Field

[0001 ] The invention relates to purification of oils. Priority

[0002] This application claims priority from United Kingdom Application GB 1409995.6, the entire contents of which are incorporated herein by cross-reference.

Background

[0003] Global demand for base oil is running at around 36 million tonne per annum. Demand is forecast by industry sources to increase incrementally in coming years. Over the past 10 years, a progressively increasing proportion of the total demand for base oil products is being met by refining increasingly more difficult to refine sour crude oil, and by re-refining used lubricant and industrial oils. These more diverse sources of raw material for refining, combined with increasing demand for more consistent and higher quality base oils and industrial oil products, is creating challenges for refining processes. The ongoing challenges are leading to more diverse and complex feedstock for key hydrogen based refining unit operations, for example catalytic hydrogenation. More difficult feedstock challenges the cost of refining, reliability of operation and consistency of refined product quality. Core challenges relate to impurities in feedstock.

[0004] There are many undesirable impurities that, when present in the feed to a catalytic hydrogenation process, increase the cost and decrease the reliability of catalytic hydrogenation as viable technology in the production of refined hydrocarbon products. When present in the reactor feed, particular impurities can poison catalysts or foul reactor systems. The nature of the poisoning and fouling can vary, and may include mechanisms such as polymerisation reactions, bonding with the active sites on a catalyst, blocking the pores in a catalyst system and fouling of fixed catalyst beds.

[0005] Similar problems exist in many and varied hydrogenation processes including, for example, processing vegetable oils and manufacturing petrochemicals. [0006] One of the core challenges with refining impure raw materials is that some impurities, for example phosphates, have the potential to generate strong conjugate acid-base systems that release complexing ligands or form insoluble salt systems which can poison or foul catalytic processes.

[0007] Refining of used oil demonstrates the challenge particularly well. Used oil feed to refining operations might contain a blend of oil products collected after use, including for example industrial, crankcase, hydraulic, gear and transmission oils. Modern oil and lubricant systems that form the basis of these materials carry a range of chemical additi ves that persist in the oil once used. The additive chemicals and systems typify the types of poisoning and fouling substances which may be encountered when feeding complex and impure feedstock to hydrogenation processes.

[0008] Additives which are insoluble in oil may be introduced into a lubricant using an alkylated complexing system for metal components of the additive. For example dialkyl dithiophosphates are used to complex zinc so as to solubilize the zinc in the oil. Various other metal complexing systems are also in current use. The interactions of these materials with oil s are further complicated by other additives with strong detergency and surface chemical properties, including antifoam agents.

[0009] The metallic components of these additive systems can be removed by complexing the metal species out of the oil leaving an oil soluble alkylated ligand system in the treated oil. The residual alkylated ligands however remain soluble in the oil and can represent catalyst poisoning and fouling impurities in hydrogenation reactor feed. Problems of fouling and catalyst degradation by, for example, phosphates are well documented in crude oil refining, as well other applications for catalytic hydrogenation processes. Pre-treatment of organometallic complexes contained in oil by complexing out the metal and separating the resultant metal salt is an inadequate pre-treatment of oil prior to hydrogenation since the residual oil soluble alkylated ligand system remains a catalyst fouling and poisoning problem.

[00010] There is therefore a need for an improved method for removing impurities such as metal complexing species from oils so as to facilitate oil recycling.

Summary of Invention [0001 1 ] The invention provides a method for reducing the concentration of a contaminant in an oil. The method comprises: a) providing a mixture of the oil having the contaminant therein, hydrogen, and an aqueous solution of a basic additive; and then b) exposing the mixture to a hydrogenation catalyst at a reaction temperature between 200°C and about 500°C and at a reaction pressure sufficient for at least some of said aqueous solution to exist as a partially condensed vapour at said temperature, so as to form a multiphase product mixture and then c) separating the oil from the product mixture.

[00012] The following options may be used in conjunction with the invention as described above, either individually or in any suitable combination.

[00013] The contaminant may comprise an acid or a conjugate base thereof, or may comprise a substance which, under the conditions of step b), forms an acid or a conjugate base thereof, wherein the acid or conjugate base is capable of poisoning or fouling the hydrogenation system. It may for example comprise, or be, a phosphorus containing compound. Alternatively or additionally it may comprise, or be, a sulfur containing compound. The basic additive may be capable of inhibiting or preventing the poisoning or fouling of the hydrogenation system by the acid or conjugate base. It may be capable of displacing the acid or conjugate base from the catalyst. It may be a stronger base than the conjugate base of the acid, or of the contaminant.

[00014] In step b), at least some of the aqueous solution may be in the form of a partially condensed vapour. At least some may be in the form of bulk water. Step b) may be conducted in a sealed reactor. It may be conducted in a reactor which is capable of excluding air and/or oxygen. It may be conducted in a reactor which is capable of maintaining the required pressure during step b).

[00015] The method may include the step of dissolving the basic additive in water to fonn the aqueous solution prior to said solution being combined with the oil and the hydrogen to fonn the mixture of step a).

[00016] The aqueous solution of the basic additive may be combined with the oil and the hydrogen after the oil and the hydrogen have been brought to about the reaction temperature and to about the reaction pressure.

[00017] The reaction pressure may be about 2 to about 18 MPa. [00018] The basic additive may be calcium hydroxide, potassium hydroxide, ammonium hydroxide, sodium hydroxide, ammonia or some other water soluble hydroxide, or may be an organic amine. It may be a mixture of any two or more of these. Organic amines may form ammonia during step b).

[00019] The method may comprise the preliminary step, prior to step a), of analyzing the oil so as to determine the concentration of the contaminant therein and thereby also the mass flow rate of said contaminant, and then identifying from said concentration a suitable concentration and flow rate of the solution of basic additive for use in step a). The aqueous solution of the basic additive may therefore be supplied to the hydrogenation reactor at a mass flow rate that will displace the contaminating conjugate base into the water phase.

[00020] The basic additive may be present in step a) in sufficient quantity to ensure at least about 90% removal of the contaminant, optionally at least about 99% thereof. The molar flow rate of the basic additive may be about the same as the molar flow rate of the contaminant or may be greater than the molar flow rate of the contaminant. It may be sufficient to prevent or to substantially prevent fouling of the catalyst.

[00021 ] The method may additionally comprise passing the product mixture through a cross- exchanger which heats the oil and the hydrogen, and optionally also the aqueous solution of basic additive, prior to step b).

[00022] Step c) may include the step of separating the product mixture into a gaseous phase containing unreacted hydrogen and a liquid phase containing product oil. The unreacted hydrogen in the gaseous phase may then be recycled so as to produce the mixture of step a). In doing so, the gaseous phase may be cooled so as to condense a liquid therefrom. Alternatively or additionally the gaseous phase may be cooled by exposing it to a cooling liquid, e.g. an aqueous liquid, so as to produce a liquid containing both aqueous and non-aqueous phases. The gaseous phase may be scrubbed following the condensing so as to remove impurities such as hydrogen sulfide therefrom. The liquid may be separated into an aqueous phase and a non-aqueous phase. The non-aqueous phase may be combined with the liquid phase from the separating step.

[00023] The liquid phase from the separating step may be cooled. An aqueous stream may subsequently be separated therefrom. [00024] The product mixture may be degassed prior to separating the aqueous stream therefrom. The degassing may comprise a vacuum degassing step. It may also comprise a step of degassing at or above ambient pressure prior to the vacuum degassing step. The degassed stream may be combined with water prior to separating the aqueous stream from the cooled liquid phase. Thus the degassed stream may be washed with water so as to remove water soluble contaminants.

[00025] The invention also encompasses an oil produced by the method described above.

Brief Description of Drawings

[00026] Fi gure 1 shows a diagrammatic representation of one embodiment of the method of the present invention.

Description of Embodiments

Definitions

[00027] In the present specification the following definitions apply.

[00028] Feed oil: any oil used as a feedstock for the method. Commonly an "oil" will be an aliphatic oil, a naphthenic oil, an aromatic oil, a natural or synthetic ester base oil (typically a tri-glyceride) or a mixture of such oils. In this specification the tenn "base oil" and related tenns do not indicate that the oil is, or contains, a base.

[00029] Contaminant: any undesirable substance within the feed oil. Common contaminants include sulfurs, sulphates, organosulphates (e.g. sulphate esters), phosphorus, phosphates, organophosphates (e.g. phosphate esters), phosphonates, organophosphonates (e.g. phosphonate esters), thiophosphates, organothiophosphates (e.g. thiophosphate esters), dithiophosphates, organodithiophosphates (e.g. dithiophosphate esters), other metal complexing species etc. Other possible contaminants include carboxylic esters and other carbonyl compounds, halogenated compounds e.g. halogenated hydrocarbons, oxidation products of oils etc. More than one contaminant, and more than one type of contaminant, may be present in the oil used in the present method. Contaminants may generate acids or their conjugate bases in situ in the hydrogenation reactor of the present method. In such cases, the in situ generated acids or conjugate bases may be referred to herein also as contaminants. [00030] Hydrogen: unless otherwise stated, this refers to elemental, or molecular, hydrogen (H ₂ ). It is commonly either in a gaseous state or in solution or both.

[00031 ] Base: a compound capable of accepting a proton, or a Lewis conjugate base, being any compound that can donate a pair of non-bonding electrons. The "basic additive" of the present invention is a base. In the present invention, basic additives may be hydroxides or compounds which react with water to produce hydroxide ions. They may be alkalis. Suitable basic additives include for example ammonia, ammonium hydroxide, sodium hydroxide, potassium hydroxide, calcium hydroxide, aromatic and/or aliphatic organic amines, other water soluble metal hydroxides and mixtures of any two or more of these. Ammonia or ammonium hydroxide may be useful in that they may reduce or avoid the saponification reactions that can at time arise from use of metal hydroxides such as sodium hydroxide. The strength of a base may be characterized by its p b: the lower the pKb, the stronger the base. p b literature values for common bases usable in the present invention include ammonia (4.75), methylamine (3.4), ethylamine (3.3), calcium hydroxide (2.43), potassium hydroxide (0.5) and sodium hydroxide (0.2). It should be noted that pKb values for a particular base will vary with temperature due to increased dissociation at higher temperatures. Nevertheless, literature values of pKb, which are generally measured at ambient or standard temperature, are useful in determining suitable bases for use in the present invention for particular contaminants. The present method uses a solution of a basic additive, which is a base. This solution may optionally have undissolved basic additive (or other undissolved materials) present. Thus, for example, a solution containing dissolved basic additive and undissolved (e.g. suspended) basic additive would be within the scope of the term "solution of a basic additive". It should also be noted that "basic additive" as used herein refers to an intentionally added component of the method. By contrast, "conjugate base" is used to refer to the conjugate base of an acid where the acid or the conjugate base is a contaminant that is present in the oil as it enters the method or which is generated from such a contaminant.

[00032] Hydrogenation catalyst: any substance capable of catalyzing the reaction of hydrogen with an organic substance. The catalyst may be a metal catalyst or a mixed metal catalyst, optionally supported. The metal(s) may be a transition metal. The metal may be for example molybdenum, tungsten, chromium, iron, cobalt, nickel, platinum, palladium, iridium, osmium, ruthenium, copper, manganese, silver, rhenium, rhodium, technetium, vanadium, or any suitable combination of two or more of these. These may be in Raney form. They may be in the form of particles embedded in and/or immobilised on a support, e.g. carbon, silica, alumina, titania, aluminium or other suitable support. It may be a sulphided metal catalyst. Suitable catalysts include sulphided Ni/Mo (e.g. 2% Ni/7% Mo) on γ-alumina, platinum on γ-alumina and palladium on γ-alumina. The latter two may be reduced (e.g. hydrogen at 200-800°C) prior to use. The catalyst is commonly a solid catalyst. It may be insoluble in the liquids used in the method. It may be a heterogeneous catalyst.

[00033] Poisoning: deactivation of a catalyst. This is commonly by way of adsorption of species on the surface of the catalyst so as to reduce the activity of the catalyst. Common catalyst poisons include certain sulfur and phosphorus containing compounds. Poisoning may not necessarily result in complete deactivation of a catalyst, but may instead result in partial deactivation, i.e. reduction in catalytic activity, of a catalyst.

[00034] Critical point: the temperature and pressure for a particular substance (in the present specification water unless otherwise specified) at which an increase in either temperature or pressure results in the substance existing in a supercritical phase which is neither liquid nor vapour. The temperature at the critical point is referred to herein as the critical temperature and the pressure at the critical point is referred to herein as the critical pressure.

[00035] Conjugate base: the product of removing a proton from an acid. For example the conjugate base of acetic acid is acetate ion.

[00036] Partially condensed vapour: a fine dispersion of liquid droplets in a gas or vapour. The partially condensed vapour may be a mist or a fog. The droplets may have a number average or volume average diameter of less than about 100 microns, or less than about 50, 20, 10, 5, 2 or 1 micron. They may have a number average or volume average diameter of about 1 to about 100 microns, or about 1 to 50, 1 to 20, 1 to 10, 1 to 5, 5 to 100, 10 to 100, 50 to 100, 5 to 50, 5 to 20, 10 to 50, 10 to 20 or 20 to 50 microns, e.g. about 1 , 2, 3, 4, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90 or 100 microns.

[00037] Multiphase: consisting of more than one physical phase. Commonly this term will refer to a system in which there are more than one liquid phase, e.g. a water phase and an oil phase which is immiscible with the water phase. In some cases it may refer to a system in which two different types of phase coexist, e.g. one or more gas phases and one or more liquid phases. It may also refer to a system in which more than one physical phase coexists, e.g. solid, liquid and gas. In the reactor of the present invention, there will commonly be a bulk liquid water phase, a bulk liquid oil phase, a partially condensed water vapour phase, possibly a partially condensed oil vapour phase and a water vapour phase, as well as a solid catalyst phase.

[00038] Heat exchanger: a device for transferring heat into a fluid. Heat exchangers may comprise an electrical heating element or a combustion heating facility or may comprise some other form of heating.

[00039] Cross exchanger: a heat exchanger which transfers heat from a first (hotter) fluid to a second (cooler) fluid without chemical reaction of the first fluid and commonly without mixing of the two fluids.

[00040] Aqueous: containing water and being largely miscible with water. An aqueous liquid may be at least 50% water on a weight basis, or at least about 60, 70, 80, 90, 95 or 99% water.

[00041 ] An aspect of the present invention is that it allows for reduction, optionally prevention, of fouling or poisoning of a catalyst, a catalyst bed, a catalytic reactor or a catalytic reactor system during catalyzed hydrogenation of a feed oil contaminated by compounds capable of undergoing poisoning or fouling processes or reactions within the reactor system, while also reducing the concentration of a contaminant in the feed oil. There may be more than one contaminant in the feed oil. In this instance, the present method reduces at l east one of these contaminants, and may optionally reduce more than one, optionally all, of the contaminants. The reduction in this case is relative to the fouling or poisoning, or of the concentration of the contaminants using conventional hydrogenation methods.

[00042] The inventors have found that many oils which may be purified by catalytic

hydrogenation are contaminated by species which can reduce the efficiency of the catalyst over time, i.e. they can act as catalyst poisons or catalyst foulants. These species may be intentionally added to oils or may be derived from compounds which are intentionally added. Some contaminants, for example, are metal complexing agents such as organophosphorus compounds. The metals may be reasonably readily removed from these, leaving the complexing agent as a contaminant in the oil. These may be converted under hydrogenation conditions to phosphorus containing acids or conjugate bases thereof. Under hydrogenation conditions used hitherto, these may act as catalyst poisons. The inventors have surprisingly found that the use of certain basic additives, e.g. hydroxide, can inhibit or prevent this fouling. It is thought that the basic additive may displace such acids or conjugate bases from the catalyst, e.g. from the catalyst surface, and allow them to be removed in the aqueous portion of the reaction mixture. It is further thought that the basic additive itself may subsequently be displaced from the catalyst by sulphidic materials and also be removed in the aqueous portion of the reaction mixture. Alternatively, it is possible that the presence of the basic additive may prevent or restrict adsorption of the acids or conjugate bass to the catalyst.

[00043] The inventors consider that it is important that conditions pertain within the

hydrogenation reactor during practice of the method in which the water liquid-vapour equilibrium is biased towards the liquid phase to create a partially condensed vapour, as well as water being present in the form of bulk water and also in the vapour phase. This requires suitable conditions of temperature and pressure that allow such phases to coexist. The inventors hypothesise that, at the reaction conditions defined herein, many of the reactive contaminant species convert from being oil soluble to being water soluble during the hydrogenations reactions occurring in the reactor. The presence of a controlled water phase (high surface area vapour plus finely divided liquid droplets in dynamic equilibrium) is therefore thought to provide a mechanism to draw converted contaminant away from the reaction site on the catalyst surface and into the water phase. This therefore biases the relevant equilibriums towards complete reaction.

[00044] The contaminants discussed above may be present in the oil prior to entering the method at a level of hundreds or even thousands of ppm on a weight/volume basis or a weight/weight basis. They may be present at up to about lOOOOppm, or up to 5000, 2000 or lOOOppm.

[00045] The hydrogenation reaction is commonly conducted in a hydrogenation reactor. As discussed elsewhere, feed oil and/or one or more reagents may be preheated before they are fed to the reactor. They may be preheated to a temperature at or near the desired reaction temperature (described elsewhere herein). In a common embodiment, a recycled hydrogen stream is combined with the feed oil and the resulting stream is mixed with an aqueous solution containing the basic additive (such that the molar flow of the basic additive may be equal to or greater than the molar flow of the contaminant). This is then heated using a heat exchanger and optionally also a cross exchanger, to about the desired reaction temperature. Alternatively, the combined hydrogen and feed oil is heated using a heat exchanger and optionally also a cross exchanger, to about the desired reaction temperature and the aqueous solution containing the basic additive is then added. In this option, the aqueous solution may also be preheated, optionally to about the desired reaction temperature, prior to combining with the hydrogen and feed oil.

[00046] The quantity of basic additive is preferably sufficient to allow for at least about 90%, optionally at least about 95 or 99%, optionally substantially 100%, removal of targeted contaminants. The basic additive may be in a molar excess over the acid contaminant or the conjugate base contaminant. If the contaminant is in the form of a conjugate base, the basic additive may be in at least about 0.9 mole equivalent relative to the conjugate base, or at least about 0.95, 0.99, 1, 1 .1, 1 .2 or 1.5 mole equivalent, or about 0.9 to about 2 mole equivalents, or about 0.9 to 1.5, 0.9 to 1.1 , 0.9 to 1 , 1 to 1 .5 or 1 to 1.2 mole equivalents, e.g. about 0.9, 0.95, 0.99, 1 , 1.1 , 1.2, 1 .3, 1 .4, 1.5, 1.6, 1 .7, 1 .8, 1 .9 or 2 mole equivalents.

[00047] As noted elsewhere herein, the basic additive may be dissolved in water prior to combining the resulting basic solution with the feed oil. It will be recognized that the basic solution may be corrosive, and that the corrosiveness will depend in part on the concentration and type of the basic additive in the solution. As also noted elsewhere, sufficient water should be present to ensure that a dynamic liquid/vapour phase water equilibrium is present in the hydrogenation reactor. The ratio of water to feed oil required to achieve this will depend on the exact conditions used in the hydrogenation reactor. Thus it is preferred to use a sufficient ratio of water to basic additive so as to ensure that the basic additi ve and the contaminants remain mobilized by the water phase before and after catalytic reaction and that sufficient water is present during the reaction for the required equilibrium to be established. On the other hand, increasing the amount of water that is used will increase the overall volume of liquid passing through the reactor, will increase the energy consumption of the process, may affect catalyst l ongevity and will increase the amount of water that needs to be separated by the liquid-liquid separator. The actual amount of water may be selected so as to optimize the tradeoff between these different considerations. Commonly the ratio of oil to basic solution will be between about 200: 1 and about 5: 1 on a volume basis using a basic additive concentration between 0.1 and about 10 molar.

[00048] The basic aditive concentration may be for example between about 0.1 and about 5, 0.1 and 2, 0.1 and 1 , 0.1 and 0.5, 0.5 and 10, 1 and 10, 2 and 10, 5 and 10, 1 and 5 or 0.5 and 2M, e.g. about 0.1 , 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1 , 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 6, 7, 8, 9 or l OM. The basic additive may have a pKb at standard temperature and pressure of between about 0.1 and about 5, or about 0.1 to 4, 0.1 to 3, 0.1 to 2, 1 to 5, 2, to 5, 3 to 5, 1 to 4, 2 to 5 or 3 to 4.5, e.g. about 0.1, 0.2, 0.3, 0.4, 0.5, 1 , 1.5, 2, 2.5, 3, 3.5, 4, 4.5 or 5.

[00049] The outlet oil from the reactor will contain the oil and may additionally comprise one or more of reduction products from the contaminants, salts (e.g. obtained from the contaminants or from reduction products thereof), water, unreacted hydrogen and gaseous by-products of hydrogenation, This mixture is at elevated temperature and pressure as it exits the hydrogenation reactor and may be passed to a cross exchanger where some of its heat energy is recovered so as to preheat reagents etc. (e.g. one or more of feed oil, hydrogen, aqueous solution) prior to their entering the reactor. It may then be passed to a high pressure gas-liquid separator. This is primarily to remove gaseous hydrogen and gaseous hydrogenation by-products from the oil stream. It may be maintained at high pressure to reduce the need to recompress the recovered hydrogen prior to use. The gas stream leaving the high pressure gas-liquid separator will primarily contain hydrogen gas and will often also contain some hydrogen sulfide and volatile oil components such as high volatility hydrocarbons. It may also contain some water vapour.

[00050] This gas stream may then be mixed with water or cold oil. This serves to cool the stream and condense and/or entrain the components of lower volatility. Alternati vely the stream may be cooled using a cooler or heat exchanger. The entrained lower volatility components may then be separated from the hydrogen stream in a hydrogen separator (gas-liquid separator). The gaseous stream, which is now largely hydrogen, may then be passed to a scrubber so as to further purify it and the scrubbed hydrogen may then be recycled into the reactor. The scrubber may remove contaminants such as sulfides and mists. Suitable scrubbers, and methods for scrubbing, are well known in the art. It may for example be or comprise a water scrubber, an oxidant (e.g. peroxide) scrubber, a base (e.g. hydroxide) scrubber, an entrainment separator or some other suitable type of scrubber. The liquid stream exiting the hydrogen separator contains water together with the recoverable oil components. These may then be separated from one another in a liquid-liquid separator and the non-aqueous (commonly predominantly

hydrocarbon) stream rejoined with the oil stream exiting the high pressure liquid-liquid separator. It should be noted that in this context, reference to "gas" or "gaseous" includes any substance in a gaseous state and includes vapours (i.e. gases below their critical temperature or below the boiling point of the corresponding liquid at the pressure at the time) and gases above their cri tical temperature (or above the boil ing point of the corresponding liquid at the pressure at the time).

[00051 ] In some embodiments, the oil stream, having had most of its hydrogen removed in the high pressure gas-liquid separator, may be depressurized, commonly to approximately ambient pressure, and then passed to a liquid-liquid separator so as to remove waste water therefrom. It is at this point at which much of the water added at an early stage of the method may be removed from the oil, together with dissolved materials including hydrogenation byproducts, water soluble impurities which persist from the feed oil, salts etc.

[00052] In an elaboration of this, in other embodiments the oil stream from the high pressure gas-liquid separator described above may be passed to a low pressure gas-liquid separator. In this context, low pressure refers to pressures at or about or somewhat above atmospheric pressure (commonly about 100 to about 500kPa), but lower than the pressure of the high pressure gas-liquid separator. The purpose of this separator is to remove any residual oil-soluble high volatility substances from the oil stream which might otherwise compromise product quality. This separator commonly simply vents the oil stream at around ambient pressure so as to allow residual volatiles to flash off. In one alternative, the high pressure gas-liquid separator is not used. In this alternative, the oil from the reactor is passed directly to the low pressure separator. Vented gases would then include substantial amounts of unreacted hydrogen together with volatile oil components. The hydrogen may then be separated from oil components, scrubbed and recycled to the reactor as described above, following recompression and, if necessary, further purification, and the volatile oil components returned to the oil stream also as described above. The return may be before the low pressure gas-liquid separator, or may be into the low pressure gas-liquid separator. It will be appreciated that the oil exits the reactor at high pressure and is later stripped at reduced pressure. The reduction in pressure of the oil may occur in a single step or may be conducted in a number of steps. Thus the pressure may be reduced in a pressure reduction valve following the high pressure gas-liquid separator. Alternatively it may reduce pressure somewhat in the high-pressure gas-liquid separator and then reduce pressure sufficient to pass to the low pressure gas-liquid separator in a separate pressure reduction valve. Other alternatives will be readily apparent to the skilled person.

[00053] A useful option that may be used in conjunction with the present invention is the use of a degassing or stripping step. Thus the oil which comes from the reactor (commonly by way of a high pressure gas-liquid separator and a low pressure gas-liquid separator) may be stripped in a degassing unit. This may serve to improve the quality of the product refined oil. It is thought that sulfur compounds which are frequently present in the feed oil may at least partially persist through the reduction step or may be converted at least in part to compounds which are difficult to remove, or are incompletely removed, in the high and low (i.e. approximately ambient) pressure gas-liquid separators. Sulfur compounds which may exit the high pressure reactor in the oil, include hydrogen sulfide and other trace sulfides and bisulfides such as ammonium hydrosulfide. This may in part be due to the relatively low volatility of some of these compounds and/or to the elevated raiscibility of some of the compounds at elevated pressure and may also in part be due to the relatively high solubility in the oil of related sulfide compounds. The continued presence of such compounds compromises product quality. In order to overcome this, a stripping (degassing) step may be introduced into the process. This commonly applies moderately elevated temperatures and reduced pressure to the oil stream so as to remove sparingly volatile or entrained substances although other stripping methods are also

contemplated by the invention. In this context, the term "elevated temperature" refers to temperatures above ambient temperature and the term "reduced pressure" refers to pressures below atmospheric pressure, or sub-ambient pressure. The temperature for this step is commonly at least about 30°C, and may be at least about 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95 or 100°C, or may be between about 30 and about 100°C, or between about 50 and 100, 30 and 50, 30 and 80, 50 and 80, 60 and 100 or 60 and 90°C, e.g. about 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95 or 100°C, The pressure is commonly less than about 90kPa, or less than about 80, 70, 60, 50, 40, 30, 20, 10, 5, 4, 3, 2 or lkPa, or about 0.1 to about 90kPa, or about 0.1 to 50, 0.1 to 10, 0.1 to 5, 0.1 to 1 , 0.1 to 0.5, 1 to 10, 2 to 10, 5 to 10, 1 to 5, 1 to 90,

10 to 90, 50 to 90, 10 to 50 or 2 to 5kPa, e.g. about 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1 , 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 6, 7, 8, 9, 10, 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80 or 90kPa. These pressures are absolute pressures. Thus a pressure of l OkPa, for example, will be equivalent to a pressure of around -90kPaG (i.e. 90kPa below atmospheric pressure). It will be understood that in order to achieve a particular level of stripping, a higher temperature will generally allow for a less strong vacuum (i.e. higher pressure). The conditions used for this stripping step may be sufficient to remove sufficient volatile materials that the resulting refined

011 meets the required standard(s). Further, the higher the pressure and/or the lower the temperature, the longer time will be required in order to achieve the required level of stripping. The skilled person will readily be able to determine suitable conditions for the third variable of temperature, pressure and time if supplied with two of these. The time for stripping (i.e. the residence time of the oil in the degasser) is commonly about 0.5 to about 10 minutes, or about 0.5 to 5, 0.5 to 2, 0.5 to 1, 1 to 10, 2 to 10, 5 to 10, 1 to 5 or 2 to 5 minutes, e.g. about 0.5, 1 , 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 6, 7, 8, 9 or 10 minutes, but may be longer or shorter than this. This aspect of the process has been described in provisional application AU2014900905 and in International Application PCT/AU2014/000687 which claims priority therefrom, the entire contents of both of which are incorporated herein by cross-reference.

[00054] It is preferred that the stripping/degassing step described above be conducted before the oil is exposed to any relatively more oxidizing conditions than pertain immediately after the product mixture leaves the hydrogenation reactor, or before exposure to any oxidants. This step may be conducted under reducing conditions. It may be under non-oxidising conditions. The oil exiting the reactor may be maintained under non-oxidising conditions until after it exits the degassing unit. Oil exiting the reactor retains a certain amount of hydrogen. It may be hydrogen rich and may be hydrogen saturated. It is therefore under relatively reducing conditions. If the oil is subjected to relatively more oxidising conditions before the stripping/degassing step, some reactor product components may react (e.g. oxidise) and thereby may persist in the oil or be rendered more difficult to remove in the stripping/degassing step. This may result in these compounds or compounds derived therefrom persisting in the final product oil. These may cause the oil to fail certain of the standard quality tests described earlier. It is therefore desirable to prevent such reactions. This may be achieved by maintaining chemically non-oxidising conditions in the oil until after the stripping step. It may be facilitated by use of piping and other components between the reactor and the degasser which prevent ingress to the oil of oxidants such as oxygen.

[00055] The degassing unit used for the degassing step described above may be for example a vacuum tank degasser. This may comprise a horizontal, vertical or round vessel. A vacuum is created in the vessel. As well as serving to remove volatiles, this can also draw the oil into the tank. When the oil enters the tank, it may be atomised or sprayed into the vessel or may be distributed to a layer of internal baffle plates or other high surface area device designed for the oil to flow in a thin, commonly laminar, film, and is exposed to a vacuum that forces volatile materials to escape from the oil. In a particular embodiment therefore, the degassing or stripping may comprise atomising or spraying the oil into a vacuum chamber by means of one or more nozzles. This may be conducted without the need for internal baffle plates or similar. The vacuum pump passes the escaping volatiles from the vessel and discharges them, preferably after scrubbing to remove toxic products. Alternatively a cyclonic stripping unit may be used, in which the oil passes in a thin film around the inner walls of a vessel whilst a vacuum is applied to the inside of the vessel.

[00056] The stripped oil exiting the degassing unit may have undesirable volatile components stripped from it. It shoul d be understood that there may be a residual level of volatiles, however these will generally be of a form, concentration and chemistry that is compatible with product quality objectives. They may be present at a level which is acceptable for subsequent use, for example as a transformer oil, and may be present at a level sufficiently low to meet relevant industry and/or regulatory standards. Following the stripping/degassing, it may be beneficial to extract the oil stream with water. This comprises the steps of adding water to the oil stream exiting from the degassing unit and subsequently separating the water from the oil stream so as to remove water soluble components such as salts. It may comprise the step of agitating the oil and water stream so as to improve contact and hence improve extraction. It may also comprise the step of drying the oil stream after separating the water therefrom, so as to remove any residual water that may be present. The water extraction may be conducted using any suitable water extraction device, for example an in-line mixer, a countercurrent extractor etc.

Alternatively, of course, the water that remains in the oil from the hydrogenation reactor may serve to extract any water soluble materials from the oil, and may be separated in a liquid-liquid separator as described above.

[00057] The inventors have found that certain oil soluble ligand systems can represent a problem for catalytic hydrogenation systems. It is hypothesized that de-alkylation of such ligand systems under catalytic hydrogenation systems can generate a strong conjugate base which lead to commonly observed fouling and poisoning reactions in catalytic hydrogenation processes.

[00058] The present invention in one form represents a method for reducing or preventing catalyst fouling and/or poisoning during catalytic hydrogenation refining of oil, particularly hydrocarbon oils. Contaminants in these oils may include metal-complexing agents. They may for example include any one or more of phosphorus, phosphate, alkylated phosphate and thiophosphate, carbamate, sulfurs, sulphonated and sulphated additives and detergents, other de- metallised alkylated ligands, glycols, esters and oxidised mineral hydrocarbon oil. The method may produce refined and/or purified hydrocarbon, which may be suitable either for fractionation to produce high quality fuel and base oils, or for further processing to produce higher quality base oil or fuel. The invention therefore encompasses a method for hydrogenation refining oil contaminated by phosphorus, phosphate, phosphonated, sulfurs, sulphated and sulphonated hydrocarbons, alkylated thiophosphates or other contaminants, for example detergents, that can potentially undergo conversion to a corresponding acid, e.g. mineral acid, and/or ligands in the hydrogenation system. This may be accomplished by incorporating a method for displacing a complexing ligands from catalyst systems and blocking the formation of mineral acid. In this context, a ligands is taken to be a compound which can complex a metal atom or metal ion. It is one example of a contaminant in the feed oil of the invention.

[00059] In the method, a controlled pH separable water phase is introduced into the dynamic reaction system. Thus a controlled water feed is provided along with feed oil to a hydrogenation reactor to control reaction conditions, reactant and product partitioning and reactant equilibria in a dynamic multiphasic reaction environment. This may be achieved by combining the feed oil with pH adjusted water where the pH is adjusted using a stronger conjugate base than the corresponding conjugate base in the feed impurity at a rate such that resultant salt can be fully solubilised by the pH adjusted water phase. It is hypothesized that this prevents the acid or conjugate base thereof from poisoning the catalyst, since the basic additive in the pH adjusted water can displace any conjugate base interacting with the catalyst surface. Consequently the acid or conjugate base remains in the water phase and can be removed from the hydrogenation reactor.

[00060] The pH adjusted water (i.e. water plus basic additive) may be added to the oil at an oikwater ratio of between about 200: 1 and 5: 1 on a volume basis. The ratio of oil phase to water phase may be about 150: 1 to 5: 1, 100: 1 to 5: 1 , 50: 1 to 5: 1 , 20: 1 to 5: 1 , 10: 1 to 4: 1, 200: 1 to 10: 1 , 200: 1 to 20: 1, 200: 1 to 50: 1 , 200: 1 to 100: 1 , 100: 1 to 20: 1 or 100: 1 to 50: 1 , e.g. about 200: 1, 150: 1, 100: 1 , 90: 1, 80: 1, 70: 1, 60: 1 , 50: 1 , 40: 1 , 30: 1, 20: 1 , 15: 1 , 10:1 or 5: 1. Suitable ratios may result in the presence within the reactor of a free phase of water. They may ensure that there is sufficient water phase to maintain adequate mobility and solubility of salts.

[00061 ] The method of the present invention may be practiced as a continuous process, although in some cases it may be alternatively practiced as a batchwise process. In the case of a continuous process, ratios of reactants etc, described herein should be taken to be ratios of fl ows of those reactants. Thus for example where it is stated (above) that the pH adjusted water may be added to the oil at an oikwater ratio of between about 200: 1 and 5: 1 on a volume basis, when practiced as a continuous process this requires the flow rate of the oil to be between about 5 and 200 times that of the water on a volume basis.

[00062] The hydrogen may be introduced into the oil at a pressure of about 2 to about 18MPa, or about 2 to 15, 2 to 10, 2 to 5, 5 to 15, 10 to 15, 3 to 10 or 5 to l OMPa, e.g. about 2, 3, 4, 5, 6, 7, 8, 9, 10, 1 1, 12, 13, 14, 15, 16, 17 or 18M Pa. It may be introduced into the oil at a pressure below the critical pressure of water. These pressures may pertain in the hydrogenation reactor (i.e. they may refer to the reaction pressure). The hydrogen may be introduced in a sealed system so as to produce suitable reducing conditions.

[00063] The reaction mixture, comprising the feed oil, hydrogen, a basic additive and water, may be heated to a reaction temperature of between about 200°C and about 500°C. The temperature will commonly be below the critical temperature of water (about 374°C). The reaction temperature may be between about 200 and 400, 200 and 300, 300 and 500, 300 and 400, 250 and 350, 250 and 374 or 300 and 374°C, e.g. about 200, 250, 300, 310, 320, 330, 340, 350, 360, 370, 374, 380, 390, 400, 450 or 500°C. The pressure in the reactor should be such that at least some of said aqueous solution exists as a partially condensed vapour. It is preferably a pressure at or about the vapour-liquid phase boundary of the phase diagram at the selected reactor temperature. It may be within about 10% of the pressure at or about the vapour-liquid phase boundary at the selected reactor temperature, or within about 9, 8, 7, 6, 5, 4, 3, 2 or 1 % thereof. It may be a pressure on the liquid side of the vapour-liquid phase boundary of the phase diagram. In particular, the temperature and pressure in the hydrogenation reactor may be sub- critical, i.e. the temperature and pressure should not both be above the critical point for water. The heating may be by means of a simple heat exchanger or heater, which may be electrical or may be a combustion heater or some other suitable heater. The reaction mixture or at least a portion thereof (e.g. the feed oil/hydrogen mixture prior to combination with water and basic additive) may be preheated before this heating by passing through a cross-exchanger in which heat is transferred from the product mixture exiting the hydrogenation reactor to the reaction mixture or portion thereof. It is preferred that within the hydrogenation reactor, the conditions are maintained below the critical point for water and around or below the phase transition of water between liquid and vapour (i.e. biased towards the liquid phase, or within the liquid region of the water phase diagram) so as to ensure the presence of discrete vapour and liquid water phases. [00064] The heated reaction mixture is exposed to a hydrogenation catalyst in a hydrogenation reactor. The hydrogenation catalyst is commonly a heterogeneous catalyst, i.e. it is not soluble in the reaction mixture. The reaction may be passed over and/or through a fixed bed of hydrogenation catalyst at the reaction temperature and pressure as described above. The catalyst may be present in the hydrogenation reactor in the form of a supported catalyst, a packed bed or a fluidized bed or in some other form.

[00065] After the reaction mixture passes out of the hydrogenation reactor, it may be cooled. It may be at least partially depressurized. The resulting product stream may then be separated into oil, water (now wastewater) and gas phases. The oil phase may be collected as the primary product.

[00066] The gas phase, which consists mainly of hydrogen may be recycled into the process, commonly after scrubbing to remove acidic gases such as hydrogen sulfide. The gas phase may also remove some hydrocarbon products which may be condensed and returned to the oil phase. During the recycling it is advantageous to maintain the gas phase at high pressure so as to reduce the energy required to recompress it to a suitable pressure for reaction in the

hydrogenation reactor.

[00067] The improved method described herein may remove or reduce the need to pre-process raw materials to remove compounds with the potential to a) undergo Lewis acid/base complexing reactions, b) produce mineral acid by-products from hydrogenation reactions, c) induce salt crystallisation or deposition within the hydrogenation reactor and/or on the hydrogenation catalyst, and/or d) form gelatinous or viscous interphase materials with the propensity to foul catalytic systems. The method generally improves the hydrocarbon yield, increases the operational reliability and decreases the number of process steps required to catalytically hydrogenate difficult or hydrocarbon contaminated feedstock

[00068] The feed stream may contain (or comprise or consist of or consist essentially of):

• oil contaminated by any one or more of phosphorus, phosphate, thiophosphate, carbamate, alkylated phosphate, sulfurs, sulphate or alkylated sulphate, sulphonate or alkylated sulphonate, detergent, dispersant, contaminated hydrocarbon oil or oxidised contaminated hydrocarbon oil, and/or • a previously de-metallised waste oil feed contaminated by any one or more of phosphorus, phosphate, alkylated thiophosphate, carbamate, alkylated phosphate, sulfurs, sulphate or alkylated sulphate, sulphonate or alkylated sulphonate, ester, oxidised hydrocarbon contaminated hydrocarbon oil.

[00069] A particular embodiment of the invention is described below with reference to Fig. 1.

[00070] Filtered feed oil 10 is blended with an aqueous solution 5 that has a pH adjusted by the addition of a basic additive 30 and then pumped into a recirculating hydrogen stream 20.

Alternatively feed oil 10 and aqueous solution 5 may be pumped separately into stream 20. Make up hydrogen 40 is also added to the recirculating hydrogen stream to ensure the correct

3 hydrogen/oil feed ratio. Commonly the ratio of hydrogen feed to oil is 500Nm ^' of ¾/ m of oil.

3 3

The unit Nra ^' refers to m ^~ as measured at standard temperature and pressure (25°C/1

atmosphere), although the hydrogen is commonly added at a pressure of about 2-18MPa. The combined feed stream 50 is passed through cross exchanger 60 and then heat exchanger 70 to raise it to the desired reaction temperature before it is passed to a fixed bed catalytic

hydrogenation reactor 80. In a variation on this (not shown in Fig. 1 ), aqueous solution 5, after combination with basic additive 30, may be added to the feed oil/hydrogen stream after heat exchanger 70 and before reactor 80.

[00071 ] A controlled rate of heat transfer in heat exchanger 70 plus an adequate partial pressure of hydrogen are important in preventing coking and or polymerisation of the feed oil in the heat exchanger and hydrogenation reactor. The reactor products contain a mix of hydrogen, hydrogenated oil, other reactor gases, water and salts. This stream is passed through cross exchanger 60 so as to transfer heat energy to the feed stream 50 and also to recover heat from and cool the reactor products prior to further processing.

[00072] Reactor gases, primarily excess hydrogen, are flashed off the reactor products in a gas liquid separator 90. The gases are further cooled in a heat exchanger 110 to permit further separation of entrained condensable compounds in high pressure gas liquid separator 120. The further cooling function of heat exchanger 110 may alternately be performed by an oil or water quench to further promote the formation of a separate condensable phase in separator 120. The liquid stream from high pressure separator 120 is passed to a low pressure liquid/liquid separator 130 where the oil can be recovered and combined with the main reactor product flow while the water is removed from the process at this point as wastewater 135.

[00073] The recovered excess hydrogen stream 150 is run through a high pressure scrubber 160 to remove hydrogen sulphide created in the reactor, to form a reusable hydrogen stream 170 that is recompressed in recycle compressor 180 to produce recirculating hydrogen stream 20 at the desired pressure. To maintain hydrogen purity, a proportion of stream 170 may be vented from the process unit via purge valve 190. Make up hydrogen 40 is added as required to the recirculating hydrogen stream 20 to maintain hydrogen partial pressure and purity necessary for the primary hydrogenation reactions to occur. The combined reactor product from separators 90 and 130 is depressurised, further cooled in exchanger 140 and passed to a final liquid/liquid separator 240 where water and salts are separated from the final product and the oil is recovered as a hydrogenated oil product suitable for fractionation or further processing.

Example

[00074] Using a purpose designed continuous process bench scale reactor system, pre- demetallised general waste oil feedstock containing phosphate and alkylated phosphate, detergents and dispersants from lubricant additives were blended in process with a water solution of sodium hydroxide at 2M concentration, at an oil to sodium hydroxide solution ratio of 83 : 1 This mixture was pumped at a rate of 0.3 kg/hr into a hydrogen stream at a pressure of 3.9MPa feeding a pre-heater and heated hydrogenation reactor packed with Criterion® DN3551 standard Ni/Mo hydrogenation catalyst. The feed stream was raised to 320 C in the pre-heater and held at this temperature through the reactor.

[00075] The process was run continuously to achieve a steady state condition. The reactor products were quenched and cooled with deionized water at a rate of 0.0216 kg/hr before being depressurized and removed from the bench reactor system. The oil and water was then separated for independent analysis of the product oil and water phases.

[00076] Total Phosphorus (representing phosphates) and Total Sulfur concentrations were tested in the feed oil and subsequently in the product water and oil phases. Migration of the phosphorus out of the feed oil and into the product water phase suggests the prevention of catalyst poisoning and fouling reactions while mi gration of phosphorus out of the feed oil but not into either the product oil or water phases confirms poisoning or fouling reactions. Results of the trials are shown below:

Table 1 : Steady State Results after 8-10 days continuous bench rig run

Once at a steady state, the reactor, when run with inclusion of the basic water solution, produced constant and stable results. Reported results were for days 8 to 10, at the later stages of the run, to ensure steady state conditions reporting. Results demonstrate consistent mass transfer of phosphorus into the water phase, further demonstrating a) chemical reduction of the organo- phosphate compounds to produce a water soluble moiety (implied to be a phosphate structure) carrying the phosphorus out of the oil and into aqueous phase, and b) removal of the reacted phosphorus bearing moiety from the hydrogenation system, in and by the aqueous phase. No phosphorus was identified in the output oil. Consistent reduction of sulfur concentration confirms ongoing activity of the reaction catalyst during the runs, demonstrating absence of significant poisoning or fouling of the hydrogenation system.

[00077] The results suggest that the catalyst fouling and poisoning mechanism for phosphates and consequently other complexing ligand compounds is likely to be an acid/base driven complexing mechanism that may be overcome through the use of a stronger non-complexing conjugate base system. The stronger conjugate base is thus thought to displace the binding or fouling compounds, in the present example phosphate. The use of the water solution of the conjugate base has the added advantage of also neutralizing and scavenging other acid and mineral acid forming species commonly found in hydrogenation feed. The system of adding a base in water to the oil feed of a catalyzed hydrogenation system has other benefits. For example some contaminants in oil have the propensity to crystallize as salts in reactor systems causing fouling. The base in water additive systems, by providing a separable polar phase creates a mechanism for "washing" polar compounds, crystallized salts and the like out of the hydrogenation system, thereby reducing fouling and improving the operational robustness of hydrogenation systems.

[00078] The results also demonstrate that an appropriate conjugate acid base system may be delivered into the reaction system using a water phase that provides the added benefit of creating an additional aqueous (i.e. oil immiscible) phase into which products of catalytic reactions can partition, thereby removing them from the reaction environment and helping to drive acceptable kinetic performance of the hydrogenation reaction. The results demonstrate removal of sulphates and similar or related compounds.