Volume 62, Issue 1

At present, carbon dioxide is considered the largest contributor among greenhouse gases. This review covers the current state of problem of carbon dioxide emissions from industrial and combustion processes, the principle of photocatalysis, existing literature related to photocatalytic CO2 reduction over TiO2 based catalysts and the effects of important parameters on the process performance including light wavelength and intensity, type of reductant, metal-modified surface, temperature and pressure.

This work was focused on modeling of biochemical processes in a 40-L internal-loop airlift reactor. Due to different mixing in the specific zones of the reactor four main sections, bottom, riser, separator and downcomer, were recognized. Each zone was modeled by an adequate mixing model: bottom and separator sections by the model of ideally-stirred reactor; riser and downcomer sections by the model of plug-flow reactor with axial dispersion. In the model, the effects of mass transfer, hydrodynamics, and reaction kinetics were taken into account. The model of the reactor was experimentally verified by the aerobic enzymatic oxidation of glucose to gluconic acid. Simulations are in good agreement with experimental data.

The influence of TiOSO4 and free sulphuric acid concentrations in the starting solution on the degree of titanyl sulphate conversion to hydrated titanium dioxide and post-hydrolytic sulphuric acid was studied. Titanyl sulphate solution, an intermediate product in the commercial preparation of titanium dioxide pigments by sulphate route, was used. It was found that the degree of hydrolysis markedly depends on the studied parameters. The lower was the content of TiOSO4 in the starting solution, the higher conversion was achieved. The degree of hydrolysis at the final stage varied between 81 % (420 g TiOSO4 dm−3, 216 g H2SO4 dm−3) and 92 % (300 g TiOSO4 dm−3, 216 g H2SO4 dm−3). The same relation was obtained when changing the concentration of free H2SO4 in the starting solution. The degree of hydrolysis at the final stage varied between 49 % (261 g H2SO4 dm−3, 340 g TiOSO4 dm−3) and 96 % (136 g H2SO4 dm−3, 340 g TiOSO4 dm−3). The particle size of the obtained hydrated titanium dioxide (HTD) also depends on the initial solution composition.

Models of two important characterisation procedures for oil and oil fractions, ASTM D86 (ASTM = American Society for Testing of Materials) and EFV (Equilibrium Flash Vaporization), were presented. The purpose was to provide a basis for the construction of substitute mixtures of real components used in modelling and simulation of chemical engineering processes instead of original complex mixtures. It was shown how to deal with a possible problem of higher index of differential-algebraic model of the ASTM D86. A number of examples proved the adequacy of the presented models.

This study deals with two innovative brewing processes, high gravity batch and complete continuous beer fermentation systems. The results show a significant influence of the variables such as concentration and temperature on the yield factor of the substrate into ethanol and consequently on the productivity of the high gravity batch process. The technological feasibility of continuous production of beer based on yeast immobilization on cheap alternative carriers was also demonstrated. The influence of process parameters on fermentation performance and quality of the obtained beers was studied by sensorial analysis. No significant difference in the degree of acceptance between the obtained products and some traditional market brands was found.

L/L equilibrium data of butyric acid (BA) in aqueous solutions contacted with the solvents containing ionic liquid (IL), trihexyl-(tetradecyl)phosphonium bis 2,4,4-trimethylpentylphosphinate (Cyphos IL-104), and a related model are presented. IL-104 and its solutions in dodecane were found to be effective solvents of BA. The values of the distribution coefficients of BA were higher than those for solvents with the widely used extractant trioctylamine, especially at low acid concentrations and were also several-fold higher than those of lactic acid (LA). IL extracted BA only in its undissociated form (BAH) at pH well below pK a of the acid. The loading of IL was independent of IL concentration and it achieved a value higher than four at saturation. Complexes with 1–5 molecules of BA per one IL molecule were supposed in the mass action model in which the reactive formation of complexes (BAH)p(IL)(H2O)2 was supposed. Up to 10 % of the total extracted BA was extracted physically by dodecane as a monomer and dimer, in the solvent. The water content in the organic phase steeply decreased with the BA concentration, which was caused by splitting water-IL reverse micelles due to the formation of the BAH/IL complexes.

A methodology for hazard investigation based on the integration of a mathematical model approach into hazard and operability analysis is presented. This approach is based on mathematical modelling of a process unit where both steady-state analysis, including analysis of the steady states multiplicity and stability, and dynamic simulation are used. The dynamic simulation serves for the investigation of consequences of failures of the main controlled parameters, i.e. inlet temperature, feed temperature and feed composition. This simulation is also very useful for the determination of the influence of failure duration on the reactor behaviour. On the other hand, the steady state simulation can predict the reactor behaviour in a wide range of failure magnitude and determine the parametric zones, where shifting from one steady state to another one may occur. A fixed bed reactor for methyl tertiary-butyl ether synthesis was chosen to identify potential hazard and operational problems of a real process.

Comparison of the performance of a reactive distillation column with three different hardware configurations is presented. As a reaction system the methyl tertiary-butyl ether (MTBE) synthesis has been chosen. The sieve tray columns with catalyst (encased inside wire gauze envelopes) placed along the liquid flow path differ in the number of reactive trays. The column simulations have been performed using the nonequilibrium model. The steady state behaviour of the three different hardware configurations was studied regarding the three input parameters; feed flow rate of methanol, feed flow rate of butenes, and reflux ratio. It has been shown that by varying the location of the methanol feed stage, the columns exhibit significantly different solution diagrams using the butenes feed flow rate as a continuation parameter. Using dynamic simulations, different perturbations of the manipulated variables were found to cause transitions between multiple steady states and these were also investigated. The major objective of this paper is to demonstrate the importance of the hardware choice in the performance of a reactive distillation column e.g. during the start-up or if occasional variations of the operating parameters occur.

A set of experimental data for heterogeneously catalysed esterification of propan-1-ol and propionic acid to propyl propionate in a pilot scale reactive distillation column is presented. The catalytic section of the column was equipped with the structured packing Katapak SP-11. Both, rectifying and stripping, sections consisted of the non-reactive structured Sulzer BX packing. As catalyst, the strongly acidic ion-exchange resin Amberlyst 46 was used. The experimental results show concentration as well as temperature profiles along the column height and therefore exhibit reliable data for model validation purposes.

Experimental study of mixing time of non-Newtonian shear-thinning fluids within the transitional regime (3 × 102 < Re < 3 × 103) of liquid flow is presented. The purpose of this study was to analyze the effect of eccentricity and pumping mode of the impeller as well as of position of the tracer dosage point into the agitated liquid on mixing time. The measurements were conducted in an unbaffled agitated vessel with inner diameter D = 0.7 m equipped with an up-or down-pumping propeller located centrically (e/R = 0) or eccentrically (e/R ≠ 0) in the vessel. Experiments were carried out by means of computer-aided unsteady-state thermal method for three positions of the tracer dosage point. The experimental data show that eccentric position of the propeller in an unbaffled vessel causes a decrease of the mixing time compared to that obtained in a vessel with a centrically located propeller. Mixing time depends also on the pumping mode of the propeller as well as on the position of the tracer dosage point.

The condensation heat transfer coefficient and the two-phase pressure drop of refrigerant R-134a in a vertical plate heat exchanger were investigated experimentally. The area of the plate was divided into several segments along the vertical axis. For each of the segments, local values of the heat transfer coefficient and frictional pressure drop were calculated and presented as a function of the mean vapor quality in the segment. Owing to the thermocouples installed along the plate surface, it was possible to determine the temperature distribution and vapor quality profile inside the plate. The influences of the mass flux and the heat flux on the heat transfer coefficient and the pressure drop were also taken into account and a comparison with previously published experimental data and literature correlations was carried out.

Internal structure of carbon black produced by pyrolysis (CBp) of rubber samples from the top and bottom parts of sidewall and tread of a passenger car tire was investigated in nitrogen flow at different temperatures. The pore structure (specific surface area, pore size distribution, and porosity) of CBp and commercial CB, was compared. The development of pore structure and the increase of the specific surface area were most intensive during the thermal decomposition at temperatures ranging from 300°C to 500°C. This is caused by the intensive release of volatiles during the pyrolysis. After the pyrolysis was finished, at temperatures above 500°C, further decomposition of solid matter was associated with a slight increase of the specific surface area.

Experimentally found local heat transfer coefficients are analyzed as a function of the measuring point on the heat transfer surface area of the agitated vessel wall and of the impeller eccentricity. Eccentric Rushton turbine and A 315 impeller are considered. Local heat transfer coefficients were measured by means of the computer-aided electrochemical method. The measurements were performed in an agitated vessel with inner diameter 0.3 m, filled with liquid up to the height equal to the vessel diameter. The experiments were carried out within the turbulent regime of the Newtonian liquid flow in the agitated vessel. The results were compared with the data obtained for the agitated vessel equipped with an eccentrically located axial flow propeller or an HE 3 impeller. Experimental studies show that the distributions of the heat transfer coefficient values depend on the impeller eccentricity, impeller type and the direction of the liquid circulation in the agitated vessel.

Membrane distillation was used to produce demineralized water from ground water. The influence of feed water pretreatment carried out in a contact clarifier (softening with Ca(OH)2 and coagulation with FeSO4 · 7H2O) followed by filtration, on the process effectiveness was evaluated. It was found that the chemical pretreatment decreased the membrane fouling; however, the degree of water purification was insufficient because precipitation of small amounts of deposit on the membrane surface during the process operation was still observed. The permeate flux was gradually decreasing as a result of scaling. The morphology and composition of the fouling layer were studied using scanning electron microscopy coupled with energy dispersion spectrometry. The presence of significant amounts of silica, apart from calcium and magnesium, was determined in the formed deposit. The removal of foulants by heterogeneous crystallization performed inside the filter (70 mesh), assembled directly at the module inlet, was found to be a solution preventing the membrane scaling.

The investigations of selective methane oxidation to formaldehyde over T-Nb2O5, the mixture of M-Nb2O5 and H-Nb2O5 as well as H-Nb2O5 were carried out. The tests were conducted under atmospheric pressure, in the temperature range 420–750°C, using oxygen as the oxidizing agent. T-Nb2O5 samples were examined at the contact time 0.7–1.8 s (GHSV 2000–5143 h−1). Other polymorphic forms of niobium(V) oxide were examined at the contact time 0.9 s. Various polymorphic forms of Nb2O5 displayed various formaldehyde and carbon dioxide yield. Using H-Nb2O5 and M-Nb2O5 phases with a block type structure, made it possible to obtain higher formaldehyde selectivity (78 % at 0.9 s) as compared to T-Nb2O5 (47 % at 0.9 s), a polymorphic form which does not have a block type structure. However, the highest space time yield of formaldehyde (46 g per kg of catalyst per h) was obtained over T-Nb2O5 supported on SiO2.

The Tessier extraction method was used for speciation of Cu, Pb, Zn, As, Fe and Mn in a large concentration range in contaminated soil with various mineralogical compositions. The results were compared by X-ray fluorescence spectrometry (XRF) as a reference method using the Bland and Altman test. A sum of five fractions (exchangeable, bound to carbonates, Fe-Mn oxides, organic matter and residual forms) was compared with the total content determined on solid matrix by the reference method. A good agreement between the methods in the whole concentration range was found for Cu, Zn, As, and Fe. For Mn and Pb, XRF was found suitable to verify the sequential extraction only for concentrations above 250 mg kg−1. This was a consequence of a poorer reproducibility of Pb extraction using the Tessier scheme due to a great difference in the mineralogical composition and the diversity of the Pb species identified in soil. The poorer result of Mn was attributed to the spectral interference of Fe in XRF.

Potassium sulfate is used to produce multicomponent fertilizers, free of chlorides. The desalting out of potassium sulfate from an aqueous solution of potassium hydrosulfate was conducted using 40 mass %, 45 mass %, or 50 mass % aqueous solutions of either methanol or propan-2-ol. Composition of the resultant precipitate was analyzed using chemical methods and XRD analysis. The results of the XRD analysis revealed that the main precipitate phase is K2SO4. Small amounts of K5H3(SO4)4 were detected when the desalting out was carried out from 2.5 M KHSO4 solution using 40 mass % and 50 mass % methanol solution. When the amount of potassium bisulfate in the solution increased to 3.5 M and 3.8 M, the main phase consisted of K3H(SO4)2. Generally, the desalting out process using propan-2-ol caused the formation of K3H(SO4)2. Potassium sulfate was obtained only by desalting out the 2.5 M KHSO4 solution using 50 mass % aqueous propan-2-ol.