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A green heterogeneous acid catalyst derived from agro-industrial waste obtained from ginger straw was prepared via partial carbonization, followed by sulfonation using sulfuric acid. Three variables, including the carbonization temperature, carbonization time and sulfonation temperature, were optimized to achieve the ideal preparation conditions and the as-synthesized catalyst was characterized using X-ray diffraction, elemental analysis, scanning electron microscopy, Fourier transform infrared spectroscopy, thermogravimetric analysis, X-ray photoelectron spectroscopy, Raman spectroscopy, N 2 adsorption-desorption and acid density studies to reveal the relationship between its catalytic performance and physical-chemical properties. The results show that the ginger straw-based catalyst prepared via carbonization for 60 min at 350 °C, followed by sulfonation at 105 °C, has an amorphous carbon structure with an –SO 3 H group density of 1.05 mmol/g. In addition, the catalyst exhibits thermal stability up to 200 °C and satisfactory catalytic performance (93.2% conversion) during the esterification of oleic acid using methanol under the optimized reaction conditions (9:1 M ratio of methanol to oleic acid; catalyst loading, 7 wt%; reaction temperature, 64 °C; reaction time, 210 min). Although its catalytic activity was later found to decrease with cycling, the spent catalyst remains stable after the 5th cycle with a conversion of 65.6%. • Ginger straw is used to prepare heterogeneous acid and utilized in esterification. • The as-synthesized acid catalyst gains sulfonic acid density of 1.05 mmol/g. • Catalyzed esterification conversion of oleic acid with methanol is up to 93.2%. • Acid sites leaching plays a dominant role in catalytic reusability. [ABSTRACT FROM AUTHOR]

A novel acid-base bifunctional Zn/Ca–Zr catalyst has been synthesized successfully for biodiesel production from palm oil and acidified oil. The influence of synthetic factors on the catalytic activity of resulting Zn/Ca–Zr were discussed. Furthermore, the FAMEs yield was optimized to achieve the maximum value using the Taguchi approach. Results showed that the catalyst synthesized using a metal stoichiometric ratio of 4 : 4: 4, hydrothermal conditions, and activation temperature of 850 °C exhibited the best activity. The highest FAMEs yield was found to be 94.9% under the conditions of 5 wt% catalyst dosage, methanol/palm oil molar ratio of 20, and temperature of 170 °C at 3 h. The contribution percentage indicated that the methanol/oil molar ratio had the most significant effect on the FAMEs yield. Moreover, the Zn/Ca–Zr catalyst can catalyze the simultaneous esterification and transesterification of acidified palm oil with a 95.1% FAMEs yield and 93.3% acid reduction rate. And a 78.2% FAMEs yield can be maintained after four repeated cycles. Molecular simulations indicated the active site of Zn was more easily attacked by FFAs for esterification, while the active site of Ca was retained to adsorb methanol for transesterification, which explained the catalyst's acid-base bifunctional characteristics. [ABSTRACT FROM AUTHOR]

Abstract Thermal degradation properties of stearic acid and its esterification derivants of methyl stearate and ethyl stearate are investigated through thermogravimetric analysis. Based on experiments, which are conducted at the temperature heated rates of 10, 15 and 20 K min−1, the iso-conversional methods of Kissinger-Akahira-Sunose and Flynn-Wall-Ozawa are used to calculate the apparent activation energy. Further, the Avrami theory is used to estimate the apparent reaction order. Apparent thermodynamic parameters of the apparent enthalpy change, apparent Gibbs free energy change and apparent entropy change are calculated. Calculations of apparent kinetic and thermodynamic parameters illustrate that thermal activity of stearic acid is distinctly heightened after esterification and the derived derivants are more easily activated. Meanwhile, influences of alcohol type on esterification products are weak. Conclusions from this study make more comprehensive understanding of the thermal events of biodiesel to be favor for its commercial application. Highlights • Thermogravimetric is practical in evaluating thermal degradation of biodiesel. • Esterification derivants are more easily activated than stearic acid. • Influences of alcohol type on esterification products are weak. • Thermal degradation of biodiesel could be described by more than one model. • Kinetic and thermodynamic calculations manifest thermal degradation profoundly. [ABSTRACT FROM AUTHOR]

A series of carbon catalysts are synthesized through the arylation diazonium salt reduction approach from coal to catalyze esterification of oleic acid with methanol for biodiesel production. Under the activated carbon preparation temperature of 900 °C, mass ratio of 4-aminobenzenesulfonic acid to activated carbon of 6 and arylation temperature of 45 °C, the synthesized carbon catalyst gains the surface area and pore volume of 629.3 m 2  g −1 and 0.29 cm −3  g −1 , respectively. Besides, the carbon catalyst possesses abundant and strong active sites with the 4-sulfophenyl group density of 0.97 mmol g −1 and acid strength of 0.8 < pH < 3.3. Catalytic capability of the carbon catalyst, which is synthesized under the above optimized condition, in esterification is stronger than the commercial Amberlyst-15, where the maximum efficiency achieves 95.04% with the carbon catalyst added mass percentage of 12%, molar ratio of methanol to oleic acid of 10, esterification duration of 4 h and esterification temperature of 65 °C. Due to leaching of the 4-sulfophenyl groups, esterification efficiency declines to 77.63% for the fifth reused cycle of the carbon catalyst. Meanwhile, the regenerated carbon catalyst supplies the esterification efficiency of 86.05%. Chemical composition of the produced biodiesel is identical to pure methyl oleate and its fuel properties are in accordance with ASTM D 6751. [ABSTRACT FROM AUTHOR]

Powder coal is carbonized under nitrogen atmosphere and then treated with concentrate sulfuric acid with the assistance of microwave radiation for heterogeneous acid catalyst synthesis and the capability in catalyzing esterification of oleic acid with methanol for biodiesel production is subsequently studied. The catalysts are characterized by N 2 adsorption-desorption, ultimate analysis, X-ray diffraction, Raman spectra, attenuated total reflectance-Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and acid amount tests to obtain the physicochemical property. Microwave irradiation is a faster and simpler process than the conventional heating, and the sulfonation duration can be shortened to be 5 min. Under the carbonization temperature of 250 °C for 30 min and sulfonation temperature of 75 °C for 5 min, the synthesized catalyst gains the acid amount of 1.73 mmol g −1 and esterification efficiency of 98.1% is achieved with the catalyst dosage mass percentage of 10 wt%, molar ratio of methanol to oleic acid of 12, esterification temperature of 65 °C and esterification duration of 180 min, where the commercial Amberlyst-15 catalyst only presents the efficiency of 71.5% under the same condition. Though the catalytic capability is crippled during the recycling reusage, it can be easily regenerated with its mostly original catalytic activity. [ABSTRACT FROM AUTHOR]

The coal-based solid acid catalysts are synthesized by incomplete carbonization followed by sulfonation approach and their activities in catalyzing esterification of oleic acid with methanol are subsequently investigated. For characterizations of catalyst, N 2 adsorption and desorption, ultimate analysis, XRD, SEM, XPS, TG, FTIR and acid amount test are employed. The synthesis conditions are optimized as carbonization at 400 °C for 1 h and sulfonation at 105 °C for 2 h, where acid amount of 1.57 mmol·g −1 is measured. Ultrasound irradiation is introduced into the esterification reactor, and the effects of different operation parameters, including the ultrasonic power, catalyst dosage, molar ratio of methanol to oleic acid, reaction temperature on the esterification efficiency under ultrasound-assisted as well as sonication-free method, have been investigated. The results demonstrate that after passing the given reaction duration of 1 h, 91.4% of esterification efficiency is obtained under the optimized conditions (i.e., ultrasonic power of 270 W, catalyst dosage of 6 wt.%, methanol to oleic acid molar ratio of 10, and reaction temperature of 67 °C). 87.9% of conversion is achieved under the same operating conditions without ultrasonic irradiation. Moreover, esterification experiments indicate that this synthesized coal-based solid acid catalyst possesses favorable catalytic activity and satisfactory recyclability in biodiesel production. [ABSTRACT FROM AUTHOR]

A series of coal-based heterogeneous acid catalysts are prepared by partial carbonization followed by sulfonation approach and the performances in esterification for methyl oleate production are conducted. Characterization methods of XRD, N 2 adsorption-desorption, SEM, TG, FTIR, EDX, acid density tests and Hammett indicator method are carried out to reveal the physical and chemical characteristics of the prepared catalysts. Catalyst with the highest acid density of 1.09 mmol g −1 could be prepared under the condition of carbonization temperature at 350 °C for 2 h and sulfonation with concentrated sulfuric acid at 135 °C for 4 h. Acid value reduction of 97.29% on oleic acid through esterification with methanol, which is catalyzed by this coal-based heterogeneous acid, could be achieved under the optimized condition of 10 wt.% catalyst dosage, molar ratio of methanol/oleic acid of 10, reaction temperature at 67 °C and reaction duration of 4 h. Characterization results demonstrate that carbon in the catalyst, which is composed of aromatic carbon sheets with COOH and SO 3 H groups, is in amorphous structure and its acid strength is 3.3 < p K a < 0.8. Meanwhile, this catalyst could provide favorable thermal stability high to 220 °C and retain satisfactory catalytic activity after five cycles. In addition, catalytic capability could be reactivated with the acid value reduction efficiency of 95.30% after the fifth re-usage. [ABSTRACT FROM AUTHOR]

Abstract: This paper proposes an improved ant colony algorithm. We put multiple QoS constraints into the transition probability function of ant colony algorithm to increase the transfer probability of “excellent node”. The new algorithm considers the variation of probability and adjustment value of the pheromones together to accelerate the convergence speed, avoids falling into local optimal, and improves the delay characteristics of routing algorithm. Simulation results show that the improved algorithm is better than the typical ant colony algorithm in terms of delay and the number of iterations. [Copyright &y& Elsevier]

A steady flow with a high flow rate, oscillating flow, and audible sound waves can enhance the heat transfer performance in air-to-air heat exchangers, while the comparison of influence mechanisms and degrees of different methods is ignored. This study investigates flow instability and heat transfer characteristics in an air-to-air heat exchanger under steady flow, oscillating flow and sound waves. The results show that steady flow and oscillating flow with different amplitudes have little effect on the distribution characteristics of velocity and vortices. However, the vortices disappear and generate periodically under 140 dB. Moreover, oscillating flow and sound waves exert distinct influences on flow instability. The cold side experiences the highest increase in turbulence kinetic energy when subjected to high-amplitude oscillating flow, while the greatest increase on the hot side occurs under high-amplitude sound waves, and the influence of steady flow on turbulence kinetic energy is relatively low. Additionally, the steady flow enhances the heat transfer performance by increasing flow rate, while the oscillating flow and sound waves promote the heat transfer between the fluid and surface. Under the effect of steady flow, oscillating flow, and sound waves, the values of heat flux are 1.22, 1.24, and 1.31 times that of the initial condition with the amplitude increasing to 0.683 m/s (140 dB). The results demonstrate that with the increase in amplitude acting on the inlet, the sound waves have the greatest impact on heat transfer performance, followed by oscillating flow, and the effect of steady flow is relatively slight. The research can provide guidelines for the development of heat transfer enhancement in air-to-air heat exchangers. • Effects of steady, oscillating flow, and sound waves on heat transfer are compared. • Oscillating flow and sound waves exert the distinct effects on flow instability. • Sound waves with high amplitude alter the evolution of vortex structure. • Increase in flow instability contributes more to heat transfer than that in velocity. • Sound waves with high amplitude enhance the air heat transfer significantly. [ABSTRACT FROM AUTHOR]

Thermogravimetric analysis in conjunction with Fourier transform infrared spectroscopy (TG-FTIR) is used to investigate thermal degradation properties of oleic acid and its esterification derivants of methyl ester and ethyl ester. Based on TG experimental results, which are operated under nitrogen atmosphere from 298 to 773 K at the sample temperature heated rates of 5, 10, and 15 K min −1 , respectively, two degradation iso-conversional approaches of Kissinger-Akahira-Sunose (KAS) and Flynn-Wall-Ozawa (FWO) are mentioned to calculate the apparent activation energy, based on which the apparent pre-exponential factor is obtained. Meanwhile, Avrami theory is used for the apparent reaction order estimation. Further, thermodynamic parameters of the apparent enthalpy change, apparent Gibbs free energy change and apparent entropy change are calculated to label the thermal degradation process directly. Also, the evolved gaseous products from TG are detected by FTIR online to understand the thermal degradation comprehensively. Information about fatty acid and its methyl ester and ethyl ester derived from TG-FTIR, especially the comparison between esterification derivants and their feedstock, has been rarely reported and is expected to contribute to the commercial application of biodiesel. [ABSTRACT FROM AUTHOR]

Fenton sludge from sewage treatment plants is a kind of hazardous waste that causes serious harm to the ecological environment. In this study, the potential of preparing a novel selective catalytic reduction (SCR) denitration (deNO x) catalyst was evaluated through selective dealkalization followed by calcination using Fenton sludge. The effects of water leaching, carbon dioxide leaching, and acid leaching methods (organic and inorganic acid) on Fenton sludge dealkalization were studied, taking the total dealkalization and active component retention rates and deNO x efficiency as comprehensive considerations. Results showed that acid leaching method has the best leaching effect on free alkali and chemically combined alkali, the order of dealkalization rates was FS H2SO4 (94.23%)>FS HCl (92.18%)>FS HNO3 (89.93%)>FS CH3COOH (81.07%). Through comprehensive comparison, FS HCl exhibited the best catalytic active and excellent selective dealkalization performance, achieving relatively high total dealkalization rate while retaining the active components to the greatest extent (86.73%). On this basis, the effects of calcination temperature on catalytic activity, as well as physical and chemical properties of the catalyst were studied. The MFS-450 catalyst exhibited the largest surface area (76.53 m2/g), pore volume (0.23 cm3/g), abundant oxygen-containing functional groups, excellent surface acidity (0.779 μmol/m2), and redox properties (5.07 mmol/g). Besides, it has the best low-temperature SCR activity and the widest reaction temperature window, with nitrogen oxide (NO x) conversion exceeding 90% at temperatures between 293 and 471 °C. This research contributes a representative example of converting Fenton sludge into valuable materials and may open a new avenue to synthesizing high-activity SCR catalyst from low-cost feedstocks. [Display omitted] • Fenton sludge, as hazardous waste, was recovered and used as deNO x catalyst. • The effect of different dealkalization methods on catalytic activity was studied. • The optimal calcination temperature of the catalyst was explored. • Physical and chemical properties of the catalyst are characterized in detail. • The modified Fenton sludge catalyst showed NO x conversion reach 100% at 304–451 °C. [ABSTRACT FROM AUTHOR]

[Display omitted] • Fenton sludge is used to prepare SCR iron-based catalyst. • Physical and chemical properties of the catalyst are characterized in detail. • An alternative method was provided to dispose Fenton sludge. • The optimum acid leaching conditions were explored in detail. • NO x conversion can reach 100% at 301–450 °C. Fenton sludge is a type of industrial hazardous waste produced after the Fenton reaction treats industrial wastewater that contains a large amount of iron oxide and other metallic elements. In this study, an efficient treatment method for preparing a selective catalytic reduction catalyst from Fenton sludge is proposed. Fenton sludge was treated using a selective acid leaching method, and the effects of four main factors were systematically studied. The experimental results showed that the dealkalization extent reached 94.8% and the retention extent of active components was 90.46% under the condition of the liquid-to-solid ratio of 6 mL/g, acid leaching temperature of 80 °C, acid leaching time of 60 min and acid dosage of 20%. The modified Fenton sludge catalyst (MFS) achieved 100% NO x conversion in the temperature range 301–450 °C, which is a wide reaction temperature range and excellent low-temperature catalytic activity. The selective dealkalization treatment can effectively inhibit the high-temperature sintering of the catalyst, increase the specific surface area and porosity of the catalyst and improve the redox performance of the catalyst. Moreover, the high O β concentration, Fe3+/Fe2+ ratio and number of oxygen vacancies contributed to the excellent catalytic performance of MFS. [ABSTRACT FROM AUTHOR]

• Biodiesel is produced through transesterification catalyzed La-dolomite catalyst. • La to dolomite molar ratio is optimized as 1 for La-dolomite catalyst preparation. • Biodiesel yield of La-dolomite catalyzed transesterification is up to be 98.7%. • Biodiesel yield is 95.9% for the fifth reused cycle of La-dolomite catalyst. • Activation energy of La-dolomite catalyzed transesterification is 57.68 kJ mol−1. In this study, biodiesel production through transesterification of palm oil using the lanthanum complex dolomite (La-dolomite catalyst) as the heterogeneous base catalyst is investigated. The La-dolomite catalyst preparation is optimized with the La to dolomite molar ratio of 1 and activation temperature of 800 °C. With the catalyst added mass percentage of 7 wt%, molar ratio of methanol to oil of 18, transesterification temperature of 65 °C and transesterification duration of 180 min, the biodiesel yield of 98.7% is achieved and the activation energy of the La-dolomite catalyzed transesterification is calculated to be 57.68 kJ mol−1. The La-dolomite presents satisfying reusability and the biodiesel yield is 95.9% for the fifth reused cycle, where it is 89.1% for the pure calcined dolomite catalyst. Finally, the main physicochemical properties of the transesterification product are measured and compared with GB/T 20828–2015. This study validates the application of the La-dolomite catalyst in catalyzing transesterification for the biodiesel production. [ABSTRACT FROM AUTHOR]

A series of heterogeneous acid catalysts are synthesized from bamboo activated carbon through arylation using sulfanilic acid without reductant. Both the catalyst synthesis conditions and parameters for esterification of oleic acid with ethanol are optimized. The heterogeneous acid catalysts are characterized by XRD, FTIR, N 2 absorption-desorption, EDX and acid-base neutralization titration. At the molar ratio of benzylsulfonic acid group to bamboo activated carbon of 1, sulfonation temperature of 50 °C and sulfonation duration of 10 min, the heterogeneous acid catalyst presents the mesoporous microstructure with surface area of 225.71 m 2  g −1 and pore volume of 0.12 cm −3  g −1 , and total acid density of 1.69 mmol g −1 . With the catalyst added mass percentage of 12% (relative to the oleic acid mass) and molar ratio of ethanol to oleic acid of 7 at 85 °C for 180 min, esterification efficiency of 96% is achieved, which is higher than 91% of esterification with methanol at 65 °C. Microstructure shrinkage is the main reason for catalyst deactivation, and the regenerated heterogeneous acid supplies the catalytic efficiency of 94%. [ABSTRACT FROM AUTHOR]