Multicomponent Feed Stream Research Articles

Raman spectroscopy for real-time concurrent detection of multiple scalants on RO membranes

In-situ monitoring techniques of reverse osmosis (RO) desalination systems, particularly those with chemical sensing capabilities, can provide the means for better understanding important scaling mechanisms as well as early scaling detection. In this work, both calcium sulfate and calcium carbonate scaling on RO membranes were detected concurrently in real time using Raman spectroscopy to provide a unique chemical fingerprint. Two different sampling methodologies (manual and automated) were employed, and their performance was evaluated by comparing the Raman detection times to concurrent values of flux decline. The manual sampling strategy resulted in the detection of calcium sulfate and calcium carbonate at mean permeate flux declines of 13 ± 10 % and 22 ± 3 %, respectively. The automated sampling strategy provided better performance, with detection of calcium sulfate and calcium carbonate at mean flux declines of 8 ± 5 % and 4 ± 3 %, respectively. The increased sensitivity and decreased variability of the automated sampling strategy provided valuable preliminary insights for the selection of optimized sampling strategies. The ability to identify the chemical composition of different scaling crystals including their polymorphs is an important step toward better understanding of the crystallization pathways of multi-component feed streams used in seawater and brackish water RO desalination.

DATA: Diafiltration Apparatus for high-Throughput Analysis

Improved characterization techniques, which address knowledge gaps related to the interfacial processes that govern solute–solute selectivity and the performance of membranes in complex multi-component feed streams, are necessary to advance membrane processes. In this study, guided by the tools of data science, a diafiltration apparatus is developed to inform material and process design by rapidly characterizing membrane performance over a broad range of feed solution compositions. The apparatus doses a fixed-concentration diafiltrate solution into a stirred cell to achieve a predetermined change in the retentate concentration. Here, using an 80 mM potassium chloride (KCl) diafiltrate solution, it was shown that membrane performance, within a 5 mM to 80 mM KCl phase space, could be probed five times more quickly with one diafiltration experiment (8 h) than with an experimental campaign using traditional filtration processes (47 h). Additionally, the synergy between data analytics and instrumentation led to the incorporation of an inline conductivity probe that monitored the real-time retentate concentration. This additional information provided key insights to distinguish between the mechanisms that govern membrane separations (e.g., discriminating between adsorption or rejection based separations) and allowed for the membrane transport coefficients to be determined accurately. Ultimately, incorporating the appropriate governing phenomena identified a single set of self consistent transport parameters for commercial NF90 membranes.

A new approach for the optimization of nonsharp distillation superstructures

AbstractIn general, the optimization problem of the separation of a multicomponent feed stream into two or more multicomponent products with the use of nonsharp distillation columns is an MINLP with a nonlinear objective function. Due to the high number of variables and the high degree of nonlinearity, the presentation of a comprehensive and simple three‐phase approach was considered to solve the Mixed Integer Nonlinear Programming (MINLP) using the combination of mathematical and stochastic methods. In the method, the variables are classified into two groups: A set of variables are optimized by genetic algorithm as a stochastic algorithm; doing so converts MINLP to Linear Programming (LP), and the remaining variables are managed by solving an LP problem for known values of the former set by a regular and quick mathematical method such as simplex search. One advantage of this study is that it extracts some essential relationships between the first set of variables by the mathematical operations on the nonlinear constraints of the main problem as these variables are not optimized altogether; instead, some of them are optimized and the rest are obtained with the assistance of those relationships. Thus, the optimization workload (in both parts of GA and LP problem) is very low and the best structure can be obtained in a very short time (less than 2 min). Also, the study applies the lowest reduction on the main superstructure than previous works and therefore, the generalization of the problem is further preserved. Three published examples are used to verify the proposed method.

Design of dividing wall columns for butanol recovery in a thermochemical biomass to butanol process

In this work, ternary and quaternary dividing wall column (DWC) configurations for the separation of a multicomponent feed stream from a novel thermochemical lignocellulosic biomass to butanol process are designed, modeled and assessed. The goal is to separate the feed into four major products, with a key product being a biobutanol rich stream. Due to the complexity of DWC models, a shortcut modeling approach based on the minimum energy mountain method (also called the “Vmin diagram method”) is used to determine good initial values for the decision variables for the rigorous simulation of the DWC configurations. Furthermore, each DWC configuration is optimized to minimize the total annualized cost with the use of a derivative free algorithm coupled with a process simulator. The results show that the quaternary DWC configuration achieves up to 31% energy savings, and 15% capital savings in comparison to a conventional distillation sequence, and is thus a better option for implementation in the biofuel process.

Optimal Synthesis of Ethylene Production Process

This work addresses the energetic and economic optimization for the synthesis of distillation-based ethylene production. We employ a model-based optimization approach to determine the optimal sequencing of processes for olefins separation that involves handling a multicomponent mixture. The optimization model is formulated based on a superstructure that embeds many possible and feasible structural alternatives for processing a number of hydrocarbon components constituting gaseous ethane or liquid naphtha. We adopt linear mass balance reactor models for conversion of materials into desirable products and simple sharp distillation column models based on split fractions for product recovery from a multicomponent feed stream. The formulation leads to a mixed-integer linear program (MILP) with discrete 0–1 variables on task selection and continuous variables on input flowrate to each task. To aid convergence to the optimal system synthesis with minimum total annualized cost, the model incorporates heuristic-based logical constraints that represent design and structural specifications on engineering knowledge, design experience, and rules of thumb. The model is implemented on case studies drawn from actual operating petrochemical plants in Malaysia with reasonable computational results.

On-line and real-time monitoring of organophilic pervaporation by mass spectrometry

This work demonstrates experimentally the use of mass spectrometry (MS) for on-line, quantitative monitoring of organophilic pervaporation processes operated not only under variable conditions of temperature of condensation/downstream pressure but also when using complex multi-component feed streams. Due to its high sensitivity, mass spectrometry is particularly suitable for on-line monitoring of aromas in dilute streams under reduced pressure, as happens with natural aromas in permeate streams. Mass spectrometry is also suitable for on-line monitoring of solvent and co-solvent permeants (water and ethanol in the selected case study), enabling for on-line determination of selectivity of the solutes of interest. A new method of calibration is proposed and validated, which correlates the intensity of the characteristic mass peak m i / z for each compound of interest with its partial pressure in the permeate stream. Moreover, mass spectrometry proves to be a powerful tool for studying the fractionation of aromas, recovered by integrated pervaporation–condensation processes, allowing on-line monitoring of each solute vapour in the permeate stream. Additionally, this technique enables for accurate transient studies due to the possibility of acquiring one data point every 12–15 s (potentially less, if desired) in real-time.

Economic optimization of non-sharp separation sequences by means of evolutionary algorithms

The general distillation sequence synthesis problem featuring the separation of multicomponent feed streams into multicomponent products is addressed. Potential flowsheets include stream bypassing and mixing and use sharp separations as well as non-sharp splits where key component distribution is allowed. Compared to conventional sharp distillation sequence synthesis, this leads to a mixed-integer non-linear programming problem of increased complexity, including non-convexities as well as multi-modalities. Product specifications create additional constraints while simultaneously call for a rigorous modeling of the non-key distribution. A synthesis method is proposed that models the various flowsheet configurations with a new and flexible superstructure concept and connects the gradient-free optimization technique of application-orientedly developed Evolutionary Algorithms (EAs) to the rigorous modeling capabilities of the Aspen Plus ™ simulation system, thus enabling realistic process design and cost objective function calculation. The re-examination of two published examples illustrates the applicability and the potential of the approach.

Transmission and fractionation of micro-sized particle suspensions

In processes aimed at the fractionation of a multi-component feed stream, transmission of particles through the membrane is at least as important as retention of larger particles. In this paper, we describe the mechanisms of transmission of mono-disperse latex particles through a polymer membrane. The effects of process parameters, such as transmembrane pressure, cross flow velocity and feed concentration were investigated. In dead end filtration mode, we found that, depending on the transmembrane pressure, four particle transmission regimes could be distinguished. Particle deposition on polymer membranes and polymer microsieves was investigated in-line with confocal scanning laser microscopy (CSLM). It was observed that with the polymer membrane random depth deposition took place, while the microsieve exhibited in-pore fouling. In addition, bi-disperse particle suspensions were fractionated with dead end and cross flow membrane filtration, and various effects were charted. Based on the phenomena observed, it is concluded that the design of a fractionation process starts with defining a stable transmission regime for small particles, and subsequently choosing the process conditions for minimal deposition of the larger particles.

Synthesis of separations by batch distillation

The batch distillation synthesis problem for separating a single multicomponent feed stream into specified products using available equipment is addressed. A mathematical programming approach for solving the single column synthesis problem is presented. The method consists of proposing a superstructure which has embedded in it all possible combinations of conducting the desired separation, formulating the superstructure as an optimization problem, and solving the resulting nonlinear program using available optimization software. Standard optimization techniques and a shortcut model for batch distillation simulation are used in the proposed methodology. The sequence of overhead fractions during distillation, the cut location, and the reflux ratio policy during each cut are decision variables in the optimization formulation. The effectiveness of the proposed procedure is demonstrated on a series of example problems.

Synthesis of heat integrated nonsharp distillation sequences

This paper addresses the synthesis problem of separating a multicomponent feed stream into several multicomponent product streams of given compositions using nonsharp distillation columns while considering heat integration options. A general superstructure is proposed that contains all possible sequences (by allowing all alternatives for stream splitting, mixing and by passing) and allows heat integration between the condensers and reboilers of various columns. The pressure of each column, as well as the key component recoveries, are treated explicitly as optimization variables. The mathematical model for this superstructure is a mixed-integer nonlinear programme (MINLP). This formulation is solved using a two-level decomposition approach in which the material balance equations are solved in an outer loop while the heat integration options are optimized in an inner loop. The proposed approach is illustrated with two examples.

Synthesis of general distillation sequences—nonsharp separations

The synthesis problem of distillation sequences that separate a given multicomponent feed stream into several desired multicomponent product streams, while allowing nonsharp separations in the columns, is addressed. A superstructure is proposed that contains options for distribution of the light and heavy key components, all possible sequences and all alternatives for stream splitting, bypassing and mixing. Light and heavy key component recoveries define the nonsharpness of separation and are treated explicitly as optimization variables. This superstructure is modeled as a mixed-integer nonlinear programming (MINLP) formulation whose objective is to minimize the total annual cost. Shortcut simulations and regression analysis are used to develop cost functions to be used in this formulation. The solution of the MINLP formulation results in an optimal separation sequence that may involve sharp and/or nonsharp distillation columns. The nature of the proposed mathematical formulation is investigated and the search for a global optimum solution is performed using a new decomposition approach. The proposed approach, which is implemented automatically in the procedure NOUS (NOt Universally Sharp separation), is illustrated with six example problems and the results show that using nonsharp separations can result in savings of 10–30% and even 70% in some cases (see Example 2) as compared to sharp sequences. It is also illustrated that columns with nonadjacent key components can be included easily by extending the proposed approach.

Synthesis of distillation sequences with several multicomponent feed and product streams

In this paper the synthesis problem of distillation-based separation sequences that separate a number of multicomponent feed streams into a number of multicomponent products is addressed. A synthesis strategy is proposed that consists of: (a) the development of a distillation-based superstructure that has embedded many separation configurations as well as options for splitting, mixing and by-passing; (b) simulation runs performed for each of the distinct distillation columns involved in the superstructure; and (c) the mathematical formulation of the distillation-based superstructure as a mixed-integer linear programming problem which has as unknowns the stream interconnections. The solution of this mathematical formulation results in the optimal configuration of distillation columns that can perform the desired separation task, as well as in the optimal allocation of by-passes. The synthesis strategy is illustrated with the first two example problems while the third example demonstrates the use of the proposed approach as an initialization procedure for the general separation problem.

Separation synthesis of multicomponent feed streams into multicomponent product streams

AbstractThe synthesis problem of separation sequences that separate several multicomponent feed streams into several desired multicomponent product streams is addressed. A superstructure is proposed for this separation problem that has embedded all the alternative separation configurations of interest. This superstructure, which has as separator units the separation tasks that are defined for each separation breakpoint, involves options for series and/or parallel sequences, as well as stream splitting, mixing, and bypassing. Formulating and solving this superstructure as a nonlinear programming problem that has as unknowns the stream interconnections, results in an optimal separation sequence. This sequence, which may involve fewer separator units than those included in the superstructure, is shown to be a realistic and practical one. The synthesis approach is illustrated with four example problems.