Article pubs.acs.org/IECR
Novel Two-Step Process for the Production of Renewable Aromatic Hydrocarbons from Triacylglycerides Swapnil Fegade,† Brian Tande,*,† Alena Kubátová,‡ Wayne Seames,† and Evguenii Kozliak‡ †
Department of Chemical Engineering, University of North Dakota, 241 Centennial Drive, Stop 7101, Grand Forks, North Dakota 58202-7101, United States ‡ Department of Chemistry, University of North Dakota, P.O. Box 9024, Grand Forks, North Dakota 58202, United States S Supporting Information *
ABSTRACT: A two-step process was developed for the production of aromatic hydrocarbons from triglyceride (TG) oils. In the first reaction step, TG (soybean) oil was noncatalytically cracked and purified by distillation to produce an organic liquid product (OLP). The resulting OLP was then converted into aromatic compounds in a second reaction using a zeolite catalyst, HZSM-5. In this second reaction, three main factors were found to influence the yield of aromatic hydrocarbons: the SiO2:Al2O3 ratio in the HZSM-5, the reaction temperature and the OLP-to-catalyst ratio. Upon cursory optimization, up to 58 w/w% aromatics were obtained. Detailed analyses revealed that most of the alkenes and carboxylic acids, and even many of the unidentified/unresolved compounds, which are characteristic products of noncatalytic TG cracking, were reformed into aromatic hydrocarbons. Instead of BTEX compounds, which are the common products of C2−C8 alkene and other feedstock reforming with HZSM-5, longer-chain alkylbenzenes dominated the reformate (along with medium-size n-alkanes). Another novel feature of the two-step process was a sizable (up to 13 w/w%) concentration of alicyclic hydrocarbons, both cyclohexanes and cyclopentanes. Thus, this novel twostep process may provide a new route for the production of renewable aromatic hydrocarbons as an important coproduct with transportation fuel products.
1. INTRODUCTION Crude oil is currently the major source for the production of aromatics, which have a wide variety of uses, such as the production of polymers and for use as an octane enhancer in gasoline.1 Aromatics are also produced commercially from coal in small amounts, but most end up in the form of a pitch or asphalt products.2 Process routes also exist to synthesize certain aromatics from natural gas and natural gas-derived compounds such as propylene.3 All of these sources use fossil-derived carbon, and with the growing concerns over global climate change, there is a growing interest in developing processes that can use renewable resources for the production of aromatics and associated organic chemicals. This includes attempts to produce phenolics by the pyrolysis of lignin4 and the use of zeolite catalysts. Several studies5−11 have been conducted to explore the conversion of biomass and pyrolytic bio-oils into various hydrocarbon mixtures through the use of porous catalysts such as H−Y zeolites, HZSM-5 and H-modernite at reaction temperatures of 290 °C − 410 °C. For silica−alumina catalysts, the yields of aromatics were only between 4 and 7 w/w%, even at higher temperatures, whereas the coke yields were as high as 30 w/w%. By contrast, HZSM-5 produced only about 15 w/w% coke while yielding higher aromatic hydrocarbon concentrations. Although aromatics’ concentrations as high as 86 w/w % in the organic liquid product (OLP) were achieved with HZSM-5, the OLP yield was a disappointing 22 w/w%. This equates to a total aromatics production yield of only 19 w/w% of the original feedstock.12−14 Both edible and nonedible triglyceride (TG) oils are synthesized by a wide variety of plants, such as soybean, © XXXX American Chemical Society
canola, rapeseed, camelina and cotton, as well as by many algae and bacteria. TG oils are promising feedstocks for the production of valuable organic chemicals because they can be efficiently cracked into intermediates that can be further processed into useful chemical products15 These oils are particularly well-suited for the production of aromatic hydrocarbons, rather than phenolics.16−21 Catalytic TG cracking22,23 yields aromatic and other hydrocarbon products24−26 along with simple molecules, that is, water, CO and CO2. Catalytic conversion may occur at lower temperatures compared to thermal pyrolysis.22−24,27,28 Various catalysts have been explored for the production of fuels and chemicals from crop oil.26 Among these catalysts, the zeolite HZSM-5 has shown a high selectivity toward the production of aromatics in the specific size range of C6−C8, that is, benzene, toluene, ethylbenzenes, and xylenes (BTEX). HZSM-5′s specificity is due to its defined pore size and the specific geometry of its active acid sites. Just as with lignin conversion, one significant problem with using zeolite catalysts, including HZSM-5, is the high yield of tars/coke, which can foul the catalyst. If the tar-producing reactions could be separated from the aromatization reactions, this problem could be minimized. Our previous studies have demonstrated that TG oils can be efficiently cracked without a catalyst at temperatures above 400 °C.25 Tars formed during the cracking reactions can be separated from the more volatile components via distillation, Received: May 26, 2015 Revised: September 11, 2015 Accepted: September 12, 2015
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DOI: 10.1021/acs.iecr.5b01932 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX
Article
Industrial & Engineering Chemistry Research
soybean oil, provided by Ag Processing Inc., a cooperative located in the state of Minnesota, U.S.A., was utilized. Nitrogen gas was supplied in pressurized bottles at >99.99% purity by Praxair, Danbury, CT. Gas chromatographic (GC) grade standards for benzene, toluene, ethylbenzene, xylenes, naphthalene, and 2-chlorotoluene were purchased from SigmaAldrich, Saint Louis, Missouri, U.S.A. The ammonium forms of two different ZSM-5 catalysts having different SiO2/Al2O3 ratios (CBV5524G and CBV 2314) were purchased from Zeolyst International, Conshohocken, PA, U.S.A. According to data from the manufacturer, CBV5524G has a SiO2/Al2O3 ratio of 50, a surface area of 425 m2/g, and a particle size of
