Iranian Journal of Chemical Engineering (IJChE)

Abstract Lithium-ion batteries are widely used in various electronic devices and typically discarded after their service life, causing significant environmental damage and resource wastage. Therefore, recycling the valuable components of the batteries, such as graphite, is essential. Graphite, employed as the anode material, is one of the key components targeted for recovery. In graphite recycling operations from spent batteries, critical hydrometallurgical processes include primary and secondary leaching stages using sulfuric acid. In this research, both leaching processes were systematically optimized. The optimal conditions identified for primary leaching were a temperature of 77 °C, a sulfuric acid concentration of 1.75 M, a leaching duration of 4 hours, and a liquid-to-solid graphite powder ratio of 5. Under these conditions, the graphite purity after the primary leaching process was 99.56 wt%. Subsequently, in the secondary leaching stage, a final high purity of 99.98% was achieved for the graphite product. To evaluate the electrochemical performance of the recycled graphite, galvanostatic charge-discharge tests were conducted, which demonstrated a specific capacity of 350 mAh/g. This capacity is comparable to that of commercial graphite, confirming the effectiveness of the developed recycling process.

Abstract 1,3,5,7-tetranitro-1,3,5,7-tetraazacyclooctane (HMX) is one of the most powerful explosives of which the purity may have a significant effect on increasing the performance of rocket engines. In this research, the synthesis of high purity HMX is presented using the nitration of 1,5-diacetyl-3,7-dinitrooctahydro-1,3,5,7-tetrazocine (DADN) with a mixture of nitric acid and polyphosphoric acid. The nitration parameters including temperature, time, and the concentration of nitric acid, and polyphosphoric acid were optimized for the desirable purity and efficiency using the response surface method and central composite method (CCD). Based on the optimization, HMX was obtained with a purity of 99% and an efficiency of 92.9% at a temperature of 70°C and the time duration of 70 minutes with a molar ratio of polyphosphoric acid to nitric acid of 1:1:6.

Abstract Joule-Thomson cooling systems are used in refrigeration and liquefaction processes. There are extensive studies on Joule-Thomson cryogenic systems, but most of them coverage steady state conditions or lack from experimental data. In the present work, transient thermal behavior of Joule-Thomson cooling system including counter current helically coiled tube in tube heat exchanger, expansion valve, and collector was studied by experimental tests and simulations. The experiments were carried out by small gas liquefier and nitrogen gas as working fluid. The recuperative heat exchanger was thermally analyzed by experimental data obtained from gas liquefier. In addition, the simulations were performed by an innovative method using experimental data as variable boundary conditions. A comparison was done between presented and conventional methods. The effect of collector mass and convection heat transfer coefficient was also studied using temperature profiles along the heat exchanger. The higher convection heat transfer coefficient in low-pressure gas leads to increase in exchanging energy between two streams and faster cooling of heat exchanger materials, but the higher convection heat transfer coefficient in high-pressure gas does not influence on cool-down process.