May 19, 2017 - The characterized biodiesel complied with ASTM D 6751 and EN ... One of the main issues confronting humanity from creation to date and taken much ... increased greenhouse gases (causing climate change), degrada- tion of the ... the transesterification of vegetable oils, animal fats, and other sources of ...
Article pubs.acs.org/EF
Transesterification of Rubber Seed Oil to Biodiesel over a Calcined Waste Rubber Seed Shell Catalyst: Modeling and Optimization of Process Variables Samuel Erhigare Onoji,*,†,‡ Sunny E. Iyuke,†,‡ Anselm I. Igbafe,§ and Michael O. Daramola† †
School of Chemical & Metallurgical Engineering, University of the Witwatersrand, 1 Jan Smuts Avenue, Braamfontein 2050, Private Bag 3, Johannesburg, South Africa ‡ Petroleum and Natural Gas Processing Department, Petroleum Training Institute, PMB 20, Effurun, Nigeria § School of Chemical & Petroleum Engineering, Afe Babalola University, PMB 5454, Ado-Ekiti, Nigeria S Supporting Information *
ABSTRACT: In the present study, waste rubber seed shell (RSS) obtained from our previous study was investigated as a plausible solid base catalyst for the transesterification of esterified rubber seed oil (RSO) to biodiesel. TGA, XRF, XRD, SEM, and N2 adsorption/desorption analysis (BET) were used to characterize the catalyst. Central composite design (CCD) was employed to design the experiments conducted to study the influence of the process variables (reaction time, methanol/oil ratio, and catalyst loading) on biodiesel yield. Response surface methodology (RSM) technique, was used to optimize the process, and the quadratic model developed was statistically significant with F-value of 12.38 and p-value (95% at optimized conditions. In sub-Saharan Africa, Nigeria has an estimated 18 million hectare (ha) of wastelands in the South−South geopolitical zone suitable for the cultivation of rubber tree (Hevea brasiliensis), a nonedible oil bearing plant for latex production and seed oil for biodiesel.1 Studies by several researchers have shown that a seed of the rubber tree contains 35−60% oil that portrays it as a better competitor to other nonedible oils for biodiesel production.1,12−14 Currently, an insignificant fraction of rubber seeds are utilized for the rubber plant breeding process, and many of the seeds are left to rot away. The rubber seed shells (RSSs) generated from seeds during oil extraction pose a waste disposal problem to rubber seed oil (RSO) millers. In this study, calcined RSS was investigated as a plausible source of direct heterogeneous base catalyst for the transesterification reactions of esterified RSO to rubber seed oil methyl ester (RSOME), popularly called biodiesel. This will no doubt reduce biodiesel production cost. To the best of our knowledge, such investigations on RSS as a source of heterogeneous catalyst for biodiesel production are not available in the literature. Thermogravimetric analysis (TGA) was employed to determine a suitable calcination temperature of RSS for biodiesel synthesis. Fatty acid methyl ester (FAME) content was determined by gas chromatography−mass spectrometry (GC-MS). Structural properties of the raw and calcined RSS were examined by Xray diffraction (XRD). The surface morphology of the catalyst was examined by using scanning electron microscopy (SEM). Xray fluorescence (XRF) and N2 physisorption (at 77.3 K) were used to evaluate the elemental composition, and the textural property (specific surface area, pore volume, and pore size) of the raw and calcined RSS, respectively. Reaction time, methanol/oil ratio, and catalyst loading for the transesterification process were optimized via response surface methodology (RSM) based on central composite design (CCD). The biodiesel produced was characterized to determine its fuel properties and applicability.
(P /Po) (C − 1) P 1 = . + V [(1 − P /Po)] VmC Po VmC
(1)
where P is the partial pressure, Po is the saturation pressure, Vm is the maximum amount of nitrogen adsorbed/unit mass of catalyst at high pressure conditions required to form a complete monolayer over the entire surface of the catalyst, and C is the BET constant related to the isosteric heat of adsorption. The Barrett−Joyner−Halenda (BJH) model calculated the pore-size distributions of the raw and calcined RSS. The total pore volume is defined as the volume of liquid N2 corresponding to the amount adsorbed at a relative pressure of P/Po = 0.997, after which N2 desorption commences. 2.2.2. Acid-Catalyzed Esterification of Rubber Seed Oil. The rubber seed oil used in the study had an initial acid value of 18.02 ± 0.141 mg KOH/g oil, and an FFA level of 9.01 ± 0.07% obtained from the authors’ previous study.14 Reduction of FFA to 99%) and stirred for 5 min. The mixture was added to the oil maintained at 60 °C, and the reaction continued for 1 h at a stirring rate of 600 rpm. The esterified oil was transferred into a separating funnel and allowed to stand for 2 h. The pretreated oil was separated from the water formed, and excess methanol was evaporated in a rotary evaporator prior to acid value determination by a standard titration procedure described by ASTM. Similar experiments was carried out using 3, 4.5, and 6% vol/vol H2SO4, and their determined acid values were recorded in Table S1. The 6% vol/vol H2SO4 obtained for
