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This work proposes a novel, generalized model for bacterial disinfection formulated in light of a stochastic paradigm. The model⿿s formulation is based on an intensity of transition that is proportional to the product of general power functions of the bacteria⿿s number concentration and time; thus, the generalized stochastic model embodies the results obtained from our earlier models. The proposed model gives rise to linear and non-linear cases of the master equation whose solution can be obtained analytically as well as numerically via Monte Carlo simulation. Moreover, the generalized stochastic model has been validated with a specific instance of bacterial disinfection. The model⿿s analytical and numerical results are in excellent accord among themselves as well as with those obtained from our earlier models; in addition, the model⿿s results tend to describe the available experimental data reasonably well.

A method and software are proposed for optimal building-evacuation-route planning in terms of identifying evacuation routes and scheduling of evacuees on each route. First, the building-evacuation routes are represented by a P-graph, which gives rise to a time-expanded process-network synthesis ( P N S T ) problem that can be algorithmically solved by the P-graph framework. In the proposed method, each location and passage in the building is given by a set of attributes to be taken into account in the evacuation-route planning. The evacuation time is calculated as a minimum cost of the corresponding P N S T . In addition to the globally optimal solution, the P-graph framework provides the n-best sub-optimal solutions. The validity of the proposed method is illustrated by two examples.

Hitherto, no attempt has been made to identify exhaustively feasible pathways for any mechanism of a given reaction catalyzed by a catalyst with multiactive sites. Two stoichiometically exact and definitely feasible mechanisms have been proposed to date for the hydrogenation of ethylene to ethane on biactive-site or triactive-site platinum catalysts. One comprises seven elementary reactions, and the other comprises eight elementary reactions; nevertheless, both mechanisms involve competitive as well as noncompetitive adsorption. Any of these mechanisms gives rise to a multitude of feasible catalytic pathways. The present work exhaustively identifies such feasible pathways by resorting to the inordinately efficient graph- theoretic algorithm based on P-graphs (process graphs). The efficacy of this algorithm has been amply demonstrated by successfully deploying it for several catalysts with single-active sites, but has never been deployed for catalysts with multiactive sites as in the current work. The availability of exhaustively identified feasible pathways for both mechanisms renders it possible to stipulate that the hydrogenation of chemisorbed chemisorbed C2H5 is the rate-controlling step: This step is contained in either mechanism.

A reaction-pathway identification procedure has two distinct phases. The first phase enumerates exhaustively the feasible candidate pathways, and the second phase identifies the ultimate feasible pathway or pathways among them. Probably the most efficient way to execute the first phase is to algorithmically generate the networks of feasible candidate pathways from a predefined set of plausible elementary reactions. The available algorithmic methods for this purpose can be roughly grouped into two major classes, one based on graph theory and the other on linear algebra. Both classes of methods consider any chemical reaction system as a network of elementary reactions, thereby implying that the two classes are interrelated. This paper studies the linear algebraic concept termed direct mechanism introduced in the mid-eighties and the graph-theoretical concept termed structurally minimal pathway introduced two decades later. Herein, it has been formally proven that the two concepts are equivalent.

This contribution presents a sequel to our previously published nonlinear stochastic model for bacterial disinfection whose intensity function is explicitly proportional to the contact time of the bacteria with the disinfecting agent. In the current model, the intensity function is proportional to the square of the contact time to account for an accelerated rate of a disinfection process. The model gives rise to the process’ master equation whose solution renders it possible to obtain the analytical expressions of the process’ mean, variance (or standard deviation), and coefficient of variation. Moreover, the master equation has been simulated via the Monte Carlo method, thereby yielding the numerical estimates of these quantities. The estimates’ values are compared with those computed via the analytical expressions; they are in excellent accord. They are also compared with the available experimental data as well as with the results obtained from our earlier model.

The contact angles of the aqueous solution of ethanol and that of n-propanol on copper, aluminum, and stainless steel surfaces are reported. The contact angles were measured under atmospheric conditions, and then under vapor-liquid equilibrium conditions at 1 atm and different temperatures. The results showed the variations of the contact angles with the concentrations of aqueous solutions on different metal material surfaces with different roughness. Some unstable behavior of the wetting ability around the azeotropic point of a binary solution is reported. Influences of concentration, kind of materials, and the surface roughness on the wetting ability are discussed. The model for predicting the contact angle of alcohol aqueous solutions on metal surfaces under atmospheric and vapor-liquid two-phase equilibrium conditions at 1 atm is derived from the Young equation.

Activated carbons (ACs) have been widely deployed in the purification of gases and liquids or the separation of their mixtures. The formation of ACs entails the modification of the original interna...

A method and software are proposed for optimal assignment of vehicles to transportation tasks in terms of total cost and emission. The assignment problem is transformed into a process-network synthesis problem that can be algorithmically handled by the P-graph framework. In the proposed method, each task is given by a set of attributes to be taken account in the assignment; this is also the case for each vehicle. The overall mileage is calculated as the sum of the lengths of all the routes to be travelled during, before, after, and between the tasks (Desaulniers et al. 1998; Baita et al. 2000). Cost and emission are assigned to the mileages of each vehicle type. In addition to the globally optimal solution of the assignment problem, the P-graph framework provides the n-best suboptimal solutions that can be ranked according to multiple criteria. The viability of the proposed method is illustrated by an example.

Catalytic decomposition of methanol (MD) plays a vital role in hydrogen production, which is the desirable fuel for both proton exchange membrane and direct methanol fuel cell systems. Thus, the catalytic mechanisms, or pathways, of MD have lately been the focus of research interest. Recently, the feasible independent pathways (IPis) have been reported on the basis of a set of highly plausible elementary reactions. Nevertheless, no feasible acyclic combined pathways (APis) comprising IPis have been reported. Such APis cannot be ignored in identifying dominant pathways.

The current work demonstrates that separation-network synthesis (SNS) problems can be transformed into process-network synthesis (PNS) problems: the SNS problems constitute a particular class of PNS problems. Thus, the transformed SNS problems are solvable by resorting to the P-graph methodology originally introduced for the PNS problems. The methodology has been unequivocally proven to be inordinately effective.

Bacteria being disinfected in fluid media are discrete entities and mesoscopic in size; moreover, they are incessantly as well as irregularly in motion and in collision among themselves or with the surrounding solid surfaces. As such, it is highly likely that some of the attributes of the bacterial population, for example, their number concentration, will fluctuate randomly. This is especially the case at the tail-end of disinfection when the population of bacteria is sparse. It might be effectual, therefore, to explore the resultant random fluctuations via a stochastic paradigm. Proposed herein is a Markovian stochastic model for the rate of bacterial disinfection, whose intensity of transition takes into account the contact time of the bacteria with the disinfecting agent to eliminate any given percentage of the bacteria in terms of a nonlinear function of time. The model's master equation has been simulated by resorting to the Monte Carlo method to circumvent the undue complexities in solving it analytically or numerically via conventional numerical techniques. For illustration, the mean, the variance (standard deviation), and the coefficient of variation of the number concentration of bacteria during disinfection have been estimated through Monte Carlo simulation. The results of simulation compare favorably with the available experimental data as well as with those computed from the corresponding deterministic model.

Natural gas has emerged as a potential alternative to gasoline due to the increase in global energy demand and environmental concerns. An investigation was undertaken to explore the technical feasibility of implementing the adsorbed natural gas (ANG) storage in the fuel tanks of motor vehicles with activated carbons from biomass, e.g., sorghum and wheat. The grain-based activated carbons were prepared by chemical activation; the experimental parameters were varied to identify the optimum conditions. The porosity of the resultant activated carbons was evaluated through nitrogen adsorption; and the storage capacity, through methane adsorption. A comparative study was also carried out with commercial activated carbons from charcoal. The highest storage factor attained was 89 for compacted grain-based activated carbons from grain sorghum with a bulk density of 0.65 g/cm 3 , and the highest storage factor attained is 106 for compacted commercial activated carbons (Calgon) with a bulk density of 0.70 g/cm 3 . The storage factor was found to increase approximately linearly with increasing bulk density and to be independent of the extent of compaction. This implies that the grain-based activated carbons are the ideal candidates for the ANG storage.

Disposal of or energy recovery from rice hull can be accomplished by pyrolysis, a heterogeneous reaction whose rate tends to depend on the area of the solid reactant surface. In the present work, the surface fractal dimension, dSF an intrinsic quantitative measure for characterizing irregular particle surfaces, has been determined for rice hull as 2.42. The values of dSF of hull-derived charcoal particles at a retention time of 30 s in a fluidized bed have been determined to be 2.79 at 848 K and 3.00 at 973 and 1173 K, thereby indicating the development of a highly porous network with increasing temperature. L'elimination ou la recuperation de l'energǐe venant de l'enveloppe de riz peut l'effectuer par pyrolyse, une reaction heterogene dont la vitesse tend a dependre de la region de la surface du reactif solide⇂. Dans le present travail, on a determine la dimension fractale de surface des enveloppes, dSF, une mesure quantitative intrinseque servant a caracteriser les surfaces de particules irregulieres; la valeur obtenue est de 2,42. On a trouve que les valeurs de dSF des particules de charbon venant de l'enveloppe a un temps de retention de 30 s dans un lit fluidise est de 2.79 a 848 K et de 3.00 a 973 et 1173 K, ce qui indique le developpement d'un reseau hautement poreux avec l'augmentation de la temperature.

The optimal and near-optimal enterprise-wide networks are designed, that is synthesized, for supplying feedstocks and distributing multiple products manufactured from these feedstocks in the process industry by resorting to the graph-theoretic method based on process graphs (P-graphs). Such feedstocks and products, conveyed through supply networks, are invariably materials for which the law of mass conservation is universally valid. Moreover, any of the actions applied to or exerted on a given feedstock or product, transiting through the supply networks, will induce a change in at least one of its attributes, thereby transforming the feedstock or product. Examples of the actions are loading, blending, pumping, tracking, unloading, subdividing, and/or wrapping; and those of the attributes are chemical composition, physical state, flow characteristics, external appearance, and/or location. Thus, in the broadest sense, any supply network can be regarded as a process network. The feedstocks and the products m...

An integrated model of supply network and production planning is proposed for the collaboration among refineries manufacturing multiple fuel products at different locations. The simulation and optimization based on the model indicate the following. The distribution costs can be reduced by relocating distribution centers as well as by reconfiguring their linkages to various markets. Moreover, the multiple fuel products manufactured need to be segregated during storage and transportation to be able to satisfy the demands of the various markets. The production planning, therefore, should be an integral part of the supply-network planning, and vice versa. Specifically, the proposed integrated model is for the nationwide supply of multiple fuel products manufactured by the individual refineries. The efficacy and usefulness of the integrated model is illustrated with an example involving three refineries and four varieties of fuel products.

The catalytic mechanisms or pathways of water-gas shift (WGS) reaction have been the focus of intense research interest because of its immense importance in hydrogen production. At the outset, 116 stoichiometrically feasible independent pathways (IPi’s) have been exhaustively generated within 2 s on a PC through a novel graph-theoretic method based on P-graphs (process graphs) from a set of 17 plausible elementary reactions. This is followed by the determination of IP18 among these 116 stoichiometrically feasible IPi’s as the plausibly dominant pathway via energetic analysis. # 2008 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.

Novel processing equipment, i.e., an operating unit, such as any of various separators, is continually under development for commercialization. An innovative strategy has been proposed to establish the economically viable target price of such an operating unit through iterative flowsheet syntheses by parametrically reducing its current price. The proposed strategy resorts to a P-graph- (process-graph-) based algorithmic method for process-network synthesis. The strategy has been demonstrated to be highly efficient by determining the target price of the pervaporation unit for downstream processing of biochemically manufactured butanol, ethanol, and acetone. It is worth noting that the proposed strategy for price targeting in developing a novel and immature operating unit, such as pervaporation, is fundamentally different from that involved in retrofitting, which involves only the mature operating units at their current costs.

A spectrophotometric study of the kinetics and mechanism of the oxidation of malic acid (Mal) by chromium(VI) catalyzed by 2,2′-bipyridyl (bpy) in aqueous acidic medium was conducted in a temperature range of ∼298 to 313 K. This reaction was found to be pseudo-first order with respect to Cr(VI) and first order with respect to malic acid. Under the conditions of the pseudo-first order ([Mal]o ≫ [Cr(VI)]o), the observed rate constant (kobs) increased with the increase in [H+] and [bpy]. There was a weak negative salt effect. Based on the experimental results, a possible reaction mechanism for this oxidation catalyzed by bpy is proposed. The rate equation derived from this mechanism can explain all the experimental phenomena.

A novel class of separation-network synthesis (SNS) problems is examined, where the separators in the separation network can be affected by various separation methods subject to different constraints imposed on the product specifications. Such a class of SNS problems has been rapidly gaining importance for chemical processing in general and biochemical processing in particular. The available methods for SNS are not intended to address these problems; therefore, an efficient method is proposed here to amend this situation. The method composes algorithmically the necessary mathematical model of the super-structure on which the determination of an optimal separation network is based. The resultant mathematical model is linear, thus the proposed method renders it possible to generate the optimal solution without fail. The solution might serve as the lower bound for a separation network with a non-linear cost function. The uniqueness and efficacy of the proposed method are amply demonstrated by two examples of different complexities.

A recent paper by Callaghan et al. [1] presents 70 reaction routes (RRis), which correspond to stoichiometrically feasible independent pathways (IPis), for the water–gas shift (WGS) reaction; these 70 IPis have been generated from 17 elementary reactions by resorting to a linear algebraic method in conjunction with some heuristics. This is in stark contrast to the 116 IPis obtained by us from the same set of 17 elementary reactions. Obviously, the former is substantially fewer than the latter. Our results have been obtained by resorting to the inordinately effective graph– theoretic, algorithmic method based on P-graphs (process graph) [2–6] in less than 2 s on a PC (Intel Pentium 4, CPU 3.06 GHz; and 1G RAM) upon inputting the 17 elementary reactions. The method comprises three algorithms

A hierarchical approach is proposed to estimate the sustainability-potential of a chemical process, based on any of the alternative synthetic routes. This novel notion of sustainability-potential is a generalization of the notion of profit-potential, the estimation of which renders it possible to screen out economically nonviable processes derived from the alternative synthetic routes at the earliest stage. At the outset of assessment, all the individual alternative synthetic routes are identified by the graph-theoretic method based on process graphs (P-graphs). Subsequently, the individual alternative synthetic routes are sequentially assessed in descending order of quantifiability, in terms of available energy (or exergy), dissipation, the possible profit, and the toxicity index, respectively. The efficacy of the approach is demonstrated for the manufacture of C2H3Cl. The approach can possibly be adapted for estimating the sustainability-potential to assess the alternative production routes as represent...

A reversed two-environment model of micromixing in a flow reactor in which the feed enters a maximum mixedness environment and then passes to a segregated environment is presented. The performance equations for an arbitrary residence time distribution are developed and employed to analyse the behaviour of growth processes in a continuous stirred tank reactor under intermediate states of micromixing. The results, which are bounded by the two extremes of micromixing, indicate that micromixing is important in growth processes and that segregation appears to reduce the rate of cell production.

A mathematical model that can be used to describe cell growth in a tower fermentation system with backflow and cell sedimentation is presented. Two computation procedures to determine steady state performance are described and some results are obtained for two-, four- and eight-stage tower systems. The effects of feed geometry, backflow rate and cell sedimentation on steady-state behaviour are investigated. The results show that control of backflow, and cell sedimentation within the tower together with control of feed flow rate and feed geometry will allow a wide range of operating conditions to be realised in a tower system.

A novel holistic approach is proposed for process retrofitting. Unlike conventional approaches, the proposed approach totally resynthesizes the entire process by incorporating the operating units with enhanced performances. As such, it can take into account all possible outcomes, including the inevitable restructuring of the flowsheet’s network structure. Naturally, the proposed approach can be executed by resorting to the efficient graph-theoretic method based on P-graphs that have been originally devised for synthesizing virgin processes; nevertheless, the approach does not require the enormous effort involved in exhaustively identifying plausible operating units in synthesizing virgin processes. With the combinatorial feasibility of most operating units largely predetermined, the approach detects, with extraordinary speed, any changes in the flowsheet’s network structure incurred by retrofitting. The efficacy of the approach is demonstrated by applying it to the retrofitting of a conventional downstream process for the biochemical production of butanol through the incorporation of newly identified adsorbing units.

To prepare carbon molecular sieves (CMSs), methane was pyrolyzed in an attempt to deposit fine carbon particles on the micropore mouths of the carbon substrates being heated; the carbon substrates included grain-based activated carbons and commercial activated carbons. To explore the effects of heat treatment alone, blank experiments were conducted by heating the samples in N 2 . The resultant products were characterized by N 2 -adsorption at 77 K. Methane failed to deposit carbon at 800 °C. The porosity of activated carbons, however, was substantially influenced by heat treatment alone. The surface areas and micropore volumes of the activated carbons from grain sorghum decreased by 39.32% and 36.84%, respectively, upon heat treatment alone; this is attributable to the destruction of pore structure by sintering. In contrast, the corresponding values of the commercial activated carbons increased by 59.86% and 62.16%, respectively, upon heat treatment alone; this can be attributable to the development of microporosity.

The current effort aims at contributing to the algorithmic synthesis of a heat-integrated separation network system involving separations based on various properties, such as volatility, solubility, and permeability. This is unlike any of the previous works on heat-integrated network synthesis involving separation based only on a single property, such as volatility. The network under consideration consists of mixers, dividers, separators, utilities, and heat exchangers. The network system produces pure or multicomponent product streams from a single or multiple feed streams. Meanwhile, it satisfies the heat requirements not only between reboilers and condensers but also between hot and cold streams throughout the entire network of a production plant with the lowest possible annualized cost. The costs of the mixers and dividers are regarded as negligible: the cost of a separator, a linear function of the flowrate of its input stream without an additive constant parameter, and the cost of a utility...

Molecular sieves, including carbon molecular sieves (CMSs) manufactured from activated carbons, can be variously applied in the purification and separation of gaseous and liquid mixtures and can also serve as catalysts. CMSs are formed by depositing fine particles of carbon on the mouths of pores of such activated carbons. These carbon particles are generated by decomposing a gaseous carbon source. The formation of CMSs proceeds stochastically, which is mainly attributable to the mesoscopic sizes and complex motion of the depositing carbon particles and random distribution of the pores on the activated carbons. In this work, CMS formation is modeled as a pure-birth process with a linear intensity of transition. The resultant model gives rise to the governing equations for the mean and variance. The model is validated by comparing the analytical solutions of these equations with available experimental data. The mean value of the model is in excellent accord with the data. In addition, the kinetic constants...

Liquid dispersion in the radial direction was investigated in the riser of a viscous liquid-solid fluidized bed 0.102 m in diameter and 3.5 m in height. Pressure fluctuations in the riser were also measured and analyzed to examine the behavior of fluidized particles. Effects of liquid velocity (0.15–0.45 m/s), solid circulation rate (2–8 kg/m2s), particle size (1–3 mm), and liquid viscosity (0.96–38 mPas) on pressure fluctuations and the liquid radial dispersion coefficient were determined. The infinite space model was employed to obtain the radial dispersion coefficient from the radial concentration profiles of the tracer. The pressure fluctuations were analyzed by means of autocorrelation coefficient as well as power spectral density function. The dominant frequency obtained from the autocorrelation coefficient or power spectral density function of pressure fluctuations decreases with increasing liquid viscosity or liquid velocity, but it increases with increasing particle size. The liquid radi...

Manufacturing butanol, ethanol, and acetone through grain fermentation has been attracting increasing research interest. In the production of these chemicals from fermentation, the cost of product recovery constitutes the major portion of the total production cost. Developing cost-effective flowsheets for the downstream processing is, therefore, crucial to enhancing the economic viability of this manufacturing method. The present work is concerned with the synthesis of such a process that minimizes the cost of the downstream processing. At the outset, a wide variety of processing equipment and unit operations, i.e., operating units, is selected for possible inclusion in the process. Subsequently, the exactly defined superstructure with minimal complexity, termed maximal structure, is constructed from these operating units with the rigorous and highly efficient graph-theoretic method for process synthesis based on process graphs (P-graphs). Finally, the optimal and near-optimal flowsheets in terms of cost are identified.

A highly effective algorithmic method is proposed for optimally synthesizing an azeotropic-distillation system from an extensive set of candidate operating units, i.e., functional units. The method has been derived by resorting to the graph-theoretic approach to process-network synthesis based on process graphs (P-graphs); it also resorts to the methodology established in our previous contribution for dividing the residue curve map (RCM) of a material system, i.e., mixture, to be separated into partitioned materials. This allows the entire space of the RCM to be taken into account in composing networks of candidate operating units, thereby preventing the localization of search. Moreover, the RCM is transformed into the flow-rate map, where any material is quantitatively defined by the molar flow rates of its components instead of the concentrations as in the RCM. This renders it possible to eliminate the nonlinearity in the governing equations of the candidate operating units. The efficacy of the method i...

The permeability of chrome-tanned cattle hide was determined separately with distilled water and an 89-weight percent aqueous glycerol solution in the light of a simplified Darcy's law. The resultant permeability has been found to depend on the location from which the sample is taken on the original hide. The frequency distribution of the values of the permeability has been shown to be lognormal, thereby giving rise to a two parameter-description of the distribution.

The production of activated carbons from grain sorghum with phosphoric acid activation has been studied by means of two processes, i.e., one-stage and two-stage. The former comprises simultaneous carbonization and activation after impregnation; the latter, the carbonization of the precursor at 300 degrees C for 15 min, followed by the activation of the resultant char after impregnation with phosphoric acid. The preparation conditions, e.g., activation duration, phosphoric acid concentration, and activation temperature, have been varied to determine the optimal processing conditions. The optimal activation conditions for the highest surface areas have been determined to be 600 and 500 degrees C with a phosphoric acid concentration of 35% for the one-stage and two-stage processes, respectively. The two-stage process has been found to greatly enhance the porosity development, especially the microporosity.

A rigorous method for identifying biochemical reaction or metabolic pathways through its systematic synthesis has been established. The current method for synthesizing networks of metabolic pathways follows the general framework of a highly exacting combinatorial method. The method is capable of generating not only all combinatorially independent, feasible reaction networks only once, but also those combinations of independent pathways. A case study involving the conversion of glucose to pyruvate with 14 elementary reactions illustrates the efficiency and efficacy of the method. All the results have been obtained with a PC (Pentium-III 550 MHz, 256 MB RAM) within 1 s.

The present work proposes a P-graph based approach capable of systematically generating all combinatorially feasible alternative sequences for both continuous and batch azeotropic distillation systems when the feeds, products, and operating units and their concomitant intermediate materials are known. To facilitate synthesis, a highly effective method has been established to identify processing or operating units necessary for constructing azeotropic-distillation systems by means of first principles and logical sequencing of such units. The materials represented in the space of the residue curve map are partitioned into lumped materials bounded by thermodynamic boundaries and pinches, e.g. distillation boundaries and liquid–liquid phase equilibrium envelope. Subsequently, the operating units are identified on the basis of these lumped materials. The proposed approach automatically discards the operating units and intermediates whose inclusion will lead to infeasible sequences. The efficacy of the approach is illustrated with a realistic example.

The available algorithmic methods often fail to yield with certainty the global optima in solving even a relatively simple class of separation-network synthesis problem for which the cost functions are considered to be linear. This is attributable to two complications; firstly the super-structures on which the solutions are based are incomplete; and the secondly, the mathematical programming models derived for the problems are unnecessarily cumbersome. To circumvent these complications, a novel method is proposed here to generate the complete super-structure and the corresponding mathematical programming model necessary for the separation-network synthesis problem with linear cost function. The efficacy of the proposed method is demonstrated by re-examining four published problems for which the optima obtained are claimed to be global. For all the problems re-examined, the costs of the solutions resulting from the present method are the same or as much as 30% lower than those of the published solutions.

A rigorous foundation is given for the logical formulation of process network synthesis on the basis of the combinatorial axioms of feasible processing networks.