Product Distribution

Production-distribution planning is the most important part in supply chain management. To solve this integrated planning problem, either analytic or simulation approach have been developed. However, these two approaches have their own demerits in problem solving. In this paper, a hybrid approach is proposed which is a speci c problem solving procedure combin-ing analytic and simulation method to solve production-distribution problems in supply chain. To illustrate the modelling of the problem, a multiperiod, multiproduct, multishop production and distribution problem is considered in supply chain environment. The machine capacity and distribution capacity constraints in the analytic model are considered as stochastic factors and adjusted by the proposed speci c process according to the results from independently developed simulation model which includes general production-distribution characteristics.

A thermodynamic equilibrium analysis on the multi-reaction system for carbon dioxide reforming of methane in view of carbon formation was performed with Aspen plus based on direct minimization of Gibbs free energy method. The effects of CO 2 /CH 4 ratio (0.5–3), reaction temperature (573–1473 K) and pressure (1–25 atm) on equilibrium conversions, product compositions and solid carbon were studied. Numerical analysis revealed that the optimal working conditions for syngas production in Fischer–Tropsch synthesis were at temperatures higher than 1173 K for CO 2 /CH 4 ratio being 1 at which about 4 mol of syngas (H 2 /CO = 1) could be produced from 2 mol of reactants with negligible amount of carbon formation. Although temperatures above 973 K had suppressed the carbon formation, the moles of water formed increased especially at higher CO 2 /CH 4 ratios (being 2 and 3). The increment could be attributed to RWGS reaction attested by the enhanced number of CO moles, declined H 2 moles and...

The biggest producers and exporters of agricultural products have been adopting the genetic engineering in order to improve the factors productivity and the firms profits In the last decade, the United States of America (US) and the European Union (EU) have established a high divergent regulation on production, distribution and consumption of genetically modified organisms (GMOs). Apparently, the EU´s complex legislative framework related to GMOs was intend to satisfy the European consumers which are concerned about food safety and whish to make more informed choice about the food they eat. The aim of this paper is to understand the potential motivations behind the different policies on GM products adopted by US and EU.

An optimization-based control framework that simultaneously determines the optimal inventory and product pricing policies is developed for multi-product, multi-echelon supply chain networks. The optimization problem aims at adjusting the available manufacturing resources, product transportation, inventories and prices for the entire supply chain network to satisfy demand while maximizing network's revenues and service level, through the minimization of unsatisfied demand, over a specified rolling time horizon. The control scheme employs model predictive control principles with local feedback inventory controllers for the satisfaction of the overall objectives. Customer demand responses to product prices are taken directly into consideration through the explicit utilization of demand elasticity. The optimal manipulation of the product prices acts as an additional instrument for the efficient operation of the supply chain through the direction of product demand in less congested parts of the network

Companies strive to position themselves to maximize the value they add to the supply chains in which they are embedded. This raises strategic questions such as: Which durable resources should be developed to enhance current core competencies? Which activities should be externalized and to which potential partner should they be given? Which internal activities should be preserved and developed? How should the resources of the enterprise be allocated to activities? The aim of this paper is to propose a mathematical programming model of the extended enterprise which can be used to investigate this type of strategic networking issues. A number of general network modeling constructs are ®rst proposed. A model to optimize the supply chain structure under speci®c assumptions on the nature of production, cost and value functions in typical production/distribution companies is then derived. A heuristic to obtain solutions from the model is also presented. Finally, an example based on a refrigerator company is used to illustrate the usefulness of the approach.

The reaction of an equimolar mixture of H2 and CO was studied over ZrOr at 350 to 45O"C, 35 atm total pressure, and varying residence times. The isosynthesis reaction mechanisms were studied by monitoring the incorporation of oxygenated compounds into the isosynthesis products. Propionaldehyde and [t3C]acetone, [i3C]isopropanol, and [W]methanol were added to the CO/Hz reactant stream. Their effect on the isosynthesis product distributions and on the isotopic distribution of the products was monitored as a function of oxygenate feed rate. Propionaldehyde, acetone, and methanol were found to incorporate into the isosynthesis products. The isotopic distribution of the products was used to support an isosynthesis reaction scheme that involves CO insertion into a bound aldehyde or ketone as the major chain growth step and a second chain growth step that involves condensation between methoxide and a surface bound enolate. Q 1988 Academic press, IK.

In this paper the reaction of allene with carbon dioxide is discussed, using [RhCl(C 2 H 4 )(P i Pr 3 )] 2 as catalyst. An unprecedented formal '2'/2' allene Á/CO 2 reaction to afford a four-membered lactone is described. The influence of the temperature and pressure on the reaction of allene and CO 2 is highlighted. The role of addition of hydrogen to the reaction system, as modulator of the products distribution is discussed. The behavior of the catalyst [RhCl(C 2 H 4 )(P i Pr 3 )] 2 towards H 2 is also described and the structure of the resulting Rh Ã/hydride species inferred through a theoretical study. #

The low temperature microwave activation of biomass has been investigated as a novel, energy efficient route to bio-oils. The properties of the bio-oil produced were considered in terms of fuel suitability. Water content, elemental composition and calorific value have all been found to be comparable to and in many cases better than conventional pyrolysis oils. Compositional analysis shows further differences

The hydrogenation of maleic acid was investigated using a bimetallic Ru–Re/C catalyst powder in a semi-batch stirred slurry reactor with the main objective of developing a kinetic model that would provide reliable predictions of the observed reactant and product ...

The reaction of trichloroethylene (C2HCI3) with water vapor or molecular hydrogen has been studied in a low-pressure [ca. 5 Torr (0.67 kPa)] microwave plasma tubular flow reactor. The experimental apparatus included feed introduction systems, a microwave plasma reactor, and full product analysis by flame ionization and thermal-conductivity gas chromatography, mass spectrometry, and specific ion or pH detection for hydrogen chloride [HCI]. Conversions of CeHC13 in the range 50 to almost 100% are achieved. Product analyses indicate conversion to HCI, some light hydrocarbons, nonparent chlorocarbons, and soot C(s). For the H20 case, carbon monoxide and trace carbon dioxide were produced in place of some light hydrocarbons and Cc~). At least 85 mole % of chlorine (CI) from the converted parent C2HCl s forms thermodynamically stable HCI at parent conversions of 80% or more. The remaining chlorine was present as nonparent chlorocarbons. Preliminary kinetic analyses were performed. The global reaction in the plasma was found to follow one-half-order kinetic dependence on each of C2HCl 3 and H20 or H 2. Elementary plasma reaction mechanisms are presented to account for CeHCI 3 conversion and the observed product distribution.

The rate of oxidation of sulfite, S( IV), in seawater was measured as a function of pH (4.0-8.5), temperature ( 1%45"C), and salinity (O-35). The observed rate constant, k, in seawater at a pH = 8.2 was found to be second order with respect to S( IV) and half order with respect to oxygen: -d[S(ZI')]/dt = k[S(ZV)]2[0,]o.5. The resulting values of k ( M-'.5 min-') have been fitted to a function of ionic strength, I, and temperature, T(K): log k = 19.54 -5069.47/T + 14.74Z".5 -2.931-2877.0Z0.'/T, and the standard error is 0.05 in log k.

The performance and stability of supported Pd catalysts were investigated in the partial oxidation of geraniol with molecular oxygen in dense CO 2 . All catalysts deactivated to a certain extent in the continuous-flow reactor; the least stable among them was Pd/Al 2 O 3 . Beside oxidative dehydrogenation, isomerization and hydrogenation reactions were also catalyzed by Pd. The initial selectivity of Pd to citral formation was only 50-60% but improved up to 90% with time-on-stream. The extensive catalyst deactivation and the shift in product distribution are (partly) attributed to formation of geranic (neric) acid, and the acid-catalyzed dimerization and oligomerization of reactant and products leading to site blocking by the high molecular weight by-products. ATR-IR spectroscopy revealed that no CO was present on the Pd surface during geraniol oxidation though it appeared in the absence of oxygen. A shift from two-phase to single phase conditions diminished the reaction rate, presumably due to accumulation of water co-product on the catalyst surface. Despite of the initial deactivation of Pd/SiO 2 , an outstanding TOF of 169 h À1 was achieved on the stabilized catalyst under steady state conditions, at 80 8C and 150 bar. #

The oxidation of sulfide in seawater is an overall second-order reaction, first-order with respect to both sulfide and oxygen. The major products formed from the oxidation of H2S with 02 have been measured in water and seawater as a function of pH (4-lo), temperature ( IO-45'C), and salinity (O-36). The major products formed from the oxidation of H2S were SO:-, S20:-, and SO:-. The pH dependence of the product distribution has been attributed to the effect of pH on the rate of the individual reaction steps. A kinetic model was developed to account for the distribution of the reactants and products. The model is based on the following overall reactions: H2S + O2 2 Products (S09), H2S03 + O2 2 Products ( SOa), and H2S + H2S03 + O2 2 Products ( S203).

Multi-objective optimization Risk management Uncertainty a b s t r a c t In this paper we present a decision-support tool to address the strategic planning of hydrogen supply chains for vehicle use under uncertainty in the operating costs. Given is a superstructure of alternatives that embeds a set of available technologies to produce, store and deliver hydrogen. The objective of our study is to determine the optimal design of the productionedistribution network capable of fulfilling a predefined hydrogen demand.

tert-Butylanilines are used in pharmaceuticals, pesticides, plastics, additives and dyes. They are usually prepared by reacting aniline in presence of liquid acid catalysts with pure isobutylene or C 4 fraction from naphtha crackers containing isobutylene. These processes suffer from problems of use of highly corrosive liquid acids and also the source of isobutylene. Both C-and N-alkylation are possible in the case of aniline depending on reaction conditions such as temperature, source of isobutylene and type of catalyst. In the current study, several solid acids, majority of which were heteropolyacids (HPAs) supported on different clays, were evaluated with both methyl tert-butyl ether (MTBE) and tert-butanol as alkylating agents in a pressure reactor under autogenous pressure.

Nowadays, different power generation strategies for grid-connected systems can be found, ranging from single high power plants (tens and hundreds of MW), to thousands of small wattage (below 1 kW) microgenerators. This paper studies a new power topology for the latter, based on a bidirectional Flyback converter. The comparison with the standard topology for this kind of converters is carried out, and the constraints for the control scheme are also studied.

Thermal decomposition of polypropylene (PP) was studied in the presence of wood flour, lignin, cellulose and charcoal in order to understand the pyrolytic behavior of the mixture of these components occurring in waste. Thermogravimetry/mass spectrometry was applied for monitoring the weight loss and the product evolution profiles under slow heating conditions. The formation of oligomeric products was analyzed by pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). Since the charring reactions of wood are still proceeding during the PP decomposition, the interactions between PP and char devolatilization are expected to be rather pronounced. The effect of the freshly formed pyrolytic chars on the decomposition of PP was simulated by mixing PP with pure activated charcoal. Activated charcoal had the most significant effect on the decomposition profile and the product distribution of polypropylene. In the presence of charcoal the decomposition shifted to lower temperature and the DTG curve became broader. The presence of charcoal promotes the formation of monomer and dimer. The effect of wood flour, lignin and cellulose is less pronounced. Though the decomposition starts at lower temperature in the presence of these additives and the DTG curve became broader, the temperature of the maximum decomposition rate and the char yields did not change significantly.

The aim of this study was to investigate the possibilities of using a by-product (red mud) from alumina production as a catalyst for recovery of waste. The conversion of waste mineral oil (WMO) and waste mineral oil/municipal waste plastic (WMO/MWP) blends over red mud (RM), a commercial hydrocracking catalyst (silica-alumina), and a commercial hydrotreating catalyst (Ni-Mo/alumina) to fuel has been studied. The effect of the catalyst and the temperature on the product distribution (gas, liquid, and wax) and the properties of liquid products were investigated. In the case of hydrotreatment of WMO, the liquids obtained over RM at both 400°and 425°C had larger amounts of lowboiling hydrocarbons than that of thermal or catalytic treatment with hydrotreating catalyst. Gas chromatography and nuclear magnetic resonance analysis of the liquid products showed that RM had hydrogenation and cracking activity in hydrotreatment of WMO. In coprocessing of WMO with municipal waste plastics, temperature had an important effect as well as the amount of MWP in the blend and the catalyst type. The hydrocracking at 400°C produced no liquid product. In hydrocracking at 425°C, the product distribution varied with catalyst type and MWP amount. The commercial hydrocracking catalyst had more cracking ability in the conversion of WMO/MWP to liquid and gas fuel than RM. In the case of hydrocracking over RM, the largest amount of liquid having satisfactory quality was obtained only from the blend containing 20% MWP.

Refinery production planning is usually performed using the refinery battery limit constraints. Two associated problems are the oil uploading and product distribution problems. These problems have traditionally been solved separately, and they have constraints that could render the solution of the planning problem infeasible or less profitable. The goal of this paper is to explore the benefits of the integration of production planning with these two models.

We develop an integrated production-distribution model for a deteriorating item in a two-echelon supply chain. The supplier's production batch size is restricted to an integer multiple of the discrete delivery lot quantity to the buyer. Exact cost functions for the supplier, the buyer and the entire supply chain are developed. These lead to the determination of individual optimal policies, as well as the optimal policy for the overall, integrated supply chain. We outline a procedure for determining the optimal supply chain decisions with the objective of minimizing the total system cost. Our approach is illustrated through a numerical example.

In this study some literature data on the pyrolysis characteristics of biomass under inert atmosphere were structured and analyzed, constituting a guide to the conversion behavior of a fuel particle within the temperature range of 200e1000 C. Data is presented for both pyrolytic product distribution (yields of char, total liquids, water, total gas and individual gas species) and properties (elemental composition and heating value) showing clear dependencies on peak temperature. Empirical relationships are derived from the collected data, over a wide range of pyrolysis conditions and considering a variety of fuels, including relations between the yields of gas-phase volatiles and thermochemical properties of char, tar and gas. An empirical model for the stoichiometry of biomass pyrolysis is presented, where empirical parameters are introduced to close the conservation equations describing the process. The composition of pyrolytic volatiles is described by means of a relevant number of species: H 2 O, tar, CO 2 , CO, H 2 , CH 4 and other light hydrocarbons. The model is here primarily used as a tool in the analysis of the general trends of biomass pyrolysis, enabling also to verify the consistency of the collected data. Comparison of model results with the literature data shows that the information on product properties is well correlated with the one on product distribution. The prediction capability of the model is briefly addressed, with the results showing that the yields of volatiles released from a specific biomass are predicted with a reasonable accuracy. Particle models of the type presented in this study can be useful as a submodel in comprehensive reactor models simulating pyrolysis, gasification or combustion processes.

A study on gasification of empty fruit bunch (EFB), a waste of the palm oil industry, was investigated. The composition and particle size distribution of feedstock were determined and the thermal degradation behaviour was analysed by a thermogravimetric analysis (TGA). Then fluidized bed bench scale gasification unit was used to investigate the effect of the operating parameters on EFB air gasification namely reactor temperature in the range of 700–1000 °C, feedstock particle size in the range of 0.3–1.0 mm and equivalence ratio (ER) in the range of 0.15–0.35. The main gas species generated, as identified by a gas chromatography (GC), were H2, CO, CO2 and CH4. With temperature increasing from 700 °C to 1000 °C, the total gas yield was enhanced greatly and reached the maximum value (∼92 wt.%, on the raw biomass sample basis) at 1000 °C with big portions of H2 (38.02 vol.%) and CO (36.36 vol.%). Feedstock particle size showed an influence on the upgrading of H2, CO and CH4 yields. The feedstock particle size of 0.3–0.5 mm, was found to obtain a higher H2 yield (33.93 vol.%), and higher LHV of gas product (15.26 MJ/m3). Equivalence ratio (ER) showed a significant influence on the upgrading of hydrogen production and product distribution. The optimum ER (0.25) was found to attain a higher H2 yield (27.31 vol.%) at 850 °C. Due to the low efficiency of bench scale gasification unit the system needs to be scaling-up. The cost analysis for scale-up EFB gasification unit showed that the hydrogen supply cost is RM 6.70/kg EFB ($2.11/kg = $0.18/Nm3).

The way in which reagents are mixed can have a large influence on the product distribution of a chemical reaction. This has been analysed earlier when micromixing is the limiting mixing step. Additional segregation at a larger scale has only been treated in detail when the local turbulent dispersion of a feed stream was relevant. Here additional segregation due to the finite disintegration rate of large concentration eddies is represented by a feasible structure to describe the environment within which micromixing and chemical reaction take place. The resulting model contains one time constant each for micro-and mesomixing. Their estimation is discussed and applied to predicting the yields of fast complex reactions in plug-flow static mixers and in a semibatch stirred tank reactor under conditions where neither macromixing nor turbulent dispersion were limiting. The comparison with measured yields is good for micromixing and fairly satisfactory for inertial-convective mesomixing, Further research on this step is needed.

This paper addresses the theoretical aspects of passive intermodulation (PIM) generation in printed transmission lines. In order to elucidate the mechanisms of PIM generation, a new model of the transmission line length with distributed nonlinearity is proposed. The developed model has been validated by the near-field measurements of PIM product distributions along the microstrip lines. The contributions of nonlinear mixing, power dissipation, and load matching to PIM products have been analyzed in detail. The obtained results reveal the fundamental properties of PIM generation in finite lengths of printed lines with distributed nonlinearity and identify possible means for PIM mitigation. It was shown for the first time that the reverse PIM products in a matched transmission line with distributed nonlinearity are generated due to nonlinear scattering.

Pyrolysis and gasification are two of the more promising utilization methods for the conversion of biomass toward a clean fuel source. To truly understand and model these processes requires detailed knowledge ranging from structural information of raw biomass, elemental composition, gas-phase reaction kinetics and mechanisms, and product distributions (both desired and undesired). The various analytical methods of biomass pyrolysis/gasification processing are discussed, including reactor types, analytical tools, and recent examples in the areas of (a) compositional analysis, (b) structural analysis, (c) reaction mechanisms, and (d) kinetic studies on biomass thermochemical processing.

Growing awareness of environmental problems during recent years has led to increased demand for environmental information about seafood products. In particular, this report is an attempt to evaluate the manufacturing process of canned-tuna products. Bearing in mind the lifestyles of people in the 21st century, canned products are one of the commonest ways in which seafood products are presented. Spain is the second largest exporter of processed tuna in the world, behind Thailand. The fish and shellfish canning industry is mainly grouped in Galicia where 65% of the total production takes place.

Polypropylene, polystyrene, high density polyethylene and their mixtures and real-world plastic waste were investigated for the production of hydrogen in a two-stage pyrolysis-gasification reactor. The experiments were carried out at gasification temperatures of 800 or 850°C with or without a Ni-Mg-Al catalyst. The influence of plastic type on the product distribution and hydrogen production in relation to process conditions were investigated. The reacted Ni-Mg-Al catalysts were analyzed by temperatureprogrammed oxidation and scanning electron microscopy. The results showed that lower gas yield (11.2 wt.% related to the mass of plastic) was obtained for the non-catalytic non-steam pyrolysis-gasification of polystyrene at the gasification temperature of 800°C, compared with the polypropylene (59.6 wt.%) and high density polyethylene (53.5 wt.%) and waste plastic (45.5 wt.%). In addition, the largest oil product was observed for the non-catalytic pyrolysis-gasification of polystyrene. The presence of the Ni-Mg-Al catalyst greatly improved the steam pyrolysis-gasification of plastics for hydrogen production. The steam catalytic pyrolysis-gasification of polystyrene presented the lowest hydrogen production of 0.155 and 0.196 (g H 2 /g polystyrene) at the gasification temperatures of 800 and 850°C, respectively. More coke was deposited on the catalyst for the pyrolysis-gasification of polypropylene and waste plastic compared with steam catalytic pyrolysis-gasification of polystyrene and high density polyethylene. Filamentous carbons were observed for the used Ni-Mg-Al catalysts from the pyrolysis-gasification of polypropylene, high density polyethylene, waste plastic and mixed plastics. However, the formation of filamentous carbons on the coked catalyst from the pyrolysis-gasification of polystyrene was low.

... Channel coordination plays a strategically important role in a multi-channel context. ... The rapid growth in internet sales has been aided by a parallel increase in the efficiency ... Rosenbloom (2007) discussed that while multi-channel marketing strategy becomes a major force in the ...

m.a.a.m.leenders@uva.nl T he motion picture industry has provided a fruitful research domain for scholars in marketing and other disciplines. The industry has high economic importance and is appealing to researchers because it offers both rich data that cover the entire product lifecycle for many new products and because it provides many unsolved "puzzles." Although the amount of scholarly research in this area is rapidly growing, its impact on practice has not been as significant as in other industries (e.g., consumer packaged goods). In this article, we discuss critical practical issues for the motion picture industry, review existing knowledge on those issues, and outline promising research directions. Our review is organized around the three key stages in the value chain for theatrical motion pictures: production, distribution, and exhibition. Focusing on what we believe are critical managerial issues, we propose various conjectures-framed either as research challenges or specific research hypotheses-related to each stage in the value chain and often involved in understanding consumer moviegoing behavior.

The global electrical energy consumption is still rising and there is a steady demand to increase the power capacity. The production, distribution and the use of the energy should be as technological efficient as possible and incentives to save energy at the end-user should be set up. The deregulation of energy has lowered the investment in larger power plants, which

The effects of temperature, residence time, and pressure on the degradation of polyethylene (PE) to oil were investigated in supercritical water (SCW) using a 180-mL continuous reactor. The yield of oil product increases with the increase of temperature, reaching 79% at 530°C, and then decreases as the temperature further increases. The yield of gas product increases from 3% to 22% as the temperature increases from 500°C to 550°C. The product distribution shifts toward shorter chain hydrocarbons with the prolongation of reaction time. Furthermore, the ratio of alkenes to alkanes of products increases with the increase of temperature and pressure, and decreases with increasing reaction time. The effect of pressure on both products’ yield and composition is less significant.

In Malaysia, there has been interest in the utilization of palm oil and oil palm biomass for the production of environmental friendly biofuels. A biorefinery based on palm oil and oil palm biomass for the production of biofuels has been proposed. The catalytic technology plays major role in the different processing stages in a biorefinery for the production of liquid as well as gaseous biofuels. There are number of challenges to find suitable catalytic technology to be used in a typical biorefinery. These challenges include (1) economic barriers, (2) catalysts that facilitate highly selective conversion of substrate to desired products and (3) the issues related to design, operation and control of catalytic reactor. Therefore, the catalytic technology is one of the critical factors that control the successful operation of biorefinery. There are number of catalytic processes in a biorefinery which convert the renewable feedstocks into the desired biofuels. These include biodiesel production from palm oil, catalytic cracking of palm oil for the production of biofuels, the production of hydrogen as well as syngas from biomass gasification, Fischer-Tropsch synthesis (FTS) for the conversion of syngas into liquid fuels and upgrading of liquid/gas fuels obtained from liquefaction/pyrolysis of biomass. The selection of catalysts for these processes is essential in determining the product distribution (olefins, paraffins and oxygenated products). The integration of catalytic technology with compatible separation processes is a key challenge for biorefinery operation from the economic point of view. This paper focuses on different types of catalysts and their role in the catalytic processes for the production of biofuels in a typical palm oil and oil palm biomass-based biorefinery.

Just-in-time (JIT) purchasing is a systems approach for developing and operating the purchasing function. JIT purchasing along with the total quality management in many industries has been successful in reducing inventory and increasing the overall effectiveness of purchasing function and hence the productivity of manufacturing. JIT purchasing methods are successful not only in Japan, but also in many countries like, South Korea, Taiwan, USA, UK, Germany, France, Hong Kong, etc. JIT purchasing has tremendous effects on the operations of production, distribution, and accounting. An attempt has been made in this paper to review the literature available on JIT purchasing with an objective to establish a framework for improving the effectiveness of purchasing function. In addition, some future research directions on JIT purchasing are indicated. . 0925-5273/99/$ -see front matter 1999 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 5 -5 2 7 3 ( 9 8 ) 0 0 0 2 5 -5

The global electrical energy consumption is still rising and there is a steady demand to increase the power capacity. It is expected that it has to be doubled within 20 years. The production, distribution and use of the energy should be as technological efficient as possible and incentives to save energy at the end-user should be set up. Deregulation of energy has lowered the investment in larger power plants, which means the need for new electrical power sources may be increased in the near future. Two major technologies will play important roles to solve the future problems. One is to change the electrical power production sources from the conventional, fossil (and short term) based energy sources to renewable energy resources. Another is to use high efficient power electronics in power generation, power transmission/distribution and end-user application. This paper discuss the most emerging renewable energy sources, wind energy, which by means of power electronics are changing from being minor energy sources to be acting as important power sources in the electrical network.

The kinetics of toluene disproportionation has been studied over both unmodified and Si-Mg modified ZSM-5 catalysts using an integral reactor and taking into account the reversioility of the reaction. It has been found that xylene dealkylation is the major secondary reaction, whereas toluene dealkylation can be considered negligible. For the unmodified ZSM-5, heterogeneous models based in the alkyl-transfer mechanism allowed the experimental results to be fit better than first and second pseudohomogeneous models, the best concordance being obtained when toluene adsorption is assumed as the rate-limiting step. The corresponding kinetic equation has been further applied to the modified zeolite (SiMg/ZSM-5), leading to the development of a kinetic model which includes the effect of the toluene and p-xylene intracrystalline diffusion rate and the presence of nonselective acid sites on the external zeolite surface. This model describes adequately the selective formation of p-xylene over modified ZSM-5, reproducing the experimental product distribution with an average relative error of 2.8%.

Hydrocracking is a petroleum refining process where cracking occurs simultaneously with hydrogenation to convert heavy petroleum feedstocks into desired lighter products. In this study, multi-objective optimization of an industrial hydrocracking unit has been performed for the first time, to find scope for further improvements and to provide a range of optimal solutions. The reactor model was simulated based on a discrete lumped model approach to kinetic modeling. The kinetic and product distribution parameters were fine-tuned using available industrial data. The real-coded elitist nondominated sorting genetic algorithm was used to carry out the multi-objective optimization study. The Pareto-optimal solutions for the hydrocracker unit are presented, and their significant features are discussed.

Several compositions of palladium-loaded calcium hydroxyapatite Pd(x)/CaHAp were prepared and characterized by XRD, IR, and UVvisible spectroscopy and temperature-programmed reduction (TPR). The acid-base properties of the samples were studied with the use of butan-2-ol conversion and IR spectroscopy coupled with lutidine adsorption/desorption. Calcium hydroxyapatite bears Lewis acid sites of moderate strength and a limited number of Brønsted acid sites, which produce butenes by dehydration. The selectivity of the dehydrogenation reaction (formation of methyl ethyl ketone) is very limited in the absence of oxygen but indicates the existence on the surface of phosphate of basic sites that are as essential as the acid sites in the direct synthesis of methyl isobutyl ketone (MIBK) from acetone and H 2 . Dispersion of Pd on the hydroxyapatite introduces redox properties and the bifunctionality needed in the hydrogenation of mesityl oxide (MO). Temperature-programmed reduction (TPR) of Pd(x)/CaHAp catalysts shows a sharp peak of H 2 consumption between 268 and 276 K, depending on palladium loading, followed by a negative peak at about 338 K, which is associated with the decomposition of β-PdH. Hydrogen chemisorption measurements carried out at 353 K allowed the determination of the size of palladium particles, which varies between 8 and 28 nm. The Pd(x)/CaHAp catalysts showed good performance in the low-pressure one-step synthesis of MIBK. They are stable under the experimental conditions, and they exhibit a MIBK and MIBC selectivity that reaches 92% for a conversion of 22% and an optimal Pd loading of 2 wt%. Other parameters of the reaction (such as temperature of reaction, residence time, H 2 /acetone ratio) were studied. They all play an important role in acetone conversion and product distribution. However, the reaction temperature has the most significant influence, since a maximum of the global conversion was observed at 423 K.  2005 Elsevier Inc. All rights reserved. (M. Ziyad).

Managing operations in today's competitive marketplace poses signi®cant challenges. The traditional thought was that there were so many con¯icts in the multiple demands on the operations function that trade-os were made in achieving excellence in one or more of these dimensions. Thus, for example, if a ®rm competed on the dimensions of¯exibility and quality, cost was of secondary concern. This type of thinking was motivated by the fact that customers requiring product variety and high quality were typically willing to pay a premium price. Similarly, if the competitive pressures required the supply of low cost products (i.e., price was the major competitive force), then¯exibility in terms of new product variety was not necessarily a major priority for the ®rm and hence, was sacri®ced. This type of analysis forced the traditional operations manager to visualize the trade-os between competitive priorities were a way of life.

This study in its entirety sought to investigate the impact o f van selling on product distribution with keen interest on the selected fast moving consumer goods in Kenya. To achieve this, selected companies' representatives were asked to give their responses to the factors that led their firms to adopt van selling and the impact of the same on product distribution. This was a survey study which targeted a number o f fast moving consumer goods in Kenya but given their variations and large number only a few were selected for this study as they are representative. Convenience sampling method was used to select the

A study was done of the thermal decomposition of urea under open reaction vessel conditions by thermogravimetric analysis (TGA), high performance liquid chromatography (HPLC), Fourier transform-infrared (FT-IR), and an ammonium ion-selective electrode (ISE). Both evolved gases and urea residue were analyzed, and profiles of substances present versus temperature are given. Major reaction intermediates are also identified. Plausible reaction schemes based on product distribution in relation to temperature are proposed. Our data indicate that at temperatures in excess of 190 • C, cyanuric acid (CYA), ammelide and ammeline are produced primarily from biuret. Biuret itself is a result of prior reaction of cyanic acid, HNCO, with intact urea. Cyanic acid is primarily a result of urea decomposition at temperatures in excess of 152 • C. CYA and ammelide first appear at approximately 175 • C, but the reaction rate is very slow. At temperatures in excess of 193 • C, alternate reactions involving the decomposition of biuret substantially increases reaction rates. Several parallel processes compete for the production of products. Production of CYA, ammeline and ammelide appears complete at 250 • C, after which sublimation and eventual decomposition of products occurs.