GB2567884A

GB2567884A - Method for the recycling used lubricating oils

Info

Publication number: GB2567884A
Application number: GB1717932.6A
Authority: GB
Inventors: Heinrich Erxleben Hermann; Robinson Catherine; Van Zyl Tegan
Original assignee: Ffs Refiners Pty Ltd
Current assignee: Ffs Refiners Pty Ltd
Priority date: 2017-10-31
Filing date: 2017-10-31
Publication date: 2019-05-01
Also published as: GB201717932D0

Abstract

The invention relates to a method of recycling used lubricating oil. The method comprises the steps of evaporating water and light hydrocarbon from the oil using an evaporator, thermally degrading some of the oil additives held in the oil while keeping oil contaminants in suspension, chemically separating the degraded additives and/or contaminants from the oil, physically removing the chemically separated degraded additives and/or contaminants from the oil, and hydro-treating the oil to produce base oils of multiple grades. The chemical separation comprises the steps of de-ashing the oil using a de-ashing agent, and coagulating, using a coagulant, carbon in the oil and coagulating metal precipitates in the oil which are formed by the de-ashing. The physical removal of the chemically separated degraded additives and/or contaminants from the oil comprises the steps of filtering the oil to remove the inorganic salts and coagulated carbon formed during the chemical separation steps.

Description

METHOD FOR THE RECYCLING USED LUBRICATING OILS

Field of the invention

The invention relates to methods and processes used to recycle or refine used or waste lubricating oils.

Background of the invention

Lubricating oils used in industrial and automotive applications typically contain additive packages which include corrosion inhibitors, anti-foams; detergents; dispersants and emulsifiers amongst other things. It is the presence of these additives that makes lubricating oil so difficult to recycle as in these applications it is critical that any additives or contaminants formed in the process, such as carbon and dust, are kept in suspension and do not settle out in engines or other industrial equipment.

Used lubricating oil typically contains 3-20% water and 0.3 - 1% ash or incombustible contaminants. Crude refining can make this oil suitable for use in robust heavy fuel oil applications and this is where the bulk of the collected material ends up. The remainder of the used oil that is not collected, which is as much as 70% in South Africa, is often just dumped to landfill or even dumped into storm water systems.

Existing methods are not environmentally friendly and generate high amounts of solid and/or liquid effluent. The solid waste is not suited to be disposed of at a landfill.

Tighter environmental legislation is making it increasingly difficult to both burn and dump liquid hydrocarbon “wastes”. There is therefore a drive to adopt a life cycle approach to used lubricating oils by converting them back to base oils.

Earlier patents focus on mechanical removal of the coarse solids through filtration, centrifugation or by similar means. These processes typically provide a medium fuel oil of low quality. This kind of mechanical separation does not affect the additive package present in the oil and the organometallics and finely divided carbon therefore remain in suspension.

-2Further developments in the field related to the chemical removal of the additives. The main additives used are anti-oxidants, detergents, dispersants, anti-wear additives, anticorrosion additives and anti-foams. Most of these additives are ash-less but some are metal-based and contain primarily zinc, calcium, iron and phosphorus. The approach to chemically de-ash these used oils was generally the addition of a reagent to react with these metals to form salts which could be subsequently removed.

The majority of the known processes either involved the addition of an acid to form a soluble salt which was then removed in an aqueous form, or the addition of a quaternary salt to form an insoluble salt which was then removed as sludge. These de-ashing methods are relatively successful in removing the metallic contaminants and ash content of the final product fuel could be as low as 0.1%.

A disadvantage of these processes is the generation of a large amount of effluent or solid waste which then needs to be disposed of in an environmentally friendly manner. A further disadvantage is that although the reagents added successfully remove the ash, they do not generally remove the suspended carbon or soot present in the used lubrication oil. The suspended carbon means the fuel has a high sediment content which can cause problems in pumps and combustion applications. It also means the fuel is unsuitable for further processing such as hydro-treating as this carbon would destroy catalyst activity. In existing de-ashing methods, the level of Phosphorus produced is high. Phosphorus is acknowledged as a catalyst poison which deactivates catalysts and renders the catalysts ineffective.

Currently, the majority of processes actively recycling lubricating oil are using distillation technology. Distillation units running at high temperature and under high vacuum to avoid cracking, can produce a clean, clear and bright distillate fraction which can be successfully hydro-treated to form a base oil. The main disadvantages to these thermal processes are that they are capital intensive and have a relatively low yield. Conversion yields are as low as between 50-65%. They are also unlikely to produce significant amounts of heavier grade base oils due to the higher boiling point fractions being left behind in the distillation process. The bottom layers formed from these distillation processes are also difficult to place in the market due to the high ash content thereof, which may be between 3-5%, as well as the high viscosity of the bottom layers.

-3 US 4,789,460 teaches an improved process for filtering contaminants from oil. A polyalkoxyalkylamine is admixed with the oil in an amount sufficient to improve the filtration rate thereof. The polyalkoxyalkylamine serves to coagulate soot particles and other ash-forming contaminants in the oil, thereby producing a precipitate which is more easily removed from the oil. Ethanolamine is not used in this process, and the same steps are not followed in terms of order of operation as opposed to the invention. Furthermore it does not include the combined additives found in the invention.

US 4,287,049 teaches a process of reclaiming of used lubricating oils, in which the oil is contacted with an aqueous ammonium salt treating agent in the presence of a polyhydroxy compound. The polyhydroxy compound is used to agglomerate pre-existing soot particles in the oil, thereby producing a precipitate which is more easily removed along with the particulate matter. Ethanolamine is not used in this process, and the same steps are not followed in terms of order of operation as opposed to the invention. Furthermore it does not include the combined additives found in the invention.

US 2,568,583 teaches a method of reclaiming used lubricating oils, in which an N-phenyl alkylol amine is mixed with the oil to cause the impurities in the oil to flocculate and thereafter the aggregate of impurities are separated by settling, filtering or by centrifuging. While ethanolamine is an N-phenyl alkylol amine, the invention differs from the ‘583 patent in that there is no heat soak or thermal degradation step, filtering the oil to remove the coagulated carbon is carried out at lower temperature (50 - 93 °C), there is no deashing agent used, and flocculation occurs in a shorter period of time. The same steps are not followed in terms of order of operation in the ‘583 patent as opposed to the method of the invention. Furthermore it does not include the combined additives found in the invention.

EP 0 574 272 provides an improved process of producing base stock oil from used lubrication oils. The process includes pretreating the used oil by adding an alkali compound. Ethanolamine is not used in this process, and the same steps are not followed in terms of order of operation as opposed to the invention. Furthermore it does not include the combined additives found in the invention.

US 1,882,002 teaches a process for treating used lubricating oils, wherein triethanolamine

-4is added to the oil in order to effect the coagulation of suspended and dissolved impurities in the oil which can then be separated from the oil. While the ‘002 patent includes triethanolamine, the invention differs from the ‘002 patent in that there is no heat soak or thermal degradation step, and the coagulation step is carried out at a temperature of 90 °C. There is no de-ashing agent used, and coagulation occurs in 30 minutes. The same steps are not followed in terms of order of operation as those followed in the invention, the ‘002 does not have the same advantages and yields that the invention does. Furthermore it does not include the combined additives found in the invention.

The inventors are of the opinion that the described invention provides a novel and inventive method of recycling used lubricating oils which overcomes or at least partially alleviates some of the above mentioned shortcomings of existing methods or processes.

Summary of the invention

According to an aspect of the invention there is provided a method of recycling used lubricating oil, the method comprising the steps of:

evaporating water and light hydrocarbon from the oil using an evaporator; thermally degrading some of the oil additives held in the oil while keeping oil contaminants in suspension;

chemically separating the degraded additives and/or contaminants from the oil, comprising the steps of;

de-ashing the oil using a de-ashing agent; and coagulating, using a coagulant, carbon in the oil and coagulating metal precipitates in the oil which are formed by the de-ashing; and physically removing the chemically separated degraded additives and/or contaminants from the oil, comprising the steps of;

filtering the oil to remove the inorganic salts and coagulated carbon formed during the chemical separation steps; and hydro-treating the oil to produce base oils of multiple grades.

The de-ashing agent preferably consists of an aqueous mixture of an ammonium salt.

-5 The coagulant is preferably an ethanolamine.

When evaporating water and light hydrocarbon using an evaporator, used lubricating oil, having a typical water content of 5-20%, is fed to an evaporator. This evaporator preferably runs at atmospheric pressures and temperatures of between 120°C and 140°C.

The oil may then be transferred to the thermal degradation step. The thermal degradation step preferably includes a heat-soak step. The dried used oil is preferably heated to temperatures between 300°C and 350°C. The oil is preferably maintained between the above temperatures for a period of 30 minutes to 2 hours in a pressure vessel with removable baffles. The oil may be heated, either directly by a furnace or indirectly with an appropriate heat transfer fluid. The oil is preferably heated to between 320°C and 380°C. The oil may enter a baffled vessel through the top of the vessel and flow is maintained at such a rate to ensure the oil is maintained for a minimum of 20 minutes at a selected temperature or temperature range. The heat-soak step may thermally degrade some of the additives and keeps the contaminants in suspension.

Both the temperature range and the residence time may be determined by the balance between sufficient temperature and time in order for degradation of the additive package in the oil to occur while avoiding excessive temperatures and times which lead to the oil becoming thermally cracked. Cracking typically occurs when the oil is heated to temperatures above 350 °C, which is not preferable as the flash-point and viscosity of the oil is reduced, which may impact the yield.

Only once the additives have been degraded may ash and carbon contaminants be chemically separated and thereafter physically removed.

When chemically separating the degraded additives and/or contaminants, the oil may be transferred to a reactor where it may be treated with an de-ashing agent. The reaction of the de-ashing agent with the degraded additives results in the precipitation of the contaminants.

The amount of the de-ashing agent added to the oil is dependent on the level of metal contaminants in the oil that the de-ashing agent is required to react with. Preferably, the quantities of the de-ashing agent are between 1% and 5%, based on dry weight. The de-6ashing agent must be added to water having a temperature of between 60 °C to 90 °C, to allow dissolution before being injected into the reactor. Enough de-ashing agent is preferably added such that the de-ashing agent stoichometrically reacts with the metals present in the oil. An excess may be required to ensure a full reaction. Therefore, 1% is the preferred quantity, but up to 5% may be required.

A coagulant may be added to the de-ashing agent and oil. The coagulant is preferably injected concurrently with the de-ashing agent into the oil. The coagulant may coagulate the finely divided carbon present in the oil, and may further coagulate the metal precipitates formed by the de-ashing agent. The coagulant is preferably added in the reactor in a concentration of between 0.5% and 1%. Enough coagulant is added to coagulate effectively without having an impact on the quality of the final product as glycol remains in the oil.

The reactor may be heated to a minimum of 70°C and the de-ashing agent may be allowed to react with the oil for between 20 minutes and 6 hours. A temperature greater than 70 °C increases the reaction rate but is below boiling temperature. The initial reaction temperatures are required to be below 100 °C as the reaction occurs in the aqueous phase. The time period is dependent on the rate of reaction which is dependent on the temperature, water content, mixing, ash content, and de-ashing agent concentration. The temperature in the reactor may slowly be increased to between 100°C and 120°C to remove the water from the de-ashing agent. Viscosity of the oil is reduced with temperature which helps with reaction rates.

The coagulation of the contaminants in the oil may allow for easier filtration of the treated oil.

The contaminants may be physically removed by filtration. The oil is processed through a filter to remove the inorganic salts formed during the de-ashing step and the coagulated carbon. A filter aid, preferably diatomaceous earth, is added to improve the quality of the filtrate and the flux rate through the filter. Filtration is preferably carried out at temperatures between 100°C and 150°C. Higher temperatures reduce the viscosity of the oil to be filtered. A temperature of 150°C is approximately the maximum achievable with steam. The filtrate may be substantially free of ash, including metals, and suspended

-7carbon. The filtrate may also have low levels of Phosphorus. The Phosphorus levels may be as low as 50 parts per million (ppm).

The final stage of the method is hydrogenation through a hydro-treater and a vacuum distillation unit. The distillation unit allows for the production of multiple grades of lubricating oil.

The filtered product may be processed through the hydro-treater using a combination of guard and active catalysts, as well as hydrogen. This process preferably takes place at temperatures between 280°C and 350°C, and pressures between 20 bar and 80 bar. The hydrogenated product may then be processed through a vacuum distillation unit in order to produce base oils of the desired grades. The hydrogenation reaction occurs at these temperatures and pressures. Higher pressures may allow for deeper hydrogenation and an improved product.

The base oils may require some colour correction which is typically achieved through filtration with a bleaching earth.

The hydrogenated product may be sold as a refined base oil.

The method removes both the additive package and the suspended carbon, which makes the resulting product of the method suitable for further treatment into base oil. The method is environmentally friendly in that it generates lower amounts of solid or liquid effluent as opposed to the amounts generated by known methods. Furthermore, the solid waste that is generated by the method described herein may be disposed of in a landfill due to the solid waste having a low calorific value. The conversion of used lubricating oil to base oil is in the region of between 75 - 90%. Should all hydrogenated product be converted to base oils of different grades, the yields may be as high as 90%. The conversion of used lubricating oil to base oil is typically 85%. The product that may be considered lost or unconverted may be used as a high value heating fuel. Furthermore, low levels of Phosphorus are achieved during the de-ashing step.

Brief description of the drawing

-8Figure 1 is a schematic representation of a method for recycling used lubricating oil.

Detailed description of the invention

It will be appreciated by those skilled in the art that the invention is not restricted in its use to the particular application described. It will further be appreciated that the invention is not limited to the embodiment/s disclosed, but is capable of various rearrangements, modifications and substitutions without departing from the scope of the invention as set forth.

Used lubricating oil, having a typical water content of 5-20%, is fed to an evaporator (1). This evaporator runs at atmospheric pressures and temperatures of between 120 and 140°C. The role of this evaporator is to remove the water and the light hydrocarbons present in the used oil.

The dry oil is then transferred to the heat-soak process (2). Here the oil is heated, either directly by a fired heater or indirectly with an appropriate heat transfer fluid, to between 320 and 380“C. The oil enters the baffled vessel through the top of the vessel and flow is maintained at such a rate to ensure a minimum residence of 20 minutes at the assigned temperature. The purpose of this heat-soak step is to thermally degrade some of the additives keeping the contaminants in suspension. Only once these have been degraded can the ash and carbon be chemically and physically removed.

The oil is then transferred via a storage tank to the reactor (3). Here the oil is treated with a de-ashing agent, most commonly an aqueous mixture of an ammonium salt. The amount of the de-ashing agent added is dependent on the level of metal contaminants in the oil that it is required to react with, however typical dosages are between 1 and 5% (on a dry weight basis) of the de-ashing agent. The ammonium salts are added to just enough water to allow dissolution before being injected into the reactor. A coagulant is concurrently injected with the ammonium salt solution. The coagulant used in this invention is an ethanolamine and it is responsible for coagulating the finely divided carbon present in the oil as well as the metal precipitates formed by the de-ashing agent. The coagulation of these contaminants allows for easier filtration of the treated product. The coagulating agent is added in a

-9concentration of between 0.5 and 1% in the reactor. The reactor is heated to a minimum of 70°C and the de-ashing chemical allowed to react with the oil for between 20 minutes and six hours. The temperature in the reactor can be slowly increased to between 100 and 120°C to remove the water added with the de-ashing agent.

The dried product is then processed through a filter to remove the inorganic salts formed during the de-ashing step and the coagulated carbon. A filter aid, such as diatomaceous earth is typically added to improve the quality of the filtrate and the flux rate through the filter. Filtration is typically carried out at temperatures between 100 and 150°C. The filtrate is now substantially free of ash (i.e. metals) and suspended carbon. It also has low levels of phosphorus at less than 50ppm. These phosphorus levels are not typically achieved through standard de-ashing methods and are important as phosphorus is acknowledged as a catalyst poison.

The filtered product is then processed through a hydro-treater using a combination of guard and active catalysts and hydrogen; at temperatures between 280 and 350°C and pressures between 20 and 80bar. The hydrogenated product can then be processed through a vacuum distillation unit in order to produce base oils of the desired grades. These base oils may require some colour correction which is typically achieved through filtration with a bleaching earth.

Table 1: Summary of the results achieved

	Unit Operation*
Parameter	Feed	2 (Postfiltration)	3 (PostHydrogenation)
Ash (%)	0.69	<0.01	<0.01
Sediment (%)	> 1.5	<0.10	<0.10
Viscosity @ 40C (cSt)	75	38	44
Sulphur (%)	0.6	0.30	<0.05
Calcium (ppm)	1325	< 10	0
Zinc (ppm)	1010	< 10	0
Iron (ppm)	545	<10	0
Phosphorus (ppm)	892	<50	0
Water (%)	9.9	<0.5	<0.5

* Product quality exiting the unit operation

Claims

1. A method of recycling used lubricating oil, the method comprising the steps of:

2. The method as claimed in claim 1, wherein the coagulant is an ethanolamine.

3. The method as claimed in claim 1 or 2, wherein the de-ashing agent consists of an aqueous mixture of an ammonium salt.

4. The method as claimed in any one of the preceding claims, wherein the evaporator runs at atmospheric pressures and temperatures of between 120°C and 140°C.

5. The method as claimed in any one of the preceding claims, wherein the thermal degradation step includes a heat-soak step.

6. The method as claimed in claim 5, wherein the oil dried by the evaporator is heated directly by a furnace or indirectly with an appropriate heat transfer fluid during the heat-soak step.

7. The method as claimed in claim 5 or 6, wherein the oil dried by the evaporator is heated to temperatures between 300°C and 350°C during the heat-soak step, and the oil is maintained between the said temperatures for a period of 30 minutes to 2 hours in a pressure vessel with removable baffles.

8. The method as claimed in claim 6, wherein the oil is heated to between 320°C and 380°C during the heat-soak step, wherein the oil enters a baffled vessel through the top of the vessel and the flow is maintained at such a rate to ensure the oil is maintained for a minimum of 20 minutes at a selected temperature or temperature range.

9. The method as claimed in any one of the preceding claims, wherein the chemical separation step includes separating the degraded additives and/or contaminants by transferred the thermally degraded oil to a reactor to be treated with the de-ashing agent, wherein the reaction of the de-ashing agent with the degraded additives results in the precipitation of the contaminants.

10. The method as claimed in claim 9, wherein the quantities of the de-ashing agent are between 1% and 5%, based on dry weight.

11. The method as claimed in claim 9 or 10, wherein the de-ashing agent is added to water having a temperature of between 60 °C to 90 °C, to allow dissolution before being injected into the reactor.

12. The method as claimed in any one of claims 9 to 11, wherein the coagulant is added to the de-ashing agent and oil, and wherein the coagulant coagulates finely divided carbon present in the oil, and further coagulates the metal precipitates formed by the de-ashing agent.

13. The method as claimed in any one of claims 9 to 12, wherein the coagulant is injected into the oil concurrently with the de-ashing agent.

14. The method as claimed in any one of claims 9 to 13, wherein the coagulant is added

- 12in the reactor in a concentration of between 0.5% and 1%.

15. The method as claimed in any one of claims 9 to 14, wherein the reactor is heated to a minimum of 70°C and the de-ashing agent is allowed to react with the oil for between 20 minutes and 6 hours.

16. The method as claimed in any one of claims 9 to 15, wherein the temperature in the reactor may is gradually increased from 70°C to between 100°C and 120°C to remove the water from the de-ashing agent.

17. The method as claimed in any one of the preceding claims, wherein during the filtration step, the oil is processed through a filter to remove the inorganic salts formed during the de-ashing step and the coagulated carbon.

18. The method as claimed in claim 17, wherein a filter aid is added to improve the quality of the filtrate and the flux rate through the filter.

19. The method as claimed in claim 18, wherein the filter aid includes diatomaceous earth.

20. The method as claimed in any one of claims 17 to 19, wherein filtration is carried out at temperatures between 100°C and 150°C.

21. The method as claimed in any one of claims 17 to 20, the filtrate includes Phosphorus levels as low as 50 parts per million (ppm).

22. The method as claimed in any one of the preceding claims, wherein the hydrotreatment step is hydrogenation through a hydro-treater and a vacuum distillation unit.

23. The method as claimed in claim 22, wherein the filtered product is processed through the hydro-treater using a combination of guard catalysts, active catalysts,

- 13 and/or hydrogen.

24. The method as claimed in claim 22 or 23, wherein the hydrogenation takes place at temperatures between 280°C and 350°C, and pressures between 20 bar and 80 bar.

25. The method as claimed in any one of claims 22 to 24, wherein the base oils are colour corrected by filtration with a bleaching earth.

26. The method as claimed in any one of the preceding claims, wherein the method is generates lower amounts of solid and/or liquid effluent as opposed to known methods.

27. The method as claimed in claim 26, wherein the solid effluent generated is disposable in a landfill due to the solid waste having a low calorific value.

28. The method as claimed in any one of the preceding claims, wherein the conversion yield of used lubricating oil to base oil is between 75 - 90%.

29. The method as claimed in any one of claims 22 to 27, wherein the conversion yield of used lubricating oil to base oil is 90% if all the hydrogenated product is converted to base oils of different grades.

30. The method as claimed in any one of claims 1 to 27, wherein the conversion yield of used lubricating oil to base oil is 85%.