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Published in Separation and Purification Technology. Free download:https://authors.elsevier.com/a/1ghmT4wbrTBXso

Published in Journal of Molecular Liquids. Free download:https://authors.elsevier.com/a/1gI~1c8qpWkDv

The BET equation is commonly used to describe type II sigmoid isotherms of water contaminants. However, there are some type II isotherms that do not agree with the BET equation. In this paper, three modified BET equations (Aguerre–Suarez–Viollaz, Pantuso–Tolaba–Aguerre, and Aranovich–Donohue) are evaluated against published isotherm data of dysprosium, reactive blue 5G, and naphthenic acid. In the cases studied, the three modified BET equations are shown to outperform the original BET equation. The Aranovich–Donohue equation is a promising isotherm model, offering accurate data correlations and statistically significant parameter estimates. In particular, it is very effective in tracing the atypical curve shapes of the reactive blue 5G and naphthenic acid isotherms. Although the Aranovich–Donohue equation has not attracted much attention, it is a practical alternative to the widely used BET equation for correlating adsorption isotherms of water contaminants.

Equilibrium data for aqueous adsorption systems are often correlated using isotherm models originally developed for adsorption at the gas-solid interface. A prominent example is the Langmuir isotherm, which has been used in thousands of investigations to describe the adsorption of dissolved substances at the liquid-solid interface. Another example is the Kiselev isotherm, which was proposed to account for adsorption at the gas-solid interface when adsorbate-adsorbate interactions are significant. Researchers who have applied the Kiselev isotherm to adsorption data for liquid-solid systems were puzzled by the fact that data fittings in most cases returned negative values for the adsorbate-adsorbate association equilibrium constant. It is shown in the present study that the data fitting problem is a direct consequence of misusing the Kiselev isotherm. In all previous studies, the Kiselev isotherm was used to fit type I isotherm data. Because the concept of adsorbate-adsorbate interactions is incompatible with a type I isotherm, fitting the Kiselev isotherm to such data can lead to nonsensical parameter estimates. The Kiselev isotherm was devised to account for type V isotherms exhibiting a sigmoid or S-shaped data trend. Physically meaningful parameter estimates can be obtained if the Kiselev isotherm is applied to type V isotherm data.

Breakthrough curves of water contaminants are usually analyzed using simple fixed bed models such as the Bohart-Adams, Thomas, and Yoon-Nelson equations, which are by design symmetric. Because breakthrough data often follow an asymmetric pattern, the use of models that do not account for asymmetry could lead to poor fits, consequently resulting in erroneous estimates of breakthrough and exhaustion times. To address this issue, the Bohart-Adams, Thomas, and Yoon-Nelson models were modified by a logarithmic transformation to enhance their data fitting ability. The three modified models were found capable of providing robust fits to seven separate sets of previously reported asymmetric breakthrough data of water contaminants (fluoride, methylene blue, salicylic acid, lead, mercury, nickel, and arsenic), with reported residual root mean square error (RRMSE) values ranging from 0.019 to 0.046. In consequence, the new models were found capable of providing reliable estimates of breakthrough and exhaustion times corresponding to any predetermined concentration level. By contrast, the three original models were found to perform poorly, reporting inferior RRMSE values ranging from 0.038 to 0.086 for data fits and providing grossly inaccurate estimates of breakthrough and exhaustion times. The new models contain only parameters that appear in the original models, and are highly flexible, being able to assume virtually all monotonically increasing sigmoid shapes. They represent a far more accurate alternative to the original models.

In a comment on my article [1] published in this journal, Hu and Zhang [2] assert that I had misinterpreted the Bohart-Adams equation derived by Amundson and that the Bohart-Adams equation lacks the bed voidage parameter. I argue that Hu and Zhang are wrong on both counts. I further contend that their version of the Bohart-Adams equation derived by Amundson contains a glaring error of a rudimentary nature.

Fixed bed adsorption studies often report asymmetric breakthrough curves which exhibit a tailing phenomenon as the effluent approaches the influent concentration. Evaluations of models capable of describing such curves are lacking in the literature. This paper examines the ability of the Gompertz equation to correlate asymmetric breakthrough data collated from reports published in the environmental adsorption literature. It is shown that the Gompertz equation, which has received little attention in this field of research, is able to track asymmetric breakthrough curves displaying a moderate degree of tailing. The logistic equation, which is mathematically analogous to the Bohart-Adams, Thomas, and Yoon-Nelson models, cannot effectively describe such asymmetric data. The Gompertz equation provides only an approximate representation of breakthrough data exhibiting a pronounced degree of tailing. To fit such data, this paper presents two modified forms of the Gompertz equation, which are shown to be highly accurate (R2 > 0.996). The Gompertz equation and the two modified versions are useful additions to the toolbox of breakthrough curve modeling which has long been filled with the Bohart-Adams, Thomas, and Yoon-Nelson models. These popular logistic-based equations are confined to fitting symmetric breakthrough curves.

This communication discusses the fixed bed modeling results of the recent paper published by Ang et al. (2020) in this journal.

In the water and wastewater treatment field several simplistic models of packed bed dynamics such as the Bohart-Adams, Thomas, and Yoon-Nelson models are frequently used by investigators to fit adsorption breakthrough data. The century-old Bohart-Adams model is arguably the best known one which also serves as the foundation of the bed depth-service time equation. In recent years a substantial body of literature on the subject of fixed bed modeling has however claimed that it is inferior to other models. The present paper shows that such claims are incorrect and misleading because of biased comparisons in which the fitting ability of an oversimplified version of the Bohart-Adams model was compared with those of the Thomas and Yoon-Nelson models. The oversimplified Bohart-Adams equation is in effect an exponential function which predicts an exponentially increasing breakthrough value with time. As such, it is unable to fit typical breakthrough curves which are S-shaped or sigmoidal. It can be shown that a proper version of the Bohart-Adams model gives fit quality similar to those of the Thomas and Yoon-Nelson models. This is not unexpected since the three simplistic fixed bed models can be expressed in terms of the logistic equation of population growth; that is, mathematically they are equivalent.

Adsorption is an important process for arsenic removal from drinking water supplies. Fixed bed column processes are the preferred mode of operation owing to their simplicity and proven performance. Mathematical models can facilitate the design and optimization of fixed bed adsorbers. For systems exhibiting linear isotherm behavior over the relevant concentration range, their performance can be predicted using models that are amenable to analytical solutions. The predictive utility of an asymptotic solution of the homogeneous surface diffusion model (HSDM) and an approximate solution of a linear driving force model (LDFM) under linear isotherm approximation was evaluated in this study. A previously published pilot test on arsenic breakthrough in a fixed bed adsorber of polymer-supported nanoparticles was modeled. Model parameters were estimated on the basis of some easily determined batch measurements. The pilot test yielded 27,000 bed volumes at 10 μg/L arsenic. The two analytical solutions predicted 24,200 and 27,100 bed volumes. Despite the simplicity of the HSDM and LDFM solutions, their predictions agreed well with the experimental data. These analytical solutions are very straightforward, easy to apply, and provide acceptable modeling power.

Introducing purification devices into hydrogen systems can enhance the extent of hydrogen reuse. However, the economic performance of a purification device depends on its appropriate placement within a hydrogen system. Based on some established graphical methods, this paper explores the influences of the feed concentration on the purification proces s . A simple and systematic graphical method is proposed for identifying the OPP (optimal purification process) by extending the well-known pinch technology method. The proposed method can determine the OPP with the minimum feed flow rate and minimum tail gas flow rate under the condition of maximizing the HUS (hydrogen utility savings). The corresponding feed streams of the OPP also can be identified easily in the purification polygon. Furthermore, the conception of minimum separation work is used to compare different purification processes. A realistic case study is used to illustrate the applicability of the proposed method. Three different scenarios are analyzed and the results show that notable reductions in the minimum separation work consumption can be achieved (22%, 34% and 16% for the three scenarios).

In hydrogen networks, purifiers are quite often used to reduce operating costs. They should be properly integrated with the whole network in order to maximize the benefit. In this paper, a graphical method is proposed for targeting the minimum fresh resource consumption of hydrogen networks considering separation performance of purifiers. The material balance of the whole hydrogen network shows that the extent of fresh hydrogen reduction is subject to the maximum hydrogen surplus. Based on such observation, the mass transfer triangle is developed to describe the hydrogen transformation from maximum hydrogen surplus to fresh hydrogen. With both the purity and the flow rate of purification streams optimized, the minimum fresh hydrogen consumption can be determined through the proposed graphical method. Two cases are studied to illustrate the proposed methodology.

We have developed a process model to simulate the behavior of an industrial-scale pressurized Lurgi fixed-bed coal gasifier using Aspen Plus and General Algebraic Modeling System (GAMS). Reaction characteristics in the fixed-bed gasifier comprising four sequential reaction zones—drying, pyrolysis, combustion and gasification are respectively modeled. A non-linear programming (NLP) model is developed for the pyrolysis zone to estimate the products composition which includes char, coal gases and distillable liquids. A four-stage model with restricted equilibrium temperature is used to study the thermodynamic equilibrium characteristics and calculate the composition of syngas in the combustion and gasification zones. The thermodynamic analysis shows that the exergetic efficiency of the fixed-bed gasifier is mainly determined by the oxygen/coal ratio. The exergetic efficiency of the process will reach an optimum value of 78.3% when the oxygen/coal and steam/coal mass ratios are 0.14 and 0.80, respectively.

Centrifugal pumps are widely used in cooling water systems to transport cooling water to its users. They are installed in the header line of the feed pipe, constituting a main pump network. The pressure head of the main pumps must be large enough to satisfy the pressure heads of all coolers. The pressure drop of parallel branch pipes must be balanced by reducing the opening of valves for some coolers, incurring an energy penalty on some pumps. To attain energy savings, this paper proposes an auxiliary pump network whereby auxiliary pumps are installed in parallel branch pipes. A superstructure-based mathematical model is developed to optimize the total cost of the main and auxiliary pump networks. The optimal number of auxiliary pumps and their installation locations are determined by solving the model with a simulated annealing algorithm. The effectiveness of the model is tested by a case study based on the cooling water network of a refinery.

A new method based on the heat duty–time (Q–t) diagram is proposed for heat integration of heat exchanger networks featuring batch streams. Using the Q–t diagram method, the energy targets and the structure of the initial heat exchanger network can be easily obtained. The method can be used both for direct and indirect heat integration of batch streams. For indirect heat integration, the heat degradation of intermediate media is considered. A case study on optimizing the heat exchanger network of a hydrazine hydrate plant is used to illustrate the application of the method. The results show that integration of this heat exchanger network without considering its batch streams can limit the total energy savings.

Two types of waste paper materials, newspaper and office paper, were evaluated for their potential to be used as renewable feedstock for the production of fermentable sugars via the enzymatic hydrolysis of their cellulose fractions. The effects of four factors (hydrolysis time, enzyme loading, surfactant addition and phosphoric acid pretreatment) on the extent of sugar yield were assessed and quantified by using a methodical approach based on response surface methodology. The statistical experimental design used in this study requires fewer experimental runs compared to some commonly used experimental designs. In the newspaper hydrolysis case, response surface plots revealed that the degree of sugar release increased with an increase in hydrolysis time but it was hardly affected by the enzyme loading and acid pretreatment factors. The surfactant addition factor exhibited a positive effect when the enzyme loading level was relatively low. With office paper as the substrate, three of the four factors (hydrolysis time, enzyme loading and acid pretreatment) exhibited positive effects on the extent of sugar release. At local optimum conditions, the maximum sugar yield from office paper was found to be 0.82 g of reducing sugars per gram of paper, which was about 4.8 times higher than the maximum sugar release from the newspaper substrate.

For a hydrogen network with purification, it is postulated that different Purification Feed Flow Rates (PFFRs) will exert different effects on the hydrogen utility consumption. To optimize a hydrogen network with purification reuse, the effect of the PFFR on the hydrogen utility consumption should thus be analyzed systematically. However, no in-depth studies on this subject matter are available in the open literature. This work aims to bridge this research gap by establishing the relationship between the PFFR and the hydrogen utility consumption. According to the concepts of hydrogen surplus and pinch point, the characteristic of the pinch point is analyzed first, and it is found that the pinch point can only appear at the sink-tie-line which can intersect the source purity profile. Then, the quantitative relationship between the hydrogen utility adjustment and the hydrogen surplus is deduced, and a numerical method for identifying the pinch point and the minimum hydrogen utility consumption target is developed. Based on this, the quantitative relationship between the PFFR and the hydrogen surplus at each sink-tie-line is deduced. The upper bound of the PFFR can be identified from the hydrogen surplus variation diagram. The proposed numerical approach for targeting the hydrogen pinch problems and a systematic graphic method for identifying the limiting PFFR have the merit of being conceptually simple and easy to apply. Two cases are studied to illustrate the applicability of the proposed method.

Instability is a severe barrier to the successful development and evolution of industrial symbiosis systems. In this paper, a novel approach for stability analysis of industrial symbiosis systems is proposed. Two parameters (symbiosis profit and symbiosis cost) are defined on the basis of profit consideration. With the introduction of asymmetric distribution coefficient as a quantitative index, the distribution of symbiosis cost and symbiosis profit can be analyzed. An illustrative example demonstrates that the approach can be used to assess the stability of a hypothetical coal-based symbiosis system under different states. Specifically, the impact of changes in the system structure and external environment on the stability of the coal-based symbiosis system is investigated. The results confirm the practical applicability and effectiveness of the proposed approach.

In the oil refining and petrochemical industry, hydrogen flows in so-called hydrogen networks are a common feature. A practical problem in hydrogen network analysis is to identify the minimum fresh hydrogen input flowrate to ensure that the hydrogen streams produced by combining the flows of internal sources satisfy certain concentration specifications of sinks for hydrogen and impurities such as H2S. To tackle this problem, this paper presents a novel graphical procedure, much inspired by the pioneering work of Shelley and El-Halwagi (2000) that makes use of the unique features of ternary composition diagram for three-component systems. In addition, accounting for constraints on flowrates inside a ternary visualization diagram is another novel aspect of this graphical method. Two literature case studies based on hydrogen systems with multiple impurities are solved to illustrate the effectiveness and elegance of the proposed method.

Calculating emergy flows within a typical chemical production system is challenging because it is made up of various interconnected reaction, separation, heating and cooling units with extensive recycle of material and energy. The complexity of the interior structure of a chemical production system, if not carefully considered, could pose problems in emergy calculation. The difficulty is further compounded by the fact that the rules of emergy algebra are somewhat opaque and incomplete. This article shows that complex chemical production systems may be decomposed into four basic structures: series, parallel, bypass and feedback, which can greatly facilitate the process of emergy calculation. Systematic procedures for calculating the emergy flows of the four basic structures without violating the basic rules of emergy algebra are given in detail. Special attention has been paid to the feedback structure, which is analyzed using a novel concept known as virtual emergy flow. An illustrative example based on a hypothetical system made up of the four basic structures and a case study based on an actual polypropylene production system are used to demonstrate the efficacy of the emergy calculation procedures presented in this study.

Optimization of industrial water networks made up of several water-using processes can reduce freshwater usage and wastewater production. A common feature of previous water network studies is that each water-using operation is assumed to have a single outlet stream. In this paper, a superstructure and a mathematical programing model are proposed for optimization of a water network with both single and two outflow water-using processes. A two outflow water-using process has two outlet streams with different impurity concentrations, in which one has a lower concentration and the other a higher concentration. Outlet stream with a high concentration can be reused in other water-using processes, regenerated in a regeneration system or discharged, while the outlet stream with a low concentration can only be reused in other water-using processes. These intricacies are accounted for in the mathematical model. For a two outflow water-using process, the main parameters are the allocation rates of flowrate and mass load which may be determined through consideration of the process’s performance characteristics. The optimization methodology is demonstrated through a case study of a water network consisting of four single outflow water-using units, one two outflow water-using unit and a regeneration unit.

This paper proposes the principles of how to define a boundary for heat integration in petrochemical complexes which are composed of several interconnected processing units. In order to obtain retrofit schemes that offer significant energy saving potential and are easy to implement, heat integration strategies are also developed in this study. Two case studies based on an aniline plant and an aromatic hydrocarbon plant, each one comprising several processing units, are presented to illustrate the application of these principles and strategies. The boundary for heat integration in each plant can be the whole plant or its individual processing units, the choice of which is determined by their energy saving potentials. Based on energy saving potential, each processing unit in the aniline plant was selected as the boundary for heat integration. The boundary for heat integration in the aromatic hydrocarbon plant, by contrast, was the whole plant. Retrofit schemes for the heat exchanger networks of the two plants, developed using pinch analysis, revealed that significant heating utility savings could be realized with a small number of network structure modifications.

Increase in refining demand and tighter environmental regulations have led to sharp increases in hydrogen consumption of oil refineries. Hydrogen conservation and effective use are of interest to refineries whose operations and profitability are constrained by hydrogen. Purification is widely used in hydrogen networks of refineries to reduce hydrogen production load. To minimize hydrogen utility consumption, it is necessary to optimize the hydrogen network with purification as a whole. In this paper, for hydrogen purification process, a triangle rule (which can be generalized to polygon rule) is proposed for graphical representation of its mass balance. The proposed procedure treats the product concentration and recovery rate of the purification process as adjustable parameters. An ensuing graphical method is developed for targeting the pinch point and minimum utility consumption of the hydrogen system with purification reuse. This graphical method can be used for any purification devices and in systems with any utility concentration. A refinery case is studied to demonstrate the optimization method.

Emergy analysis is able to account for ecosystems’ contribution to industrial activity. Accordingly, it is an ecologically conscious tool useful for assessing the environmental impact and sustainability of industrial systems. The emergy-based approach requires proper system boundary definitions and uses several standard indices. In this article some perspectives on the deficiencies of three standard emergy indicators – environmental loading ratio (ELR), emergy yield ratio (EYR) and emergy index of sustainability (EIS) – when applied to industrial systems involving waste management are put forward and suggestions for overcoming them given. In addition, in order to account for the impact of waste emissions on the environment, a simple impact amplification factor is proposed for inclusion in the improved emergy indicators. To demonstrate their usefulness and highlight their superiority over standard indices, the improved emergy indicators are used to evaluate the interaction between a commercial polyethylene production process incorporating waste management and its surrounding environment.

Hydrogenation units are often operated at high pressure, requiring the use of compressors which are one of the most expensive chemical processing equipment. Optimizing a hydrogen network should therefore take into consideration not only purity and flowrate constraints but also pressure requirements. In this paper, based on the hydrogen surplus diagram approach, the average pressure profiles of hydrogen sources and sinks are proposed through the introduction of a system’s minimum pressure drop Δp. Combined with the traditional purity profiles, whether a source can meet a sink either for hydrogen concentration or for pressure requirements can be determined intuitively. In cases where the pressure of a source is not sufficient for a sink, installing a hydrogen compressor or using another source with higher purity and pressure could be potential solutions. A cost equation is established to determine which of the two solutions is economically more viable. For different matching situations between sources and sinks, strategies for optimum placement of compression equipment within a given hydrogen network are proposed. A case study is used to illustrate the application and effectiveness of the proposed method.

The Bohart-Adams model and the so-called Thomas model are commonly used in the modeling of fixed bed breakthrough curves in environmental sorption and biosorption research. Some authors fit the two equations to the same set of experimental breakthrough data and compare their modeling capabilities, implying that the two expressions are separate and independent models. This article clarifies unambiguously and demonstrates conclusively that the two models are in reality mathematically equivalent to each other and their parameters interchangeable. The salient features of the Bohart-Adams model and the genuine Thomas model are outlined here and their relationship delineated. The main difference between the Bohart-Adams and actual Thomas models lies in the form of the sorption isotherm assumed. The former assumes a rectangular (irreversible) isotherm while the latter assumes a Langmuir (favorable) isotherm. It is shown that, when the sorption isotherm is highly favorable, the actual Thomas model reduces to the Bohart-Adams model.

On the grand composite curve of a heat exchange network, a heat pocket exists when a local heat source above the pinch point or a local heat sink below the pinch point appears. In this paper, heat recovery in the heat pocket is presented by combining the pinch technology and exergy analysis. When the heat pocket is big, hot streams in the pocket can be used to generate a higher level utility, and the cold streams in the pocket can be heated by a lower level utility. In this way, exergy loss can be reduced, and the process's efficiency can be improved. The heat exchange network of a hydrogen production process is used as a case study. The energy performance of the heat exchange network can be further improved by recovering the heat in the heat pocket, compared with the scheme based only on pinch technology.

The removal of methyl violet 2B, a cationic dye, from water using two kinds of strong-acid cation exchange membranes, ICE 450 supported (with sulfonic acid groups and ion exchange capacity of 9.6–31 μeq/47 mm disc) and P81 (with phosphate groups and ion exchange capacity of 312 μeq/47 mm disc), was investigated in this study. In the batch process, the adsorption isotherm results show that the P81 membrane exhibited a greater maximum adsorption capacity than the ICE 450 supported membrane. However, the latter exhibited stronger and faster dye adsorption behaviors. Different desorption solutions were tested in the batch desorption process and, for both membranes, the best desorption performance (∼100%) was achieved with an aqueous solution containing 1 M NaCl in 60% methanol. In the membrane chromatography process with one piece of 47 mm membrane at a flow rate of 1 or 8 mL/min, complete dye removal and recovery from a 20 mL feed with an initial dye concentration of 0.015 g/L could be achieved for both membranes. The performance of both membranes remained practically unaltered during three successive cycles of dye adsorption and desorption. Lastly, to mimic the effluent produced by a typical dyehouse, a synthetic dye wastewater made up of 0.03 g/L methyl violet 2B and 2 g/L Na 2 SO 4 at pH 3 and 100 °C was prepared and treated by both membranes in the membrane chromatography process. The extent of dye removal was decreased to 84–93% for the P81 membrane, which may be attributable to either salt ion competition or pH influence. By contrast, the ICE 450 supported membrane could attain nearly complete dye adsorption and desorption.

Two commercial anion exchange membranes, strong basic (SB6407) and weak basic (DE81), were evaluated for the removal of anionic reactive dyes, Cibacron blue 3GA (three sulfonic acid groups per dye molecule) and Cibacron red 3BA (four sulfonic acid groups per dye molecule), from water in this study. The adsorption isotherm results show that the Langmuir maximum adsorption capacities of Cibacron blue 3GA (31.5mg/cm(3) for SB6407 and 25.5mg/cm(3) for DE81) were greater than those of Cibacron red 3BA (24.5mg/cm(3) for SB6407 and 18.5mg/cm(3) for DE81). For each reactive dye, the capacity for SB6407 was higher than DE81 based on the same membrane volume. However, consideration of the number of ion exchange sites interacting with a dye molecule indicates that the DE81 results are close to the theoretical values while the SB6407 membrane had some unused binding sites. In addition, Cibacron red 3BA demonstrated faster and stronger binding with both anion exchange membranes than Cibacron blue 3GA. Both dyes could bind with strong basic SB6407 more quickly and stronger. In the batch desorption process, different desorption solutions were tested and the mixtures of salt, acid, or base in methanol solution (e.g. 1N KSCN in 60% methanol or 1N HCl in 60% methanol) achieved better performance. Finally, in the flow process with one piece of anion exchange membrane (initial dye concentration of 0.05g/L), SB6407 was found superior to DE81 in dye recovery and both membranes retained their original uptake capacities over three cycles of adsorption, washing, and desorption.