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Research Article pubs.acs.org/journal/ascecg

Coproducing Value-Added Chemicals and Hydrogen with Electrocatalytic Glycerol Oxidation Technology: Experimental and Techno-Economic Investigations Hyung Ju Kim,*,†,‡ Youngmin Kim,† Daewon Lee,† Jeong-Rang Kim,† Ho-Jeong Chae,†,‡ Soon-Yong Jeong,†,‡ Beom-Sik Kim,†,‡ Jechan Lee,§,⊥ George W. Huber,*,§ Jaewon Byun,∥ Sunghoon Kim,∥ and Jeehoon Han*,∥,# †

Carbon Resources Institute, Korea Research Institute of Chemical Technology, 141 Gajeong-ro, Yuseong, Daejeon 34114, South Korea ‡ Department of Green Chemistry and Biotechnology, University of Science and Technology, 113 Gwahangno, Yuseong, Daejeon 34113, South Korea § Department of Chemical and Biological Engineering, University of WisconsinMadison, 1415 Engineering Drive, Madison, Wisconsin 53706, United States ∥ School of Semiconductor and Chemical Engineering, Chonbuk National University, 567 Baekje-Daero, Deokjin-gu, Jeonju 54896, South Korea # School of Chemical Engineering, Chonbuk National University, 567 Baekje-Daero, Deokjin-gu, Jeonju 54896, South Korea S Supporting Information *

ABSTRACT: The electrocatalytic oxidation technology of biomass-derived oxygenates such as glycerol presents a promising method of coproducing renewable chemicals and hydrogen in an electrochemical reactor system that uses oxidation chemistry and existing proton exchange membrane technology to electrocatalytically convert oxygenates into value-added chemicals and hydrogen. In this paper, we first demonstrate the techno-economic feasibility of the electrocatalytic glycerol oxidation technology with our experimental investigations. Simple and direct conversion of glycerol into glyceraldehyde (GAD), glyceric acid (GLA), and hydroxypyruvic acid (HPA) by anodic oxidation in an electrocatalytic batch reactor over Pt/C catalysts was performed with only water as a stoichiometric chemical oxidant. We also conducted conventional catalytic (non-electrocatalytic) glycerol oxidation using a catalytic batch reactor with pressurized oxygen as the oxidant to compare conventional catalytic performances to that of the electrocatalytic reactor. The electrocatalytic glycerol oxidation process had a yield for GAD, GLA, and HPA production that was ∼1.7 times higher than that of the nonelectrocatalytic process. The turnover frequency of the electrocatalytic process is comparable to and even higher than that of a non-electrocatalytic system. On the basis of the experimental results, we develop process simulation models for both the electrocatalytic and non-electrocatalytic processes and then analyze the energy efficiency and economics of the process models. The minimum selling price (MSP) of GLA for the electrocatalytic process was $2.30/kg of GLA compared to $4.91/kg of GLA for the non-electrocatalytic process. KEYWORDS: Biofuels, Electrochemistry, Glycerol oxidation, Process design, Economic analysis

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INTRODUCTION Glycerol is obtained as a byproduct of biodiesel production with 0.1 kg of crude glycerol byproduct formed for every 1.0 kg of biodiesel produced.1−9 Global glycerol production [4.3 million metric tons (t)/year] exceeded the demand for glycerol (2.0 million t/year) in 2015.10 As the amount of excess glycerol increases, it is expected to progressively lower the price, thereby becoming largely available for glycerol derivatives. In particular, the demand for glycerol derivatives has grown at an annual rate © 2017 American Chemical Society

of 58%, and it reached 0.4 million t/year in 2015. Potential oxidation derivatives of glycerol include glyceraldehyde (GAD), glyceric acid (GLA), hydroxypyruvic acid (HPA), dihydroxyacetone (DHA), tartronic acid (TTA), glycolic acid (GCA), and oxalic acid (OXA).11−13 These products can be mainly Received: March 22, 2017 Revised: June 27, 2017 Published: June 30, 2017 6626

DOI: 10.1021/acssuschemeng.7b00868 ACS Sustainable Chem. Eng. 2017, 5, 6626−6634

Research Article

ACS Sustainable Chemistry & Engineering

Figure 1. Glycerol conversion vs product selectivity with (a) a glycerol/Pt ratio of 195 at 0.9 V, (b) a glycerol/Pt ratio of 195 at 1.1 V, (c) a glycerol/ Pt ratio of 975 at 0.9 V, and (d) a glycerol/Pt ratio of 975 at 1.1 V in the electrocatalytic reactor system for glycerol oxidation at 60 °C over 20 wt % Pt/C. Feed solutions: (a and b) 0.1 M in 0.5 M H2SO4 and (c and d) 0.5 M glycerol in 0.5 M H2SO4. The anode applied potentials for the electrocatalytic reactor were 0.9 and 1.1 V (vs SHE).

used as a monomer of polymers (polyesters and nylons)14 and as an ingredient in cosmetics.15 Therefore, it would be highly desirable to develop a cost-effective synthesis method for the selective production of GAD, GLA, and HPA from the oxidation of glycerol. Glycerol oxidation is typically performed using stoichiometric oxidants like O2. By controlling the reaction conditions (temperature, O2 pressure, pH, and feed-to-metal ratio) and the catalyst used (particle size, support, metal loading, etc.), one can oxidize either the primary or the secondary hydroxyl group.16−19 Catalytic glycerol oxidations have been reported with Pt-, Pd-, and Au-based catalysts.2,15,20−23 Several research groups have shown that C3 reaction products such as HPA can be produced by glycerol oxidation with Pt-based catalysts; however, the selectivity for these products decreases as the conversion increases.24−29 Also, Pt/C and Pd/C catalysts gave some selectivity for GLA in the catalytic glycerol oxidation reactor, but the main reaction products yielded nondesirable C1 products such as CO2, HCHO, and HCOOH by C−C bond breaking.24,26,30 Electrochemical conversion of glycerol has been used to produce oxidized chemicals31−33 and electrical energy.34−36 In particular, selective electrocatalytic oxidation technology uses oxidation chemistry and an existing proton exchange membrane (PEM) to electrocatalytically convert glycerol into valuable chemicals.17,33 Recently, we reported that an electrochemical process can be used to oxidize glycerol to GAD and GLA even without using a stoichiometric chemical oxidant like O2 or

H2O2 in electrocatalytic reactors.31 This electrocatalytic glycerol oxidation occurs in one reactor. The simplicity of the reactor design and the reaction process has the potential to decrease the operating costs compared to those of a conventional heterogeneous catalytic reactor. In electrochemical reactions, a change in electrode potential can be used to control the rate and product selectivity.37,38 Another key advantage of the electrocatalytic approach compared to the conventional catalytic process is that hydrogen is produced as a byproduct.17,31 The electrocatalytic oxidation of glycerol produces GLA, protons, and electrons at the anode. The only exception is that the electrons generated by water are used as a stoichiometric oxidant when the acid forms. The protons are transported to the cathode from the anode via the electrolyte in the electrochemical reactor. At the cathode, they combine with the electrons to form hydrogen gas. The reactions in the electrocatalytic reactor are as follows (eqs 1−3): anode: C3H8O3 + H 2O → C3H6O4 + 4H+ + 4e−

(1)

cathode: 4H+ + 4e− → 2H 2

(2)

overall: C3H8O3 + H 2O → C3H6O4 + 2H 2

(3)

The generated hydrogen gas at the cathode side is a valuable byproduct that could be used for other hydrogenation reactions or combusted to produce heat and electricity. Many current methods of biomass conversion require the use of large quantities of H2 gas.39−47 This usage of hydrogen gas 6627


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Table 1. Glycerol Conversions and Product Selectivities at Different Glycerol/Pt Molar Ratios for the Electrocatalytic and NonElectrocatalytic Glycerol Oxidation Using Batch Reactors at 60 °C over 20 wt % Pt/C product selectivityd (%) reactor system electrocatalytic reactor

non-electrocatalytic reactor

glycerol/Pt molar ratioa

oxidation sourceb

mass balancec (%)

glycerol conversiond (%)

GAD

GLA

HPA

0.1 M glycerol and 0.5 M H2SO4

195

0.9 V

92.4

64.1

20.0

67.3

3.7

1.3

0

0

0.5 M glycerol and 0.5 M H2SO4

975

1.1 V 0.9 V

98.4 99.7

89.5 37.6

2.6 74.9

90.0 22.1

0.6 2.2

0 0.5

4.3 0

1.0 0

1 M glycerol and 0.5 M H2SO4

1951

1.1 V 0.9 V

97.4 99.0

67.2 15.6

34.2 88.6

46.0 10.4

9.6 0

1.7 0

5.4 0

0.4 0

0.1 M glycerol and 0.5 M H2SO4 0.5 M glycerol and 0.5 M H2SO4

195

1.1 V 100 psia O2

101.0 86.7

24.5 78.2

62.7 8.2

27.5 53.9

2.3 7.1

0 7.7

8.7 8.8

0 1.0

975

100 psia O2

94.1

45.1

43.4

34.7

1.4

8.3

6.0

0.3

feed solution

TTA GCA

OXA

a

Substrate/metal molar ratio. bThe anode applied potentials for the electrocatalytic reactor were 0.9 and 1.1 V (vs SHE). The oxygen pressure for the non-electrocatalytic reactor was 100 psia. cMass balance was determined on the basis of the observed C2 and C3 products. dGlycerol conversion and product selectivity were calculated after a 10 h reaction and identified in liquid C2 and C3 products. Liquid samples after the reaction were analyzed by high-performance liquid chromatography. Abbreviations: GAD, glyceraldehyde; GLA, glyceric acid; HPA, hydroxypyruvic acid; TTA, tartronic acid; GCA, glycolic acid; OXA, oxalic acid.

respect to the reference of a standard hydrogen electrode (SHE) from that of Ag/AgCl in this study. As the glycerol/Pt molar ratio increases from 195 to 1951, glycerol conversion decreases and product selectivity at the same conversion level changes (see Figure 1 and Table S2). This result shows that glycerol conversion and product distribution can be controlled by changing the glycerol/Pt ratio. At applied potentials of 0.9 and 1.1 V, GAD selectivity increases and GLA and HPA selectivities decrease at the same conversion level as that of the glycerol/Pt ratio increases seen in Figure 1, Table 1, and Table S2. At the same glycerol/Pt ratio, glycerol conversion increases when the potential is increased from 0.9 to 1.1 V. Moreover, more oxidized products such as GCA and OXA were obtained by increasing the potential at the same glycerol/Pt ratio. This means that it is possible to selectively control the reaction pathway by changing the electrode potential. A change in electrode potential in the electrocatalytic process is related to that of the Gibbs free energy according to the equation ΔG = −nFΔE, where ΔG is the Gibbs free energy of reaction or adsorption, ΔE is the electrode potential, n is the number of electrons, and F is Faraday’s constant (96485.34 C/mol). The electrode potential affects the Gibbs chemisorption energy of the products if the electrocatalytic process contains an adsorbed product. Thus, the electrode potential control in the electrocatalytic system may be used to manipulate and tune the relative rates of competing electrocatalytic processes and the product selectivity.31,32 Non-Electrocatalytic Glycerol Oxidation: Effects of the Glycerol/Pt Ratio and Addition of a H2SO4 Solution. Glycerol oxidation was also conducted in a conventional catalytic reactor at the same temperature using different concentrations of the feed. The conventional catalytic reactor differs from the electrocatalytic reactor in that a stoichiometric oxidant is required. This oxidant was supplied in the form of pressurized oxygen gas. Figure S2, Table 1, and Table S2 show the glycerol conversion and product selectivity with different glycerol/Pt molar ratios for non-electrocatalytic glycerol oxidation with 100 psia O2 using a batch reactor at 60 °C over 20 wt % Pt/C. The GAD and HPA selectivities increase, and GLA selectivity decreases at the same conversion level as

constitutes a large fraction of the overall operating cost of these technologies. The cost of hydrogen gas is approximately $1/kg near hydrogen pipelines but can increase ≥10-fold when storage and transportation are required.48,49 The simple and compact electrocatalytic reactor design has the benefit of being able to be installed in remote locations, where biomass is plentiful and inexpensive. Thus, this electrocatalytic glycerol oxidation process may provide the advantages or synergistic effects when it is combined with the biomass conversion process that needs hydrogen gas for the reaction. Here we first investigate the techno-economic feasibility of electrocatalytic glycerol oxidation technology to coproduce chemicals and hydrogen with our experimental studies. A simple and direct conversion of glycerol into GAD, GLA, and HPA by anodic oxidation was performed in an electrocatalytic batch reactor over Pt/C catalysts. Reaction performances such as rates, turnover frequencies (TOFs), conversion, selectivity, H2 production rate, and Faradaic efficiency for electrocatalytic glycerol oxidation are investigated and obtained by changing the glycerol/Pt mole ratio and electrode potential. Glycerol oxidation was also conducted in a conventional catalytic reactor to obtain a basis for comparison of the electrocatalytic results. A process simulation model was developed to estimate the techno-economic feasibility of the large-scale production strategy of electrocatalytic glycerol oxidation compared to the conventional catalytic (non-electrocatalytic) glycerol oxidation process.

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RESULTS AND DISCUSSION Electrocatalytic Glycerol Oxidation: Effects of the Glycerol/Pt Ratio and Electrode Potential. A simple and direct conversion of glycerol into GAD, GLA, and HPA by anodic oxidation in an electrocatalytic batch reactor was performed using the electrons produced with only water as a stoichiometric chemical oxidant. Figure 1 and Table 1 show the glycerol conversion and product selectivity at different glycerol/ Pt molar ratios (using different feed concentrations of glycerol) for electrocatalytic glycerol oxidation using a batch reactor at 60 °C over 20 wt % Pt/C. It should be noted that the potentials used for the electrocatalytic batch reaction are expressed with 6628


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ACS Sustainable Chemistry & Engineering the glycerol/Pt ratio increases from 195 to 975, which is similar to the trend for the electrocatalytic process shown in Figure 1, Figure S3, Table 1, and Table S2. This result suggests that the glycerol conversion and product selectivity can also be optimized by controlling the reaction conditions such as the glycerol/Pt mole ratio in the non-electrocatalytic process with pressurized oxygen. Glycerol oxidation in the conventional catalytic batch reactor was performed with and without 0.5 M sulfuric acid to investigate the effect of acidity on glycerol oxidation (Figure S2 and Tables S3 and S4). The glycerol solution in 0.5 M sulfuric acid had TOF values lower than those for the glycerol solution in only water with glycerol/Pt ratios of 195 and 975. As shown in Figure S2, Table 1, and Tables S2 and S3, the selectivity of GAD, GLA, and HPA increased in the presence of acid. These results show how operating with a sulfuric acid solution can decrease the rate of C−C bond cleavage and subsequently produce oxidation products. Changes in the TOF and H2 Production Rate in the Electrocatalytic Reactor System. Figure 2 shows the

Figure 3. Comparison of (a) product yields of the non-electrocatalytic and electrocatalytic processes and (b) Faradaic efficiency results at different glycerol/Pt molar ratios in the electrocatalytic reactor for glycerol oxidation at 60 °C over 20 wt % Pt/C. The yield and Faradaic efficiency for the production of GAD, GLA, and HPA were obtained and calculated after a 10 h reaction. The anode applied potentials for the electrocatalytic reactor were 0.9 and 1.1 V (vs SHE). The oxygen pressure for the non-electrocatalytic reactor was 100 psia.

Figure 2. Changes in the TOF with glycerol oxidation at the anode and the H2 production rate at the cathode at different glycerol/Pt molar ratios in the electrocatalytic reactor system at 60 °C over 20 wt % Pt/C. TOFs and rates were calculated at a conversion of 95− 99%) with high purities (>99.0 wt %). After the recovery of GLA, GAD, and HPA, 45000 t of GLA/year, 29000 t of GAD/ year, and 9000 t of HPA/year are obtained as the main products, and the organic waste (unconverted glycerol and byproducts) is burned to generate process heat in the heat production step. The electrocatalytic glycerol oxidation strategy shows that the overall glycerol-to-chemicals carbon yield is 60.8%: the glycerol-to-GLA, glycerol-to-GAD, and glycerol-toHPA carbon yields are 31.3, 23.2, and 6.3%, respectively, and they are numerically calculated by dividing the moles of carbon of the glycerol by the moles of carbon of the products using the ASPEN Plus Process Simulator. Table S7 provides the associated stream data for the electrocatalytic process. Like the electrocatalytic process, the integrated process for the nonelectrocatalytic glycerol oxidation strategy consists of six main processing steps (see Figures S7 and S8). The non-electro-

contributing to the desired products (GAD, GLA, and HPA) to the overall charge. The Faradaic efficiency of the electrocatalytic reactor relates how much electrical energy is converted to usable chemical energy.37,38 Excess electrical energy can be converted to heat or contribute to undesired chemical products. Figure 3b also shows that the electrocatalytic oxidation system has higher Faradaic efficiencies of >90% at a potential of 0.9 V and for all investigated glycerol/Pt mole ratios. At the higher potential of 1.1 V, a Faradaic efficiency of >80% was obtained by increasing the glycerol/Pt ratio from 195 to 975, and it slightly decreased to 72.3% at a glycerol/Pt ratio of 1951. In the electrocatalytic glycerol oxidation process, the conversion of glycerol into GAD, GLA, and HPA and the product distribution were changed by controlling the glycerol/Pt mole ratio and the electrode potential. The glycerol conversion and product selectivity were also changed with the glycerol/Pt mole ratio in the non-electrocatalytic process. On the basis of these results, the reaction pathways for glycerol oxidation over a Pt/C catalyst are proposed in Figure S5. The glycerol oxidation on a Pt catalyst mainly leads to the formation of GAD, GLA, and HPA, and the latter species is subsequently oxidized to GCA, TTA, and OXA. As shown in this study, a larger TOF and hydrogen production rate were obtained, and a higher product yield and Faradaic efficiency were achieved with a glycerol/Pt ratio of 975 (feed of 0.5 M glycerol in 0.5 M H2SO4 used) and an electrode potential of 1.1 V. On the basis of the experimental results under these conditions, process designs and technoeconomic evaluations of the electrocatalytic glycerol oxidation technology are discussed starting in the next section on how this electrocatalytic glycerol oxidation technology can be efficient and economically feasible compared to the nonelectrocatalytic glycerol oxidation technology. Process Synthesis for Electrocatalytic and NonElectrocatalytic Processes. We developed two integrated process designs based on the technologies (electrocatalytic glycerol oxidation and non-electrocatalytic glycerol oxidation) outlined in the previous experimental sections for the 6630


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Operating Costs and Revenues. The operating costs and revenue streams for both the electrocatalytic and nonelectrocatalytic glycerol oxidation strategies are compared in Table 2. Operating costs consist of raw material costs, utility

catalytic process follows a similar processing sequence used for the electrocatalytic process; however, the major difference is the use of oxygen (23000 t/year) in the non-electrocatalytic reactor (NR-1 in Figure S7). Moreover, a gas−liquid separator (NS-2) is used to separate the unreacted oxygen gas from the reaction mixture; as a result, 13% of the unreacted oxygen gas is recycled back to NR-1. After the removal of oxygen, the liquid mixture (containing GLA, GAD, HPA, water, unconverted glycerol, byproducts, and SA) passes through the GLA/GAD/HPA recovery step that is similar to the electrocatalytic oxidation strategy. After the GLA/GAD/HPA recovery step, 24000 t of GLA/year, 25000 t of GAD/year, and 5000 t of HPA/year are obtained with high purities (99.0 wt %). Table S8 provides the associated stream data for the non-electrocatalytic process. The overall glycerol-to-chemicals carbon yield for the non-electrocatalytic strategy (40.6%) is 20.2% lower than that of the electrocatalytic strategy mainly because of a significant decrease (14.9%) in the GLA yields. Energy Analysis of the Electrocatalytic and NonElectrocatalytic Processes. In this section, an energy analysis was performed for the proposed processes in both the electrocatalytic and non-electrocatalytic glycerol oxidation systems (see Figures S11−S16). When 127000 t of glycerol/ year, which has an energy content of 73 MW, is processed, the electrocatalytic oxidation strategy requires 235 MW of heating energy, 226 MW of cooling energy, and 14 MW of electricity. The energy contents of the main products (15, 14, and 2 MW for GLA, GAD, and HPA, respectively) and H2 are 31 and 14 MW, respectively. When the conventional resources-to-heat efficiency is 71%,50 17 MW of heat is generated from the combustion of byproducts (unconverted glycerol, TTA, and OXA). Here, the off-site heat supply, which is calculated as the difference between the heating energy requirement and the onsite heat generation, is estimated to be 218 MW. Thus, 355 MW of off-site primary energy is required when the resourcesto-heat and resources-to-electricity generation efficiencies are 71 and 30%, respectively.50 Compared to that of the electrocatalytic glycerol oxidation strategy, the off-site primary energy supply (293 MW) is 17% lower because the nonelectrocatalytic glycerol oxidation strategy does not require electricity for glycerol oxidation and has a larger amount of onsite heat generation (28 MW) as a result of higher yields of byproducts. The energy efficiency was calculated as the ratio of the energy output (GLA, GAD, HPA, and H2) to the energy input (glycerol and primary energy) for both the electrocatalytic and non-electrocatalytic strategies. The energy efficiency of the electrocatalytic glycerol oxidation strategy (10.6%) is 5.2% higher than that of the non-electrocatalytic glycerol oxidation strategy (5.8%) because there is a 111% higher energy output from the electrocatalytic oxidation strategy despite its 17% higher energy input. To increase the energy efficiency, we performed heat integration by designing a heat exchanger network (HEN). After heat integration, the heats are transferred between the hot and cold process streams, and the heating energy requirements for the electrocatalytic and non-electrocatalytic strategies are reduced by the recovery of 24 and 23 MW to 211 and 213 MW, respectively. Consequently, the energy efficiencies for the electrocatalytic and nonelectrocatalytic strategies increased to 11.5 and 6.4%, respectively. In the Supporting Information, Figures S9−S14 show the detailed design of the HEN and energy flow diagrams for both the electrocatalytic and non-electrocatalytic strategies.

Table 2. Capital Costs, Operating Costs, and Revenue Streams of the Electrocatalytic and Non-Electrocatalytic Glycerol Oxidation Strategies electrocatalytic glycerol oxidation ($/year)

non-electrocatalytic glycerol oxidation ($/year)

capital costs GLA/GAD/ HPA production GLA/GAD/ HPA recovery WWT storage heat production others (utility)

29850018 10655335

31758888 10649087

7734300

8017521

4682189 632079 4176162

4523676 455424 5628819

1969952

2484361

operating costs raw material costs glycerol water SA O2 Ca(OH)2 WWT chemical other operating costsa utility costs steam cooling water electricity fixed operating costs

151459693 85331356 64847223 2961 6255710 − 13262682 962779

142204095 86964941 64847223 − 6255710 1626520 13262682 972805

8478060

9002084

50944386 39271960 3340798 8331628 6705892

39378361 35846448 3484960 46954 6858709

76960179 52890899 16583674 7485606

56713277 46896841 9816436 −

revenues GAD HPA H2 a

Other operating costs include catalyst refurbishing and disposal costs.

costs, fixed operating costs, and other operating costs. The total operating costs for both the electrocatalytic and non-electrocatalytic strategies are $151.5 million/year (electrocatalytic glycerol oxidation strategy) and $142.2 million/year (nonelectrocatalytic glycerol oxidation strategy). The largest portion of the total operating cost for both strategies is the raw material costs, especially the glycerol cost ($64.8 million/year, 43−46% of the total operating cost). Additionally, the utility costs, especially the steam cost ($39.3 million/year for the electrocatalytic strategy and $35.8 million/year for the non-electrocatalytic strategy, 25−26% of the total operating cost), are the second largest portion of the total operating cost for the electrocatalytic and non-electrocatalytic strategies. Here, the reason for the higher total operating cost for the electrocatalytic strategy compared to that for the non-electrocatalytic strategy is the higher electricity cost (a difference of $8.3 million/year), although the high oxygen cost ($1.6 million/year) is not 6631


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Figure 5. Comparison of the costs and revenues of the electrocatalytic and non-electrocatalytic glycerol oxidation strategies.

non-electrocatalytic glycerol oxidation strategy, the net manufacturing cost is $117.3 million/year [the difference between the total production cost ($174.0 million/year) and the other revenues ($56.7 million/year)]. The MSP of GLA for the non-electrocatalytic glycerol oxidation strategy ($4.91/kg of GLA) is out of the range of prices for glycerol derivatives (details shown in Figure 5). Although the total production cost for the electrocatalytic strategy was 4% higher than that of the non-electrocatalytic strategy, the MSP of GLA for the electrocatalytic strategy was 53% lower than that of the nonelectrocatalytic strategy. This is because of the difference between the GLA production and the other revenues in the proposed strategies. The level of annual GLA production of the electrocatalytic glycerol oxidation strategy was 90% higher than that of the non-electrocatalytic glycerol oxidation strategy. Additionally, the other revenues for the electrocatalytic strategy were 36% higher than that of the non-electrocatalytic strategy. In addition, Figures S15 and S16 show the contribution to the MSP from the process section, and Tables S17 and S18 provide a detailed discounted cash flow analysis for the electrocatalytic and non-electrocatalytic strategies. Sensitivity Analysis. Key economic parameters (glycerol cost, GAD price, and steam cost) that have large impacts on the MSP were investigated in this study. Thus, we performed a sensitivity analysis to identify and know how the variations in the key economic parameters affect the MSPs for the electrocatalytic and non-electrocatalytic strategies (see Figure 6). When the glycerol cost is decreased by 20%, the MSPs of the electrocatalytic and non-electrocatalytic strategies decrease by 12.4 and 11.0%, respectively. Moreover, the MSPs of the electrocatalytic glycerol oxidation and non-electrocatalytic glycerol oxidation strategies are decreased by 10.1 and 7.9%, respectively, when the GAD price is increased by 20%. Finally, the MSPs of the electrocatalytic and non-electrocatalytic strategies are decreased by 7.5 and 6.1%, respectively, when the steam cost is decreased by 20%. As a result, when the parameters for glycerol cost, GAD price, and steam cost are adjusted simultaneously, the MSPs of GLA for the electro-

required for the electrocatalytic reactor system. The revenue streams consist of income from GAD, HPA, and H2. The total revenue for the electrocatalytic glycerol oxidation strategy is $77.0 million/year, which is 36% higher than that of the nonelectrocatalytic glycerol oxidation strategy ($56.7 million/year) mainly because of the hydrogen revenue (with a difference of $7.5 million/year) and higher HPA and GAD revenue (with a difference of $6.8 million/year and $6.0 million/year, respectively). Minimum Selling Price for the Electrocatalytic and Non-Electrocatalytic Processes. We analyzed the economic feasibility of the proposed processes for both the electrocatalytic and non-electrocatalytic glycerol oxidation strategies using the most probable scenario of the pioneer plant analysis. First, we determined a minimum selling price (MSP, the price that makes the net present value equal to zero) for the GLA using a discounted cash flow analysis51 with various economic assumptions and parameters (see Table S16). The MSP was expressed in terms of dollars per kilogram of GLA, which can be calculated on the basis of the annual amount of production of GLA and the net manufacturing cost [which is the difference between the total production cost and the other revenues (GAD, HPA, and H2)]. Here, the total production cost can be obtained as follows. First, the total installed cost is converted to a fixed capital investment (FCI) that includes direct costs and indirect costs. The FCI is divided by the capital cost growth (0.64). Then, the total capital investment (TCI) is calculated by the sum of the FCI divided by the capital cost growth, land cost, and working capital. The TCI is annualized with the capital charge rate calculated from the discounted cash flow analysis. Finally, the total production cost was determined as the sum of the annualized TCI and total operating cost. The net manufacturing cost for the electrocatalytic glycerol oxidation strategy is $104.3 million/year [the difference between the total production cost ($181.3 million/year) and the other revenues ($77.0 million/year)]. As shown in Figure 5, the MSP of GLA for the electrocatalytic glycerol oxidation strategy is $2.30/kg of GLA, and it is in the range of current prices for glycerol derivatives ($0.7−3.0/kg). In the case of the 6632


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process systems engineering results (Figures S6−S16 and Tables S7−S18) (PDF)

AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]. *E-mail: [email protected]. *E-mail: [email protected]. ORCID

Hyung Ju Kim: 0000-0002-3489-6488 Youngmin Kim: 0000-0002-6893-5270 Jechan Lee: 0000-0002-9759-361X Jeehoon Han: 0000-0001-5268-2128 Present Address ⊥

J.L.: Department of Environment and Energy, Sejong University, Seoul 05006, South Korea.

Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by the KRICT projects (SI1701-05 and KK1706-G09) from the Korea Research Institute of Chemical Technology.

Figure 6. Tornado charts to illustrate the impact of ±20% changes in key economic parameters on the MSP of GLA: (a) electrocatalytic glycerol oxidation strategy and (b) non-electrocatalytic glycerol oxidation strategy.

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(1) Huber, G. W.; Iborra, S.; Corma, A. Synthesis of Transportation Fuels from Biomass: Chemistry, Catalysts, and Engineering. Chem. Rev. 2006, 106 (9), 4044. (2) Behr, A.; Eilting, J.; Irawadi, K.; Leschinski, J.; Lindner, F. Improved utilisation of renewable resources: New important derivatives of glycerol. Green Chem. 2008, 10 (1), 13. (3) Gallezot, P. Conversion of biomass to selected chemical products. Chem. Soc. Rev. 2012, 41 (4), 1538. (4) Gallezot, P. Catalytic Conversion of Biomass: Challenges and Issues. ChemSusChem 2008, 1 (8−9), 734. (5) Cui, M.-S.; Deng, J.; Li, X.-L.; Fu, Y. Production of 4Hydroxymethylfurfural from Derivatives of Biomass-Derived Glycerol for Chemicals and Polymers. ACS Sustainable Chem. Eng. 2016, 4 (3), 1707. (6) Mizugaki, T.; Arundhathi, R.; Mitsudome, T.; Jitsukawa, K.; Kaneda, K. Highly Efficient and Selective Transformations of Glycerol Using Reusable Heterogeneous Catalysts. ACS Sustainable Chem. Eng. 2014, 2 (4), 574. (7) Priya, S. S.; Bhanuchander, P.; Kumar, V. P.; Dumbre, D. K.; Periasamy, S. R.; Bhargava, S. K.; Lakshmi Kantam, M.; Chary, K. V. R. Platinum Supported on H-Mordenite: A Highly Efficient Catalyst for Selective Hydrogenolysis of Glycerol to 1,3-Propanediol. ACS Sustainable Chem. Eng. 2016, 4 (3), 1212. (8) Sotto, N.; Cazorla, C.; Villette, C.; Billamboz, M.; Len, C. Toward the Sustainable Synthesis of Biosourced Divinylglycol from Glycerol. ACS Sustainable Chem. Eng. 2016, 4 (12), 6996. (9) Wu, Z.; Zhao, K.; Ge, S.; Qiao, Z.; Gao, J.; Dou, T.; Yip, A. C. K.; Zhang, M. Selective Conversion of Glycerol into Propylene: SingleStep versus Tandem Process. ACS Sustainable Chem. Eng. 2016, 4 (8), 4192. (10) Ciriminna, R.; Pina, C. D.; Rossi, M.; Pagliaro, M. Understanding the glycerol market. Eur. J. Lipid Sci. Technol. 2014, 116 (10), 1432. (11) Zhang, Z.; Xin, L.; Qi, J.; Wang, Z.; Li, W. Selective electroconversion of glycerol to glycolate on carbon nanotube supported gold catalyst. Green Chem. 2012, 14 (8), 2150. (12) Kwon, Y.; Koper, M. T. M. Combining Voltammetry with HPLC: Application to Electro-Oxidation of Glycerol. Anal. Chem. 2010, 82 (13), 5420.

catalytic and non-electrocatalytic glycerol oxidation strategies can be decreased to $1.61/kg and $3.68/kg, respectively.

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CONCLUSION Electrocatalytic glycerol oxidation can be used to coproduce valuable chemicals and hydrogen without using stoichiometric chemical oxidants. An electrocatalytic oxidation reactor system produced GAD, GLA, and HPA at yields of ≤62% at a glycerol/Pt molar ratio of 975 with an applied potential of 1.1 V over a Pt/C catalyst. A conventional catalytic (non-electrocatalytic) oxidation reactor with pressurized O2 produced a similar TOF and similar rates but a lower yield of GAD, GLA, and HPA (41.4%). We did process designs and technoeconomic evaluations for the electrocatalytic and non-electrocatalytic oxidation processes based on our experimental results. An energy efficiency of 10.6% for the electrocatalytic glycerol oxidation strategy was 5.2% higher than that of the nonelectrocatalytic glycerol oxidation strategy. The MSP of GLA for the electrocatalytic process of $2.30/kg of GLA was lower than the value of $4.91/kg of GLA for the non-electrocatalytic process, which is in the range of current market prices for glycerol derivatives ($0.7−3.0/kg). This result could be attributed to the high yields of the reaction products and to the additional production of hydrogen in the electrocatalytic process.

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REFERENCES

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acssuschemeng.7b00868. Experimental and analytical methods, additional experimental results (Figures S1−S5 and Tables S1−S6), and 6633


Research Article

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