PL242673B1 - Method for producing nanoporous sorbents with selective adsorptive properties - Google Patents

Abstract

The subject of the application is a method for the production of activated carbons consisting in the carbonization of a carbon precursor in the absence of oxygen in the temperature range from 300°C to 600°C and activation with the use of surface-developing agents, characterized in that the carbonization step is carried out in an atmosphere of methane as an inert gas which is also a source of thermal energy, with carbonization being carried out at a temperature increase of 5 - 20°C/min, and then activation from 30 to 100 min, at a temperature of 800 - 900°C, using as surface developing substances: carbon dioxide, water vapor and carbon dioxide and water vapor simultaneously in various quantitative ratios.

Description

The subject of the invention is a method of producing nanoporous sorbents with selective adsorption properties.

The invention belongs to the technical field of chemical engineering and materials engineering.

The high standard of life and health of people depends mainly on guaranteeing very good conditions for protection in the material sphere, but also in the sphere of environmental comfort. This guarantees no impact of the environment on health and social conditions. In this approach, environmental pollution with various types of gaseous and solid waste (dust) effectively destroys all outlays on health care and medicine. The costs of preventing social diseases resulting from environmental pollution, including lung and heart diseases and undesirable genetic changes, invested in the sphere of health protection, are many times higher than the costs of preventing the impact of the environment on citizens.

So far, lignite has been mainly used only for energy purposes. In such applications, it is responsible for the emission of exhaust gases into the atmosphere, including significant amounts of CO2. Reducing carbon dioxide emissions to the atmosphere will eliminate the possibility of using lignite in the energy sector in the long term. The inability to use this raw material will significantly reduce its extraction.

In many developed countries, lignite is used as a precursor for the production of activated carbons.

Thanks to its properties, activated carbon is an irreplaceable adsorption material in industry. The economic aspect of obtaining, application versatility, as well as the ability to control the porous structure allow for a wide range of applications in many fields of science, technology and medicine. You can constantly find newer scientific reports and inventions that use carbon with a developed structure. Therefore, for these and many other reasons, it is of interest to many research and industrial centers.

In the work of Brian C. Young, Edwin S. Olson, Curtis L. Knudson, and Ronald C. Timpe; Activated carbons from North Dakota lignite and leonardite; University of North Dakota Energy & Environmental Research Center (EERC) Grand Forks, ND 58202 describes the preparation of activated carbons from lignite and leonardite. Initially, the precursor was fragmented and subjected to derivatographic analysis in order to determine the optimal temperatures of the carbonization and activation processes. Three carbonization temperatures (350°C, 480°C and 550°C) were determined for the tests, while the activation was carried out by obtaining a series of materials at a temperature of 700°C through 750°C, etc. up to 1000°C. The porous structure was developed with steam for 10 or 20 minutes at a volume ratio of steam to nitrogen of 20/80. Finally, the materials were purified with hydrochloric and hydrofluoric acid. The obtained adsorbents were used to absorb sulfur dioxide. The most effective activated carbon stored in its volume 10.9% by mass of the argon stream containing 10,000 ppm SO2.

In 2012, S. Bhutto, M. N. Khan, Preparation and characterization of activated carbon from lignite coal by chemical activation and its application for lead removal from wastewater, IJCEES 3(3) pp. 28-39. 2012, where the preparation of the preparation of activated carbons from lignite using chemical activation was presented. The raw material was initially screened, cleaned and dried at 100°C, omitting the carbonization process, which should be noted. The process of developing the porous structure was carried out for 24 hours using H 2 SO 4 acid. The obtained product was used to remove Pb (II+) ions from the sewage. The maximum adsorption was 333.30 mg/g.

A similar application of activated carbons for liquid phase adsorption can be found in L. Guocheng, H. Jiao, L. Liu, MA Hongwen, F. Qinfang, W. Limei, W. Mingquan, Z. Yihe, The Adsorption of Phenol by Lignite Activated Carbon, Separation Science and Engineering, Chinese Journal of Chemical Engineering, pp. 380-385 19(3) 2011. In the published studies, activated carbons were used to adsorb water-soluble phenol.,

Yan Wu, Jing-Pei Cao, Xiao-Yan Zhao, Zhi-Qiang Hao, Qi-Qi Zhuang, Jun-Sheng Zhu, Xing-Yong Wang, Xian-Yong Wei, Preparation of porous carbons by hydrothermal carbonization and KOH activation , of lignite and their performance for electric double layer capacitor, Electrochimica Acta, pp. 397-407 252 (20) 2017, a series of porous carbons has been characterized. The process consisted of pre-treatment - hydrothermal carbonization, followed by chemical activation with KOH.

The activated carbons obtained were used for double-layer capacitors (EDLC). In the discussion of the results, a detailed influence of the material preparation parameters on the final pore structure and electrochemical properties was presented. An important aspect of the obtained coals was mainly developed structure in the range of microporosity. The porosity of the adsorbents was characterized using low-temperature (-196°C) nitrogen adsorption-desorption isotherms. The best developed specific surface area of coal presented in the paper was 3162 m ² /g. The electrochemical performance of an electrically symmetric double-layer capacitor (EDLC) made of porous carbons was investigated using cyclic voltammetry and electrochemical impedance spectroscopy.

In research conducted by F.J.M. Carrott and others described in P.J.M. Carrott, I.P.P., Cansado, P.A.M. Mourao, M.M.L. Ribeiro Carrott, N.D.B. Louro, A. Albiniak, E. Broniek, M. JasieńkoHałat, On the use of ethanol for evaluating microporositv of activated carbons prepared from Polish lignite, Fuel Processing Technology, pp. 34-38, 103, 2012, lignite from Poland was used. A series of microporous activated carbons were obtained by chemical activation (KOH) or steam activation. Adsorbents were characterized using N2 adsorption at 77 K and CO2 at 298 K. The adsorption efficiency of ethanol, benzene and cyclohexane was presented in the paper. The analysis of isotherms involved the use of the as method. The work confirmed an important aspect that ethanol is an experimentally convenient adsorption agent for research purposes and can be used as a standard in experiments characterizing activated carbons. A particularly interesting observation was that ethanol can access all the microporosity even in samples containing ultramicropores.

In the literature, one can find reports on the use of brown coal to obtain coals whose specific surface was developed with carbon dioxide in a rotary tubular furnace, see I. Karaman. E. Yagmura, A. Banford, Z. Aktas, The effect of process parameters on the carbon dioxide based production of activated carbon from lignite in a rotary reactor, Fuel Processing Technology, pp. 34-41, 118, 2014. Such materials are characterized by a structure dominated by micropores (according to UIPAC 0.5 to 2 nm). In the presented experiments, the effects of changes in the final product in relation to various parameters of the production process were determined; temperature, activation time, pre-oxidation time, CO2 flow rate, heating rate and rotation rate. The specific surface area (Sbet) of the described materials ranged from 331.5 m ² /g to 696.4 m ² /g, total pore volume from 0.18 cm ³ /g to 0.46 cm ³ /g. It was important to present the efficiency of all processes, which ranged from 11.06% to 61.06%. Tests have shown that increasing the CO2 flow significantly increases the development of the BET surface of the products. In addition, the work showed that the reactor should rotate during the activation process, because such action intensifies the development of the activated carbon surface by up to 16%. Reactor rotation has been found to be an effective way to increase the production of activated carbon in terms of surface area without significantly reducing productivity due to mechanical destruction of the grains.

Also known from the state of the art are numerous patent applications relating to the discussed issues.

From the Polish patent No. Pat. 163458 "Method of obtaining activated carbon in a fluidized bed" there is a known solution in which a coal-bearing raw material was introduced into the activation reactor next to the char.

There are also solutions in which crushed undried molasses (Pat. 223461) and dried molasses (Pat. 228402) are used for the production of activated carbon.

From the Polish patent No. Pat. 1935331 it is known to use activated carbon containing K2CO3 or K2CO3/MnO2 components to remove hydrogen sulphide and odors from the sewage system.

The aim of the invention is to develop a method of producing a new group of nanoporous sorbents with selective adsorption properties, which are modified carbon materials with a developed surface. An innovative carbonization and activation process was developed to develop the porous surface using CO2, H2O and KOH.

The process according to the invention consists in preliminary grinding and drying of lignite in known devices, then heating the raw material to a temperature between 300°C and 600°C and in these conditions putting it in contact with methane, the temperature of which is slightly higher than the temperature of coal. This process, called coal carbonization, is carried out in a continuous flow apparatus, preferably in a Herreshoff-type plate furnace. The residence time of coal in contact with methane is selected depending on the grain size of the raw material, and the weight proportions of methane to coal range between 0.05 kg ^CH4 /kgC and 2.5 kg ^CH4 /kgC. In the carbonization stage, a partial decomposition of gaseous methane takes place, and the emerging carbon atoms encounter solid particles and settle on them, creating 2D structures similar in geometric properties to flake graphene particles. The hydrogen formed during the partial decomposition of methane, favorably reduces volatile organic compounds and increases the chemical activity of coal. Gases containing unreacted methane, volatile compounds from coal carbonization, small amounts of hydrogen and small amounts of coal dust are directed to the combustion furnace, thanks to which energy is obtained to heat coal, methane and carbon dioxide and steam used for activation (further part of the process) water.

After the carbonization process, the carbon is directed to the activation stage. The activation step should be understood as a process in which the coal surface is developed at high temperature (and possibly at elevated pressure, more often at normal pressure) by creating pores (cavities, voids) using various substances showing the nature of a weak oxidant at elevated temperature relative to coal. (0 oxidation state). There are chemical activation (using e.g. KOH, H3PO4, ZnCl) or physical activation (O2, CO2, water vapour). For this purpose, the coal is heated with gaseous carbon dioxide to a temperature of 400°C to 800°C and treated (contacted) with gaseous carbon dioxide or gaseous carbon dioxide with an admixture of superheated steam. The volume fraction and superheating of the water vapor are selected so that no condensation occurs anywhere in the apparatus. The contact between the heated gases and the coal is preferably carried out in a Herreshoff-type tray furnace. The contact time is determined by the quality of the coal discharged from the carbonization stage. The weight proportions between carbon dioxide and carbon after carbonization range from 0.05 kg ^CO2 /kgC to 6 kg ^CO2 /kgC. The coal discharged from the apparatus is cooled by a stream of methane and fresh carbon dioxide supplied to the activation process. After activation, gases are returned to the activation process in 80 - 98% of their initial amount. The excess of gases "Perch Gas" is added to methane after carbonization and directed to the kiln.

The essence of the invention is a method of producing activated carbons consisting in the carbonization of a carbon precursor without access to oxygen in the temperature range from 300°C to 600°C and activation with the use of agents developing the specific surface, characterized in that the carbonization step is carried out in an atmosphere of methane as an inert gas which is also a source of thermal energy, carbonization is carried out at a temperature increase of 5-20°C/min, and then activation from 30 to 100 min, at a temperature of 800-900°C, using as surface developing substances: carbon dioxide, water vapor and carbon dioxide and water vapor simultaneously in various quantitative ratios.

Preferably, the carbonization process proceeds in conditions with partial decomposition of methane.

Preferably, the weight ratio of methane to brown coal is in the range of 0.05 to 2.5 kg ^CH4 /kgC.

Preferably when. methane together with gaseous components after carbonization is an energy carrier, and the process is autothermal.

The invention has been implemented in two embodiments, where:

Example I

1,000 kg of lignite with an average grain size of 12 mm and a moisture content of 10% by weight was introduced into the process. After the milling process, the average grain size was 0.8 mm and the moisture content dropped to 9%. 0.989 kg of coal with a grain size of 0.8 mm and 0.010 kg of water vapor and 0.001 kg of coal dust were discharged from the mill. The raw material prepared in this way was heated to 450°C and fed to the carbonization stage, to which 0.300 kg of methane was also introduced. After one hour, 0.480 kg of coal was completely removed from the apparatus. 0.260 kg of methane, 0.090 kg of water vapor and 0.459 kg of gasified volatile substances, including hydrogen produced as a result of methane reduction, remained in the gaseous phase. Methane in the amount of 0.040 kg was reduced to carbon and hydrogen. 0.480 kg of coal after carbonization was directed to the activation process. This intermediate was heated to 680°C and contacted with 1.000 kg of carbon dioxide gas and 0.010 kg of steam. The process of contacting the two phases was carried out for 1.5 hours, and then 0.465 kg of activated carbon was discharged from the apparatus, which was cooled in two stages directly with a stream of cold methane and carbon dioxide to a temperature of 50°C. Gases containing 1.000 kg of carbon dioxide and 0.010 kg of water vapor and 0.015 kg of coal dust were separated into two streams. The first stream containing 0.90 kg of carbon dioxide, 0.009 kg of water vapor and 0.0135 kg of coal dust was returned to the activation process by adding carbon dioxide and superheated steam to this stream in balance amounts, the second stream containing 0.10 kg of carbon dioxide, 0.001 kg of steam and 0.0015 kg of coal dust were added to the methane stream after carbonization and directed to the furnace.

As a result of the process carried out in this way, 0.465 kg of activated carbon with an average grain size of 0.75 mm and a specific surface area of about 2120 m ² /g of product was obtained.

Flue gases from the process are mainly carbon dioxide, water vapor and small amounts of sulfur and nitrogen oxides from brown coal gasification products. The content of these components does not exceed the level of 0.02% vol. (200 ppm) for sulfur compounds and 0.005% vol. (50 ppm) for nitrogen compounds.

Example II

1,000 kg of lignite is crushed to obtain grains with a size of 0.2-0.3 mm, which are then dried in order to get rid of water unnecessarily burdening the structure of the raw material. The dry mass is then placed in an oven with a methane flow rate of 0.5 l/m and carbonized at 500°C with a temperature increase of 20°C/min. Subsequently, the char obtained is transferred to the second zone of the furnace and the activation process is carried out for 30 minutes at a temperature of 850°C with a flow of 0.5 l/min CO2 as a factor developing the porous structure. Finally, the sample is removed from the hot zone of the furnace while cooling it in a stream of methane, which is heated and used in another process step. In the presented way, activated carbon is obtained characterized by high strength and grain fraction in the range of 0.9-0.26 mm while maintaining high efficiency. Characterizing the porous structure of activated carbon, micropores and narrow mesopores predominate. The resulting adsorbent effectively absorbs volatile organic compounds from the gaseous phase, including carcinogens, e.g. benzene, which are particularly effective.

Claims (4)

1. A method of producing activated carbons consisting in the carbonization of a carbon precursor in the absence of oxygen in the temperature range from 300°C to 600°C and activation with the use of surface-developing agents, characterized in that the carbonization step is carried out in an atmosphere of methane as an inert gas, which is at the same time a source of thermal energy, carbonization is carried out at a temperature increase of 5-20 ° C / min, and then activation from 30 to 100 min, at a temperature of 800-900 ° C, using as surface developing substances: carbon dioxide, water vapor and carbon dioxide carbon and water vapor simultaneously in various quantitative ratios. 2. The method of claim 1, characterized in that the carbonization process takes place in conditions with partial decomposition of methane. 3. The method according to claims 1 and 2, characterized in that the weight ratio of methane to brown coal is in the range of 0.05 to 2.5 kg ^CH4 /kgC. 4. The method according to claims 1, 2 and 3, characterized in that methane together with gaseous components after carbonization is an energy carrier and the process is autothermal.