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Renewable Isoprene by Sequential Hydrogenation of Itaconic Acid and Dehydra-Decyclization of 3-Methyl-Tetrahydrofuran Omar A. Abdelrahman, Dae Sung Park, Katherine P Vinter, Charles S. Spanjers, Limin Ren, Hong Je Cho, Kechun Zhang, Wei Fan, Michael Tsapatsis, and Paul J. Dauenhauer ACS Catal., Just Accepted Manuscript • DOI: 10.1021/acscatal.6b03335 • Publication Date (Web): 19 Jan 2017 Downloaded from http://pubs.acs.org on January 20, 2017
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ACS Catalysis
Renewable Isoprene by Sequential Hydrogenation of Itaconic Acid and Dehydra-Decyclization of 3-Methyl-Tetrahydrofuran 1, †
Omar A. Abdelrahman, 1,2, †Dae Sung Park, 1Katherine P. Vinter, 1,2Charles S. Spanjers, 1Limin Ren, 3 Hong Je Cho, 1,2Kechun Zhang, 3Wei Fan, 1Michael Tsapatsis, 1,2,*Paul J. Dauenhauer
1. University of Minnesota, Department of Chemical Engineering and Materials Science, 421 Washington Ave. SE, Minneapolis, MN, 55455 U.S.A. 2. Center for Sustainable Polymers, a National Science Foundation Center for Chemical Innovation. 209 Smith Hall, 207 Pleasant Street SE, Minneapolis, MN, 55455 U.S.A. 3. University of Massachusetts Amherst, Department of Chemical Engineering, 686 North Pleasant Street, Amherst, MA 01003 U.S.A. † Authors Contributed Equally. *Corresponding Author:
[email protected] Abstract. Catalytic hydrogenation of itaconic acid (obtained from glucose fermentation) yields 3methyl-tetrahydrofuran (3-MTHF), which then undergoes catalytic dehydra-decyclization to isoprene. It is demonstrated that a one-pot cascade reaction converts itaconic acid to 3-MTHF at ~80% yield with PdRe/C catalyst and 1000 psig H2. Subsequent gas-phase catalytic ring opening and dehydration of 3MTHF with phosphorous-containing zeolites including P-BEA, P-MFI, and P-SPP (self-pillared pentasil) exhibits 90% selectivity to dienes (70% isoprene, 20% pentadienes) at 20-25% conversion. Keywords: Isoprene, Itaconic Acid, Zeolite, Phosphorous, Hydrogenation Body. Natural rubber is the precipitated polymer chain product (~106 Da) obtained from the latex of rubber trees (Hevea brasiliensis)[1] as an important material for automobile tires. The dominant form of natural rubber consists of isoprene units (2-methyl-1,3-butadiene) polymerized to form poly(cis-1,4isoprene)[2], a natural polymer from southeast Asia[3]. Isoprene is also currently manufactured as a byproduct of naphtha and gas oil cracking, serving as one of the major monomers for rubber and elastomers[4]. The majority of fossil-derived isoprene is used to produce poly(cis-1,4-isoprene) as a synthetic ‘natural’ rubber, providing a non-renewable source of rubbery material at the scale of one million tons per year[5]. Renewable synthetic ‘natural’ rubber (RSNR) or ‘biobased poly-isoprene’ requires isoprene from alternative renewable feedstocks such as glucose. Genencor and Goodyear have pursued microbial fermentation to BioIsopreneTM via engineered bacteria[6], with competitive synthetic biology routes to renewable isoprene pursued by Amyris and Michelin[7]. Five existing thermochemical pathways to isoprene also include: (i) acetone addition to acetylene followed by partial hydrogenation and dehydration[5,8], (ii) propylene dimerization[9], (iii) isoamylene dehydrogenation[10], (iv) isopentane dehydrogenation[11], and (v) the Prins condensation of isobutene and formaldehyde[12,13]. Any of these five processes can be renewable provided the feedstocks are sourced from biomass; for example, dehydration of glucose-derived isobutanol produces isobutene[14,15]. In this work, we propose a hybrid process (fermentation followed by thermochemical catalysis)[16] to renewable isoprene as depicted in Figure 1A. Fermentation of glucose produces itaconic acid (IA)[17] or its isomer, mesaconic acid (MA)[18,19]. These feedstocks have a four-carbon straight chain backbone and a single-carbon branch (e.g. methyl group) between terminal carboxylic acid groups. We have previously demonstrated that a two-step sequential hydrogenation produces high yield of 2-methyl-1,4butanediol (MBDO) from IA or MA[20]. Here, we propose that both steps can be combined in a single pot
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with a third step of tandem dehydration and cyclization to form 3-methyl-tetrahydrofuran (3-MTHF); as depicted in Fig. 1A, 3-MTHF is the thermodynamically-preferred product above room temperature. Finally, 3-MTHF undergoes combined dehydration and ring-opening in the vapor phase with solid acid catalysts to form isoprene. Experiments to evaluate the hydrogenation of IA to 3-MTHF were conducted in a liquid phase batch reactor under hydrogen gas pressure. A gas immersion impeller entrained H2 within the liquid, and the system pressure was varied in the 500-1500 psig range, while the reactor liquid temperature was varied between 100-200 °C. Supported metal catalysts including 5 wt% Ru/C, 5 wt% Ru/Al2O3, 10 wt% Pd/C, 5 wt% Pd/SiO2, (10wt%Pd-10wt%Re)/C, and (10wt%Pd-5wt%Re)/C were added to the liquid. Solid acid co-catalysts including silica-alumina (SA) and Amberlyst-15 were also added to the liquid for some trials to promote the conversion of MBDO to 3-MTHF. Itaconic acid (5 wt%) was dissolved in water at the start of the experiment, and the liquid was sampled after 24 hrs and analyzed by gas chromatography (GC) with quantitative carbon detection (QCD)[21,22]. Three of twenty experimental conditions are depicted in Fig. 1B, and full details of experimental trials are available in the supporting information (Tables S4-S5, Figures S3-S7). From the data in Fig. 1B, it is evident that (10wt%Pd10wt%Re)/C at 200 °C and 1000 psig H2 results in complete conversion of IA and ~80% yield of 3MTHF. The remaining carbon was primarily converted to 2-methyl-1-butanol (MBO). Dehydra-decyclization of 3-MTHF to isoprene was evaluated in two experimental reactor systems: a pulsed microcatalytic reactor and a packed-bed flow reactor. By the first method, screening of catalysts and reaction conditions was conducted using the previously developed microcatalytic method[23,24]; a pulse of organic reactant flowed over a fixed bed of catalyst to determine conversion, product yield and/or catalytic kinetics[25,26]. The data of Figure 2 were obtained by implementing the microcatalytic method as a fixed catalyst bed within the quartz liner of a gas chromatograph (GC). Catalyst particles were held between quartz wool plugs, and the entire assembly was inserted into the GC inlet (Fig. S2). Characterization of the GC inlet microcatalytic reactor demonstrated repeatable temperature control (200-400 °C) and reactant gas flow rates (organic compounds and helium carrier gas) of 6.0-1200 sccm, corresponding to space velocities of 0.9-180 s-1. An experimental trial consisted of a 1.0 µL liquid injection of 3-MTHF with a GC autosampler; injected liquid vaporized over quartz wool and flowed through the catalyst bed, before entering the GC column for quantification. Complete details are available in the supporting information. Screening of solid acid catalysts for dehydra-decyclization of 3-MTHF revealed a broad range of activity and selectivity to diene products when evaluated at varying temperature (200-400 °C) and space velocity (0.9-90 s-1) as shown in Figure 2. The predominant diene product with all catalysts was isoprene with smaller amounts of 1,3-pentadienes and even less 1,4-pentadiene (Fig. S8). Niobia (Nb2O5) and SnBEA (Si/Sn 125) were relatively inactive, while SiO2-Al2O3, ZSM-5 (Si/Al 140), and faujasite (H-Y, Si/Al 30) were active but only moderately selective to isoprene (5-40%) and all dienes (10-55%). In contrast, phosphorous-containing self-pillared pentasil (P-SPP)[27,28,29,30] exhibited high activity with high selectivity to isoprene (~70%) and dienes (~90%). The considered catalysts provided a comparison between commercially-available solid acids and P-containing zeolites (with or without Al). Complete experimental details are in the supporting information (Tables S6-S16). Dehydra-decyclization of 3-MTHF with phosphorous-containing zeolites was further evaluated over a range of experimental conditions (Figure 3) and zeolite structures (Figure 4A and 4B). As shown in Figure 3, approximately 112 experiments considered the variation of reactor space velocity (0.9-180 s1 ) and temperature (225-400 °C) with P-SPP catalyst; the data set was then fit to a fifth-order threedimensional polynomial for depiction (Figure S14). From this large data set, it is evident that isoprene selectivity is maximized at low space velocity (~1 s-1) and moderate temperature (~325 °C). Linear
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pentadienes are favored at higher temperature (~350 °C), while C3-C4 alkenes are optimal at high space velocity (>10 s-1) and low temperature (
