Abstract
Biofuel is a type of fuel that is made from biomass using modern techniques rather than the relatively slow geological processes that lead to the development of fossil fuels. In Europe, biodiesel is the most widely used biofuel. The sanitary ware industry generates a lot of hazardous waste, such as waste gypsum molds. These molds are broken, pulverized, and reacted with NaCO3 to make CaCO3, which is then heated to produce CaO. The resulting CaO catalyzes the reaction between waste frying oil and methanol for biodiesel synthesis. To evaluate the effect of reaction parameters on the production of biodiesel, the independent reaction parameters that were chosen are as follows: reaction temperature in the range 50–70°C, methanol to oil (M:O) molar ratio in the range 9–15, catalyst loading in the range 1–5%, and time in the range 2–6 hrs. The influence of the independent factors on the reaction-dependent responses was evaluated and it was found that reaction temperature and methanol-to-oil ratio have a major effect on the biodiesel yield. Reaction condition optimization has been studied to maximize biodiesel yield at minimum reaction conditions. The optimum process conditions are 93.4% biodiesel yield at an M:O molar ratio of 15 : 1, catalyst loading of 1%, reaction temperature of 53.6°C, and reaction time of 2 h. The results showed that resulted biodiesel catalyst (CaO) can be used one time; then, a fresh catalyst will be used.
1. Introduction
The consumption of vast amounts of human energy in the form of fuel and natural gases is causing an increase in the price of petroleum oil in the global oil market. These energies are limited and can only be used for a certain amount of time. As a result, research is currently focused on the utilization of alternative renewable fuels [1–3].
Biofuels like biodiesel, bioethanol, biomethanol, biogas, and biohydrogen are renewable alternatives to fossil fuels and biomass. Many of them can be used in the transport sector [4–6]. Biodiesel is typically generated by transesterifying vegetable or animal lipids with chemical catalysts and then purified to remove any residual glycerine, unreacted reactants, and leached catalyst. Wet washing is the most common washing method which uses water or acidified water but it produced a huge amount of wastewater and consumed energy and time. The alternative method for biodiesel washing is dry washing using an adsorbent solid, ion exchanger, and membrane. One of the most efficient adsorbents is silica which purified biodiesel produced from waste cooking oils [7].
Biodiesel has many advantages: biodegradability, nonflammable and low toxicity, safer handling, higher combustion efficiency, and higher cetane number and flashpoint. There are also some disadvantages of using biodiesel like lower calorific value, higher pour and cloud point fuel, and corroding to copper and brass [6, 8].
Triglycerides can be converted with a high yield to biodiesel using homogeneous alkali catalysts. Homogeneous catalysis products are difficult to separate, and also homogeneous acid catalysts have corrosive effects on equipment. Researchers used heterogeneous catalysts because they are noncorrosive, nontoxic, and easily separated for recycling to address these issues [9–12].
Solid wastes can be used as a catalyst in the transesterification reaction used for biodiesel production as well. Alagumalai et al. mentioned various types of solid waste catalysts that were effectively used in biodiesel production, such as biomass-derived ash, industrial waste ash, industrial slag, mud-based solids, rock-based solids, waste scale, waste shell, and waste animal bones. Biomass-derived ash is like banana peels, coconut husk ash, peanut husk ash, and rice husk ash. Industrial waste ash is like coal fly ash and palm oil mill boiler ash. Industrial slags are carbide slag, blast furnace slag, biomass gasifier slag, and magnesium plant slag. Mud-based solids are like red mud and lime mud. Rock-based solids are dolomite rock, shale rock, and kaolinite rock. Waste scales are like fish scales and wastewater scales. Waste shells are like eggshells and mollusk shells [13, 14].
Correia et al. developed calcium oxide derived from natural sources (crab shell and eggshell) for use as a catalyst in the transesterification of vegetable oil. The findings revealed that these materials had promising transesterification potential for biodiesel production [15]. From waste eggshells and waste cooking oil, biodiesel is manufactured. Asri et al. created a solid CaO-based catalyst. The results showed that the catalyst could be used to convert used cooking oil into biodiesel with a comparatively high yield of 75.92 percent when the reaction temperature, reaction time, molar ratio to methanol, and catalyst amount were set to 65°C, 7 h, 1 : 15, and 6%, respectively, [16]. Widayat et al. create heterogeneous biodiesel catalysts using three different CaO sources. The CaO catalyst was made from limestone, calcium hydroxide, and calcium carbonate and was thermally processed at 900 degrees Celsius in a muffle furnace. The results revealed that the CaO catalyst derived from limestone has superior properties to those derived from calcium hydrate and calcium carbonate. The limestone catalyst produced 89.98 percent biodiesel, the Ca (OH)2 catalyst produced 85.15 percent, and the CaCO3 catalyst produced 78.71 percent [17].
Sanitary ware industry is where toilets and sinks are produced. Gypsum molds were used to form these products using the slip casting technique. It consists mainly of calcium sulphate dehydrate. The slip process is pouring a slurry of raw materials (slip) into a mold, which is often constructed of porous gypsum using hoses. In a filtration-like process, water drains from the mold, leaving behind a solid cake that sits on the mold’s internal surface. If the body to be shaped is hollow, as in sanitary ware or some dinnerware, adequate time is given for the requisite wall thickness to build up and excess slip to be drained from the mold. In the sanitary ware industry, these molds were inefficient for doing their task as their pores were blocked. Hundreds of tonnes of used gypsum molds are discarded annually by ceramic plants. The gypsum waste itself is not dangerous, but when it is mixed with organic matter and exposed to rain in an anaerobic environment, there is a possibility of groundwater pollution due to sulphate leaching. Millions of tons of waste gypsum molds are annually discarded by sanitary ware plants in the world [18, 19].
The goal of this study is to look at the feasibility of using sanitary ware solid waste which is the waste gypsum molds as a source for a heterogeneous solid catalyst in biodiesel synthesis and to use response surface methods to determine the best reaction conditions.
2. Research Methodology
2.1. Raw Materials
The used raw materials were as follows: (a)Waste cooking sunflower oil supplied from Egyptian cafes with chemical composition and physical that are shown in Table 1 and Table 2.(b)Sanitary ware waste supplied from Blezza factory in Dumyat, Egypt(c)Sodium carbonate that was provided by Al-Ahram Chemical Company Ltd., Egypt(d)99% methanol was provided by Morgan Chemical Company Ltd., Egypt
2.2. Solid Waste Preparation
The solid molds were collected from the ceramic factory where it was crushed and ground.
2.3. Assessment of Solid Waste and the Biodiesel Catalyst
The X-ray fluorescence (XRF) technique is used to evaluate the amounts of certain oxides in elemental composition. The analysis was done at a humidity of 44% and a temperature of 22°C. This test followed ASTM guidelines (C114-18) [25].
Using a PANalytical computer-certified program and the International Center of Diffraction Database, X-ray diffraction can identify the phases contained in a substance (XRD) (ICDD). The anode material was copper, and the scan was continuous. 30 mA and 40 KV were the default settings.
The particle size distribution determination using ASTM D 422/2007 was used [26]. The sieves meet The sieves meet ASTM E 11/2009 standards [27].
2.4. Collection and Preparation of Waste Sunflower Cooking Oil
Sunflower cooking oil was a waste product in many cafes (WFCO). Any suspended particulates, fried food particles, and other impurities were removed using a centrifuge and filter; after that, it was dried at 105°C for two hours for water removal.
2.5. Biodiesel Catalyst Preparation (CaO)
(1)The following reaction was done to produce calcium oxide from the calcium sulphate dihydrate that was found in the waste. The reaction time is half an hour at room temperature. The concentration of each reactant is 0.6mol/l (2)CaCO3 was calcined at 900°C for 2 h and then stored in desiccators to protect the produced calcium oxide which reacts with water from humidity
2.6. Experimental Work Done to Produce Biodiesel
Round bottom glassy flask is fitted with a reflux condenser to prevent methanol scape, thermometer to measure the reaction temperature, and magnetic stirrer with heater for reaction mixing and heating was used for the transesterification reaction between the waste cooking sunflower oil and methanol in the presence of CaO as a heterogeneous catalyst as shown in Figure 1. Once the reaction ended, the solid waste was filtered using filter paper; then, the biodiesel and glycerol were separated using a separating funnel for 2 hours; then, methanol was removed by drying at 80°C for 30 minutes.
2.7. Experimental Design
Design-Expert version 13 was used to design the experimental work using the surface methodology technique (RSM) to generate a full analysis of the process [28]. The process response is the conversion of biodiesel, while the reaction variables are the following: (1)Reaction time in the range between 2 and 6hrs(2)Methanol-to-oil molar ratio in the range between 9 and 15(3)Catalyst loading in the range between 1 and 5%.(4)Reaction temperature in the range between 50 and 70°C(5)Stirring rate is constant and equals 750 rpm
The processing parameters and ranges were likewise set by Al-Sakkari et al. [29]. The central composite design technique (CCD) was used to minimize the experimental runs, so it produced thirty experimental runs as in Table 3. The conditions in experimental runs 25 to 30 represent the design center point. The optimization process has an economic target to minimize the biodiesel production cost by both reaction temperature and time, minimizing the maximum production of biodiesel.
2.8. Optimum Biodiesel Sample Analysis
Two types of analysis were done on the optimum sample to make sure that it is biodiesel. These analyses are as follows: (1)Physicochemical properties determination. The results were compared with both biodiesel standards European Biodiesel Standard, EN14214 (EN 14214: 2013 V2 + A1, 2018) [30] and ASTM D6751 [31].(2)Gas chromatography (GC) test to determine the following (i)Total FAME and methyl linoleate analysis according to the standard EN 14103 [32](ii)Free and total and free glycerol in addition to triglycerides according to the standard EN14105 [33].
2.9. Biodiesel Catalyst (CaO) Reusability
A reusable test was done under the resulted optimum conditions. At the end of the reaction, the reaction product was filtered to remove the heterogeneous catalyst CaO, then washed with methanol to remove the remaining glycerol, and dried for methanol removal. The reaction conversion was calculated at the point of reuse to determine the catalyst efficiency and strength.
3. Results and Discussion
3.1. Chemical Analysis of Sanitary Ware Waste
Chemical analysis was performed using the XRF technique and the results were compared with those of a local Egyptian ore (El Ballah–North-Eastern Egypt) as shown in the following table. Table 4 also shows a comparison with pure CaSO4.2H2O.
Chemical analysis showed the powder to have a composition very close to that of natural gypsum. The relatively high content of insoluble matter is probably due to the presence of organic matter resulting from pretreatment of the mold before casting to prevent sticking of the formed ware to the walls of the mold besides possible diffusion of organic deflocculants usually added to the slip through the pores of the mold. This can also account for the slightly elevated figure of combined water, which is determined by heating up to 1000°C and could include the oxidation of organic impurities.
3.2. Mineralogical Analysis of Raw Materials and the Biodiesel Catalyst
3.2.1. Mineralogical Analysis of Sanitary Ware Waste
Figure 2 shows the XRD pattern of waste gypsum powder. Figure 3 shows the peak list of the reference sample (calcium sulfate hydrate) in blue color in comparison with sanitary ware waste powder in orange color. X-ray diffraction analysis proved that it consists almost exclusively of the dehydrate CaSO4.2H2O. The peak positions and relative intensities of the waste sanitary ware powder and reference data are an excellent match.
3.2.2. Mineralogical Analysis of Produced CaCO3
The mineralogical study in Figure 4 reveals that it is primarily composed of the calcite (CaCO3) phase, with a trace of cristobalite (SiO2).
3.2.3. Mineralogical Analysis of Biodiesel Catalyst (CaO)
Figure 5 shows the XRD pattern of CaO. Figure 6 shows the peak list of the reference sample (pure calcium oxide) in blue color and the biodiesel catalyst (CaO) in orange. X-ray diffraction analysis proved that it consists almost exclusively of CaO. The peak positions and relative intensities of the biodiesel catalyst and reference data are an excellent match. CaO was proved to be an excellent biodiesel catalyst as shown in previous research [29, 34, 35].
3.3. SEM Results of CaO
The SEM analysis of the used biodiesel catalyst is shown in Figure 7. As per SEM pictures, the generated CaO catalyst is irregular in shape, porous in structure, and includes active sites. In other words, there were a variety of particle sizes and shapes, indicating that the catalyst has a larger surface area for reaction.
3.4. Screen Analysis of Biodiesel Catalyst (CaO)
The cumulative screen analysis curve of calcium oxide is shown in Figure 8. The catalyst is extremely fine, as shown in this diagram. The average particle size was 0.78 micrometers.
3.5. Analysis of Variance (ANOVA) and Process Modeling
The biodiesel conversion was calculated at each experimental run. A regression equation or model that relates the reaction response to the reaction parameters was created using Design-Expert version 13. values must be less than 0.05 because ANOVA determines the resulted model at a 95% confidence level or a 5% significant level. Given the number of factors, samples, and significant level, a design expert program can calculate the critical values for each model. The values of critical must be compared with the values of the model to determine the significance of the model. The optimum model is the quadratic one, this was determined using the ANOVA analysis technique. Because several terms in the quadratic model are negligible and their values are bigger than 0.1, the model is simplified to a quadratic model. The ANOVA technique generates the reduced quadratic model as an optimum model as shown in the following equation. The result table, which summarizes the ANOVA analysis, is Table 5. where represents the biodiesel conversion, which is affected by reaction time , is the methanol-to-oil ratio, is the catalyst loading, and is the reaction temperature.
Coefficient values, adj, and were calculated to check the validity of the hypothesized model and were reported to be 0.9056 and 0.9317, respectively, indicating that the projected model is very significant. As demonstrated in Figure 9, the calculated and experimental results for biodiesel conversion exhibit reasonable agreement.
3.6. Effect of Reaction Conditions on Biodiesel Conversion
Figure 10 shows the effect of each reaction parameter on biodiesel conversion. The M:O ratio and the reaction temperature have the greatest impact on biodiesel conversion. As the reaction temperature and M:O ratio rise, the conversion of biodiesel rises.
(a) Reaction time (hr)
(b) Methanol/oil ratio
(c) Catalyst loading (%)
(d) Temperature (°C)
3.7. The Reaction Parameter Interactions and the Biodiesel Conversion Relationship
As a surface and contour graph, Figure 11 depicts the relationship between biodiesel conversion and the M:O ratio and catalyst loading interaction (BC). As a surface and contour graph, Figure 12 depicts the relationship between biodiesel conversion and the M:O ratio, as well as the reaction temperature interaction (BD). The M:O ratio and the temperature reaction interaction (BD) have the largest impact on biodiesel conversion, according to the findings.
3.8. Process Optimization
The design expert program generated 100 ideal options within the required parameters. The best conditions were found to be an M:O molar ratio of 15 : 1, a catalyst loading of 1%, a reaction temperature of 53.6°C, a reaction period of 2 hours, and a stirring velocity of 750 rpm, with a biodiesel conversion of 93.4 percent. Table 6 and Table 7 show the optimization constraints and the program’s generated solutions and their desirability.
3.9. Analysis for Resulted Optimum Sample
Table 8 lists the physicochemical parameters and their standard limits. All of the measured parameters are compiled with both EN14214 (EN 14214: 2013 V2 + A1, 2018) and ASTM D 6751 [31].
Table 9 shows the results of the Gas Chromatography (GC) experiments for the best sample. Both European standards EN 14103 [32] and EN 14105 [33] prove that the produced biodiesel meets the stated specifications. Free glycerol and total glycerol equal 0.012 and 0.02% (m/m), respectively, according to EN 14105 [33]. Similarly, monoglycerides, diglycerides, and triglycerides concentration according to EN 14105 equals 0.0033, 0.0058, and 0.0656% (w/w), respectively [33]. Finally, the total FAME concentration equals 97.5% (m/m) according to EN 14105 [33].
3.10. CaO Reusability
Figure 13 demonstrates that conversion declined from 93 percent after the first usage to 65 percent after the second usage and then declined to 38 percent by the completion of the third use. The deposition of glycerol on the catalyst’s active center is the main reason for the decrease in the catalyst’s activity. The second reason is that active CaO is slaking into less active carbonate and bicarbonate forms. The results showed that CaO could not be reused again. This is the same result as the results obtained in previous research [29, 34, 41], Sai [40].
3.11. Comparison with Previous Research
A comparison between the results of the previous research and that of this current work is shown in Table 10. The benefit and the advantage of this study can be concluded in the following points based on its results and the below-mentioned comparison: (1)This study gives a high biodiesel yield at the lowest reaction time and temperature so it used the lowest energy compared with the others(2)The resulted biodiesel catalyst is generated from solid waste, not like the 5th study in the following table(3)This study used a high ratio of methanol-to-oil and this extra methanol is being separated from the resulting biodiesel by distillation then recycled and reused(4)The amount of used catalyst is the lowest compared with the other studies so its separation after the reaction is easier(5)This study reused a dangerous solid waste and waste cooking oil to produce biodiesel so the process cost will be minimum and save the environment at the same time
4. Conclusion
It has been studied that CaO produced from sanitary ware waste could be used as a solid heterogeneous catalyst in the synthesis of economically feasible biodiesel from waste sunflower oil. Reaction temperature, methanol-to-oil (M:O) molar ratio, reaction time, and catalyst loading were chosen as four independent reaction parameters to investigate their impact on biodiesel synthesis. Thirty experimental runs were carried out to reduce the number of experiments. The impact of all reaction parameters on biodiesel yield was assessed using a response surface technique. A model modeling biodiesel conversion as a function of all independent factors has been created. Within the required criteria, the Design-Expert program has developed the top 100 possibilities, which include lowering the cost of biodiesel production and increasing the volume of biodiesel produced. An M:O molar ratio of 15 : 1, a catalyst loading of 1%, a reaction temperature of 53.6 oC, a reaction time of 2 hours, and a stirring rate of 750 rpm were found to be the optimal conditions, providing a biodiesel conversion of 93.4 percent. The biodiesel that was produced met all of the needed biodiesel requirements. According to the reusability test, CaO cannot be reused.
Data Availability
All data generated or analysed during this study are available in this article.
Conflicts of Interest
The author states that she has no known competing financial interests or close connections that could have influenced the research presented in this study.
Acknowledgments
M. H. Roushdy, the first author, wishes to express her heartfelt gratitude to Prof. Magdi F. Abadir of Cairo University.