Showing papers in "Chemical Engineering & Technology in 2000"

Optimization of Hydrodynamic Cavitation Using a Model Reaction

Abstract: The decomposition of potassium iodide to liberate iodine, the model reaction to study cavitational effects, has been carried out under different cavitational conditions. The effect of various parameters (inlet pressure, flow geometry of orifice plates) on the iodine liberation rate has been studied. It is found that the flow geometry of the orifice plates considerably affects the rate of the iodine liberation. Recommendations are given for the arrangement of the holes in order to achieve maximum benefits from the hydrodynamic cavitation. The experimental results obtained in the present work are very much consistent with the results based on the theoretical model developed for the hydrodynamic cavitation. Due to this fact, it can be said that the model can be extended to any geometry of construction in the hydrodynamic cavitation setup and will be helpful in designing cavitational reactors.

Wood Hydrolysis and Hydrolyzate Detoxification for Subsequent Xylitol Production

Abstract: This study deals with two different aspects of the transformation of lignocellulosics into xylitol: the optimization of conditions for wood hydrolysis and the setting-up of an adequate hydrolyzate detoxification procedure necessary to obtain high xylitol yields in the successive fermentation process. A comparison between the processes of wood autohydrolysis (steam explosion) and pre-hydrolysis with dilute sulfuric acid, carried out batch-wise in laboratory scale, shows comparable yields, either in terms of final concentrations of xylose and pentose sugars in the hydrolyzate or of solubilised fraction of wood. On the other hand, notwithstanding the longer time required, the pre-hydrolysis with dilute sulfuric acid produced acid hydrolyzates with lower contents of inhibiting substances (furfural, acetic acid, etc.). In order to obtain satisfactory xylitol yields from the hydrolysate produced by steam explosion, samples of this hydrolyzate were submitted to different detoxification techniques and then fermented batch-wise by a Pachysolen tannophilus strain previously adapted to this substrate. The best detoxification was performed by adding to the traditional overliming with Ca(OH)2 and sulfite reduction, three steps of a) filtration to remove insoluble substances, b) stripping of acetic acid and furfural, and c) lignin-derived compounds removal by adsorption on charcoal. The fermentation of this hydrolyzate was very effective, achieving a final xylitol concentration of 39.5 g/l from 89.0 g/l xylose after 96 h, corresponding to a volumetric productivity of 0.41 g/lh and a product yield of 0.63 g/g.

Chemisorption of N2O and H2 for the Surface Determination of Copper Catalysts

Abstract: Metal surface areas are usually determined by selective chemisorption of a suitable probe molecule (e.g., CO, H 2 , O 2 ). In this contribution, a comparison of different methods using N 2 O as a probe molecule is presented. The experiments comprise isothermal N 2 O flow experiments, transient decomposition experiments and the pulse flow chemisorption of N 2 O in an He carrier stream. The main object of these experiments was to clarify the influence of the reaction parameters (temperature, contact time, sample mass, etc) on the specific Cu surface area determined. As a further independent method for the determination of Cu surface areas the temperature-programmed desorption of hydrogen (H 2 TPD) has been applied.

Three‐Phase Nitrobenzene Hydrogenation over Supported Glass Fiber Catalysts: Reaction Kinetics Study

Abstract: The catalytic properties of Pd and Pt supported on woven glass fibers (GF) were investigated in the three-phase hydrogenation of nitrobenzene (NB). Over all catalysts, a 100 % yield of aniline was attained. The catalytic activity for the best catalysts was two times higher than the activity of commercial Pt/C catalyst traditionally used for liquid‐phase hydrogenation. The intrinsic reaction kinetics were studied and a reaction scheme is suggested. The direct formation of aniline from NB was observed over Pd/ GF with traces of intermediates. Four intermediate products were detected during aniline formation over Pt/GF: nitrosobenzene, phenylhydroxylamine, azoxybenzene, and azobenzene. The Eley-Rideal kinetic model fits the experimental data well. The parameters of the model were determined as a function of initial NB concentration and hydrogen pressure. Pt and Pd supported on GF in woven fabrics are suggested as suitable materials for reactors with a structured catalytic bed in multiphase reactor performance.

Modeling, Control, and Optimization of Ideal Internal Thermally Coupled Distillation Columns

Abstract: Internal Thermally Coupled Distillation Columns (ITCDIC) are the frontier of energy saving distillation research. In this paper, the ideal ITCDIC is considered. A novel mathematical model and a related simulation algorithm are proposed. The dynamic responses of open-loop, PID controllers and the responses of closed-loops are carried out. The results show that the ITCDIC is a self-balance process and could be operated smoothly with two PID controllers; the steady-state optimization met the need of ITCDIC optimization. Furthermore, a steady-state optimization model of the operation parameters is presented, which can be used to directly obtain the optimal operation parameters simultaneously guaranteeing not only the product quality and the maximum energy savings but also the dynamic operability and controllability. The benzene-toluene system is studied as an illustrative example.

Gold catalysts for the partial hydrogenation of acrolein

Abstract: The manufacture of unsaturated alcohols through selective hydrogenation of α,β-unsaturated aldehydes continues to be a topical issue. The objective of this study is to investigate the use of supported gold catalysts for the partial hydrogenation of acrolein to allyl alcohol. So far, in catalyst research or even chemical engineering gold has not attracted much attention as a catalyst mainly because of its chemical inertness. The intrinsic inertness of gold, however, can be influenced when the metal is applied with a high dispersity to a suitable support.

Use of Pervaporation-Bioreactor Hybrid Processes in Biotechnology

Abstract: Pervaporation is a membrane separation process with considerable innovative possibilities in the area of biotechnology. Above all, the combination of bioreactor and pervaporation has potential in the longer term as an alternative to conventional batch processes. This article considers the state of the art pervaporation-bioreactor hybrid processes. The possible applications of such hybrid processes are discussed and compared with conventional processes. It becomes apparent that the use of pervaporation-bioreactor hybrid processes can avoid product inhibition and greatly enhance the productivity of biotechnological processes.

Production of spherical beads by JetCutting

Abstract: Until now, the production of spherical and monodisperse small beads from higher-viscosity fluids was hardly possible. JetCutting is a new, simple and efficient cutting technology for the production of monodisperse beads of small particle size from low- to high-viscosity fluids in large quantities. Since spherical beads are intermdiate or products in various industries, e.g., the pharmaceutical, chemical and food industries, manifold applications are possible. Offering further advantages, the JetCutter has a great potential to replace convential technologies for bead production.

The Potential of Energy Saving by Gas‐Phase Adsorption Processes

Abstract: In large chemical plants multicomponent fluid mixtures are separated in fractions or in pure components. Dealing with gaseous mixtures, separations can be carried out by cryogenic distillation, adsorption followed by temperature swing adsorption (TSA) or pressure swing adsorption (PSA) or membrane processes, as gas permeation or pervaporation. When separation is carried out with membrane processes, the purification efficiency is often not sufficient if ultrapure products are the objective of the process. In the case of cryogenic distillation and adsorption product purity is not a problem. The investment cost of membrane as well as cryogenic separation processes are high in comparison to adsorption separation plants but the increase of investment cost versus capacity is smaller for cryogenic plants compared to membrane and adsorption units [1]. Therefore, the installation of a cryogenic process may be advantageous in very large plants designed for ultrapure products whereas adsorption is often the domain for plants with medium capacity. The future of membrane separation depends on the development of more efficient membranes.

Effects of the Stirred Tank's Design on Power Consumption and Mixing Time in Liquid Phase

Abstract: The influence of the stirrer type and of the geometrical parameters of both tank and agitator (clearance of an impeller from tank bottom, impeller diameter, draft tube and geometry of the tank bottom) on power consumption and mixing time in liquid phase under turbulent regime conditions (Re > 104) have been studied. Different types of agitators have been used, namely Rushton turbine, 45° pitched-blade turbine, MIXEL TT and TTP propellers and 1-stage or 2-stage EKATO-INTERMIG propellers. All these stirrers were tested with the same power consumption per unit mass of liquid. On the basis of measured power consumption per unit mass, which is required to achieve the same degree of mixing, the results obtained in the present work show that the TTP propeller is the most efficient in liquid phase. Recommendations on the optimum geometric configuration have been made for each type of stirrer.

Extraction of Carboxylic Acids from Aqueous Solutions with the Extractant System Alcohol/Trin‐Alkylamines

Abstract: A frequent problem in the production of organic compounds via partial oxidation are unwanted byproducts, like acetic acid. In this article, the convenient method for working-up the aqueous acidic effluents (containing up to 10 wt% acid) after removing the main product is the extraction. The influence of various extractant systems containing organic solvents and trialkylamines on distribution coefficients and selectivities of acids has been studied. Acetic acid and lactic acid served as model compounds for acidic byproducts and acidic fermentation products, respectively. Experimental results indicate that combinations of tri-n-hexylamine and an alcohol show greatest synergistic effects and as a consequence comparably high distribution coefficients.

Scale Continuous Microwave Dry‐Media Reactor – Part II: Application to Waxy Esters Production

Abstract: The solvent free esterification reaction between stearic acid and stearyl alcohol has been examined with a montmorillonite clay as catalyst. To aim for industrial application the system has been studied on reaction rate, product purity, catalyst behavior and water removal as function of the process conditions. To avoid an etherification side reaction and to aim for the highest reaction rate, the temperature should be strictly maintained at 170 °C. This is provided on larger scale by the application of microwave heating. Although the examined Bronsted acid clay was found to lose its catalytic activity at very low water activities, a yield of 95 % pure stearyl stearate can be obtained by simply filtering of the clay without solvent extraction or distillation. The “waxy” esterification reaction was investigated with the pilot plant continuous microwave dry-media reactor (CMDR). The reaction time needed for 95 % yield was reduced by a factor 20–30 in comparison with industrial conventional reactors. This was due to the more homogeneous heat transfer of microwaves, which allows to reach a higher bulk temperature.

Pilot scale continuous microwave dry-media reactor - Part 1 : Design and modeling

Abstract: This work presents a new pilot plant continuous microwave dry-media reactor (CMDR) for industrial chemical applications. The CMDR consists of a 6 kW conveyor microwave oven with a subsequent hot air holding section. This microwave reactor has been designed for dry media or solvent-free reactions and can treat through-put in the range of 10–100 kg/h. The microwave heating behavior on the small scale is analyzed and the results are used to estimate the electromagnetic field requirements on the large scale. The temperature and the electric field distribution in the reactor are modeled and experimentally validated. In the second part of this study, a “waxy” esterification reaction was investigated with the CMDR. The reaction time needed for 95% yield was reduced by a factor of 20–30 compared to conventional industrial reactors. This was due to the more homogeneous heat transfer of microwaves, which allows a higher bulk temperature to be reached.

Highly Efficient Composite Membranes for Ethanol-Water Pervaporation

Abstract: Composite membranes with ultrathin separation layer were prepared by alternate adsorption of cationic and anionic polyelectrolytes onto porous support membranes. The utility of these membranes for ethanol-water pervaporation was investigated. It was found that the separation capability is highest if polyelectrolytes with high charge density, such as polyethyleneimine (PEI) and polyvinylsulfate (PVS), are used. Under optimum conditions, the PEI/PVS separation layer is highly efficient in water enrichment in the permeate. A separation factor α up to 1000 could be detected, the flux simulatenously being 590 g/m 2 .h. Effects of annealing of the membrane and change of the pervaporation temperature are also discussed.

Process for Total Degradation of Organic Wastes by Mediated Electrooxidation

Abstract: A semitechnical plant for indirect electrochemical oxidation and the results concerning degradation of real pesticides, simulates for chemical warfare agents and industrial wastes, are presented.

What’s New in Industrial Polymerization with Supercritical Solvents? A Short Review

Abstract: This review attempts to answer the following questions: what are the interest and benefits of polymerizing in supercritical media and what type of polymer and polymerization process can be used? Supercritical fluids (SCFs) in theory offer many advantages since they have intermediate propertics between liquids and gases. Also, at a time when the environment is undergoing such great impacts as the depletion of the ozone layer by chlorofluorocarbons (CFCs), the use of CO 2 seems an attractive a ternative for sustainability and conservation. This is why heterogeneous polymerization methods, particularly suspension and dispersion processes, ofter great potential with an SCF as a suspending medium. Unfortunately, polyolefins and other commodities, such as poly(vinyl chloride) (PVC), may not benefit from SCF technology today for profitability reasons, but acrylics, styrenics and other fluorinated plastics are open to this new technology. Furthermore. SCFs may have an impact on polyamides, polycarbenates and other speciality poly mers.

Sedimentation Velocity of Solids in Finite Size Vessels

Abstract: The Richardson-Zaki equation is by far the most popular empirical equation used to describe the velocity-voidage relationship for sedimenting solid-liquid homogeneous suspensions, using only two empirical parameters. In this work some of Richardson and Zaki suggestions for the two parameters are challenged on the basis of new and old experimental evidence.

Electrochemical Reduction of Oxygen at Pyrolyzed Iron and Cobalt N4-Chelates on Carbon Black Supports

Abstract: Besides platinum, various nonnoble metal compounds, when prepared appropriately, are suitable for the electrochemical reduction of oxygen in liquid electrolytes and PEM-fuel cells. Pyrolyzed N4-chelates, such as phthalocyanines, tetraazaannulenes and porphyrins with a central metal atom of iron or cobalt, are a very important group of compounds and have been investigated in the past. It was found that the catalytic activity, especially of phthalocyanines, was high when prepared on carbon black supports at high temperatures (400-900 °C). Investigations on tetraazaannulenes and porphyrins yielded similar results. Non-noble metal compounds of cyclame (1,4,8,11-tetraazacyclotetradecane), which are also N4-chelates, were not investigated as thoroughly. However, the catalytic activities of iron and cobalt cyclames were low, compared to those of phthalocyanines. With the (GC-MS) analysis of both decomposition products, it could be shown that the mechanism of the N4-chelate decomposition is of decisive importance for the catalytic activity.

Hydrosilylation Reactions in Single and Two Phases

Abstract: The essential objects of this work were the optimization of the Pt catalyst and the investigation of solvent combinations to enable the recycling of the catalyst by the technique of two liquid phases.

Telomerization of Carbon Dioxide and 1,3‐Butadiene: Process Development in a Miniplant

Abstract: The scope of this work was to investigate a process concept for the synthesis of δ-lactone from carbon dioxide and 1,3-butadiene with process integrated catalyst recycling The process development was done on the laboratory scale and was supported by stationary process simulation The resulting process concept was verified in a miniplant which can now be used for process optimization

Nitrogen Oxides Scrubbing with Alkaline Solutions

Abstract: The absorption of NOx into sodium hydroxide solutions was studied in a small packed column. A simple mathematical model developed for this absorption was used for the determination of rate parameters relative to NOx species in such solutions. While hydrolysis is the main controlling step for NO2, N2O4 and N2O3 species, nitrous acid HNO2 plays an essential role for the NOx absorption in NaOH solutions. Our mechanistic and kinetic findings were validated as the model has worked with fair success in predicting both NOx removal efficiencies and liquid phase compositions.

Kinetic Investigation of Reaction Between Metallic Silver and Nitric Acid Solutions

Abstract: In this study, the reaction kinetics between metallic silver and nitric acid solutions was investigated by taking into consideration the parameters of temperature, solid-to-liquid ratio, stirring speed, nitric acid concentration, particle size and addition of sodium nitrite. It was determined that the dissolution rate of the process increased with decreasing particle size and solid-to-liquid ratio, and increasing nitric acid concentration, reaction temperature and the amount of the sodium nitrite in the solution. In addition, it was observed that the stirring speed had more effect on the dissolution rate at low stirring speeds than at high stirring speeds. In the present study, the examination of shrinking core models of fluid-solid systems showed that the dissolution of metallic silver in the nitric acid solutions was controlled by the reaction on the surface. A semiempirical model, which represented well the process, was developed by statistical methods. The activation energy of the process was found to be 57.66 kJ mol–1.

Design Optimization of a Crude Oil Distillation Process

Abstract: In this work, the optimal design of a crude oil distillation unit was made. Since the method used here is based on the general optimization framework, it is possible to design the process systematically. The results of this study gave better performances than that of the existing process. The process in this study is currently in operation and has the capacity of 150,000 BPSD. Feed locations, heat duties of pumparounds and operating conditions of the preheat train are selected as variables, and the energy consumption, operating cost and annual cost are formulated as objective functions. The optimal feed locations of both the main column and stabilizer are obtained by solving rigorous models and mixed integer nonlinear programming. Considering the results of the optimal feed tray, the cost optimization is carried over to obtain the optimal annual cost, which considers both the capital and operating cost, which is decreased from US$10,649,000/year to USdollar;9,185,230/year.

Joint treatment of wastewater from table olive processing and urban wastewater. Integrated ozonation-aerobic oxidation

Abstract: Integrated ozonation-aerobic biodegradation of table olive wastewater (diluted 1:25 with synthetic urban wastewater) is presented as a suitable technology to purify this kind of effluent. Use of ozone is recommended as a pre-treatment step since it shows a high reactivity toward phenolic compounds (found in this type of wastewater) reducing, at the same time, the alkalinity of the media for further biological processing. An ozone dose of 45 mg L–1 (flow rate 20 L h–1) for a period of 35 min has been found to achieve the following goals: decrease pH, decrease phenolic content, and increase of biodegradability. The aerobic oxidation process followed first order kinetics as measured by COD depletion profiles versus time. The Arrhenius expression k = 183exp(–2214/T) was obtained for experiments of ozonated wastewater biodegradation completed at different temperatures and neutral pH.

Liquid Phase RTD Studies in Sectionalized Bubble Column

Abstract: The liquid phase backmixing has been reduced significantly by introducing horizontal perforated sieve plates into a 6.2 cm diameter and 77 cm height and in a 20 cm diameter and 90 cm height bubble columns. For the visbreaking operation of the petroleum residue, where the bubble column is used as soaker such a sectionalization has been suggested. The effect of the introduction of different gas quantities at various axial locations has also been studied to check the effect of increasing gas quantity formed in the visbreaking operation. The nonideality in the liquid phase backmixing has been studied by measuring liquid phase RTD and analysed by using one parameter dispersion model. A new parameter FP (flow parameter) has been defined and a correlation to predict liquid phase dispersion coefficient has been developed which covers the entire range of variables used in the present work.

Volumetric Mass Transfer Coefficient of Oxygen in An Internal Loop Airlift Reactor with a Convergence‐Divergence Draft Tube

Abstract: Experimental measurements of hydrodynamics and the volumetric mass transfer coefficient of oxygen (VMTCO) in an internal loop airlift reactor with different types of draft tubes are reported for the two-phase systems, air/water and air/carboxyl methyl cellulose (CMC) solution, and a three-phase system, air/water/resin particle, respectively The properties of convergence-divergence draft tubes with three different structural parameters are compared with those of the conventional column draft tube The results indicate that gas holdups in convergence-divergence draft tubes are higher than those in conventional draft tubes, the volumetric mass transfer coefficient of oxygen increases with increasing superficial air flow rates The convergence-divergence draft tubes all show higher mass transfer capacity than the traditional ones A 10% higher mass transfer coefficient is observed for the three structural parameters In the air/CMC system, the volumetric mass transfer coefficient of oxygen decreases with increasing bulk viscosity, while in the three-phase system VMTCO increases with the resin particle loading The correlation equation of the volumetric mass transfer coefficient with the operating conditions and structural parameters is established

Measurement of Local Phase Holdups in a Two‐ and Three‐Phase Bubble Column

Abstract: A new invasive sensing probe for the measurement of local phase holdups in two- and three-phase reactors is described. The local gas and solids holdups in a bubble column with a volume of V=2 m 3 at varying operating conditions (gas velocity, sparger design, solids content and density) are measured by means of differential pressure measurement in combination with either time domain reflectometry or electrical conductivity measurement. The phase distribution profiles at two- and three-phase operating conditions are described. The influence of the sparger design on the shape of these profiles, the influence of the solid phase on the gas distribution, the solids distribution and the gas-stow effect above the sparger because of a dense particle layer are capable of experimental proof for the first time.