Studies on Biodiesel Production form Waste Cooking Oil using Process Intensification Techniques

Abstract

Current, globally depleting fossilized fuel reserves, increasing environmental pollution and problems are the key motivating factors to pursue research on an alternative fuel derived from biomass, which can fulfil the ever-increasing energy demand for sustainable development. In this regard, biodiesel as a sustainable alternative helps in the protection of the environment due to its non-toxic, renewable, and biodegradable nature and produces less sulphur emissions and greenhouse gases. It is easy to use as well as clean and safe to handle as compared to gasoline diesel. The present research work is mainly motivated on design and development of an environment-friendly, energy-effective and industrially viable process intensification (PI)-based techniques {Ultrasound, Microwave, and Conjoint (microwave + ultrasound technique} using both homogeneous (potassium hydroxide, KOH) and heterogeneous (calcium oxide, CaO) catalyst to synthesize biodiesel from waste cooking oil (WCO) and blended oils. The outcomes of independently studied ultrasound process observed to have enhanced the biodiesel yield (98 % for KOH and 96.45 % for CaO catalyzed conditions) and significantly reduce the reaction period (10 min), making the process energy-efficient in comparison to the mechanical stirring (MS) technique. The optimization study of process parameters was performed using a Box-Behnken design of experiments method.

Similarly, an independent study on microwave-assisted biodiesel production technique which has shown significant results in terms of lower reaction time (9.6 – 9.7 min), with higher yield (96.77 % for KOH and 90.5 % for CaO catalyzed conditions) and high energy-efficiency has been, observed in the current work. In this process, the optimization of process parameters was done using the full factorial design of experiments. The scarcity of feedstock is the major concern for biodiesel production, and this can be resolved by blending the available non-edible feedstock. This approach will provide option to prepare a low-cost feedstock with large availability. Therefore, considering this view, lastly the conjoint effect of microwave + ultrasound was experimented on the blends of WCO and raw castor oil (RCO). For the first time, such a unique combination of oils was selected for biodiesel production. The optimization of process parameters was performed via the Box-Behnken design of experiments. The study showed that the conjoint effect of the microwave + ultrasound technique produce biodiesel with improved fuel properties. Also, higher biodiesel yield (93.38 % for KOH and 92.19 % for CaO catalyzed conditions), lower reaction time (10 min), and energy requirements makes it an energy-efficient process in comparison to each microwave and ultrasound subsystem used independently for blended oil as well as superior than the MS technique. The reaction kinetic analysis was performed for all three PI reactor systems applying assumptions of pseudo-first-order kinetic, which was found to be the best fit in for all catalyst systems in these respective techniques. The activation energies for PI techniques were observed to have reduced significantly (ultrasound reduces the activation energy by 1.7 and 1.5 times in comparison to MS for KOH and CaO conditions, reduction in activation energy using the microwave reduces the activation energy by 2.6 and 1.7 times in comparison to MS for KOH and CaO conditions, and for conjoint technique the activation energy was reduced by 2.5 and 1.8 times for KOH and CaO catalyzed conditions) in comparison to MS technique. Further, energy analyses were performed for all the above-mentioned processes. Parameters like dissipated power, delivered power, and percentage efficiency were estimated and analyzed. These analyses effectively displayed the PI techniques (11 times for ultrasound, 21 times for microwave and 3 times for conjoint technique) are energyefficient operations in comparison to MS technique. Based on the batch size process optimization results, commercialization potentiality of all the three techniques was tested by performing a scale-up study. A ten-fold scale up of 50 mL batch size was selected to perform the experiments based on the optimized parameters and it showed that about 90 % biodiesel yield was obtained within a short span of 15 – 20 min. Using large scale ultrasound and microwave equipment which are widely available in market the commercialization of PI techniques can be done. All the processes have shown bright prospects for commercialization for small scale applications with certain modifications (based on type of equipment) in process equipment and design parameters. All the PI techniques’ performances were compared with the MS technique in each case of catalyst systems and found superior. The physicochemical properties of produced biodiesel were correlated with ASTM petrodiesel standard and biodiesel fuel standards. All the fuel properties found to comply within ASTM biodiesel standard limits and at par with the petrodiesel. Thus, the present work demonstrated a successful comprehensive study of PI techniques in reference to the MS process to assess the overall performance of the PI techniques.