Improvement of 1,3-Butadiene Separation in 2,3-Butanediol Dehydration Using Extractive Distillation

processes

Article Improvement of 1,3-Butadiene Separation in 2,3-Butanediol Dehydration Using Extractive Distillation

Daesung Song 1 , Young-Gak Yoon 2, Seung-Kwon Seo 2 and Chul-Jin Lee 2,* 1 Department of Civil, Safety & Environmental Engineering, Hankyong National University, 327 Jungang-ro, Anseong-si, Gyenggi-do 17579, Korea 2 School of Chemical Engineering and Materials Science, Chung-Ang University, 84 Heukseok-ro, Dongjak-gu, Seoul 06974, Korea * Correspondence: [email protected]; Tel.: +82-2-820-5941

Received: 28 March 2019; Accepted: 20 June 2019; Published: 1 July 2019

Abstract: This study was performed to investigate the extractive distillation for 1,3-butadiene (1,3-BD) purification as a part of the 2,3-butanediol (2,3-BDO) dehydration process. The separation of 1,3-BD from 1-butene produced as a 2,3-BDO dehydration by-product while using distillation is complicated due to the similar volatilities of the two compounds. Thus, an extractive distillation system is proposed for the effective recovery of 1,3-BD, and is compared with a conventional distillation system in terms of its performance and economic feasibility. A higher 1,3-BD recovery rate was achieved while using the proposed system and the relative profitabilities of both separation systems were analyzed according to the market price of 1,3-BD, which is a decisive variable for economic feasibility.

Keywords: 2,3-butanediol dehydration; distillation; extractive distillation; 1,3-butadiene; 1-butene; economic feasibility

1. Introduction 1,3-Butadiene (1,3-BD), which is a particularly useful platform chemical, is traditionally produced via the steam cracking process while using a petroleum-derived feedstock. However, the traditional 1,3-BD process suffers from environmental and technical issues, because petroleum is a non-renewable resource and its production fluctuates with the market. The emissions and by-products of petroleum can harm soils, surface groundwater, and other ecosystems. In addition, steam-cracking in the traditional 1,3-BD process requires high temperatures and a great amount of energy [1]. Some researchers have attempted to develop bio-fermentation for the production of 1,3-BD to resolve these issues. The biotechnological routes for producing 1,3-BD begin with the synthesis of 2,3-butanediol (2,3-BDO) from different species of microorganisms [2]. Studies have been conducted to determine the optimal synthesis route and reaction conditions, including the oxygen concentration, pH, temperature, and substrate [3], for high product yields during bio-fermentation. Many studies have also investigated the conversion of 2,3-BDO to 1,3-BD and the required catalysts. Duan et al. [4] investigated the vapor phase catalytic dehydration of 2,3-BDO with several rare-earth-oxide catalysts and experimentally determined the selectivity of each catalyst. Similarly, Nguyen et al. [5] developed a one-step catalytic dehydration of 2,3-BDO while using rare-earth phosphate catalysts that was efficient for the production of 1,3-BD with high selectivity. Kim et al. [6] analyzed the nature of the active centers of silica-supported alkali phosphate catalysts during the conversion of 2,3-BDO. Song [7] developed a pilot-scale reactor model for the dehydration of 2,3-BDO to form 1,3-BD and methyl ethyl ketone (MEK) while using reaction kinetics and a deactivation model of an amorphous calcium phosphate catalyst.

Processes 2019, 7, 410; doi:10.3390/pr7070410 www.mdpi.com/journal/processes Processes 2019, 7, 410 2 of 11

Process intensification for integrating utility energy has been performed since the distillation process for separating products from bio-fermentation and dehydration requires a large amount of heat and many column stages. Haider et al. [8] introduced feed preheater and vapor exchangers, which significantly reduced the amount of energy that is consumed by the reboiler and condenser of the 2,3-BDO recovery column. Hong et al. [9] developed a hybrid 2,3-BDO recovery column combined with multiple evaporators, which showed that the preliminary evaporators and heat integration design substantially increased the energy efficiency. Penner et al. [10] assessed the thermodynamic efficiencies of different separation process designs combining reverse osmosis, extraction, reactive distillation, decantation, and salting-out extraction to purify 2,3-BDO and MEK. Distillation is conventionally used to purify 1,3-BD from the associated by-products (1-butene, 2-butene, water, etc.) of 2,3-BDO dehydration, similarly to the 2,3-BDO recovery processes. Song et al. [11] demonstrated a conceptual design to produce 1,3-BD via 2,3-BDO dehydration, including a detailed distillation process for the recovery of 1,3-BD and MEK. A recent study showed that a combined extraction and distillation process for 2,3-BDO recovery reduced the costs when compared to those of a conventional distillation configuration [12]. Extractive distillation is considered to be an alternative purification method to overcome the similar volatilities of 1,3-BD and 1-butene [13], which enabled the efficient separation by using a miscible, high-boiling point, and relatively nonvolatile solvent that changes the relative volatilities of 1,3-BD and 1-butene. In summary, earlier catalytic studies focused on increasing the selectivity toward the target product and analyzing the catalytic behaviors in the 2,3-BDO dehydration process. The modeling and simulation contributed to the improvement of subsequent separation processes. However, a comparison of conventional and extractive distillation processes for the recovery of 1,3-BD from bio-fermentation products has not yet been reported to the best of our knowledge. In addition, several studies have reported that 1,3-BD production from 2,3-BDO dehydration is highly dependent on the market price of 2,3-BDO [14,15]. This implies that the choice of process design (i.e., conventional or extractive distillation) for 1,3-BD separation depends on the market price of 1,3-BD. This research was performed to investigate the extractive distillation process that is used to purify 1,3-BD in 2,3-BDO dehydration. The prior dehydration process of the proposed model is based on a kinetic model with regard to the amorphous calcium phosphate catalyst [11]. Comparative analysis of conventional and extractive distillation was performed in terms of the performance and economic feasibility. The costs of conventional and extractive distillation were estimated via a techno-economic analysis, and the market price of 1,3-BD for which the extractive distillation process showed better economic feasibility than the conventional process was calculated. This work contributes to the literature in the following aspects:

- Provides steady-state simulation results for conventional and extractive distillation processes for the recovery of 1,3-BD from bio-fermentation products. - Calculates an advantageous price of 1,3-BD for the selection of the extractive distillation.

The overall 2,3-BDO dehydration process is explained in Section2, providing a theoretical background. The conventional and extractive distillation processes are described in Section3. The 1,3-BD recovery rates and economic assessments are compared in Section4 while using modified payback time, which considers the differences in initial investments and profits for both processes to evaluate the economic feasibility of the extractive distillation system.

2. Theoretical Background

The 2,3-Butanediol (2,3-BDO) Dehydration Process Figure1 shows a block flow diagram of a previously developed process, where 1,3-BD and MEK are produced from 2,3-BDO dehydration [11]. This process separates 1,3-BD and MEK from by-products, such as water, 1-butene, and 2-butene. The water is discharged to the top side of a quencher and the others migrate to the bottom side. The top-side stream flows to a 1,3-BD purification Processes 2019, 7, 410 3 of 11

Processes 2019, 7, x FOR PEER REVIEW 3 of 12 unit, which consists of a 3-phase decanter, cyclohexane removal column, and two normal distillation columns.columns. Some of the components of the stream, including MEK, are separatedseparated inin thethe three-phasethree-phase decanter.decanter. A stream containing cyclohexane andand 1,3-BD is then transported from the MEK puriﬁcationpurification unit.unit. Cyclohexane is eliminated in the cyclohexane removalremoval column and the stream is recycled toto thethe waterwater removalremoval unit.unit. MEKMEK isis recoveredrecovered throughthrough thethe waterwater removalremoval unitunit andand MEKMEK puriﬁcationpurification unit.unit.

FigureFigure 1.1. Block ﬂowflow diagram of the process used to produceproduce 1,3-Butadiene (1,3-BD) and methyl ethyl ketoneketone (MEK)(MEK) [[11].11].

AsAs shown in Figure1 1,, thethe distillationdistillation columnscolumns areare usedused toto purifypurify 1,3-BD1,3-BD (target(target processprocess inin bold).bold). AchievingAchieving recoveryrecovery of of high high purity purity 1,3-BD 1,3-BD (>99%) (>99%) through through distillation distillation is difficult, is becausedifficult, the because volatilities the ofvolatilities 1,3-BD and of 1,3-BD 1-butene and are 1-butene quite similar,are quite as similar, shown as in shown Figure 2in. Figure Hence, 2. the Hence, 1,3-BD the recovery1,3-BD recovery rate is estimatedrate is estimated to be 94% to whenbe 94% distillation when distillation is only used, is only and theused, residual and the 1,3-BD residual flows 1,3-BD out the flows top-side out of the the top- 1st normalside of distillationthe 1st normal column distillation with 1-butene, column which with causes 1-butene, an overall which loss causes of 1,3-BD. an Therefore,overall loss an of extractive 1,3-BD. distillationTherefore,Processes 2019 systeman, 7, xextractive FOR was PEER developed REVIEWdistillation as ansystem alternative was developed method to as improve an alternative the recovery method rate to of improve 1,3-BD.4 of the 12 recovery rate of 1,3-BD. 1 Vapor-Liquid Equilibrium 0.9 (1,3-BD and 1-Butene) 0.8 Y=X line 0.7 0.6 0.5 0.4 0.3 0.2 Vapor Mole Fraction (1-Butene) Fraction Mole Vapor 0.1 0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 Liquid Mole Fraction (1-Butene)

FigureFigure 2.2. Vapor-liquidVapor-liquid equilibriumequilibrium curvecurve ofof 1,3-BD1,3-BD andand 1-butene.1-butene.

3. Process Design

Two distillation processes—conventional and extractive distillation—were designed while using Aspen Plus v8.6 software. The essential features of the two processes are described later in this section. The detailed column specifications, product specifications, and stream information are provided in Supplementary Materials (Tables S1–S5).

3.1. The Thermodynamic Property Model The products of 2,3-BDO dehydration are alkenes, ketones, and water, which can be phase separated. The non-random two-liquid model (NRTL), universal quasi-chemical model (UNIQUAC), and their variants were candidates for the simulation and they were selected while using decision trees [16]. However, the simulation software (Aspen Plus v8.6, AspenTech, Bedford, Massachusetts, USA) cannot process interaction parameters that are related to N-methyl-2-pyrrolidone (NMP). Thus, the primary missing interaction parameters (NMP/1,3-BD, NMP/1-butene, and NMP/2-butene) were estimated while using the UNIQUAC functional group activity coefficients (UNIFAC). The NRTL- binary parameters that were used in the developed models are listed in the Supplementary Materials (Tables S6–S10). The NRTL1 and NRTL2 parameters were used for the vapor-liquid equilibrium (VLE) and (vapor)-liquid-liquid equilibrium, respectively.

3.2. The Conventional Distillation Process A conventional distillation system that is composed of two successive distillation columns was used for 1,3-BD purification, as shown in Figure 3. The first distillation column separated 1-butene (BD-1BUTENE) from the feed stream (BD-FEED). Approximately 5.0% of the total amount of 1,3-BD was lost during this separation. In the second distillation column, 2-butene (BD-2BUTENE) is removed from the inlet (BD-1), which caused a 0.94% loss in the total amount of 1,3-BD. Through these distillation processes, 5.9% (211 kg/h) of the total 1,3-BD is lost and utilized as fuel.

Processes 2019, 7, 410 4 of 11

3. Process Design Two distillation processes—conventional and extractive distillation—were designed while using Aspen Plus v8.6 software. The essential features of the two processes are described later in this section. The detailed column speciﬁcations, product speciﬁcations, and stream information are provided in Supplementary Materials (Tables S1–S5).

3.1. The Thermodynamic Property Model The products of 2,3-BDO dehydration are alkenes, ketones, and water, which can be phase separated. The non-random two-liquid model (NRTL), universal quasi-chemical model (UNIQUAC), and their variants were candidates for the simulation and they were selected while using decision trees [16]. However, the simulation software (Aspen Plus v8.6, AspenTech, Bedford, Massachusetts, USA) cannot process interaction parameters that are related to N-methyl-2-pyrrolidone (NMP). Thus, the primary missing interaction parameters (NMP/1,3-BD, NMP/1-butene, and NMP/2-butene) were estimated while using the UNIQUAC functional group activity coeﬃcients (UNIFAC). The NRTL-binary parameters that were used in the developed models are listed in the Supplementary Materials (Tables S6–S10). The NRTL1 and NRTL2 parameters were used for the vapor-liquid equilibrium (VLE) and (vapor)-liquid-liquid equilibrium, respectively.

3.2. The Conventional Distillation Process A conventional distillation system that is composed of two successive distillation columns was used for 1,3-BD puriﬁcation, as shown in Figure3. The ﬁrst distillation column separated 1-butene (BD-1BUTENE) from the feed stream (BD-FEED). Approximately 5.0% of the total amount of 1,3-BD was lost during this separation. In the second distillation column, 2-butene (BD-2BUTENE) is removed from the inlet (BD-1), which caused a 0.94% loss in the total amount of 1,3-BD. Through these distillation processes, 5.9% (211 kg/h) of the total 1,3-BD is lost and utilized as fuel. Processes 2019, 7, x FOR PEER REVIEW 5 of 12

Main Routes of 1,3-BD BD-WATER

BD- D-BD 1BUTENE BD-FEED

BD-1 BD- 1st 2nd 2BUTENE Distillation Distillation Column Column Figure 3. The 1,3-BD purification puriﬁcation unitunit for the conventional distillation process [[11].11].

3.3. The Extractive Distillation Process The proposedproposed process process utilizes utilizes extractive extractive distillation distillation instead instead of two of successive two successive distillation distillation columns forcolumns 1,3-BD for puriﬁcation. 1,3-BD purification. Several Several solvents solvents can be can used be inused extractive in extractive distillation distillation to separate to separate 1,3-BD, 1,3- includingBD, including acetonitrile, acetonitrile, dimethylformamide dimethylformamide (DMF), (DMF and NMP.Extractive), and NMP. Extractive distillations distillations that use acetonitrile that use andacetonitrile DMF to and recover DMF 1,3-BD to recover have been1,3-BD previously have been investigated. previously investigated. However, the However, application the of application acetonitrile isof notacetonitrile favored dueis not to favored its toxicity. due DMF to its can toxicity. be hydrolyzed DMF can into be hydrolyzed formic acid duringinto formic this process, acid during which this is corrosiveprocess, which to carbon is corrosive steel. Therefore, to carbon NMP steel. is Theref widelyore, used NMP to recover is widely 1,3-BD used because to recover of its 1,3-BD high solubility because andof its selectivity high solubility toward and unsaturated selectivity hydrocarbonstoward unsaturated [17]. hydrocarbons [17]. The extractiveextractive distillation system consists of anan extractiveextractive distillationdistillation column, NMP recovery column, heavy-impurity removal drum, stripper, and BD recovery column, as illustrated in Figure 44.. TheThe boldbold lines lines represent represent the the main main routes routes for 1,3-BDfor 1,3- recovery.BD recovery. The feed The streamfeed stream (BD-FEED), (BD-FEED), which mainlywhich mainly contains 1,3-BD, water, 1-butene, and 2-butene, flows to the extractive distillation process for 1,3-BD purification.

Main Routes of 1,3-BD

BD-4 BD-3 MU-NMP OFFGAS

BD-2 Waste- Water1 Heavy MU-H2O Extractive BD NMP Impurities Distillation Stripper Recovery Recovery Removal Column Column Drum BD-FEED Column

H2O ED-BD H2O- BD-1 NMP5 H2O- H2O- Waste- NMP1 NMP2 Water2 H2O- NMP3

H2O- NMP4 Figure 4. The 1,3-BD purification unit used for the extractive distillation process.

The VLE for 1,3-BD and 1-butene changes due to the solubility variance of 1,3-BD in NMP when NMP is introduced at the top of the extractive distillation column in the liquid phase, as shown in Figure 5. The make-up water decreases the operating temperature, reducing the operating costs and preventing 1,3-BD oligomerization [18]. In the extractive distillation column, 1,3-BD, water, and NMP (BD-1) are transported to the stripper where most of the 1-butene (OFFGAS) is transported to the top side. Subsequently, part of the 1,3-BD, water, and NMP (H2O-NMP1) are discharged to the bottom of the stripper and 1,3-BD (BD-3) is recycled from the top side of the NMP recovery column. The highly-purified 1,3-BD (ED-BD) is then separated from the water (Waste-Water1) through the bottom of the BD recovery column. The NMP is recycled into the extractive distillation column with water (H2O-NMP3 and H2O-NMP4). In addition, the heavy-impurity removal drum eliminates impurities heavier than NMP, such as 1,3-BD oligomers.

Processes 2019, 7, x FOR PEER REVIEW 5 of 12

Main Routes of 1,3-BD BD-WATER

BD- D-BD 1BUTENE BD-FEED

BD-1 BD- 1st 2nd 2BUTENE Distillation Distillation Column Column Figure 3. The 1,3-BD purification unit for the conventional distillation process [11].

3.3. The Extractive Distillation Process The proposed process utilizes extractive distillation instead of two successive distillation columns for 1,3-BD purification. Several solvents can be used in extractive distillation to separate 1,3- BD, including acetonitrile, dimethylformamide (DMF), and NMP. Extractive distillations that use acetonitrile and DMF to recover 1,3-BD have been previously investigated. However, the application of acetonitrile is not favored due to its toxicity. DMF can be hydrolyzed into formic acid during this process, which is corrosive to carbon steel. Therefore, NMP is widely used to recover 1,3-BD because of its high solubility and selectivity toward unsaturated hydrocarbons [17]. ProcessesThe2019 ,extractive7, 410 distillation system consists of an extractive distillation column, NMP recovery5 of 11 column, heavy-impurity removal drum, stripper, and BD recovery column, as illustrated in Figure 4. The bold lines represent the main routes for 1,3-BD recovery. The feed stream (BD-FEED), which containsmainly 1,3-BD,contains water,1,3-BD, 1-butene, water, 1-butene, and 2-butene, and 2-butene ﬂows, flows to the to extractivethe extractive distillation distillation process process for for 1,3-BD1,3-BD puriﬁcation. purification.

Main Routes of 1,3-BD

BD-4 BD-3 MU-NMP OFFGAS

BD-2 Waste- Water1 Heavy MU-H2O Extractive BD NMP Impurities Distillation Stripper Recovery Recovery Removal Column Column Drum BD-FEED Column

H2O ED-BD H2O- BD-1 NMP5 H2O- H2O- Waste- NMP1 NMP2 Water2 H2O- NMP3

H2O- NMP4 FigureFigure 4. 4.The The 1,3-BD 1,3-BD puriﬁcation purification unit un usedit used for for the the extractive extractive distillation distillation process. process.

TheThe VLE VLE for for 1,3-BD 1,3-BD and and 1-butene 1-butene changes changes due due to to the the solubility solubility variance variance of of 1,3-BD 1,3-BD in in NMP NMP when when NMPNMP is is introduced introduced at at the the top top of of the the extractive extractive distillation distillation column column in in the the liquid liquid phase, phase, as as shown shown in in FigureFigure5. 5. The The make-up make-up water water decreasesdecreases thethe operatingoperating temperature, temperature, reducing reducing the the operating operating costs costs and andpreventing preventing 1,3-BD 1,3-BD oligomerization oligomerization [18]. [18 In]. the In theextractive extractive distillation distillation column, column, 1,3-BD, 1,3-BD, water, water, and andNMP NMP(BD-1) (BD-1) are transported are transported to the to stripper the stripper where where mostmost of the of 1-butene the 1-butene (OFFGAS) (OFFGAS) is transported is transported to the totop theside. top Subsequently, side. Subsequently, part of part the of1,3-BD, the 1,3-BD, water, water, and NMP and NMP(H2O-NMP1) (H2O-NMP1) are discharged are discharged to the tobottom the bottomof the ofstripper the stripper and 1,3-BD and 1,3-BD (BD-3) (BD-3) is recycled is recycled from from the top the topside side of the of theNMP NMP recovery recovery column. column. The Thehighly-purified highly-puriﬁed 1,3-BD 1,3-BD (ED-BD) (ED-BD) is then is then separated separated from from the water the water (Waste-Water1) (Waste-Water1) through through the bottom the bottomof the ofBD the recovery BD recovery column. column. The NMP The is NMPrecycled is recycledinto the extractive into the extractive distillation distillation column with column water with(H2 waterO-NMP3 (H2 O-NMP3and H2O-NMP4). and H2O-NMP4). In addition, In addition,the heavy-impurity the heavy-impurity removal drum removal eliminates drum eliminates impurities Processes 2019, 7, x FOR PEER REVIEW 6 of 12 impuritiesheavier than heavier NMP, than such NMP, as 1,3-BD such as oligomers. 1,3-BD oligomers.

1 Vapor-Liquid Equilibrium 0.9 (1,3-BD and 1-Butene) 0.8 Y=X line 0.7 0.6 0.5 0.4 0.3 0.2 Vapor Mole Fraction (1-Butene) Vapor 0.1 0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 Liquid Mole Fraction (1-Butene)

Figure 5. Vapor-liquid equilibrium curve of 1,3-BD and 1-butene upon introduction of N-methyl-2- Figure 5. Vapor-liquid equilibrium curve of 1,3-BD and 1-butene upon introduction of N-methyl-2- pyrrolidone (NMP). pyrrolidone (NMP).

4. Results and Discussion

4.1. Column Specifications and Performance Table 1 summarizes the column specifications and total heat duty for both of the processes used herein for 1,3-BD purification. Although the conventional distillation process uses fewer columns than the extractive distillation process, its total number of column stages and heat duty values are higher than those of the extractive distillation process. This is because the separation of 1,3-BD from 1-butene via distillation requires a large amount of heat and many column stages, as explained in Section 2. The heat duty and the number of stages in the column (first distillation column) were approximately 2.51 MW and 80 stages, respectively. In addition, the second distillation column required 56 stages, owing to the similar boiling points of 1,3-BD and 2-butene.

Table 1. Summary of number of columns, number of stages, heat duty, and compressor electricity that are required for the processes tested herein.

Conventional Distillation Process Extractive Distillation Process Number of Number Heat duty Name Heat duty (MW) Name stages of stages (MW) Extractive 1st distillation 80 2.51 distillation 36 1.43 column column Column 2nd distillation 56 1.08 Stripper 15 1.05 column NMP recovery - - - 5 0.675 column BD recovery - - - 15 0.0165 column Compressor None Electricity [kW] 51.3

Table 2 summarizes the stream information (BD-FEED), amount of 1,3-BD recovered using each process, and recovery rates. The recovery rate was calculated, as follows (Equation (1)):

Processes 2019, 7, 410 6 of 11

4. Results and Discussion

4.1. Column Specifications and Performance Table1 summarizes the column specifications and total heat duty for both of the processes used herein for 1,3-BD purification. Although the conventional distillation process uses fewer columns than the extractive distillation process, its total number of column stages and heat duty values are higher than those of the extractive distillation process. This is because the separation of 1,3-BD from 1-butene via distillation requires a large amount of heat and many column stages, as explained in Section2. The heat duty and the number of stages in the column (first distillation column) were approximately 2.51 MW and 80 stages, respectively. In addition, the second distillation column required 56 stages, owing to the similar boiling points of 1,3-BD and 2-butene.

Table 1. Summary of number of columns, number of stages, heat duty, and compressor electricity that are required for the processes tested herein.

Conventional Distillation Process Extractive Distillation Process Number of Number Heat duty Name Heat duty (MW) Name stages of stages (MW) Extractive Column 1st distillation 80 2.51 distillation 36 1.43 column column 2nd distillation 56 1.08 Stripper 15 1.05 column NMP recovery --- 5 0.675 column BD recovery --- 15 0.0165 column Compressor None Electricity [kW] 51.3

Table2 summarizes the stream information (BD-FEED), amount of 1,3-BD recovered using each process, and recovery rates. The recovery rate was calculated, as follows (Equation (1)):

BDD(ED) BD[kg] RBD[%] = − 100. (1) BDBD FEED[kg] × −

Here, RBD represents the 1,3-BD recovery rate in the process, BDD(ED) BD indicates the amount of − 1,3-BD in the conventional distillation process (or extractive distillation process), and BDBD FEED is the − amount of 1,3-BD that is transported to the 1,3-BD purification unit. The simulation results show that 94% and 99% of the 1,3-BD can be recovered via conventional and extractive distillation processes, respectively. The 1,3-BD purified while using both processes satisfied the product specification (>99% purity), as presented in the Supplementary Materials (S8).

Table 2. Performance comparison of the distillation and extractive distillation processes.

Stream BD-FEED D-BD [11] ED-BD Property Mass ﬂow rate (kg/h) 3628 3367 32 Mass fraction 1,3-BD 0.977 0.99 0.993 1,3-BD recovery rate (%) 94 99

4.2. Economic Assessment The economic feasibility of the 1,3-BD puriﬁcation units was analyzed for the conventional and extractive distillation processes. Estimating the economics of the subsequent steps of the two processes Processes 2019, 7, 410 7 of 11 is unnecessary because they are identical. Figure6 compares the economic assessment results, which include the total capital cost, total operating cost, and revenue. The calculation method, equations, and estimated values are included in the Supplementary Materials (Table S11). The following assumptions were used for the economic analysis.

(1) The plant is located on the west coast of the USA. (2) The plant operates for 8000 h annually. (3) The plant is constructed using stainless steel (SS304 or SS316) because 1,3-BD is corrosive to carbon steel. Processes 2019, 7, x FOR PEER REVIEW 8 of 12

Figure 6. Comparison of the economics of the conventional and extractive distillation processes: Figure 6. Comparison of the economics of the conventional and extractive distillation processes: (a) (a) Revenue; (b) purchase cost of equipment; (c) total capital cost; and, (d) total operating cost [11,19]. Revenue; (b) purchase cost of equipment; (c) total capital cost; and, (d) total operating cost [11,19]. The total capital cost of the extractive distillation process is higher than that of the conventional The total capital cost of the extractive distillation process is higher than that of the conventional distillation process due to the increased number of columns and the additional compressor required. distillation process due to the increased number of columns and the additional compressor required. However, the operating costs of the two processes are similar, even though that of the extractive However, the operating costs of the two processes are similar, even though that of the extractive distillation process includes the costs of make-up water and NMP, because the ﬁrst distillation column distillation process includes the costs of make-up water and NMP, because the first distillation in the conventional distillation process requires much higher energy at approximately 3.59 MW. column in the conventional distillation process requires much higher energy at approximately 3.59 The revenue was calculated by assuming that 1,3-BD was priced at $3/kg, including fuel, and that the MW. The revenue was calculated by assuming that 1,3-BD was priced at $3/kg, including fuel, and recovery rate increased from approximately 94% to 99%. that the recovery rate increased from approximately 94% to 99%.

4.3. Economic Feasibility with a Changing 1,3-BD Price The payback time is the time that is required to recover an investment cost in terms of profits. The payback time can be estimated, as follows (Equation (2)): Payback Time (year) = . (2) ( )

The total fixed capital investment was estimated as the sum of the total capital cost and working capital, which was calculated as 20% of the total capital cost. The start-up cost was 10% of the total fixed capital investment and the taxes were also considered while using Turton’s method. The depreciation was 5% of the total fixed capital cost, which is similar to that of the running time of similar plants [20,21]. The modified payback time was used to compare the economic feasibility of the two processes, which is the time that is required to recover the difference in the investment between the conventional and extractive distillation processes with respect to the difference in their profits. The modified payback time was calculated, as follows (Equation (3)):

Processes 2019, 7, 410 8 of 11

4.3. Economic Feasibility with a Changing 1,3-BD Price The payback time is the time that is required to recover an investment cost in terms of proﬁts. The payback time can be estimated, as follows (Equation (2)):

Total ﬁxed capital investment + Startup cos t Payback Time (year) = . (2) Proﬁt (after taxes) + Depreciation

The total fixed capital investment was estimated as the sum of the total capital cost and working capital, which was calculated as 20% of the total capital cost. The start-up cost was 10% of the total fixed capital investment and the taxes were also considered while using Turton’s method. The depreciation was 5% of the total fixed capital cost, which is similar to that of the running time of similar plants [20,21]. The modified payback time was used to compare the economic feasibility of the two processes, which is the time that is required to recover the difference in the investment between the conventional Processesand 2019 extractive, 7, x FOR PEER distillation REVIEW processes with respect to the difference in their profits. The modified9 of payback12 time was calculated, as follows (Equation (3)): Modified Payback Time (year) = Difference (Total fixed capital investment + Start up cos(3) t ) Modified Payback ( ) Time (year) = . (3) Difference (Profit after taxes. + Depreciation) ( ) If the modified payback time is <3 years, which is the normal time that is required for constructing Ifa profitablethe modified commercial payback plant, time the is extractive<3 years, distillationwhich is the process normal is more time profitable that is required than conventional for constructingdistillation a profitable because commercial the difference plant, in the the investment extractive fordistillation both the process processes is canmore be profitable recovered than using the conventionaldifference distillation in profits withinbecause three the yearsdifference [20]. in the investment for both the processes can be recovered Next,using wethe considereddifference in the profits profitability within three of the years 1,3-BD [20]. purification process, which is significantly Next,influenced we considered by the market the profitability price of 1,3-BD. of the Its 1,3-BD price is purification highly dependent process, on which the automobile is significantly tire market, influencedas depicted by the inmarket Figure price7. of 1,3-BD. Its price is highly dependent on the automobile tire market, as depicted in Figure 7. 6.50 1,040 6.00 1,3-BD ($/kg) 1,020 5.50 5.00 1,000 4.50 4.00 980 3.50 ($/kg) 960

3.00 (1000ton) 2.50 940 2.00 920 1.50 1.00 900 2009 2010 2011 2012 2013 2014 2015 Year

Figure 7. The price of 1,3-BD and the consumption of automobile tires (2009–2015) [22]. Figure 7. The price of 1,3-BD and the consumption of automobile tires (2009–2015) [22]. FigureFigure 8 shows8 shows the modified the modified payback payback time timewith withthe changing the changing prices prices of 1,3-BD, of 1,3-BD, for which for which the the profitabilityprofitability can be can determined be determined while whileusing usinga paybac a paybackk time of time three of threeyears. years. When When the price the priceof 1,3-BD of 1,3-BD is $2.85/kg,is $2.85 the/kg, modified the modified payback payback time is time three is threeyears. years. Therefore, Therefore, when whenthe price the priceof 1,3-BD of 1,3-BD is higher is higher than $2.85/kg,than $2.85 the/kg, extractive the extractive distillation distillation process process is more is moreprofitable. profitable. Otherwise, Otherwise, the normal the normal distillation distillation systemsystem more moreeconomically economically separates separates 1,3-BD 1,3-BD from 1- frombutene 1-butene (gray (grayzone in zone Figure in Figure 8), even8), eventhough though the the 1,3-BD recovery rate is relatively low. The conventional distillation process is currently more profitable than extractive distillation, given that the average price from 2013 to 2015 was $2.5/kg.

Processes 2019, 7, 410 9 of 11

1,3-BD recovery rate is relatively low. The conventional distillation process is currently more proﬁtable thanProcesses extractive 2019, 7, x distillation,FOR PEER REVIEW given that the average price from 2013 to 2015 was $2.5/kg. 10 of 12

6.0 Distillation Process Extractive 5.5 Distillation Process 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 Modified Payback Time (yr) Time Modified Payback 2.85 $/kg 1.0 2.00 2.25 2.50 2.75 3.00 3.25 3.50 3.75 4.00 1,3-BD Price ($/kg)

Figure 8. Process feasibility with changing 1,3-BD price. Figure 8. Process feasibility with changing 1,3-BD price. 5. Conclusions 5. Conclusions An extractive distillation process was proposed to increase the 1,3-BD recovery rates by efficiently separatingAn extractive 1,3-BD from distillation 1-butene, process and its was performance proposed was to comparedincrease the with 1,3-BD that of recovery the conventional rates by distillationefficiently separating process. Conventional1,3-BD from 1-butene, and extractive and its distillation performance processes was compared were designed, with that and of thethe 1,3-BDconventional recovery distillation rates were process. estimated Conventional to be approximately and extractive 94% distillation and 99%, processes respectively. were Both designed, of the processesand the 1,3-BD were analyzedrecovery inrates terms were of estimated their economic to be feasibility.approximately Based 94% on and the modified99%, respectively. payback time,Both whichof the processes uses the diwerefference analyzed between in terms the conventionalof their economic and feasibility. extractive Based distillation on the processes modified inpayback terms oftime, the which investment uses the and difference profit, the between extractive the distillation conventional process and isextractive more profitable distillation when processes the price in ofterms 1,3-BD of the is investment$2.85/kg. When and profit, considering the extractive that the currentdistillation market process price is of more 1,3-BD profitable is approximately when the ≥ $2.5price/kg of (2013–2015), 1,3-BD is the≥$2.85/kg. conventional When distillation considering process that retains the itscurrent economic market advantages price inof the1,3-BD current is businessapproximately environment. $2.5/kg However, (2013–2015), extractive the convention distillational will distillation become more process profitable retains when its theeconomic 1,3-BD priceadvantages increases in tothe> current$2.85/kg. business environment. However, extractive distillation will become more profitable when the 1,3-BD price increases to >$2.85/kg. Supplementary Materials: The following are available online at http://www.mdpi.com/2227-9717/7/7/410/s1, Table S1: Stream information of distillation process, Table S2: Stream information of extractive distillation process;Author TableContributions: S3: Product D.S. Specification; performed Table all S4:the Columnsimulation Specification works, guided of distillation by C.-J.L. process, Y.-G.Y. Table conducted S5: Column all Specificationeconomic analysis of extractive and wrote distillation the paper, process; while S.-K.S. Table revised S6: Data the Source final document. of Binary Parameters, Table S7: Binary Parameters (NRTL1) of distillation process, Table S8: Binary Parameters (NRTL1) of extractive distillation processes; TableFunding: S9: Binary This research Parameters received (NRTL2) no external of distillation funding. process, Table S10: Binary Parameters (NRTL2) of extractive distillation processes; Table S11: Detailed Economic Assessment, Table S12: Revenue and Utility Summary of distillationAcknowledgments: and extractive This research distillation was processes. supported by the Chung-Ang University Research Scholarship Grants in 2017 and the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (No. Author2019R1G1A1003364). Contributions: D.S. performed all the simulation works, guided by C.-J.L. Y.-G.Y. conducted all economic analysis and wrote the paper, while S.-K.S. revised the final document. Funding:Conflicts Thisof Interest research: The received authors no declare external no funding. conflict of interest. Acknowledgments: This research was supported by the Chung-Ang University Research Scholarship Grants in 2017 and the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (No. 2019R1G1A1003364). Conflicts of Interest: The authors declare no conflict of interest.

Processes 2019, 7, 410 10 of 11

Nomenclature

1,3-BD 1,3-Butadiene 2,3-BDO 2,3-Butanediol DMF Dimethylformamide ED-BD 1,3-BD product stream of the extractive distillation process ISBL Inside battery limits NMP N-methyl-2-pyrrolidone NRTL Non-random two-liquid model NRTL-RK Non-random two-liquid Redlich–Kwong model OSBL Outside battery limits D-BD 1,3-BD product stream of the distillation process UNIFAC UNIQUAC functional group activity coeﬃcient UNIQUAC Universal quasi-chemical model VLE Vapor-liquid equilibrium

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