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Chemical and biological-based isoprene production: Green metrics
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Chemical and biological-based isoprene production: Green metrics Ana R.C. Morais a , Sylwia Dworakowska b , Alberto Reis a , Luisa Gouveia a , Cristina T. Matos a , Dariusz Bogdał b , Rafał Bogel-Łukasik a,∗ a
Laboratório Nacional de Energia e Geologia, I.P., Unidade de Bioenergia, Estrada do Pac¸o do Lumiar 22, 1649-038 Lisboa, Portugal Department of Biotechnology and Physical Chemistry, Faculty of Chemical Engineering and Technology, Cracow University of Technology, Warszawska 24, 31-155 Cracow, Poland b
a r t i c l e
i n f o
Article history: Received 18 July 2013 Received in revised form 20 May 2014 Accepted 21 May 2014 Available online xxx Keywords: Green metrics Isoprene Escherichia coli E-factor Economic evaluation Land use
a b s t r a c t Green metrics is a methodology which allows the greenness of either new or already existing processes to be assessed. This paper is a part of a special issue devoted to green metrics in which this methodology is applied to different processes to assess bio and petrochemical routes. In this work, green metrics were used as a tool to validate and compare the petrochemical and biological processes of isoprene production. The Sumitomo process has been selected for this comparison as it is beneficial because of it using less expensive C1 components as well as the fact that it has lower investment costs for a single-step process. The production of isoprene through a modified Escherichia coli bacterial process has been selected for comparison with the fossil pathway. The green metrics evaluation was performed for both processes to produce isoprene and to target 50,000 tonnes of isoprene yearly. Although, the calculated costs for the bio-isoprene are slightly higher than the actual market price of its fossil counterpart, the results obtained reveal that the bacteria-based isoprene production is able to substitute the petrochemical process, with material and energy efficiency. This conclusion has also been proved by the increasing number of industrial interest in bioisoprene. The challenge comes from the land use needed for the production of a carbon source which might be solved by the use of waste and residues which are rich in carbohydrates or lignocellulosic biomass which can be converted to simple sugars. © 2014 Elsevier B.V. All rights reserved.
1. Introduction Isoprene (C5 H8 , 2-methyl-1,3-butadiene) is a hydrocarbon, which is colourless and a volatile liquid at room temperature. Isoprene occurs extensively in nature at very low concentrations being metabolised by several organisms such as animals, plants (including macro- and microalgae), fungi and bacteria [1–3]. Isoprene is a key chemical commodity required to manufacture a diverse range of industrial products, including (in over of 95%) a wide variety of elastomers used in surgical gloves, motor mounts, rubber bands, golf balls, condoms and shoes. However, the most important use of isoprene is the production of synthetic rubber (cispolyisoprene) in tire manufacturing (cars and trucks). Furthermore, 5% of the worldwide production of isoprene is dedicated to produce chemicals, which are used as intermediates for pharmaceuticals, vitamins, flavourings, perfumes, and epoxy hardeners [2,4,5].
∗ Corresponding author. Tel.: +351 210924600. E-mail addresses: [email protected] (D. Bogdał), [email protected] (R. Bogel-Łukasik).
Isoprene was first synthesised in 1860 by C.E. Williams through the pyrolysis of natural rubber. Nowadays, most isoprene production comes from fossil fuel resources. The three major producers of high-purity isoprene are Nizhnekamskneftekhim, SynthezKauchuk and Togliattikauchuk from Russia with a production of 427,500 tonnes in 2011. The next largest world producers of isoprene are Goodyear and Shell (USA) [6]. Dehydrogenation of isopentane as well as synthesis of isoprene from isobutylene and formaldehyde are commonly used in Russia, whereas direct isolation of isoprene from C5 stream by extractive distillation is executed in the USA [7]. Global industrial production of synthetic isoprene from petrochemical feedstocks is close to 1 million tonnes per year and currently isoprene consumption is around 850,000 tonnes annually [8]. A large amount of the isoprene produced annually is liberated by plants which collectively release approximately 500 million tonnes of carbon per year [9], making isoprene the dominant gaseous hydrocarbon produced by vegetation. This amount of isoprene is sufficient to produce 60 billion car and truck tyres, which is 50 times the current global manufacturing of 1.2 billion tyres [2]. However, the use of isoprene from plants and animals for commercial purposes is still economically
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unfeasible, although the use of latex produced by Hevea (rubber trees) to produce rubber is one example of economically efficient biological production [10]. Taking into account the growing demand for isoprene, the recent pressure on fossil fuels, and the environmental concerns related to global warming, there is an increased need for the production of chemicals such as isoprene from renewable sources. Both, the materials and processes should be more efficient, sustainable, cost-effective and environmentally friendly (e.g., using biological processes). An industrial production of bioisoprene is an interesting option and for this reason many leading tyre producers perform advanced studies in this direction [11]. Goodyear, a well-known tyre manufacturer that produces around 200 million tyres a year, works with Genencor to engineer bacteria which will produce bioisoprene [12]. Bridgestone is also co-developing bioisoprene in collaboration with Ajinomoto, through fermentation [13]. The Michelin Company has a joint venture with Amyris to develop the bioisoprene process [14].
cracking fractions is considerably more efficient than the synthesis of this commodity in the chemical manner since there is enough ethylene produced to satisfy the large share of isoprene demands [4]. Due to the limited availability of isoprene as a by-product in the production of ethylene, much effort has been devoted to develop synthetic methods of isoprene production. There are main four synthetic routes leading to isoprene [4,15]: (i) addition of acetone to acetylene to form 2-methyl-3-butyne-2-ol and subsequent partial hydrogenation and dehydration (Snamprogetti process) used by ANIC and Karbochem, (ii) dimerization of propene to isohexene followed by demethanation (Goodyear – Scientific Design process), (iii) dismutation of isobutene and 2-butene to form 2-methyl2-butene followed by dehydrogenation, (iv) double addition of formaldehyde to isobutene resulting in 4,4-dimethyl-1,3-dioxane followed by dehydration and cleavage of formaldehyde. The fourth process has been scaled up into industrial processes by several companies (Bayer, IFP, Marathon Oil, Kuraray and the CIS).
Recently this route was improved and simplified by Sumitomo Chemical through use of less expensive feedstock i.e. CH3 OH and O2 in the presence of catalysts: H3 PO4 –MoO3 /SiO2 and mixed oxide systems based on Mo–Bi–P–Si, Mo–Sb–P–Si, or H3 PO4 –V–Si [15].
The goal of this work is to compare the petrochemical and biological (bacteria-based) processes for isoprene production using green metrics (material and energy efficiency, economic evaluation, and land use).
This process has not been yet practiced commercially, but is similar to the commercial ones [4]. Furthermore the Sumitomo route is a subject of great interest because it has some advantages such as less expensive C1 components used in the synthesis, as well as, lower investment costs of a single-step process. For this reason this process has been selected as a potential petrochemical route of isoprene production and was compared with the one using bacteria.
2. Production 2.1. Petrochemical processes
2.2. Bio-based process
Over the years many technological processes of isoprene production have been proposed and studied. Today the main world isoprene production occurs via separation from C5 cracked fractions obtained as a by-product in the pyrolysis of hydrocarbons to ethylene. There are two possible technologies available to produce isoprene from C5 streams (after separation of cyclopentadiene). The first one is isolation by extractive distillation (with N-methylpyrrolidone (BASF), dimethylformamide (Nippon Zeon) or acetonitrile (Shell, Goodrich-Arco); isoprene productivity of ca. 30,000 tonnes per year) or fractional distillation as an azeotrope with n-pentane (Goodyear; not yet commercialised). The second assumes the dehydrogenation of isopentane and isopentenes (methylbutenes) using Fe2 O3 –Cr2 O3 –K2 CO3 catalyst at 600 ◦ C with a yield of 85% (CIS, Shell, Arco, Exxon). Direct isolation allows obtaining of isoprene without additional synthetic steps thus making this method more preferred since isoprene concentration in a typical C5 stream is 14–23 wt% [4,5,15]. The isoprene production yield is typically very low and is in the order of 2%–5% of the ethylene yield [15]. The efficiency of the process might be increased by converting gas oil as a starting material instead of naphtha. On the other hand, recovery of isoprene from C5
Two principal pathways have been identified for the biosynthesis of isoprene by bacteria: cytosolic mevalonate (MVA) and plastidial 1-deoxy-d-xylulose-5-phosphate (DOXP) pathways [16]. Bacteria are able to produce isoprene by DOXP as well as by the MVA pathway by gene modification [17,18]. Isoprene can be produced by both, Gram-positive and Gramnegative bacteria, under facultative anaerobic conditions through the carbon source oxidation process. Among different genus, Bacillus seems to be the best producer of isoprene [19]. Yang et al. reported isoprene biosynthesis by a genetically engineered bacterial strain, obtained by co-expressing an optimised MVA pathway and the isoprene synthase (IspSPa ) (from the higher plant Populus alba) on Escherischia coli [17]. This strain allowed isoprene production up to 6.3 g L−1 under 40 h of fed-batch fermentation. The Danisco US Inc. together with The Goodyear Tire & Rubber Company patented the isoprene production method, using Bacillus bacteria. A modified strain achieves an isoprene production yield from glucose of 8.9% at 40 h or even 10.7% at 59 h [20]. Other key players on the tyres market are also developing the technologies to produce bioisoprene. Ajinomoto and other tyre company Bridgestone Corp as well as Michelin with Amyris are working on the development
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of bioisoprene [13]. Considering the large interest of the major tyre producers it can be foreseen that bioisoprene will become in a near future a commodity produced from natural resources substituting fossil feedstock.
3. Metrics Material and energy efficiencies, economic evaluation and land use have been selected to evaluate the greenness of the examined isoprene production processes. These four metrics have been selected among numerous others existing in the literature [21]. The selection has been made by the UBIOCHEM COST Action and the selected metrics were chosen as the most representative which tackle all features of sustainability such as environmental, economic and social aspects [22]. For the bacterial isoprene production process, the assumptions regarding the economic (glucose cost of 250 D tonne−1 ) and energetic inputs according to literature data were used [23–28]. For petrochemical pathway of isoprene production, the assumptions are given together with the calculations of the particular metric.
3.1. Material efficiency and E-factor
3
Table 1 Theoretical calculations of the amount of chemicals used in the production of isoprene. Input/kg
Output/kg
Isobutylenea Oxygen Catalyst
1.37 0.39 0.001
Isoprene
Methaneb Syngasc Methanold
0.74 1.26 1.17
Syngas Methanol Isoprene
1.26 1.17 1
input (isobutylene, methane, oxygen, catalyst)
2.501
output (isoprene)
1
E-factor Material efficiency a b c d
1.50 0.40
Selectivity of 60% [15]. Selectivity of 80% [30]. Selectivity of 99% [31]. Selectivity of 40% [15].
Table 2 Bacteria isoprene production process and the obtained E-factor and material efficiency data. Input/kg
E-factor is the simplest metric permitting to assess the greenness of the process [29]. The E-factor according to Sheldon is defined as E-factor = mass of wastes/mass of products. The E-factor might serve to calculate also the material efficiency of the process and thus the last can be described by the equation: Material efficiency =
1 E-factor + 1 =
mass of products . mass of products + mass of waste
3.1.1. Fossil based process Naphtha cracking is a complex process and there is a lack of detailed information about each of the steps related to isoprene. Therefore the complexity of the isoprene is enormous and for this reason the Sumitomo process was selected for analysis. The Sumitomo process involves the use of isobutylene, methanol and oxygen and it can be ascribed by the following equation:
1
Bacteria Glucose Nutrients E-factor Material efficiency
Output/kg 538.0a 11747.1a 2684.4a
Bacterial biomass Glucose Nutrients Isoprene
3814.0a 64.5a 912.7b 823.0
1.19c 0.46c
a
Yang et al. [17], for the batch production of isoprene in 40 h. For calculations the excess of nutrients was considered to be 34% [23]. c Calculated considering output of glucose and nutrients as wastes – bacterial biomass is co-product. b
3.1.2. Bacterial process For the bacterial pathway considered in this study, isoprene is produced under fed-batch fermentation over 40 h. To model the bacterial process the SuperPro Designer [24] software has been used considering the particular production steps and chemicals used. To produce isoprene, bacteria metabolises a carbon source (e.g. glucose) and converts it into the final product – isoprene. The
Methanol required for this reaction might be produced from the natural gas according to the following reaction:
Summarising, the stoichiometry of these reactions is C4 H8 + CH4 + 0.5O2 → C5 H8 + H2 O + H2 and the overall conversion is equal to 12% whereas selectivity is 60% (based on isobutene) and 40% (based on methanol) [15]. Therefore, considering this data the calculations of the material efficiency can be presented as in Table 1. Therefore, the calculation of selected metrics reveals that Efactor is as high as 1.5 and material efficiency is 0.40.
glucose conversion yield to isoprene was considered to be at the level of 7% according to the findings of Yang et al. [17]. The bacteria culture medium composition was considered to be equal as in the literature [17]. Apart from isoprene, this process leads to the production of bacterial biomass which has a lower value than for example algae biomass [32]. However, it can be used as a raw material for energy purposes [32,33] and so its formation as a co-product
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Table 3 Input and output of the energy in the isoprene production by fossil route. Input (GJ tonne−1 )
Table 5 Cost breakdown of petrochemical isoprene production (D tonne−1 ).
Output (GJ tonne−1 )
a
Isobutylene Methanec Cumulative energy demand of isobutylened
66.1 41.1 53.1
Total
160.3
Isopreneb
Total
Capital cost depreciation (20 years) 46.8
46.8
HHV isobutylene = 48.238 MJ kg−1 [35]. b HHV isoprene = 46.8 MJ kg−1 [27]. c HHV of methane = 55.5 MJ kg−1 [36]. d Isobutylene is produced from a natural gas and crude oil [15] thus cumulative energy demand of isobutylene is a HHV of isobutylene increased by 10%. a
1849.50 79.18 871.88 0.0001
Operating labour cost Non-operating labour cost Waste treatment Maintenance Miscellaneous Total labour and others
1.3 0.8 50.9 328.5 164.3
Labour and others
Utilities
was also considered. Table 2 presents the material efficiency data used in this work. The biological process of isoprene production by bacteria reveals that E-factor is 1.19 while the material efficiency is as high as 0.46. Both processes show similar results of E-factor and material efficiency. Slightly better results were obtained for biotechnological route although E-factor for both processes is similar and is in the order of E-factor for bulky compounds as demonstrated in literature [29,34]. 3.2. Energy efficiency and total energy input The energy demands are foci of today industrial processes. The assessment of the energy balance is compulsory for current and new processes. The simple way to perform this evaluation is an energy efficiency that can be described in the following manner: Energy efficiency = energyproducts /energyinput . 3.2.1. Fossil based process The fossil process of isoprene production involves the use of methane and isobutylene. Therefore the stoichiometric energy balance of this process can be calculated based on the material efficiency and the heating values of both chemicals. The summarised energy balance is demonstrated in Table 3. The obtained data demonstrate that the energy demand for production of isoprene is 160.3 GJ tonne−1 and the energy efficiency of the process calculated according to the formula presented above is 0.29. 3.2.2. Bacterial process The energy efficiency and total energy input data for the bacteria isoprene production are presented in Table 4. The calculations have been made on the same basis as for the fossil process considering the calorific value of glucose [28], nutrients [25] as well as bacterial biomass [37]. The stoichiometric energy inputs for production of isoprene are as high as 276.9 GJ tonne−1 . Moreover, the obtained data allows
821.4
Isobutylenea Methaneb Oxygenc Catalystd Total raw material cost
Feedstock
a b c d
Supplies and utilities
2800.6
545.8 164.7
164.7
1.35 D tonne−1 [39]. 107 D tonne−1 [40]. 2235.6 D tonne−1 [41]. Assumed to be 0.1 D tonne−1 .
calculating the energy efficiency considering the biomass produced as end product similarly as in the case of material efficiency. The obtained value is as high as 0.55 for the bacterial process. Comparing both studied processes the energy efficiency is twofold higher for biological process due to the co-production of bacterial biomass which contributes positively to the energy balance of the biological process. 3.3. Costs The economics of the process is a key factor determining the feasibility of the process and its implementation. For this reason the economy of each technology must be scrutinised and for this reason the economic efficiency metric has been selected and analysed to verify the feasibility of either biological or petrochemical processes. 3.3.1. Fossil based process The cost of isoprene production in Sumitomo route was estimated using the Anderson’s rules concerning determination of relative contribution of variable costs to the total product cost [38]. The cost analysis is presented in Table 5 and Fig. 1. The overall isoprene production price is 4332.6 D tonne−1 . The analysis of the economic evaluation drives to the conclusion that the cost of raw material is a dominant part of the overall cost of isoprene and corresponds to 65% of the overall production cost. Almost 1/5 of the overall cost of isoprene is related to the depreciation and 13% to labour and other costs. Comparing the commercial price of isoprene to the obtained in this work it can be stated that the value estimated in this work is higher than the commercial one (around 1500 D tonne−1 )[42] although is the same order of magnitude confirming the viability of the used metrics.
Table 4 Input and output of the energy in the isoprene production by bacteria. Input (GJ tonne−1 )
Output (GJ tonne−1 )
Glucose Nutrients
231.5a 45.4c
Isoprene Biomass Excess of nutrients and glucose
46.8b 106.8d 15.7c
Total
276.9
Total
168.9
HHV of glucose of 16.3 MJ kg−1 [28]. b HHV isoprene of 46.78 MJ kg−1 [27]. c For calculation of energy consumption for nutrients data from BIOGRACE project were used [25]. d HHV dry Escherichia coli biomass (water content – 0.84 mass%) of 23.04 MJ kg−1 [37]. a
Fig. 1. Cost breakdown of the petrochemical isoprene production.
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Table 6 Cost breakdown of the bacteria isoprene production (D tonne−1 ). Capital cost depreciation (20 years) 2768.10 14.63 333.78
Operating labour cost Non-operating labour cost Waste treatment Maintenance Miscellaneous Total labour and others
1.4 0.9 15.5 364.2 342.6
Labour and others
Utilities a b c
Supplies and utilities
Table 7 Metrics of the isoprene production pathways evaluated in this work. 227.73
Glucosea Waterb Nutrientsc Total raw material cost
Feedstock
3115.51
Metric
Fossil
E-factor Material efficiency Energy efficiency Isoprene production cost (D tonne−1 ) Land use (ha tonne−1 )
1.50 0.40 0.29 4333 0
Bacteria 1.19 0.46 0.55 4950 0.8
3.4. Land use 724.59
164.7
5
881.71
250 D tonne−1 [43]. 0.1 D m−3 [24]. 400 D tonne−1 [23].
3.3.2. Bacterial process The economic evaluation of the isoprene production has been made using the assumptions presented above using SuperPro Design software [24]. The cost breakdown for the bacteria isoprene production process is presented in Table 6 and Fig. 2. The economic evaluation analysis depicts that the cost of raw material is a dominant part of the overall cost of isoprene. A 63% of the overall cost of isoprene corresponds principally to cost of nutrients and carbon source (glucose). An 18% of the overall price of isoprene is the cost of utilities, mainly electricity. Depreciation as well as labour and other costs contribute with almost 20% to the overall isoprene production cost. In comparison to the market price of bioisoprene (2–3.4 kD tonne−1 [43]) it can be stated that the obtained price of bioisoprene of 4949.5 D is in the line with the market one and slightly higher than those of its fossil counterpart [42]. Additionally, the cost optimisation which can be achieved in the large scale facility, namely, by (i) the extension of depreciation time to realistic 20 years, (ii) broad automatisation of the production facility and due to this reduction of human resources’ needs, (iii) integration of some production units into larger once e.g. in the separation step, (iv) reduction of non-working hours of some production units e.g. separation units in 10 tonne scale as well as (v) reduction of the raw material market price due to the large demand and by this better negotiation position with glucose suppliers. That is why the cost breakdown is totally different in both analysed cases and the current one is more similar to acrylonitrile process [44] reported in this issue.
The competition between food and fuel and limited arable land shows the importance of the land use as a metric to be evaluated. Hence among selected metrics, land use needed for production of isoprene was considered. For the consistency of the land use calculations agreed for this special issue, its definition runs as follows: “The amount (in hectares) of good agricultural soil (in Champagne, France) required to produce 1 tonne of product” [22]. Other goods such as chemicals, fuels, electricity, feed and food obtained from the same crop were allocated proportionally. 3.4.1. Fossil based process The land use has been considered to include solely the need of agriculture land to produce the raw material. Additionally, it has been assumed that either classical petrochemical refinery as well as biorefinery occupies similar areas. Therefore the land use for petrochemical route of isoprene synthesis has been set to 0. 3.4.2. Bacterial process According to the 2011 report of the Food and Agriculture Organisation of the United Nations (FAOSTAT) [30], the yield for the production of sugar beet in France was 86.5 tonne/ha. Thus, assuming a complete conversion of sugar in sugar beet into fermentation sugars the production of glucose per hectare would be 18.2 tonne/ha. Therefore to produce 50,000 tonne of isoprene annually 399,730 ha of sugar beet plantation is needed. That gives 0.8 ha/tonne of sugar beet plantation. 4. The comparison of green metrics for both processes of isoprene production The results of green metrics for isoprene production on the petrochemical and biotechnological way are presented in Table 7. The obtained data shows that biological process is less material and energy demanding in comparison to fossil pathway. The production cost of both processes is comparable. The only disadvantage of the bacterial process is a fact that this process requires the carbon source which is normally produced from the agriculture crops cultivated on the arable land. The way to overcome this problem is the possibility of using wastes or residues rich in carbohydrates or lignocellulosic biomass and convert it to sugars [45,46] which can be assimilated by microorganisms [47]. 5. Conclusions
Fig. 2. Cost breakdown of the bacteria isoprene production.
The green metrics applied to the target biological pathways of isoprene production allowed evaluating and comparing the performance of both processes in terms of: material and energy efficiency, economic viability and land use. Analysis of the obtained data showed that biotechnological pathway of isoprene production is potentially feasible to substitute the fossil isoprene production either from the material efficiency or from the economic point of view. The calculated costs for the bio-isoprene are relatively close to the market price of bio-isoprene and only slightly higher than the actual cost of its fossil counterpart. The significant deficiency of
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the bacterial isoprene production process is a need of carbon source that obligates to use the agricultural land thus may influence the food and feed price. Acknowledgments This work was supported by the European Commission through financing of the COST CM0903 Action UBIOCHEM “Utilisation of Biomass for Sustainable Fuels & Chemicals” and the Fundac¸ão para a Ciência e a Tecnologia (FCT, Portugal) through project of Cooperac¸ão Científica e Tecnológica FCT/Polónia – 2013/2014, “”Green metrics” em bioenergia”. References [1] Y. Yokouchi, Y. Ambe, J. Geophys. Res.: Atmos. 93 (1988) 3751. [2] G. Whited, E. Feher, D. Benko, M. Cervin, G. Chotani, J. Mcauliffe, R. LaDuca, E. Ben-Shashan, K. Sanford, Ind. Biotechnol. 6 (2010) 152. [3] J. Kuzma, M. Nemecekmarshall, W.H. Pollock, R. Fall, Curr. Microbiol. 30 (1995) 97. [4] H.M. Lybarger, Isoprene in Kirk–Othmer Encyclopedia of Chemical Technology, John Wiley & Sons, Inc., 2000. [5] H.M. Weitz, E. Loser, Isoprene in Ullmann’s Encyclopedia of Industrial Chemistry, Wiley-VCH Verlag GmbG & Co. KGaA, 2000. [6] Isoprene, IHS Chemicals, 2011, http://www.ihs.com/products/chemical/ planning/ceh/isoprene.aspx [7] G.O. Ezinkwo, V.F. Tretjakov, R.M. Talyshinky, A.M. Ilolov, T.A. Mutombo, Catal. Sustain. Energy 1 (2013) 100. [8] GlycosBioTM , 2013, http://www.glycosbio.com/ [9] A. Guenther, T. Karl, P. Harley, C. Wiedinmyer, P.I. Palmer, C. Geron, Atmos. Chem. Phys. 6 (2006) 3181. [10] R. Wititsuwannak, P. Pasitkul, K. Kanokwiroon, D. Wititsulwannakul, Phytochemistry 69 (2008) 339. [11] Y. Armitage, TCE 866 (2013) 48. [12] Genencor BioIsoprene Monomer, 2010, http://www.genencor.com/uploads/tx tcdaniscofiles/GENC-10053 BioIsoprene Backgrounder prt.pdf [13] D. De Guzman, Ajinomoto, Bridgestone in Bio-isoprene, 2012, http://www.icis. com/blogs/green-chemicals/2012/06/ajinomoto-bridgestone-in-bio-i/ [14] Michelin Team Up with Amyris to Make Tyres from Bio-isoprene, 2011, http://www.nnfcc.co.uk/news/michelin-team-up-with-amyris-to-make-tires7from-bio-isoprene [15] K. Weissermel, H.-J. Arpe, Industrial Organic Chemistry, Wiley-VCH GmbH&Co. KGaA, Weinheim, Germany, 2003. [16] F. Bouvier, A. Rahier, B. Camara, Prog. Lipid Res. 44 (2005) 357. [17] J.M. Yang, M. Xian, S.Z. Su, G. Zhao, Q.J. Nie, X.L. Jiang, Y.N. Zheng, W. Liu, PLoS ONE 7 (2012) e33509. [18] E.I. Wilding, J.R. Brown, A.P. Bryant, A.F. Chalker, D.J. Holmes, K.A. Ingraham, S. Iordanescu, Y.S. Chi, M. Rosenberg, M.N. Gwynn, J. Bacteriol. 182 (2000) 4319.
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Chemical and biological-based isoprene production: Green metrics Ana R.C. Morais a , Sylwia Dworakowska b , Alberto Reis a , Luisa Gouveia a , Cristina T. Matos a , Dariusz Bogdał b , Rafał Bogel-Łukasik a,∗ a
Laboratório Nacional de Energia e Geologia, I.P., Unidade de Bioenergia, Estrada do Pac¸o do Lumiar 22, 1649-038 Lisboa, Portugal Department of Biotechnology and Physical Chemistry, Faculty of Chemical Engineering and Technology, Cracow University of Technology, Warszawska 24, 31-155 Cracow, Poland b
a r t i c l e
i n f o
Article history: Received 18 July 2013 Received in revised form 20 May 2014 Accepted 21 May 2014 Available online xxx Keywords: Green metrics Isoprene Escherichia coli E-factor Economic evaluation Land use
a b s t r a c t Green metrics is a methodology which allows the greenness of either new or already existing processes to be assessed. This paper is a part of a special issue devoted to green metrics in which this methodology is applied to different processes to assess bio and petrochemical routes. In this work, green metrics were used as a tool to validate and compare the petrochemical and biological processes of isoprene production. The Sumitomo process has been selected for this comparison as it is beneficial because of it using less expensive C1 components as well as the fact that it has lower investment costs for a single-step process. The production of isoprene through a modified Escherichia coli bacterial process has been selected for comparison with the fossil pathway. The green metrics evaluation was performed for both processes to produce isoprene and to target 50,000 tonnes of isoprene yearly. Although, the calculated costs for the bio-isoprene are slightly higher than the actual market price of its fossil counterpart, the results obtained reveal that the bacteria-based isoprene production is able to substitute the petrochemical process, with material and energy efficiency. This conclusion has also been proved by the increasing number of industrial interest in bioisoprene. The challenge comes from the land use needed for the production of a carbon source which might be solved by the use of waste and residues which are rich in carbohydrates or lignocellulosic biomass which can be converted to simple sugars. © 2014 Elsevier B.V. All rights reserved.
1. Introduction Isoprene (C5 H8 , 2-methyl-1,3-butadiene) is a hydrocarbon, which is colourless and a volatile liquid at room temperature. Isoprene occurs extensively in nature at very low concentrations being metabolised by several organisms such as animals, plants (including macro- and microalgae), fungi and bacteria [1–3]. Isoprene is a key chemical commodity required to manufacture a diverse range of industrial products, including (in over of 95%) a wide variety of elastomers used in surgical gloves, motor mounts, rubber bands, golf balls, condoms and shoes. However, the most important use of isoprene is the production of synthetic rubber (cispolyisoprene) in tire manufacturing (cars and trucks). Furthermore, 5% of the worldwide production of isoprene is dedicated to produce chemicals, which are used as intermediates for pharmaceuticals, vitamins, flavourings, perfumes, and epoxy hardeners [2,4,5].
∗ Corresponding author. Tel.: +351 210924600. E-mail addresses: [email protected] (D. Bogdał), [email protected] (R. Bogel-Łukasik).
Isoprene was first synthesised in 1860 by C.E. Williams through the pyrolysis of natural rubber. Nowadays, most isoprene production comes from fossil fuel resources. The three major producers of high-purity isoprene are Nizhnekamskneftekhim, SynthezKauchuk and Togliattikauchuk from Russia with a production of 427,500 tonnes in 2011. The next largest world producers of isoprene are Goodyear and Shell (USA) [6]. Dehydrogenation of isopentane as well as synthesis of isoprene from isobutylene and formaldehyde are commonly used in Russia, whereas direct isolation of isoprene from C5 stream by extractive distillation is executed in the USA [7]. Global industrial production of synthetic isoprene from petrochemical feedstocks is close to 1 million tonnes per year and currently isoprene consumption is around 850,000 tonnes annually [8]. A large amount of the isoprene produced annually is liberated by plants which collectively release approximately 500 million tonnes of carbon per year [9], making isoprene the dominant gaseous hydrocarbon produced by vegetation. This amount of isoprene is sufficient to produce 60 billion car and truck tyres, which is 50 times the current global manufacturing of 1.2 billion tyres [2]. However, the use of isoprene from plants and animals for commercial purposes is still economically
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unfeasible, although the use of latex produced by Hevea (rubber trees) to produce rubber is one example of economically efficient biological production [10]. Taking into account the growing demand for isoprene, the recent pressure on fossil fuels, and the environmental concerns related to global warming, there is an increased need for the production of chemicals such as isoprene from renewable sources. Both, the materials and processes should be more efficient, sustainable, cost-effective and environmentally friendly (e.g., using biological processes). An industrial production of bioisoprene is an interesting option and for this reason many leading tyre producers perform advanced studies in this direction [11]. Goodyear, a well-known tyre manufacturer that produces around 200 million tyres a year, works with Genencor to engineer bacteria which will produce bioisoprene [12]. Bridgestone is also co-developing bioisoprene in collaboration with Ajinomoto, through fermentation [13]. The Michelin Company has a joint venture with Amyris to develop the bioisoprene process [14].
cracking fractions is considerably more efficient than the synthesis of this commodity in the chemical manner since there is enough ethylene produced to satisfy the large share of isoprene demands [4]. Due to the limited availability of isoprene as a by-product in the production of ethylene, much effort has been devoted to develop synthetic methods of isoprene production. There are main four synthetic routes leading to isoprene [4,15]: (i) addition of acetone to acetylene to form 2-methyl-3-butyne-2-ol and subsequent partial hydrogenation and dehydration (Snamprogetti process) used by ANIC and Karbochem, (ii) dimerization of propene to isohexene followed by demethanation (Goodyear – Scientific Design process), (iii) dismutation of isobutene and 2-butene to form 2-methyl2-butene followed by dehydrogenation, (iv) double addition of formaldehyde to isobutene resulting in 4,4-dimethyl-1,3-dioxane followed by dehydration and cleavage of formaldehyde. The fourth process has been scaled up into industrial processes by several companies (Bayer, IFP, Marathon Oil, Kuraray and the CIS).
Recently this route was improved and simplified by Sumitomo Chemical through use of less expensive feedstock i.e. CH3 OH and O2 in the presence of catalysts: H3 PO4 –MoO3 /SiO2 and mixed oxide systems based on Mo–Bi–P–Si, Mo–Sb–P–Si, or H3 PO4 –V–Si [15].
The goal of this work is to compare the petrochemical and biological (bacteria-based) processes for isoprene production using green metrics (material and energy efficiency, economic evaluation, and land use).
This process has not been yet practiced commercially, but is similar to the commercial ones [4]. Furthermore the Sumitomo route is a subject of great interest because it has some advantages such as less expensive C1 components used in the synthesis, as well as, lower investment costs of a single-step process. For this reason this process has been selected as a potential petrochemical route of isoprene production and was compared with the one using bacteria.
2. Production 2.1. Petrochemical processes
2.2. Bio-based process
Over the years many technological processes of isoprene production have been proposed and studied. Today the main world isoprene production occurs via separation from C5 cracked fractions obtained as a by-product in the pyrolysis of hydrocarbons to ethylene. There are two possible technologies available to produce isoprene from C5 streams (after separation of cyclopentadiene). The first one is isolation by extractive distillation (with N-methylpyrrolidone (BASF), dimethylformamide (Nippon Zeon) or acetonitrile (Shell, Goodrich-Arco); isoprene productivity of ca. 30,000 tonnes per year) or fractional distillation as an azeotrope with n-pentane (Goodyear; not yet commercialised). The second assumes the dehydrogenation of isopentane and isopentenes (methylbutenes) using Fe2 O3 –Cr2 O3 –K2 CO3 catalyst at 600 ◦ C with a yield of 85% (CIS, Shell, Arco, Exxon). Direct isolation allows obtaining of isoprene without additional synthetic steps thus making this method more preferred since isoprene concentration in a typical C5 stream is 14–23 wt% [4,5,15]. The isoprene production yield is typically very low and is in the order of 2%–5% of the ethylene yield [15]. The efficiency of the process might be increased by converting gas oil as a starting material instead of naphtha. On the other hand, recovery of isoprene from C5
Two principal pathways have been identified for the biosynthesis of isoprene by bacteria: cytosolic mevalonate (MVA) and plastidial 1-deoxy-d-xylulose-5-phosphate (DOXP) pathways [16]. Bacteria are able to produce isoprene by DOXP as well as by the MVA pathway by gene modification [17,18]. Isoprene can be produced by both, Gram-positive and Gramnegative bacteria, under facultative anaerobic conditions through the carbon source oxidation process. Among different genus, Bacillus seems to be the best producer of isoprene [19]. Yang et al. reported isoprene biosynthesis by a genetically engineered bacterial strain, obtained by co-expressing an optimised MVA pathway and the isoprene synthase (IspSPa ) (from the higher plant Populus alba) on Escherischia coli [17]. This strain allowed isoprene production up to 6.3 g L−1 under 40 h of fed-batch fermentation. The Danisco US Inc. together with The Goodyear Tire & Rubber Company patented the isoprene production method, using Bacillus bacteria. A modified strain achieves an isoprene production yield from glucose of 8.9% at 40 h or even 10.7% at 59 h [20]. Other key players on the tyres market are also developing the technologies to produce bioisoprene. Ajinomoto and other tyre company Bridgestone Corp as well as Michelin with Amyris are working on the development
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of bioisoprene [13]. Considering the large interest of the major tyre producers it can be foreseen that bioisoprene will become in a near future a commodity produced from natural resources substituting fossil feedstock.
3. Metrics Material and energy efficiencies, economic evaluation and land use have been selected to evaluate the greenness of the examined isoprene production processes. These four metrics have been selected among numerous others existing in the literature [21]. The selection has been made by the UBIOCHEM COST Action and the selected metrics were chosen as the most representative which tackle all features of sustainability such as environmental, economic and social aspects [22]. For the bacterial isoprene production process, the assumptions regarding the economic (glucose cost of 250 D tonne−1 ) and energetic inputs according to literature data were used [23–28]. For petrochemical pathway of isoprene production, the assumptions are given together with the calculations of the particular metric.
3.1. Material efficiency and E-factor
3
Table 1 Theoretical calculations of the amount of chemicals used in the production of isoprene. Input/kg
Output/kg
Isobutylenea Oxygen Catalyst
1.37 0.39 0.001
Isoprene
Methaneb Syngasc Methanold
0.74 1.26 1.17
Syngas Methanol Isoprene
1.26 1.17 1
input (isobutylene, methane, oxygen, catalyst)
2.501
output (isoprene)
1
E-factor Material efficiency a b c d
1.50 0.40
Selectivity of 60% [15]. Selectivity of 80% [30]. Selectivity of 99% [31]. Selectivity of 40% [15].
Table 2 Bacteria isoprene production process and the obtained E-factor and material efficiency data. Input/kg
E-factor is the simplest metric permitting to assess the greenness of the process [29]. The E-factor according to Sheldon is defined as E-factor = mass of wastes/mass of products. The E-factor might serve to calculate also the material efficiency of the process and thus the last can be described by the equation: Material efficiency =
1 E-factor + 1 =
mass of products . mass of products + mass of waste
3.1.1. Fossil based process Naphtha cracking is a complex process and there is a lack of detailed information about each of the steps related to isoprene. Therefore the complexity of the isoprene is enormous and for this reason the Sumitomo process was selected for analysis. The Sumitomo process involves the use of isobutylene, methanol and oxygen and it can be ascribed by the following equation:
1
Bacteria Glucose Nutrients E-factor Material efficiency
Output/kg 538.0a 11747.1a 2684.4a
Bacterial biomass Glucose Nutrients Isoprene
3814.0a 64.5a 912.7b 823.0
1.19c 0.46c
a
Yang et al. [17], for the batch production of isoprene in 40 h. For calculations the excess of nutrients was considered to be 34% [23]. c Calculated considering output of glucose and nutrients as wastes – bacterial biomass is co-product. b
3.1.2. Bacterial process For the bacterial pathway considered in this study, isoprene is produced under fed-batch fermentation over 40 h. To model the bacterial process the SuperPro Designer [24] software has been used considering the particular production steps and chemicals used. To produce isoprene, bacteria metabolises a carbon source (e.g. glucose) and converts it into the final product – isoprene. The
Methanol required for this reaction might be produced from the natural gas according to the following reaction:
Summarising, the stoichiometry of these reactions is C4 H8 + CH4 + 0.5O2 → C5 H8 + H2 O + H2 and the overall conversion is equal to 12% whereas selectivity is 60% (based on isobutene) and 40% (based on methanol) [15]. Therefore, considering this data the calculations of the material efficiency can be presented as in Table 1. Therefore, the calculation of selected metrics reveals that Efactor is as high as 1.5 and material efficiency is 0.40.
glucose conversion yield to isoprene was considered to be at the level of 7% according to the findings of Yang et al. [17]. The bacteria culture medium composition was considered to be equal as in the literature [17]. Apart from isoprene, this process leads to the production of bacterial biomass which has a lower value than for example algae biomass [32]. However, it can be used as a raw material for energy purposes [32,33] and so its formation as a co-product
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Table 3 Input and output of the energy in the isoprene production by fossil route. Input (GJ tonne−1 )
Table 5 Cost breakdown of petrochemical isoprene production (D tonne−1 ).
Output (GJ tonne−1 )
a
Isobutylene Methanec Cumulative energy demand of isobutylened
66.1 41.1 53.1
Total
160.3
Isopreneb
Total
Capital cost depreciation (20 years) 46.8
46.8
HHV isobutylene = 48.238 MJ kg−1 [35]. b HHV isoprene = 46.8 MJ kg−1 [27]. c HHV of methane = 55.5 MJ kg−1 [36]. d Isobutylene is produced from a natural gas and crude oil [15] thus cumulative energy demand of isobutylene is a HHV of isobutylene increased by 10%. a
1849.50 79.18 871.88 0.0001
Operating labour cost Non-operating labour cost Waste treatment Maintenance Miscellaneous Total labour and others
1.3 0.8 50.9 328.5 164.3
Labour and others
Utilities
was also considered. Table 2 presents the material efficiency data used in this work. The biological process of isoprene production by bacteria reveals that E-factor is 1.19 while the material efficiency is as high as 0.46. Both processes show similar results of E-factor and material efficiency. Slightly better results were obtained for biotechnological route although E-factor for both processes is similar and is in the order of E-factor for bulky compounds as demonstrated in literature [29,34]. 3.2. Energy efficiency and total energy input The energy demands are foci of today industrial processes. The assessment of the energy balance is compulsory for current and new processes. The simple way to perform this evaluation is an energy efficiency that can be described in the following manner: Energy efficiency = energyproducts /energyinput . 3.2.1. Fossil based process The fossil process of isoprene production involves the use of methane and isobutylene. Therefore the stoichiometric energy balance of this process can be calculated based on the material efficiency and the heating values of both chemicals. The summarised energy balance is demonstrated in Table 3. The obtained data demonstrate that the energy demand for production of isoprene is 160.3 GJ tonne−1 and the energy efficiency of the process calculated according to the formula presented above is 0.29. 3.2.2. Bacterial process The energy efficiency and total energy input data for the bacteria isoprene production are presented in Table 4. The calculations have been made on the same basis as for the fossil process considering the calorific value of glucose [28], nutrients [25] as well as bacterial biomass [37]. The stoichiometric energy inputs for production of isoprene are as high as 276.9 GJ tonne−1 . Moreover, the obtained data allows
821.4
Isobutylenea Methaneb Oxygenc Catalystd Total raw material cost
Feedstock
a b c d
Supplies and utilities
2800.6
545.8 164.7
164.7
1.35 D tonne−1 [39]. 107 D tonne−1 [40]. 2235.6 D tonne−1 [41]. Assumed to be 0.1 D tonne−1 .
calculating the energy efficiency considering the biomass produced as end product similarly as in the case of material efficiency. The obtained value is as high as 0.55 for the bacterial process. Comparing both studied processes the energy efficiency is twofold higher for biological process due to the co-production of bacterial biomass which contributes positively to the energy balance of the biological process. 3.3. Costs The economics of the process is a key factor determining the feasibility of the process and its implementation. For this reason the economy of each technology must be scrutinised and for this reason the economic efficiency metric has been selected and analysed to verify the feasibility of either biological or petrochemical processes. 3.3.1. Fossil based process The cost of isoprene production in Sumitomo route was estimated using the Anderson’s rules concerning determination of relative contribution of variable costs to the total product cost [38]. The cost analysis is presented in Table 5 and Fig. 1. The overall isoprene production price is 4332.6 D tonne−1 . The analysis of the economic evaluation drives to the conclusion that the cost of raw material is a dominant part of the overall cost of isoprene and corresponds to 65% of the overall production cost. Almost 1/5 of the overall cost of isoprene is related to the depreciation and 13% to labour and other costs. Comparing the commercial price of isoprene to the obtained in this work it can be stated that the value estimated in this work is higher than the commercial one (around 1500 D tonne−1 )[42] although is the same order of magnitude confirming the viability of the used metrics.
Table 4 Input and output of the energy in the isoprene production by bacteria. Input (GJ tonne−1 )
Output (GJ tonne−1 )
Glucose Nutrients
231.5a 45.4c
Isoprene Biomass Excess of nutrients and glucose
46.8b 106.8d 15.7c
Total
276.9
Total
168.9
HHV of glucose of 16.3 MJ kg−1 [28]. b HHV isoprene of 46.78 MJ kg−1 [27]. c For calculation of energy consumption for nutrients data from BIOGRACE project were used [25]. d HHV dry Escherichia coli biomass (water content – 0.84 mass%) of 23.04 MJ kg−1 [37]. a
Fig. 1. Cost breakdown of the petrochemical isoprene production.
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Table 6 Cost breakdown of the bacteria isoprene production (D tonne−1 ). Capital cost depreciation (20 years) 2768.10 14.63 333.78
Operating labour cost Non-operating labour cost Waste treatment Maintenance Miscellaneous Total labour and others
1.4 0.9 15.5 364.2 342.6
Labour and others
Utilities a b c
Supplies and utilities
Table 7 Metrics of the isoprene production pathways evaluated in this work. 227.73
Glucosea Waterb Nutrientsc Total raw material cost
Feedstock
3115.51
Metric
Fossil
E-factor Material efficiency Energy efficiency Isoprene production cost (D tonne−1 ) Land use (ha tonne−1 )
1.50 0.40 0.29 4333 0
Bacteria 1.19 0.46 0.55 4950 0.8
3.4. Land use 724.59
164.7
5
881.71
250 D tonne−1 [43]. 0.1 D m−3 [24]. 400 D tonne−1 [23].
3.3.2. Bacterial process The economic evaluation of the isoprene production has been made using the assumptions presented above using SuperPro Design software [24]. The cost breakdown for the bacteria isoprene production process is presented in Table 6 and Fig. 2. The economic evaluation analysis depicts that the cost of raw material is a dominant part of the overall cost of isoprene. A 63% of the overall cost of isoprene corresponds principally to cost of nutrients and carbon source (glucose). An 18% of the overall price of isoprene is the cost of utilities, mainly electricity. Depreciation as well as labour and other costs contribute with almost 20% to the overall isoprene production cost. In comparison to the market price of bioisoprene (2–3.4 kD tonne−1 [43]) it can be stated that the obtained price of bioisoprene of 4949.5 D is in the line with the market one and slightly higher than those of its fossil counterpart [42]. Additionally, the cost optimisation which can be achieved in the large scale facility, namely, by (i) the extension of depreciation time to realistic 20 years, (ii) broad automatisation of the production facility and due to this reduction of human resources’ needs, (iii) integration of some production units into larger once e.g. in the separation step, (iv) reduction of non-working hours of some production units e.g. separation units in 10 tonne scale as well as (v) reduction of the raw material market price due to the large demand and by this better negotiation position with glucose suppliers. That is why the cost breakdown is totally different in both analysed cases and the current one is more similar to acrylonitrile process [44] reported in this issue.
The competition between food and fuel and limited arable land shows the importance of the land use as a metric to be evaluated. Hence among selected metrics, land use needed for production of isoprene was considered. For the consistency of the land use calculations agreed for this special issue, its definition runs as follows: “The amount (in hectares) of good agricultural soil (in Champagne, France) required to produce 1 tonne of product” [22]. Other goods such as chemicals, fuels, electricity, feed and food obtained from the same crop were allocated proportionally. 3.4.1. Fossil based process The land use has been considered to include solely the need of agriculture land to produce the raw material. Additionally, it has been assumed that either classical petrochemical refinery as well as biorefinery occupies similar areas. Therefore the land use for petrochemical route of isoprene synthesis has been set to 0. 3.4.2. Bacterial process According to the 2011 report of the Food and Agriculture Organisation of the United Nations (FAOSTAT) [30], the yield for the production of sugar beet in France was 86.5 tonne/ha. Thus, assuming a complete conversion of sugar in sugar beet into fermentation sugars the production of glucose per hectare would be 18.2 tonne/ha. Therefore to produce 50,000 tonne of isoprene annually 399,730 ha of sugar beet plantation is needed. That gives 0.8 ha/tonne of sugar beet plantation. 4. The comparison of green metrics for both processes of isoprene production The results of green metrics for isoprene production on the petrochemical and biotechnological way are presented in Table 7. The obtained data shows that biological process is less material and energy demanding in comparison to fossil pathway. The production cost of both processes is comparable. The only disadvantage of the bacterial process is a fact that this process requires the carbon source which is normally produced from the agriculture crops cultivated on the arable land. The way to overcome this problem is the possibility of using wastes or residues rich in carbohydrates or lignocellulosic biomass and convert it to sugars [45,46] which can be assimilated by microorganisms [47]. 5. Conclusions
Fig. 2. Cost breakdown of the bacteria isoprene production.
The green metrics applied to the target biological pathways of isoprene production allowed evaluating and comparing the performance of both processes in terms of: material and energy efficiency, economic viability and land use. Analysis of the obtained data showed that biotechnological pathway of isoprene production is potentially feasible to substitute the fossil isoprene production either from the material efficiency or from the economic point of view. The calculated costs for the bio-isoprene are relatively close to the market price of bio-isoprene and only slightly higher than the actual cost of its fossil counterpart. The significant deficiency of
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Please cite this article in press as: A.R.C. Morais, et al., Chemical and biological-based isoprene production: Green metrics, Catal. Today (2014), http://dx.doi.org/10.1016/j.cattod.2014.05.033