ARTICLE pubs.acs.org/EF
Fourier Transform Infrared Spectroscopic Method for Monitoring Hydroprocessing of Vegetable Oils To Produce Hydrocarbon-Based Biofuel Jitendra K. Satyarthi and Darbha Srinivas* National Chemical Laboratory, Dr. Homi Bhabha Road, Pune 411 008, India ABSTRACT: A novel Fourier transform infrared spectroscopic method is reported, for the first time, to estimate the conversion of vegetable oil (soybean oil, for example) to hydrocarbon-based biofuel via hydroprocessing. The infrared peak attributed to the carboxyl group (O CdO) is used as a marker to determine the conversion of fatty acid glycerides in soybean oil to hydrocarbons. Unlike the conventional gas chromatographic method, this new method of estimation is fast and requires no derivatization of the sample and predetermination of response factors of each chemical component in vegetable oil/product samples. 1H and 13C nuclear magnetic resonance spectroscopy techniques are also reported to substantiate and confirm the purity and product formation in the hydroprocessing reaction.
1. INTRODUCTION Depleting fossil fuel resources and growing concerns about greenhouse gas emissions are the two major factors steering our focus toward renewable fuels. Biofuel is a renewable energy resource produced from natural (plant) materials.1 3 The most common biofuels are bioethanol produced from corn, wheat, and sugar beet and biodiesel [fatty acid methyl esters (FAMEs)] produced from vegetable oils by transesterification with methanol.4,5 Although FAME is suitable for blending with petroleum-derived diesel fuels, it suffers from the drawbacks of long-term storage stability (because of unsaturation units in the structure), low energy content (because of oxygen/ester moiety), poor coldflow properties, and non-suitability of biodiesel diesel blends containing more than 20 30 vol % FAMEs. Hydroprocessing is an alternative route to convert vegetable oils into high-quality diesel fuel that is fully compatible for blending in any amount with petroleum-derived diesel or to use it as such.6,7 This process can be directly accommodated in the existing refineries. Hydroprocessing requires hydrogen gas to selectively eliminate the linkage oxygen as water and carbon dioxide. The resulting products are the respective diesel-like hydrocarbons. Paraffin-like liquid fuel obtained by hydrotreatment of vegetable oil and fats is sometimes termed as second-generation biodiesel or green diesel.6 Unlike the first generation (FAME biodiesel), this new generation biodiesel (hydrocarbons) is more favorable for industrial applications, being compatible with the current engines and even avoiding the need to be blended with petrol fuels if isomerized.6,7 This is an emerging area. In hydrotreating, removal of oxygen is accomplished through hydrodeoxygenation (HDO) and other direct mechanisms, such as hydrodecarbonylation (HDCN), hydrodecarboxylation (HDCX), and hydrogenation (Scheme 1).8 NExBTL9,10 and UOP/Eni Ecofining7 have commercialized the process for converting vegetable oil feedstock into iso-paraffinrich diesel substitute (green diesel), which is aromatic and sulfurfree diesel fuel and has a very high cetane value. The cold-flow properties of the fuel can be adjusted in the process to meet a climate-specific cloud point in either neat or blended forms. r 2011 American Chemical Society
Conventional hydrotreating catalysts (supported NiMo and CoMo after sulfidation) are used even in this transformation. Recently, several studies for the conversion of different fatty acids and their esters (triglycerides and methyl ester) into a mixture of hydrocarbons have been published.11 20 Conventionally, gas chromatographic (GC) techniques are used to follow the conversion and to determine the product yield and selectivity. The GC method has some disadvantages for its online monitoring applications. At lower conversions of vegetable oils (95% of the total biohydrocarbon product. The hydrocarbon fraction with greater than 18 carbon atoms in the chain was found to be 3 4%, and the fraction with less than 15 carbon atoms in the chain was
