Confrontation of various adsorption models for assessing the porous structure of activated carbons

International audienceHerein, a comprehensive analysis of DFT methods as a tool for evaluating the impact of the nature of the activating agent on the porous structure of activated carbons derived from hazelnut shells is given. The study was based on the use of NLDFT, QSDFT, and 2D-NLDFT methods applied to nitrogen adsorption isotherms, and the results were compared with those formerly obtained by using DR, BET, and LBET methods. Analyses conducted with NLDFT, QSDFT, and 2D-NLDFT revealed a very strong dependence of the results on assumptions about the specific pore model, which calls into question the reliability and credibility of these methods. However, if one takes into account the measurement errors that may during the determination of the adsorption isotherms, as well as the difficulty of selecting a representative sample in a batch of materials (most often non-homogeneous) to be analysed, some imperfections of the DFT methods become acceptable. The analyses in question revealed some limitations of the LBET method which became obvious when the analysis concerned bimodal porous materials with a considerable proportion of mesopores. In such cases, the LBET method, which was formerly designed for analysing microporous materials, may become less reliable

Computer Analysis of the Effects of Time and Gas Atmosphere of the Chemical Activation on the Development of the Porous Structure of Activated Carbons Derived from Oil Palm Shell

The results of the advanced computer analysis of the influence of time and gas atmosphere of the chemical activation process on the microporous structure formation of activated carbons prepared from oil palm shell via microwave irradiation and activation, using potassium hydroxide as an activation agent, are presented in this paper. The quenched solid density functional theory (QSDFT) and the new numerical clustering-based adsorption analysis (LBET) methods were used especially in the analysis of the microporous structure of the activated carbons, taking into account the surface heterogeneity, and the results obtained were confronted with the simple results achieved earlier using Brunauer–Emmett–Teller (BET) and T-plot methods. On the basis of the computer analysis carried out and taking into account the results obtained, it has been shown that the material with the best adsorption properties and suitable for practical industrial applications is activated carbon obtained in a gaseous nitrogen atmosphere at an activation time of 30 min. Moreover, the value of the heterogeneity parameter indicates that the surface area of this activated carbon is homogeneous, which is of particular importance in the practical application. The paper emphasizes that an erroneous approach to the interpretation of analytical results based on gas adsorption isotherms, which consists in basing conclusions only on the values of a single parameter such as specific surface area or micropore volume, should be avoided. Therefore, it is recommended to use in the analysis of measurement data, several methods of porous structure analysis, including methods considering the heterogeneity of the surface, and when interpreting the results one should also take into account the adsorption process for which the analyzed materials are dedicated

Computer Analysis of the Porous Structure of Activated Carbons Derived from Various Biomass Materials by Chemical Activation

In this study, the preparation of activated carbons from various materials of biomass origin by activation with potassium hydroxide and a comprehensive computer analysis of their porous structure and adsorption properties based on benzene (C6H6) adsorption isotherms were carried out. In particular, the influence of the mass ratio of the activator’s dry mass to the char mass on the formation of the microporous structure of the obtained activated carbons was analysed. The summary of the analyses carried out based on benzene adsorption isotherms begged the conclusion that activated carbon with a maximum adsorption volume in the first adsorbed layer and homogeneous surface can be obtained from ebony wood at a mass ratio of the activator to the char of R = 3. The obtained results confirmed the superiority of the new numerical-clustering-based adsorption analysis (LBET) method over simple methods of porous structure analysis, such as the Brunauer–Emmett–Teller (BET) and Dubinin–Raduskevich (DR) methods. The LBET method is particularly useful in the evaluation of the influence of the methods and conditions of production of activated carbons on the formation of their porous structure. This method, together with an appropriate economic analysis, can help in the precise selection of methods and conditions for the process of obtaining activated carbons at specific manufacturing costs, and thus makes it possible to obtain materials that can successfully compete with those of other technologies used in industrial practice and everyday life

The attempt to assess the fire risk of non-forest terrestrial ecosystems of Biebrza National Park – A case study

On 19th April, the largest wildfire of the entire history of Biebrza National Park broke out and consumed 5526 ha, mostly overdried grassland with sedges and reeds of Biebrza marshes. The very rapid spread of the fire in the open space, with the blowing wind changing directions and the inaccessibility of the area for fire-fighting vehicles were the main reasons of this third largest wildfire in Poland, after the tragic forest fires in Kuźnia Raciborska (9060 ha burnt) and Potrzebowice (5600 ha burnt) in the memorable year of 1992. After this event, activities were undertaken to develop a fire protection plan for the Biebrza National Park

Effect of synthesis conditions on the porous texture of activated carbons obtained from Tara Rubber by FeCl3 activation

Abstract This paper presents the results of an unique analysis of the influence of the mass ratio of activator FeCl3 to precursor and the temperature of the activation process on the formation of the porous structure of activated carbons obtained from Tara Rubber by FeCl3 activation. The study used the new numerical clustering based adsorption analysis method and the quenched solid density functional theory, taking into account, among other things, the heterogeneity of the analysed surface which is a new approach rarely used in the analysis of the porous structure of adsorbents. On the basis of the calculation results, it was concluded that the activated carbon with the most developed porous texture was obtained at a mass ratio (FeCl3:Tara Rubber) of 2, at an activation process temperature of 800 °C. This activated carbon is also characterised by the lowest degree of surface heterogeneity and at the same time, however, the widest range of micropores compared to activated carbons obtained at other mass ratios. The analyses carried out further demonstrated the valuable and complementary information obtained from the structure analysis methods and their high utility in practical applications, especially in the development of new industrial technologies for the production of adsorbents and the selection of optimal conditions for their production

Impact of forest stands dieback as a result of bark beetle (Ips typographus) outbreak on the fire risk in the Białowieża Forest

Białowieża Forest, due to its unique character, requires a specific approach to the management of this area, including fire risk assessment. This is particularly important with regard to the recent bark beetle (Ips typographus) outbreak, which has contributed to the local dieback of Norway spruce stands on a total area of approx. 11.5 thousand hectares during the 2012-2022 period. The article presents the most important results of the implemented projects related to the fire protection of the Białowieża Forest. The analysis of potential fire hazard should take into account both dead wood and the impact of tree stand dieback, which resulted in the emergence of grasses as the dominant plant cover that poses a high risk not only for the possibility of fire, but also for its rapid spread. During 2012-2022 fuelload of the studied areas increased almost sevenfold compared to 2011 (15.8 t/ha), reaching an average maximum value of 108.9 t/ha in 2017. However, the progressive decomposition of dead wood and the decreasing amount of fine combustible material (fire-active biomass) caused that the fire risk in turn gradually decreased. After a period of about 10 years after the stand dieback, the fire risk caused by the dead wood left behind has reached a minimum level and the possibility of initiating the burning of such material was significantly reduced. Despite the decreasing fire hazard from dead wood, the fire risk will remain high for many years due to the presence of grass cover, especially during periods when it dries out. The analysis of the fire risk in the Białowieża Forest caused by the spruce bark beetle outbreak formed the basis for the development of the "Fire Protection and Forest Fire Fighting Plan for the Polish Part of the Białowieża Forest Transboundary World Heritage Site", which includes: fire risk assessment, fire detection, communication and alarm system, fire roads, water stores, equipment for fire fighting and rules for conducting rescue and fire-fighting operations

The attempt to assess the fire risk of non-forest terrestrial ecosystems of Biebrza National Park - A case study

On 19th April, the largest wildfire of the entire history of Biebrza National Park broke out and consumed 5526 ha, mostly overdried grassland with sedges and reeds of Biebrza marshes. The very rapid spread of the fire in the open space, with the blowing wind changing directions and the inaccessibility of the area for fire-fighting vehicles were the main reasons of this third largest wildfire in Poland, after the tragic forest fires in Kuźnia Raciborska (9060 ha burnt) and Potrzebowice (5600 ha burnt) in the memorable year of 1992. After this event, activities were undertaken to develop a fire protection plan for the Biebrza National Park. It took into account an innovative approach during the analysis of the existing fire risk, primarily regarding the non-forest terrestrial ecosystems composed of herbaceous vegetation, which constitutes as much as 61.2% of the park’s area, and to propose protection methods adequate to the threat. The work was completed in the framework of the project entitled ‘Development of the method for assessing the fire risk of non-forest ecosystems and the principles of fire protection for the Biebrza National Park – stage I,’ commissioned for the Forest Research Institute by the Biebrza National Park, financed by the State Forests from the forest fund, in accordance with the contract EZ.0290.1.24.2020. The article presents a preliminary method of classifying the fire risk of non-forest ecosystems, considering the occurrence of the fires in the Biebrza National Park in the years 2007–2020 and the type of vegetation burnt. This method, after supplementary field tests planned in 2021, will enable evaluation of the fire risk, which shall be a premise for the development of a fire protection plan

Analysis of the Influence of Activated Carbons’ Production Conditions on the Porous Structure Formation on the Basis of Carbon Dioxide Adsorption Isotherms

The results of a study of the impact of activation temperature and the mass ratio of the activator to the carbonised precursor on the porous structure of nitrogen-doped activated carbons obtained from lotus leaves by carbonisation and chemical activation with sodium amide (NaNH2) are presented. The analyses were carried out via the new numerical clustering-based adsorption analysis, the Brunauer–Emmett–Teller, the Dubinin–Raduskevich, and the density functional theory methods applied to carbon dioxide adsorption isotherms. Carbon dioxide adsorption isotherms’ analysis provided much more detailed and reliable information about the pore structure analysed. The analyses showed that the surface area of the analysed activated carbons is strongly heterogeneous, but the analysed activated carbons are characterised by a bimodal pore structure, i.e., peaks are clearly visible, first in the range of pore size from about 0.6 to 2.0 nm and second in the range from about 2.0 to 4.0 nm. This pore structure provides optimal adsorption performance of carbon dioxide molecules in the pore structure both for adsorption at atmospheric pressure, which requires the presence of narrow pores for the highest packing density, as well as for adsorption at higher pressures, which requires the presence of large micropores and small mesopores. However, there are no micropores smaller than 0.5 nm in the analysed activated carbons, which precludes their use for carbon dioxide adsorption for processes conducted at pressures less than 0.01 MPa

Dynamic forest fire risk evaluation in Poland

The weather conditions determine the dynamic forest fire risk. In Poland, the dynamic forest fire risk is calculated using a method elaborated at the Forest Research Institute. The forest fire risk degree (4-level scale) is calculated every day at 9:00 am and at 1:00 pm during the fire season (1.03 till 30.09) for 60 prognostic zones selected on the basis of stand and climatic conditions. 97% of all annual forest fires occur during the fire season. Surface fires are a significant part of the fires (90%) and occur in forest stands where pine is the dominant species. The purpose of the research was to prepare a new method of forecasting forest fire risk, which would enable a more precise method of evaluation of the risk of an outbreak of fire in relation to the existing and forecast meteorological conditions in forests. The results obtained during testing of this method indicate a high accuracy in forecasting fire risk and a satisfactory precision of formulae for calculating moisture content of pine litter