Titania supported Co-Mn-Al oxide catalysts in total oxidation of ethanol

Catalytic activity of the Co-Mn-Al mixed oxide catalysts (Co:Mn:Al molar ratio of 4:1:1) supported over titania was examined in total oxidation of ethanol. The prepared catalysts were characterized by chemical analysis (AAS), surface area measurements, and temperature programmed techniques (TPR, TPD). In ethanol oxidation, the catalysts activity gradually increased with increasing active phase content. Low concentration of Co-Mn-Al oxides in the catalyst negatively affected formation of reaction byproducts: carbon monoxide production steeply increased when Co + Mn metals concentration were lower than 5 wt.%. On the other hand, formation of the second main reaction intermediate, acetaldehyde was limited, when acidity of the catalyst was not high, i.e. concentration of Co-Mn metals over titania was low.     

Acid-catalyzed decomposition of stable 1-(2,1-benzisothiazol-3-yl)-3-phenyltriazenes

The acid-catalyzed decomposition of unusually stable 1-(2,1-benzisothiazol-3-yl)-3-phenyltriazenes in either aqueous perchloric acid or an aqueous mixture of perchloric and acetic acid was studied under pseudo-first order reaction conditions at 25 °C. Different products were obtained according to substitution on nitrogen N-3. For a triazene carrying hydrogen, the corresponding 3-amino-2,1-benzisothiazole and benzenediazonium salts were formed whereas in the case of substitution by an alkyl group (methyl and n-butyl) the 2,1-benzisothiazole-3-diazonium salt and N-alkylaniline were obtained. The observed rate constant (k_obs) of the acid-catalyzed decomposition increased, initially, nonlinearly with increasing concentration of acid. Subsequently, k_obs decreased slightly and at high acid concentration, increased steeply once again. An A-S_E2 mechanism in which protonation of the triazene nitrogen proceeds simultaneously with cleavage of the N–N bond is proposed. Tautomerism of 1-(2,1-benzisothiazol-3-yl)-3-phenyltriazene was investigated using ¹H NMR spectroscopy.     

Physico-chemical properties of ethanol – Compilation of existing data

Physico-chemical properties of ethanol and aqueous solutions of ethanol are important for chemical engineering calculation, modelling and evaluation of processes during ethanol production and its use for food and non-food applications. The majority of these properties are possible to find in handbooks and tables as Yaws (1999): Chemical Properties Handbook; Miller and Yaws (1976): Correlation constants for liquids; Lide (2007–2008): CRC Handbook of Chemistry and Physics; Hole?ek (2007): Chemical-engineering tables; Critical Data Tables and other literature. Some of them are also accessible online. The goal of this paper is to present the formulas and developed algorithms for calculation of extended properties of ethanol collected from literature. Extended properties include density, vapor pressure, surface tension, viscosity, molar and specific heat capacity, enthalpy of vaporization, thermal conductivity and static relative permittivity (dielectric constant) of ethanol.     

Hybrid charge control for stick-slip piezoelectric actuators

The article describes an analog electronic circuit for driving stick-slip piezoelectric linear actuators. The task for the amplifier is to provide a high-voltage asymmetric sawtooth-like signal and feed it into a capacitive load. Generation of excessive heat must be avoided while maximizing the slew rate. In order to guarantee a steady translation, the hysteretic behaviour of the piezoelectric material must be compensated. Combination of a charge control scheme with switching is proposed as an efficient solution. Laboratory experiments confirm the superiority of this tailored solution over other existing techniques based on versatile linear voltage amplifiers.     

Probabilistic Nonlocal Theory for Quasibrittle Fracture Initiation and Size Effect.?II: Application

The nonlocal probabilistic theory developed in Part I is applied in numerical studies of plain concrete beams and is compared to the existing test data on the modulus of rupture. For normal size test beams, the deterministic theory is found to dominate and give adequate predictions for the mean. But the present probabilistic theory can further provide the standard deviation and the entire probability distribution (calculated via Latin hypercube sampling). For very large beam sizes, the statistical size effect dominates and the mean prediction approaches asymptotically the classical Weibull size effect. This is contrary to structures failing only after the formation of a large crack, for which the classical Weibull size effect is asymptotically approached for very small structure sizes. Comparison to the existing test data on the modulus of rupture demonstrates good agreement with both the measured means and the scatter breadth.     

Dynamic extension - A new principle for a vacuum primary standard for UHV-range (10-10 Pa) calibration of hot cathode ionisation gauges

The main obstacle in the construction of primary vacuum standards for very low pressures - ultra-high vacuum (UHV) - is outgassing from the walls of the apparatus. Thus, principles utilising a higher pumping rate in the calibration chamber, e.g., the pressure ratio technique, seem to be more useful for this range. However, a serious problem is inherent in this method, namely, that the gas in the calibration chamber is not in equilibrium and thus cannot be characterised by a single scalar pressure value, although such a value is then used to evaluate the measurement. This discrepancy can be overcome by using a hot cathode ionisation gauge as a transfer standard calibrated by the dynamic extension method.The dynamic extension method is explained and compared with the pressure ratio technique. The basic conditions for achieving acceptable uncertainty values are considered.     

Effect of longwall face advance rate on spontaneous heating process in the gob area - CFD modelling

A commercial CFD software programme, FLUENT, was used to study the oxidation process of coal in the mined-out longwall (gob) area. A three-dimensional, single-phase model with a continuously advancing longwall face has been developed. For the model, the gob longwall area was designed on the basis of the actual longwall panel operating in the Ostrava-Karviná Coal Mines (OKD, Czech Republic). The behaviour of the coal to oxygen was modelled using the results arising mainly from the former laboratory-scale experiments with Czech bituminous coals. Basically, the technique of pulse flow calorimetry and measurements at a continuous airflow reactor were applied during the laboratory investigations. In the contribution, the main focus was to understand the effect of the longwall face advancing speed on the oxidation heat production as well as evolution of the gases in the gob area. Simultaneously, the effect of coal crushing in the mined-out area on the spontaneous heating process was examined.Numerical simulations confirmed the existence of a “favourable” zone for the onset and development of the spontaneous heating process in the gob area. The location and the maximal temperature reached in the “favourable” zone were found to be significantly affected by the advancing rate of the coalface. The slower the advancing rate is, the higher the maximal temperature and smaller the depth of the “favourable” zone in the gob area are. When the rate drops to a certain “critical” value, spontaneous heating turns to flammable combustion of the coal. The value of the “critical” advancing rate was confirmed to increase if the grain size of the coal left in the gob decreases. Numerical examinations of carbon monoxide concentrations then proved that small incidents of spontaneous heating could occur in the gob area that need not be detected in the airflow of the longwall tail gate.     

Optimum Arrangement of Tube Coil in Radiation Type of Tubular Furnace

Tube coil arrangement dominantly influences the thermal-hydraulics characteristics of furnace and its economy. The presented method is based on standard long-used design methods (Lobo-Evans method, Belokon method). It is shown how these standard global design methods can be (for common-operating conditions) suitably generalized and simplified. It allows (for the purpose of optimum design of coil arrangement) to arrange the basic heat transfer equation for radiant chamber. In connection with investment cost relations for individual furnace subsystems (tube coil, burners, lining, etc.) and operating cost relations (fuel consumption, fluid pumping cost), the final objective function of total cost can be obtained. This objective function then allows finding the optimum coil arrangement from minimum total cost point of view. Moreover, the obtained results allow one to formulate some general recommendations suitable for furnace designers. The developed method can be used for the individual solution of a radiation-type of tubular furnaces and also for the first (preliminary) design stage usually connected with a proposal for the customer when only basic process and furnace design data are known. The developed method can be also used for the effective solution of the integration of radiation furnaces into processes. The application of the developed method is demonstrated through a case study—the optimum arrangement of coil in a gas plant regeneration furnace.     

Solving production scheduling with earliness/tardiness penalties by constraint programming

This paper deals with an application of constraint programming in production scheduling with earliness and tardiness penalties that reflects the scheduling part of the Just-In-Time inventory strategy. Two scheduling problems are studied, an industrial case study problem of lacquer production scheduling, and also the job-shop scheduling problem with earliness/tardiness costs. The paper presents two algorithms that help the constraint programming solver to find solutions of these complex problems. The first algorithm, called the cost directed initialization, performs a greedy initialization of the search tree. The second one, called the time reversing transformation and designed for lacquer production scheduling, reformulates the problem to be more easily searchable when the default search or the cost directed initialization is used. The conducted experiments, using case study instances and randomly generated problem instances, show that our algorithms outperform generic approaches, and on average give better results than other nontrivial algorithms.