Volume 20, Issue 3

In this work, the structural and tribological behavior of graphene oxide samples as a grease addi-tive was studied. By Nd:YAG laser ablation system and using graphite target at two laser energy of 0.3 W and 0.6 W, graphene oxide (GO) samples were successfully prepared. GO samples were characterized using Raman spectroscopy, field emission scanning electron microscopy (FESEM), Fourier transform infrared spectroscopy (FTIR) and energy dispersive X-ray spectroscopy (EDAX). Also, tribological behaviors of the lubricating grease, with and without the graphene oxide in grease, by the pin-on disc tribometer were determined. The Raman spectroscopy measurements showed D and G bound, which confirmed the successful synthesis of the graphene oxide sample and also the I D / I G , decreased by increasing laser power due to decreasing disorder in graphene oxide structure. FESEM images show that by ablating carbon atoms from graphite target in water, particles assemble to form a GO micro-cluster due to thermodynamically agglomeration with average size of about 3–4 µm, which the size of them depends on the laser pulse energy. Based on FTIR and EDAX analysis, GO sample which prepared at lower laser energy possessed the highest content of oxygen and oxygen functional groups. In addition, the results of tribological behavior showed that the friction-reducing ability and antiwear property of the grease can be improved effectively with the addition of GO. However, it is revealed that the small size GO has a better lubricating performance and therefore cluster size appears to play a role in the degree of wear protection due to its impact on the physical and chemical properties. The results of this study indicate that the GO sample prepared at lower laser energy (0.3 W) has a smaller size and the higher the oxygen content therefore provide better friction-reducing and anti-wear effect. Also, additive of graphene oxide in lubricating grease decreases coefficient of friction as well as wear. Based on our results, the application of GO as an additive in grease leads to increased performance of the lubricated kinematic machine.

The aim of this study is to achieve the hydro-liquefaction of asphaltene for the production of liquid fuel. The oil soluble molybdenum catalysts, molybdenum dialkyl dithiophosphate, and nickel carboxylate precursor with different carbon chains, were synthesized. The catalysts were characterized by ICP-OES, TEM and XPS. Their catalytic performance for the hydro-liquefaction of asphaltene to liquid fuels was investigated in a slurry bed reactor by using decalin as hydrogen donor and dispersant. The results show that the bimetal catalytic system composed of molybdenum dialkyl dithiophosphate and caproic acid nickel produces more MoS 2 and NiS x active species. The metal contents of which accounts for 81.8 and 81.0 wt% of the total amount of Mo and Ni, respectively, and thus exhibits the best catalytic performance among the catalysts studied. The liquid yield of the asphaltene hydrogenation over the bimetal catalyst is 84.6 wt%, which is much higher than that over other catalysts, and the coke content is only 8.6 wt% under the conditions of 1000 μg/g of total metal addition, 1:1 Mo/Ni metal mass ratio and 1:1 asphaltene/naphthalene mass ratio. The content of saturated and aromatic components in the liquid products of asphaltene hydrogenation of the bimetal catalyst system is 78.9 wt%, which is a high-quality liquid fuel component.

Multiple purification of zinc sulfate solution is an important process for zinc hydrometallurgy, and large quantities of copper-cadmium residues are generated as byproducts in this process. Copper-cadmium residues contain a large number of valuable metals that must be recovered. A comprehensive extraction process has been proposed using sulfuric acid as the leaching reagent and hydrogen peroxide as the oxidizing reagent. The effects of acid concentration, leaching temperature, leaching time, liquid-to-solid ratio, hydrogen peroxide dosage and stirring speed on the leaching efficiency were investigated. The optimum conditions were determined as an acid concentration of 150 g/L, liquid-to-solid ratio of 4:1, hydrogen peroxide amount of 20 mL, time of 60 min, temperature of 30 °C, particle size of −d75 μm, and agitation rate of 300 r/min. It was concluded that the leaching efficiency of copper and cadmium reached 97%, but because of the existence of zinc sulfide in the residues, a lower leaching efficiency of zinc was obtained. Furthermore, the leaching kinetics of copper was also studied based on the shrinking core model. The activation energy for copper leaching was 5.06 kJ/mol, and the leaching process was controlled by the diffusion through the product layer.

For an air staged combustion boiler, the rational organization of jets to form closing-to-wall film using as little air as possible plays a key role in resolving the high temperature corrosion problems. In this work, a comprehensive computational fluid dynamics (CFD) model including hydrodynamics and coal combustion is established for a 660 MW opposed wall fired boiler. Based on the grid independence and model validation, the flow field, temperature profile, and species concentration are predicted, and the influences of the structure of nozzles and the operation parameter of jets are further evaluated. The results show that the corrosion area of the side wall is dependent on the jet projection velocity and nozzle structures. The increase of the jet velocity does not always have an active influence on the reduction of corrosive area. Only increasing the nozzle diameter does not always have a positive impact on the improvement of the corrosion. The increase of the jet inclination angle can extend the jet trajectory, contributing to increase the oxygen coverage area. Reasonably adjusting the jet inclination angle of each layer can obtain the lower corrosion area. The increase of jet row number leads to a decrease in the spacing between rows, which enables the downstream jet to penetrate deeper into the cross stream. By increasing the number of jet layers and reducing the jet velocity of each layer, the lowest corrosion area can be obtained.

Coking wastewater (CWW) is known as a highly polluting effluent. This study deals with the degradation of pollutants in terms of COD, phenol and cyanide present in CWW using catalytic wet air oxidation (CWAO) process. CWAO was carried out in batch mode using various catalysts. The investigated operating parameters are initial pH (pH i ) 3–11, temperature ( T ) 100–160 °C, air partial pressure ( p air ) 2–6 MPa, catalyst mass loading ( C w ) 2–5 g/L and treatment time ( t R ) of 0–6 h. Among various catalysts, the copper chloride was proved to be best for degradation of pollutants. The optimum conditions were evaluated for the degradation of organic compounds as T 130 °C, p air 8.8 MPa, C w 3 g/L and t R  = 6 h. The maximum percentage reduction of COD, phenol, and cyanide was achieved through experiment at T 160 °C, p air 12.2 MPa, C w 5 g/L and t R 6 h as 97.32%, 97.94% and 99.87%, respectively. The kinetics studies were also performed to evaluate the rate constant ( k ), and reaction order with respect to COD, phenol, CN, C W and p air .

An electrocatalytic membrane reactor (ECMR) with an anode consisting of Pt nanoparticles (NPs) loaded on a Ti membrane electrode (Pt NPs/Ti) was designed to oxidize cyclohexanone (K) to produce sodium adipate (SA) under mild conditions. The effects of residence time, reaction temperature, current density and initial K concentration on K conversion were investigated. Optimization experiments were conducted to determine the effects of and interactions between different operating parameters on K conversion using a central composite design within the response surface methodology. A 88.3% conversion of K and 99% selectivity to SA were obtained by the ECMR under the optimum conditions of reaction temperature = 30.8 °C, K concentration = 22.54 mmol L −1 , residence time = 25 min and current density = 2.07 mA cm −2 . The high performance of the ECMR is attributed to electrocatalytic oxidation (at the Pt NPs/Ti electrode), convection-enhanced mass transfer, and the timely removal of the desired products.

Gas-particle flows in circulating fluidized beds (CFB) with wide particle size distributions were simulated using the Eulerian-Eulerian approach to analyze the effects of the particle phase division and the applicability of the particle-particle drag model. The results indicate that the simulation is not accurate by just using a single average particle diameter when the particle size distribution includes a critical particle diameter. A binary particle phase division criterion was then developed to establish two particle phases representing two types of particles with different flow patterns. Coupling the Eulerian-Eulerian approach with the new criterion enabled accurate predictions of the pressures, particle volume fractions, and particle mass circulation rates that were in agreement with experimental data. The influences of different particle-particle drag models were also investigated to show that the simulation using the Syamlal model was not accurate due to the overestimated particle-particle drag, while the results without particle-particle drag and with the Manger model were similar and much more accurate. Moreover, the flow mechanism for the non-uniformity of particle circulation rates in the parallel circulating loops of the CFB boiler was revealed. This study improves the Eulerian-Eulerian simulations of fluidization with wide particle size distributions and further deepens the understanding of flow characteristics in CFB.

Rapid generation of natural gas hydrates is the basis for the application of hydrate storage and transportation. In this work, the kinetic parameters of methane hydrate formation (gas consumption, gas consumption rate constant and reaction space velocity) both in the liquid continuous impinging stream (LIS) system and sodium dodecyl sulfate (SDS) + water and LIS combination system were investigated in a liquid-continuous impinging stream reactor. The gas consumption rate constant was 3.40 × 10 −8  mol 2  s −1  J −1 without the impinging stream, while it increased with the increase of impinging strength and reached the maximum value of 3.68 × 10 −8  mol 2  s −1  J −1 when the impinging strength was 0.21. In the SDS + water and LIS combination system, when the SDS concentration was 600 mg/L, the maximum gas consumption rate constant was 3.99 × 10 −8  mol 2  s −1  J −1 without the impinging stream, while it reached the maximum value of 4.61 × 10 −8  mol 2  s −1  J −1 when the impinging strength was 0.38. The results showed that the impinging stream can effectively promote the formation rate of methane hydrate, and single mechanical promotion was better than non-promoting mode but combination promotion methods was better than single mechanical promotion.