Formation of Adsorption Properties of Carbon Nanostructured Materials by Thermochemical Activation of Sludge-Lignin

Pyrolysis is an effective way to process waste of the pulp and paper industry, in particular, sludge-lignin, which makes it possible to obtain a commercial product – a carbon adsorbent. The method of thermochemical activation using sodium and potassium hydroxides is now widely used in pyrolysis of wood waste processing. This method enables the production of carbon nanostructured materials with high adsorption properties, especially when adsorbed from the liquid phase. The paper studies the influence of conditions for the synthesis of carbon adsorbents of sludge-lignin on their adsorption properties using sodium hydroxide as an activating agent. Sludge-lignin was obtained under laboratory conditions by treating lignin-containing wastewater with aluminum oxychloride coagulant. We applied the method of the planned experiment: a rotatable central composite design of the second order for three factors. We studied the influence of the main factors determining the adsorption properties of coals, namely, temperature, pyrolysis duration and sodium hydroxide dosage, on the values of output parameters characterizing the adsorption efficiency from the liquid phase, i.e. the iodine number and the adsorption capacity of methylene blue removal. We obtained experimental data, which were used to construct response surfaces illustrating the influence of the experimental factors on the output parameters. The positive effect of pyrolysis temperature and alkali dosage on the adsorption properties of the synthesized coals was found. The following results were obtained: the adsorption activity for iodine – 300 %, for methylene blue – 1000 mg/g; indicating a developed micro- and mesoporous surface and the possibility of using these compounds for adsorption of both gases and vapors, and organic substances from solutions. Therefore, samples of activated carbons synthesized from sludge-lignin were tested as lignin adsorbents of lignin-containing wastewater. The obtained dependences correlate well with the data describing the influence of pyrolysis parameters on the coal adsorption capacity of methylene blue removal. The high efficiency of adsorbents of sludge-lignin in the removal of lignin from solutions was shown. The value of the specific adsorption was about 1500 mg/g.

Dawn of a new era in industrial photochemistry: the scale-up of micro- and mesostructured photoreactors

Photochemical activation routes are gaining the attention of the scientific community since they can offer an alternative to the traditional chemical industry that mainly utilizes thermochemical activation of molecules. Photoreactions are fast and selective, which would potentially reduce the downstream costs significantly if the process is optimized properly. With the transition towards green chemistry, the traditional batch photoreactor operation is becoming abundant in this field. Process intensification efforts led to micro- and mesostructured flow photoreactors. In this work, we are reviewing structured photoreactors by elaborating on the bottleneck of this field: the development of an efficient scale-up strategy. In line with this, micro- and mesostructured bench-scale photoreactors were evaluated based on a new benchmark called photochemical space time yield (mol·day−1·kW−1), which takes into account the energy efficiency of the photoreactors. It was manifested that along with the selection of the photoreactor dimensions and an appropriate light source, optimization of the process conditions, such as the residence time and the concentration of the photoactive molecule is also crucial for an efficient photoreactor operation. In this paper, we are aiming to give a comprehensive understanding for scale-up strategies by benchmarking selected photoreactors and by discussing transport phenomena in several other photoreactors.

Electrical properties of composites based on nanoporous carbon material

In this work, the morphological and electrical properties of the composite nanoporous carbon material/thermally expanded graphite or acetylene black have been investigated. Nanoporous carbon material was obtained from plant materials by its thermochemical activation based on potassium hydroxide. The dependence of the specific capacity of the nanoporous carbon/electrolyte electrochemical system on the applied potential was determined by the impedance spectroscopy method. Furthermore, the concentration of charge transfer and the density of states, as well as the flat-band potential of the system under research, were determined based on the Mott-Schottky model.

Electrochemical properties of nanoporous carbon materials obtained from raw materials of plant origin (hemp shives)

The paper reveals the results of electrochemical studies of activated nanoporous carbon material (NPC) as an electrode material for electrochemical capacitors (EC), the charge of which is accumulated in an electrical double layer (EDL). NPC material has been obtained from raw material of plant origin (hemp shives) by thermochemical activation using phosphoric acid. It has been established that there is an optimal ratio between the amount of acid and precursor based on plant biomass that is equal to 0.75:1. The specific surface area of ​​the obtained NPCwas ~ 2000 m2/g, and the maximum specific capacitance of EC models based on them was ~ 113 F/g. At the same time, the contribution of the EDL capacitance to the total capacitance is 60-80 %.

ACTIVE CARBONS, OBTAINED BY THERMOCHEMICAL ACTIVATION OF RAPE STRAW

The presence of a huge amount of waste of plant origin, including annually renewable, is a high innovative resource for obtaining a variety of useful products of large and small-tonnage chemistry. Processing straw of agricultural crops into activated carbons (AC), which are successfully used in various industries and agriculture, is one of the possible directions of using agricultural waste (AIC) to obtain new functional materials with specific properties. The paper presents studies on the physicochemical properties and structural characteristics of activated carbons based on rape straw and discusses the prospects of their application for solving the most important problems of the agricultural sector. The effect of thermochemical activation temperature (650–750 °С) on the characteristics of the porous structure of adsorbents was studied. The characteristics are calculated on the basis of isotherms of low-temperature (77 K) nitrogen adsorption-desorption. Temperature dependences of the specific surface area, total pore volume, and micropore volume were obtained. It was found that KOH promotes surface development and the formation of a porous system in the entire temperature range.

Thermochemical activation of hydrogen in the process of desorption from metal hydride

The results of mass spectrometric studies of the energy state of hydrogen molecules with the usage of the electron impact ionization efficiency curves measurement method, both during desorption and in the mode of hydrogen flowing through the metal hydride layer, are presented. The dependences of the breakdown voltage on the pressure in the gas-discharge chamber for an electric discharge in activated hydrogen are obtained. Those dependencies indicate a significant decrease in the ionization potential of hydrogen under the electric current influence. Within the framework of the presented material, the results of hydrogen emission from hydride-forming materials based on LaNi5 are presented and an assessment of its thermodynamic state is given, which made it possible to study the energy-physical characteristics of gas-discharge processes. The possibility of practical use of metal hydride activation to increase the energy and operational efficiency of electric-discharge hydrogen systems is shown.