Pseudo-adiabatic Conditions Research Articles

Calorimetric and kinetic evaluation of thermal stability and process safety in tert-butyl peroxy-2-ethylhexanoate and tert-butyl peroxybenzoate

This study evaluated the thermal stability and process safety of tert-butyl peroxybenzoate (TBPB), tert-butyl peroxy-2-ethylhexanoate (TBPO), and their mixture. Thermogravimetric (TG) analysis, differential scanning calorimetry (DSC), and accelerated rate calorimetry were used to elucidate the thermal behavior and breakdown kinetics. The TG results indicated moderate to low breakdown temperatures for all samples, demonstrating their thermal stability. DSC revealed onset temperatures for exothermic disintegration between 66.66 °C and 104.23 °C. The mixture had two distinct exothermic peaks, signifying the thermal decomposition of the mixture was such that the characteristic temperature and heat of the reaction were between those of TBPB and TBPO. Using Heat–Wait–Search methodology, the study identified thermal runaway exothermically. Under pseudoadiabatic conditions, the mixture exhibited greater increases in temperature and pressure—of 115.06 °C and 28.77 bar, respectively—compared with the individual compounds. To elucidate the apparent activation energy (Ea) and reaction kinetics, the study applied models developed by Arrhenius, Flynn-Wall-Ozawa, Friedman, Kissinger, and Starink. The Ea values obtained based on the TG, DSC, and ARC experiments were approximately 50.47, 98.19, and 99.71 kJ/mol, respectively, and were lower than those of TBPB and TBPO pure substances. The self-accelerating decomposition temperature of TBPB/TBPO decreased from 34 to 32 °C as the packaging of TBPB/TBPO was increased from 25 to 100 kg and was more than 10 °C lower than that of the individual substance. These findings offer a framework for evaluating the thermal risks associated with TBPB and TBPO, particularly when mixed. They contribute to the safe transit, storage, and handling of industrial organic peroxides, enriching our collective understanding of the stability and safety of these compounds.

Adiabatic plasma-catalytic reactor configuration: Energy efficiency enhancement by plasma and thermal synergies on CO2 methanation

Abstract In the present work, CO2 methanation was performed in an adiabatic hybrid plasma-catalytic system, activated only by DBD plasma and without external heating. It was found that both plasma discharges and the reaction exothermicity were two important activation pathways. In order to discern between both phenomena, the role of the released heat was studied in two reactor configurations, pseudo-adiabatic and adiabatic approaches, revealing that conversions were sharply increased as soon as the reactor was thermally insulated. Accordingly, DBD plasma reactor isolation is an interesting approach to take advantage of the released heat in plasma-catalysis CO2 methanation and other exothermic reactions. However, a balance between the plasma power and the reacting flow must be adjusted because an excess of heat could be counterproductive for the reaction. In this sense, it was inferred that a way to control the released heat is by means of the inlet gas flow. In optimal adiabatic conditions (140,000 mL·h−1·g−1 and 18 kJ·mol−1), the energy efficiency of the process was increased up to 73%, highly upgrading the 40% efficiency at conventional pseudo-adiabatic conditions (40,000 mL·h−1·g−1 and 146 kJ·mol−1). At this efficiency level, hybrid plasma-catalysis can compete directly with thermally activated reactors for CO2 methanation with an unprecedented energy consumption of 130 kJ·molCH4−1.

Thermal risk assessment of tert-butylperoxy-2-ethylhexyl carbonate for storage and transport

Tert-butylperoxy-2-ethylhexyl ester (TBEC) is a typical organic peroxide that is used in pharmaceuticals, materials, intermediates or as a polymerization initiator, and it has a large amount of consumption. We examined the thermal risks of TBEC during storage and transport by using differential scanning calorimetry and thermal activity monitor III to investigate its thermal stability and thermal hazards. Non-isothermal and isothermal experiments were used to calculate the apparent activation energy (E(α)), compare the calculated kinetic data, pre-exponential factor, and other parameters, and infer the thermal behaviour of TBEC under pseudo-adiabatic conditions. According to the calculation results, the E(α) under non-isothermal conditions calculated through the Friedman isothermal kinetic method ranged from 91.47 to 177.35 kJ mol−1. E(α) under isothermal conditions ranged from 157.18 to 143.28 kJ mol−1. TBEC was also tested under pseudo-adiabatic conditions using vent sizing package 2 to investigate uncontrolled thermal runaway. The calculated self-accelerating decomposition temperature was 34.0 °C. Our results provide an insight into the thermal decomposition of TBEC and supply reliable data for its storage and transport processes.

Effect of pre-adsorbed water in hydrophobic polymeric resin on adsorption equilibrium and breakthrough of 1,2-dichloroethane

Hot steam regeneration of an adsorbed bed is widely used in practical processes, so it is crucial to understand the effect of residual water contained in the adsorbent on VOCs adsorption. In this work, the influence of pre-adsorbed water in hypercrosslinked resin (HY-1) on the adsorption of 1,2-dichloroethane (DCE) was studied under both isothermal and pseudo-adiabatic conditions. Under isothermal conditions, the initial water had a slightly negative influence on adsorption capacities, and a negative influence on the breakthrough capacity lower than 9.3%, decreasing with higher DCE concentrations. Moreover, the influence of initial water in HY-1 on temperature rise and breakthrough adsorption capacities in fixed beds was also investigated under pseudo-adiabatic conditions. On the dry resin, a significant temperature rise (about 50 °C) inside the bed was observed when 200 mg/L of DCE was adsorbed. Compared to the dry resin, the temperature rise in the bed could be controlled to under 5 °C; the breakthrough adsorption capacities of DCE on the wet resin increased by 12.4–37.6%.

Study of a Cu-CuO chemical loop for the calcination of CaCO3 in a fixed bed reactor

The use of a Cu/CuO chemical loop to supply the heat required to carry out the calcination of CaCO3 in a fixed-bed reactor is experimentally evaluated. The effects of the fuel gas composition, the Cu/Ca molar ratio, the temperature of the solids bed and possible side reactions on the reduction/calcination stage are studied under pseudo-adiabatic conditions in a fixed-bed reactor (i.d.×L=0.038m×0.92m) using commercial Ca- and Cu-based materials. It was observed that initial temperatures in the solids bed of more than 650°C make it possible to achieve the complete calcination of CaCO3. Suitable Cu/Ca molar ratios, depending on the composition of the gaseous fuel used to reduce CuO, can moderate the increase in temperature in the reduction front and allow the simultaneous calcination of CaCO3. The multicycle operation at high temperature modifies the chemical composition of the functional materials and leads to the formation of mixed Ca-Cu oxides that are able to capture CO2, which affect the CO2 sorption capacity of these materials. Moreover, the influence of O2 dilution in the inlet gas upon the temperature profiles during the Cu oxidation stage was assessed. The recirculation of a large part of the product gas resulting from the oxidation stage moderates the temperature profile and the complete conversion of the Cu-based solids is achieved in a relatively sharp oxidation front despite the low O2 content in the feed (i.e., 3vol% O2). The experimental results are in close agreement with the predictions of a one-dimensional reactor model that incorporates existing information taken from the literature on the kinetics, fluid dynamics and heat transfer.

Partial Oxidation and CO2-ATR of Methane over Rh/LaMnO3 Honeycomb Catalysts

Catalytic partial oxidation of methane has been studied over structured bi-functional catalysts containing LaMnO3 perovskite and Rh. The effects of the noble metal content and of substrate morphology and thermal conductivity have been investigated under high temperature pseudo-adiabatic conditions. Several reaction conditions have been explored by means of changing CH4/O2 ratio and GHSV and of adding CO2. Synergistic effect between active phases has been detected even if best performance has been expressed by the catalyst containing the largest amount of Rh. Catalytic performance can be improved by a proper choice of the substrate; high cell density honeycombs showed increased syngas yields, while a better heat management can be obtained depositing the active phase onto high thermal conductivity substrate. H2/CO ratio can be modified by CO2 addition. Partial oxidation and CO2 autothermal reforming of methane have been studied on bi-functional Rh–LaMnO3 honeycomb catalysts. The effects of Rh content, honeycomb cell density and thermal conducitivity have been evaluated.

Rh–La(Mn,Co)O 3 monolithic catalysts for the combustion of methane under fuel-rich conditions

Novel Rh–La(Mn,Co)O 3 structured catalysts were developed for the partial oxidation of methane to syngas intended as a preliminary conversion step in combustion systems such as power turbines and utility burners employing a fuel-rich fuel-lean approach to reduce NO x formation. Active components were impregnated on La–γ-Al 2O 3 washcoated honeycomb monoliths and the catalysts were characterised by BET, SEM/EDS, H 2-TPR, and in situ FT-IR under reaction conditions. Catalytic partial oxidation of methane was tested under both pseudo-isothermal and pseudo-adiabatic conditions showing that the process can be conducted with high yield and selectivity: improved and stable performances were found especially in the case of Rh–LaMnO 3 catalyst, due to the synergism between active sites and to the stabilization of the noble metal.

Development of a dual functional structured catalyst for partial oxidation of methane to syngas

Rh-LaCoO 3 structured catalysts for the oxidative production of syngas from methane were developed by deposition of the active components on La-γ-Al 2O 3 washcoated honeycomb monoliths. SEM/EDS analysis showed a good adhesion of the washcoat layer and a uniform distribution of La and Co, while Rh was favourably located on the outer shell. Catalytic partial oxidation of methane was tested under both isothermal and pseudo-adiabatic conditions showing that the process can be conducted with high yield and selectivity and stable performance at short contact times over the novel catalysts, characterised by a limited content of noble metal and no need for pre-reduction. Further experiments of CO 2 autothermal reforming indicated the possibility to enhance CO production and to reduce the H 2/CO ratio through secondary endothermic reactions consuming CO 2, which are autothermally self-sustained in a single catalytic reactor operated at short contact time by the heat generated through partial oxidation reactions.

Deactivation in pseudo-adiabatic reactors

Deactivation phenomena in adiabatic reactors can be evaluated from the progress of the temperature profile. For studies of pseudo-adiabatic conditions, the compensation heat may blur the results. This problem is analyzed and a simple criterion is formulated for the design of the test unit. The result is illustrated by practical examples.