Search Results (28)

Traditional methods for synthesizing single-site catalysts are typically complicated and require special chemicals due to their tendency to agglomerate. In this study, we present a self-disperse copper-based catalyst synthesized via a dry mixing method for acetylene hydrochlorination. During the reaction, the copper precursor compounds, i.e., CuBr, and CuI, were converted to CuCl. Subsequently, the formed CuCl crystals underwent a significant structural transformation, leading to the formation of small clusters and Cu single sites. The catalytic activity of 5% CuCl + C prepared through the dry mixing method decreased from 93.7% to 92.9% after 100 h of reaction under the condition of GHSV (C₂H₂) = 60 mL·h⁻¹·g⁻¹. A comparison of the 5% CuCl + C with the 5% CuCl/C obtained by the impregnation method reveals that the catalytic stability of the former was higher than the one prepared by the conventional impregnation method. The exceptional catalytic performance can be attributed to the reaction-induced active sites being highly dispersed and the porous structure of activated carbon being maximally preserved, which was confirmed by HAADF-STEM, BET, TPR, and TG. The reaction-induced dispersion of CuCl on carbon provides a new strategy for preparing single-site catalysts for acetylene hydrochlorination. Full article

Ionic liquids (ILs) are green solvents involved in chemical reaction and separation processes. In this paper, four ILs-based metal catalysts were prepared by dissolving four transition metal chlorides into 1-butyl-3-methylimidazolium chloride ([Bmim]Cl). Their catalytic performance was measured, and the catalytic mechanism was studied via density functional theory (DFT) based on the analysis of the Mayer bonding order, Mulliken charge, molecular electrostatic potential (ESP), electron localization function (ELF), and partial density of states (PDOS). The results show that the catalytic activity follows the order [Bmim]Cl-RuCl₃ > [Bmim]Cl-AgCl > [Bmim]Cl-CuCl₂ > [Bmim]Cl-CuCl. [Bmim]Cl helps to dissolve and activate HCl, and the metal chlorides can greatly reduce the activation energy of the reaction. This study provides new insights into the catalytic mechanism of IL, transition metals, and their synergistic effect from a microscopic point of view and sheds light on the development of new catalysts for acetylene hydrochlorination. Full article

Printed circuit boards (PCBs) make up 3 to 5% of all electronic waste. The metal content of spent PCBs can reach 40%. They usually contain valuable metals, such as Ag, Au, and Pd, as well as other metals such as Cu, Sn, Pb, Cd, Cr, Zn, Ni, and Mn. However, the metallic part of a whole PCB is 40–60% including the Cu layers between the fiberglass–polymer layers. The paper describes the economics of the valuable metal (Ag, Au, Pd)-containing concentrate preparation from a raw PCB. We considered the influence of the pre-treatment method of PCBs before the extraction of valuable metals on the extraction self-cost change. The disintegration method is based on the high-energy impact of the particles of the material to be ground, thus causing the separation of the metallic components of the PCB. In the course of the work, single and double direct grinding using the method of disintegration was studied. For the calculation, the test batch of 10,000 kg of two types of PCB was taken for estimation of the self costs and potential profit in the case of complete valuable metals (Ag, Au, Pd) plus Cu extraction. It was shown that from 10,000 kg of studied PCB, it is possible to obtain 1144 and 1644 kg of metal-rich concentrate, which should be further subjected to electro-hydrochlorination for metals leaching. The novelty of this research lies in the fact that a technical and economic analysis has been carried out on a newly developed combined technology for processing electronic waste. This included mechanical processing and electrochemical leaching with the help of the active chlorine that is formed in situ. The real (not specially selected or prepared) waste PCBs were used for the process’s economical efficiency evaluation. The main findings showed that despite the high content of Cu in the studied PCBs, the commercial value was insignificant in relation to the total income from the Ag, Au, and Pd sale. A correlation was established between the self-cost decrease after separative disintegration of PCBs by metal content increase (by specific metals such as Au, Ag, Pd, and Cu) with the metal potential yield after extraction. Full article

The development of environmentally friendly and energy-saving processes for recycling electronic waste (e-waste) is still relevant today. The research presented in this work relates to hydrometallurgy, namely, the electrochemical leaching of metals from e-waste under the action of alternating current (AC) into hydrochloric acid solutions of electrolytes, and can be used for leaching both noble and non-ferrous metals from secondary raw materials. The main object of the study was disintegrator-crushed mixed computer PCBs metal-rich powders with a particle size (d) of <90 µm. The impact of such leaching process parameters as temperature (T_el) and composition of the electrolyte solution, AC density (i) on the electrodes, experiment duration (t_ex) while maintaining a constant electrolyte temperature (60 °C, 70 °C, and 80 °C) on the metal (Au, Ag, Cu, Al, Ni, Pb, Sn, Ti, Zn, and Fe) leaching efficiency has been studied. In addition, under similar experimental conditions, but without external control of T_el, the kinetics of metal leaching from raw material powders obtained via PCBs single and double crushing in a disintegrator has been also presented. Comparison of raw material powders obtained from different batches of the source material showed both the variability of its chemical composition and the different kinetics of Au and Ag leaching under the same experimental conditions. The optimal conditions for pretreatment of the raw material obtained by single crushing in a disintegrator (C_HCl = 6 mol·L⁻¹, i = 0.88 A·cm⁻², t_ex = 1 h, solid-to-liquid ratio—8.6 g·L⁻¹ and without external control of T_el) were determined. It has been shown that this electrochemical pretreatment is accompanied by transition of only base metals into the electrolyte solution, making it possible to significantly reduce their concentration in the final solution. Under pretreatment conditions, the following degree of metal leaching (R_Me) has been established: R_Cu = 98.2%, R_Al = 62.8%, R_Ni = 53.4%, R_Pb = 93.2%, R_Sn = 98.0%, R_Ti = 88.5%, R_Zn = 61.6%, and R_Fe = 78.8%. As a result of a subsequent two-hour electrochemical treatment of a solid residue, the degree of leaching of gold and silver was 73.6% and 86.7%, respectively. The presented results provide a broader understanding of the possibility of using the proposed electrochemical hydrochlorination method for noble and base metals leaching from waste PCBs. The novelty and practical value of this research is a validation of the developed technology in laboratory conditions using the real batch of the PCBs. This approach may also be useful to researchers involved in the recycling of other types of secondary raw materials. Full article

Exploring the fluidization behaviors and chemical performance in silicon tetrachloride (SiCl₄) hydrochlorination processes within a fluidized bed reactor (FBR) poses significant challenges. In this study, we developed an Eulerian-granular model (EGM) by integrating the Eulerian–Eulerian two-fluid model with the kinetic theory of granular flow (KTGF). The effect of fluidization velocities on the flow regime, heat transfer, and chemical reaction performance were investigated. The applicability of the simulation method and the validity of the model were confirmed through comprehensive comparisons, including the simulated values of the maximum bed expansion height (H_max) with theoretical values derived from empirical formulas and the simulated gas temperature profile with Hsu’s experimental data. The results indicate that the present EGM can be feasible to describe the variation of the flow regime within the FBR. An increase in bed voidage over time, coinciding with transitions in the flow regime, can be observed. Particularly noteworthy was the attainment of a more uniform distribution of SiCl₄ under the bubbling fluidization state. Furthermore, the FBR possess high heat transfer characteristics, and the reaction gas can reach the set temperature of the bed after entering a small distance (about 10 mm). The presence of circulating bubbles within the FBR enhances the mixing uniformity of the SiCl₄ reaction gas and silicon particles, particularly in the central and upper regions of the bed under the bubbling fluidization state. As a result, the predicted highest concentration of SiHCl₃ was 13.08% and the conversion rate of SiCl₄ was 28.97% under the bubbling fluidization state. Our results can provide a theoretical basis for further understanding of the hydrochlorination process of SiCl₄ within the FBR. Full article

This paper presents the results of the leaching of metals from computer PCBs by electrochemical hydrochlorination using alternating current (AC) with an industrial frequency (50 Hz). Leaching was carried out with a disintegrator-crushed computer motherboard with a particle size (d) of <90 μm. In the course of the research, the leaching efficiency of metals including Fe, Sn, Mn, Al, Cu, Zn, Pb, Ni, Ti, Sb, Cr, Co and V was evaluated depending on process parameters, such as AC density, experiment duration, hydrochloric acid concentration in the electrolyte solution, solid/liquid ratio, electrolyte temperature, and the loading option of raw material (loading option 1 involving loading into the electrolyte solution, and loading option 2 involving loading into the filter containers attached to electrodes). The research results showed that AC superimposition significantly intensifies the leaching of metals. It was established that the complete leaching of metals including Al, Mn, Sn, Ti and Zn, under experimental conditions (loading option 2, C_HCl = 6 mol·L⁻¹, i = 0.80 A·cm⁻², S/L = 8.6 g·L⁻¹), is reached after 1.5 h, and that of Cu and Ni is reached after 2 h from the beginning of the experiment. At the same time, the degree of leaching of other metals after 2 h is Co-78.8%, Cr-84.4%, Sb-91.7%, Fe-98.9%, V-98.1% and Pb-5.1%. The paper also reports the results on the leaching of all abovementioned metals, as well as Ag and Pd, with disintegrator-crushed mixed computer PCBs with d < 90 μm and loading option 1. Full article

Vinyl chloride, the monomer of polyvinyl chloride, is produced primarily via acetylene hydrochlorination catalyzed by environmentally toxic carbon-supported HgCl₂. Recently, nitrogen-doped carbon materials have been explored as metal-free catalysts to substitute toxic HgCl₂. Herein, we describe the development of a cationic covalent triazine network (cCTN, cCTN-700) that selectively catalyzes acetylene hydrochlorination. cCTN-700 exhibited excellent catalytic activity with initial acetylene conversion, reaching ~99% and a vinyl chloride selectivity of >98% at 200 °C during a 45 h test. X-ray photoelectron spectroscopy, temperature programmed desorption, and charge calculation results revealed that the active sites for the catalytic reaction were the carbon atoms bonded to the pyridinic N and positively charged nitrogen atoms (viologenic N⁺) of the viologen moieties in cCTN-700, similar to the active sites in Au-based catalysts but different from the those in previously reported nitrogen-doped carbon materials. This research focuses on using cationic covalent triazine polymers for selective acetylene hydrochlorination. Full article

When obtaining sulfuric acid from pyrite concentrates, a significant amount of waste is generated in the form of pyrite cinders that require disposal. The methods used in processing this raw material are, as a rule, the pyrometallurgical processes of chlorination and chloride sublimation, the disadvantages of which include increased energy consumption and a lack of complexity in the extraction of valuable components. Hydrometallurgical processes are in less demand due to their multi-stage nature and complexity of execution. The method of chemical activation developed at the JSC “Institute of Metallurgy and Ore Beneficiation” makes it possible to isolate iron and non-ferrous metals into separate, middling products and to concentrate noble metals in the cake at the first stage. Physical and chemical studies of the cake found that its basis comprises iron compounds. The silver in the cake is associated with pyrite, while the gold is associated with hematite; it is also possible to find gold in the form of AuCl₃. The content of gold in the cake is 1.5 g/t, and the silver content is 17.7 g/t. Based on physical and chemical studies and data from the literature, various versions of the hydrochlorination method are proposed to open the cake. Full article

The poor stability of carbon materials doped with nitrogen limited their development in acetylene hydrochlorination. Therefore, investigating the deactivation reasons of carbon catalysts and researching regeneration methods became the research focus. Herein, carbon-nitrogen materials were synthesized by one-step pyrolysis, which using biomass materials with high nitrogen content, the synthesized material was used in an acetylene hydrochlorination reaction. The acetylene conversion rate of D-GH-800 catalyst was up to 99%, but the catalytic activity decreased by 30% after 60 h reaction. Thermogravimetric analysis results showed that the coke content was 5.87%, resulting in catalyst deactivation. Temperature-programmed desorption verified that the deactivation was due to the strong adsorption and difficult desorption of acetylene by the D-GH-800 catalyst, resulting in the accumulation of acetylene on the catalyst surface to form carbon polymers and leading to the pore blockage phenomenon. Furthermore, based on the catalyst deactivation by carbon accumulation, we proposed a new idea of regeneration by ZnCl₂ activation to eliminate carbon deposition in the pores of the deactivated catalyst. As a result, the activity of D-GH-800 was recovered, and lifetime was also extended. Our strategy illustrated the mechanism of carbon deposition, and the recoverability of the catalyst has promising applications. Full article

Pincer ligand supported Ru^II chloride complexes may be used for acetylene hydrochlorination as non-mercury molecular catalysts. Based on theoretical calculations, the catalytic mechanism and the interaction between catalysts and reactants has been evaluated, indicating that the (pincer)Ru^IICl₂ platform supports electrophilic proton-ruthenation of C₂H₂. Energy decomposition studies further illustrate the electron-rich property of the Ru^II center, which can increase the negative charge of C₂H₂ via 4d-electron backdonation. Thus, the electrophilic reaction mechanism is favored due to lower energetic barriers. By improving the electron-donating ability of ligands, this lowering of energetic barriers can be enhanced. Therefore, non-mercury catalysts for acetylene hydrochlorination with milder reaction conditions and higher catalytic activity can be designed. Full article

Modern technologies for recycling electronic waste (e-waste) have high economic efficiency and environmental safety requirements. Among the existing technologies, hydrometallurgy is considered to be the most promising technology for e-waste recycling. Increasing attention paid to the chlorination method is associated with the complex recycling of low-grade ores containing noble metals and the raw materials of secondary polymetallic. In this paper, we propose a new scheme for leaching metals from computer printed circuit boards (PCBs) pre-crushed in a disintegrator: The processes of chlorine production and hydrochlorination are implemented in one reactor under the action of an alternating current (AC) of industrial frequency (50 Hz). Three fine fractions of raw material powders with particle size d < 90 µm, d = 90–180 µm, and d = 180–350 µm were used as research objects and the finest fraction of the raw material (d < 90 µm) was studied in more detail. It was found that complete leaching of gold is achieved from fractions of raw materials with a particle size d = 90–180 µm and d = 180–350 µm, containing 277 ppm and 67 ppm of the gold, respectively, at an experiment duration (t_ex) of 2 h, a current density (i) of 0.66 A·cm⁻², and a solid/liquid (S/L) ratio of 8.6 g·L⁻¹. Under the same conditions of the electrochemical leaching process from the fraction of raw materials with a particle size of d < 90 µm and a gold content of 824 ppm, the degree of metal leaching is 80.5%. At the same time, with an increase in particle size in the raw material fractions from d < 90 µm to d = 180–350 µm and a copper content in the raw material from 1.40% to 6.13%, an increase in the degree of its leaching from 81.6% to 95.2%, respectively, is observed. In the framework of the preliminary study presented in this work, for the finest raw material fraction with d < 90 μm the highest gold leaching degree (86.3%) was achieved under the following experimental conditions: t_ex= 4 h, C_HCl = 6 M, i = 0.88 A·cm^–2, S/L ratio—8.6 g·L^–1 and the highest copper leaching degree (94.2%) was achieved under the following experimental conditions: t_ex = 2 h, C_HCl = 6 M, i = 0.64 A·cm^–2, and S/L ratio—2.9 g·L^–1. Full article

Due to its prevalence in nature and its particular properties, silicon is one of the most popular materials in various industries. Currently, metallurgical silicon is obtained by carbothermal reduction of quartz, which is then subjected to hydrochlorination and multiple chlorination in order to obtain solar silicon. This mini-review provides a brief analysis of alternative methods for obtaining silicon by electrolysis of molten salts. The review covers factors determining the choice of composition of molten salts, typical silicon precipitates obtained by electrolysis of molten salts, assessment of the possibility of using electrolytic silicon in microelectronics, representative test results for the use of electrolytic silicon in the composition of lithium-ion current sources, and representative test results for the use of electrolytic silicon for solar energy conversion. This paper concludes by noting the tasks that need to be solved for the practical implementation of methods for the electrolytic production of silicon, for the development of new devices and materials for energy distribution and microelectronic application. Full article

A systematic study of the kinetics of supported-ionic-liquid-phase (SILP) Au catalysis (Au-IL/AC) has been established in the continuous gas-phase hydrochlorination of acetylene. We reveal that the effect of ionic liquid (IL) film on substrate diffusion can be eliminated. The reaction order of the catalyst indicates that Au is confirmed to exist as a monomer in the IL film of the Au-IL/AC system, which is different from the fast equilibrium of the “Au dimer and monomer” for the classical Au/AC catalyst. The homogeneous reaction micro-environment is confirmed for Au-IL/AC since the activation energy was little changed under both heterogeneous and homogeneous catalysis, further verifying the monatomic characteristics of Au in Au-IL/AC. Due to the supported IL film, the reaction order of hydrogen chloride was decreased from 1 to 0.5 while creating a hydrogen chloride enrichment system around Au, which provides the possibility of producing vinyl chloride with an equal substrates feed ratio. This kinetic-perspective-based revelation of the catalytic behavior of the metal active sites confined in IL film enriches and expands the SILP catalytic system for acetylene hydrochlorination. Full article

We report the influence of sp² content in carbon catalyst on the catalytic activity for acetylene hydrochlorination. Nanodiamonds (NDs) were used as the precursor and calcinated under different temperatures. The resulting ND500, ND700, ND900, and ND1100 catalysts were characterized, and the sp² content increased with increasing calcination temperature. The specific activities of the catalysts first increased and then decreased with increasing sp² content. The highest catalytic activity could be obtained in the ND-900 catalyst with a sp² value of 43.9%. The density functional theory results showed that the adsorption sites for acetylene and hydrogen chloride were located at the interface between sp² and sp³ configuration. Full article

Activated carbon-supported HgCl₂ catalyst has been used widely in acetylene hydrochlorination in the chlor-alkali chemical industry. However, HgCl₂ is an extremely toxic pollutant. It is not only harmful to human health but also pollutes the environment. Therefore, the design and synthesis of mercury-free and environmentally benign catalysts with high activity has become an urgent need for vinyl chloride monomer (VCM) production. This review summarizes research progress on the design and development of mercury-free catalysts for acetylene hydrochlorination. Three types of catalysts for acetylene hydrochlorination in the chlor-alkali chemical industry are discussed. These catalysts are a noble metal catalyst, non-noble metal catalyst, and non-metallic catalyst. This review serves as a guide in terms of the catalyst design, properties, and catalytic mechanism of mercury-free catalyst for the acetylene hydrochlorination of VCM. The key problems and issues are discussed, and future trends are envisioned. Full article