Process Design and Evaluation of Value-added ... - Springer Link

Biotechnology and Bioprocess Engineering 17: 1055-1061 (2012) DOI 10.1007/s12257-012-0257-1

RESEARCH PAPER

Process Design and Evaluation of Value-added Chemicals Production from Biomass A-Ra Go, Jae Wook Ko, Sang Jun Lee, Seung Wook Kim, Sung Ok Han, Jinwon Lee, Han Min Woo, Youngsoon Um, Jaewook Nam, and Chulhwan Park

Received: 19 April 2012 / Revised: 8 May 2012 / Accepted: 13 May 2012 © The Korean Society for Biotechnology and Bioengineering and Springer 2012

Abstract Three different biodiesel production processes were simulated using the SuperPro Designer program. The process for producing biodiesel from soybean oil and methanol was designed using commercial chemical catalysts. This chemical process was compared with the biological process catalyzed by immobilized enzymes. In addition, a hybrid process consisting of catalytic biodiesel production and enzymatic glycerol carbonate production was designed and simulated for the conversion of waste glycerol to value-added chemical. Finally, the economics and productivity of these processes were evaluated to determine economic feasibility.

A-Ra Go, Jae Wook Ko, Chulhwan Park* Department of Chemical Engineering, Kwangwoon University, Seoul 139-701, Korea Tel: +82-2-940-5173; Fax: +82-2-912-5173 E-mail: [email protected] Sang Jun Lee, Seung Wook Kim Department of Chemical Biological Engineering, Korea University, Seoul 136-701, Korea Sung Ok Han School of Life Science and Biotechnology, Korea University, Seoul 136701, Korea Jinwon Lee Department of Chemical and Biomolecular Engineering, Sogang University, Seoul 121-742, Korea Han Min Woo, Youngsoon Um Clean Energy Research Center, Korea Institute of Science and Technology, Seoul 136-791, Korea Jaewook Nam* School of Chemical Engineering, Sungkyunkwan University, Suwon 440746, Korea Tel: +82-31-290-7349; Fax: +82-31-290-7272 E-mail: [email protected]

Keywords: biodiesel, glycerol carbonate, glycerol, enzyme, process design, simulation

1. Introduction Due to depleted fossil fuel resources and rising environmental concerns, renewable energy is an attractive alternative for fossil fuels [1]. Biodiesel is one of strong candidates and is produced from renewable resources and emits less environmental pollutants than fossil fuels [2]. Biodiesel is typically produced from the transesterification of vegetable or animal oils with alcohol. The reaction is usually enhanced or expedited by chemical and biological catalysts, but thus far only chemical catalysts have been used in commercial biodiesel production [3]. A chemical process using chemical catalysts has some advantages, such as a relatively shorter reaction time and lower catalyst cost than a biological process using enzymes. However, the chemical process requires the chemical pretreatment of raw materials, complex processing steps for the glycerol recovery, high energy supply for transesterification, and the wastewater treatment that is accompanied by additional costs [4-6]. In contrast, the biological process using immobilized enzymes has low energy requirements, an easy separation process, and less polluting emissions [7]. However, commercialization of the biological process is often impeded by slow reaction time and expensive enzyme costs. Decreasing the reaction time and raising the economic feasibility through the use of immobilized lipase are the common research topics in recent studies towards the development of this process in the near future. In addition to attempts to cut down the cost of the biodiesel production, by-products are the other factors that

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make production profitable. For example, 10% (wt/wt) glycerol is one of these and recently the price drop due to the increased biodiesel production, even though the worldwide supply surged excessively. Consequently, there were numerous studies on converting glycerol into high valueadded products [8,9]. Glycerol carbonate (4-hydroxymethyl1,3-dioxolan-2-one), a glycerol derivative, is an odorless, hydrophilic liquid that can be used in battery electrolytes, monomers for polymerization, medical solvents, chemical intermediates and in biolubricants owing to its adhesion to metallic surfaces and resistance to oxidation, hydrolysis, and pressure [8]. There have been several reports on the enzymatic production of glycerol carbonate from glycerol, which have indicated the possibility for coproduction of biodiesel and glycerol carbonate [10,11]. The enzymatic synthesis of glycerol carbonate has several advantages: it occurs under mild conditions, it has higher selectivity than chemical synthesis, and it has lower chance to produce enantiomer [10]. We propose three process designs (Fig. 1): biodiesel production by chemical catalyst (P-BDC), biodiesel production by enzyme (P-BDE), and a hybrid process of biodiesel production by chemical catalyst and glycerol carbonate production by enzyme (HP-BDC-GCE). The details of these processes were investigated using the process simulator SuperPro Designer, developed at Intelligent (Scotch Plains, NJ, USA). Finally, the economic feasibilities for those processes were estimated and compared with each other for the production of valuable chemicals, based on biomass.

2. Materials and Methods 2.1. Process design 2.1.1. Process design for biodiesel production by chemical catalyst (P-BDC) P-BDC contained three processing sections: (1) reaction process, (2) biodiesel purification process, and (3) glycerol recovery process (Fig. 2) [12-14]. In the reaction process, biodiesel (0.83 $/kg [15]) and glycerol (0.25 $/kg [16]) were produced from the transesterification of soybean oil (0.37 $/kg [17]) with methanol (0.25 $/kg [15]) (R-101). This reaction was catalyzed by a base catalyst (NaOCH3, 0.23 $/kg [15]). The product from the reaction was separated into biodiesel and waste glycerol in the biodiesel purification process (V-101). The separated biodiesel was passed through a washing process to improve its quality and the waste glycerol was recovered as pure glycerol through neutralization and distillation processes (C-101, C-102).

Biotechnology and Bioprocess Engineering 17: 1055-1061 (2012)

Fig. 1. Schematic diagram of the three processes used in this study.

The reactants for biodiesel reaction are triglycerides and an alcohol. Various oils such as vegetable oils, animal fats, and waste oils are generally used as raw materials, but in this study, we choose soybean oils as the raw material for P-BDC. Among the chemical catalysts widely used in industry, base catalysts are currently used rather than acid catalysts due to their superior reaction activity and weaker corrosive effect on the reactors [18]. Considering the economics and reactivity, methanol and base catalyst (NaOCH3) were utilized as the alcohol and catalyst for P-BDC. One mol of triglyceride and 3 mol of alcohol were reacted in catalyst media and converted to 3 mol of biodiesel and 1 mol of glycerol. The reaction was performed in Reactor #1 (R-101) at 60oC for 60 min to give a 90% conversion. After the reaction, the produced glycerol was separated by the centrifugation process (DC-101). In the biodiesel purification process, various by-products were removed from the biodiesel. The biodiesel stream (S-113) was separated by centrifugation and contained catalysts and soap. The stream was washed by water and HCl (2.0 $/kg [19]), then the biodiesel and washing agent were separated by centrifugation. The resulting biodiesel contained some water, but water content should be down to 0.045% to satisfy the regular standard (maximum of 0.050% (v/v)) of ASTM (the American Society for Testing and Materials). The operation was performed by the flash vaporization unit (V-105). Additional process steps were included to obtain highpurity glycerol from waste glycerol. As the biodiesel purification process, soap was removed by HCl (R-103). The fatty acids produced in this step were removed as organic wastes by centrifugation, and the 4.5 pH of the glycerol stream was neutralized with NaOH (0.41 $/kg [13]) (R-105). A two-step distillation process was designed to remove methanol (C-101) and then water and residual

Process Design and Evaluation of Value-added Chemicals Production from Biomass

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Fig. 2. Process design for biodiesel production by chemical catalyst (P-BDC).

Fig. 3. Process design for biodiesel production by enzyme (P-BDE).

methanol (C-102). This glycerol purification process achieves a final glycerol purity of over 90%. 2.1.2. Process design for biodiesel production by enzyme (P-BDE) A lipid degradation enzyme, lipase, was used as a catalyst in P-BDE (Fig. 3). Immobilized lipase (Novozym 435,

1,060 $/kg [13]) was used for easy recovery and reuse of the enzyme [20]. In this process, we assumed that the enzyme recycled 10 times. Biodiesel yield was 93% after 24 h reaction (R-101) [21] and the immobilized enzymes were recovered by centrifugation (DS-101). P-BDE has easier purification and separation processes compared to P-BDC because enzyme removal and washing

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Fig. 4. Hybrid process design for biodiesel production by chemical catalyst and by glycerol carbonate production via enzyme (HP-BDCGCE).

processes were not required. After enzyme recovery, oil/ fat removal centrifugation (DC-101) was performed to separate the biodiesel and glycerol. Biodiesel as the upper product was distilled to ensure a high purity (of over 90%) by removal or unreacted material (C-102). Glycerol, as the bottom product, was distilled due to methanol removal (C101) to give a final purity of over 90%. 2.1.3. Hybrid process design for biodiesel production by chemical catalyst and glycerol carbonate production by enzyme (HP-BDC-GCE) Converting glycerol into glycerol carbonate is a potential solution for the current worldwide excessive glycerol supply [11]. Therefore, a hybrid process (i.e., biodiesel production by chemical catalyst and glycerol carbonate production by the enzyme [HP-BDC-GCE]), are proposed and simulated in this study (Fig. 4). Dimethyl carbonate (DMC, 1.21 $/kg [22]) is an ecofriendly material due to its non-toxicity [5,23]. One mol of glycerol and 1.5 mol of DMC were converted to 1 mol of

glycerol carbonate and 2 mol of methanol using immobilized enzyme, which was used for biodiesel production in a tetrahydrofuran (THF) solvent [11]. As in P-BDE case, the enzyme is assumed to be recycled 10 times. One mol of glycerol was converted to 1 mol of glycerol carbonate at 60oC after a 30 h reaction (R-106). The immobilized enzyme was removed by centrifugation for the removal of solids (DS-101). THF and methanol were process solvents and the byproduct was eliminated by distillation process (C-103), so that no waste removal process was required. The remaining DMC was recycled in the distillation process (C-104), to give a final yield of over 90% of glycerol carbonate.

3. Results and Discussion 3.1. Process evaluation for P-BDC, P-BDE, and HPBDC-GCE P-BDC, P-BDE, and HP-BDC-GCE were designed,


Table 1. Reaction conditions and raw material data for the three processes Conditions and raw materials Reaction Catalyst Temperature (oC) Time (h) Yield (%)

P-BDC*

NaOCH3 60 1 90.0

Raw materials Soybean oil (kg/h) 4,246.8 Methanol (kg/h) 459.1 13.3 NaOCH3 (kg/h) Novozym 435 (kg/h) HCl (kg/h) 10.6 Water (kg/h) 185.8 NaOH (kg/h) 1.8 DMC (kg/h) -

P-BDE*

HP-BDC-GCE*

Novozym 435 30 24 93.8

NaOCH3, Novozym 435 60, 60 1, 30 90.0, 100

4,640.0 873.6 185.6 -

4,246.8 459.1 13.3 212.0 10.6 185.8 1.8 409.0

*

P-BDC: Chemical process for biodiesel production. P-BDE: Enzymatic process for biodiesel production. * HP-BDC-GCE: Hybrid process for chemical biodiesel production and enzymatic glycerol carbonate production. *

simulated, and analyzed as continuous processes [24,25]. Annual biodiesel production over 330 days in this process simulation was approximately 34,000 tones [26]. The reaction conditions and raw material quantities are shown in Table 1. In P-BDC, 4,246 kg/h of soybean oil was supplied. A transesterification reactor (Fig. 2, R-101, R-102) for biodiesel production and a reactor for removal of both catalysts and salts were also required (Fig. 2, R-103, R-104, R-105). These reactors and their lines could be corroded by the acid and base reagents used as catalysts for biodiesel

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production. This corrosion can lead to additional cost for replacement and repair. The unit product cost ($/kg) for biodiesel production was 0.485 $/kg (Table 2). The gross margin (for economic evaluation), return on investment (ROI) and payback time were 43.21%, 90.19% and 1.11 years, respectively. P-BDE needed 4,640 kg/h of soybean oil, and the unit product cost for biodiesel production was calculated to be 5.193 $/kg. Due to the lower waste production and the higher recyclability of catalyst, i.e. enzyme, the process can be considered as eco-friendly when compared to P-BDC. However, the process is not economically viable due to the high cost of the catalyst and to the long reaction time [19]. Thus, the raw material cost accounted for a large portion of the overall cost for annual process operation. In particular, the high enzyme price [13] increased the annual operation cost that makes the process unprofitable. Enhancing the economic aspect of P-BDE, e.g. the decrease of enzyme cost, the increase of enzyme recycling and the decrease of reaction time, can solve this problem. For example, an enzyme price of under 4 $/kg or under 2 $/kg would yield a gross margin of 7.98 or 18.14% and payback time of 5.27 or 3.23 years, respectively. When the enzyme is recycled over 200 times (or equivalently the enzyme price is about 5.3 $/kg), a gross margin and payback time will be 1.37% and 8.97 years, respectively. HP-BDC-GCE also required 4,246 kg/h of soybean oil, 409 kg/h of DMC, and 212 kg/h of enzyme to synthesize glycerol carbonate from glycerol subsequent to the primary biodiesel production process. HP-BDC-GCE consisted of reactors of P-BDC and a reactor for synthesizing glycerol carbonate from glycerol (R-106, Fig. 4). The unit product cost for biodiesel and glycerol carbonate production was calculated to be 5.905 $/kg. The gross margin, ROI, and

Table 2. Executive summary for the three processes P-BDC* Project totals Investment ($) Main product rate (kg MP/yr) Annual operation cost ($/yr) Unit product cost ($/kg) Main revenue ($/yr) Other revenue ($/yr) Total revenue ($/yr) Process indices Gross margin (%) ROI (%) Payback time (yr) *

15,578,247 34,033,429 16,512,649 0.485 28,247,746 831,398 29,079,145

43.21 90.19 1.11

P-BDE* 24,429,705 33,999,996 176,559,609 5.193 28,219,997 711,123 28,931,120

-

P-BDC : Chemical process for biodiesel production. P-BDE: Enzymatic process for biodiesel production. * HP-BDC-GCE: Hybrid process for chemical biodiesel production and enzymatic glycerol carbonate production. *

HP-BDC-GCE* 26,710,142 33,992,268 200,719,890 5.905 28,213,583 223,895,024 252,108,607

20.38 201.92 0.50

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payback time were 20.38%, 201.92% and 0.50 years, respectively.

R&D Center (ABC) of Korea, a grant funded by the Ministry of Education, Science and Technology (20100029799), by the National Agenda Project (NAP) of the Korea Research Council of Fundamental Science and Technology (KRCF) and by a Research Grant of Kwangwoon University (2012).

3.2. Process comparison The glycerol carbonate produced in HP-BDC-GCE is anticipated to substitute for propylene carbonate, which is an intermediate industrial and medical solvent [10]. HPBDC-GCE is an extension of P-BDC, and the cost for the production of glycerol carbonate was added. In comparing the three processes, P-BDE showed the highest operating cost due to the relatively expensive enzyme cost; P-BDC revealed the lowest process cost. Although the investment cost of HP-BDC-GCE is higher than that of P-BDC due to the greater number of process units, the economic evaluation of items, such as ROI and payback time, appeared to be reasonable compared to the other two processes because the process includes glycerol carbonate production that is a value-added product. Then, HP-BDC-GCE is expected to be a prospective process in consideration of these results.

4. Conclusion In this study, three biodiesel production processes were analyzed by the process simulator (SuperPro Designer). Commercially available chemical process, P-BDC and other alternative processes with enzymes, P-BDE and HPBDC-GCE, were simulated. All of them were subjected to economic evaluation. The investment cost and unit cost of production of P-BDC were cheaper than those of the other two processes due to the low cost of the chemical catalyst compared to the enzyme. Even though P-BDE can be considered as eco-friendly, the process operating cost and unit product cost of P-BDE were too expensive due to the high enzyme cost. Although the investment cost of HPBDC-GCE was higher than that of P-BDC, the ROI and payback time, which are items of economic evaluation, were reasonable because the process produces glycerol carbonate as a value-added chemical. We expect that maximizing production of both chemicals and adding recycling process of the immobilized enzyme could decrease the production cost and thereby raise the economic viability of the process up to a commercially acceptable level. Based on these results, fundamental research for collecting processing data for reaction and recycling enzymes and developing additional valuable materials that can be produced from biomass production can be anticipated.

Acknowledgments This research was supported by the Advanced Biomass

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