J. of Supercritical Fluids 119 (2017) 26–35 Contents lists available at ScienceDirect The Journal of Supercritical Fluids j o ur na l ho me page: www.elsevier.com/locate/supflu Biomass conversion to bio-oil using sub-critical water: Study of model compounds for food processing waste R. Posmanik a,∗ , D.A. Cantero a , A. Malkani a , D.L. Sills a,b , J.W. Tester a a School of Chemical and Biomolecular Engineering, Cornell University, Ithaca, NY 14853, United States b Department of Civil & Environmental Engineering, Bucknell University, Lewisburg, PA 17837, United States a r t i c l e i n f o Article history: Received 6 July 2016 Received in revised form 7 September 2016 Accepted 7 September 2016 Keywords: Hydrothermal liquefaction Biomass Subcritical water Bio-oil a b s t r a c t The hydrothermal conversions of three model compounds—starch, bovine serum albumin and linoleic acid—and their binary and ternary mixtures were evaluated. Batch experiments were operated at 250–350 ◦ C, 5–20 MPa for 10–60 min. Bio-oil produced from sugars, proteins and their mixtures contained ∼70% carbon and ∼15% oxygen (w/w) with higher heating values than those of the substrates. When treated individually, bio-oil yields showed the following behavior: lipids > sugars > proteins. Dehydration and condensation reactions among intermediates were hypothesized to enhance the production of bio-oil via the hydrothermal conversion of sugar and lipid mixtures. The ternary mixtures (sugar + oil + protein) exhibit the best performance for bio-oil production, likely due to similar chemical reactions, catalyzed by alkalinity from protein degradation. Results of this study demonstrate that the bio-oil yields for hydrothermal liquefaction of sugars, proteins and lipids may be maximized by selective design of feed- stock composition. © 2016 Elsevier B.V. All rights reserved. 1. Introduction Sustainable management of food wastes is a global challenge. Approximately one-third of food produced globally for human con- sumption is either lost or wasted [1]. In the U.S., industrial-scale food production produces 36 million tons of food waste per year, generated from animal processing, as well as fruits, vegetables, dairy products and grain production [2]. Natural decomposition of food wastes in landfills produces greenhouse gases such as methane, as well as sludge that contaminates soil and water [3]. On the other hand, food waste represents an excellent resource for renewable energy and nutrient products as it has high caloric and nutritional values [4]. In addition, food wastes are a suitable feedstock for the production of liquid transportation fuels [5,6]. The food industry produces a variety of waste streams that represent potential feedstocks for fuel production. The fruit and vegetable industry, for example, produces large amounts of waste such as peels, shells, seeds and bagasse [3]. These wastes are sources of valuable compounds such as sugars, fibers, fatty acids, and phe- nolic compounds. The grain industry produces waste generated by the production and processing of vegetable oils (mainly, soybean, ∗ Corresponding author. E-mail addresses: rp332@cornell.edu, royposmanik@gmail.com, posmanik@post.bgu.ac.il (R. Posmanik). sunflower and canola). Vegetable oil production generates partially defatted residues, which are rich in plant fibers, proteins and some lipids [7]. Cheese and yogurt production generates large volumes of liquid waste which is considered to be the major contributor to the environmental pollution from the dairy sector [8]. Whey, for example, is a by-product of yogurt and cheese manufacturing rich in soluble proteins as well as lactose and minerals [9]. The meat and fish processing industries represent another polluting indus- try due to the high organic contents of their wastes [10], which contain fats, bones, meat, blood, salts and chemicals [11]. Although some of these waste streams are reused, mainly as animal feed, the majority of food processing wastes is not valorized and should be considered as an alternative feedstock for bioenergy produc- tion [3]. In addition, all common uses of food waste, which include downstream land application (e.g., composting and animal feed), may lead to the propagation of human and livestock illnesses as a result of foodborne pathogens’ survival during common waste management treatments [12]. Hydrothermal biomass processing at temperatures and pres- sures near and below the critical point (374.2 ◦ C and 22.1 MPa) provides an excellent opportunity for processing food waste streams that contain high water contents [13,14]. Specifically, hydrothermal processing can produce valuable energy products, while reducing the enthalpy requirement associated with the vaporization of water [15]. Typical hydrothermal liquefaction (HTL) http://dx.doi.org/10.1016/j.supflu.2016.09.004 0896-8446/© 2016 Elsevier B.V. All rights reserved.