A new catalyst for hydrodesulfurization of heavy residue

Catalytic hydrodesulfurization plays an important role in the conversion of sulfur laden residual oils. Cobalt molybdate catalysts are more commonly used for this process. In the present study, a precipitation technique at constant pH value was used to prepare alumina support. This material has very narrow pore size distribution centered around the pore diameter of about 8 nm. It also has a large surface area and pore volume and, therefore, can be used as a support for CoMo RDS catalysts. The results of temperature-programmed desorption of ammonia indicated that this catalyst has higher surface acidity than the conventional catalysts. The high surface acidity could enhance the cracking ability of the catalyst. The RDS reaction results showed that the samples prepared by precipitation are more active and more stable than the conventional catalysts, at least in the first 72 h. The results can be attributed to its unique pore structure and high surface acidity.

---

. . pH. 8 . CoMo . , , . , , , , , - 72 . .

     

An Efficient and Highly Chemoselective Method to Desilylate Silyl Ethers

An efficient and highly chemoselective desilylating method is described. Trimethylsilyl ethers (0.25 M) in a CH₃OH/CCl₄ (1:1) solvent mixture are deprotected to their corresponding alcohols with ultrasound in a commercial ultrasonic cleaning bath. Selective deprotection of tert-butyldimethylsilyl ethers of benzyl alcohols and phenols is achieved under ultrasonic conditions. We deprotected also tert-butyldimethylsilyl ethers of primary alcohols, whereas tert-butyldimethylsilyl ethers of secondary and tertiary alcohols are stable under these conditions.     

Weakly Asymmetric Non-Simple Exclusion Process and the Kardar–Parisi–Zhang Equation

We analyze a class of non-simple exclusion processes and the corresponding growth models by generalizing the discrete Cole–Hopf transformation of Gärtner (Stoch Process Appl, 27:233–260, 1987). We identify the main non-linearity and eliminate it by imposing a gradient type condition. For hopping range at most 3, using the generalized transformation, we prove the convergence of the exclusion process toward the Kardar–Parisi–Zhang (kpz) equation. This is the first universality result under the weak asymmetry concerning interacting particle systems. While this class of exclusion processes are not explicitly solvable, under the weak asymmetry we obtain the exact one-point limiting distribution for the step initial condition by using the previous result of Amir et al. (Commun Pure Appl Math, 64(4): 466–537, 2011) and our convergence result.     

Multi-objective parallel machine scheduling problems by considering controllable processing times

This study examines parallel machine scheduling problems with controllable processing times. The processing time of each job can be between lower and upper bounds, and a cost is associated with the processing of a job on a machine. The processing time of a job can be decreased, which may lower the cycle time, although doing so would incur additional costs. This study develops two multi-objective mathematical models, which consist of two and three inconsistent objective functions, respectively. The first model minimizes the total manufacturing cost (TMC) and the total weighted tardiness (TWT) simultaneously, while the second uses makespan (C_max) as an additional objective function. In contrast to conventional mathematical models, efficient solutions are attained using the lexicographic weighted Tchebycheff method (LWT). Experimental results indicate that the LWT yields better-spread solutions and obtains more non-dominated solutions than its alternative, that is the weighted-sum method, which is a widely used yet promising approach to achieve multi-objective optimization. Results of this study also demonstrate that in purchasing machines, the variation in the fixed costs associated with the processing of jobs on machines is critical to reducing TWT. Moreover, using C_max as an additional objective function typically improves TWT and worsens TMC.     

Photodissociation dynamics of acetaldehyde at 267 nm: A computational study of the CO-forming channels

A recent experiment on the 267 nm photolysis of gaseous acetaldehyde reveals that the molecular products (CO + CH₄) present product state distributions with computation –experiment discrepancy. This work aims to provide solution to such issue. The direct dynamics simulation of classical trajectories and the generalized multi-center impulsive model (GMCIM) are both utilized to predict the product state distributions of CO and CH₄ from 267 nm photolysis of acetaldehyde. Comparison with the experimental observation provides an assessment of the conventional approach of minimum energy path within the framework of three-center transition state (TS) and CH₃-roaming pathways. The result shows that the high-speed products observed in experiment are likely formed via the three-center TS pathway. The reasons that lead to the discrepancy between computation and experiments in previous studies are also investigated. A better agreement between computational and state-resolved experimental results can be achieved by selecting specific internal states of CO product from the computational data.     

Electron-Transfer Protocol for the Hydroxyalkenylation of Alkenes Using 1,2-Bis(phenylsulfonyl)ethylene

We report a protocol for alkene hydroxyalkenylation. Using a persulfate anion as a one-electron-oxidation reagent and 1,2-bis(phenylsulfonyl)ethylene as a radical acceptor in the presence of water, alkenes were converted into the corresponding 1-phenylsulfonyl-4-hydroxyalkenes in good to high yields. The hydroxyalkenylation process involves the nucleophilic hydroxylation of alkene radical cations to give β-hydroxyalkyl radicals, which, after a radical addition/β-elimination sequence, provide the products. We also report a photocatalytic protocol for alkoxyalkenylation.     

A high-discernment microflow cytometer with microweir structure

Using a simple and reliable isotropic wet etching process, we fabricated a microflow cytometer in which cells/particles are concentrated in the center of the sample stream using a 2-D hydrodynamic focusing technique and an microweir structure. Having focused the cells/particles, they are detected and counted using a LIF method. The experimental and numerical results confirm the effectiveness of the hydrodynamic sheath flows in squeezing the cells/particles into a narrow stream in the horizontal X-Y plane. Furthermore, it is shown numerically that the microweir structure results in the separation of the cells/particles in the vertical X-Z plane such that they pass through the detection region in a sequential fashion and can therefore be counted with a high degree of precision. The experimental results obtained using fluorescent polystyrene beads with diameters of 5 and 10 microm, respectively, confirm the suitability of the proposed device for microfluidic applications requiring the high-precision counting of particles or cells within a sample flow.