Article pubs.acs.org/IECR
Multiobjective Optimization Applied to the Integration of Polyamide and Cellulose Acetate Reverse Osmosis Membranes in Hybrid Cascades for Ultrapurification of Wet Chemicals R. Abejón,†,‡ A. Garea,*,† and A. Irabien† †
Departamento de Ingenierías Química y Biomolecular, Universidad de Cantabria, Avda. Los Castros s/n, 39005 Santander, Cantabria, Spain ‡ Institut Européen des Membranes, UMR 5635 (CNRS-ENSCM-UM2), CC 047, Université de Montpellier 2, 2 Place Eugène Bataillon, 34095 Montpellier Cedex 5, France S Supporting Information *
ABSTRACT: The present work is focused on three main aims. The first one is the comparison of commercial polyamide (BE from Woongjin Chemical) and cellulose acetate (CE from GE Osmonics) reverse osmosis membranes when applied to the ultrapurification of aqueous hydrogen peroxide solutions. The second one is the search for possible advantages of combination of both types of membranes, which show quite different characteristics, under a hybrid cascade configuration. The results demonstrated that the employment of only polyamide membrane cascades is more competitive than hybrid systems for this application. The third one is the analysis of the influence of the product quality over the optimal economic cascades. The polyamide membrane systems were then formulated adding product quality metrics to economic criteria to afford a bicriteria nonlinear programming (NLP) problem. The Pareto solutions to the multiobjective problem were generated via the epsilon constraint method. On the one hand, maximum economic profit solutions corresponded with the configurations applying bypass. On the other hand, maximum quality solutions were obtained by low recovery rates (specifically in the last stages of the cascade).
1. INTRODUCTION Electronic chemicals, which are the chemicals and materials used to manufacture and package semiconductors and printed circuit boards, require extremely low content of metallic impurities to minimize reliability problems in microdevices.1,2 In order to avoid contamination because of the chemicals themselves, ultrapurification processes become necessary to achieve these exigent limits.3 Hydrogen peroxide (H2O2) is one of the most employed liquid phase electronic chemicals, which are also called wet chemicals, because it is employed for cleaning silicon wafer surfaces of organic matter, particulated contamination, and metallic impurities.4−6 It is also useful to remove photoresists and etch copper on printed circuit boards. For the particular case of hydrogen peroxide, the requirements imposed to be accepted as electronic grade chemicals are defined by the SEMI C30-1110 Document.7 This standard was developed by the SEMI organization, which is the global industry association serving the manufacturing supply chains for the microelectronic, display, and photovoltaic industries, and includes the main characteristics electronic grade hydrogen peroxide must fulfill. Therefore, hydrogen peroxide was selected as a case study for investigation of wet chemical ultrapurification by reverse osmosis membranes. Reverse osmosis membrane processes have demonstrated their technical and economic viability for hydrogen peroxide ultrapurification from technical grade chemical to semiconductor requirements.8,9 Both polyamide (PA) and cellulose acetate (CA) reverse osmosis membranes have been tested for this purpose.10 These types of membranes show very different characteristics, specifically when they are applied to separation processes in such an oxidant medium as © 2014 American Chemical Society
concentrated hydrogen peroxide. Both permeate productivity and solute removal efficiency of PA membranes use to be higher than those of CA membranes.11−13 However, the chemical resistance of CA membranes is the property that counterbalances their performance drawbacks. CA membranes exhibit comparatively better long-term stability under oxidative conditions than PA membranes. The most studied case of reverse osmosis membranes degradation because of oxidant chemicals is the application of disinfectant products based on chlorine derivatives which are commonly used in the fields of brackish and seawater desalination, wastewater treatments, and membrane bioreactors to control biofouling.14−16 The general trends identified for chlorine-based chemical can be extrapolated to concentrated hydrogen peroxide but taking into consideration drastic reductions on the lifetimes of the membranes.10,17 Thereby, it can be concluded that PA membranes appear as more productive in terms of permeate flux and rejection performance, but the effective lifetime of CA membranes is longer when they are employed for hydrogen peroxide ultrapurification. While the incorporation of different pressure-driven membrane technologies such as microfiltration, ultrafiltration, nanofiltration, or reverse osmosis to design advanced separation processes is common.18−23 separation processes that combine different types of membranes of the same technology have not Received: Revised: Accepted: Published: 1006
June 24, 2014 November 26, 2014 December 23, 2014 December 23, 2014 DOI: 10.1021/ie502525z Ind. Eng. Chem. Res. 2015, 54, 1006−1014
Article
Industrial & Engineering Chemistry Research
The ultrapurification of hydrogen peroxide was selected as a case study. Industrial-scale membrane cascades were designed to be coupled to a hydrogen peroxide production plant with a capacity of 9000 ton/y of technical grade peroxide. The metallic impurity content of the technical grade peroxide can be found in ref 28. A membrane cascade was proposed for each electronic SEMI grade, from 1 to 5. The reverse osmosis membranes selected for the cascades were the BE model from Woongjin Chemical, which is made of polyamide (PA), and the CE model from GE Osmonics, which is made of cellulose acetate (CA). Both membranes have been selected among different reverse osmosis membranes which were tested for hydrogen peroxide ultrapurification.29 The transport model parameters obtained after a complete characterization of the membrane performance can be found in a previous work,10 and the rest of the technical and economic parameters required by the model are shown in Table 1.
been studied so deeply, but their integration within a membrane cascade has been even less investigated. Membrane cascades can be very useful to implement demanding separation processes when moderate rejection limits the application of a single membrane stage.24,25 Integrated countercurrent cascades combine high selectivity for solute removal and elevated mass yield and have been successfully applied to wet chemicals ultrapurification.26 The technical and economic consequences of the selection between PA and CA membranes for the ultrapurification cascade have just started to be investigated.10 Nonetheless, both types of membranes seemed to be competitive within different economic scenarios conditions, so the objective of the present work was to advance in the analysis of the potential of optimal PA and CA membrane cascades for hydrogen peroxide ultrapurification and the comparison between both classes of cascades. The referenced papers of this research group summarized the results obtained working with PA and CA membranes for the purification of hydrogen peroxide grade 1, experimental and simulation results of the optimized systems. The novelty of this work can be resumed in two tasks: (i) the economic optimization of the systems to produce hydrogen peroxide from grade 1 to grade 5, the strictest quality product and (ii) the introduction of the quality requirements into the optimization problem by the multiobjective formulation where the hybrid cascades that combine PA and CA membranes are also considered and contrast the results with those corresponding to installations employing only one type of membranes.
Table 1. Technical and Economic Parameters of the Proposed Model Technical Parameters parameter η LTmemPA LTmemCA LTinst
2. CASCADE MODELING AND CASE STUDY Descriptions of n-stage integrated countercurrent membranes have been given in previous publications of this research group.10,26 The proposed mathematical model for this type of integrated countercurrent membrane cascades is based on overall and solute (metallic impurities) material balances and the simplified Kedem−Katchalsky membrane transport equations.27 The economic considerations of the model are based on the assessment of the total daily revenues (Rev) and costs (TC) and the corresponding profit (Z) as difference between both terms. The electronic grade hydrogen peroxide obtained as the final stage permeate is the product of the ultrapurification system, but the retentate of the first stage can also be considered as a valuable byproduct, since it can be commercialized as nonelectronic grade chemical, so these two circumstances have to be taken into consideration to evaluate the revenues of the process. The total costs of the process are defined as the sum of the capital costs (CC) and the operation costs (OC). The capital costs attributable to membranes or to the rest of the installation are differentiated, while the operation costs are itemized into four categories: raw materials, labor, energy, and maintenance. The electronic grade hydrogen peroxide quality is formulated as a dimensionless safety factor SF, defined as the quotient between the limit concentration (fixed by SEMI standard limiting requirements) CSEMI and the product concentration CEG: SF =
CSEMI failure concentration = C EG design concentration
unit
value
d d d Economic Parameters
0.70 3 9 1825
parameter
unit
value
Kmemb Ymemb Yraw YEG1 YEG2 YEG3 YEG4 YEG5 Yby Ylab Yelec CCclean
$/m2 $/m3 $/m3 $/m3 $/m3 $/m3 $/m3 $/m3 $/h $/kW·h $/d
0.12 50 790 2592 3537 3780 8721 11826 600 7 0.08 2590
The daily profit Z was selected as objective function to maximize. All the model variables have been expressed in terms of the independent operation variables (recovery ratios Reci and applied pressures ΔPi). Constraints for the independent variables have been set to limit their values to defined ranges: 0.3−0.9 for recovery ratios, 10−40 bar for applied pressures over PA membranes, and 10−30 bar over CA membranes. The problem resulted in mathematical terms as a nonlinear programming one (NLP), which can be expressed as follows: max N (x) = {Z(x)} s.t.
h(x) = 0 g (x) ≥ 0 xL ≤ x ≤ xU
(1)
x ∈ 9n
According to the definition of the safety factor SF, each metallic solute implies a different safety factor. Nonetheless, the safety factor of the final product is the minimal value among the several individual factors corresponding to each metal.
where Z is the daily profit, x is the vector of continuous independent variables ΔP(i) and Rec(i), h is the vector of equality constraint functions (material balance equations, 1007
DOI: 10.1021/ie502525z Ind. Eng. Chem. Res. 2015, 54, 1006−1014
Article
Industrial & Engineering Chemistry Research transport equations, and economic considerations), and g is the vector of inequality constraint functions that define the product requirements based on the concentration limits for each metal imposed by the SEMI standard. The General Algebraic Modeling System (GAMS) is a highlevel modeling system for mathematical programming and optimization. It consists of a language compiler and a stable of integrated high-performance solvers. This software was selected as optimization tool to manage the model using CONOPT3 solver. All the problems have been run on a dual core processor PC at 1.60 GHz with 2 GB RAM, and the most demanding runs (above 2500 variables and 10 300 nonzero elements) have taken no more than 340 CPU seconds, counting between 5000 and 6500 iterations to finish.
Table 2. Economic Breakdown of the Optimization Results H2O2 grades grade 1
grade 2
grade 3
grade 4
grade 5
6
7
165657 189132 23474 3977 1371 2607 19497 19110 168 20 199
232170 255896 23726 4213 1604 2609 19512 19110 168 23 211
36
49
129995 186755 56760 34982 31261 3721 21778 19110 168 751 1749
184473 253981 69508 46861 42726 4135 22647 19110 168 1026 2343
27
36
124571 184284 59713 37710 33894 3816 22003 19110 168 839 1886
175498 247333 71835 48998 44788 4210 22837 19110 168 1109 2450
a
number of stages 2 economic terms ($/d) Z 34928 Rev 57405 TC 22477 CC 3041 CCmemb 446 CCinst 2595 OC 19436 OCraw 19110 OClab 168 OCen 6 OCm 152
3. RESULTS AND DISCUSSION 3.1. Economic Optimization of Simple Cascades. The main optimization results for both types of membranes, which include the optimal number of stages in the cascades and the maximum economic profit, can be seen in Figure 1, whereas all
PA membrane 4 5 54696 59668 77677 82891 22972 23223 3505 3741 904 1137 2601 2604 19467 19482 19110 19110 168 168 13 17 175 187 CA membrane 13 24
number of stages 8 economic terms ($/d) Z 33692 44595 38147 Rev 57332 74662 79134 TC 23640 30067 40988 CC 4132 10117 20291 CCmemb 1488 7264 17083 CCinst 2644 2853 3208 OC 19508 19950 20696 OCraw 19110 19110 19110 OClab 168 168 168 OCen 23 166 404 OCm 207 506 1015 CA membrane (suboptimal) number of stages 5 10 21 economic terms ($/d) Z 32601 43989 37584 Rev 57022 73881 78639 TC 24421 29893 41055 CC 4853 9949 20348 CCmemb 2184 7102 17138 CCinst 2669 2847 3210 OC 19568 19944 20706 OCraw 19110 19110 19110 OClab 168 168 168 OCen 48 168 411 OCm 243 497 1017
Figure 1. Optimal PA and CA membrane cascades for production of each grade.
the corresponding economic terms are shown in Table 2. This table incorporates another third case which is called CA suboptimal. The CA suboptimal solution was defined as that solution which was able to obtain more than 95% of the maximum profit corresponding to the optimal CA cascade with the lowest number of CA membrane employing stages. As can be observed in Figure 2, the differences between the optimal solutions and a solution with a number of stages close to the optimal value were not very significant for CA cascades. For example, the profits of the cascades comprising 48 and 50 stages for SEMI grade 5 production were around 750 $/d lower than the optimal profit by a 49-stage cascade, which resulted in differences below 0.4%. For this reason, it was decided to determine the CA suboptimal solutions, as they can be considered more easily operated and controlled systems (for the case of grade 5, the suboptimal solution implied the elimination of 13 stages) when 5% reductions on profit were assumed. In order to obtain totally comparable results, the quality of the products obtained by optimal PA membrane cascades was imposed as production target for the CA membranes cascades. PA cascades were optimized in a previous work,26 and while sodium was the limiting impurity (impurity whose concentration is closer to the SEMI limit) for all the PA cascades, sodium was only the limiting impurity for SEMI grade 1 peroxide obtained by CA cascades. For the rest of the grades (from 2−5) boron became the most problematic impurity. This fact was easily
a
PA results from the work of Abejón et al.26
explained by the very poor rejection that the CA membrane shows for boron, with a rejection coefficient below 0.17 even for the highest applied pressure that produces the uppermost removal. Nevertheless, it is clear that the CA cascades can not be considered competitive when compared with PA ones, as the profit differences were always favorable to the use of the latter membranes. The higher the quality of the produced hydrogen peroxide, the more advantageous the PA cascade: more than 1200 dollars of extra daily profit were obtained for SEMI grade 1 chemical, but the difference increased to more than 47 000 $/d for grade 5. The CA suboptimal systems are the least profitable ones. Although a reduced complexity was anticipated because of a lower number of stages when compared to the optimal cascades, the comparison of the costs due to membranes 1008
DOI: 10.1021/ie502525z Ind. Eng. Chem. Res. 2015, 54, 1006−1014
Article
Industrial & Engineering Chemistry Research
Figure 3. Mean recovery ratio for each optimal CA cascade. Figure 2. Comparison of optimal PA and CA membrane cascades with no optimal cascades for grade 5 peroxide production.
Table 4. As it can be seen, the percentage contribution of the membranes to the total costs increased until more than 65% for
demonstrated that the suboptimal cascades required higher total membrane area. This fact can be explained by the need of more recirculated streamflow to obtain the same quality in less stages and the corresponding extra area required in the stages which received these recirculated flows. Therefore, the design and employment of CA suboptimal cascades can be hardly justified. The optimal operation conditions for grade 1 peroxide production by both types of cascades are shown in Table 3. As
Table 4. Cost Contributions under Optimal Conditions H2O2 grades contributions to total costs (%) CC CCmemb CCinst OC OCraw OClab OCen OCm
Table 3. Optimal Operation Conditions for SEMI Grade 1 Production PA membrane
CA membrane
stage
Rec
ΔP (bar)
Rec
ΔP (bar)
1 2 3 4 5 6 7 8
0.900 0.900
40 40
0.900 0.900 0.900 0.744 0.900 0.698 0.900 0.900
30 30 30 30 30 30 30 30
CC CCmemb CCinst OC OCraw OClab OCen OCm a
it can be observed, the optimal PA cascade was characterized by maximum allowed values for both recovery ratios and applied pressure (the upper limits for these variables were 0.9 and 40 bar respectively). This situation was recurrent for the rest of grades, since the optimal values were always the fixed upper limits. For the CA cascade, the optimal applied pressures were also the maximum allowed values (in this case 30 bar), but the recovery ratios in some stages were not equal to the upper limit: values for the fourth and sixth stages were lower than 0.9. After an analysis of the resting grades, the same trend was found. The applied pressures were 30 bar for all the cases, but the recovery ratios took values from 0.3 to 0.9. Figure 3 shows the evolution of the mean values for the recovery ratios in the optimal CA cascades. The lower the impurities in the obtained chemical, the lower the mean recovery ratio. It decreased from 0.855 for grade 1 to 0.555 for grade 5. It can be concluded that the most exigent purity requirements can be only reached by the CA cascades when high recirculation of partially purified streams is implemented, fact that implies low recovery ratios. This condition involves higher total membrane areas in the systems, which has to be added to the higher number of stages. The breakdown of the total costs for the optimal solutions with the corresponding percentage contributions are compiled in
grade 1 grade 2 grade 3 grade 4 grade 5 PA membrane 13.5 15.3 2.0 4.0 11.5 11.3 86.5 84.7 85.0 83.2 0.8 0.7
