IT201800011015A1 - PROCESS FOR THE PREPARATION OF ACTIVATED CARBON FROM PETROLEUM RESIDUES - Google Patents

Description

PROCEDURE FOR PREPARING ACTIVATED CARBON FROM PETROLEUM RESIDUES

Description

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

Refinery or hydroconversion processes of heavy petroleum products lead to the formation of purge streams, petroleum residues, which typically contain unconverted feedstock, metals of the used catalyst, catalyst and carbon residues. It is therefore clear how important it is for the purpose of improving production efficiency and the conversion of a refinery or the hydroconversion processes of heavy hydrocarbons, to treat the purge trying to enhance the components that properly treated can generate activated carbon. The purge can be treated in such a way as to separate a stream of light, or clarified, from a solid phase known as a “cake”.

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

In the present patent application for heavy petroleum products we mean crude oils, heavy crudes, bitumens from tar sands, distillation residues, heavy distillation cuts, deasphalting residues, synthetic oils produced by the Fischer Tropsch process, vegetable oils, oils derived from coke and bituminous shales, oils obtained by thermal decomposition of waste, polymers, biomass.

In the present patent application, the term "purge" means organic streams in the slurry phase that contain an amount of hydrocarbons having a boiling point greater than or equal to 540 ° C greater than 65% by weight, an amount of asphaltenes greater than or equal at 20% by weight and characterized by the presence of solids contents greater than or equal to 4% by weight, the rest being hydrocarbons having a boiling point between 350 ° C and 500 ° C. The purging solids contain carbon residues and metal compounds which may contain transition metal sulphides, such as molybdenum, iron, nickel and vanadium, and having sub-millimeter dimensions.

For the purposes of this discussion, the term "solid" means the fraction insoluble in tetrahydrofuran, indicated in this text with the initials 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 based on their insolubility in n-paraffins (typically having 5 to 7 C5-C7 carbon atoms). Such compounds generally consist of polycondensed aromatic cores variously branched and joined together through linear chains. These compounds can contain heteroatoms (S, N) which give them their polar nature.

In the present patent application, the term "cake" means a solid material at room temperature with glassy characteristics (ie the appearance of the cake has the characteristics of glass) which make it easy to grind and consequently transportable even for long stretches without requiring a particular thermostating. This characteristic persists at temperatures ranging in the range between 50 ° C and 60 ° C.

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

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

The cake contains solids as defined above in the text of this patent application.

The solids of the cake contain carbon residues and metal compounds that may contain transition metal sulphides, such as molybdenum, iron, nickel and vanadium, and having submillimeter dimensions.

In the present patent application the term "clarified" means a hydrocarbon residue free of solids and metals, with a content of asphaltenes lower than that initially present in the purge, and fluid already at temperatures between 100 ° C and 160 ° ° C.

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

In the present patent application, all the operating conditions indicated in the text must be understood as preferred conditions even if not expressly stated.

For the purposes of this discussion, the term "understand" or "include" also includes the term "consist in" or "essentially consisting of".

For the purposes of this discussion, the definitions of the intervals always include the extremes unless otherwise specified.

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 between 500 to 2500 m <2> / g, due to its high porosity.

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

The possibility of using petroleum residues for the preparation of activated carbon is known (GB 701174, 1951, Standard oil). The process requires that the residue is subjected to coking and / or distillation and subsequently treated with an activating agent at high temperatures.

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

The process involves 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 production of activated carbon and a process for increasing its surface area.

A carboxylic acid of an aromatic 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. To increase the surface area of the activated carbon, it is impregnated with a base and subsequently with an acid anhydride.

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

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

Typically in the preparation of an activated carbon, the raw material is initially subjected to a 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.

Activation can take place physically, for example by treatment at high temperatures in the presence of CO2, O2 or steam at temperatures between 800 ° C and 1000 ° C,

causing the decomposition of a portion of the material of

departure and production of numerous pores and cracks.

Activation can also take place chemically, for example

for example for treatment at high temperatures in

presence of ZnCl2, mineral acids such as H3PO4,

HNO3, K2CO3, Na2CO3, KOH, NaOH. The temperature at which

occurs is generally between 400 ° C and 1000 ° C.

After the removal of the chemical agent through

an extraction remains the porous structure of the coal

activated.

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 understood

between 20% and 60%.

It is therefore the subject of this application for

patent a process for the preparation of coal

active, preferably the described activated carbon e

claimed in the present patent application,

using refinery residues as a source of carbon

or hydroconversion processes of petroleum products

heavy, which includes the following stages:

● Heat a purge to a higher temperature or

equal to 185 ° C and not more than 220 ° C,

● Separate this heated bleed with

static sedimentation forming a current of

clarified and a cake;

● Subject the cake directly to activation by way

physics or chemistry, and excluding that the cake is

subjected to a step of pyrolysis before the step of

activation, forming activated carbon, e

● Then cool down to room temperature e

wash said activated carbon with water, possibly in

presence of an acid, selected for example from hydrochloric acid, acetic acid, sulfuric acid, up to neutral pH; so

● dry the washed activated carbon at a temperature between 50 ° C and 200 ° C.

A further embodiment of the present invention constitutes the activated carbons, obtainable with the process described and claimed, which have the following characteristics:

- Features type I reversible 77K nitrogen adsorption / desorption isotherms

- A specific surface area (SSA) greater than or equal to 1800m <2> / g, preferably between 2000 m <2> / g and 3000 m <2> / g,

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

- a contribution of the mesoporous component of between 5% and 30% by volume, preferably between 10% and 20% by volume with respect to the total volume of the pores;

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

The activated carbons thus obtained make it possible to valorise refinery residues or hydroconversion processes of heavy petroleum products.

The activated carbon thus obtained has a high surface area (SSA) greater than or equal to 1800m <2> / g, preferably between 2000 m <2> / g and 3000 m <2> / g, which makes it particularly effective in gas adsorption. 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, i.e. the weight of activated carbon

with respect to the cake used, preferably between

45 and 70%.

Detailed description.

The Applicant now describes the procedure in detail

for the preparation of activated carbon, subject of the

this patent application.

A refinery or process purge stream

hydroconversion is heated to a temperature

greater than or equal to 185 ° C and not more than 220 ° C,

preferably between 200 ° C and 220 ° C.

The purge is then subjected to

static sedimentation by progressively lowering and in

controlled way the temperature up to the temperature

minimum of 100 ° C, preferably between 100 ° C and

170 ° C, more preferably between 100 ° C and 160 ° C.

Controlled lowering of the temperature can take place

in different ways:

● through the use of an adequately equipped tank

sized and thermostated, for example thermostated

to hot-oil, or

● by mixing the hot stream from

decant, for example heated purge, with a

cold current, for example the clarified it can

be at a temperature ranging from 200 ° C to

80 ° C, considering the appropriate heat balance of

system for calculating the flow rates.

The lowering of the temperature can be of a value

which 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.

Using one of the two previous modes for controlled lowering of the temperature, the temperature varies by a value that 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 asphaltenes insoluble and at the same time make the clarified part movable, allowing its extraction.

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

During the sedimentation phase, the purge is not stirred. Sedimentation forms a light phase, called clarified, and a heavy phase, called cake, depending on the density.

The cake is directly subjected to physical or chemical activation and subsequently cooled to room temperature forming activated carbon. There is no pyrolysis phase before the activation phase.

Activation can preferably take place physically by means of a treatment at high temperatures in the presence of CO2 or water vapor; or chemically, by treatment at high temperatures in the presence of a compound preferably selected from ZnCl2, K2CO3, Na2CO3, KOH, NaOH, mineral acids, such as for example H3PO4 or HNO3. A preferred activation (carbonization) method provides for the treatment with KOH, at KOH / cake ratios ranging from 0.5 / 1 to 5/1, preferably from 1/1 to 3/1. The temperature of the activation treatment (carbonization) is preferably between 500 ° C and 900 ° C and the time between 1 hour and 10 hours, preferably from 1.5 to 8 hours. Activation is typically carried out in the presence of a nitrogen flow between 50 ml / min and 300 ml / min.

Washing is then carried out with water, optionally in the presence of an acid, for example selected from hydrochloric acid, acetic acid or hydrogen sulphide, until a neutral pH is reached; then said washed activated carbon is dried at a temperature comprised between 50 ° C and 200 ° C.

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

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

- a specific surface area (SSA) greater than or equal to 1800m <2> / g, preferably between 2000 m <2> / g and 3000 m <2> / g,

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

- a contribution of the mesoporous component of between 5% and 30% by volume, preferably between 10% and 20% by volume with respect to the total volume of the pores;

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

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

The activated carbon thus prepared can be used effectively in gas adsorption processes, in particular 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 activated carbon is a material that has high adsorbing capacity.

Activated carbon can be used in the field of filtration, purification, deodorization and discoloration of fluids, gas adsorption.

In particular in the case of methane adsorption, activated carbons can act as adsorbents in the ANG (Adsorbed Natural Gas) technology. ANG technology allows the storage of natural gas through solid materials and has advantages both in terms of gravimetric and volumetric energy density, as well as in terms of safety and energy efficiency. In principle, it avoids 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 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 less than 100 bar, preferably less than 70 bar, more preferably less than 50 bar) and at the same or close temperature. at room temperature, and allows to store, in a pressure vessel filled with this material, a greater quantity of gas than 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 key feature for adsorbents is their specific surface area (SSA).

The preferred activated carbons for the ANG technology are mainly microporous. In accordance with the IUPAC terminology "Manual of Symbols and Terminology" (1972), Appendix 2, Part I Coll. Surface Chem. Pure Appl. Chem., Vol. 31, p. 578, micropores are defined as pores with a diameter of less than 2 nm, mesopores those with a diameter 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 the adsorption-desorption isotherms of N2 at liquid nitrogen temperature (77 K), using a Micromeritics ASAP 2020 instrument.

Before 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. Gurvitsch's total specific pore volume (VP) at 0.99 of p / p0. The microporous fraction of the porosity is determined using the DFT method on the basis of the cumulative distribution curves of the pores as a function of their diameter. Microporous volume is considered to be the volume of pores with a diameter less than or equal to 2nm.

High pressure methane adsorption measurements were performed using the Rubotherm Isosorp magnetic suspension balance. Before the measurement, the samples are pretreated in vacuum at 200 ° C for 15 hours. The adsorption tests were performed at 25 ° C.

The methane is charged with successive pressure increases of 5 bar, leaving an equilibrium time of 3 hours for each pressure. To determine the mass of adsorbed gas, the mass variation Δm as a function of the pressure and the buoyancy force are added, which is a function of the volume of the empty system, the volume of the sample and the density of the gas displaced at the analysis pressure and temperature. . The adsorption values reported always refer to excess adsorption, where excess adsorption means the determination of the amount of gas that interacts with the porous surface of the adsorbent.

In the literature it is described that adsorption is particularly relevant within micropores (d <2nm), in which the Van der Waals attraction forces between the gas molecule and the surface of the solid allow for 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 methane molecules comprised between 2 and 4, therefore diameters comprised between 0.8 and 1.5 nm, have been identified as optimal. Furthermore, the additional presence of mesopores (pores with a diameter between 2 and 5 nm), constitutes a further element capable of favoring the diffusion from the massive gaseous stream (existing outside the adsorbent particles) towards the micropores responsible for the phenomenon of adsorption. The textural characteristics required in the case of ANG application are particularly stringent, compared to those required for other applications of activated carbon (eg: filtration, purification, deodorization and discoloration of fluids).

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

Below are some examples for a better understanding of the invention and the scope of application while not constituting 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: Purge Analysis

A purge sample from the refinery is placed in an oven, pulverized in nitrogen, and with Temperature T1 set at 200 ° C. Once the sample is completely homogeneous, the stove Set Point is set at 100 ° C. After about 0.5 hours of permanence at 100 ° C, the supernatant or clarified liquid is removed. The dense phase that remains in the can constitutes the "cake" phase. The cake and KOH (weight ratio KOH: cake 3: 1) are mixed and ground in a ball mill for 30 minutes at 300 rpm. Then, the mixture is introduced into a horizontal oven in a nitrogen atmosphere.

The activation conditions are:

- T: 700ºC

- Time: 2 hours

- Atmosphere: N2 100 ml / min.

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

Activated carbon is washed with a 20% vol. Solution. 37% HCl for 1 hour under stirring. 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 yield in activated carbon is 50% by weight with respect to the cake weight.

Textural properties and 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 - sample AC2.

The cake obtained as described in example 1, is loaded into a reactor which is pressurized at 10 bar 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 the cake.

Claims (9)

CLAIMS 1. A process for the preparation of coal active, using residues as a source of carbon refinery or hydroconversion processes of heavy petroleum products, which includes the following steps: ● Heat a purge to a temperature greater than or equal to 185 ° C and not more than 220 ° C, ● Separate this heated purge by static sedimentation forming a current of clarified and a cake; ● Subject the cake directly to activation by physical or chemical, and excluding that the cake is subjected to a pyrolysis phase before the activation phase, forming activated carbon, e ● Then cool to temperature environment and wash with water called coal active, possibly in the presence of an acid, up to neutral pH; so ● dry the washed activated carbon a temperature between 50 ° C and 200 ° C. 2. The process according to claim 1 wherein i refinery or process residues hydroconversion are heated to one temperature between 200 ° C and 220 ° C. 3. The method according to claims 1 or 2 in which the temperature is lowered in the range between 100 ° C and 170 ° C. 4. The procedure according to any one of the claims 1 to 3 in which the lowering controlled temperature takes place: ● by using a suitably sized and thermostated tank, or ● by mixing the hot stream to be decanted with a cold stream. 5. The process according to any one of claims 1 to 4 in which the physical activation takes place by treatment at high temperatures in the presence of CO2 or water vapor. 6. The process according to any one of claims 1 to 5 in which the activation takes place chemically by treatment at high temperatures in the presence of a compound selected from ZnCl2, K2CO3, Na2CO3, KOH, NaOH, mineral acids. 7. The process according to claim 6 wherein the compound is KOH, with KOH / cake ratios ranging from 0.5 / 1 to 5/1. The process according to any one of claims 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 one of claims 1 to 8, which have the following characteristics: - have reversible type I nitrogen adsorption / desorption isotherms at 77K; - A specific surface area (SSA) greater than or equal to 1800m <2> / g; - a total volume of pores greater than or equal to 0.8ml / g, of which the contribution of the microporous component is between 70% and 95% by volume; - a contribution of the mesoporous component between 5% and 30% by volume with respect to the total volume of the pores; - an adsorption capacity of methane greater than or equal to 14% by weight.