WO2020121254A1

WO2020121254A1 - Process for the preparation of activated carbon starting from petroleum residues

Info

Publication number: WO2020121254A1
Application number: PCT/IB2019/060725
Authority: WO
Inventors: Alberto Landoni; Angela Carati
Original assignee: Eni SpA
Current assignee: Eni SpA
Priority date: 2018-12-12
Filing date: 2019-12-12
Publication date: 2020-06-18
Anticipated expiration: 2021-06-12
Also published as: IT201800011015A1

Abstract

This invention relates to a process for the activated carbon preparation, using residues from refinery or hydroconversion processes of heavy petroleum products as carbon sources, which includes the following steps: • heating a purge at a temperature greater than or equal to 185 °C and not over 220 °C, • separating said heated purge by static sedimentation forming a clarified stream and a cake; • subjecting the cake directly to activation by physical or chemical route, and by excluding that the cake is subjected to a pyrolysis phase before the activation phase, forming activated carbon, and • then cooling such activated carbon at room temperature and washing with water, possibly in the presence of an acid, up to neutral pH; then • drying the washed activated carbon at a temperature comprised between 50 °C and 200 °C.

Description

"PROCESS FOR THE PREPARATION OF ACTIVATED CARBON STARTING

FROM PETROLEUM RESIDUES"

CROSS-REFERENCE TO RELATED APPLICATIONS

This Patent Application claims priority from Italian Patent Application No. 102018000011015 filed on December 12, 2018, the entire disclosure of which is incorporated herein by reference.

TECHNICAL FIELD

This invention relates to a process for the preparation of activated carbon, starting from petroleum residues of refinery or hydroconversion processes of heavy oil products .

Refinery or hydroconversion processes of heavy oil products lead to the formation of purge streams, oil residues, which typically contain an unconverted charge, metals of the used catalyst, catalyst and carbonaceous residues.

It is therefore clear that it is important for the purposes of improving production efficiency and conversion of a refinery or of hydroconversion processes of heavy hydrocarbons, to treat the purge trying to valorise the components that, when properly treated, can generate activated carbon.

The purge can be treated in such a way as to separate a light, or clarified, stream from a solid phase known as " cake " .

The object of the present invention is therefore that of valorising the cake with which it is possible to prepare an activated carbon which has high surface areas and a high microporous volume.

In the present patent application heavy oil products mean crude oils, heavy crude oil, bitumen from tar sands, distillation residues, heavy distillation cuts, deasphalting residues, synthetic oils produced 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 streams in slurry phase which 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 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 having a boiling point comprised between 350°C and 500°C. Purge solids contain carbonaceous residues and metal compounds which may contain sulphides of transition metals, such as for example molybdenum, iron, nickel and vanadium, and having sub-millimetric dimensions.

For the purposes of this discussion, the term "solid" means the fraction insoluble in tetrahydrofuran, indicated in this text by the acronym THF-i.

For the purposes of this discussion, the term "asphaltenes" means the organic fraction soluble in tetrahydrofuran but insoluble in n-pentane.

Asphaltenes are classified according to their insolubility in n-paraffins (typically having 5 to 7 C5-C7 carbon atoms) . Such compounds are generally constituted by nuclei of polycondensate aromatics that are variously branched and linked together through linear chains. Such compounds may contain heteroatoms (S, N) in their inside which give them their polar nature.

In the present patent application the term "cake" means a solid material at room temperature with vitreous characteristics (that is the appearance of the cake has glass-like characteristics) which make it easily grindable and consequently transportable even for long stretches without making a particular thermostatic control necessary. This characteristic remains at temperatures ranging from 50°C to 60°C.

The cake is hard at room temperature with a softening point comprised between 80°C and 100°C and a degree of penetration from 2 dmm to 5 dmm (dmm indicates decimillimeters ) . The softening point is the temperature at which the solid cake becomes soft and indicates the dependence of the cake consistency on the temperature. The degree of penetration 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 known weight.

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

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

Cake solids contain carbonaceous residues and metal compounds which may contain sulphides of transition metals, such as for example molybdenum, iron, nickel and vanadium, and having sub-millimeter dimensions.

In the present patent application, the term "clarified" means a hydrocarbon residue without solids and metals, with a content of asphaltenes lower than that initially present in the purge, and fluid already at temperatures in the range between 100°C and 160°C.

In the present patent application, the term "maltenes" means the set of those compounds soluble in both Tetrahydrofuran and n-pentane.

In the present patent application, all the operating conditions reported in the text must be understood as preferred conditions even if not expressly declared. For the purposes of the present discussion the term "comprise" or "include" also comprises the term "consist in" or "essentially consisting of" .

For the purposes of the present discussion the definitions of the intervals always comprise the extreme values unless otherwise specified.

BACKGROUND ART

Activated carbons are materials containing mainly amorphous carbon, having a highly porous structure. The main property of activated carbon is the high specific surface area, typically comprised between 500 and 2500 m²/g, due to its high porosity.

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

The possibility of using petroleum residues for the activated carbon preparation is known (GB 701174, 1951,

Standard oil) . The process requires the residue to be subjected to coking and/or distillation and subsequently treated by an activating agent at high temperatures.

GB 1215794 describes a high efficiency process for the production of activated carbons which have a high surface area, control of the pore size and of the 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 by heat treatment forming activated carbon. GB 1287275 describes a process for the activated carbon preparation and a process for increasing the surface area thereof . A carboxylic acid of an aromatic acid is heated to a temperature and for a time sufficient for decarboxylation to occur. The compound is impregnated with a base and subsequently treated with anhydride to form activated carbon. In order to increase the surface area of the activated carbon, the latter is impregnated with a base and then with an acid anhydride.

US 2,556,859 describes a process for the preparation of carbon that is highly selective towards some molecules, and in particular towards linear chain hydrocarbons such as n-paraffins and iso-paraffins. The process provides for carbonaceous material to be subjected to coking at high temperatures forming carbon which is subsequently activated at high temperatures in a first stage using water vapour and subsequently in an inert atmosphere.

US 3994829 describes a process for the activated carbon preparation by thermally treating and thermally deacidifying carbonaceous material, thereby carbonizing the material obtained eliminating the volatile components. Finally, the carbonized product is activated in a certain furnace .

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 phase can be carried out in inert gas, under pyrolysis conditions.

Subsequently the carbonaceous residue is subjected to the activation process.

The activation can take place by physical route, for example by treatment at high temperatures in the presence of CO2, O2 or steam at temperatures comprised between 800°C and 1000°C, causing the decomposition of a portion of the starting material and the production of numerous pores and cracks . The activation can also take place by chemical route, for example by treatment at high temperatures in the presence of ZnCl2, mineral acids such as for example H3PO4, HNO3, K2CO3, Na2CC>3, KOH, NaOH. The temperature at which it occurs is generally comprised between 400°C and 1000°C. After removal of the chemical agent through an extraction, the porous structure of the activated carbon remains.

The yield in activated carbon 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%.

DISCLOSURE OF INVENTION

The object of the present patent application is therefore a process for the activated carbon preparation, preferably the activated carbon described and claimed in the present patent application, using residues from refinery or hydroconversion processes of heavy oil products as a carbon source, which comprises the following steps:

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

• separating said heated purge by static sedimentation forming a clarified stream and a cake;

• subjecting the cake directly to activation by physical or chemical route, and by excluding that the cake is subjected to a pyrolysis phase before the activation phase, forming activated carbon, and

• then cooling such activated carbon to room temperature and washing said activated carbon with water, possibly in the presence of an acid, for example, selected from hydrochloric acid, acetic acid, sulphuric acid, up to a neutral pH; then

• drying the washed activated carbon at a temperature comprised between 50 °C and 200 °C. Activated carbons, obtainable with the described and claimed process, constitute a further embodiment of the present invention, which have the following characteristics :

- it features reversible type I nitrogen adsorption/desorption isotherms at 77K;

- a specific surface area (SSA) greater than or equal to 1800m²/g, preferably comprised between 2000 m²/g and 3000 m²/g,

- a total pore volume greater than or equal to 0.8 ml/g, of which the microporous component contribution is comprised between 70% and 95% by volume, preferably comprised between 80% and 90% by volume.

- a 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;

- an adsorption capacity of methane greater than or equal to 14% by weight.

The activated carbons thus obtained allow to exploit the residues of refinery or hydroconversion processes of heavy petroleum products.

The activated carbon thus obtained has a high surface area (SSA) greater than or equal to 1800m²/g, preferably comprised between 2000 m²/g and 3000 m²/g, which makes it particularly effective in the adsorption of gases.

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

The activated carbons thus obtained have yields greater than 45% by weight, that is the weight of activated carbon with respect to the used cake, preferably comprised between 45 and 70% . DETAILED DESCRIPTION

The Applicant now describes in detail the process for the activated carbon preparation, object of the present patent application .

A purge stream of refinery or hydroconversion processes 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 by lowering the temperature in a progressive and controlled manner to a 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, for example a hot-oil thermostat, or

* by mixing the warm stream to be decanted, for example the heated purge, with a cold stream, for example the clarified which can be at a temperature ranging from 200°C to 80°C, considering the appropriate thermal balance of the system to calculate the flow rates thereof .

The lowering of the temperature can be of a value ranging 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.

Using one of the two previous methods for the controlled lowering of the temperature, the temperature varies by a value which falls in the range 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 at the same time 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 stirred. The sedimentation forms a light phase, called clarified, and a heavy phase, called cake, as a function of density. The cake is subjected directly to activation by physical or chemical way and subsequently cooled to room temperature forming activated carbon. No pyrolysis phase is envisaged before the activation phase.

The activation can preferably take place by physical route through a treatment at high temperatures in the presence of CO2 or water vapour; or by chemical route, by treatment at high temperatures in the presence of a compound preferably selected from ZnCl2, K2CO3, Na2CC>3, KOH, NaOH, mineral acids, such as for example H3PO4 or HNO3.

A preferred activation (carbonization) method envisages the treatment with KOH, at KOH/cake ratios from 0.5/1 to 5/1, preferably from 1/1 to 3/1.

The temperature of the activation (carbonization) 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 carried out in the presence of a nitrogen flow comprised between 50 ml/min and 300 ml/min.

Then it is proceeded with washing with water, possibly in the presence of an acid, for example selected from hydrochloric acid, acetic acid or hydrogen sulphide, until reaching a neutral pH; then said washed activated carbon is dried at a temperature comprised from 50°C to 200°C.

At the end of the process an activated carbon is obtained with a high surface area and a high porous volume. Therefore, activated carbons, obtainable with the described and claimed process, constitute a further embodiment of the present invention, which have the following characteristics:

- reversible type I nitrogen adsorption/desorption isotherms at 77K;

- an adsorption capacity of methane greater than or equal to 14% by weight.

The activated carbons thus prepared have yields greater than 45% by weight (the weight of activated carbon with respect to the cake precursor used) , preferably comprised between 45 and 70%.

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

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

The activated carbons can be used in the context of filtration, purification, deodorization and discolouration of fluids, gas adsorption.

In particular, in the case of methane adsorption, the activated carbons can act as adsorbents in the ANG

(Adsorbed Natural Gas) technology. The 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 allows avoiding the need for high pressures (typical of the CNG Compressed Natural Gas) technology and/or low temperatures (typical of the LNG, Liquefied Natural Gas, technology) for the storage of natural gas .

The technology is based on the adsorption of gas molecules on a porous adsorbent material at relatively low pressure (for example maximum adsorption pressure lower than 100 bar, preferably lower than 70 bar, more preferably lower than 50 bar) and at a temperature equal or close to room temperature, and allows storing, in a pressure vessel filled with this material, a greater quantity of gas compared to the same empty vessel at the same pressure. This increase in gas storage capacity is mainly due to the formation of a thin layer of high-density gas molecules 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) .

The preferred activated carbons for the ANG technology are mainly microporous. According to the IUPAC terminology "Manual of Symbols and Terminology" (1972), Appendix 2, Part I Coll. Surface Chem. Pure Appl . Chem., Vol. 31, page 578, the pores with a diameter less than 2 nm are defined micropores, those with a diameter comprised between 2 and 50 nm are defined macropores, those with a diameter greater than 50 nm are defined macropores. The surface area and the porosity of the samples were determined by the N2 adsorption-desorption isotherms at the temperature of liquid nitrogen (77 K) , using a Micromeritics ASAP 2020 tool .

Before acquiring the isotherms, the samples (~ 30 mg) in powder form are degassed for 16 hours at 200°C under vacuum. The specific surface area (SSA) is evaluated using the BET method. The total specific Gurvitsch volume (VP) of the pores at 0.99 of p/pO. 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 as microporous volume.

Adsorption measurements of high-pressure methane were performed using the Rubotherm Isosorp magnetic suspension balance. Before the measurement the samples are pre-treated under vacuum at 200°C for 15 hours. Adsorption tests were performed at 25°C. The methane is loaded with successive pressure increments of 5 bar, leaving a 3-hour equilibrium time for each pressure. For the determination of the mass of adsorbed gas, the mass variation Am as a function of the pressure is added to the buoyancy force, which is a function of the volume of the empty system, the sample volume and the density of the gas moved at the analysis pressure and temperature. The adsorption values reported are always referred 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 adsorption is particularly relevant inside the micropores (d <2nm) , in which the Van der Waals attraction forces between gas molecule and the surface of the solid allow 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] the pores characterized by dimensions equal to the sum of the diameters of a number of methane molecules comprised between 2 and 4, therefore diameters comprised between 0.8 and 1.5 nm were identified as optimal. Furthermore, the additional presence of mesopores (pores with a diameter comprised between 2 and 5 nm) , constitutes a further element able to promote the diffusion of the massive gaseous stream (existing outside the adsorbent particles) towards the micropores responsible for the adsorption phenomenon. The textural characteristics required in the case of ANG application are particularly stringent, compared to those required for the other applications of activated carbons (e.g.: filtration, purification, deodorization and discolouration of fluids) .

The possible applications of the ANG technology range from the storage of fuel for vehicular transport (Natural Gas Vehicles - NGV) , to the storage for industrial operations, to the transport of NG in cylinders for small-scale use as an alternative to acetylene, up to the transport of NG on a large scale. In the latter sense, the 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 sea from the gas production site to the destination point.

Some examples are given below for a better understanding of the invention and of the scope of application despite they do not constitute in any way a limitation of the scope of the present invention. EXAMPLE 1 : Preparation of activated carbon starting from the cake of a refinery purge, activated without the pyrolysis phase before the activation phase - sample AC1.

Table 1: Analysis of the purge

A sample of purge from a refinery is placed in a stove, nitrogen blanketed, and with Temperature T1 set at 200°C. Once the complete homogeneity of the sample is reached, the set point of the stove is set at 100°C. After about

0.5 hours stay at 100°C the supernatant or clarified liquid is removed. The dense phase that remains in the bottom constitutes the "cake" phase.

The cake and KOH (K0H:cake 3:1 weight ratio) are mixed and ground in a ball mill for 30 minutes at 300 rpm. Then, the mixture is introduced into a horizontal kiln in a nitrogen atmosphere .

The conditions of activation are:

~ T: 700²C

— Time: 2 hours

~ Atmosphere: N2 100 ml/min.

After 2 hours, the sample is cooled in N2 to room temperature .

The activated carbon is washed with a 20% vol. solution of HC1 at 37% for 1 hour under stirring. After acid washing, the activated carbon is filtered and washed with water up to neutral pH. Finally, it is dried for 15 hours at 75°C. The yield in activated carbon is 50% by weight with respect to the weight of cake. The textural properties and the adsorption capacity of methane are shown in Table 2.

Table 2: Textural and performance characterization

COMPARATIVE EXAMPLE 1: Preparation of activated carbon starting from the cake of a refinery purge, in two steps: pyrolysis and activation - AC2 sample.

The cake obtained as described in Example 1 is loaded into a reactor which is pressurized at 10 bars with N2 and heated to 460°C. Once the temperature is 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, as described in Example 1. The yield in activated carbon is 40% by weight with respect to the weight of cake.

Claims

1. Process for the preparation of activated carbon, using residues from refinery or hydroconversion processes of heavy petroleum products as carbon sources, which comprises the following steps:

• separating said heated purge by static sedimentation obtaining a clarified stream and a cake ;

• then cooling such activated carbon at room temperature and washing with water, possibly in the presence of an acid, up to neutral pH; then

• drying such washed activated carbon at a temperature between 50°C and 200°C.

2. Process according to claim 1, wherein the residues of refinery or hydroconversion process are heated at a temperature ranging from 200°C to 220°C.

3. Process according to claims 1 or 2, wherein the temperature is lowered in the range between 100 °C and 170⁰ C .

4. Process according to any one of Claims 1 to 3, in which controlled temperature lowering takes place:

• by using an adequately sized and thermostated tank, or

by mixing the hot current to be decanted with a cold flow.

5. Process according to any one of Claims 1 to 4, wherein the physical activation takes place by treatment at high temperatures in the presence of CO₂ or water vapour .

6. Process according to any one of Claims 1 to 5, wherein the activation is carried out chemically by treatment at high temperatures in the presence of a compound selected from ZnCl2, K2CO3, Na2CC>3, KOH, NaOH, mineral acids .

7. Process according to claim 6, wherein the compound is KOH, at KOH/cake ratios ranging from 0.5/1 to 5/1.

8. Process according to any of the claims from 1 to 7, wherein the temperature of the activation treatment is between 500°C and 900°C and the time between 1 hour and 10 hours .

9. Activated carbon, obtainable with the process according to any of the claims from 1 to 8, having the following characteristics:

- reversible type I nitrogen adsorption/desorption isotherms at 77K;

- a specific surface area (SSA) greater than or equal to 1800 m²/g;

- a total pore volume greater than or equal to 0.8 ml/g, of which the microporous component contribution is between 70% and 95% by volume;

- a contribution of the mesoporous component comprised between 5% and 30% by volume with respect to the total pore volume;

- an adsorption capacity of methane greater than or equal to 14% by weight.