reactions Article Heterogeneously Catalyzed γ-Valerolactone Hydrogenation into 1,4-Pentanediol in Milder Reaction Conditions Irina Simakova 1,2,* , Yulia Demidova 1,2, Mikhail Simonov 1,2 , Sergey Prikhod’ko 1,2, Prashant Niphadkar 3, Vijay Bokade 3, Paresh Dhepe 3 and Dmitry Yu. Murzin 4,* 1 Boreskov Institute of Catalysis, pr. Lavrentieva, 5, 630090 Novosibirsk, Russia; [email protected] (Y.D.); [email protected] (M.S.); [email protected] (S.P.) 2 Novosibirsk State University, Pirogova 2, 630090 Novosibirsk, Russia 3 CSIR-National Chemical Laboratory, Dr. Homi Bhabha Road, Pune 411008, India; [email protected] (P.N.); [email protected] (V.B.); [email protected] (P.D.) 4 Johan Gadolin Process Chemistry Centre, Åbo Akademi University, Biskopsgatan 8, FI-20500 Turku/Åbo, Finland * Correspondence: [email protected] (I.S.); dmurzin@abo.fi (D.Y.M.) Received: 20 September 2020; Accepted: 14 October 2020; Published: 16 October 2020 Abstract: Hydrogenation of γ-valerolactone (GVL) in polar solvents (n-butanol, 1,4-dioxane) to 1,4-pentanediol (PDO) and 2-methyltetrahydrofuran (MTHF) was performed at 363–443 K in a fixed bed reactor under overall H2 pressure of 0.7–1.3 MPa. Preliminary screening in a batch reactior was performed with a series of Ru, Ir, Pt, Co, and Cu catalysts, earlier efficiently applied for levulinic acid hydrogenation to GVL. The fresh catalysts were analyzed by transmission electron microscopy (TEM), X-ray fluorescent analysis (XRF), temperature programmed reduction by H2 (H2-TPR), and N2 physisorption. Cu/SiO2 prepared by reduction of copper hydroxosilicate with chrysocolla mineral structure provided better selectivity of 67% towards PDO at 32% GVL conversion in a continuous flow reactor. This catalyst was applied to study the effect of temperature, hydrogen pressure, and contact time. The main reaction products were PDO, MTHF, and traces of pentanol, while no valeric acid was observed. Activity and selectivity to PDO over Cu/SiO2 did not change over 9 h, indicating a fair resistance of copper to leaching. Keywords: 1,4-pentanediol; γ-valerolactone; hydrogenation; biodiols; Cu; Co; Ir; Re; Pt; Ru; biomass conversion 1. Introduction Nowadays, lignocellulose-derived carboxylic acids are widely involved as starting materials for the production of commercial chemicals and transport fuel additives [1–3]. Levulinic acid (LA) is considered to be the platform molecule that can be converted into different value-added chemicals [4]. Volatility of fossil fuels prices and their current relatively low levels [5] make alternative, i.e., biomass-derived, fuels not competitive pricewise with counterparts on the basis of petroleum; therefore, production of high value-added chemicals from biomass is deemed to be a more efficient strategy than production of biofuels [6]. Among such high value-added chemicals, bio-based polymers could be mentioned as being a feasible alternative to various synthetic polymers currently produced using predominantly crude oil as a feedstock [7]. Moreover, some of the bio-based polymers such as polylactic acid are biodegradable, which is another advantage of their utilization. On the contrary, production of petroleum-based polymers is largely unsustainable, calling for their efficient recycling. Otherwise, a large increase of waste plastics and, subsequently, environmental pollution are becoming Reactions 2020, 1, 54–71; doi:10.3390/reactions1020006 www.mdpi.com/journal/reactions Reactions 2020, 3, x FOR PEER REVIEW 2 of 18 Reactions 2020, 1 55 efficient recycling. Otherwise, a large increase of waste plastics and, subsequently, environmental pollution are becoming of tremendous concern [8]. New strategies to replace conventional petroleum- ofbased tremendous polymers concern with [renewable8]. New strategies alternatives to replace are being conventional developed, petroleum-based involving starting polymers material with renewableplatform molecules alternatives with are beingan appropriate developed, involvingmolecular startingstructure material derived platform from moleculesbiomass, withsuch anas appropriateagricultural molecularwastes (wheat structure straw, derived corn stover) from biomass,or forest suchresidues. as agricultural Such biogenic wastes diols, (wheat such straw,as 1,4- cornpentanediol stover) or(PDO), forest can residues. be prepared Such biogenic either from diols, γ-valerolactone such as 1,4-pentanediol (GVL) originating (PDO), can from be preparedLA or its eitheresters fromthroughγ-valerolactone hydrogenation (GVL) or originating directly from from LA LA oresters its esters (Scheme through 1). PDO hydrogenation is considered or directly as an fromalternative LA esters bio-derived (Scheme 1monomer). PDO is to considered produce asbiodegra an alternativedable polyesters bio-derived with monomer a high strength to produce [9], biodegradablewhich are globally polyesters increasingly with a in high demand strength [10]. [9 ],It whichis worth are noting globally that increasingly PDO has wide in demand application [10]. Itareas is worth that notingare also that used PDO as has an wide intermediate application in areasthe production that are also of used fine aschemicals, an intermediate cosmetics, in the or productionpharmaceuticals of fine [11,12]. chemicals, cosmetics, or pharmaceuticals [11,12]. SchemeScheme 1.1. PossiblePossible routes routes of of 1,4-pentanediol 1,4-pentanediol (PDO) (PDO) formation formation from from levulinic levulinic acid acid (LA) (LA) and and γ- γvalerolactone-valerolactone (GVL). (GVL). CatalyticCatalytic hydrogenationhydrogenation ofof GVLGVL toto PDOPDO waswas conductedconducted selectivelyselectively overover homogeneoushomogeneous catalystscatalysts onon the the basis basis of of Ru Ru [10 ,[10,13,14],13,14], Co [Co15, 16[15,16],], and Feand [17 Fe], for[17], which for almostwhich 100%almost product 100% yieldproduct was yield reported. was However,reported. fromHowever, the viewpoint from the ofviewpoint industrial of implementation,industrial implementation, homogeneous homogeneous catalysts are catalysts inferior are to heterogeneousinferior to heterogeneous ones owing ones todi owingfficulties to difficulties in separating in separating the catalyst the fromcatalyst the from reaction the reaction media. media. Some catalysts based on noble metals (Ru [9,18], Pt [19], Rh-MoOx/SiO [20]) were studied in the liquid-phase Some catalysts based on noble metals (Ru [9,18], Pt [19], Rh-MoOx/SiO2 2 [20]) were studied in the GVLliquid-phase hydrogenation, GVL hydrogenation, not demonstrating not ademonstrati high selectivityng a forhigh the selectivity PDO formation. for the Hydrogenation PDO formation. of GVLHydrogenation over solid catalysts of GVL inover a fixed-bed solid catalysts reactor in under a fixed-bed hydrogen reactor pressure under (0.2–2.0 hydrogen MPa) pressure was reported (0.2–2.0 to proceedMPa) was over reported various to catalysts proceed based over onvarious noble catalyst and non-nobles based on metals noble [21 and]. The non-noble former onesmetals bearing [21]. The Pd andformer Pt, asones well bearing as nickel-based Pd and Pt, catalysts, as well didas nickel-based not result in catalysts, the desired did PDO not yieldresult under in the mild desired reaction PDO conditions.yield under Themild highest reaction yield conditions. of PDO The was highest achieved yield over of PDO 40 wt.% was Cuachieved/ZnO catalyst over 40 atwt.% 140 Cu/ZnO◦C and pressurecatalyst at of 140 1.5 MPa,°C and resulting pressure in of GVL 1.5 MPa, conversion resulting of 82.3%in GVL and conversion selectivity of to82.3% PDO and 99.2%, selectivity while atto higherPDO 99.2%, temperatures, while at 2-methyltetrahydrofuran higher temperatures, 2-methyltetrahydrofuran and 1-pentanol were formed. and 1-pentanol Activity of were Cu/ZnO formed. was stronglyActivity influencedof Cu/ZnO bywas the strongly calcination influenced temperature, by the resulting calcination in atemperature, higher activity resulting upon calcinationin a higher temperatureactivity upon elevation. calcination The temperature use of Cu/MgO elevation. catalysts The with use di offferent Cu/MgO copper catalysts content with was different also found copper to be econtentffective was [22]. also The found optimal to physicalbe effective chemical [22]. The parameters optimal physical of the catalyst chemical and parameters reaction conditions of the catalyst were copperand reaction loading conditions of 18%, reaction were temperaturecopper loading of 473 of K,18%, and reaction hydrogen temperature pressure of of 10 473 MPa. K, Underand hydrogen optimal conditions,pressure of the 10 PDOMPa. yield Under was optimal 94.4% atconditions, 90.5% GVL the conversion. PDO yield The was catalyst 94.4% at displayed 90.5% GVL stable conversion. behavior overThe 10catalyst h and displayed could be reused.stable behavior Copper-based over 10 catalysts h and could have be also reused. been studied Copper-based in [9,18 ,catalysts23]. Cu/ZrO have2 catalyst demonstrated, for example, a high selectivity of 99% and GVL conversion of 97% at 473 K and also been studied in [9,18,23]. Cu/ZrO2 catalyst demonstrated, for example, a high selectivity of 99% hydrogenand GVL pressureconversion of 6 of MPa 97% [9 ].at The 473 main K and drawback hydrogen of GVLpressure conversion of 6 MPa into [9]. PDO The over main copper drawback catalysts of supported on ZnO, MgO, and ZrO was a requirement of high hydrogen pressures (6–10 MPa) and GVL conversion into PDO over 2copper catalysts supported on ZnO, MgO, and ZrO2 was a