Title

Modeling the energy content of solid alcohol and biodiesel produced from waste cooking oils (WCO) of kitchens and the feasibility of its application in domestic usage

Principal Investigator

Dr. Ramin Nabizadeh

Abstract

Waste cooking oil (WCO) can be economically and efficiently recycled as a low-cost and renewable raw material for the generation of solid alcohol and biodiesel. This study investigated the WCO recycling from catering facilities in Tehran (Iran) as a precursor for solid alcohol and biodiesel synthesis by a simple one-step method with the mixture design approach for solid alcohol production and D-optimal design approach for biodiesel production to determine the heating value, the micromorphology and physicochemical properties, and the feasibility of using solid alcohol as candle warmer. High-speed centrifugation of original waste cooking oil (O-WCO) divided O-WCO into two components as the supernatant of WCO (S-WCO) with higher iodine value and the bottom of WCO (B-WCO) with lower iodine value. Results of SEM, FTIR and XRD showed that production of solid alcohol based on B-WCO by reaction of NaOH with B-WCO in ethanol, the FASSs were generated. The FASSs were scattered homogeneously in ethanol at 100 °C and created a three-dimensional porous polycrystalline network (3DPPN) after chilling, that enclosed the ethanol molecules and generated solid alcohol. The regression analysis indicated that two components of NaOH*Oil have the positive coefficients (synergistically), while two components of Oil*Alcohol had the negative coefficients (antagonistically). The optimal preparation conditions for solid alcohol with heating value 8715.23 kJ/kg were determined as follows: 0.2 wt.% alcohol, 0.0275 wt.% NaOH, 0.7725 wt.% B-WCO and reaction time 45 min. The heating value for solid alcohol based on B-WCO (8885.47 kcal/kg) is higher than control groups such as solid alcohol based on O-WCO (8084.05 kcal/kg), S-WCO (8119.24 kcal/kg) and butter (8117.93 kcal/kg) and fossil fuels such as coal (4000-7000 kcal/kg), coke (6500 kcal/kg), charcoal (7000 kcal/kg), and carbon (8000 kcal/kg). Hence, the heating value of solid alcohol based on B-WCO is closed to heating value of natural gas (8600 kcal/kg) and can be used as a type of new solid fuel such as candle warmer with many advantages such as higher melting point, environmentally friendly fuel, without harmful gases, higher combustion time, residue small, without dark smoke, easiness in packing, perfectly hygienic, no need to heat, smoothness in quality, convenience in use, and easy transport and storage. Hence, solid alcohol based on B-WCO can be motivated to use as a kind of new solid fuel or as a kind of green energy. In addition, High values of coefficient of determination (R2= 0.924), R2 adjusted (0.916), cross-validation (Q2=0.904) and model validity (0.921), and reproducibility (0.908) indicate the suitability of the model for biodiesel production. Hence, the results showed that the heating value produced by biodiesel combustion follows the quadratic model. Between methanol to oil ratio, catalyst and reaction temperature with response variable (heating value) with 95% confidence (p-value <0.001) were significantly, while no significant relationship between response variable and reaction time (p-value> 0.05). Considering the F-value is higher than 0.05 (0.761) and P-value is much less than 0.0001, it is observed that the quadratic model is statistically very significant at the 95% confidence level. In addition, the influence of major factors such as methanol to oil ratio, sodium hydroxide as catalyst and reaction temperature on heating value (kcal/kg) as response variable was investigated by the quadratic model. The results showed that with increasing the ratio of methanol to oil, the weight percentage of catalyst and the reaction temperature the heating value increases, decreases and decreases, respectively. The maximum heating value obtained from biodiesel occurs when the reaction temperature was at 50°C, the catalyst was at 0.56 wt.% and the ratio of methanol to oil was at 10 (dimensionless). Furthermore, the finding of this work showed that the optimal preparation conditions for biodiesel with heating value 9500.47 kcal/kg using D-optimal design approach were determined as follows: methanol to oil ratio at 10, catalyst at 0.56 wt.%, reaction temperature at 50°C and reaction time at 45 min. Moreover, comparison of physical and chemical properties of biodiesel produced from supernatant waste cooking oil (S-WCO) under optimal conditions is consistent with the results of other different standards (EN 14214: 2012, ASTM D6751-12, ASTM D 6751-07b and DIN V 51606). The most important biodiesel fatty acid methyl esters produced in this study included oleic (41.26%), linoleic (35.04%), palmitic (17.36%), stearic (3.64%), palmitoleic (0.57%) and myristic (0.36%). Objective observations at the pilot scale showed that the use of mixtures (biodiesel and diesel fuel) and pure biodiesel in the diesel engine did not cause any problems such as engine ripping, engine shutdown and carbon-fouled plug. The total energy input and energy output are calculated as 34.269 and 41.161 MJ/L, respectively. Waste cooking oil has the highest share of total energy input (73.57%). Direct and indirect energy forms consist of 2.785 MJ/L which is equivalent to 8.125% and 31.48 MJ/L which is equivalent to 91.87% of total energy input, respectively. The shares of renewable and non-renewable energies are 73.78% which is equivalent to 25.28 MJ/L and 26.22% which is equivalent to 8.986 MJ/L of the total energy input. specific energy, net energy and energy intensiveness energy of biodiesel production were 24.36 MJ/kg, 7.892 MJ/L and 25.41 $/MJ, respectively. In addition, energy intensity cost, energy intensiveness value, energy ratio cost of biodiesel production were 0.373 kg/$, 13.82 $/MJ and 0.316 (dimensionless), respectively.

Year

2019