RESUMO
Biochar is an eco-friendly carbon material whose properties allow it to be used as a sorbent for wastewater treatment or soil remediation. The paper presents the results of research related to the pyrolysis process of apple waste after supercritical CO2 extraction with the simultaneous use of physical activation. The research assessed the influence of the temperature of the pyrolysis process and steam activation on the structural properties of the obtained biochar, i.e. specific surface, porous structure, and presence of functional groups. The results obtained confirmed that lower temperature pyrolysis produces biochar characterised by the presence of functional groups and ordered structure. On the other hand, high temperature pyrolysis with simultaneous steam activation determines microporosity and high values of the specific surface area. Taking into consideration pollutant sorption mechanisms (physical and chemical sorption), the obtained biochar materials can be used as sorbents in water and wastewater treatment.
RESUMO
The aim of this study was to assess whether electrical parameters (capacitance and conductivity) of fresh engine oils-tested over a wide range of measurement voltage frequencies-can be used for oil quality assessment and its identification, based on physicochemical properties. The study encompassed 41 commercial engine oils with different quality ratings (American Petroleum Institute (API) and European Automobile Manufacturers' Association (ACEA)). As part of the study, the oils were tested for their total base number (TBN) and total acid number (TAN), as well as their electrical parameters, including impedance magnitude, phase shift angle, conductance, susceptance, capacitance and quality factor. Next, the results for all of the samples were examined for correlations between the mean electrical parameters and the test voltage frequency. A statistical analysis (k-means and agglomerative hierarchical clustering) was applied to group oils with similar readings, drawing on the values for all electrical parameters to produce group oils with the highest similarity to each other into clusters. The results show that the electrical-based diagnostics of fresh engine oils can serve as a highly selective method for identifying oil quality, offering much higher resolution than assessments based on the TBN or the TAN. This is further supported by the cluster analysis, with five clusters generated for electrical parameters of the oils, compared to only three generated for TAN- and TBN-based measurements. Out of all the tested electrical parameters, capacitance, impedance magnitude and quality factor were found to be the most promising for diagnostic purposes. The value of electrical parameters of fresh engine oils is mostly dependent on the test voltage frequency (with the exception of capacitance). The correlations identified in the course of the study can be used to select for those frequency ranges that offer the highest diagnostic utility.
