing distillates takes place.

It is well known that conventional process steps in refineries are atmospheric distillation, vacuum distillation, cracking processes, refining processes and reforming processes. Thermal cracking, catalytic cracking and hydrocracking are used as cracking processes. Thermal cracking has the advantage that heavy, relatively heavily contaminated oils can be used.

Typical thermal cracking processes are visbreaking, which is carried out at relatively low temperatures of approx. 400-500 ° C, normal thermal cracking at approx. 500-600 ° C and coking, which is carried out at approx. 500 ° C. Catalytic cracking processes are generally carried out in a fixed bed, fluidized bed or fluidized bed at about 400-500 ° C. According to the invention, these cracking processes are also suitable as a thermal treatment stage.

The refining of refinery streams serves to remove the heteroatoms, especially nitrogen and sulfur, which are present in the crude fractions in the form of compounds. Although refining processes can also consist of chemical reactions, such as the oxidation of strong-smelling mercaptans to low-smelling disulfides, refining by hydrogenation in the presence of sulfur-resistant catalysts, which usually contain combinations of Ni, Co, Mo and W as metal components, is the most most procedures used. The heteroatoms S, N and O occur as H₂S, NH₃ and H₂O. Unsaturated compounds are converted into saturated hydrocarbons. The hydrogenating refining can be used under very different conditions, for example 25-100 bar and 300-400 ° C are typical, but also significantly higher pressures up to e.g. 300 bar can be used.

In the usual refinery operation, bottom products from atmospheric distillation, from vacuum distillation or mixtures of both are split in thermal crackers.

The investigations of the applicant have led to the result that it is not possible to process contaminated oils if they are used, even in pre-cleaned form, such as after water separation and filtration, directly in a distillation stage, be it atmospheric or under vacuum, since in Because of the low thermal stability of waste oils compared to crude oil fractions, the columns very soon coke and deposit different materials to such an extent that the distillations have to be switched off and cleaned. However, if the contaminated oils are first used in a thermal treatment stage consisting of a thermal or catalytic cracking stage, one can take into account further inventive features surprisingly perform properly, although the entire cracking product is then used in the distillations.

The investigations of the applicant have shown that when contaminated oils such as waste oils are heated, considerable amounts of carboxylic acids, in particular acetic acid, can be formed in addition to the formation of hydrogen chloride.

If, for example, contaminated oil such as e.g. Used oil without pre-cleaning in a Visbreaker one of the under standard conditions of approx. 10 bar and 20 min. Dwell time and operated at a temperature up to about 450 ° C, there are significant chemical conversions that can lead to the elimination of HCl and formation of the carboxylic acids. The details of the course of these conversions are not known.

Although the use in a visbreaker as a thermal cracking stage is a preferred embodiment of the present invention, other thermal or catalytic cracking processes with very good results can also be used according to the invention, even if, as is known to the person skilled in the art, these are operated under very different conditions.

The carboxylic acids, mainly as acetic acid, are removed via the top of the atmospheric distillation column downstream of the Visbreaker or at an upper side draw, and HCl also escapes.

It is advantageous according to the invention to keep the top temperature of the distillation column above 150 ° C., preferably at> 180 ° C., in order to prevent corrosion. This can be adjusted by regulating the purchase quantities.

Corrosion protection additives are advantageously added to the condensation system on the head in order to avoid corrosion there too. Gas oil cutting, which usually has a boiling range of 170-360 ° C, but can also be cut differently if required, still contains chlorine-containing compounds. The bottom of atmospheric distillation is a vacuum subjected to distillation, the vacuum distillate also contains chlorine-containing compounds.

The distillate that boils more easily in the atmospheric distillation than gas oil can, however, be obtained free of critical chlorine-containing components such as polychlorobi- and -terphenylene or polychlorodiphenylmethanes, as can the bottom of the vacuum distillation.

According to the invention, gas oil and / or vacuum distillate are now subjected to a hydrogenating catalytic refining, the hydrogenation-active metals, in particular combinations of Ni / Co / Mo and tungsten, being on conventional supports such as amorphous or crystalline zeolites, Al₂O₃, aluminum silicates, SiO₂ and the like.

The hydrogenating refining can take place in a wide pressure range of 25-300 bar and 280-500 ° C. A preferred mode of operation is 25-100 bar and 280-400 ° C, particularly preferred are 30-70 bar and 300-380 ° C.

The products obtained are completely chlorine-free and can be used or processed like conventional refinery cuts.

A base, in particular NaOH, is preferably added to the thermal or, if appropriate, catalytic cracking stage. Advantageously, 20-40 mol% of gram atom of chlorine can be used in the feed product, but NaOH can be varied within wide limits up to stoichiometric or even stoichiometric amounts. An amount less than 20 mol% per gram atom of chlorine is less advantageous.

The amount of contaminated oil used, e.g. Waste oil can be> 0 to 35% by weight of the total use in the thermal treatment stage, preferably> 0-20% by weight and particularly preferably> 0-15% by weight.

With amounts higher than 35% by weight, strong coke formation and strong foaming can occur. Defoamers can be added to reduce or prevent foaming in the entire application area. Here, the expert known defoamers suitable for such purposes are used. In the event that vacuum distillation is not to be carried out, the bottom of the atmospheric distillation can, for example, be fed directly to gasification. The soot in the gasification largely absorbs the ashes of the contaminated oils.

The figure serves as an example for a more detailed explanation.

From tank 1, 10% by weight of a waste oil consisting of numerous components together with 90% by weight of vacuum residue 2 from a vacuum distillation unit of a refinery were used in Visbreaker 3. A soaker 4 is connected downstream to increase the residence time. The thermal cracking units are exemplary. Other thermal or catalytic crackers can also be used according to the invention with very good results. The cracked product now passes through 5 into atmospheric distillation 6. Light gasoline is removed via 7, 10 acetic acid or water containing acetic acid, 8 a naphtha cut and 9 a gas oil (medium oil) cut containing chlorine compounds.

The bottom product is used in vacuum distillation 11.

Vacuum distillate reaches hydrogenation reactor 13 via 12. Via 9 gas oil can also be used directly in 13. Hydrogen is added via 14.

A hydrocarbon product above 15 which is completely chlorine-free is withdrawn from the hydrogenation reactor.

The system was operated without problems for 16 weeks in the manner described.

For comparison, waste oil from 1 over 16 was run directly after 6. After 2 weeks, the coking in the column, in particular in the hot part, was such that coking and caking of amine compounds were present that the distillation had to be stopped. This confirms the statement cited on page 4 from the reference K. Müller, "Waste oil recycling" from page 101.

The present invention therefore represents a method for the first time ready, which allows large quantities of contaminated oils to be processed in normal refining operations without operational disruptions, whereby flawless hydrocarbon streams which can be fed to customary further processing are obtained.

The bottom product of the vacuum distillation 11 can be supplied to gasification, for example a shell or Texaco gasification 17, or can be drawn off as heavy fuel oil via 18. The bottom product of column 6 can also be fed directly via 17 or 18 via 19. Over 20 synthesis gas is withdrawn.

Claims (10)

1. A process for reprocessing contaminated oils, characterised in that a thermal treatment of the contaminated oil, comprising a thermal or catalytic cracking stage, is carried out, that distillates containing chlorine compounds are removed by distillation and that the distillates containing chlorine compounds are subjected to hydrofining.

2. The process as claimed in claim 1, characterised in that the reprocessing by distillation comprises atmospheric distillation and subsequent vacuum distillation.

3. The process as claimed in claim 2, characterised in that the gas oil cut from the atmospheric distillation and the vacuum distillate are subjected to a hydrogenating catalytic treatment.

4. The process as claimed in claims 2 to 3, characterised in that the overhead temperature of the atmospheric distillation is maintained at > 150°C, preferably > 180°C.

5. The process as claimed in claims 1 to 4, characterised in that a base is added to the thermal treatment stage.

6. The process as claimed in claims 1 to 5, characterised in that NaOH is added to the thermal treatment stage.

7. The process as claimed in claims 1 to 6, characterised in that the hydrogenating treatment is carried out at 25-300 bars and 280-500°C, preferably at 25-100 bars and 300-400°C and most preferably at 30-70 bars and 320-380°C.

8. The process as claimed in claims 1 to 7, characterised in that visbreaking is employed as thermal treatment stage.

9. The process as claimed in claims 1 to 8, characterised in that the amount of contaminated oil, based on the overall feed to the thermal treatment stage, is  > 0-35 wt%, preferably  > 0-20 wt% and especially preferably  > 0-15 wt%.

10. The process as claimed in claims 1 to 9, characterised in that the bottoms from atmospheric distillation and/or the bottoms from vacuum distillation are supplied to a gasification unit for the production of synthesis gas.

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