This patent application claims priority from Italian patent application

no. 10201800001 1026 filed on December 12, 2018, the entire disclosure of which is incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to an activated carbon and process for preparing an activated carbon with low metal content, starting from oil residues of refinery or of hydroconversion processes of heavy oil products with a high metal content.

The refinery processes or hydroconversion processes of heavy oil products lead to the formation of purge streams that typically contain an unconverted oil fed, metals in the oil fed and/or some catalyst used, catalyst and carbonaceous residues.

It is therefore understood how important it is for the purposes of improving the efficiency of production and the conversion of a refinery or of hydroconversion processes of heavy hydrocarbons, to treat the purge in an attempt to exploit the components which, when appropriately treated, can generate activated carbon.

The purge can be treated so as to separate a light stream, or clarified, from a solid phase known as“cake”.

The aim of the present invention is therefore to exploit the light components of the purge, clarified, with which it is possible to prepare an activated carbon that has a high surface area and high microporous volume.

In the present patent application,“heavy oil products” means crude oils, heavy crude oils, bitumens from oil sands, distillation residues, heavy distillation cuts, deasphalting residues, synthetic oil products from the Fischer Tropsch process, vegetable oils, oils derived from coke and oil shale, oils obtained by thermal decomposition of waste, polymers, biomass.

In the present patent application, the term“purge” means organic currents in the slurry phase that contain a quantity of hydrocarbons having a boiling point greater than or equal to 540°C greater than 65% by weight, a quantity of asphaltenes greater than or equal to 20% by weight and characterized by the presence of levels of solids greater than or equal to 4% by weight, the rest being hydrocarbons that have a boiling point comprised between 350°C and 500°C. The solids of the purge contain carbonaceous residues and metal compounds that may contain transition metal sulfides, such as molybdenum, iron, nickel and vanadium, and having sub-millimetric dimensions.

For the purpose of the present patent application, the term“solid” means the fraction that is insoluble in tetrahydrofuran, indicated herein by the initials THF-i.

For the purpose of the present patent application, the term“asphaltenes” means the organic fraction that is soluble in tetrahydrofuran but insoluble in n-pentane.

Asphaltenes are classified on the basis of their insolubility in n-paraffins (typically having from 5 to 7 carbon atoms C5-C7). Such compounds generally consist of nuclei of aromatic polycondensates with varying degrees of branching and joined together through linear chains. Such compounds may contain heteroatoms (S, N) within them, which give them a polar nature.

In the present patent application, the term“cake” means a material that is solid at room temperature with vitreous characteristics (i.e. the appearance of the cake has glass-like characteristics) which make it easy to grind and therefore to transport long distances without requiring any particular thermostat-regulation. Such characteristic persists at temperatures that vary in the range comprised between 50°C and 60°C.

The cake is hard at room temperature with a softening point comprised between 80°C and 100°C and a penetration degree from 2 dmm to 5 dmm (dmm indicates

decimillimeters). The softening point is the temperature at which the cake from being solid becomes soft and indicates the dependence of the consistency of the cake on the temperature. The penetration degree is measured according to the ASTM-D5-06 method and expresses in decimillimeters the penetration undergone by the material, at room temperature, by a needle of a known weight.

The consistency of the cake is due to the presence of solids (THFi) in a greater concentration with respect to the other currents and the presence of asphaltenic compounds.

The cake contains solids as previously defined in the text of the present patent application.

The solids of the cake contain carbonaceous residues and metal compounds that may contain transition metal sulfides, such as molybdenum, iron, nickel and vanadium, and having sub-millimetric dimensions.

In the present patent application, the term“clarified” means a hydrocarbon residue free from solids and metals, with an asphaltene content lower than that initially present in the purge, and already fluid at temperatures comprised in the range between 100°C and 160°C.

In the present patent application, the term“maltenes” means the set of compounds that are soluble in both tetrahydrofuran and in n-pentane.

In the present patent application, all the operating conditions included in the text must be considered as preferred conditions even if this is not specifically stated.

For the purpose of this text the term“comprise” or“include” also comprises the term “consist in” or“essentially consisting of”.

For the purpose of this text the definitions of the intervals always comprise the extremes unless specified otherwise.

Activated carbons are materials mainly containing amorphous carbon, having a highly porous structure. The main property of the activated carbon is the high specific surface area, typically comprised between 500 and 2500 m ² /g, due to its high porosity.

The activated carbons may be produced starting from a wide variety of raw materials with high carbon content, such as peat, coal, lignite, wood and coconut. In addition to materials of natural origin, production lines have been developed that use synthetic resins or other polymeric materials as raw material, such as polyvinylidene chloride (PVDC), or refinery residues or petroleum coke.

BACKGROUND ART

The possibility of using petroleum residues for preparing activated carbons is known (GB 701 174, 1951 , Standard oil). The process envisages the residue being subjected to coking and/or distillation and then treated using an activating agent at high temperatures. The activated carbons obtained contain any heavy metals present in the oil residue.

GB 1215794 describes a high efficiency process for the production of activated carbons that have a high surface area, control of the pore dimensions and pore distribution and high selectivity.

The process envisages treating an aromatic carboxylic acid with at least one electrolyte forming a salt, then the salt is decomposed through heat treatment forming activated carbon.

GB 1287275 describes a process for the production of activated carbon and a process for increasing the surface area thereof.

A carboxylic acid of an aromatic compound is heated to a temperature and for a sufficient amount of time so that decarboxylation takes place. The compound is impregnated with a base and then treated with anhydride for forming activated carbon. To increase the surface area of the activated carbon, it is impregnated with a base and then with an acid anhydride.

US 2,556,859 describes a process for the preparation of highly selective carbon towards some molecules, and in particular towards linear chain hydrocarbons such as n-paraffins and iso-paraffins. The process envisages carbonaceous material being subjected to coking at high temperatures forming carbon that is subsequently activated at high temperatures in a first step using water vapor and subsequently in an inert atmosphere. US 3994829 describes a process for preparing activated carbon by heat treating and thermally deacidifying carbonaceous material, therefore carbonizing the material obtained removing the volatile components. Finally, the carbonized product is activated in a certain furnace.

If activated carbons with low metal content are to be obtained, the choice of the petroleum residues is limited to the choice of residues with low metal content. This excludes the possibility of exploiting refinery oil residues or residues of hydroconversion processes of heavy petroleum products due to the presence of metals in high

concentrations. The activated carbons obtained starting from petroleum residues containing heavy metals can be further enriched in the metals contained in the oil residue itself, depending on the loss of weight and leaching of metals that occur during the preparation of the activated carbon itself.

Typically, in the preparation of an activated carbon, the raw material is initially subjected to high temperature in the presence of a gas, removing hydrocarbons and other gaseous products. This step can be performed in inert gas, in pyrolysis conditions.

Subsequently the carbon residue is subjected to the activation process. The activation can take place by physical route, e.g. by treatment at high temperatures in the presence of CO2, C>2 or steam at temperatures comprised between 800°C and 1000°C, causing the decomposition of a part of the starting material and the production of numerous pores and cracks.

The activation can also take place by chemical route, e.g. by treatment at high

temperatures in the presence of ZnCh, mineral acids such as H ₃ PO4, HNO ₃ , K2CO ₃ , Na ₂ CC> ₃ , KOH, NaOH. The temperature at which this takes place is generally comprised between 400°C and 1000°C. After the removal of the chemical agent through extraction, the porous structure of the activated carbon remains.

The activated carbon yield depends on the degree of activation: a high degree of activation is associated with a low yield. In general the yield can be comprised between 20% and 60%.

The activated carbons according to the present invention allow to exploit purges of refinery or of hydroconversion processes of heavy oil products. The activated carbon described and claimed does not contain heavy metals in significant quantities, i.e. it has a heavy metal content less than or equal to 50 ppm, with important effects on its manageability.

Thanks to the careful optimization and strict control of the pyrolysis and activation conditions, the activated carbons have the desired textural characteristics.

DISCLOSURE OF INVENTION

Therefore, the subject matter of the present patent application is an activated carbon that has the following characteristics:

It presents reversible type I nitrogen adsorption/desorption isotherms at 77K,

A specific surface area (SSA) greater than or equal to 2000m ² /g, preferably comprised between 2000 m ² /g and 3000 m ² /g, Total pore volume greater than or equal to 1 ml/g, of which the microporous component contribution is comprised between 70% and 95% by volume, preferably comprised between 80% and 90% by volume.

Contribution of the mesoporous component comprised between 5% and 30% by volume, preferably comprised between 10% and 20% by volume, with respect to the total pore volume;

Adsorption capacity of methane greater than or equal to 17% by weight;

Total content of heavy metals less than or equal to 50 ppm.

The subject matter of the present patent application is a process for preparing activated carbon, preferably the activated carbon described and claimed in the present patent application, using purge of refinery or hydroconversion processes of heavy oil products as carbon sources, which comprises the following steps:

• Heating a purge to a temperature greater than or equal to 185°C and not over 220°C,

· Separating said heated purge by static sedimentation obtaining a clarified stream and a cake;

• Subjecting such clarified stream to pyrolysis at temperatures comprised between 250°C and 600°C, heating in one or more steps, forming a solid carbon fraction, which is defined from now on as "pyrolyzate”;

· Subjecting the pyrolyzate to activation, either physically or chemically, to form

activated carbon;

• Subsequently cooling the activated carbon to room temperature and if necessary washing said activated carbon with water up to neutral pH;

Subsequently drying the cooled activated carbon and optionally washed with water at a temperature comprised between 50°C and 200°C. Further subject matter of the present invention is the activated carbons, that can be obtained with the process described and claimed, which have the following

characteristics:

It presents reversible type I nitrogen adsorption/desorption isotherms at 77K, - Specific surface area (SSA) greater than or equal to 2000m ² /g, preferably

comprised between 2000 m ² /g and 3000 m ² /g,

Total pore volume greater than or equal to 1 ml/g, of which the microporous component contribution is comprised between 70% and 95% by volume, preferably comprised between 80% and 90% by volume.

- Contribution of the mesoporous component comprised between 5% and 30% by volume, preferably comprised between 10% and 20% by volume, with respect to the total pore volume;

Adsorption capacity of methane greater than or equal to 17% by weight;

Total content of heavy metals less than or equal to 50 ppm.

BEST MODE FOR CARRYING OUT THE INVENTION

The Applicant now describes in detail the new activated carbons.

Said activated carbons have reversible type I nitrogen adsorption/desorption isotherms at 77K, typical of microporous materials, with a minority contribution of mesopores. The isotherms highlight a quick, almost vertical, increase in adsorbed moles typical of microporous materials at very low relative pressures; at higher pressures a gradual increase in adsorbed moles is observed up to P/P0 about 0.3, a value beyond which there is a plateau indicating that the material no longer adsorbs despite the pressure increase. The specific surface area (SSA) of the activated carbons according to the present patent application is greater than or equal to 2000 m ² /g, preferably comprised between 2000 m ² /g and 3000 m ² /g; the total volume of the pores of said activated carbons is greater than or equal to 1 ml/g, of which the contribution of the microporous component is comprised between 70% and 95% by volume, preferably comprised between 80% and 90% by volume. Furthermore, there is a contribution of the mesopores comprised between 5% and 30% by volume, preferably comprised between 10% and 20% by volume, with respect to the total pore volume. The activated carbon described and claimed has an adsorption capacity of methane greater than or equal to 17% by weight. The activated carbon described does not contain heavy metals, i.e. the total heavy metal content is less than or equal to 50ppm.

The Applicant now describes in detail the process for preparing activated carbon, according to the present patent application.

A purge stream of refinery or hydroconversion process is heated to a temperature greater than or equal to 185°C and not over 220°C, preferably between 200°C and 220°C.

Subsequently the purge is subjected to static sedimentation gradually and in a controlled way lowering the temperature to the minimum temperature of 100°C, preferably comprised between 100°C and 170°C, more preferably comprised between 100°C and 160°C. The controlled lowering of the temperature can take place in different ways:

* by using an adequately sized and thermostated tank, e.g. hot-oil thermostated, or

* by mixing the hot current to be decanted with a cold current, e.g. the heated purge, with a cold current, e.g. the clarified stream which can be at a temperature that varies from 200°C to 80°C, considering the appropriate thermal balance of the system for calculating the flow rates thereof.

The lowering of the temperature is of a value that varies from 3°C per minute to 10°C per minute, preferably from 5°C per minute to 10°C per minute, more preferably 10°C per minute.

During static sedimentation, the temperature must be such as to make the asphaltenes insoluble and simultaneously make the clarified part movable allowing the extraction thereof.

In the temperature range comprised between 100°C and 160°C the separation of the dense phase is optimal.

During the sedimentation phase the purge is not agitated. Sedimentation forms a light phase, known as the clarified, and a heavy phase, known as cake, according to the density.

The clarified is subjected to pyrolysis at temperatures comprised between 250°C and 600°C, heating said current in one or more steps and thus forming a pyrolyzate.

Pyrolysis can take place in two or more steps at intermediate temperatures comprised between 250°C and 600°C. Each pyrolysis step can have a duration comprised between 30 minutes and 10 hours, for a total pyrolysis time comprised between 1 hour and 30 hours. Pyrolysis can take place at a pressure comprised between 1 and 30 bar.

Pressurization typically takes place using N ₂ , but other methods known to a person skilled in the art can be used.

The pyrolyzate is subjected to physical or chemical activation and subsequent cooling to room temperature.

The activation can preferably take place by physical route through treatment at high temperatures in the presence of C0 ₂ or water vapor; or by chemical route, through treatment at high temperatures in the presence of a compound preferably selected from ZnCI ₂ , K ₂ CC> ₃ , Na ₂ CC> ₃ , KOH, NaOH, mineral acids, such as H ₃ PO4 or HNO ₃ .

A preferred activation method envisages treatment with KOH, at KOH/pyrolyzate ratios comprised from 0.5/1 to 5/1 , preferably from 1/1 to 3/1.

The temperature of the activation treatment is preferably comprised between 500°C and 900°C and the time between 1 hour and 10 hours, preferably from 1.5 to 8 hours. The activation is typically performed in the presence of a nitrogen flow comprised between 50 ml/min and 300 ml/min. This is followed by washing with water, possibly in the presence of an acid, e.g. selected from hydrochloric acid, acetic acid or hydrogen sulfide, until neutral pH is reached; finally, to drying at a temperature comprised between 50°C and 200°C.

At the end of the process an activated carbon is obtained with low metal content, high surface area and high porous volume.

Preferably the process described and claimed prepares the activated carbons according to the present patent application.

Further subject matter of the present invention is also the activated carbons, that can be obtained with the process described and claimed, which have the following

characteristics:

it presents reversible type I nitrogen adsorption/desorption isotherms at 77K, Specific surface area (SSA) greater than or equal to 2000 m ² /g, preferably comprised between 2000 m ² /g and 3000 m ² /g,

Total pore volume greater than or equal to 1 ml/g, of which the microporous component contribution is comprised between 70% and 95% by volume, preferably comprised between 80% and 90% by volume.

Contribution of the mesoporous component comprised between 5% and 30% by volume, preferably comprised between 10% and 20% by volume;

Adsorption capacity of methane greater than or equal to 17% by weight;

Total content of heavy metals less than or equal to 50 ppm.

The activated carbon thus prepared may be effectively used in gas adsorption processes, in particular methane gas.

Thanks to the high specific surface area activated carbon is able to absorb within its porous system many molecules of other substances, therefore activated carbon is a material with high adsorbent capacities.

Activated carbons can be used in the area of filtration, purification, deodorization and decoloration of fluids, gas adsorption.

In particular, in the case of the adsorption of methane, activated carbons can act as adsorbents in ANG (Adsorbed Natural Gas) technology. ANG technology allows the storage of natural gas through solid materials and has advantages both in gravimetric and volumetric energy density terms and in relation to safety and energy efficiency. In principle it prevents the need for high pressures typical of CNG (Compressed Natural Gas) technology and/or low temperatures typical of LNG (Liquefied Natural Gas) technologies) for the storage of the natural gas.

The technology is based on the adsorption of gas molecules on a porous adsorbent material at relatively low pressure (e.g. maximum adsorption pressure less than 100 bar, preferably less than 70 bar, more preferably less than 50 bar) and at a temperature equal or proximal to room temperature, and allows a greater quantity of gas to be stored in a pressurized container filled with such material, with respect to the same empty container at the same pressure. This increase in the storage capacity of the gas is mainly due to the formation of a thin layer of gas molecules at high density on the surface of the material.

The adsorption capacity is strongly influenced by the material used. As already specified, adsorption is a surface process and, therefore, a fundamental characteristic for adsorbents is their specific surface area (SSA).

Preferred activated carbons for ANG technology are mainly microporous.

In accordance with lUPAC terminology“Manual of Symbols and Terminology” (1972), Appendix 2, Part I Coll. Surface Chem. Pure Appl. Chem., Vol. 31 , pag. 578, the definition of micropores is pores with a diameter less than 2 nm, mesopores those with a diameter comprised between 2 and 50 nm, macropores those with a diameter greater than 50 nm.

The surface area and porosity of the samples were determined by adsorption-desorption isotherms of N ₂ at the temperature of liquid nitrogen (77 K), using a Micromeritics ASAP 2020 tool.

Prior to the acquisition of the isotherms, the samples (~ 30 mg) in powder are degassed for 16 hours at 200°C in vacuum. The specific surface area (SSA) is evaluated using the BET method. The specific total Gurvitsch pore volume (PV) at p/pO is 0.99. The microporous fraction of the porosity is determined using the DFT method based on the cumulative distribution curves of the pores as a function of their diameter. The volume of pores with a diameter less than or equal to 2nm is considered a microporous volume.

The adsorption measurements of methane at high pressure were performed using the Rubotherm Isosorp magnetic suspension balance. Prior to measurement the samples are pre-treated in vacuum at 200°C for 15 hours. The adsorption tests were performed at 25°C. The methane is loaded with successive pressure increases of 5 bar, leaving for every pressure an equilibrium time of 3 hours. For determining the mass of adsorbed gas, the mass variation Am as a function of the pressure is added to the buoyant force, which is a function of the volume of the empty system, the volume of the sample and the density of the gas moved at the analysis pressure and temperature. The adsorption values reported always refer to excess adsorption, where excess adsorption means the determination of the quantity of gas that interacts with the porous surface of the adsorbent.

In literature it is described that the adsorption is particularly significant inside micropores (d<2nm), in which the Van der Waals attraction forces between a gas molecule and solid surface enable a significant interaction between gas and solid. In particular, on the basis of simulations based on molecular dynamics [K.R. Matranga, A.L. Myers, E.D. Glandt, Chem. Eng. Sci., 47 (1992) 1569; R.F. Cracknell, P. Gordon, K.E. Gubbin, J. Phys.

Chem., 97 (1993) 494] pores characterized by dimensions equal to the sum of the diameters of a number of molecules of methane comprised between 2 and 4, therefore diameters comprised between 0.8 and 1.5 nm, were identified as being optimal.

Furthermore, the additional presence of mesopores (pores having a diameter comprised between 2 nm and 5 nm) constitutes a further element able to promote the diffusion of the massive gaseous current (existing outside the particles of adsorbent) towards the micropores responsible for the adsorption phenomenon.

The textural characteristics required in the case of ANG application are particularly strict, with respect to those required for other activated carbon applications (e.g.: filtration, purification, deodorization and decoloration of fluids).

The possible applications of ANG technology range from the storage of fuel for vehicle transport (Natural Gas Vehicles - NGV), to storage for industrial operations, to NG transport in cylinders for use on a small scale as an alternative to acetylene, to large scale transport of NG. In the latter sense, ANG technology can therefore be considered as a valid option for the transport of NG in the absence of existing pipelines, using ANG tanks transported by road or by sea from the gas production site to the destination point. Below are some examples for better understanding of the invention and within the scope of application, although not constituting in any way a limitation to the scope of the present invention.

EXAMPLE 1 : Preparation of activated carbon using a purge from refinery, with the static sedimentation phase - sample AC1 .

Table 1 shows the analysis of the purge used. Table 1 : purge analysis

The sample of purge from the refinery is placed in an oven, pressurized in nitrogen, and with temperature T 1 set to 200°C. After reaching complete homogeneity of the sample the set point of the oven is set to 100°C. After about 0.5 hours at 100°C the supernatant or“clarified” liquid is removed. The dense phase that remains in the bottom is the“cake” phase.

The“clarified” sample is loaded into a reactor that is pressurized at 10 bar with N ₂ and heated to 460°C. Once the temperature has been reached, the pyrolysis treatment continues for 90 minutes. Then the reactor is cooled to room temperature under pressure. The pyrolyzed sample is activated with KOH, respecting the KOH: pyrolyzed carbon weight ratio of 3:1.

The pyrolyzed carbon and KOH are mixed and ground in a ball mill for 30 minutes at 300 rpm. Then, the mixture is placed into a horizontal oven in nitrogen atmosphere.

The activation conditions are:

- T: 700 ^e C

Time: 2 hours

Atmosphere: N ₂ 100 ml/min.

After 2 hours, the sample was cooled in N ₂ to room temperature. The activated carbon is washed with a 20% vol. solution of HCI at 37% for 1 hour with agitation. After the acid wash, the activated carbon is filtered and washed with water to neutral pH. Finally, it is dried for 15 hours at 75°C.

The results are shown in Table 2.

COMPARATIVE EXAMPLE 1 : Preparation of activated carbon using a refinery purge, in the absence of the static sedimentation phase - sample AC2.

A sample of refinery purge such as that used in example 1 is directly subjected to pyrolysis and activation in the same conditions as example 1 . In this case the static sedimentation phase is omitted.

The results are shown in Table 2.

Table 2: Textural, composition and performance characterization in the methane adsorption of the two samples.

Example 2

Preparation of activated carbon using the same refinery purge used in example 1.

Example 1 is repeated, except that pyrolysis is performed under the following conditions: 1 bar with N ₂ , at 460°C for 1.5 hours.

The activated carbon obtained after treatment with KOH (under the same conditions as example 1 ) has SSA = 2449 m ² /g, a total pore volume of 1.07ml/g, of which 84% by volume are micropores. Example 3

Preparation of activated carbon using the same refinery purge used in example 1.

Example 1 is repeated, except that pyrolysis is performed under the following conditions: 1 bar with N ₂ , at 370°C for 5 hours.

The activated carbon obtained after treatment with KOH (under the same conditions as example 1 ) has SSA = 2476 m ² /g, a total pore volume of 1.13ml/g, of which 80% by volume are micropores.