NO821871L - PROCEDURE FOR THE MANUFACTURING OF A MAIN ASH-FREE OIL - Google Patents

Abstract

In a process for cleaning used lubricating oil, ash-forming constituents are removed by adding a treatment agent in the form of an ammonium salt, e.g. diammonium hydrogen phosphate. The resulting solid wastes are removed by filtration, and the filtrate, the partially purified oil, is subjected to vacuum distillation with steam in a fractionation column. One or more of the resulting fractions may then optionally be subjected to decolorization and deodorization steps.

Description

Process for producing a substantially ash-free oil

The invention relates to a method for reducing the ash content in lubricating oil containing ash-forming components. Another aspect of the invention relates to a method for treating used lubricating oils to obtain purified oil that is suitable for use as . fuel oil, in lubricating grease compositions or in the production of lubricating oil compositions.

It is estimated that used motor oil is produced there in the USA

in an amount of 4.2 million m 3 per year. Part of this used oil has been used as fuel oil, and some has been used on the country's gravel roads for dust control. Much of the oil has simply been dumped into sewers, landfills and secluded alleyways. As the world's petroleum reserves decrease, it becomes more and more important that this used oil is taken care of and used for as long as possible.

A major obstacle to reusing used oil in many applications includes the presence of various ash-forming impurities which remain dispersed in the oil due to the very effective dispersing properties of the additives in modern lubrication tanks.

Materials present in a typical used crankcase oil that are considered to contribute to the ash content of the oil include carbon particles less than 1 µm in size, inorganic materials such as atmospheric dust, metal particles, lead and other metal compounds that originate in the combustion of fuel . Besides lead, which is generally present in combinations of 1.0-2.5% by weight, there are also significant amounts of zinc, barium, calcium, phosphorus and iron in the used crankcase oil. Examination of the used oil under an optical microscope with a magnification of 600 times shows the very effective dispersion properties of modern lubricating oils. The particle size of the particulate material is estimated from this microscopic examination to be 0.1-1 um. with practically no occurrence of agglomerates in the oil.

The presence of ash-forming components in used oil limits the extent to which the material can be used economically without ecological damage. E.g. if the used oil is reused as fuel oil, this can give rise to serious atmospheric pollution when the oil contains more than 1% lead. Also results. such fuel oil is often included in the maintenance costs of the burner and refractory material, which offsets the difference in the purchase price of used oil and ordinary fuel oil.

It is obviously in the nation's interest to provide economical means of removing the impurities from used oil, so that it can be reused in a practical way.

Recently, a technique has been developed for cleaning used oil where the used oil is reacted with an aqueous solution of an ammonium salt as a treatment agent, the aqueous phase is then removed, and the resulting mass containing the oil phase is separated by filtration. Such a technique is described in US-PS 4,151,072.

It is a purpose of the invention to provide an improvement of the method described in US-PS 4,151,072.

Another purpose of the invention is to provide a method for obtaining from used motor oil a number of oil fractions which are suitable for new use in the production of mixed oil compositions.

A method of the invention provides a way to obtain such useful fractions without the use of hydrogen treatment.

Another embodiment of the invention provides a way to reduce the severity of the conditions a hydrotreating catalyst must be subjected to in order to obtain the desired fractions.

Another purpose of the invention is to increase the lifetime of the used hydrogen treatment catalyst.

Another purpose of the invention is to reduce the amount of hydrogen required in the recycling process.

According to the present invention, a method has been provided for producing a largely ash-free oil starting material from a lubricating oil containing ash-forming components, which method comprises: (1) contacting the lubricating oil with an aqueous solution of a treatment agent comprising an ammonium salt which can reacting with the ash-forming constituents and causing them to be removed under conditions sufficient to disperse said agent in the lubricating oil and react the agent with ash-forming constituents in the lubricating oil, (2) removing a major portion of the water from said mixture obtained by combining the aqueous solution and the lubricating oil, (3) separating the solids from the oil obtained from step (2) to obtain a partially purified oil, (4) vacuum distillation of the partially purified oil with steam dilution to obtain a number of oil fractions with different boiling ranges, and (5) removal of color and odor from at least one of said oil fractions with different boiling ranges using either hydrogen treatment or clay treatment.

Fig. 1 is a schematic representation of a particular process using the present invention.

The invention is applicable to the washing off of oil where the ash-forming components can be brought to a form where they can be removed by means of the treatment agent. The invention is particularly applicable to the purification of oil that has been used to lubricate internal combustion engines, e.g. crankcase oils in petrol engines or diesel engines. Other sources of used oils include steam turbine oils, transmission and gear oils, steam engine oils, hydraulic oils, heat transfer oils and the like.

The oils that are generally used for the production of lubricants for internal combustion engines are the refinery lubricating oil fractions from alkaline, mixed or naphthenic crude oils. Their viscosity is generally in the range 100-1,800 SUS at 38°C. The oils also contain various additives such as oxidation inhibitors (e.g. barium, calcium and zinc alkyl thiophosphates, di-t-butyl-p-cresol, etc), anti-wear agents (e.g. organic lead compounds such as lead diorganophosphorus dithioates, zinc -dialkyldithiophosphates,. etc), rust inhibitors (e.g. calcium and sodium sulphonates, etc), dispersants (e.g. calcium and barium sulphonates and

-phenoxides etc), viscosity-improving agents (e.g. polyisobutylenes, poly-(alkylstyrenes) etc), detergents

(e.g. calcium and barium salts of, alkylbenzenesulfonic acids)

and detergents of the ash-free type, e.g. alkyl substituted succinimides etc

If desired, the water contained in the untreated used lubricating oil can be removed before it is used in the method according to the invention. Such a separation can easily be carried out by removing the water phase which may be present in the storage tanks for the used lubricating oil.

The ammonium salt treatment agents which are useful in the method according to the invention are those selected from the group of ammonium sulphate, ammonium bisulphate, ammonium phosphate, diammonium hydrogen phosphate, ammonium dihydrogen phosphate, ammonium thiosulphate, ammonium polyphosphates such as ammonium metaphosphate, urea sulphate, guanidine sulphate, urea phosphate and guanidine phosphate and mixtures thereof. The aforementioned treatment agents can be formed in situ if desired, e.g. by combining ammonia and/or ammonium hydroxide with sulfuric acid and/or phosphoric acid and/or an ammonium hydrogen sulphate or phosphate, i.e. ammonium bisulphate, diammonium hydrogen phosphate and/or ammonium dihydrogen phosphate. When the treatment agent is formed in situ, the reagents used can be introduced simultaneously or one after the other.

Although the concentration of treatment agent in the aqueous solution of the treatment agent is not critical and more dilute solutions can be used, the profitability of the process is promoted by the use of relatively concentrated solutions so that the amount of water. which will later be removed, should not be too large. In general, the concentration of treatment agent in the aqueous solution is in the range 30-95% by weight, typically approx. 80% by weight calculated on an aqueous solution which is saturated with the treatment agent at 25°C. There will often be some water in used oil, and in these cases the concentration of the treatment agent can be adjusted accordingly.

In the method according to the invention, the treatment agent should preferably be used in an amount which is at least sufficient to react with almost all the metal components in the used oil. Although the weight ratio between treatment agent and oil can vary over wide areas depending partly on the nature and concentration of the metal-containing components in the oil and the special treatment agents to be used, it will generally lie in the range 0.002:1-0.05:1, usually in the range 0.005:1-

0.015:1, and typically it is approx. 0.01:1. Although larger quantities of treatment agent can be used, in most cases this will be a waste of treatment agent.

Water may be removed from the mixture obtained by combining the aqueous solution and oil in any suitable manner. Distillation is the preferred method for removing water. In general, the distillation is carried out at a temperature in the range 100-140°C and a pressure in the range 34.5-

172 kPa for a period of time which is sufficient to effect the removal of a larger part of the water. Light hydrocarbons present in the oil boiling under the distillation conditions, e.g. petrol, will of course be separated from the oil together with the water.

The solids are separated from the treated oil in any suitable manner. Currently, filtering is preferred. In general, it is desirable to use a filter aid in the filtering process. Filter aids which are useful in carrying out the invention include those selected from the group consisting of diatomaceous earth, perlite and cellulose fibres. The currently preferred filter aid is diatomaceous earth.

Furthermore, it is currently preferred to postpone the oil

for a heat soak (heat soak) at a temperature in the range 320-420°C before the filtration step. One such method is

described in US-PS 4,247,389. Such heat soaking is typically carried out at pressure in the range from atmospheric pressure to approx. 2.7 5 MPa.

The partially purified oil is then vacuum distilled to produce a number of fractions with different boiling ranges. The vacuum distillation should be carried out under conditions which reduce cracking and pre-coking of the oil to a minimum.

A particularly preferred technique for achieving this goal is to provide high dilution with superheated steam in the vacuum distillation column. The temperature in the fractionation column is kept below 371°C. Preferably, the maximum temperature is not higher than 343°C, and the pressure is in the range 90-200 mm Hg, preferably 93-103 mm Hg (12.4-13.8 kPa).

The steam which is fed to the bottom of the column below the point where the oil feed material is introduced is generally used in amounts of 0.05-0.2 weight percent calculated on the oil feed material, preferably approx. 0.1% by weight.

In a particularly preferred embodiment, superheated steam is also added to the oil feed material before its passage through the heater where it is heated for transfer to the fractionation column. The use of steam in this way provides further dilution and helps to reduce to a minimum the breakdown of the oil in the heat exchanger tubes in the heater.

The different fractions obtained can be collected in storage vessels and further processed separately or combined as desired. If they are treated separately, the fractions that need further purification can be passed through a single decolorization and deodorization zone in a separate (blocked out) manner, i.e. one at a time as desired. Alternatively, the separate fractions can be passed through decolorization and odor removal zones that are specially designed for the particular fraction. Although the different lubricating oil fractions are recombined and passed through a single decolorization and. odor removal zone., the products obtained are generally of much better quality than those obtained by previously known methods where the heavy fractions are not removed before the final purification*; The bottom products from the fractionation column, although they; are heavier than those that would generally be used in mixing in lubricating oils, are relatively metal-free and can be further processed for other purposes, e.g. heavy.gear oils or asphalt additives. If desired, the heavy fractions can be sent to a cracking zone for production. fuel fractions. ;The decolorization and deodorization step or steps may be carried out by any of a number of methods useful for this purpose, e.g. clay treatment or mild hydrogen treatment. Although the hydrogen treatment method is preferred, it is more expensive and satisfactory products can be obtained using only clay treatment. In clay touch, excellent results are obtainable by mixing the oil with 24-120 g of clay per liter of oil, preferably 36-60 g/liter and heating the resulting slurry to a temperature of 149-371°C, preferably 260-343°C in periods of 30 minutes - 3 hours. Times longer than approx. 3 hours contributes to oxidation of the oil, while larger amounts of clay only increase the amount of waste material that must be dumped. Oxidation can also be regulated by introducing an inert atmosphere, e.g. H2 or N2 in the tank. Alternatively, a steam injection will also <:>give excellent results as, in addition to regulating oxidation, it helps to remove impurities from the oil. It is preferred that the oil and clay are separated as soon as possible after the contact time has expired to obtain a better product. Separation can be achieved with any well-known separation method, e.g. filtering. Any acid activated bleaching clay such as "Filtrol grade 20", "Superfiltrol" or "Tonsil" was found to give satisfactory results. Mild hydrogenation as an alternative method of imparting odor and color improvement to the reprocessed lubricating oil is preferred if sufficient quantities of hydrogen are available at practical prices. Typical conditions for hydrogenation to produce a satisfactory finished lubricating oil with neutral odor and light color include an operating temperature of approx. 315-371°C with a preferred temperature of approx. 343°C. The partial pressure of hydrogen can lie in the range 2.75-6.2 MPa with a preferred level close to 4.48 MPa. Volume rates can vary between 0.5 and 2.5 vQl/vol/h with a preferred value of 1. Hydrogen rates of 44.5- ;356 1/1 have been found to be satisfactory with a preferred rate of 267 1/1. The catalyst used can be virtually any of the known hydrofinishing catalysts which promote desired reactions leading to the removal of unwanted unsaturated materials and polar compounds. A metal in group II A, II B., VI B or VIII of the periodic table, an oxide of a metal from group II A, II B, VI B or VIII or a sulphide of a metal in group II A, II B , VI B or VIII are satisfactory as catalyst material. Typical catalysts are cobalt molybdate and nickel molybdate on an inert substrate, e.g. aluminum oxide. A further understanding of the present invention will be obtained from the following description of a preferred embodiment of the present invention, as shown in fig. 1. On fig. 1, used oil from a storage tank 101 is led via a line 102 to a heater 103 and a contactor 106. Aqueous treatment agent, e.g. diammonium hydrogen phosphate from a filling tank 105 is introduced via a line 104. If desired, precursors for the treatment agent in the form of ammonia, phosphoric acid and water can be introduced into the heated oil on the downstream side of the heater 103, whereby the treatment agent is formed in situ in the line 102 and the contactor 106. The oil from. the heater 103 is fed in mixture with the treatment agent into the first stirred contactor 106 where the mixture is kept under stirring for a time which is sufficient to react with at least part of the ash-forming components in the oil. Preferably, a recycling stream is led through a line 152 to a pump 153 and then through a heater 154 before it. is returned to the contactor 106, providing heat and agitation to the contents of the contactor. Agitators can also be used. ;The mixture is then led via a line 107 to a second contactor 109 which is maintained at a temperature in the range of 110-140°C for a period of time sufficient to cause distillation of a greater part of the water and at least some of the light hydrocarbons present. Thus, while held in the contactor 109, substantially all of the water and at least a portion of the light hydrocarbon components in the mixture are removed via a line 110 and led to a separator 111 where a hydrocarbon layer and a water layer are allowed to form. The hydrocarbon phase can then be transferred via a line 112 to storage 113. The aqueous layer can be removed and disposed of or used for any desired purpose. Preferably, a recycle stream is passed through a line 155 to a pump 156 and then through a heater 108 before being returned to the contactor 109, which provides heat and agitation to the contents of the reactor. Agitators can also be used. ;The resulting mixture comprising a hot oil phase which is substantially free of water is conveyed via line 114 to a third contactor where it is subjected to agitation and a temperature in the range of 140-200°C to remove additional water and lighter components. Preferably, a recycle stream is passed through a conduit 157 to a pump 158 and then through a heater 115 before returning to a contactor 116, providing heat and agitation to the contents of the contactor. Any remaining water and light hydrocarbons are removed from the contactor. 116 .via a line 159. ;If desired, any one or two or all of the contactors 106, 109, 116 can be provided with jackets heated by steam or another heat source to help keep the contents of the contactors at the desired temperatures . Any one or two or all of the contactors 106, 109, 116 may be equipped with stirring means to provide additional agitation. In a practically possible, but currently less preferred arrangement, a stirring device in any one or more of the three contactors can be used instead of the recirculation system used with the corresponding one or more of the three contactors, possibly further up< Arming is provided by heaters in the pipeline in front of the contactors and/or heated mantles around the contactors. Furthermore, if desired, one or two or all of the lines 103, 107 and 114 can feed into the recirculation current for the contactors 106 or 109 and 116, i.e. into the wires 152 or 155 and 157, instead of directly into the respective contactor as shown. In a preferred technique, the feed stream in line 102, instead of being led directly into contactor 106, is led into line 152 on the inlet side of pump 153. In an even more preferred technique, pump 153 is a high-volume pump which will cause the oil to flow in the turbulent area in order to promote heat transfer and reduce deposition of coating in line 152. The heated oil from contactor 116 is led via line 117 through a heater 163 to a fourth contactor 164 where the mixture is subjected to stirring at a temperature in the range of 320-420° C for a period sufficient to result in a product which, when subsequently filtered, will contain less ash than it would have contained had it not been so heated. Preferably, a recycle stream is passed through a line 165 to a pump 166 and then through a heater 167 before being returned to a contactor 164, thereby providing heat and agitation to the contents of the contactor 164. Any remaining water or light constituents can be removed from the contactor 164. via line 168. Treated oil from contactor 164 is passed through a line 169 through a cooling device 170 where the oil is cooled to a temperature in the range of 150-180°C and then into a fifth contactor 171 where it is mixed with filter aid obtained via a conduit 118, preferably as a slurry in light hydrocarbons obtained from a fill tank 119. In a presently preferred embodiment, not shown, the oil from contactor 164 is cooled at least in part as a result of passage in indirect heat exchange with the feed material passing through conduit 102, whereby the heat in the oil in line 120 is used to heat the oil feed material in line ing 102. After mixing with filter aid, the resulting mixture is led via a line 172 to a filter 121 which can optionally be pre-coated with filter aid. The application of the heat soaking step in the present invention can in many cases lead to a reduction in the amount of filter aid which is necessary for a suitable filtration rate. ;Filter cake from filter 121 is removed via a line 147 and optionally conveyed to a furnace 148 from which, after burning or calcination, at least a portion of the resulting ash containing filter aid may be sent to dumping via a line 149 or recycled via lines 120 and 160 to a slurry replenishment tank 119 for further use in the system. New filter aid is added through line 160. Light hydrocarbons for use in making the slurry can be recovered from the integrated process and can be fed to tank 119 via line 151. The filtered oil, which is largely free of ash-forming constituents, is then combined with superheated steam and passed through a heater .200. The steam-diluted oil feedstock is then fed into the lower portion of a vacuum distillation column 201. Superheated steam is fed into an even lower portion of the vacuum fractionation column via line 203. Distillation in the presence of this steam allows vaporization and distillation of lubricating oil. at moderate vacuums and at temperature conditions that are sufficiently low to avoid thermal decomposition of the oil fractions. The preferred fractionation column as shown in FIG. 1 comprises five offset deflection plates 202 with 50% of the area cut away, i.e. plates that project halfway into the column and are arranged below the inlet point for the oil feed material and above the inlet point for the operating steam that comes in via the line 203.. 01je feed material combined with bla. The steam is introduced into the column via a distributor 204 for the feed material, which distributor comprises a channel formed by a plate with ponds extending around approx. 1/3 of the column's circumference. The column 201 is divided into three main zones with plate 205 for total drawoff plate and plate 206 for partial drawoff. Both plates 205 and 206 are provided with overflow pipes for liquid. The plate 206 for partial extraction is provided with a second overflow pipe for liquid with an upper height that is between the upper height of the first pipe for this plate and the intermediate height of the plate for partial extraction. Four areas of the packing material.207-210 for static mixing are obtained. Any packing material with low pressure drop for static mixing can be used. Examples include intalox saddles, sulzers, pallet rings and the like. Area 210 preferably comprises a layer of KOCH Sulzer over a layer of intalox saddles, e.g. Norton 40 Intalox. The layer with Intalox serves to protect the Sulzer material from sticking and clogging. ;The column shown allows the extraction of two side-flow fractions via lines 211 and 212, a top-flow fraction via line 213 and a bottom-flow fraction via line 214. ;Parts of the fraction removed via line 2L2 are returned as liquid to liquid distributors in the column via lines 215 and 216. The overhead fraction is fed via line 213 to a condenser 217 where steam and lighter hydrocarbons are separated from the oil to obtain an overhead oil fraction. A portion of the top flow fraction recirculates via a line 218 to a liquid distributor arranged above the gasket 207. The recirculation which is. provided via line 216, provides additional return flow for the system. The recirculation provided via line 215 is used to ensure that tray 205 does not run dry. In a preferred embodiment, steam from an accumulator 217 together with the light hydrocarbons is cooled and led to a phase separator where the hydrocarbons and water are separated. The recovered water is then recycled to provide at least a portion of the water used for production and operating steam for the fractionation column. In a preferred embodiment, the fractionation apparatus designed as shown in fig. 1. The part of the fractionating apparatus that contains the trays and the packing is approx. 1.5 m in diameter and approx..12 m long. The lot containing the 50% cut off deflection plates is approx. 0.69 m in diameter and approx. 1.8 m long. The section for collecting bottom products below the inlet for the operating steam is approx. 0.46 m in diameter and 0.9 m long. ;The plate for distribution of the feed material projects inwards to a point bounded by an arc which is at all points 0.46 m from the adjacent wall in the column. The plate protrudes outwards from approx. 1/3 of the perimeter of the column wall. Dams project upwards from the inner edges of the plate at a height of approx. 0.46 m. ;The first layer of gasket 210 is arranged approx. 1.1 m from the bottom of the batch, in the column having a diameter of 1.5 m. This packing layer preferably comprises a 0.3 m layer of Norton 4 0 Intalox under a 0.6 m layer of KOCH.Sulzer. ;The next layer of gasket 209 is arranged approx. 1.8 m above the top of the packing 210 and includes a 1.2 m layer of KOCH Sulzer. The packing 208 is a 1.2 m layer of KOCH Sulzer which in turn is arranged approx. 1.1 m above the top of pack 209. And finally pack 207, a 1.8 m layer of KOCH Sulzer, is arranged approx. 1.75 m above the top of the packing 208. This special fractionator design permits smooth operation under a wide range of operating conditions. For example, it can easily be operated so that the peak flow can be as much as 40 weight percent of the oil feed material. Alternatively, it can be operated so that either Fraction No. 2 or Fraction No. 3 can be as much as 50 percent by weight of the oil feed material. Furthermore, the column can be operated when as much as 15 percent by weight of the oil feed material is removed as bottoms. Typical examples calculated for the quantities of the various flows, below these extreme points for the operation, are shown in table I. ;The typical and preferred operating areas.for. The demetallization and filtration steps in the preferred oil purification process are as indicated in the table on that page in US-PS 4,247,389 containing columns 9 and 10. The fractions obtained from vacuum fractionation can subjected to decolorization and deodorization as needed" The present invention is particularly useful as the oil fractions to be used in a mixing operation will in many cases not require the decolorization and deodorization step. The invention is further advantageous because the fractionation results in fractions that have been sufficiently non-volatile that they will generally meet flash point standards without further treatment. A particularly preferred technique for cleaning fractions from the vacuum fractionator, especially for the bottom fraction, comprises passing the fraction through a layer of adsorbent, and. then through a hydrogen treatment device. The adsorbent can be bauxite, activated carbon, silica gel, clay, activated aluminum oxide, combinations thereof and the like. The adsorbent serves to: cause breakdown and destruction of the ammonium salts of sulphonic acids and the ashless detergents in the oil. The adsorbent further serves to collect a small part of the resulting products and thereby prevents the passage of such unwanted decomposition products to the hydrogen treatment apparatus. Such adsorbents can be regenerated in the usual way and used again. The adsorbent preferably contains 0.2-20 percent by weight of at least one metal selected from group VIB and group Vlll metals, this percent by weight is calculated on the total weight of modified adsorbent. This modified adsorbent can be prepared by impregnating the adsorbent with an aqueous solution of a water-soluble compound of a group VIB or group VIII metal followed by evaporation ay. water. Water-soluble compounds currently preferred for this purpose are iron compounds such as iron (III) ammonium oxalate. iron (III) - ammonium citrate iron (III) sulphate and iron (II) ammonium sulphate.

From. what has been stated above, it should be obvious that the present invention provides an improved method for cleaning used lubricating oil. Reasonable variations and modifications can obviously be made without deviating from the idea and scope of the invention.

Claims (9)

1. Process for producing a largely ash-free oil starting material from a lubricating oil containing ash-forming components, characterized by (1) contacting the lubricating oil with an aqueous solution of a treating agent comprising an ammonium salt capable of reacting with the ash-forming constituents and causing them to be removed under conditions sufficient to disperse said agent in the lubricating oil and react the agent with the ash-forming constituents , in the lubricating oil, (2) removing a major portion of the water from the mixture obtained by combining the aqueous solution and the lubricating oil; (3) separating the solids from the oil obtained from step (2) to obtain a partially purified oil; (4) vacuum distillation of the partially purified oil with steam dilution to obtain a variety of oil fractions with different boiling ranges, and (5) removal of color and odor from at least one of said oil fractions with different boiling ranges using either hydrogen treatment or clay treatment. 2. Method as specified in claim 1, characterized in that all decolorization and odor removal is achieved by clay treatment. 3. Method as stated in claim 1 or 2, characterized in that only the bottom products from the fractionation column are subjected to decolorization and odor removal. 4. Method as stated in claim 1, characterized in that at least one of the oil fractions from step (4) is not subjected to decolorization and odor removal. 5. Method as stated in any one of claims 1-4, characterized in that the ammonium salt is diammonium hydrogen phosphate. 6. Method as set forth in any one of claims 1-5, characterized in that the product from step (2) is subjected to a heat soaking step before carrying out step (3), the said heat soaking step comprising heating the oil at a temperature in the range 320-420°C for a period of time which is sufficient to break down at least a large part of the ammonium salts of sulphonic acid or dialkyl-dithiophosphoric acid which may be present. 7. Method as stated in claim 6, characterized in that the bottom products from the vacuum distillation are passed through an adsorption agent. and then through a hydrogen treatment device. 8. Method as stated in claim 7, characterized in that the adsorbent comprises clay. 9. Method as stated in claim 1, characterized in that the different fractions are collected and each separately subjected to hydrogen treatment by passing them through the same hydrogen treatment zone in sequence.