Catalysis Today 239 (2015) 710Contents lists available at ScienceDirectCatalysis Todayj our nal homepage: www. el sevi er . com/ l ocat e/ cat t odSustainabilitymetricsof1-butanolMaartenUyttebroek,WouterVanHecke,KarolienVanbroekhovenVITO, Separation and Conversion Technology, Boeretang 200, 2400 Mol, BelgiumarticleinfoArticle history:Received 12 July 2013Received in revised form23 October 2013Accepted 31 October 2013Available online 8 December 2013Keywords:SustainabilityMetrics1-ButanolBiobasedEfciencyLand useabstractTheproductionofchemicalsfromrenewableresourcesoftenhastocompetewitha petrochemicalpro-cess,optimizedduringseveraldecades.Foursustainabilitymetricswereusedtocomparetheproductionof1-butanolviathepetrochemicalandbiobasedprocesses:materialefciency,energyefciency,landuseand totalcosts.Theselectedpetrochemicalprocessis theoxosynthesis,i.e.,thehydroformylationofpropene,followedby thehydrogenationoftheformedaldehydeswithayieldof95%1-butanol.Theselectedbiobasedprocessistheanaerobiccontinuousacetonebutanolethanol(ABE)fermentationonglucosesubstratefrommaizestarchandaproductrecoveryviadistillationwitha yieldof0.42gABEg1glucose.Thepetrochemicalprocesshas signicantlyhighermaterialandenergyefciencies,comparedtothebiobasedprocess.Forthebiobasedprocess,landisusedtoproducethebiomass(0.29haton1),whilenolandisusedforthepetrochemicalprocess.Productioncostsarehigherforthebiobasedprocess(1041EURton1),comparedtothepetrochemicalprocess(915EURton1). Basedon thefourmetrics,thepetrochemicalprocessis preferabletothebiobasedprocess.However,biomassforsustainablefuelsandchemicalswillbetheonlyresourceforfuturegenerations.Theefciencyofthebiobutanolproductioncanbeimprovedby alteringupstreamprocesses,bymetabolicengineering,by decreasingbyproductformationandby improvinginsituproductrecoverytechniques.2013ElsevierB.V.Allrightsreserved.1. Introduction1-Butanol or n-butanol is an aliphatic saturated C4 alcohol withmolecular formula C4H9OH(MW74.12gmol1). 1-Butanol is a col-orless liquid with a characteristic odor. It is completely misciblewith common organic solvents, but only sparingly soluble in water(7.7wt% at 20C) [1]. The main effect of exposure to excessive con-centrations is irritation of the mucous membranes and depressionof the central nervous system. Animal studies have shown lowacute oral, dermal and inhalation toxicity [1].1-Butanol is a bulk chemical with a diverse use. It is used prin-cipally for surface coating [1]. It is used directly as solvent for var-nishes or it is converted into derivatives that are used as solvents ormonomers. 1-Butanol prevents blushing of certain coatings whenthey dry under humid conditions. It can also be used to regulatethe viscosity and to improve the owproperties of varnishes. Butylacrylate is since the 1990s an essential component of latex paints.1-Butanol can also be used for the production of butylamines. It isused in the plastics and textile sector, for example as a coagulationbath for spinning acrylic bers. The use of 1-butanol in 2010 was30% in butyl acrylate, 25% in butyl acetate, 20% in plasticizers andresins, 15% as solvent and 10% in glycol ethers and esters [1].Corresponding author. Tel.: +32 14 33 57 46.E-mail address: maarten.uyttebroek@vito.be (M.Uyttebroek).A recent application of 1-butanol is its use as a direct replace-ment of gasoline or as a fuel additive. Biobutanol is expected to playan important role in the next generation of biofuels [2]. It is a betterfuel than bioethanol due to the higher energy density of 1-butanol(29.2MJL1), compared to 19.6MJL1for ethanol. 1-Butanol hasalso a lower tendency than ethanol to absorb water. It is also lesscorrosive for certain motor parts, compared to ethanol.The 1-butanol capacity in the world in 2010 was3.6million tons[1]. However, there wasan excess capacity for 1-butanol produc-tion with a plant utilization of 83% in 2010 [1].2. Production2.1. Petrochemical processesFor the production of 1-butanol, there are three petrochemicalprocesses with industrial importance, as shown in Fig. 1: (a) theoxo synthesis, (b) the Reppe synthesis and (c) the crotonaldehydehydrogenation [1,3].The most important process is the oxo synthesis, i.e., the hydro-formylation of propene, followed by the hydrogenation of theformed aldehydes. Carbon monoxide and hydrogen are added tothe C C double bond in the liquid phase in the presence of catalystslike Co, Rh or Ru. An isomeric aldehyde mixture of 1-butanal and2-methylpropanal is obtained. Catalytic hydrogenation of the alde-hydes leads to the formation of the corresponding alcohols. Until0920-5861/$ see front matter 2013 Elsevier B.V. All rights reserved.http://dx.doi.org/10.1016/j.cattod.2013.10.0948 M. Uyttebroek et al. / Catalysis Today 239 (2015) 710C H3CH2C H3CHOCatalystCO / H2+C H3CHOCH3C H3OHCatalytic hydrogenationaC H3CH2CatalystCO / H2OC H3OH+C H3C H3OH+2 CO2C H3CHO 2Aldol condensationC H3CHOOHDehydration C H3CHO+H2OC H3OHHydrogenationbcFig. 1. Petrochemical processes for the production of 1-butanol: (a) oxo synthesis,(b) Reppe synthesis, and (c) crotonaldehyde hydrogenation [3].the 1970s, a high pressure of 2030106Pa CO/H2 at 100180Cin the presence of a Co-catalyst was used. It yielded about 75%1-butanol and 25% 2-methyl-1-propanol (or isobutanol). Newpro-cesses at lower pressure of 15106Pa with a Rh-catalyst yieldedup to 95% 1-butanol and 5% 2-methyl-1-propanol. In 2010, thebiggest producers were BASF, Oxea Group and the Dow ChemicalCompany [1].1-Butanol can also be produced by the Reppe synthesis, i.e.,the carbonylation of propene, developed by Reppe in 1942. In thisprocess, propene, carbon monoxide and water react at a pressureof 0.52106Pa and a temperature of 100C in the presence ofa catalyst (tertiary ammonium salt or polynuclear iron carbonylhydrides) [1]. 1-Butanol and 2-methyl-1-propanol are directlyformed in a ratio of 86:14. The Reppe process was not as successfulas the oxo synthesis withthe Co catalyst despite the more favorableratio of n-butanol to isobutanol and the milder reaction conditions.This was due to the more expensive process technology.Until the 1950s, the petrochemical route for production of1-butanol was based on an aldol condensation of acetaldehyde,followed by a dehydration and subsequent hydrogenation of cro-tonaldehyde. With the development of the oxo synthesis, thisprocess was abandoned. The aldol condensation was performed atambient temperature and pressure in the presence of alkaline cat-alysts. The dehydration was induced by acidication with acetic orphosphoric acids and subsequent distillation. The hydrogenationwas performed in the gas or liquid phase with a Cu catalyst. About1000kg of 1-butanol were obtained from1350kg of acetaldehyde[1].2.2. Biobased processThe biological formation of 1-butanol has a long history [2],starting in 1862 with a fermentation report of Pasteur [4]. Theacetonebutanolethanol (ABE) fermentation became the secondlargest biotechnological process ever performed, only beaten involume by ethanol fermentation. During World WarI, acetonehelped the ABE fermentation to an industrial breakthrough for thepreparation of cordite, used in munition during the war. Weiz-mannpatentedtheproductionof acetoneandalcohols fromstarchymaterial by a mixed culture of mainly Clostridium acetobutylicumin 1915. There was almost no use of butanol during the war. Afterthe war, 1-butanol was used for the production of butyl acetate,a solvent for quick-drying lacquers, needed in large amounts bythe growing automobile industry. Up to 1950, about two thirds ofthe butanol supply in the world came fromthe biological process.The largest plant was located in the USA with a total ABE fer-mentation capacity of 18168m3. Facilities in South Africa and theformer Soviet Union (using lignocellulose hydrolysates) operateduntil the 1980s and until 2004 in China (using continuous culturetechnology). The decline of the fermentation process wascausedby increasing substrate costs (molasses) and low crude oil prices,leading to cheaper petrochemical production [2]. Recently, the ABEfermentation has gained renewed interest from the biofuel pointof view.Butanol can be produced fromvarious commercial rawmateri-als like molasses, whey permeate and corn [5]. Mostly clostridia(strictly or moderately anaerobic, spore-forming, Gram-positivebacteria) performthe ABE fermentation fromglucose or starch in acomplex manner. The most widely studied clostridia are C. aceto-butylicum and C. beijerinckii.During the acidogenic growth phase,organic acids like lactic, acetic and butyric acid and H2 and CO2 areformed. In the stationary, solventogenic phase, acetone, 1-butanoland ethanol are produced [6]. In a typical fermentation with C. ace-tobutylicum, the total ABE concentration is 20gL1in an ABE ratioof 3:6:1 and a yield of 0.290.33gABEg1glucose [5]. Qureshi andBlaschek [7] reported on a fermentation with the mutant strain C.beijerinckii BA101 with a total ABE concentration of 33gL1in aABE ratio of 3:16:1 and a yield of 0.400.50gABEg1glucose.Most of the enzymes and corresponding genes have been char-acterized. To reduce the relatively high substrate costs, cheaplow-grade agricultural substrates that cannot be used for food orfeed are favored [6]. Also lignocellulosic substrates are investi-gated, but solventogenic clostridia cannot hydrolyse cellulose, soa hydrolytic pretreatment of the lignocellulose is required. Dueto the inhibitory effects of butanol, the nal product titers andthe initial carbohydrate concentrations are relatively low, whilebyproduct formation (acetone and ethanol) complicates the down-streamprocessing. Several strategies are investigated to overcomethese problems. Metabolic engineering is investigated to targetincreased product specicity (less byproducts) and increased 1-butanol titers, while in situ product removal can be used to reduceproduct inhibition. The default technology for recovery of biobu-tanol is distillation, the most energy intensive step in the entireproduction process [8]. For 1-butanol, energetic gains are expectedby combining it with a selective and efcient primary recoverystep. Therefore, integrating the fermentation with the rst step ofthe downstreamprocess by using a suitable in situ product recov-ery technique is an interesting strategy to overcome the abovedescribed problems. The energy consumption, overall economics,robustness and long-term performance of the integrated technol-ogy will dene the success of such integrated process schemes andshould be studied in more detail.3. MetricsTo compare the petrochemical process with the biobasedprocess for 1-butanol, four sustainability metrics were chosen:Table 1Material balance for a 1-butanol fermentation plant [5].kgFeedGlucose 3.7E+08ProductButanol 1.2E+08Acetone 2.4E+07Ethanol 7.5E+06Gases 2.3E+08Fiber and protein 8.8E+07Germ/oil 2.0E+07Cell mass 4.2E+07Polysaccharide 3.2E+07M. Uyttebroek et al. / Catalysis Today 239 (2015) 710 9Table2Overviewof the four sustainability metrics for 1-butanol for the petrochemical and biobased processes.Process Material efciency (%) Energy input (GJ ton1) Land use (ha ton1) Total costs (EURton1)Petrochemical: oxo synthesis 92 69 0 915Biobased: ABE fermentation 2742 116 0.29 1041material efciency (E factor), energy efciency, land use and totalproduction costs. The rationale of these metrics is described bySheldon and Sanders [9].The selected petrochemical process is the oxo synthesis over aRh catalyst with a yield of 95% 1-butanol. The selected biobasedprocess is the anaerobic continuous ABE fermentation on glucosesubstrate frommaize starch and a product recovery via distillationwith a yield of 0.42gABEg1glucose [6].3.1. Material efciency and E factorFor the petrochemical process, the hydroformylation ofpropene with carbon monoxide and hydrogen, followed by thehydrogenation of the formed aldehydes is shown in chemical equa-tion (1). The reforming of methane to syngas is shown in chemicalequation (2). The overall stoichiometric reaction for the productionof 1-butanol is described in chemical equation (3).C3H6+CO + H2 C4H8O + H2 C4H9OH (1)CH4+H2O CO + 3H2(2)C3H6+CH4+H2O C4H9OH + H2(3)With a 95% yield of 1-butanol, 0.60kg propene is used for theproduction of 1kg 1-butanol. For the production of 1kg syngasat 95% yield, used for the production of 1kg 1-butanol, 0.50kgmethane is used. An E factor of 0.1 can be calculated with exclu-sion of the water used. This leads to a very high material efciencyof 92%. This is in accordance with Sheldon [10], whoreported anE factor of