Comparative study of biodiesel production from different waste oil sources for optimum operation con

Abstract

Keywords: Biodiesel; Fuel Source; Catalyst; Diesel Engine; Brake Power

Introduction

Energy crises are one of the most challenges facing the world in the near future due to the increasing development in the machining utilization. Industry and transportation sectors are consumed the large share of energy in which internal combustion engine are widely used. These sectors are mainly depend on fossil fuel which represents the main share of world marketing [1]. Fossil fuel is considered as a depleting fuel with limited resources available in a certain regions of the world, its prices increases with time due to the increasing demand. Moreover, this type of fuel is considered as the main source of pollution which contributes directly to the global warming [2]. World fuel demand have been increased continuously due to population growth and modern technology utilization, especially liquid fuel [3]. The large consumption, depletion of fossil fuel, and growing up for different industries lead the governments of different countries in the world to search for an alternative fuel instead of the fossil fuel. Besides that, the fossil fuel can effects on the environment generally and on the human health specially [4,5]. Biodiesel is a natural resource and an appropriate choice for various countries dependent on import, in order to use natural resources in best manner for other basic needs [6]. Biodiesel is the most viable alternative for mineral diesel due to their comparable characteristics [7]. The main advantage of this fuel is the variety of their sources which is available in almost all the regions in the whole world. It can be produced locally from edible or inedible vegetable oils and animals fats. In all proportions the biodiesel fuel is miscible with Petroleum-diesel. However, sometimes biodiesel blended with petroleum-diesel which denoted as BX like; B5, B20, and B50. The blend B5 indicates that, a blend composes of 5% and 95% percentage of biodiesel and Petroleumdiesel respectively. Biodiesel can demonstrating similar to Petroleum-diesel in terms of Cetane number [8,9]. Cetane number is a property that expresses the quality ignition of the fuel. The other properties exhibited by biodiesel are widely similar to petroleum-diesel which are heat of combustion, cloud and pour points, oxidative stability and viscosity [10,11]. The degradation capacity of biodiesel is many times faster than diesel. Within 28 days, pure biodiesel degrades 85 to 88 percent in water. Biodiesel flash point is much more than that of diesel fuel. Accordingly, blended biodiesel-diesel fuel’s flash point increases with increasing the percentage of biodiesel in the blend. Therefore, biodiesel and blends of biodiesel with diesel are safer to handle and storage [12]. The main obstacle facing biodiesel commercialization is the world food security that will affect from the utilization of edible oils as a biodiesel fuel source. Response Surface Method (RSM) is widely utilized as a statistical technique in different applications [13]. This software is considered as a viable tool to declare relationship between the correlate input parameters and their response

for optimum operation conditions through a set of polynomial functions [14]. This technique is adopted successfully in many studies for optimization biodiesel fuel production and engine performance [15–18]. Vegetable oil can be used as an alternative fuel for diesel engines and heating oil burners. In order to run these engines that designed to burn petroleum-diesel fuel, vegetable oil which has high viscosity must be lowered as possible. Many problems will be faced due to higher viscosity such as starter problem, carbon build up on the piston, knocking, damage of the engines, and incomplete combustion [19]. Mono-alkyl esters of fatty acids can be called biodiesel when it derived from vegetable oils or animal fat oils [20,21]. Biodiesel can be manufactured from edible (vegetable or animal) oil, and non-edible (vegetable or animal) oil [22]. The production of biodiesel are the most commonly used (vegetable and non vegetable) oil such as palm, soybean, sunflower, rapeseed canola, cotton seed, animal fat and Jatropha. Waste oil like grilled chicken waste oil (GCWO) which is animal based source and waste cooking oil (WCO) can be preferred as low priced sources and from other sides like an economic, waste management, and also because the rate of edible vegetable oil are higher than that from diesel fuel [23]. The aim of the current study is to investigate biodiesel production from different sources of waste oil using transesterification method. Waste cooking oil and grilled chicken waste oil have been chosen for the biodiesel preparation as they are available in the local restaurant and from domestic use as a waste products which represent a source for biodiesel production that are free of cost. The impact of different variables includes; reaction temperature, reaction time, catalyst type and concentration have been analyzed for optimum production conditions. Engine test has been conducted to assess fuel suitability for operating diesel engine.

Methodology

In this study two types of locally available waste oil have been investigated; grilled chicken waste oil (GCWO) which is animal based source and waste cooking oil (WCO) which is from sunflower (plants seeds based). The waste oil has been collected from the local restaurants (free from cost) and used in this study. The effects of different parameters such as, reaction temperature, reaction time, catalyst weight % on the biodiesel yield from different sources were investigated. The yield of biodiesel strongly depends on the reaction temperature [24], catalyst concentration [25] and reaction time [26] which can be considered as an important parameter effected the conversion of biodiesel. One of the major common catalysts used in biodiesel production is the potassium hydroxide [27] which has been used in this study.

Transesterification process was carried to produce biodiesel in alkali based batch as shown in figure 1 [28]. The reaction flask setup was made such that, it could process under various operating condition. The process is conducted using potassium hydroxide catalyst at a percentage of 0.3 wt%, 0.45 wt%, 0.6 wt%, 0.75 wt% and 0.9 wt at 0.15 increments. A reaction time of 1, 2 and 3 h and a reaction temperature of 50, 60, 70 and 80 (±1°C) has been considered at 1atm pressure. The different properties of produced biodiesel were measured in according to the ASTM standard test methods for each property as shown in table 1. The tested properties include kinematic viscosity at 40°C, specific gravity at 15°C, acid value (AV), flash point, cloud and pour point, and calorific value. Each test was repeated in triplicate for high accuracy and reliable results.

Response Surface Method (RSM) is a useful statistical technique for optimization in many engineering applications. [13]. This method consists of a set of statistical equations which implemented the linear function or square polynomial function to indicate the interaction among output responses and its input variables to obtain the optimum operation conditions. Costumer defined designs of RSM has been adopted in this study as an optimization technique [17]. Three input variables have been considered in the current study that optimized to obtain the output response. Based on Customer defined design of RSM, the discrete function has been adopted according to the used variables in the current experiments. Adoption of the settings of discrete factor can achieve more convenient experiment to perform with minimal effect on the analysis accuracy [13]. The basic and simple RSM model is based on a linear function and can be presents as in the following equation [16,17]: Y = βo + ∑ ik βi Xi + ε

In case that the linear model shows any curvature, a model of second order should be implemented as presents in the following equation [16,17]: Y = βo + ∑ ik βi Xi + ∑ ik<1 βij Xi X j + ε

In the current study, to indicate the point of critical function (optimum), quadratic model has been used as the suitable model for this case and presented in the following equation [16,17]: Y = βo + ∑ ik βi Xi2 + ∑ ik<1 ∑ βij Xi X j + ε

where k represents the number of input variables (X), β is the constant term and ε is the residual associated to the experiments. The choice of optimum variables conditions may be implemented for multi response to enhance biodiesel production and improve engine performance. In order to the

Table 1. ASTM standard test methods and specifications Properties

Method

selected parameters, the approach of desirability function was adopted and performed using Design Expert software. Reaction temperature and catalyst ratio were considered as influences parameters in this study. All specified candidate set of points based on the implemented technique. The output responses from this optimization include biodiesel yield (%) and conversion (%). The required number of runs for these experiments was set based on the number of considered parameters and level of optimization. Engine test was conducted to evaluate the different investigated fuel samples using single cylinder Yanmar TF 120 diesel engine. The engine is a 4-stroke water cooled direct injection with a cylinder bore, stroke length and connecting road length of 92 mm, 96 mm and 149.5 mm respectively. The engine maximum output power is 12 kW at 2400 rpm. The test is conducted at increasing speed from 1200 rpm to 2400 rpm with 300 rpm increment and constant 50% engine load. The brake power (BP) calculated based on collected torque and speed using the following equation: BP (kW ) =

where N is the engine speed (rpm), T is the measured engine torque (N.m). Brake specific fuel consumption (BSFC) is calculated based on mass flow rate of the fuel and the obtained brake power using the following equation:   kg  m .h = × 3600 BSFC   kW  BP

where ṁ is the mass flow rate. Brake thermal efficiency (BTE) is a measured of fuel conversion efficiency and calculated based on calculated brake power, mass flow rate and heating value of the fuel using the following equation: BTE(%) =

where HV is the heating value of the fuel (MJ/kg). Specific fuel consumption was calculated based on the obtained power and the measured fuel flow using fuel flow meter. Figure 2 presents the schematic diagram for engine experimental set-up used in this study.

Results And Discussion

In this work, GCWO was collected from chicken grill and WCO was the collected from the waste of frying oil in the restaurants that used cooking oil for frying. base catalysts of potassium hydroxide (KOH) at 0.3 wt%, 0.45 wt%,

21. Equipment screen panel, 22. Control valve, 23. Exhaust,

the optimization results for the impact of reaction temperature on the yield of biodiesel from GCWO at constant atmospheric pressure (1 atm) and different reaction temperatures of 50oC, 60oC, 70oC and 80oC. The figure shows the influence of base catalyst on the yield of biodiesel with increasing ratio of KOH concentrations. According to the results obtained, the maximum yield was achieved from GWO at 0.4 wt% of KOH catalyst. An increasing in base catalyst more than this limit, the transesterification reaction affected and the yield decreased. The maximum biodiesel yield obtained from GWO is found to be 94.935 achieved

at a temperature of 60 oC with 0.4% KOH concentration as shown in Figure 4. Figure 5 presents the optimization results for the impact of reaction temperature on the yield of biodiesel from WCO at constant atmospheric pressure (1 atm) and different reaction temperatures of 50oC, 60oC, 70oC and 80oC. The figure presents the influence of base catalyst on the yield of biodiesel with increasing ratio of KOH concentrations. According to the results obtained, maximum yield was achieved from WCO at 0.4 wt% of KOH catalyst. An increasing in base catalyst more than this limit, the transesterification reaction affected and the yield decreased. This can be explained as the further concentration means mass transfer become very important. The yield of biodiesel production increased gradually with increasing reaction temperature then tends to decrease after a certain maximum value. On the other hand, it presents constant trend of decrease with increasing catalyst concentration. The maximum biodiesel yield obtained from WCO is found to be

Gcwob WCOB

Figure 8. Optimum biodiesel conversion conditions with GCWO.

greater than waste cooking oil. Optimum operating conditions obtained are 600C, 3hr, and 0.4 wt% for reaction temperature, reaction time and KOH catalyst respectively. The higher yield and conversion were at low temperature, but methyl ester conversion was good at increased temperature. It must be taking into account that highest reaction temperature more than the boiling point for CH3OH can effect mainly on the yield and conversion of biodiesel and also causing evaporation of alcohol (CH3OH). To ensure that the biodiesel produced meets the ASTM D6751 standard limits, analysis for checking its properties were conducted as presents in Table 2. It is obvious that produced biodiesel meets the standard specifications listed in Table 1. However, though the same production procedures adopted, investigated biodiesel samples reveals varying properties due to their different original source. Kinematic viscosity is an essential parameter controlling fuel droplets size and fuel spry penetration; in turn fuel spray formation affects the mixture combustion progress and efficiency. High viscosity leads to large fuel droplets and improper spry formation, on the other hand, very low viscosity may results in fuel leakage through the fuel system lines connections. The results in table 2 show that both biodiesels have kinematic viscosity values higher than that

Figure 11. Variation of Engine BP with increasing engine speed.

Figure 12. Variation of Engine BSFC with increasing engine speed.

of diesel. However, these values are within the biodiesel fuel standard limits shown in table 1 with lower value for GCWOB compared to WCOB. Fuel density is an important indicator to compare the amount of fuel consumed using different fuel samples as the fuel system handling fuel based on volume bases. Different fuel samples show comparable density value closed to that of diesel fuel. Though ASTM standard didn’t include certain limits for heating value, it can be considered as the main indicator for the engine output power. The results show that both biodiesels have heating values lower than that of diesel with lower value for WCOB compared to GCWOB. Both fuels meet the requirement of cetane number value mentioned in ASTM D6751 with better value for GCWOB which is higher than that of diesel fuel. This indicates better ignition quality and smooth engine operation with GCWOB. The high flash point of biodiesel fuel indicates safe storage and handling compared to diesel. Through WCO has higher acid value compared to diesel and GCWOB, it is still meet the ASTM D6751 standard. Figures 11 and 12 shows the engine test results for brake power (BP) and brake specific fuel consumption (BSFC) respectively, at constant half engine load. During the whole engine speed, the obtained engine BP with both biodiesels found to be lower that of diesel fuel. However, better engine BP obtained with GCWOB compared to WCOB during the whole engine speed. The reduction in BP at 1800 rpm found to be about 20 with GCWOB and 26.6 with WCOB compared to diesel which can be attributed to the lower calorific value and higher viscosity of biodiesel fuel compared to diesel fuel as shown in Table 2 [29]. On the other hand, higher BP by about 8.3% obtained with GCWOB compared to WCOB. Moreover, both biodiesels reveals higher BSFC during the whole engine speed. The maximum increase is found to be 11.7% and 18.8 with GCWOB and WCOB respectively at 1800 rpm engine speed which can be attributed to the lower heating value and higher density of biodiesel fuel compared to diesel fuel as shown in Table 2 [30]. Accordingly, lower

BSFC by about 6.3% obtained with GCWOB compared to WCOB which may be attributed to the higher heating value and lower density for GCWOB compared to WCOB. Same trend for BP and BSFC was observed with WCOB from different mixed sources [31]. However, the results indicated a reduction in BP of 34.5% and an increase of 28% in BSFC with biodiesel compared to pure diesel. This indicates better engine performance with WCO biodiesel from single specified source. Though property measurement shows a reduction of 7.8% in the heating value of GCWOB compared to diesel fuel, the cetane number is enhanced by about 6% which can contribute in improving the combustion efficiency. From economic point of view, the cost of produced biodiesel will be much more lower than the cost of mineral diesel as their source is free which represent about 75% of the total biodiesel production cost.

Conclusion

In this work, biodiesel fuel has been produced from grilled chicken waste oil (GCWO) and waste cooking oil (WCO) using potassium hydroxide as homogenous catalysts. According to the results obtained in this study the following finding can be addressed; - Biodiesel yield and conversion obtained from grilled chicken waste oil was greater than waste cooking oil. Maximum yield and conversion of biodiesel are 94.935% and 97.54% respectively achieved at optimum operating variables are 60 oC reaction temperature, 3h reaction time and 0.45% wt KOH concentrations. - Though property measurement shows a reduction of 7.8% in the heating value of GCWOB compared to diesel fuel, the cetane number is enhanced by about 6% which can contribute in improving the combustion efficiency. - The obtained engine BP with both biodiesels found to be lower that of diesel fuel and the better engine

BP obtained with GCWOB compared to WCOB during the whole engine speed. Higher BP by about 8.3% obtained with GCWOB compared to WCOB. - Both biodiesels reveals higher BSFC during the whole engine speed with maximum increase found to be 11.7% and 18.8 with GCWOB and WCOB respectively at 1800 rpm engine speed. Accordingly, Lower BSFC by about 6.3% obtained with GCWOB compared to WCOB. - Biodiesel fuel from GCWO reveals better production characteristics, fuel property and engine performance compared to WCOB. Accordingly, waste oil can be considered as a source of biodiesel which is locally available and free of cost that can be used in the future as a viable source of biodiesel in the future that can be used and in the same time reduce the environmental impact of these waste through re-use of these oil.

Acknowledgments

The authors would like to thank Tikrit University and its staff, especially the College of Petroleum Process Engineering, And Northern Technical University.

Data Availability Statement

The authors confirm that the data that supports the findings of this study are available within the article. Raw data that support the finding of this study are available from the corresponding author, upon reasonable request.

Conflict Of Interest

The author declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Ethics

There are no ethical issues with the publication of this manuscript.

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