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In no event shall the Royal Society of Chemistry be held responsible for any errors or omissions in this Accepted Manuscript or any consequences arising from the use of any information it contains. www.rsc.org/greenchem Page 1 of 21 Green Chemistry Green Chemistry RSCPublishing CRITICAL REVIEW Catalytic Routes towards Acrylic Acid, Adipic Acid and ε-Caprolactam starting from Biorenewables Cite this: DOI: 10.1039/x0xx00000x Rolf Beerthuis, Gadi Rothenberg and N. Raveendran Shiju* Received 00th January 2012, The majority of bulk chemicals are derived from crude oil, but the move to biorenewable resources is Accepted 00th January 2012 gaining both societal and commercial interest. Reviewing this transition, we first summarise the types of today’s biomass sources and their economical relevance. Then, we assess the biobased productions DOI: 10.1039/x0xx00000x of three important bulk chemicals: acrylic acid, adipic acid and ε-caprolactam. These are the key www.rsc.org/ monomers for high-end polymers (polyacrylates, nylon 6.6 and nylon 6, respectively) and are all produced globally in excess of two million metric tons per year. The biobased routes for each target molecule are analysed separately, comparing the conventional processes with their sustainable alternatives. Some processes have already received extensive scientific attention. Other, more novel Manuscript routes are also considered. We find several common trends: For all three compounds, there are no commercial methods for direct conversion of biobased feedstocks. However, combinations of biotechnologically produced platform chemicals with subsequent chemical modifications are emerging and showing promising results. We then discuss several distinct strategies to implement biorenewable processes. For each biotechnological and chemocatalytic route, current efficiencies and limitations are presented, but we urge that these routes should be assessed mainly on their potentials and prospects for future application. Today, biorenewable routes cannot yet compete with their petrochemical equivalents. However, given that most are still in the early stages of development, we foresee their commercial implementation in the next two decades. Accepted 1. Introduction Crude oil is currently the feedstock for manufacturing most bulk and fine chemicals. This causes competition over the available resources with the fuels for automotive and power industry, creating fluctuating prices of chemical feedstocks (Fig. 1).1, 2 Combined with concerns over the environmental impact of petrochemical processing, the chemical industry is Chemistry considering sustainable and more environmentally-friendly alternatives. The biorenewable production of many chemicals emits less greenhouse gases (GHGs) and employs more 3, 4 environmentally-friendly chemistry. However, the transition faces high technological and economical barriers. Fig. 1 Annual average prices for ethylene, propylene and 1,3-butadiene in $/ton.5 Here, we address this transition for three important bulk Green chemicals: acrylic acid, adipic acid, and ε-caprolactam. Each of In 2012, more than 60% of all fibres produced worldwide these is produced at over two million metric tons per annum were synthetic materials6 (Fig. 2, left). Of these synthetic fibres, (Mtpa) with current market prices around $1,500 per ton. the largest part was embodied by polyesters and poly-olefins (Fig. 2, right), such as poly(ethylene terephthalate) (PET), polyethylene (PE) and poly-propylene (PP). PET is made from Van ’t Hoff Institute for Molecular Sciences, University of Amsterdam, ethylene glycol (EG) and terephthalic acid (TPA). Though P.O. Box 94157, 1090GD Amsterdam, The Netherlands. E-mail: [email protected]. Web: http://hims.uva.nl/hcsc. biobased EG is commercially available, the non-availability of 7 † Electronic Supplementary Information (ESI) available: [summary of biobased TPA prevents production of fully biorenewable PET. 8 processes discussed in this review]. See DOI: 10.1039/x0xx00000x Braskem produces 200,000 tons of biobased PE in Brazil, using ethylene obtained by dehydrating bioethanol. However, This journal is © The Royal Society of Chemistry 2013 J. Name., 2013, 00, 1-3 | 1 Green Chemistry Page 2 of 21 ARTICLE Journal Name biobased PE is currently still more expensive than petrobased Over the last decades, much research went into PE. An emerging route towards biobased propylene is by biorenewable chemicals and chemical biomass utilization.12-20 producing ethanol and butane from sugars by fermentation, The growing interest in biorenewables focused mainly on subsequent dehydration and metathesis of ethylene and butene producing platform chemicals, which can be applied in the to propylene. However, developing process technology that can synthesis for various compounds. It is therefore important to economically compete with petrobased PP is a challenge.9 also review the influence of ‘white biotechnology’ or industrial These monomers are incorporated in a great many chemical and biorefineries, on manufacturing bulk chemicals. For producing economical value chains. Moreover, their prices are low: below acrylic acid, adipic acid and ε-caprolactam, no commercial $1,500 per metric ton.10 Conversely, the bulk chemicals that we biotechnological routes are currently employed. Emerging will cover here are relatively expensive, ensuring economical platform chemicals from biotechnology may present margins for innovative alternatives. economically viable routes. However, most research deals with specific advancements, rather than giving an overall view. To assess the current processes and possible advancements made with biorenewable feedstocks, we first analyse the available biomass constituents and biobased feedstock (Table 1). The benchmark prices are averaged across regions and qualities, giving a general impression of availability of biobased feedstocks and their incorporation into chemical value chains. Fig. 2 Overviews by weight percentage. Left: Global fibre market, in 2012. Right: 7 Table 1 Overview of available biomass feedstocks. Constituents of synthetic fibres market, by general polymer classes, in 2012. Manuscript Global Benchmark Biobased Acrylic acid is used for making polyacrylic acid and Chemical formula production price feedstock a a various acrylic esters, known for superabsorbent properties and (Mtpa) (U.S. $/ton) 21 starch glucose polymers 75 500 attractive properties in co-polymerization (Fig. 3). These are used in a range of synthetic products, including diapers, 1, 22 glucose H-(C=O)-(CHOH)5-H 175 500 plastics, synthetic rubber, coatings and paint formulations.11 23 H-(CHOH)4-(C=O)- fructose 7 900 Adipic acid and ε-caprolactam are used as monomers for (CH2OH) making nylon 6.6 and nylon 6, respectively (Fig. 3). These are 2, 24 ethanol CH3CH2OH 65 750 the archetypes of polyamides, accounting for 85–90% of the virgin oils1, 25 various triglycerides 155 1,100 Accepted world nylon market. Polyamides are applied chiefly in fibre and (CH OH)-(CHOH)- textile industry and thus have competitive end-uses, yet glycerol26-28 2 1 850 (CH2OH) dissimilar properties. In terms of performance, nylon 6 has 29, 30 lysine C6H14N2O2 0.85 1,900 better processability and resistance to wear, while nylon 6.6 has 29, 31, 32 better heat resistance and mechanical properties.11 glutamic acid C5H9NO4 1.6 1,300 a Worldwide production and price indexes for 2012. Here, we will focus only on the technical analyses of the biorenewable routes and refrain from any economic analyses. 33-36 Full economical assessments are needed for reliable Chemistry estimations and conclusions. As rough economical estimations are often subjective, we feel that those should be avoided. The combined results give a critical overview on the transition from petrobased to biorenewable productions of acrylic acid, adipic acid and ε-caprolactam. To understand the developments, we will examine the biobased pathways, and Green compare these to petrochemical pathways. We use examples of on-purpose reactions towards target molecules, focusing on the most recent and efficient to date. 2. Implementing biorenewable chemicals There are various incentives for applying biorenewables in the Fig. 3 Structures of acrylic acid, adipic acid, ε-caprolactam and their major end- chemical industry. Government regulations are putting pressure products. on chemical companies to make more environmentally-friendly products. However, these companies can only provide products 2 | J. Name., 2012, 00, 1-3 This journal is © The Royal Society of Chemistry 2012 Page 3 of 21 Green Chemistry Journal Name ARTICLE that are commercially competitive. The discussion on using Coca-Cola in the YXY project.