CZ16277U1 - Sorbent of activated charcoal type - Google Patents

Description

Activated carbon type sorbent

Technical field

The invention relates to an activated carbon type sorbent prepared from a carbonaceous substrate having a suitable grain size by activation under selected process conditions. The sorbent is suitable for the purification of liquids, in particular waste water, in the separation of mixtures in the liquid phase and for the purification and separation of industrial gases, in particular for the capture of polychlorinated dibenzodioxins and dibenzofurans. BACKGROUND OF THE INVENTION

Sorbents of this type are porous substances consisting mainly of carbon. They are prepared by heat treatment of either natural feedstocks, such as coconut shells, wood and other biomass, coal, tar and pitch, or carbon-rich synthetic materials, such as waste rubber. Their preparation is based on thermal treatment of the feedstock and, if necessary, subsequent activation of the treatment products, for example with water vapor, carbon dioxide, nitrogen or suitable inert gases or mixtures thereof. Specific-acting chemicals such as zinc chloride or potassium hydroxide can also be used for activation. Patent application EP 488 105 discloses activated carbon made of rubber worn tires. This activated carbon has a specific surface area of 150 to 500 m ² / g, a pore size of 10 to 40 nm and a pore volume of 1.3 to 5 ml / g. It is suitable for the capture of sulfur and nitrogen oxides in the combustion of heavy petroleum derivatives. Patent CZ 282 859 discloses activated carbon prepared from a partial oxidation product of hydrocarbons, which is activated by annealing in an inert gas stream optionally containing water vapor, and which is further processed by extraction with water or dilute acid. EP 1 276 694 discloses a process for producing spherical activated carbon having a particle diameter of about 0.4 mm, a density of 0.4 to 0.8 kg / l and a specific surface area of 0.8 to 1.5 m ² / g. The process for producing this activated carbon consists in pyrolysis of spheroidal polymer particles, such as styrene or divinylbenzene, into which free-radical-forming acidic sulfonic groups are introduced. The poly25 meters are first subjected to continuous pre-carbonization, after which they are carbonized and finally subjected to activation at a temperature of from 850 to 960 [deg.] C., the activation medium disclosing a mixture of water vapor and nitrogen.

In general, the purpose of reprocessing carbon-rich feedstocks is to reduce the content of non-carbonaceous fractions and to create a solid skeleton with a large internal surface and controlled porosity.

The essence of the technical solution

An activated carbon type sorbent prepared by activating the carbonaceous substrate by heating to a temperature of 600 to 1000 ° C, optionally in the presence of an activating medium suitable for gas phase purification and separation or liquid phase purification and separation, is obtained by heat treatment of the solid carbon residue. % by weight pyrolysis of waste unsorted polyethylene terephthalate; carbon has a specific surface area of 100 to 1500 m ² g ¹ and a pore volume of from 0.25 to 0.75 cm ³ g '.

The grain size of the starting carbon substrate is preferably up to 500 microns and the specific surface area of the sorbent is from 500 to 1250 m ² g -1.

The properties of the activated carbon type sorbent according to the present invention are to a large extent dependent on the process conditions of heating and activation, as shown by the exemplary embodiments of the present invention.

The preparation of the activated carbon sorbent consists in that the solid carbon residue from the pyrolysis of the waste unsorted polyethylene terephthalate is mechanically adjusted to a suitable grain size that is optimal for the reaction activation process and the intended use of the product. The particulate treated charge is activated in a suitable heating device in a moderate stream of gaseous medium at

Temperature range of 600 to 1000 ° C for several hours. The thermal gradient of the charge heating temperature corresponds to the type of equipment used, which may be stationary or rotary. By heating, the volatile combustible content is reduced in the treated batch, the amount of ash is increased and the surface is increased. The product may contain up to 98 wt. carbon. The properties of the heating products are improved by activation, i.e., by heat treatment of the batch under continuous flow of a suitable gaseous medium. Water vapor, nitrogen, oxygen, carbon dioxide, or mixtures of the aforementioned gases may be used in a suitable ratio. The presence of the activating medium induces a partial gasification of a portion of the carbon present, which is accompanied by a mass loss of the solid phase while increasing the specific surface area. The surface of the product thus formed has a high sorption capability, which is characterized by a total specific surface area, measured by BET, in the range of 100 to 1500 m ² g '. The achieved specific surface area depends on the input parameters of the charge, ie on its granularity and on the process conditions of heating or cooling. activation, that is, the time and temperature of the gaseous medium used during activation and its amount. Increasing the activation time beyond about 20 hours no longer results in a significant increase in the specific surface area; the process is accompanied by a significant weight loss of the reworked batch as the time increases to 15.

Examples of technical solution

The dependence of the surface area of the sorbents reached on the activation time was verified in such a way that under constant process conditions, ie a temperature rise gradient of 5 ° C / min to a temperature of 870 ° C, which was then constant throughout the activation. medium, which was fed in an amount corresponding to 1.9 ml / min of liquid water and at a particle size of 150 to 500 microns of the embedded carbon substrate.

The activation times and respective surface area, pore volume and carbon content values are given in Table 1:

Activation time (hrs) Specific surface area (m ² g ¹ ) Pore volume (cm ³ g ^-1 ) Content C (% by weight) 1 480 0.285 93.69 2 651 0.354 95.22 3 804 0.441 96.50 4 941 0.531 94.00 5 1098 0.560 93.90 6 1125 0.630 94.10

Under the same process conditions and a constant activation time of 5 hours, the influence of the batch composition composition on the specific surface area and the volume of sorbent pores formed was monitored.

The density composition of the charge and the respective specific surface area and pore volume of the sorbents are given in the table below. 2:

Charge Grain (pm) Specific surface area (m ² g ') Pore volume (cm ³ g '') 50 to 150 965 0.539 0 to 50 1220 0,716

Examples of the use of active carbon sorbents

Examples 1 to 4 were carried out with a sorbent according to the invention with a specific surface area of 1125 m ² g · 'and a grain size of 50 to 150 micrometers, which was activated for 6 hours by steam at 870 ° C.

Example 1: Adsorption of benzene

Benzene adsorption was performed gravimetrically. The sorbent weight was 0.9842 g.

The sample was soaked with 2.0 ml benzene. After wetting with benzene, a slurry was formed, which was then dried to a free-flowing state and further dried at 105 ° C for 1.5 hours.

-2EN 16277 Ul

The adsorption weight was 1.1863 g. After conversion per gram of carbon, it was determined that 205 mg of benzene was adsorbed, corresponding to 20.5% by weight of the weight.

Example 2: Adsorption of humic substances

Verification and adsorption of humic substances was carried out in a column packed with 0.9896 g of sorbent. A 9 mm diameter SPE LC-Si hopper was used. The bottom and top of the column were sealed with a polypropylene frit. The column height of the sample was 33 mm. Potassium humate in an aqueous solution was used for the humic adsorption assay

92.9 mgl · ¹ . 500 ml of potassium humate solution were passed through the column under gentle vacuum. The final concentration of potassium humate in the solution after passing through the column was 57.9 mgl · ¹ .

Example 3: Adsorption of monovalent phenols

Verification and adsorption of monovalent phenols was performed on a 9 mm diameter SPE LC-Si discharge column. The bottom and top of the column was sealed with a polypropylene frit. The sorbent column height was 33 mm. The monovalent phenol adsorption assay was performed with medium polar 2,5-dimethylphenol. 500 ml of a solution of 2,5-dimethylphenol at a concentration of 8.70 ± 0.87 mgl · ¹ flowed through a sample of sorbent weighing 0.9969 g, under a slight vacuum. After passing the solution through the column, the concentration of the 2,5-dimethylphenol solution was found to be 0.03 mgl · ¹ ± 0.01 mgl · ¹ .

Example 4: Adsorption of monovalent chlorinated phenols

A test for the verification of adsorption of monovalent chlorinated phenols was carried out on a 9 mm diameter SPE LC-Si discharge column with a bottom and top closed with a polypropylene frit.

The column contents were 0.9296 g, the sorbent column height was 32 mm. The adsorption test for monovalent chlorinated phenols was carried out with a sample of 500 ml of a solution of polar 2,5-dichlorophenol at a concentration of 21,731 mgl · ¹ (expressed as AOX = adsorbable organic halogen halides (Cl)). After passing the sample solution through the column, the final concentration of 2,5-dichlorophenol was determined to be 0.009 mgl · ¹ (expressed as AOX (Cl)).

Example 5: Hydrocarbon adsorption tests and the possibility of using a sorbent as a chromatographic column

The solid residue from the pyrolysis of waste unsorted polyethylene terephthalate was ground and milled to a grain size of 50 to 150 µm and was activated with steam at 870 ° C for 5 hours. A specific surface area of 965 m ² g ^-1 was achieved. A Teflon 1 m long packed column was prepared to test and verify adsorption for the C-C ₅ hydrocarbon separation. The column flow rate was 30 ml / min nitrogen, column temperature 190 ° C, injector temperature 150 ° C, and flame ionization detector (FID) temperature 300 ° C. A calibration mixture of methane, ethene, ethane, propene, propane, isobutane, n-butane, isopentane and n-pentane was used for the adsorption and hydrocarbon separation tests. The relative elution times and hydrocarbon separation under the conditions described above were as follows: methane 1.0 min, ethene and ethane 6.0 min, propene 18 min, other hydrocarbons ie propane, C ₄ and C ₅ were not detected. Higher hydrocarbons are not released and are trapped by the sorbent.

The hydrocarbon separation tests were also verified in programmed temperature mode: initial column temperature 130 ° C (1st isotherm), dwell time 0 min., Temperature rise 5 C / min, 2nd isotherm 200 ° C and at dwell 30 min. Under these conditions, the hydrocarbon separation was expressed as relative elution times with the following separation: methane 2 min, ethene 6 min, ethane 8 min, propene 16 min. This confirmed the validity of the first test.

Further tests were performed with a thermal conductivity detector (TCD). A new 1.0 m long, 1/8 diameter stainless steel packing column was prepared for the tests. The laboratory prepared mixtures of hydrogen, air, methane and carbon dioxide were used for adsorption and separation of permanent gases. The first tests were performed isothermally at 100 ° C, 40 ml / min argon flow, 150 ° C injector temperature, 150 ° C TCD detector temperature and 80 mA current. The packed column consisted of activated carbon with a specific surface area of 965 m ² g ^-1 with a grain size of 50 to 150 µm. Relative elution

The times and separation of permanent gases under the above conditions were as follows: hydrogen

0.183 min, air 0.415 min, methane 1.281 min, and carbon dioxide 2.984 min. Additional tests were performed isothermally at a temperature of 130 ° C, a flow rate of 35 ml / min helium (maximum difference in thermal conductivity of helium and monitored components), injector and TCD temperature 150 ° C, current 100 mA. A laboratory-prepared mixture of hydrogen, air, methane, water was used for adsorption and separation of permanent gases and a mixture of air and carbon dioxide was dosed separately. The relative elution times and permanent gas divisions were determined as follows: hydrogen 0.163 min, air 0.335 min, methane 0.911 min, water 1.747 min and carbon monoxide 1.960 min. Tests carried out at a reduced column temperature of 60 ° C result in partial separation of air and carbon monoxide.

Chromatographic control tests confirmed that the activated carbon sorbent prepared according to the present invention is a suitable material for the purification of flue gases from waste incineration plants, especially as a so-called dioxin filter for the capture of polychlorinated dibenzodioxins and dibenzofurans (PCDD and PCDF).

Claims (3)

15 PROTECTION REQUIREMENTS An activated carbon type sorbent prepared by activating a carbonaceous substrate containing 90 to 98 wt. carbon by heating to a temperature of 600 to 1000 ° C, optionally in the presence of an activating medium, characterized in that it has a specific surface area of 100 to 1500 m ² g 'and a pore volume of 0.25 to 0.75 cm ³ g ·', is a solid residue from the pyrolysis of waste polyethylene terephthalate. A sorbent according to claim 1, characterized in that it adsorbs both polar and non-polar organic substances, with the exception of hydrocarbons having carbon numbers of four or less at temperatures of about 200 ° C. Sorbent according to claim 1 or 2, characterized in that it has a grain size of up to 500 25 microns and a specific surface area of from 500 to 1250 m ² g -1, effective in capturing polychlorinated dibenzodioxins and dibenzofurans from the waste gases.