Catalytic Conversion of Ethanol to Liquid Hydrocarbons by Tin

Letter Cite This: ACS Appl. Energy Mater. XXXX, XXX, XXX−XXX

www.acsaem.org

Catalytic Conversion of Ethanol to Liquid Hydrocarbons by TinPromoted Raney Nickel Supported on Alumina Sukhendu Mandal*,† and Ayusman Sen*,‡ †

School of Chemistry, Indian Institute of Science Education and Research Thiruvananthapuram, Kerala, India 695551, Department of Chemistry, The Pennsylvania State University, University Park, Pennsylvania 16802, United States

‡

ACS Appl. Energy Mater. Downloaded from pubs.acs.org by 5.188.216.204 on 03/31/19. For personal use only.

S Supporting Information *

ABSTRACT: The vast utilization of petroleum majorly affects the economy and the environment. Due to this impact, researchers have shown a great interest in synthesizing of biomass-derived products, and these products replace petroleum utility in transportation as fuel. Ethanol from biomass is an essential component of the gasoline pool; however, ethanol is not an ideal candidate as a liquid fuel due to its low energy density and high solubility in water. Therefore, it is of high interest to convert ethanol to a more traditional liquid hydrocarbon that can be combined with petroleum-derived fuels. Here, we report the use of a cost-effective catalyst, tin-promoted Raney nickel, for the effective conversion of ethanol to liquid hydrocarbons (up to C17), with reduced aromatic content. KEYWORDS: catalysis, ethanol, fuel, hydrocarbon and Raney nickel

T

the products contain a mixture of hydrocarbon products containing saturated, unsaturated, and aromatic hydrocarbons. The conversion of ethanol is mostly carried out through heterogeneous acid catalysts at moderately elevated temperatures. Among those, zeolites are commonly used for this purpose and H-ZSM-5 is virtually omnivorous.14−17 Conversion of ethanol to higher hydrocarbons using non-zeolite catalysts is a challenge.18 Hydrocarbon production via ethanol cracking requires an effective catalyst that encourages saturated hydrocarbon formation (C−O scission followed by hydrogenation). An effective catalyst should have activity for cleavage of the C−O bond with simultaneous control of undesired side products formation, such as coke. Davda et al. showed that supported rhodium, ruthenium, and nickel show high selectivity for saturated hydrocarbon production through C−O bonds cleavage.19,20 Among the three metals (Rh, Ru, and Ni), the coke formation follows the order Ru > Ni ∼ Rh. The high cost and scarcity of rhodium and ruthenium have motivated researchers to develop a catalyst based on nickel without compromising the selectivity.19,20 It was also reported that nickel (Ni), tin (Sn), and Al2O3 based catalysts have shown excellent activity and selectivity in the production of saturated hydrocarbons from ethanol.21,22 Here we show that tin-promoted Raney nickel significantly decreases the rate of undesired coke formation and increases the yield and selectivity toward the more desirable saturated liquid hydrocarbons. This supported Ni−Sn catalyst illustrates the potential of bimetallic catalysts for ethanol conversion with a higher yield of value-added liquid hydrocarbons and low aromatic

he anticipation of usage and demand for transportation fuels such as diesel, gasoline, and kerosene has increased rapidly. Notably, all these fuel products are obtained by refining petroleum. In this context, the utilization of petroleum makes a significant impact on the economy and also raises political and environmental issues. To resolve this, alternative use of biomass products has been explored immediately. Remarkably, the utility of these biomass-derived products replaces transportation fuels.1−3 It is also suggested that increased carbon dioxide emissions from the combustion of fossil fuels can be partially mitigated by the use of fuels derived from biomass. However, the conversion of biomass-derived liquids to transportation fuels needs the removal of oxygenated functionalities to increase the energy density and to gain desirable combustion properties. Of particular importance is the conversion of biomass into “drop-in” petroleum-derived fuel substitutes. Ethanol from biomass is an essential component of the gasoline pool; however, ethanol is not an ideal candidate for liquid fuels due to its low energy density, high volatility, and high solubility in water. Therefore, it is of high interest to convert ethanol to more traditional liquid hydrocarbon fuels.4−7 Currently, the conversion of biomass to fuels typically involve multistep and energy-intensive processes. This includes the production of ethanol by fermentation of biomass, high-pressure liquefaction of biomass, and biodiesel from vegetable oils.8−10 In addition, using zeolite catalysts, liquid hydrocarbons can be processed from biomass-derived carbohydrates at the operating temperatures 570−920 K. In this process, zeolite catalyst suffers from deactivation due to coking and frequent regeneration by combustion of the deposited coke is required.4−10 There have been several reports of the conversion of ethanol and higher alcohols to hydrocarbons.11−13 But in these cases, © XXXX American Chemical Society

Received: January 21, 2019 Accepted: March 27, 2019 Published: March 27, 2019 A

DOI: 10.1021/acsaem.9b00118 ACS Appl. Energy Mater. XXXX, XXX, XXX−XXX

Letter

ACS Applied Energy Materials

Conversion and coke formation are shown with respect to the Sn:Raney-Ni molar ratio in Figure 1. Addition of tin to

species. The product could be integrated with petroleum or gasoline in a considerably higher ratio than ethanol. Due to this effectiveness and cost efficiency, this catalyst system has the potential to reduce the cost of the fuel. We prepared the tin-promoted Raney nickel catalyst by adding tributyl tin acetate to Raney nickel followed by reduction with hydrogen. The as-prepared catalyst was then mixed with Al2O3 for catalytic reactions (see the Supporting Information (SI)). Reactions were carried out in batch reactors by exposing the substrate to the as-prepared catalyst under an inert atmosphere at 300 °C for 10 h. Under our operating conditions, complete ethanol conversion to water, diethyl ether, and hydrocarbons ranging from 1 to 17 carbon atoms was observed. The higher hydrocarbons arise from either the initial dehydration of ethanol to ethylene, which is subsequently oligomerized to higher hydrocarbons, or through cleavage of the C−O bond of diethyl ether, also formed by ethanol dehydration. Ethanol dehydration is catalyzed by acidic sites associated with alumina support.21,22 Table 1 shows experimental results for ethanol and ethylene conversion over Raney Ni−Sn. Alumina support was not Table 1. Experimental Data for Ethanol and Ethylene Conversion to Hydrocarbons over Raney Ni−Sna for given reactant condition temperature (K) pressure (bar) feed (mol) gas phase composition (rel mol %) CH4 C2H6 C3H8 C4H10 liquid phase composition (relative ratios) saturated C−H:vinylic C−H:aromatic C−H

ethanol

ethylene

573 68.9 0.14

573 68.9 0.18

81 16 2.75 0.25

57 39 2.5 1.5

55:10:1c

62:1:4

Figure 1. Conversion and coke formation (%) vs mol percentage of tin addition to the Raney nickel catalyst for ethylene and ethanol (inset) conversion.

Raney nickel significantly decreases undesirable coke formation and improves product conversion. Moreover, the presence of tin promotes the formation of saturated hydrocarbons. For example, in ethanol conversion, the ratios for saturated C−H: [vinylic C−H and C−H α to oxygen (from ether)]:aromatic C−H with and without the presence of 6 mol % tin promoter are 55:10:1, and 1:10:0.1, respectively (Figures S6 and S7). In the case of ethylene conversion, the corresponding ratios for saturated C−H, vinylic C−H, and aromatic C−H are 62:1:4 and 48:1:1, respectively (Figures S8 and S9).’ The conversion of ethanol presumably starts with dehydration on Brønsted acid sites present on an alumina support to give either ethylene or diethyl ether. By comparing Figures S3 and S4, it is clear that the presence of alumina is essential for the formation of higher hydrocarbons from ethanol. The presence of the C−C bond in ethanol allows ethylene formation through dehydration, which, in turn, can undergo oligomerization to higher hydrocarbons. However, such a mechanism should only produce hydrocarbons with an even number of carbons, whereas we observed hydrocarbon products containing both even and an odd number of carbons. This suggests secondary cracking reactions, perhaps involving ethylene. To examine this possibility, we have investigated the reaction of ethylene with n-decane under similar conditions (without alumina substrate). The results show that n-decane (C10) was converted to lower hydrocarbons (C1−C9) (Figures S10 and S11) with both odd and even numbers of carbons. The decane conversion was around 24%. Interestingly, almost no decane conversion was observed if ethylene was not added to the reaction mixture, suggesting the critical role of ethylene in the cracking process (Figure S12).

a

Reaction conditions: 0.001 mol of Raney Ni with 6 mol % Sn supported on 0.01 mol of Al2O3, 300 °C, 10 h for ethanol conversion and without Al2O3 support for ethylene conversion. Gaseous products were quantified with a known standard mixture. The ratio of liquid products was quantified by 1H NMR spectroscopy.b bThe 1H NMR spectra identified the saturated C−H, vinylic C−H, and C−H α to oxygen from ether (for ethanol case only), and aromatic C−H. The areas under the peaks gave the corresponding ratios. cIn the case of ethanol conversion the 1H NMR peaks for vinylic C−H and C−H α to oxygen from ether overlapped.

employed for ethylene conversion. The conversion was 100% for ethanol and 70% for ethylene. The product mixture was composed of both gaseous and liquid phases. The gas-phase products were saturated hydrocarbons (methane, ethane, propane, and butane) (SI Figures S1 and S2). For ethanol, the liquid phase had a water layer and an organic layer (yield of the organic layer was ∼8%), the later consisting of ether, saturated hydrocarbons, vinylic hydrocarbons, and aromatics (Figure S3). Ethanol cannot be converted to higher hydrocarbons without substrate, Al2O3 (Figure S4). The reaction of ethylene led to saturated hydrocarbons, vinylic hydrocarbons, and aromatics (Figure S5). The relative ratio of the major components in the liquid mixture was obtained by 1H NMR spectroscopy. B

DOI: 10.1021/acsaem.9b00118 ACS Appl. Energy Mater. XXXX, XXX, XXX−XXX

Letter

ACS Applied Energy Materials

alloys (Ni3Sn, Ni3Sn4, and so on). After ethanol conversion reaction, Ni0 was converted to Ni2+ and Sn0 became a mixture of SnII/SnIV (Figures S19 and S20). The undesired coke formation was reduced from 5% to 2% for ethanol conversion and from 20% to 2% for ethylene conversion by the addition of tin to Raney nickel. Coke is one of the main side products in hydrocarbon cracking. The coke formation mechanism is complex and is influenced by various factors such as cracking temperature, feed gas, and the nature of the catalyst. The polymerization-type reaction of dehydrogenated surface species significantly produced carbonaceous residues (coke). The contiguous nickel sites may be an active reaction site, and the polymerization process may be discouraged by alloying with an inert element. Thus, the addition of tin likely removes the contiguous nickel sites in the Ni−Sn alloy. In this alloy, Sn may donate an electron to nickel and that will hinder hydrocarbon polymerization.26 For example, the addition of tin to Raney nickel removes the 3fold hollow sites and suppresses the hydrocarbon polymerization on a buckled (√3 × √3)R30° Sn/Ni(111) surface.27,28 Our results demonstrate that ethanol can be converted to the components of liquid hydrocarbon fuel at a moderate temperature using a relatively inexpensive catalyst such as nickel. The Raney Ni−Sn based catalyst shows high activity and good selectivity for the production of hydrocarbons from ethanol, which has relatively low energy density. This catalyst could notably improve the liquid hydrocarbon yield. Moreover, Sn-promoted Raney Ni also decreases the aromatic contents; thereby the blended stock will be closer to the essential composition of gasoline. Therefore, the products obtained by this method could be combined with petroleum or gasoline in a considerably higher ratio than ethanol. This is one of the rare non-zeolite catalysts, which converts ethanol to liquid hydrocarbons (up to C17). Simultaneously, the undesired coke formation was reduced substantially.

Addition of tin to Raney nickel resulted in no abrupt changes on the X-ray diffraction pattern and BET (Brunauer− Emmett−Teller) surface area of the catalyst.23 The observed X-ray diffraction peaks for both catalysts listed as Raney nickel and Raney Ni−Sn primarily match with Ni (cubic) structure with a slight shift in Ni−Sn samples (Figures S13 and S14). Interestingly, for both samples, similar X-ray diffraction peak widths were observed which indicated the comparable particle sizes. We have shown the scanning electron microscopy (SEM) pictures of Raney nickel, and tin-promoted Raney nickel catalysts in Figure 2. It is well-known that Raney nickel

■

Figure 2. SEM pictures (A) after reduction of Raney Ni (before reaction), (B) after reduction of Raney Ni−Sn (before reaction), (C) after the reaction of Raney Ni−Sn (nickel rich phase), and (D) after the reaction of Raney Ni−Sn, (alumina rich phase). For panels A−D, scale bar, 50 μm. The insets are magnified 50 times with respect to the main panels.

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsaem.9b00118.

generally consists of a porous nickel framework embedded by different polymorphs of hydrated alumina particles (mainly gibbsite Al(OH)3 and bayerite) (Figures 2A and S15).24 There are two separate phases that appeared in the case of tinpromoted Raney nickel catalyst before the reaction (Figures 2B and S16) in which one is an exceptionally dominant porous region and another is a diffuse phase representing the embedded parts of the porous region.23 Substantially, the two phases could not be differentiated by X-ray microanalyses. After the promotion of tin on Raney Ni, the diffuse phase disappeared and the two new phases were seen: nickel rich region (Figures 2C and S17) and predominantly Al and O containing regions (Figures 2D and S18). To find out the chemical states of the nickel and tin species in Raney Ni−Sn, we analyzed the X-ray photoelectron spectra before and after the reactions. The peak position and shapes of Ni 2p3/2 and Sn 3d5/2 indicate a partial reduction of surface Ni and Sn atoms to Ni0 and Sn0 before reaction (Figures S19 and S20). The binding energies are slightly shifted from those of pure metallic Ni (852.7 eV) and Sn (485.0 eV), respectively.25 These shifts may be due to the formation of different types of

■

Details of catalyst preparation and characterizations and several data for catalysis reactions (PDF)

AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected] (S.M.). *E-mail: [email protected] (A.S.). ORCID

Sukhendu Mandal: 0000-0002-4725-8418 Ayusman Sen: 0000-0002-0556-9509 Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS We acknowledge funding by the Air Force Office of Scientific Research (Grant FA9550-10-1-0509). We thank Dr. Weiran Yang and Dr. Robert Minard for useful discussions and Dr. Alan Benasi and Frances Pong for help with the NMR experiments. C

DOI: 10.1021/acsaem.9b00118 ACS Appl. Energy Mater. XXXX, XXX, XXX−XXX

Letter

ACS Applied Energy Materials

■

(21) Shabaker, J. W.; Huber, G. W.; Davda, R. R.; Cortright, R. D.; Dumesic, J. A. Aqueous-phase Reforming of Ethylene Glycol over Supported Platinum Catalysts. Catal. Lett. 2003, 88, 1−8. (22) Bates, S. P.; Van Santen, R. A. The Molecular Basis of Zeolite Catalysis: A Review of Theoretical Simulations. Adv. Catal. 1998, 42, 1−114. (23) Huber, G. W.; Shabaker, J. W.; Dumesic, J. A. Raney Ni-Sn Catalyst for H2 Production from Biomass-Derived Hydrocarbons. Science 2003, 300, 2075−2077. (24) Robertson, S. D.; Freel, J.; Anderson, R. B. The Nature of Raney Nickel: VI. Transmission and Scanning Electron Microscopy Studies. J. Catal. 1972, 24, 130−145. (25) Moulder, G. E., Stickle, W. F., Sobol, P. E., Bomben, K. D., Eds. Handbook of X-ray Photoelectron Spectroscopy, 2nd ed.; Physical Electronics Division, Perkin-Elmer: Eden Prairie, MN, USA, 1992. (26) Llorca, J.; Homs, N.; Fierro, J-L. G.; Sales, J.; Piscina, P. R. d. l. Platinum-Tin Catalysts Supported on Silica Highly Selective for nHexane Dehydrogenation. J. Catal. 1997, 166, 44−52. (27) Becker, L.; Aminpirooz, S.; Hillert, B.; Pedio, M.; Haase, J.; Adams, D. L. Three-fold Coordinated Hollow Adsorption Site for Ni(111) - c(4 × 2) - CO: A Surface-Extended X-ray Absorption FineStructure Study. Phys. Rev. B: Condens. Matter Mater. Phys. 1993, 47, 9710−9714. (28) Xu, C.; Koel, B. E. Influence of Alloyed Sn Atoms on the Chemisorption Properties of Ni(111) as Probed by RAIRS and TPD Studies of Co Adsorption. Surf. Sci. 1995, 327, 38−46.

REFERENCES

(1) Li, Z.; Lepore, A.; Davison, B. H.; Narula, C. K. Catalytic Conversion of Biomass-Derived Ethanol to Liquid Hydrocarbon Blendstock: Effect pf Light Gas recirculation. Energy Fuels 2016, 30, 10611−10617. (2) Corma, A.; Iborra, S.; Velty, A. Chemical Routes for the Transformation of Biomass into Chemicals. Chem. Rev. 2007, 107, 2411−2502. (3) Perlack, R. D.; Wright, L. L.; Turhollow, A. F.; Graham, R. L.; Stokes, B. J.; Erbach, D. C. Biomass as feedstock for a bioenergy and bioproducts industry: The technical feasibility of a billion-ton annual supply, Report DOE/GO-102995-2135; U.S. Department of Energy and U.S. Department of Agriculture: Oak Ridge, TN, USA, 2005. (4) Pimentel, D. Ethanol Fuels: Energy Balance, Economics and Environmental Impacts are Negative. Nat. Resour. Res. 2003, 12, 127− 134. (5) Sun, J.; Wang, Y. Recent Advances in Catalytic Conversion of Ethanol to Chemicals. ACS Catal. 2014, 4, 1078−1090. (6) Tret’yakov, V. F. Catalytic Conversion of Bioethanol in to Hydrocarbon Fuel. Int. J. Petrochem. Sci. Eng. 2016, 1, 18−19. (7) Tret’yakov, V. F.; Talyshinskii, R. M.; Ilolov, A. M.; Budnyak, A. D. Production of aviation fuel by bioethanol conversion on zeolite catalysts. Pet. Chem. 2016, 56, 224−229. (8) Weisz, P. B.; Haag, W. O.; Rodewald, P. G. Catalytic Production of High Grade Fuel (Gasoline) from Biomass Compounds by Shapeselective Catalysis. Science 1979, 206, 57−58. (9) Mascal, M.; Nikitin, E. B. Direct, High-Yield Conversion of Cellulose into Biofuel. Angew. Chem., Int. Ed. 2008, 47, 7924−7926. (10) Kunkes, E. L.; Simonetti, D. A.; West, R. M.; Serrano-Ruiz, J. C.; Gärtner, C. A.; Dumesic, J. A. Catalytic Conversion of Biomass to Nonfunctional Hydrocarbons and Targeted Liquid-Fuel Classes. Science 2008, 322, 417−421. (11) Heveling, J.; van der Beek, A.; DePender, M. Oligomerization of Ethane Over Nickel-Exchanged Zeolite Y into a Diesel range Product. Appl. Catal. 1988, 42, 325−336. (12) Czernik, S. Catalytic Pyrolisis of Biomass. In Advances Biofules & Bio Products; Lee, J., Ed.; Springer Science & Business Media, 2012; DOI: 10.1007/978-1-4614-3348-4_9. (13) Madeira, F. F.; Gnep, N. S.; Magnoux, P.; Maury, S.; Cadran, N. Ethanol Transformation Over HFAU, HBEA and HMFI Zeolites Presenting Similar Brønsted Acidity. Appl. Catal., A 2009, 367, 39− 46. (14) Mentzel, U. V.; Shunmugavel, S.; Hruby, S. L.; Christensen, C. H.; Holm, M. S. High Yield of Liquid Range Olefins Obtained by Converting i-Propanol over Zeolite H-ZSM-5. J. Am. Chem. Soc. 2009, 131, 17009−17013. (15) Gayubo, A. G.; Aguayo, A. T.; Atutxa, A.; Aguado, R.; Bilbao, J. Transformation of Oxygenate Components of Biomass Pyrolysis Oil on a HZSM-5 Zeolite. I. Alcohols and Phenols. Ind. Eng. Chem. Res. 2004, 43, 2610−2618. (16) Tau, L. M.; Fort, A. W.; Bao, S.; Davis, B. H. Methanol to Gasoline: 14C Tracer Studies of the Conversion of Methanol/Higher Alcohol Mixtures Over ZSM-5. Fuel Process. Technol. 1990, 26, 209− 219. (17) Derouane, E. G.; Nagy, J. B.; Dejaifve, P.; van Hoff, J. H. C.; Spekman, B. P.; Védrine, J. C.; Naccache, C. Elucidation of the Mechanism of Conversion of Methanol and Ethanol to Hydrocarbons on a New Type of Synthetic Zeolite. J. Catal. 1978, 53, 40−55. (18) Comelli, R. A.; Figoli, N. S. Transformation of C1-C4 Alcohols into Hydrocarbons on an Amorphous Silica-Alumina Catalyst. Appl. Catal. 1988, 36, 299−306. (19) Davda, R. R.; Shabaker, J. W.; Huber, G. W.; Cortright, R. D.; Dumesic, J. A. Aqueous-Phase Reforming of Ethylene Glycol on Silica-Supported Metal Catalysts. Appl. Catal., B 2003, 43, 13−26. (20) Davda, R. R.; Shabaker, J. W.; Huber, G. W.; Cortright, R. D.; Dumesic, J. A. A Review of Catalytic Issues and Process Conditions for Renewable Hydrogen and Alkanes by Aqueous-Phase Reforming of Oxygenated Hydrocarbons over Supported Metal Catalysts. Appl. Catal., B 2005, 56, 171−186. D

DOI: 10.1021/acsaem.9b00118 ACS Appl. Energy Mater. XXXX, XXX, XXX−XXX