Taguchi Optimization of Solvent-Antisolvent Crystallization to Prepare Ammonium Perchlorate Particles

The sphericity and size of ammonium perchlorate (AP) particles significantly influence the properties of composite propellants. As the AP particles become more spherical, the accumulation coefficient increases, the viscosity during casting decreases, and the particle loading and burning rate increase. Hence, the production of micronized AP particles with an average size between 1 and 20 μm is important to increase the loading percentage of AP in the composite propellant. Here, the Taguchi experimental design was used to optimize the solvent-antisolvent crystallization (SAC) process for the preparation of micronized AP particles with higher sphericity. SAC parameters such as the type of antisolvent, the solvent-to-antisolvent ratio, the antisolvent temperature, the stirring speed, and the retention time were investigated at four levels. The type of antisolvent and the solvent-to-antisolvent ratio were found to mainly contribute to improving the sphericity and size of the AP particles, respectively.     

Influence of Xanthan–Curdlan Hydrogel Complex on Freeze‐Thaw Stability and Rheological Properties of Whey Protein Isolate Gel over Multiple Freeze‐Thaw Cycle

The effect of adding xanthan–curdlan hydrogel complex (XCHC) at 2 concentrations (0.25 and 0.5% w/w) on the freeze‐thaw stability of heat‐induced whey protein isolate (WPI) gel was investigated. Samples were stored at 4 °C for 24 h before subjected to 5 freeze‐thaw cycles alternating between ?16 °C (18 h) and 25 °C (6 h). Adding XCHC to the WPI solution resulted in the reduction of a significant amount of syneresis up to 5 repeated freeze‐thaw cycles. Addition of XCHC decreased the amount of syneresis from 45% in the control sample (pure WPI gel) to 31.82% and 5.44% in the samples containing 0.25% and 0.5% gum, respectively, after the 5th freeze‐thaw cycle. XCHC increased the storage modulus (G′) of the gels and minimized the changes of the G′ values over the 5 freeze‐thaw cycles, indicating improvement of the stability of the system. Furthermore, the minimum protein concentration for gel formation decreased in the presence of the XCHC. Scanning electron microscopy (SEM) images showed that addition of XCHC resulted in the formation of a well‐structured gel with numerous small pores in the network, which consequently improved the water retention ability during the temperature abuses up to 5 freeze‐thaw cycles. These results have important implications for using XCHC in the formulation of the frozen WPI‐based products with improved freeze‐thaw stability and rheological properties.     

The effect of microencapsulation with nitrocellulose on thermal properties of sodium azide particles

Based on the coacervation principle a solvent/non-solvent method has been used for microencapsulation of sodium azide (NaN₃) with fibrous nitrocellulose (NC). Scanning electron microscopy (SEM) was employed to examine the coating morphology. The thermal behavior of solid samples has been studied by means of thermogravimetry (TG) and differential scanning calorimetry (DSC). The results of TG–DTA analysis revealed that the main thermal degradation for the pure NC and NaN₃ occurs in the temperature ranges of 192–220 and 415–420 °C, respectively. The effects of some parameters, such as NC to NaN₃ weight ratio and volume and addition time of non-solvent, on coating quality and thermal properties have been investigated by SEM and thermal methods. The results of these experiments showed that the decomposition temperature of most stabilized coated sodium azide is about 50 °C higher than that of the pure sample. The DSC experiments were conducted to study the influence of the heating rate (5, 10, 15 and 20 °C/min) on the thermal decomposition processes of the pure NC, coated and pure NaN₃ samples. The results revealed that, as the heating rate was increased, decomposition temperature of the compounds was increased. Also, the kinetic parameters such as activation energy and frequency factor of the decomposition processes were obtained from the DSC data by non-isothermal methods proposed by ASTM E696 and Ozawa. Our finding showed that coated NaN₃ has lower decomposition rate with respect to the pure one.     

UVA-LED assisted persulfate/nZVI and hydrogen peroxide/nZVI for degrading 4-chlorophenol in aqueous solutions

Photocatalytic degradation of 4-chlrophenol (4-CP) using UVA-LED assisted persulfate and hydrogen peroxide activated by the nZVI (Nano Zero Valent Iron) in a batch photocatalytic reactor was investigated. The reaction involved a lab-scale photoreactor irradiated with UVA-LED light emitted at 390 nm. The efficiency of the reaction was evaluted in terms of 4-CP degradation and mineralization degree at different pH of solution, initial concentrations of nZVI, persulfate, hydrogen peroxide and 4-CP. In UVA-LED/H₂O₂/nZVI process, complete degradation of 4-CP (>99%) and 75% mineralization was achieved at pH of 3, hydrogen peroxide concentration of 0.75 mM, nZVI dosage of 1mM and initial 4-CP concentration of 25mg/L at the reaction time of 30 min. The optimum conditions obtained for the best 4-CP degradation rate were at an initial concentration of 25mg/l, persulfate concentration of 1.5mM, nZVI dosage of 1mM, pH of 3 and reaction time of 120min for UVA-LED/persulfate/nZVI process. It was also observed that the 4-CP degradation rate is dependent on initial 4-CP concentrations for both processes. The pseudo-first-order kinetic constant at 25mg/L initial concentration of 4-CP was found to be 1.4×10^?1 and 3.8×10^?2 in UVA-LED/H₂O₂/nZVI and UVA-LED/persulfate/nZVI processes, respectively. Briefly, the UVA-LED/H₂O₂/nZVI process enhanced the degradation rate of 4-CP by 3.67-times in comparison to UVA-LED/persulfate/nZVI process at 30min contact time, which serves as a new and feasible approach for the degradation of 4-CP as well as other organic contaminants containing wastewater.     

Orthogonal array design method for optimization experiments of sodium azide microencapsulation with stearic acid

In this study, an orthogonal array design (OAD), OA₉, was employed as a statistical experimental method for mircoencapsulation of sodium azide with stearic acid through a solvent/non-solvent procedure which is based on the coacervation principle. Scanning electron microscopy (SEM) was used to examine the coating morphology. The effect of stearic acid coating on sodium azide decomposition has been studied by means of differential thermal analysis (DTA), thermogravimetry (TG) and differential scanning calorimetry (DSC). Our findings revealed that stearic acid can provide an effective coating shell around sodium azide microparticle and the coating quality is affected by some parameters, such as percent of stabilizer, addition time of non-solvent, volume of non-solvent and stirring speed of the mixture (revolutions per minute, rpm). The effects of these factors on the thermal decomposition temperature of microencapsulated sample were quantitatively evaluated by the analysis of variance (ANOVA). The statistical results showed that sodium azide powder can optimally be coated and stabilized by controlling of stabilizer percent, addition time of non-solvent, and volume of non-solvent. The OAD evaluation of initial experimental data provide optimized amount of the parameters to obtain the most stabilized sample, at which the thermal decomposition temperature of sodium azide is predicted at 436 °C. The prediction is in excellent agreement with experimental result obtained at the same conditions that is 435 °C. These data could be compared to that of the pure stearic acid and sodium azide in which decomposition temperature ranges are 160–300 and 382–397 °C, respectively. Also, the kinetic parameters such as activation energy and frequency factor of the decomposition processes of pure components and microencapsulated sodium azide at optimum condition were obtained from the DSC data by non-isothermal methods proposed by ASTM E696. Our finding showed that the treated NaN₃ has much lower decomposition rate as compared to the pure one.     

Thermal decomposition of pyrotechnic mixtures containing sucrose with either potassium chlorate or potassium perchlorate

The thermal behavior of sucrose, KClO₃, KClO₄, and KClO₃ + sucrose and KClO₄ + sucrose mixtures was studied experimentally using differential thermal analysis (DTA) and thermogravimetry (TG). The mixtures (KClO₃ or KClO₄ with sucrose) are sometimes used as pyrotechnic mixtures in military activities. The results demonstrate that the ignition temperatures for KClO₃ and KClO₄ are 472 and 592 °C, respectively. On the other hand, DTA-TG of pure sucrose indicates that this compound decomposes at 180 °C before it initiates. Also, when KClO₃ is replaced by KClO₄ as oxidizer of the fuel, sucrose, the sensitivity of the mixture decreases. In addition, the ignition temperature for a mixture of KClO₃ and sucrose can be as low as 180 °C. However, replacing KClO₃ with KClO₄ elevates the ignition temperature of the mixture by at least 200 to ∼410 °C, which is a safe temperature for preventing activation of the mixture by accidental factors such as static electricity.     

Automatic abstraction in reinforcement learning using data mining techniques

In this paper, we used data mining techniques for the automatic discovering of useful temporal abstraction in reinforcement learning. This idea was motivated by the ability of data mining algorithms in automatic discovering of structures and patterns, when applied to large data sets. The state transitions and action trajectories of the learning agent are stored as the data sets for data mining techniques. The proposed state clustering algorithms partition the state space to different regions. Policies for reaching different parts of the space are separately learned and added to the model in a form of options (macro-actions). The main idea of the proposed action sequence mining is to search for patterns that occur frequently within an agent’s accumulated experience. The mined action sequences are also added to the model in a form of options. Our experiments with different data sets indicate a significant speedup of the Q-learning algorithm using the options discovered by the state clustering and action sequence mining algorithms.     

The removal of cephalexin antibiotic in aqueous solutions by ultrasonic waves/hydrogen peroxide/nickel oxide nanoparticles (US/H2O2/NiO) hybrid process

ABSTRACT

Antibiotics are non-biodegradable and can remain for a long time at aquatic environments and they have a big potential bio-accumulation in the environment. The antibiotics are broadly metabolized by humans, animals and plants and they or their metabolites, after metabolization, are entered into the aquatic environment. This study aimed to optimize the operational parameters by Taguchi design and to carry out the kinetic studies for removal of cephalexin antibiotic from aqueous solutions by US/H₂O₂/NiO hybrid process. This experimental study was performed on a laboratory scale in a 500 mL pyrex-made reactor. The main operational parameters to influence the US/H₂O₂/NiO process were identified as the initial concentration of CEX (20–80 mg/L), hydrogen peroxide (H₂O₂) (10–40 mL/L), NiO nanoparticle (2.5–10 mg/L) and reaction time (15–90 min) and therefore, the influence of these factors were studied. Under optimum conditions (pH = 3, reaction time = 90 min, CEX = 40 mg/L, NiO = 7.5 mg/L and H₂O₂ = 30 mL/L) and using the US/H₂O₂/NiO process, the removal efficiencies of CEX, COD and TOC were 93.86%, 72.46% and 54.55%, respectively. The percentage contribution of each factor was also determined. Results introduced the solution pH as the most powerful factor, and its percentage contribution value was up to 94% in the studied process. It was also identified that the removal of CEX antibiotic using the hybrid process obeys the pseudo-first-order kinetics.     

Reduction of Formaldehyde Emission from Particleboard by Phenolated Kraft Lignin

The aim of this study was the reduction of formaldehyde emission from particleboard by phenolated Kraft lignin. For this purpose, the lignin was extracted from black liquor and then modified by phenolation. During the urea formaldehyde (UF) resin synthesis different proportions of unmodified and phenolated Kraft lignins (10%, 15%, and 20%) were added at pH = 7 instead of the second urea. Physicochemical properties and structural changes of resins so prepared, as well as the internal bond (IB) strength and formaldehyde emission associated with the panels bonded with them were measured according to standard methods. The Fourier transform infrared (FTIR) analysis of lignin indicated that the content of O–H bonds increased in phenolated lignin while the aliphatic ethers C–O bonds decreased markedly in the modified lignin. Since both synthesis of UF resins and lignin phenolation are carried out under acid conditions, phenolation is an interesting way of modifying lignin for use in wood adhesive. The panels bonded with these resins showed significantly lower formaldehyde emission compared to commercial UF adhesives. The UF resin with 20% phenolated lignin exhibited less formaldehyde release without significant differences in internal bond strength and physicochemical properties compared to an unmodified UF resin. XRD analysis results indicated that addition of phenolated lignin decreased the crystallinity of the hardened UF resins.