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An Integrated Experimental/Techno-economic Analysis of the Lifetime of Pd-Au Membranes Bernardo Castro-Dominguez, Liang-Chih Ma, Ivan P. Mardilovich, Nikolaos K. Kazantzis, and Yi Hua Ma Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.6b01898 • Publication Date (Web): 07 Sep 2016 Downloaded from http://pubs.acs.org on September 10, 2016

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Industrial & Engineering Chemistry Research

An Integrated Experimental/Techno-economic Analysis of the Lifetime of Pd-Au Membranes Bernardo Castro-Dominguez1,a, Liang-Chih Maa, Ivan P. Mardilovicha, Nikolaos K. Kazantzisa,*, Yi Hua Maa a

Center of Inorganic Membrane Studies (CIMS), Department of Chemical Engineering, Worcester Polytechnic Institute, 100 Institute Road, 01609 Worcester, MA, USA.

Abstract Palladium and palladium/alloy membranes have shown to be an effective technology option for the production of pure hydrogen. In particular, Pd/Au membranes have displayed superior chemical stability and separation performance. However, the lack of industrial operating experience gives rise to technological uncertainties such as the lifetime of the membranes which could potentially prevent the deployment of this new technology option. In light of the above recognition, the primary aim of the present research work is to combine long-term H2 membrane permeance and He leak characterization tests (cumulative testing over 2.2 years) conducted to estimate the lifetime of composite asymmetric Pd/Au membranes at different thicknesses with a comprehensive economic performance assessment framework in the presence of inherent tradeoffs between permeance, thickness and membrane lifetime. The experimental results are depicted in terms of the produced H2 purity and flux at different testing times and various membrane thickness values. Using these experimental results, the lifetime of the membranes is estimated and integrated into the proposed economic assessment framework. The economic evaluation framework for H2 separation units is structured in a way that explicitly recognizes various uncertainty sources via Monte Carlo simulation techniques and assesses economic performance based on metrics such as fixed capital investment (FCI), total capital investment (TCI), total product cost (TPC) and the levelized H2 cost (LC). It is shown that the expected values of the derived FCI/TCI and LC profiles increase as the Pd layer thickness increases while the TPC one decreases with higher Pd layer thicknesses. Finally, Tornado diagrams for the LC are generated to comparatively characterize the importance of H2 permeance and membrane lifetime on the membrane system’s economic performance profile. Keywords Palladium membrane lifetime; Long-term permeance test; Economic performance assessment under uncertainty; Monte-Carlo simulation. 1

Author to whom correspondence should be sent; Address: 100 Institute Road, Department of Chemical Engineering, Worcester Polytechnic Institute, Worcester, MA 01609-2280, USA; E-mail address: [email protected], Phone number: +1-508-831-5853. *Part of this work was performed while N. Kazantzis was at Hughes Hall, University of Cambridge, UK. 1 ACS Paragon Plus Environment


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1. Introduction

The development of a hydrogen-based economy which reduces the dependence on fossil fuels and complements climate change mitigation strategies heavily relies on the generation of pure hydrogen. Therefore, the process of H2 purification is indispensable to satisfy different purity requirements such as in fuel cell technology with a minimum requirement of 99.99% as well as in hydro-cracking with only ∼70–80% purity target level [1]. Hydrogen purification can be achieved by different processes such as pressure swing adsorption (PSA), cryogenic distillation, and membrane separation [2,3,4]. Consequently, Palladium (Pd) and Pd/alloy membranes have been widely studied due to their high H2 permeability, theoretically extremely high hydrogen selectivity and chemical stability under hydrocarbon containing gas streams [5]. In particular, Pd/alloy composite membranes containing Au display a superior hydrogen flux than pure Pd membranes as well as enhanced stability and recoverability [6]. The performance of Pd/Au membranes has been successfully demonstrated under actual industrial settings by Mardilovich and Guazzone [7,8] where the performance of Pd, Pd/Au, Pd/Pt and Pd/Au/Pt membranes were tested under actual coal derived syngas for a cumulative time of 4275 h (equivalent to 178 days). Pd/Au membranes showed a high H2 purity level of 99.89% at 450 °C and 12.6 bar for over 200 h in a syngas atmosphere. Additionally, Catalano et al. [9] demonstrated the application of membrane technology applicable for membrane reactors at a large-scale used for the generation and separation of H2. Composite palladium membranes increased the CO conversion and H2 recovery in a water-gas-shift (WGS) reactor achieving a H2 production of 5.6 Nm3day-1 with a quality of 99.97-99.2%. Nevertheless, even though significant technical developments on this field have occurred since the 80’s, various physical and assorted technological features such as the ones pertaining to the lifetime of the aforementioned membranes remain uncertain. For instance, the phrase “longterm test” of membranes has been widely used in the pertinent literature ranging from 80 to 8,640 h [18,21,23] and therefore the estimation/determination of the lifetime of the membranes is fraught with challenges. Table 1 summarizes a literature review results corresponding to different “long-term” hydrogen permeation test times for Pd and Pd/Alloy membranes. Since the formation of pinholes is related to the movements of Pd crystallites [10], it is expected that at prolonged times and high temperatures which increase molecular mobility, the probability of pinhole formation increases, especially as the Pd layer thickness is reduced. Furthermore, it has been shown that the reduction of H2 flux on thicker membranes is economically unfavorable [11]. Therefore, it is naturally possible to identify a fundamental economic tradeoff between lifetime and the H2 flux as both characteristics are inherently determined by the membrane thickness. Consequently, in order to accelerate the potential industrial application of membrane technology, it is necessary to conduct a genuine long-term study that allows the seamless integration of a comprehensive analysis of the economic performance characteristics of this technology in the presence of the above fundamental tradeoff as dictated by the specific process parameters and conditions. It is important to mention that the lifetime of Pd and Pd/alloy

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membranes has been assumed in the pertinent literature to be of 5 years and that only four replacements are needed throughout a 25-year plant lifetime [12]. Due to the lack of accumulated operating experience at the commercial scale, economic evaluations for a new technology option realized by Pd-based membrane modules have been conducted based on theoretical estimates including the aforementioned lifetime. In specific, the studies reported by Ma et al. [11,13,14,15] have used detailed comprehensive baselines of economic indicators such as the Net Present Value (NPV) and Total Capital Investment (TCI), where various sources of uncertainty were also identified and integrated into the pertinent methodological framework. Their impact on the valuation profiles has been taken into account through Monte-Carlo simulation methods by which these uncertainties are propagated through the above economic models. As a result, these economic evaluations allowed for the derivation of economic performance outcomes in the form of distribution profiles that can be insightfully characterized in a statistical manner rather than single-point value approximations which occasionally lead to errors and flawed decision-making outcomes in valuation assessments [11,13,14,15,16]. Consequently, the objective of this work is to combine long-term H2 permeance results (highlighting the relationship between membrane thickness and lifetime within the context mentioned earlier) and a theoretical, yet comprehensive economic evaluation framework in the presence of uncertainty in order to explore the tradeoff between permeance-thickness and lifetime in terms of economic performance outcomes. The present paper is organized as follows: A description of the experimental procedure such as membrane fabrication and testing is described in Section 2. The structure and the associated tools of the proposed economic performance assessment framework are presented in Section 3. Section 4 encompasses the study’s main results as well as a detailed discussion on its key findings. Finally, some concluding remarks are provided in Section 5.



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Table 1. Results of long-term tests presented in the pertinent literature Membrane Thickness

Testing time

Reference

7 µm

2400 h

[17]

50-60 µm

12 months

[18]

Pure H2, 300–400◦C

50 µm

1440 h

[19]

Methanol Steam Reforming, 350 oC

15 µm

900 h

[20]

0.3-0.4 µm

160 h

[21]

Thermal cycling 25-400 oC

5.5 µm

960 h

[22]

Effect of H2S, 350-450 oC

15 µm

1200 h

[23]

19-28 µm

1100 h

[24]

Water-Gas Shift, 320-380 oC

1 µm

140 h

[25]

Pure H2 with heat treatments, 500-700 o C

4 µm

12-446 h

[26]

Natural gas reformate separation, 400 o C

4 µm

3600 h

[27]

4.7-13 µm

1200 h

[28]

4 µm

2040 h

[29]

Type of membrane

Conditions/Preparation/Application

Pd–23wt% Ag membranes/Porous stainless steel

H2/N2 mixture (50:50), 350-450 oC

Pd–23wt% Ag foils

H2/N2 mixture, 150-400 oC

Pd-25at% Ag cold-rolled membranes Pd membranes/Porous stainless steel Pd membranes/Porous titania ceramic Pd-Ag membranes/αalumina Pd-18wt% Cu membrane/Porous stainless steel Pd membranes/Porous stainless steel Pd membranes/Silicon wafer Pd membranes/Yttriastabilized zirconia/Porous stainless steel Pd membranes/ceramic Microstructured Pd23at% Ag membranes Pd-23wt% Ag membranes/Porous stainless steel

Activation via photocatalytic deposition, 400-500 oC

Pure H2, 350 oC

Pure H2, 450 oC Pure H2 with treatments), 350 oC

oxidation

(air

2. Materials and Methodology Asymmetric Pd/Au membranes were synthesized [8] on porous stainless steel (PSS) tubular supports 316L obtained from MOTT Metallurgical with an outer diameter of 0.5” and a length of 6”, having a total porous surface area of 60 cm2. One end was welded to a dense nonporous tube and to a nonporous tube on the other end. First, the supports were cleaned with acetone in an ultrasonic bath, followed by their oxidation at 600 oC for 12 h under air [30]. An 4 ACS Paragon Plus Environment

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intermediate layer of activated Al2O3 particles was deposited on the pores of the oxidized supports and cemented with Pd, as previously described [31,32]. Afterwards, the membranes were activated with SnCl2-PdCl2 and then a dense layer of pure Pd was formed via electroless plating [33,34,35]. The deposition of gold on the surface of the Pd layer was obtained through a conventional electro-deposition. Please notice that the thickness of the membranes was estimated through gravimetric methods. It was thus assumed that the Pd or Au distribution on the surface of the membrane was uniform. The composition of the four Pd- and Pd/Au membranes used in this study are shown in Table 2 while pictures are shown in Figure 1:

Table 2. Composition of the membranes shown in this study Nomenclature MA-156

Composition (Initial) 6.0 µm Pd

MA-157

2.7 µm Pd + 0.1 µm Au

MA-159

(5-15) µm Pd + 0.4 µm Au

MA-160

(4.6-10.4) µm Pd + 0.1 µm Au

Other PSS support media grade of 0.5 µm PSS support media grade of 0.5 µm PSS support media grade of 1.0 µm PSS support media grade of 0.5 µm

The membranes were characterized based on their hydrogen permeation and helium leak features at different times. These tests were conducted using a system equipped with a data acquisition board to continuously log the hydrogen flux via mass flow meters, shell-and-tubeside pressures and the temperature of the system. It is important to mention that the accuracy of the measurements was determined to be within 1% as previously described [24, 36]. Hydrogen flux was measured constantly at 350 and 450 oC and at 0.5 bar; while weekly, the membranes’ H2 and He flux was measured at ten different pressures (0.5-6 bar) to corroborate Sieverts’ behavior and estimate the ideal selectivity of the membrane. Please notice that helium leak and H2 flux were measured under pure helium stream at different pressures (0.5-6 bar). It is important to mention that the hydrogen permeance of all membranes followed Sieverts’ law (Eq. 1): P =

F

. A P

−

(1)

. P

where is the hydrogen permeance, A is the permeable surface area of the membrane, F is .

.

the hydrogen flow rate of the permeate, and P and P are the hydrogen partial pressure at the retentate and the permeate respectively. Furthermore, the ideal H2/He selectivity



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(S of the membrane (Eq.2) was used to estimate the H2 purity produced by the membrane

(Eq.3).

S

=

F F

H Purity % = #1 %

(2) 1

S

'(

&

(3)

Figure1. Depiction of the Pd-Au membranes used in this study before and after test It is also important to mention that in this work the quality of H2 was assumed to be a function of its ideal selectivity found experimentally at a pressure of 2 bar. Nonetheless this simplification engenders inevitable limitations in our approach that the reader needs to consider. For instance, as hydrogen is depleted along the membrane, the local H2 partial pressure adjacent to the membrane decreases. Likewise, radial mass transfer limitations caused by the presence of other gases induce a reduction in the total driving force for H2 permeance, affecting the actual selectivity of the membrane. Furthermore, while H2 permeance is dictated by Sieverts’ law, impurities permeate through different mechanisms (Knudsen and/or viscous flow), and therefore, their effect is expected to vary at different pressures. Nonetheless, as pointed out by Guazzone et al. [8], the ideal selectivity of various membranes (tested at a pressure of 2 bar) is of the same order as when tested under coal-derived syngas and at a pressure of 12.6 bar, suggesting that this test could be used as a screening tool for the membranes. In light of the above considerations, reasonable support is offered to the assumption used in this work The specific gas permeation tests were performed as follows: 1) After the membrane was installed in the membrane module, pure He was feed into the system and the pressure of the retentate increased to 1 bar by adjusting a back pressure regulator. 2) The temperature of the system was increased at 1oC/min up to 350 oC under pure Helium. After reaching the desired temperature, ten different retentate pressures (0.5-6 bar) were used to analyze the He leak of the membrane. 6 ACS Paragon Plus Environment

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3) Pure hydrogen was fed into the system at 350 oC for 1 day; afterwards, the flux was tested under ten different pressures. 4) The temperature was increased to 450 oC at 1oC/min and both, H2 and pure He, fluxes were tested under pure gas streams. 5) Pure H2 was fed constantly at 1 bar for a week to monitor the stability of the membrane. 6) Every week, the ten-pressure test, for H2 and He, was applied to monitor the performance of the membrane. 7) Once a membrane failure was detected, pure He was fed into the system and the temperature decreased at 1 oC/min.

3. Economic Evaluation Framework Methodology 3.1 Baseline capital investment model development In the present study, baseline capital investment models for fixed capital investment (FCI) and total capital investment (TCI) estimation of a large-scale Pd-based separation module have been developed to evaluate the effect of the lifetime and thickness of the membrane on economic performance following the standard practice in engineering system economic analysis [37]. Within the proposed modeling framework, the FCI is calculated by forming the sum of the direct and indirect costs while the TCI is computed as the sum of the FCI and the working capital (WC). All cost model inputs considered for the FCI/TCI estimation are listed in Table 3. Please notice that the cost figures of purchased equipment involving the Pd-based membrane reactor and assorted apparatus, such as pressure monitor system and the mass flow control system, are adopted from the large-scale Pd-based separation module built in Worcester Polytechnic Institute, of which the specifications are shown in Table 4 [9]. Note that the ratios with specific ranges and bases indicated in Table 3 are approximations that reflect the effect of many factors in uncertain “future states” on FCI/TCI, such as module location, type of process, and complexity of equipment. In addition, the Chemical Engineering Plant Cost Indexes (available for year 2014) were used to update all pertinent cost estimates by taking into account the time value of money in order to obtain the most recent equivalent cost figures [38]. It should be pointed out that cost indexes are used only to offer general and rather conservative estimates without considering any, otherwise quite reasonable, expectations of cost-reducing possibilities attributed to future technological advances and “learning effects”.

3.2 Baseline estimation for total product cost and levelized cost Motivated by the fact that total product cost (TPC) and levelized cost (LC) are recognized as two significant indicators broadly used in the economic performance analysis of chemical plants, the baseline TPC/LC models for hydrogen production via the large-scale Pd-based separation module are also proposed in the context of this study. The various cost components and pertinent details of the associated baseline TPC/LC models are shown in Table 5. According to standard practice in engineering economic analysis, the TPC is calculated by forming the sum 7 ACS Paragon Plus Environment


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of manufacturing cost, general expenses, and membrane replacement, while the LC is obtained from the TPC divided by the total hydrogen production output through the Pd-based separation module. Please notice that the cost of membrane replacement considered in the proposed baseline models is calculated by using the Pd/Au alloy composite membrane cost over the membrane’s lifetime. Furthermore, the values of H2 production in kg per year used for LC estimation are calculated based on the experimentally determined H2 permeance values of the Pd/Au alloy composite membranes.

Table 3. Estimation of capital investment costs for the large-scale Pd-based separation module. I. Direct Costs A. Equipment + installation + instrumentation + piping + electrical + insulation + painting 1. Purchased equipment a. Pressure monitor system (1) Manometer (range: 25000 Torr) × 2 (2) Manometer (range: 5000 Torr) × 1 (3) Digital power supply and readout × 2 b. Mass flow control system (1) Mass flow controller × 4 (2) Mass flow indicator × 2 (3) Pressure controller × 2 (4) Flow-Bus interface box × 1 (5) Digital readout/control unit blind front × 2 c. Temperature control system (1) Temperature controller × 2 (2) Profile Probe × 2 (3) Thermocouple differential analog input module × 3 (3) CompactDAQ chassis × 1 d. Computer e. Preheater (1) Shell casing (2) Ceramic fiber heater f. Pd-based membrane reactor (1) Pd/Au alloy composite membrane i) Pd cost ii) Au cost iii) 316L SS support (2) Shell casing (3) Ceramic fiber heater 2. Installation (25-55% of purchased equipment) 3. Instrumentation and controls, installed (8-50% of purchased 8 ACS Paragon Plus Environment

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equipment) 4. Piping, installed (10-80% of purchased equipment) 5. Electrical, installed (10-40% of purchased equipment) B. Buildings, process and auxiliary (10-70% of purchased equipment) C. Service facilities and yard improvements (40-100% of purchased equipment) D. Land (4-8% of purchased equipment) II. Indirect Costs A. Engineering and supervision (5-30% of direct cost) B. Legal expenses (1-3% of fixed capital investment) C. Construction expense and contractor's fee (10-20% of fixed capital investment) D. Contingency (5-15% of fixed capital investment) III. Fixed Capital Investment ( = Direct Costs + Indirect Costs ) IV. Working Capital ( 10-20% of Total Capital Investment ) V. Total Capital Investment ( = Fixed Capital Investment + Total Capital Investment )

Table 4. Large-scale Pd-based separation module specifications used for cost analysis Outer diameter of the support tube [m]

0.025

Length of the support tube [m]

0.356

Length of the porous part [m] Outer diameter of the shell casing [m] Wall thickness of shell casing [m]

0.254 0.051 0.003 05

Inner diameter of the shell casing [m] Length of the shell casing [m]

0.045 0.914

Membrane area [m2]

0.0203

Volume for shell casing [m3]

0.001 43



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Table 5. Estimation of total product cost and levelized cost for the large-scale Pdbased separation module. I. Manufacturing Cost (= direct production costs + fixed charges + plant overhead costs) A. Direct production costs 1. Raw materials (10-20% of product cost) 2. Operating labor (10-15% of product cost) 3. Direct supervisory and clerical labor (10-20% of operating labor) 4. Utilities (10-15% of product cost) 5. Maintenance and repair (2-10% fixed capital investment) 6. Operating supplies (0.5-1% of fixed capital investment) 7. Laboratory charges (10-20% of operating labor) 8. Patents and Royalties (0-6% of product cost) B. Fixed charges 1. Depreciation (10% of fixed capital investment) 2. Local taxes (1-4% of fixed capital investment) 3. Insurance (0.4-1% of fixed capital investment) 4. Financing interest (6-10% of total fixed capital investment) C. Plant overhead costs (5-15% of product cost) II. General Expenses A. Administrative costs (2-5% of product cost) B. Distribution & selling costs (2-20% of product cost) C. R&D costs (5% of product cost) III. Total Product Cost (= membrane replacement + product cost) A. Membrane replacement (= Pd/Au alloy composite membrane / membrane lifetime) B. Product cost (= manufacturing cost + general expenses) IV. Levelized Cost (= total product cost / H2 production)

3.3 Economic performance assessment framework under uncertainty: A probabilistic approach via Monte Carlo simulation methods

The proposed economic performance evaluation framework is developed in the presence of irreducible uncertainties. These sources of uncertainty enter the FCI/TCI/TPC/LC-models as uncertain model inputs (random/ variables) and as such drive the valuation profiles of this new technology option. Within this context, it should be pointed out that traditional economic performance assessment frameworks that generate single-point estimates by fixing all uncertain model inputs at ”average” values quite often lead to unsatisfactory economic performance outcome characterization and appraisals due to the “flaw of averages”, i.e. the flawed assumption 10 ACS Paragon Plus Environment

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that economic performance assessment conducted at average conditions generate the average economic performance over all possible future system states [13,14,16]. Consequently, Monte Carlo techniques are embedded into the proposed assessment framework through which the “flaw of averages” is effectively overcome while the simultaneous integration of various sources of uncertainty as multiple random model input variables (as opposed to the conventional sensitivity analysis) becomes feasible [11,13,14,15,16]. As a result, full distribution profiles of economic performance outcomes cast in terms of FCI/TCI/TPC/LC are derived in the presence of uncertainty. The derived profiles are amenable to potentially insightful statistical characterization being also viewed as “risk-reward/opportunity” profiles that enable the identification of “risks/rewards” zones (through the “value at risk” and the “value at opportunity” notions at pre-specified levels) . The latter are now used as evaluative tools/indicators in risk management and project/system valuation methods under uncertainty. Furthermore, within the context of the present study, they could potentially inform efforts to design incentives that could accelerate the realization of technology demonstration strategies at the commercial scale [9,16]. In the present study, the key objective is to develop a methodologically sound economic performance assessment and cost analysis framework for the FCI/TCI/TPC/LC estimation on an actual large-scale separation membrane module used for hydrogen production. Due to the fact that the FCI/TCI/TPC/LC models developed in the present study introduce multiple inherently uncertain inputs associated with various sources of commodity market, regulatory, and macroeconomic/financing uncertainty, the integration of Monte Carlo simulation methods into the FCI/TCI/TPC/LC-based economic performance assessment framework is deemed necessary in order to derive and more realistically characterize economic performance outcomes. The integration of Monte Carlo simulation methods into the economic assessment framework begins by identifying uncertain model input variables admitting reasonable probabilistic representations, followed by statistical sampling via the Monte Carlo simulator to generate probabilistic distribution profiles of economic performance outcomes presented in terms of the FCI/TCI/TPC/LC indicators. For the uncertain model input variables, two different types of probability distributions are considered. One type relies on the notion of a bootstrap distribution which is developed using standard re-sampling techniques under the condition that historical or experimental data are available [39,40]. The second type is a simple uniform distribution (with reasonable range derived from comprehensive recent reports, pertinent 11 ACS Paragon Plus Environment


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bibliographical sources and expert opinion; please see relevant cited references) assigned to model inputs in the absence of any reliable data at the commercial scale [35,41]. Finally, Monte Carlo simulation runs were conducted using the software package XLSim with 104 iterations for each run. Moreover, all 29 uncertainty model inputs taken into account in the proposed economic evaluation framework are listed in Table 6 along with the corresponding probability distributions.

Table 6. Probability distribution associated with various uncertain model inputs. Uncertain model input

Minimum

Pd unit price [$/g], RH Au unit price [$/g], RH H2 permeance [Nm3/m2-h-bar0.5], RH Ratio for installation, UDa Ratio for instrumentation and controls, installed, UDa Ratio for piping, installed, UDa Ratio for electrical, installed, UDa Ratio for buildings, process and auxiliary, UDa Ratio for service facilities and yard improvements, UDa Ratio for land, UDa Ratio for engineering and supervision, UDb Ratio for legal expenses, UDc Ratio for construction expense and contractor's fee, UDc Ratio for contingency, UDc Ratio for working capital, UDd Ratio for raw materials, UDe Ratio for operating labor, UDe Ratio for direct supervisory and clerical labor, UDf Ratio for utilities. UDe Ratio for maintenance and repair, UDc Ratio for operating supplies, UDc Ratio for laboratory charges, UDf Ratio for patents and Royalties, UDe Ratio for local taxes, UDc Ratio for insurance, UDc Ratio for financing interest, UDd Ratio for plant overhead costs, UDe

Most likely

Maximum

Historical data from 2011-2015, www.kitco.com Historical data from 2011-2015, www.kitco.com Experimental data in this study 25.0% 55.0% 8.0%

50.0%

10.0% 10.0%

80.0% 40.0%

10.0%

70.0%

40.0%

100.0%

4.0% 5.0% 1.0%

8.0% 30.0% 3.0%

10.0%

20.0%

5.0% 10.0% 10.0% 10.0%

15.0% 20.0% 20.0% 15.0%

10.0%

20.0%

10.0% 2.0% 0.5% 10.0% 0.0% 1.0% 0.4% 6.0% 5.0%

15.0% 10.0% 1.0% 20.0% 6.0% 4.0% 1.0% 10.0% 15.0% 12

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Ratio for administrative costs, UDe Ratio for distribution & selling costs, UDe

2.0% 2.0%

5.0% 20.0%

RH = Resample historical data, UD = Uniform distribution a Based on purchased equipment cost, b Based on direct cost, c Based on fixed capital investment, d Based on total capital investment, e Based on product cost, f Based on operating labor

4. Results 4.1 Hydrogen Permeation and He Leak Tests This study encompasses performance characterization results involving four membranes tested at 350 oC and 450 oC under pure H2 with occasional He leak tests for a cumulative time of 19,200 h or an equivalent time of 2.2 years. In addition, as shown in Figure 1, the membranes used in this work displayed an excellent visual physical integrity when compared to long-term testing results reported in the pertinent literature [18]. Nonetheless, it is important to point out that the quality of the Pd layer is microscopic in nature and thus conclusive remarks cannot be solely derived from Figure 1. The

following subsections contain a more detailed description of the testing procedures and results pertaining to the performance of each membrane. It is important to mention that four membranes were tested to generate sufficient data for the development of the proposed techno-economic performance assessment framework. First, MA-156 was synthesized in order to demonstrate the performance of pure Pd membranes. Furthermore, membrane MA-159 was tested to demonstrate the effect of the media grade of the support (0.5 vs 1.0 µm) on the durability of this technology. Finally, membranes MA-157 and MA160 were synthesized in a similar manner and their data utilized in the economic performance assessment.

a) MA-156. A 6 µm thick Pd membrane (MA-156) was synthesized, displaying an initial He leak of 0.3 sccm/bar at room temperature. The H2 permeance test of MA-156 as a function of time is shown in Figure 2. The initial H2 permeance was of 8.2 and 14.8 Nm3m-2h-1bar-0.5 at 350 o

C and 450 oC, respectively. Please notice that during testing, the membrane was oxidized at 2

bar under air at 300 oC for 34 h. After oxidation the H2 permeance increased to 16.5 and 22.8 Nm3m-2h-1bar-0.5 at 350 oC and 450 oC, respectively, corresponding to an enhancement of 101% and 54%; while the He leak did not seem to change after the oxidation stage. This increase in H2 permeance after oxidation is in agreement with previous studies [29,42]. During 850 h of further testing, the H2 permeance was stable with a permeance of 22.3 Nm3m-2h-1bar-0.5 and an ideal selectivity of 490. Furthermore, the He leak after 2150 h was 6.9 sccm/bar.



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Figure 2. Hydrogen permeance and He leak tests of MA-156 b) MA-157. Membrane MA-157 (2.7 µm Pd + 0.1 µm Au) was synthesized as a thin Pd/Au membrane and tested for 2,200 h as shown in Figure 3. After 670 h of testing under H2 atmosphere, the permeance of this gold enriched membrane had an initial value of 38 Nm3m-2h1

bar-0.5 at 450 oC with an ideal selectivity of 520. The permeance and He leak increased with

time. MA-157 had an average permeance of 45 Nm3m-2h-1bar-0.5 at 450 oC and a final He leak of 16.5 sccm/bar. It is important to mention, that to the best of our knowledge, long-term (>1000 h) testing results have not been reported for membrane thicknesses lower than 4 µm.


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Figure 3. Hydrogen permeance and He leak tests of MA-157

c) MA-159. MA-159 (5 µm Pd + 0.6 µm Au) had a He leak after synthesis of 0.01 sccm/bar. This Au enriched membrane displayed an initial H2 permeance of 7.4 Nm3m-2h-1bar-0.5 and a He leak of 0.42 sccm/bar at 350 oC. The temperature was increased to 450 oC and therefore the permeance increased gradually to 42 Nm3m-2h-1bar-0.5 after 137.5 h due to in-situ alloying. Even though the permeance remained stable, the He leak increased considerably (~35 sccm/bar) and the experiment was stopped after 800 h of testing for further investigation and characterization of the leak location. MA-159 was repaired and renamed as MA-159b. Gold rings were plated at both sides of the welding area, reducing the He leak to 0.3 sccm/bar at room temperature. The membrane was tested for 100 h at 450 oC under pure H2. The He leak increased again to 45 sccm/bar and the test was terminated. MA-159b was subjected to a mild polish treatment to remove any Pd peel off. Palladium rings were plated in the welding area close to the cap twice. This treatment reduced the overall He leak of the membrane to 30 sccm/bar. Subsequently, the first half of MA-159b was plated once, reducing the leak even further to 18 sccm/bar. Finally, a complete Pd plating treatment was conducted along the whole membrane. No detectable He leak was found at pressure differences of 2 bar. At this point MA-159b was renamed to MA-159c. MA-159c was tested for ~200 h showing a H2 permeance of 25 and 35 Nm3m-2h-1bar-0.5 at 350 and 450 oC, respectively. The He leak increased gradually to 8.3 sccm/bar. The membrane was removed from the module and plated once more to increase the Pd layer thickness to 11 µm; this 15 ACS Paragon Plus Environment


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membrane was renamed to MA-159d. MA-159d was tested for 700 h showing a stable H2 permeance of 35 Nm3m-2h-1bar-0.5, similar to the permeance displayed by MA-159c. Nevertheless, the He leak appeared to be reaching 40 sccm/bar at room temperature. The membrane was replated to 12 µm, renamed as MA-159e and tested for 1000 h showing an He leak of 15 sccm/bar by the end of the test. The permeance of MA-159e, was stable with a value of 23 and 35 Nm3m-2h-1bar-0.5at 350 and 450 oC, respectively. Notice that the membrane remained under pure He for 20 h, as indicated in Figure 4, due to a problem with the H2 security system. After this period, the permeance of the membrane showed a steady decline at 350 oC and stopped once the temperature was increased to 450 oC. After MA-159e failed, it was repaired once more and renamed as MA-159f. The membrane was tested for 1400 h showing a stable H2 permeance of 32 Nm3m-2h-1bar-0.5at 450 oC, while the He leak increased gradually from >1 to 17 sccm/bar. The cumulative test results of MA-159 after ~4000 h of continuous testing and 5 repair steps are shown in Figure 4. Overall, this membrane displayed a stable permeance as shown in Table 7. However, it diplayed a continuous He leak that seemed to decline after repair and increase as the tests proceeded. It is important to mention that, for each test session, additional palladium was deposited to cover the defects of the membrane before the test was reinitiated. Nevertheless, for MA-159b, only rings at the welding area were plated and consequently the increase in thickness was neglected. The He leak, shown in Table 7, represents the value obtained at 450 oC before the test was terminated; while the H2 permeance was taken as the average value displayed throughout the test at 450 oC. It should be pointed out that the media grade of the support influenced significantly the lifetime of the membranes, as evidenced by the lower stability displayed by MA-159 where several repairs were needed.


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Table 7. List of characteristics of MA-159 Membran Testing time / Dense Pd thickness/ e h µm MA-159 830 5 MA-159b 250 5 (rings) MA-159c 210 8.5 MA-159d 700 11 MA-159e 1000 12 MA-159f 1350 15 * Hydrogen permeance and He leak at 450oC

Final He leak* /sccm.bar-1 35 45 8.3 20.5 15 17

H2 Permeance*/ Nm3m-2h-1bar-0.5 45 40 36 34 33 31

Figure 4. Hydrogen permeance and He leak tests of MA-159

d) MA-160. The membrane MA-160 (4.6 µm Pd + 0.1 µm Au) had a stable H2 permeance of 50 Nm3m-2h-1bar-0.5 at 450 oC, as shown in Table 8. The He leak seemed to increase linearly with time; nevertheless, after 1480 h, the membrane was accidentally exposed to He for 62 h as indicated by the yellow lines in Figure 5. There was no immediate change to the membrane’s He leak; but, the performance deteriorated gradually after the He exposure, increasing its He leak to a maximum value of 14.5 sccm/bar. The H2 permeance dropped immediately by 12% to 44 Nm3m-2h-1bar-0.5 and remained constant until the end of this test; the total testing time was 2950 h. At this point the test was momentarily dismissed to identify the location of the leak as well as repair the membrane. Gold rings were plated on both sides of the welding area, reducing the He leak to 0.5 sccm/bar. The membrane renamed as MA-160b and was tested for 1000 h. Notice that the He leak increased to 45 sccm/bar by the end of the test and because of technical problems, 17 ACS Paragon Plus Environment


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the membrane was oxidized with air for 10 h, after 400 h of this test or 3350 of cumulative testing time, causing a sudden He leak growth. MA-160b was repaired by plating 5.8 µm of Pd and renamed as MA-160c. During this test, several oxidation stages can be observed due to a failure in the system. These oxidation stages occurred at the times where the temperature oscillated. These oxidations did not affect the permeance nor the He leak presented in the membrane. Subsequently, the temperature of the membrane was raised to 450 oC and its permeance was tested for ~600 h; the He leak remained stable throughout this test. Unfortunately, the system suffered another error and a third oxidation stage occurred. The membrane was then tested at 350 oC for 200 h followed by a continuous He test of 300 h. Afterwards, H2 was fed once more; nevertheless, the membrane’s permeance reduced by ~50% while the He leak remained unchanged. The membrane test was reinitiated after 5760 h of testing exhibiting a stable permeance of 20 Nm3m-2h-1bar-0.5 and an He leak of 1.5 sccm/bar. It is important to mention that at the beginning of the test, the membrane suffered from several cooling-heating cycles due to failures of the electric system; nevertheless, the He leak remained unaffected. The hydrogen permeance, on the other hand, reduced from 27 to 20 Nm3m2 -1 h bar-0.5 after the temperature fluctuation occurred at 6,630 h. Subsequently, the permeance showed a steady decline reaching a steady state value of 15 Nm3m-2h-1bar-0.5 at 8,000 h until 9,300 h. The test was terminated for system maintenance purposes and then reinitiated to test the membrane for another 1,000 h. Finally, the cumulative test results of MA-160 are shown in Figure 5 for 10,700 h of continuous testing with 3 repair steps. A summary of the performance of this membrane is shown in Table 8. The specific membrane showed a reduction in permeance of 62% but an excellent separation performance. Please notice that a subset of these permeance testing results has been previously presented [43].


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Table 8. List of characteristics of MA-160

MA-160 MA-160b MA-160c

Testing time / h 2950 1000 6750

Dense Pd thickness/ µm 4.6 4.6 (rings) 10.4

Final He leak* /sccm.bar-1 14.5 45 4.5

H2 Permeance*/ Nm3m-2h-1bar-0.5 45 43 18

Figure 5. Hydrogen permeance and He leak tests of MA-160, and yellow lines indicating

membrane oxidation stages

4.2 Membrane Lifetime Estimation From the experimental data shown, it is possible to conclude that the lifetime of pure Pd membranes (MA-156) is inferior to alloyed membranes. Certainly, as shown by Mardilovich et al. [7, 42], Au acts as a patching paste that fixes the defects formed at the surface of the membrane. Nonetheless, the presence of a coarser media grade of the support (1.0 µm vs. 0.5 µm), shown in MA-159, impacted the stability of the membrane even in the presence of Au. Consequently, the sets of data generated by membranes MA-157 and MA-160 were integrated into the economic performance assessment when the “optimal” alloy and media grade were considered.

In order to assess the effect of the membranes’ lifetime on the TPC and the LC profiles the experimentally determined values of the H2/He selectivities of the membranes at different times and thicknesses were used to calculate the hydrogen purity produced, as shown in Figure 6. 19 ACS Paragon Plus Environment


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Notice that the produced H2 quality decreases with time due to the transient formation of pinholes/defects at the surface of the membranes. These defects occur when Pd crystallites sinter due to their molecular mobility at high temperatures [10]. Certainly, this aging behavior is strongly dependent on the thickness of the membrane; for instance, as shown in Figure 6 membranes with high values of Pd layer thickness have lower decreasing rates of hydrogen purity when compared to those with low thickness values. In addition, the membrane with a 10.4 µm Pd thickness can sustain a hydrogen purity higher than 99.8% over 4500 h longer than that of a 2.7 µm thick Pd with 1400 h, indicating that a longer membrane lifetime at the specific hydrogen purity level can be achieved by increasing the Pd layer thickness. Moreover, the hydrogen purity profile at various testing times admits a rather satisfactory polynomial curve fitting as depicted in Figure 6. Notice that even though thicker membranes seem to prolong the lifetime of the membrane, the capital investment will also increase due to the need of higher Pd quantities. Furthermore, since the H2 flux of Pd-based membranes is determined by the membrane thickness (according to Fick’s law), the H2 production output will be reduced using thicker membranes as demonstrated in Figure 7. Focusing on the above issue, one of the key objectives is to evaluate the economic performance of separation modules using various membrane thicknesses while simultaneously taking into account membrane lifetime and hydrogen production.

Figure 6. Estimated ideal H2 purity for various Pd thickness values at 450°C and a retentate pressure of 2 bar


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Figure 7. Average hydrogen permeance with the standard deviation for Pd-based separation modules using various palladium layer thicknesses.

The hydrogen purity chosen for this study as the baseline value was 99.0% in order to investigate the effect of membrane thickness on economic performance of separation modules. With the aid of polynomial curve fitting techniques applied to the hydrogen purity versus elapsed testing time profile, the membrane lifetime at the hydrogen purity level of 99.0% was calculated and the pertinent estimates are listed in Table 9. Please notice that the membrane lifetime is extended by 16% when the Pd layer thickness is increased from 2.7 to 4.6 µm while increasing the Pd layer thickness from 2.7 to 10.4 µm leads to an increase of the membrane lifetime by 152%. Following the long-term testing of hydrogen permeance and the membrane lifetime estimation, an economic performance assessment is conducted and the results are presented and discussed in the next subsection.

Table 9. Lifetime estimation for Pd-based separation modules with various palladium thickness values Lifetime Pd layer thickness [µm]

H2 Purity [%]

2.7

[h]

[year]

99.0

3,113

0.36

4.6

99.0

3,597

0.41

10.4

99.0

7,856

0.90



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4.3 Economic performance assessment of Pd-based separation modules under various Pd layer thickness values Considering all uncertain model inputs listed in Table 6, the economic performance of Pd-based separation modules is evaluated with the focus placed on the effect of different Pd layer thicknesses. The pertinent results for various Pd layer thickness values are summarized in Table 10 in terms of the expected values of the derived FCI/TCI/TPC probability distribution profiles. In Table 10, the increasing expected values of the FCI/TCI as the Pd layer thickness increases are depicted, conforming to the intuitively expected behavior that higher Pd layer thickness values lead to higher capital investment due to the additional amounts of Pd needed. However, the expected value of the TPC decreases with an increase in the Pd layer thickness, indicating that a prolonged membrane lifetime and high values of Pd layer thickness can effectively reduce the TPC by lowering the membrane replacement cost.

Table 10. Pd-based separation module cost summary regarding fixed capital investment, total capital investment, and total product cost Pd layer thickness [µm] 2.7 4.6 10.4

Expected fixed capital investment

Expected total capital investment

Expected total product cost

[k$]

[k$/m2]

[k$]

[k$/m2]

[k$]

[k$/m2]

168.68 168.74 168.93

8,327 8,330 8,339

198.73 198.81 199.03

9,810 9,814 9,825

241.04 240.82 239.92

11,899 11,887 11,843

As mentioned before, H2 production is also affected by the Pd layer thickness, recognized as a cost component with a quite significant impact on economic performance of separation modules. To evaluate the economic performance of separation modules by taking into consideration the lifetime of the membranes and hydrogen production, the focus now is placed on the LC for further detailed analysis and discussion. The LC cumulative probability distribution profiles for Pd-based separation modules considered in this study for various Pd layer thicknesses are shown in Figure 8. Please notice that the distribution profiles and the corresponding statistical characterization provide valuable pieces of information regarding the various Pd layer thickness values in the present study. •

The probability (vertical axis) that the LC falls below a desirable cost target level (horizontal axis) as well as the complementary probability for the cost to be higher than the aforementioned target level can be easily inferred. For example, there is a 30% probability for the LC to be lower than 120 $/kg for the 10.4 µm Pd layer thickness case, while there is a 10% probability for the LC to be higher than 100 $/kg in the 2.7 µm Pd layer thickness case.


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•

The “value at risk” and the “value at opportunity” can be quantified at pre-specified probabilistic levels. In our case, the “value at risk” is defined as the threshold-value of P95 representing that there is a 5% probability of incurring a cost higher than this value, while the “value at opportunity” indicates that there is a 5% probability of incurring a cost lower than a P5 threshold-value.

In Figure 8, notice that the 2.7 µm Pd layer thickness case has the most attractive LC distribution profile, indicating that the hydrogen production has the more significant impact on the LC performance compared to the lifetime even though the TPC can be effectively reduced by the prolonged membrane lifetime as mentioned before. In light of the above results derived, reducing Pd layer thickness not only lowers the FCI/TCI of separation modules but also decreases the LC by increasing hydrogen production, allowing economic performance of separation modules to exhibit more appealing characteristics. A similar behavior has been shown in polymeric membranes where high gas permeability values dominate economic performance outcomes [44].

Figure 8. Cumulative probability distribution profile of levelized cost for Pd-based separation modules with various Pd layer thickness values at 450°C and a retentate pressure of 50 bar Furthermore, within the experimental range of Pd layer thickness values tested, Figure 9 shows a comparative appraisal of LC for the various Pd layer thickness values on the average/expected value level as well as levels of probability associated with “value at risk” and the “value at opportunity”. In Figure 9, the upper P95 line (a possible means of identifying “risk”) graphically shows that there is a 5% probability of incurring a cost higher than the value on the 23 ACS Paragon Plus Environment


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line, and similarly, the lower P5 line (a possible means of quantifying “opportunity”) graphically shows the 5% probability of incurring a cost lower than the value of the line. Besides, the middle line provides the expected LC values for the various Pd layer thicknesses considered. Furthermore, the P95, P5, and the expected value of LC for the separation modules using various Pd layer thicknesses are summarized in Table 11. It should be pointed out that not only does the expected LC value decreases when the Pd layer thickness reduces as noted earlier, but so does the spread/variability (quantified as P95 minus P5) of the LC – that is, the dispersion of possible economic performance outcomes. The observed reduction in the spread/variability of the LC with decreasing Pd thickness can be attributed to the fact that the extent of improvement on the LC by hydrogen production using thinner membranes is higher than that on TPC using thicker membranes, enabling the spread/variability of the LC to be effectively reduced by higher hydrogen production levels using thinner membranes.

Figure 9. P95, P5, and expected value lines of levelized cost for Pd-based separation modules with various palladium layer thickness values.


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Table 11. P95, P5, and the expected value of levelized cost for a separation module using various Pd layer thicknesses. Levelized cost [$/kg] Pd layer thickness [µm]

P5

Expected value

P95

2.7

29.7

57.6

107.6

4.6

33.0

62.7

115.7

10.4

79.8

157.4

290.2

Additionally, a sensitivity analysis on the effects of uncertainty on the expected LC-value is performed via Tornado diagrams [45], as shown in Figures 10 and 11. Tornado diagrams graphically depict the relative economic impact of variations of the uncertain inputs in the LC model over their respective ranges assuming that all other inputs remain fixed at their average/expected values. In these diagrams, each input symbolizes a “bar” as it is varies over its corresponding range and thus depicting its impact. Please notice that all bars are arranged in a way that the longer ones appear on top and shorter ones at the bottom [46] in order to comparatively assess, prioritize and rank the impact of various inputs on LC. In particular, the “lowest and highest” membrane thickness values mentioned earlier (2.7 and 10.4 µm) were considered and sized against other model inputs. For 2.7 µm membranes, the inputs and ranges considered were: Pd unit price: 18.6-28.2 $/g; Au unit price: 36.5-57.0 $/g, raw materials to product cost ratio range: 10-20%; operating labor to product cost ratio range: 10-15%; plant overhead costs to product cost ratio range: 5-15%; distribution & selling costs to product cost ratio range: 2-20%; membrane lifetime: baseline ± 20%; hydrogen permeance: 38.7-54.8 Nm3/m2-h-bar0.5. For 10.4 µm membranes the inputs and ranges were: Pd unit price: 18.6-28.2 $/g; Au unit price: 36.5-57.0 $/g, raw materials to product cost ratio range: 10-20%; operating labor to product cost ratio range: 10-15%; plant overhead costs to product cost ratio range: 515%; distribution & selling costs to product cost ratio range: 2-20%; membrane lifetime: baseline ± 20%; hydrogen permeance: 20.3-14.8 Nm3/m2-h-bar0.5.



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Figure 10. Tornado diagram for the levelized cost of hydrogen produced via Pd-based separation modules using 2.7 µm thick membranes.

Figure 11. Tornado diagram for the levelized cost of hydrogen produced via Pd-based separation modules using 10.4 µm thick membranes.

The Tornado diagrams for both membrane thickness-values show that distribution and selling costs of H2 represent the most consequential uncertain model inputs followed by the raw materials, plant overhead costs, labor and the hydrogen permeance of the membrane. It is important to mention that, in both cases, the H2 permeance of the membranes is significantly more impactful than the membrane lifetime since the LC is normalized by the H2 production rate. 26 ACS Paragon Plus Environment

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Nevertheless, when comparing Figure 10 and 11, it is possible to infer that the influence of the membrane lifetime is more critical in the case of a thinner membrane thickness value. On the other hand, thicker membranes are more sensitive to the uncertainty inherent in the cost components associated with the raw materials needed in the synthesis of the membranes under consideration (Pd and Au unit price). Therefore, one can conclude that using thinner membranes not only generates an appealing LC performance by lowering the capital cost and enhancing hydrogen production, but also reduces the dispersion of possible economic performance outcomes since the LC magnitude is numerically dominated by the hydrogen production level rather than the membrane lifetime.

5. Concluding Remarks The main aim of this work was to combine long-term H2 membrane permeance and He leak characterization tests (cumulative testing over 2.2 years) conducted to estimate the lifetime of composite asymmetric Pd/Au membranes at different thicknesses with a comprehensive economic performance assessment framework in the presence of inherent tradeoffs between permeance, thickness and membrane lifetime. In particular, four membranes were tested at 350 and 450 oC under pure H2 with occasional He leak tests for a cumulative time of 19,200 h or an equivalent time of 2.2 years. In particular, long-term (>1000 h) test results are reported for a membrane with a thickness of 2.7 µm, and to the best of our knowledge, this is the first time that such results are reported in the pertinent literature. The experimental results associated with the attained H2 purity and elapsed testing times were analyzed to estimate the membrane lifetime for different membrane thicknesses. The lifetime of the membrane was defined with respect to a H2 purity target level equal or greater than 99%. Next, the structure of an economic evaluation framework for H2 separation units was presented that explicitly recognizes various uncertainty sources via Monte Carlo simulation techniques and assesses economic performance based on metrics such as fixed capital investment (FCI), total capital investment (TCI), total product cost (TPC) and the levelized H2 cost (LC). In particular, it was found that the expected values of the FCI/TCI increase as the Pd layer thickness increases since more Pd is needed leading to higher capital investment. Nonetheless, the expected value of the TPC was shown to decrease with higher Pd layer thickness values, indicating that prolonged membrane lifetime effectively reduces the cost of membrane replacement. Furthermore, it was observed that the expected LC value as well as its spread/variability decreases as the Pd thickness is reduced; this effect is attributed to the higher hydrogen production using thinner membranes. Additionally, a sensitivity analysis, via Tornado diagrams, showed that H2 permeance is more significant than membrane lifetime on LC-based performance assessments. In summary, it was demonstrated that using thinner membranes generates more appealing LC-based performance profiles by lowering the capital cost while enhancing hydrogen production.



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Acknowledgement

Acknowledgment The authors are indebted to the anonymous reviewers as well as Professor L. Biegler for their time, effort, insightful remarks and helpful suggestions. The authors also gratefully acknowledge the financial support provided by the U.S. Department of Energy through Grant No. DEFE0004895.

References [1] Shao, L.; Low, B.T.; Chung, T.S.; Greenberg, A.R. Polymeric membranes for the hydrogen economy: Contemporary approaches and prospects for the future. J. Membr. Sci. 2009, 327, 18. [2] Grashoff, G. J.; Pilkington, C. E.; Corti, C. W. The Purification of Hydrogen. A Review of the Technology Emphasizing the Current Status of Palladium Membrane Diffusion. Platin. Met. Rev. 1983, 27, 157. [3] Damle, A. Hydrogen Fuel: Production, Transport, and Storage, CRC press, Boca Raton, FL, 2009. [4] Ramasubramanian, K.; Zhao, Y.; Winston Ho, W. S. CO2 Capture and H2 Purification: Prospects for CO2-Selective Membrane Processes. AIChE Journal. 2013, 59, 1033. [5] Hatlevik, Ø.; Gade, S.K.; Keeling, M.K.; Thoen, P.M.; Davidson, A.P.; Douglas Way, J. Palladium and palladium alloy membranes for hydrogen separation and production: History, fabrication strategies, and current performance. Sep. Purif. Techn. 2010, 73, 59. [6]Guazzone, F.; Catalano, J.; Mardilovich, I.P.; Wu, T.; Lambrecht, R.C.; Datta, S.; Kniep, J.; Pande, S.; Kazantzis, N.K.; Ma, Y.H. Enhancement of the long-term permeance, selectivity stability, and recoverability of Pd-Au membranes in coal derived syngas atmospheres. Energy Fuels. 2013, 27, 4150.


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[7] Mardilovich, I.P.; Castro-Dominguez, B.; Kazantzis, N.K.; Wu, T.; Ma, Y.H. A comprehensive performance assessment study of pilot-scale Pd and Pd/alloy membranes under extended coal-derived syngas atmosphere testing. Int. J. Hydrogen Energy. 2015, 40, 6107. [8] Guazzone, F.; Catalano, J.; Mardilovich, I.P.; Kniep, J.; Pande, S.; Wu, T.; Lambrecht, R.C.; Datta, S.; Kazantzis, N.K.; Ma, Y.H. Gas permeation field tests of composite Pd and Pd–Au membranes in actual coal derived syngas atmosphere. Int. J. Hydrogen Energy. 2012, 19, 14557. [9] Catalano, J.; Guazzone, F.; Mardilovich, I.P.; Kazantzis, N.K.; Ma, Y.H. Hydrogen Production in a Large Scale Water–Gas Shift Pd-Based Catalytic Membrane Reactor. Ind. Eng. Chem. Res. 2013, 52 (3), 1042. [10] Guazzone, F.; Ma, Y.H. Leak growth mechanism in composite Pd membranes prepared by the electroless deposition method. AIChE Journal. 2008, 54, 487-494. [11] Ma, L.C.; Kazantzis, N.K.; Ma, Y.H. Natural gas in hydrogen production: a cost study. Energy. 2015, 160, 61. [12] Gazzani, M.; Manzolini, G. Using palladium membranes for carbon capture in integrated gasification combined cycle (IGCC) power plants, Palladium membrane technology for hydrogen production, carbon capture and other applications, Woodhead Publishing Series in Energy, UK, 2015. [13] Koc, R.; Kazantzis, N.K.; Ma, Y.H. Membrane technology embedded into IGCC plants with CO2 capture: An economic performance evaluation under uncertainty. Int. J. Greenh. Gas Con. 2014, 26, 22. [14] Ma, L.C.; Castro-Dominguez, B.; Kazantzis, N.K.; Ma, Y.H. Integration of Membrane Technology into Hydrogen Production Plants With CO2 Capture: An Economic Performance Assessment Study. Int. J. Greenh. Gas Con. 2015, 42, 424. 29 ACS Paragon Plus Environment


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Levelized cost reduction utilizing thinner palladium layers 217x150mm (150 x 150 DPI)

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