Continuous production of biofuel from refined and used palm olein oil with supercritical methanol at a low molar ratio Winatta Sakdasri a , Ruengwit Sawangkeaw b , Somkiat Ngamprasertsith a,c,⇑ a Fuels Research Center, Department of Chemical Technology, Faculty of Science, Chulalongkorn University, Bangkok 10330, Thailand b The Institute of Biotechnology and Genetic Engineering, Chulalongkorn University, Institute Bldg. 3, 254 Phayathai Rd., Pathumwan, Bangkok 10330, Thailand c Center of Excellence on Petrochemical and Materials Technology, Chulalongkorn University, 254 Phayathai Road, Pathumwan, Bangkok 10330, Thailand article info Article history: Received 27 April 2015 Accepted 9 July 2015 Keywords: Biofuel Continuous flow process Palm oil Used palm oil Supercritical methanol abstract The high energy consumption and high environmental impact in the supercritical methanol (SCM) pro- cess primarily originates from the preheating of reactants and the recovery of excess alcohols. This work demonstrated the synthesis of biofuel using a lowered methanol to oil molar ratio of 12:1, instead of the 40:1–42:1 ratios that are commonly employed in conventional SCM. The apparent density of the reacting mixture was measured and applied to accurately calculate residence times in a continuous reactor. The effects of residence time were considered from 10 to 25 min. The results revealed that excessive resi- dence times reduced the ester content, especially for unsaturated esters, in the resulting biofuel. A resi- dence time of 20 min was recommended to simultaneously achieve a maximum ester content of 90% and a triglyceride conversion of up to 99%. Used palm olein oil with high free fatty acid (4.56 wt.%) can be employed as a feedstock and give a maximum ester content of 80%. In addition, the side reaction between glycerol and methanol at 400 °C and 15 MPa showed a positive effect in increasing fuel yield by 2%–7%. Ó 2015 Elsevier Ltd. All rights reserved. 1. Introduction Biofuels are a source of renewable energy derived from living organisms and can be used as a substitute for petroleum fossil fuels. The obvious advantages of biofuels, such as being biodegrad- able, nontoxic, and environmentally friendly, have attracted many researchers to develop biofuel production methods, especially bio- diesel. The supercritical alcohol (SCA) process through the transes- terification reaction is a novel technology for producing biodiesel due to its many advantages over the conventional catalyst biodie- sel process. For example, the process is catalyst-free, has a short time reaction, offers high yields of biodiesel and high purity of the by-product (glycerol), and involves simple separation and purification steps [1–4]. The main operating parameters that influ- ence the transesterification under supercritical conditions are tem- perature, pressure, alcohol to oil molar ratio, and reaction time. As shown in Table 1, the supercritical reaction of a variety of refined vegetable oils has been investigated over a wide range of operating temperatures (280–350 °C), pressures (20–35 MPa), and reaction times (4–30 min), depending on the types of feedstock and reactor. A very high fatty acid alkyl ester (FAAE) content, up to 80–100%, has been reported. Note that the investigated range of alcohol to oil molar ratio was narrow, 40:1–42:1. Furthermore, the supercrit- ical alcohol (SCA) process is able to use waste cooking oil (high FFA and water contents) as feedstock, as also illustrated in Table 1. The high FFA and water content, up to 36 and 30 wt.%, respectively, do not significantly reduce the yields and reaction rates [5,6]. However, the synthesis of biodiesel using the SCA process suf- fers a drawback from its alcohol to oil molar ratio (40:1–42:1), which is high when compared with the stoichiometric ratio of 3:1. As proposed in a life cycle assessment (LCA) of biodiesel pro- duction with supercritical methanol (SCM) [7], a high methanol to oil molar ratio requires a large energy input for preheating and recovering alcohols. Such inputs produce a significant environ- mental load. In addition, Wang et al. [8] and Anitescu et al. [9] noted that preheating and recovery of alcohols result in high energy consumption and high production costs in biodiesel pro- duction using supercritical methanol. The SCA process conducted at high temperature (400–450 °C) and moderate pressure (10.0–20.0 MPa) has been investigated and shown the ability to markedly reduce the alcohol to oil molar ratio to 9:1–12:1, including in batch and continuous operations [9–11]. In addition, use of a laboratory batch reactor for biofuel production from palm olein oil with SCM and supercritical ethanol (SCE) at 400 °C and 15 MPa was successfully evaluated in our http://dx.doi.org/10.1016/j.enconman.2015.07.027 0196-8904/Ó 2015 Elsevier Ltd. All rights reserved. ⇑ Corresponding author at: Fuels Research Center, Department of Chemical Technology, Faculty of Science, Chulalongkorn University, Bangkok 10330, Thailand. Tel.: +66 22187678. E-mail address: somkiat.n@chula.ac.th (S. Ngamprasertsith). Energy Conversion and Management 103 (2015) 934–942 Contents lists available at ScienceDirect Energy Conversion and Management journal homepage: www.elsevier.com/locate/enconman