Effect of Temperature and Tapioca Flour Concentration on Manufacture of CaO·SiO2 Heterogeneous Catalyst Pellets Made from Brick Burning Ash for Biodiesel Synthesis

Abstract

Solid catalysts are the best choice for an effective large-scale biodiesel production process. This study aimed to analyze the characteristics of catalysts due to the influence of variations in sintering temperature and binder composition on heterogeneous catalysts of CaO·SiO₂ pellets made from brick-burning residue. The catalyst was made by the sol-gel method with silica insoles with 5% KOH solvent, CaO soles with HNO₃ solvent of 1.5 N, and a CaO:SiO₂ ratio of 1:5. The amount of tapioca flour binders was 1%, 2%, 3%, 4%, and 5%. The resulting gel was made into a catalyst powder, sintered at various temperatures of 600 °C, 700 °C, 800 °C, 900 °C, and 1000 °C, then pelleted with a hydraulic press with a diameter of 9 mm. Catalysts were tested with density test, hardness test, PSA, XRF, XRD, and SEM. The characteristics of the CaO·SiO₂ catalysts were influenced by the composition of the binding material and the sintering temperature. The test results show that the influence of variations in the composition of the binder fluctuates because the characteristics of the catalyst are also affected by the compaction process. The higher the sintering temperature, the better the catalyst will be, but if the temperature is too high it can cause agglomeration.

1. Introduction

Developed and developing countries are still very dependent on the use of fossil fuels, even though prolonged use of these fuels causes air pollution and global warming [1,2]. About 85% of the world’s energy needs are still met by fossil fuels [3,4]. However, with the depletion of fossil fuel reserves due to their unsustainable nature, renewable energy is increasingly being looked at as an alternative energy substitute [2,5,6]. Renewable energy is expected to overcome the problems of limited fossil energy and the environmental anomalies it raises [4,7,8]. One alternative energy is biofuel, and the use of biofuel is expected to reduce dependence on fossil fuels.

Among the types of biofuels, biodiesel or fatty acid methyl esters (FAME) are seen as having great potential to become the main substitute for mineral diesel in many countries because they are renewable, sustainable, can reduce global warming and greenhouse gas emissions, are non-toxic and biodegradable. They have advantages compared to mineral diesel in that biodiesel combustion does not produce sulfur or has very little sulfur content, exhaust gas emissions such as carbon dioxide (CO₂), carbon monoxide (CO), and nitrogen oxides (NOx) are low, and they can be mixed with mineral diesel fuel in a certain ratio [4,7,9,10,11,12,13,14,15,16,17,18,19,20]. FAME can be used as a mixture of mineral diesel fuel or pure [10,18]. In its application, biodiesel has a composition of 10–100% mineral diesel. Biodiesel, when compared to mineral diesel, has the disadvantage of relatively higher production costs [4].

Biodiesel is a mixture of methyl esters, ethyl esters, and long-chain fatty acids, mostly produced by esterification of free fatty acids or trans-esterification of animal fats, vegetable oils, and used cooking oil with short-chain alcohols such as methanol or ethanol [21]. Biodiesel can be made from palm oil, whose production is abundant in countries such as Indonesia and Malaysia. Biodiesel production from CPO currently competes with CPO for food needs [22,23]. The life cycle assessment (LCA) of the biodiesel production process, which aims to calculate the potential environmental pollution impact of the biodiesel production process, has been widely studied [15,24,25,26,27,28].

Biodiesel can be produced by esterification and transesterification processes. Trans-esterification is most often chosen to convert vegetable oil or animal oil into biodiesel [16,17,18,19,29]. Some examples of trans-esterification processes use homogeneous base catalysts such as sodium hydroxide and potassium hydroxide [17,18]. In general, the biodiesel production process still leaves a lot of unprocessed reactants. Biodiesel production from vegetable oil is conventionally carried out at temperatures between 50 °C and 60 °C with a reaction time of 1–6 h and a conversion rate of up to 89.72% [30,31].

In general, biodiesel production is carried out through the trans-esterification of oils, fats, or greases with low-carbon alcohols with the help of a catalyst, which can be carried out using a homogeneous base and acid catalyst [7,32]. Homogeneous alkaline catalysts have high catalytic effectiveness under mild conditions and are therefore used more frequently than acid catalysts [7,33]. The homogeneous acid or base catalysts are very advantageous in terms of biodiesel yield, but the complications associated with their corrosive nature for the reactor and their separation from the mixture give rise to the downside of these catalysts. In addition, the water washing and purification steps to achieve the specified fuel quality ultimately lead to quite high production costs [7,34].

Heterogeneous catalysts have been further developed to address the drawbacks of using homogeneous catalysts. The use of heterogeneous catalysts for biodiesel production is most effective and feasible because of their easy separation, non-corrosive properties, and environmental friendliness [7,35]. From the results of a literature review, the application of acid and base heterogeneous catalysts presents different properties. The trans-esterification process with a heterogeneous base catalyst is considered more promising due to the longer reaction time and higher reaction temperature compared to the trans-esterification process using an acid catalyst [7,36,37]. Therefore, the process of exploring various categories of heterogeneous base catalysts was carried out in the past, such as using metal oxides, calcined hydrotalcite, alkali metal supports, and anion exchange resins [7,38,39,40,41].

Research studies are focused on the current biodiesel production process to find effective catalysts. Solid catalysts are optimum for large-scale biodiesel production [42]. During biodiesel production, the solid catalyst does not dissolve in the reaction mixture, so it can be easily separated from the product. Biodiesel products do not contain catalyst impurities, so the cost of the final separation process can be reduced. Solid catalysts have another advantage as they can be regenerated and reused and do not require acid and wastewater treatment at the separation stage. Thus, using solid catalysts makes the biodiesel production process simpler and more efficient [43]. One of the solid catalysts for biodiesel production is CaO·SiO₂, where this catalyst can be obtained from ash processing from burning bricks and limestone. The manufacture of bricks in Indonesia for building needs begins with the processing of the soil and shaping it into bricks according to standard sizes. Soil that has been formed must be dried in sunlight. The dry bricks are then arranged in such a way that they are fired to turn them into usable bricks. This burning process lasts for days, with an indication that the burning is complete when the bricks that were previously gray turn red. The main fuel used is rice husk, where the rice husk is used as a covering material for the stacked bricks with cavities for burning wood or charcoal as a lighter for burning the rice husks. Rice husks and the other fuels namely wood and charcoal are all burned to ashes.

Ash from burning bricks contains silica (SiO₂), alumina (Al₂O₃), iron oxide (Fe₂O₃), calcium oxide (CaO), and contains other additional elements, namely magnesium oxide (MgO), titanium oxide (TiO₂), base (Na₂O, and K₂O), sulfur trioxide (SO₃), phosphorus oxide (P₂O₅), and carbon [44]. The active silica-alumina compounds contained in the residual combustion ash can react with calcium hydroxide at room temperature and the presence of water at a certain level can form stable compounds with binding properties [45]. Another material used is limestone (CaCO₃), which is non-hydraulic lime obtained from the combustion of natural stone whose composition is of the minerals calcite and aragonite, which are different crystal forms of CaCO₃. To obtain calcium oxide (CaO) compounds, it is necessary to carry out a calcination process using heat at a temperature of approximately 900 °C for 8 h. By calcination, carbon dioxide (CO₂) contained in calcium carbonate (CaCO₃) is released, and only lime remains, that is, calcium oxide (CaO) [46,47].

The manufacture of solid catalysts requires additional materials in the form of binding materials. A binder or adhesive is a material that is deliberately added to the catalyst formula to combine all the raw materials used in the catalyst manufacturing process [48]. According to Masri et al., adhesives are needed to bind material components to give a compact structure that is not easily destroyed and is easily formed in the pellet-making process [49].

The binding material used in the manufacture of this catalyst is tapioca flour. Tapioca is a common plant that can be found in almost every tropical country. Tapioca can be dissolved in water without additives that can degrade the properties of the pure material. Morphological analysis has proved that tapioca binders are able to provide good binding.

In a study by Pandiangan et al., the synthesis of CaO·SiO₂ used limestone (CaCO₃) and rice husk silica with the sol-gel method [50]. The results showed that the CaO·SiO₂ sample was able to convert coconut oil into a mixture of methyl esters, while the best performance was shown by a catalyst with a CaO content of 25%, with a level of conversion of 93.1%. Chen et al., examined two catalysts that were successfully synthesized through a biomimetic silicification approach with eggshell raw materials and Na₂SiO₃ [51]. When used for transesterification, CaO·SiO₂ catalysts show a decrease in catalyst activity and reusability, along with an increase in the number of Si compounds. In the study of Gan et al., the synthesis of CaO·SiO₂ from the residual combustion of rice husks was analyzed [52]. In this study, washing rice husks with hydrochloric acid and sulfuric acid was carried out before burning to obtain a purer silica. The results showed that all samples produced amorphous silica (SiO₂) and the average particle size ranged from 0.50 to 0.70 μm, while the surface area of the resulting silica after washing the rice husks with hydrochloric acid was higher (218 m²/g) compared with sulfuric acid (209 m²/g)

This study aimed to analyze the influence of the composition of the binding material and the influence of the sintering temperature on the characteristics of the catalyst produced. The characteristic tests on the catalysts included density tests, hardness tests, particle size analysis (PSA), X-ray fluorescence (XRF), X-ray diffraction (XRD), and scanning electron microscopy (SEM).

2. Results

2.1. Effect of Binder Composition on Characteristics of CaO·SiO₂ Pellet Catalyst

A study of the effect of binder concentration on catalyst pellets was carried out on catalyst pellets made using a method of sintering at 600 °C, compaction at 90 kg/cm², with a particle size of 57.425 µm.

2.1.1. Density Analysis

Density is defined as mass per volume. If the mass is constant, a decrease in volume causes the mass density to rise. This is because the catalyst space has been filled [53]. Density is a function of the density of the individual grains, porosity, and the liquid that fills the pores. In heterogeneous catalysts, density is a metric indicating the pore size or number of pores, which is related to the identification of the contact surface area on the catalyst. The porosity of the catalyst can be characterized by adsorption isotherms, usually with nitrogen. Apart from closed pores and macropores (>50 nm), the total pore volume and pore size distribution can be measured. The total surface area of the catalyst is usually measured by nitrogen adsorption using the BET method. This is a fundamental characteristic of most heterogeneous catalysts and is subject to change during preparation, conditioning, use, and especially when exposed to excessive temperatures. Changes that occur over the life of the catalyst almost always lead to a loss of surface area of the catalyst.

The density of the CaO·SiO₂ pellet catalyst was measured by the Quantachrome Instrument, which uses helium gas as a fluid to enter the interior pores of the material. Figure 1 shows the analysis of catalyst density. The composition of the material affects the hardness value. The hardness value is influenced by the composition of the binder material, the compaction process at the time of molding, and the way in which the product is removed from the mold. The resulting CaO·SiO₂ catalyst showed density variations, but all samples had densities of more than 2 g/cc.

2.1.2. Compressive Strength Analysis

The compressive test on the CaO·SiO₂ catalyst was carried out by applying pressure to the sample to determine the resistance of the pellets. Figure 2 illustrates the results of the analysis of compressive strength on the catalyst. The hardness value varies due to various factors, including differences in pellet lengths. Longer pellets usually require a greater load to break down than shorter pellets. Another factor is the presence of gaps or gaps in the pellets themselves caused by the manufacturing process, where the pellets are formed, and produced by the application of compression forces that differ as well as depending on the type of pellet material [54].

A good pellet has a hardness level that is neither too hard nor too soft [55]. This fluctuating phenomenon may be due to the binding composition and the compaction process. The compressive strength was significantly influenced by the degree of fastening component. The use of different catalysts and binders changes the dispersion rate of solid particles, resulting in higher compaction density and compressive strength [56].

2.1.3. PSA Analysis

A particle size analyzer (PSA) was used to analyze particle size. The results of the PSA analysis on the CaO·SiO₂ catalyst can be seen in Figure 3. Through particle size analysis, it is expected that the resulting size distribution is in the range of good size uniformity. A good uniformity range is at nano-size, which is between 0.6 nm to 7 µm. The results of the CaO·SiO₂ catalyst test showed that the catalyst obtained was microporous in the range of 120 nm–100 µm [57]. The results obtained also showed that the uniformity obtained was quite good, but for the binder variable 4, there was a considerable difference compared to the other variables.

2.1.4. XRF Analysis

XRF is used to determine the elements contained in the CaO·SiO₂ catalyst both qualitatively and quantitatively. The results of XRF analysis on the CaO·SiO₂ catalysts with the addition of tapioca as a binder in varying percentage amounts are shown in Figure 4. It can be seen that the effect of the amount of tapioca binder has no direct positive or negative correlation when referring to the Ca and Si content values. The Ca and Si graphs show fluctuating changes with the increasing amount of tapioca binder given. This is because the main constituent of tapioca is carbon (C). The content of silica (Si) and calcium (Ca) in the catalyst with the addition of tapioca binder also showed relatively lower conditions compared to the content of Si and Ca in the raw material. This is due to the non-optimal extraction process.

The extraction process was carried out with 5% KOH solution for 60 minutes. Extraction of silica with KOH solution showed that the higher the extraction time and the KOH concentration used, the higher the silica recovery [58]. The optimum silica extraction results occurred in 10% KOH solvent with an extraction time of 90 minutes. In the activation process with KOH, a silica dissolution process occurs, where silica dissolution causes structural changes to reduce silica in the material [59]. CaO is a stabilizer that can increase strength and chemical resistance [60,61]. CaO with a low percentage can provide good resistance because the amount of CaO that is too high will damage the resistance of the catalyst to acid [62].

2.1.5. XRD Analysis

To determine the crystallinity of the catalyst we used the X-ray diffraction method. The results of the XRD analysis on the CaO·SiO₂ catalyst can be seen in Figure 5. The crystals obtained are crystalline and have more than one crystal orientation with different scattering fields [63]. Overall, the results of structural detection using match software showed the presence of peaks of CaO·SiO₂ compounds in the form of pavlovskyite (Ca₈-O₁₈-Si₅).

Based on Figure 5, the analysis results showed that the XRD spectrum at variable 1 (binder 1%) showed 3 peaks 2θ = 31.6°, 33.6°, 44.0° with a pavlovskyite intensity of 64.4%. Variable 2 (2% binder) showed 3 peaks 2θ = 31.5°, 33.6°, 43.9° with a pavlovskyite intensity of 60.6%. Variable 3 (3% binder) showed 3 peaks 2θ = 31.5°, 29.5°, 33.6° with pavlovskyite intensity 69.8%. Variable 4 (4% binder) showed 3 peaks of 2θ = 31.2°, 33.3°, 43.6° with a pavlovskyite intensity of 79.3%. Finally, variable 5 (binder 5%) showed 3 peaks 2θ = 23.7°, 29.5°, 41.3° with a SiO₂ intensity of 88.5% and pavlovskyite as much as 10.9%.

The difference in binder crystallinity is due to the crystal size, the number of crystal regions, the orientation of the double helix within the crystal area, and the degree of interaction between the double helixes [64]. Based on Gao et al., modified starch has only dispersive area peaks and no crystalline peaks are indicated [65]. This is because the region of the original starch crystal was completely damaged during the modification process.

2.1.6. SEM Analysis

The morphological structure of the CaO·SiO₂ catalyst surface was examined using SEM (scanning electron microscopy) with a magnification of 10,000×. Figure 6 shows the results of the SEM examination of the CaO·SiO₂ catalyst surface.

The surface morphology of the CaO·SiO₂ sample at a 1% binding composition (Figure 6A) using an SEM tool with a magnification of 10,000× shows that the surface has a visible grain border, with pores forming uneven clusters. With the addition of binders, with the sample of CaO·SiO₂ at a binder composition of 2% (Figure 6B), the grain boundary remains in the form of grains of relatively small size scattered inhomogeneously on the surface of the sample. The grains at the 3% binder composition (Figure 6C) look smaller and more densely distributed. At a binder composition of 4% (Figure 6D), the grain boundary again becomes larger, and the distribution is inhomogeneous. Finally, at the 5% binder composition (Figure 6E), the grain appears very large compared to the other variables with a larger gap.

Based on previous studies, the SEM of the original starch granule has a rounded shape with the tip cut off on one side on the surface of the original starch granule which is smooth without gaps or pores [66,67].

2.2. Effect of Sintering Temperature on Characteristics of CaO·SiO₂ Pellet Catalyst

A study of the effect of the sintering temperature on catalyst pellets was carried out on catalyst pellets made using the method of binder concentration of 5% w/w and compaction at 90 kg/cm².

2.2.1. Density Analysis

Figure 7 shows that with increasing sintering temperature, the density decreases. The sintering process can change the inner structure of the crystal. The higher the sintering temperature, the lower the density value [68]. This is because, during heating, a reactive sintering process occurs, which usually results in additional porosity. This phenomenon can be caused by impurities, additives, or other products formed during the sintering process. In Figure 7, it can be seen that the trend chart of Ca content decreases with increasing temperature. This is because the heating process at high temperatures can damage non-crystalline structures [69].

2.2.2. Compressive Strength Analysis

Particle hardness is affected by the sintering process. In Figure 8, the hardness test results show that the hardness value decreases in the temperature range of 600 °C to 900 °C but begins to rise again in the temperature range of 900 °C to 1000 °C. Strength has a relationship with density, where if the density is high, the tendency of the value of strength will rise. Density is influenced by the degree of grain density in filling the space. Hardness is also affected by the strong bonding that occurs in constituent grains or particles. The larger the bonding area, the more force or strength will also rise. Another factor in favor of the hardness value is the presence of constituent elements that have a composition large enough to increase the hardness value or strength of the catalyst pellets.

2.2.3. PSA Analysis

The particle size analysis (PSA) results were expected to show that the resulting size distribution was in a range with good size uniformity. A good uniformity range is at nano-size, i.e., between 0.6 nm–7 μm. The results of the CaO·SiO₂ catalyst test shown in Figure 9 shows that the catalyst obtained was microporous in the range of 120 nm–100 μm [16]. In the results obtained, it can be seen in the trend graph that variations in sintering temperature affect the particle size of the catalyst and the degree of crystallinity of the sample. The sintering process aims to increase strength so that the growth of catalyst grains becomes smoother.

According to Chai et al., the increase in sintering temperature affects the size of the granules, namely becoming smaller and more homogeneous [70]. In the temperature range of 600–800 °C, it is seen that the particle size becomes smaller as the sintering temperature increases. This is because the heating is between the optimum temperature of silica reactivity, namely at a temperature of 550–800 °C [71]. The sintering process with a relatively high temperature, allows for a change in the structure where the particles bind to each other and the grain size becomes larger so that it covers the entire surface. This occurs in catalysts with a temperature treatment of 900–1000 °C.

The greater the sintering temperature given, the greater is also the size of the particles formed. This is because the higher the sintering temperature given to the sample, the greater the energy the atom receives to diffuse and agglomerate. So, the size of the crystals formed becomes bigger and the bonds between atoms become stronger and more regular [72]. Mohammadikish et al. suggested that an agglomerate can form at high-temperature treatments [73].

2.2.4. XRF Analysis

Figure 10 shows trend graphic data on Ca content decreasing with increasing sintering temperature given in this study. This shows a negative correlation between the increase in sintering temperature and the level of Ca content in the catalyst. This condition is due to the heating process at high temperatures which can damage the non-crystal structure [69]. The Si element experiences conditions that are opposite to the Ca element. The trend of Si content shows an increase with increasing sintering temperature. According to Cloutimon et al., this is due to the loss of organic compounds during the heating process [74].

The content of silica (Si) and calcium (Ca) in the catalyst treated with sintering temperatures between 600 °C and 900 °C also showed the same conditions as the catalyst conditions with variations in the amount of binder added, which was still relatively lower than the content of the raw materials. The same factors that cause this as the catalyst with binder variations are the pre-treatment of the extraction phase which is less than optimal and the activation process with KOH [58,59].

2.2.5. XRD Analysis

X-ray diffraction (XRD) characterization is an analytical method used to identify crystalline phases in materials by determining lattice structure parameters and obtaining particle size [75]. The results of the XRD analysis on the CaO·SiO₂ catalyst can be seen in Figure 11. Based on the analysis of amber G13, it can be seen that all variables have a diffraction pattern that indicates that the CaO·SiO₂ formed is a crystal. The crystal obtained is crystalline, with more than one crystal orientation and different scattering fields [65]. From the picture, it can be seen that the variation in the sintering temperature does not affect the angular shift, but affects the high intensity formed. The greater the sintering temperature, then the intensity formed on each of the crystal planes becomes increasingly higher.

Overall, the results of the structure detected using match software showed the presence of a peak compound CaO·SiO₂ in the form of pavlovskyite (Ca₈-O₁₈-Si₅). The spectrum of variable 5 (1000 °C) showed 3 sharply tapered peaks at 2 theta, i.e., 23.7°, 29.5°, and 41.3° indicating that the SiO₂ compound was of intensity 88.5% and the pavlovskyite compound was 10.9%. Variable 6 (900 °C) shows 3 theta, i.e., 31.6°, 56.2°, and 23.7° which indicates the presence of pavlovskyite with an intensity of 76.6%. In variable 7 (800 °C) it shows 3 sharply tapered peaks at 2 theta, i.e., 31.9°, 23.9°, and 29.7° which indicates the presence of pavlovskyite with an intensity of 80.4%. Furthermore, variable 8 (700 °C) showed 3 sharply tapered peaks at 2 theta, i.e., 29.5°, 34.0°, and 23.8° indicating the presence of pavlovskyite with an intensity of 69.8%.

Finally, variable 9 (600 °C) shows 3 peaks that taper sharply at 2 theta namely 34.1°, 23.9°, and 29.7° which indicates the presence of SiO₂ with an intensity of 46.7% and pavlovskyite as much as 46.3%. The results of X-ray diffraction on variables showed a peak characteristic of calcium oxide (CaO) at an angle of 2θ of ±23°, which was confirmed in accordance with the CaO standard (JCPDS No. 82-1690). The diffraction pattern in silica samples was evaluated by comparing the peak d values in the sample with the peaks of the SiO₂ JCPDS (Joint Committee for Powder Diffraction Standard) standard with the number 341382. The SiO₂ phase is found in the area of 34–56° with sharp peaks indicating that silica has high crystallinity. The results obtained are in accordance with the research of Adam et al., Mourhly, et al., and Rosalia, et al., which stated that silica rice husks are crystalline [76,77,78].

2.2.6. SEM Analysis

The morphological form of the catalyst surface is shown in Figure 12. The surface morphology of the CaO·SiO₂ sample at 600 °C (Figure 12A) shows that the surface has not experienced a grain boundary, with a fairly large pore size forming unevenly distributed clusters. This is thought to be because the sample is heated at a relatively low temperature. As the temperature rises, the CaO·SiO₂ catalyst at 700 °C (Figure 12B) begins to see the presence of a grain boundary in the form of granules with a relatively large size scattered inhomogeneously, only on the surface of the sample.

At 800 °C (Figure 12C) the grain size begins to appear enlarged but has not yet formed a collection of grains and the pores begin to multiply, forming an uneven surface. The heating process at high temperatures causes the pores to shrink and change so that the pores are completely closed and the boundaries of the granules l disappear [79]. At a temperature of 900 °C (Figure 12D), it is shown that in the catalyst an agglomeration process occurs and clusters begin to appear stacked; there is no visible grain boundary with the presence of pores of non-uniform size and uneven distribution. At a temperature of 1000 °C (Figure 12E), SEM results show that the catalyst is spherical with the formation of cluster groups that are suspected of cluster formation due to the agglomeration process, the visible grain boundary, and the presence of pores of non-uniform size and uneven distribution, which are due to the presence of high-temperature treatment of the material.

The results explain that the change in the uniformity of the size of the solids was influenced by the temperature given to each sample. With the increase in sintering temperature, there is an increase in the uniformity of the morphological form of the catalyst surface [80]. However, temperatures that are too high can provide a catalyst-sintering effect that triggers agglomerations in the catalyst particles [81].

3. Discussion

3.1. The Influence of Binder on Catalyst Pellet Characteristics

In this study, the percentage of binder varied from 1% to 5% and did not significantly impact the trend of changes in the density and strength of the catalyst pellets. It is possible that these percentages, although they vary, have close ranges and are insufficient to provide sufficient binding effect to influence the increase in the value of the catalyst strength.

The existing data on density values and catalyst strength are still dominated by the influence of the magnitude of compaction strength and the influence of the catalyst pellet manufacturing process [82,83].

3.2. The Influence of Sintering on Catalyst Pellet Characteristics

The sintering process affects the strength value of the catalyst pellets. This is because at 600 °C, particles and granules retain their uniform size and do not change their shape, size, or phase. Changes begin to occur as the sintering temperature rises, but are not complete. When the temperature reaches 1000 °C, the phase becomes homogeneous and stable. This gives the catalyst a strong pattern when compressed, as shown in Figure 10.

The difference in strength conditions between 600 °C and 1000 °C is due to the fact that at 1000 °C, uniformity occurs after a phase shift and the size becomes larger, resulting in a larger gap than when compacted at 600 °C.

According to Abbaszadeh et al., the higher the density, the higher is the mechanical strength [84]. The interfaith bond between CaO·SiO₂ powders weakens, resulting in a weak voltage transmission mechanism and, as a result, a low compressive strength is created [43,85,86]. CaO·SiO₂ catalysts with a sintering temperature variation of 600 °C have the highest compressive strength value when compared to other variations. This is in line with the XRF data, which reveals that variable 9 (600 °C) has a greater concentration of Ca than others. The concentration of CaO in the form of Ca will provide resistance to a material [62].

4. Materials and Methods

4.1. Research Materials

The materials used in this study were brick-burning residual ash, CaCO₃, KOH 5%, HNO₃ 1.5N, tapioca flour, and aqua dest.

4.2. Research Tools

The two main pieces of equipment used in this study consisted of tools for catalyst synthesis and tools for compacting catalyst pellets. The set of tools used in the study can be seen in Figure 13 and Figure 14.

4.3. Research Procedure

4.3.1. Catalyst Preparation

The ash from the burning of bricks was separated from impurities such as soil and then sifted using a sieve to make it homogeneous in size.

4.3.2. CaO Sol Manufacturing

CaO was produced by calcining CaCO₃ for 8 h at a temperature of 900 °C. CaO powder weighing 6 g was mixed with 100 mL of HNO₃ solution 1.5 N. The resulting mixture was stirred for 30 min to form a homogeneous solution.

4.3.3. Silica Sol Manufacturing

Silica was obtained from 50 g of ash from the burning of bricks that had been soaked in 500 mL of 5% KOH solution and then boiled for about 60 min. The next stage was filtration, intending to separate the silica filtrate produced from the ash from the burning of the bricks. This final solution was referred to as a silica sol.

4.3.4. Preparation of CaO·SiO₂ Gel

CaO soles and SiO₂ soles were mixed in a ratio of 1:5, namely SiO₂ soles of 500 mL and CaO soles of 100 mL, then tapioca flour binders were added in the specified amounts of 1% w/w, 2% w/w, 3% w/w, 4% w/w, and 5% w/w. At a temperature of 85 °C, they were stirred for 60 min. The gel was then filtered and dried in the oven at 220 °C for 5 h. Grinding turned the dry gel into powder. A sieve was used to sift the powder.

4.3.5. Sintering

The sintering process used furnaces with temperatures of 600 °C, 700 °C, 800 °C, 900°C, and 1000 °C. The sintering process took place within three hours.

4.3.6. Compacting

Hydraulic presses were used to make solids or pellets from sifted and sintered powders from dry gels. A mold of 9 mm diameter was used, and a compaction force of 90 kg/cm² applied, resulting in 0.5 g of catalyst pellets for each sample.

5. Conclusions

From the results of the study, the following can be concluded:

• The effects of binder composition on CaO·SiO₂ catalysts are that along with the increase in the binder composition of tapioca flour, the density tends to fluctuate, the compressive strength fluctuates, the particle size becomes smaller, %Si and Ca content fluctuates, and the crystal phase formed is pavlovskyite (Ca₈-O₁₈-Si₅) of varying intensity.

• The effects of sintering temperature on CaO·SiO₂ catalysts are that as the temperature increases, the density tends to decrease, the compressive strength decreases, the particle size gets bigger, the percentage of Si and Ca content fluctuates, and the crystalline phase formed is pavlovskyite (Ca₈-O₁₈-Si₅) of increased intensity. This is because some of the catalysts experience agglomeration.

• In the variation in binder composition, the morphology of the catalyst has an irregular microstructure but has fairly good stability. In sintering temperature variations, the catalyst morphology tends to change the size uniformity due to agglomeration.

Author Contributions

Conceptualization, W.W., S.S. (Sulardjaka Sulardjaka), S.S. (Syaiful Syaiful) and N.I.; methodology, W.W., N.I. and S.S. (Sulardjaka Sulardjaka).; formal analysis, W.W., N.I., S.S. (Sulardjaka Sulardjaka), F.F. and F.H.; investigation, F.F., F.H. and N.I.; resources, W.W., F.F., F.H. and N.I.; writing—original draft preparation, F.F., F.H. and N.I.; writing—review and editing, S.S. (Sulardjaka Sulardjaka), S.S. (Syaiful Syaiful) and W.W. All authors have read and agreed to the published version of the manuscript.

Data Availability Statement

Data is contained within the article.

Acknowledgments

The authors would like to thank the Ministry of Research and Technology Republic Indonesia for funding contract number 169/SP2H/AMD/LT/DRPM/2020.

Conflicts of Interest

The authors declare no conflict of interest.

Footnotes

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Figures

Figure 1. Relationship of binder composition (%) with density (g/cc).

Figure 2. Relationship of binder composition (%) with compressive strength (MPa).

Figure 3. Relationship of binder composition (%) with particle size (μm).

Figure 4. XRF analysis results on CaO·SiO2 catalyst treated with varying amounts of tapioca flour binder.

Figure 5. XRD analysis results on CaO·SiO2 catalyst treated with varying amounts of tapioca flour binder.

Figure 6. Morphology of CaO·SiO2 catalyst: (A) binder 1%; (B) binder 2%; (C) binder 3%; (D) binder 4%; (E) binder 5%.

Figure 7. Relationship of sintering temperature (°C) with density (g/cc).

Figure 8. Relationship of sintering temperature (°C) with compressive strength (MPa).

Figure 9. Relationship of sintering temperature (°C) with particle size (μm).

Figure 10. XRF analysis results on CaO·SiO2 catalyst subjected to variations in sintering temperature.

Figure 11. XRD analysis results on CaO·SiO2 catalyst subjected to variations in sintering temperature.

Figure 12. Morphology of CaO·SiO2 catalyst: (A) sintering temperature 600 °C; (B) sintering temperature 700 °C; (C) sintering temperature 800 °C; (D) sintering temperature 900 °C; (E) sintering temperature 1000 °C.

Figure 13. Series on catalyst synthesis process tools.

Figure 14. Series on catalyst forming process tools.

References

1. Martins, F.; Felgueiras, C.; Smitkova, M. Fossil fuel energy consumption in European countries. Energy Procedia; 2018; 153, pp. 107-111. [DOI: https://dx.doi.org/10.1016/j.egypro.2018.10.050]

2. Munfarida, S.; Widayat, W.; Satriadi, H.; Cahyono, B.; Hadiyanto, H.; Philia, J.; Prameswari, J. Geothermal industry waste-derived catalyst for enhanced biohydrogen production. Chemosphere; 2020; 258, 127274. [DOI: https://dx.doi.org/10.1016/j.chemosphere.2020.127274]

3. Lee, S.L.; Wong, Y.C.; Tan, Y.P.; Yew, S.Y. Transesterification of palm oil to bio-diesel by using waste obtuse horn shell-derived CaO catalyst. Energy Convers. Manag.; 2015; 93, pp. 282-288. [DOI: https://dx.doi.org/10.1016/j.enconman.2014.12.067]

4. Hadiyanto, H.; Lestari, S.P.; Widayat, W. Preparation and Characterization of Anadara Granosa Shells and CaCO₃ as Heterogeneous Catalyst for Biodiesel Production. Bull. Chem. React. Eng. Catal.; 2016; 11, pp. 21-26. [DOI: https://dx.doi.org/10.9767/bcrec.11.1.402.21-26]

5. Day, C.; Day, G. Climate change, fossil fuel prices, and depletion: The rationale for a falling export tax. Econ. Model.; 2017; 63, pp. 153-160. [DOI: https://dx.doi.org/10.1016/j.econmod.2017.01.006]

6. Wan, L.; Liu, H.; Skala, D. Biodiesel production from soybean oil in subcritical methanol using MnCO₃/ZnO as catalyst. Appl. Catal. B Environ.; 2014; 152, pp. 352-359. [DOI: https://dx.doi.org/10.1016/j.apcatb.2014.01.033]

7. Hussain, F.; Alshahrani, S.; Abbas, M.M.; Khan, H.M.; Jamil, A.; Yaqoob, H.; Soudagar, M.E.M.; Imran, M.; Ahmad, M.; Munir, M. Waste Animal Bones as Catalysts for Biodiesel Production; A Mini Review. Catalysts; 2021; 11, 630. [DOI: https://dx.doi.org/10.3390/catal11050630]

8. Soudagar, M.E.M.; Mujtaba, M.A.; Safaei, M.R.; Afzal, A.; Ahmed, W.; Banapurmath, N.R.; Hossain, N.; Bashir, S.; Badruddin, I.A.; Goodarzi, M. et al. Effect of Sr@ZnO nanoparticles and Ricinus communis biodiesel-diesel fuel blends on modified CRDI diesel engine characteristics. Energy; 2021; 215, 119094. [DOI: https://dx.doi.org/10.1016/j.energy.2020.119094]

9. Nur, Z.A.S.; Taufiq-Yap, Y.H.; Nizah, M.F.R.; Teo, S.H.; Syazwani, O.N.; Islam, A. Production of biodiesel from palm oil using modified Malaysian natural dolomites. Energy Convers. Manag.; 2014; 78, pp. 738-744.

10. Permadi, W.A.W.; Jovita, C.; Murest, P.P.W.; Widayat, W. The Effect of KI and KIO₃ Impregnation on Prepared Hydroxyapatite Catalyst on Biodiesel Production. AIP Conf. Proc.; 2019; 2202, 20055. [DOI: https://dx.doi.org/10.1063/1.5141668]

11. Khan, H.M.; Ali, C.H.; Iqbal, T.; Yasin, S.; Sulaiman, M.; Mahmood, H.; Raashid, M.; Pasha, M.; Mu, B. Current scenario and potential of biodiesel production from waste cooking oil in Pakistan: An overview. Chin. J. Chem. Eng.; 2019; 27, pp. 2238-2250. [DOI: https://dx.doi.org/10.1016/j.cjche.2018.12.010]

12. Mujtaba, M.; Cho, H.M.; Masjuki, H.; Kalam, M.; Ong, H.; Gul, M.; Harith, M.; Yusoff, M. Critical review on sesame seed oil and its methyl ester on cold flow and oxidation stability. Energy Rep.; 2020; 6, pp. 40-54. [DOI: https://dx.doi.org/10.1016/j.egyr.2019.11.160]

13. Chuah, L.F.; Suzanna, F.; Abdul Aziz, A.R.; Bokhari, A. Performance of refined and waste cooking oils derived from palm olein on synthesis methyl ester via mechanical stirring. Aust. J. Basic Appl. Sci.; 2015; 9, pp. 445-448.

14. Satriadi, H.; Pratiwi, I.Y.; Khuriyah, M.; Widayat, W.; Hadiyanto, H.; Prameswari, J. Geothermal solid waste derived Ni/Zeolite catalyst for waste cooking oil processing. Chemosphere; 2022; 286, 131618. [DOI: https://dx.doi.org/10.1016/j.chemosphere.2021.131618]

15. Wahyono, Y.; Hadiyanto, H.; Budihardjo, M.A.; Widayat, W. Energy Balance Calculation with Life Cycle Assessment for Production of Palm Biodiesel in Indonesia. E3S Web Conf.; 2019; 125, 10005. [DOI: https://dx.doi.org/10.1051/e3sconf/201912510005]

16. Widayat, W.; Hantoro, S.; Aji, B.; Supriyandi, S. Biodiesel Production from Jatropha Curcas Oil and Palm Oil by Using Undirect Ultrasonic Assisted. Proceedings of the International Conference on Sustainable Energy Engineering and Application (ICSEEA); Jakarta, Indonesia, 3–5 October 2016; [DOI: https://dx.doi.org/10.1109/ICSEEA.2016.7873579]

17. Widayat, W.; Satriadi, H.; Nafiega, F.N.; Alimin, A.J.; Ali, M.F.M. Biodiesel Production From Multistock As Feed With Direct Ultrasound Assisted. AIP Conf. Proc.; 2015; 1699, 30020.

18. Widayat, W.; Satriadi, H.; Yuariski, O.; Murwono, D. Biodiesel Production from Bulk Frying Oil with Ultrasound assisted. Res. J. Appl. Sci. Eng. Technol.; 2013; 6, pp. 1732-1739. [DOI: https://dx.doi.org/10.19026/rjaset.6.3896]

19. Widayat, W.; Aulia, H.N.; Hadiyanto, H.; Sasongko, S.B. Kinetic Study on Ultrasound Assisted Biodiesel Production from Waste Cooking Oil. J. Eng. Technol. Sci.; 2015; 47, pp. 374-388. [DOI: https://dx.doi.org/10.5614/j.eng.technol.sci.2015.47.4.3]

20. Knothe, G.; Razon, L.F. Biodiesel Fuels. Prog. Energy Combust. Sci.; 2017; 58, pp. 36-59. [DOI: https://dx.doi.org/10.1016/j.pecs.2016.08.001]

21. Syukri, S.; Fadhil, F.; Yetria, R.; Yulia, E.P.; Mai, E.; Upita, S. Synthesis of Graphene Oxide Enriched Natural Kaolinite Clay and Its Application For Biodiesel Production. Int. J. Renew. Energy Dev.; 2021; 10, pp. 307-315. [DOI: https://dx.doi.org/10.14710/ijred.2021.32915]

22. Atabani, A.E.; Silitonga, A.S.; Ong, H.C.; Mahlia, T.M.I.; Masjuki, H.H.; Badruddin, I.; Hussain, F. Non-edible vegetable oils: A critical evaluation of oil extraction, fatty acid compositions, biodiesel production, characteristics, engine performance and emissions production. Renew. Sustain. Energy Rev.; 2012; 18, pp. 211-245. [DOI: https://dx.doi.org/10.1016/j.rser.2012.10.013]

23. Fajar, B.; Wilis, W.; Widayat, W. The optimization process of biodiesel production using multiple feedstock (CPO and Jatropha) with assistance of ultrasound at 40 kHz. AIP Conf. Proc.; 1737; 2016, 60013. [DOI: https://dx.doi.org/10.1063/1.4949320]

24. Budiman, A.; Kusumaningtyas, R.D.; Pradana, Y.S.; Lestari, N.A. Biodiesel: Bahan Baku, Proses dan Teknologi; Gadjah Mada University Press: Yogyakarta, Indonesia, 2017.

25. ISO 14040 Environmental Management—Life Cycle Assessment—Principles and Framework; ISO: Geneva, Switzerland, 2006.

26. Pleanjai, S.; Gheewala, S.H.; Garivait, S. Environmental evaluation of biodiesel production from palm oil in a life cycle perspective. Proceedings of the Joint International Conference on Sustainable Energy and Environment (SEE); Thailand, 1–3 December 2004; Volume 21, pp. 604-608.

27. Hasibuan, S.; Thaheer, H. Life Cycle Impact Assessment Produksi Biodiesel Sawit untuk Mendukung Keberlanjutan Hilirisasi Industri Sawit Indonesia. Proceedings of the Seminar Nasional Inovasi dan Aplikasi Teknologi di Industri (SENIATI); Malang, Indonesia, 20 November 2017; Volume 3, pp. C47.1-C47.6.

28. Siregar, K.; Tambunan, A.H.; Irwanto, A.K.; Wirawan, S.S.; Araki, T. A Comparison of Life Cycle Assessment on Oil Palm (Elaeis guineensis Jacq.) and Physic Nut (Jatropha curcas Linn.) as Feedstock for Biodiesel Production in Indonesia. Energy Procedia; 2015; 65, pp. 170-179. [DOI: https://dx.doi.org/10.1016/j.egypro.2015.01.054]

29. Wan, S.W.; Chang, C.C. China’s motor fuels from tung oil. Ind. Eng. Chem.; 2007; 39, pp. 1543-1548.

30. Kalam, M.A.; Masjuki, H.H. Biodiesel from palm oil-an analysis of its properties and potential. Biomass Bioenergy; 2022; 23, pp. 471-479. [DOI: https://dx.doi.org/10.1016/S0961-9534(02)00085-5]

31. Widayat, W.; Suherman, S. Biodiesel Production from Rubber Seed Oil via Esterification Process. Int. J. Renew. Energy Dev.; 2012; 1, pp. 57-60. [DOI: https://dx.doi.org/10.14710/ijred.1.2.57-60]

32. Shan, R.; Chen, G.; Yan, B.; Shi, J.; Liu, C. Porous CaO-based catalyst derived from PSS-induced mineralization for biodiesel production enhancement. Energy Convers. Manag.; 2015; 106, pp. 405-413. [DOI: https://dx.doi.org/10.1016/j.enconman.2015.09.064]

33. Su, F.; Guo, Y. Advancements in solid acid catalysts for biodiesel production. Green Chem.; 2014; 16, pp. 2934-2957. [DOI: https://dx.doi.org/10.1039/C3GC42333F]

34. Luque, R.; Lovett, J.C.; Datta, B.; Clancy, J.; Campelo, J.M.; Romero, A.A. Biodiesel as feasible petrol fuel replacement: A multidisciplinary overview. Energy Environ. Sci.; 2010; 3, pp. 1706-1721. [DOI: https://dx.doi.org/10.1039/c0ee00085j]

35. Kumar, M.; Sharma, M.P. Selection of potential oils for biodiesel production. Renew. Sustain. Energy Rev.; 2016; 56, pp. 1129-1138. [DOI: https://dx.doi.org/10.1016/j.rser.2015.12.032]

36. Semwal, S.; Arora, A.K.; Badoni, R.P.; Tuli, D.K. Biodiesel production using heterogeneous catalysts. Bioresour. Technol.; 2011; 102, pp. 2151-2161. [DOI: https://dx.doi.org/10.1016/j.biortech.2010.10.080] [PubMed: https://www.ncbi.nlm.nih.gov/pubmed/21106371]

37. Mujtaba, M.; Masjuki, H.; Kalam, M.; Ong, H.C.; Gul, M.; Farooq, M.; Soudagar, M.E.M.; Ahmed, W.; Harith, M.; Yusoff, M. Ultrasound-assisted process optimization and tribological characteristics of biodiesel from palm-sesame oil via response surface methodology and extreme learning machine-Cuckoo search. Renew. Energy; 2020; 158, pp. 202-214. [DOI: https://dx.doi.org/10.1016/j.renene.2020.05.158]

38. Amani, H.; Ahmad, Z.; Hameed, B. Highly active alumina-supported Cs-Zr mixed oxide catalysts for low-temperature transesterification of waste cooking oil. Appl. Catal. A Gen.; 2014; 487, pp. 16-25. [DOI: https://dx.doi.org/10.1016/j.apcata.2014.08.038]

39. Lee, A.F.; Bennett, J.A.; Manayil, J.C.; Wilson, K. Heterogeneous catalysis for sustainable biodiesel production via esterification and transesterification. Chem. Soc. Rev.; 2014; 43, pp. 7887-7916. [DOI: https://dx.doi.org/10.1039/C4CS00189C]

40. Lu, Y.; Zhang, Z.; Xu, Y.; Liu, Q.; Qian, G. CaFeAl mixed oxide derived heterogeneous catalysts for transesterification of soybean oil to biodiesel. Bioresour. Technol.; 2015; 190, pp. 438-441. [DOI: https://dx.doi.org/10.1016/j.biortech.2015.02.046]

41. Paterson, G.; Issariyakul, T.; Baroi, C.; Bassi, A.; Dalai, A. Ion-exchange resins as catalysts in transesterification of triolein. Catal. Today; 2013; 212, pp. 157-163. [DOI: https://dx.doi.org/10.1016/j.cattod.2012.10.013]

42. Fukuda, H.; Kondo, A.; Noda, H. Biodiesel Fuel Production by Transesterification of Oils. J. Biosci. Bioeng.; 2001; 92, pp. 405-416. [DOI: https://dx.doi.org/10.1016/S1389-1723(01)80288-7]

43. Chisti, Y. Biodiesel from microalgae. J. Biotechnol. Adv.; 2007; 25, pp. 294-306. [DOI: https://dx.doi.org/10.1016/j.biotechadv.2007.02.001]

44. Mao, L.; Dai, Z.; Wu, Y.; Hu, L.; Zhang, W. Evaluating physical-mechanical properties and long periods environmental risk of fired clay bricks incorporated with electroplating sludge. J. Constr. Build. Mater.; 2019; 227, 116716.

45. Sembiring, S.; Simanjuntak, W.; Situmeang, R.; Riyanto, A.; Karo-Karo, P. Effect of alumina addition on the phase transformation and crystallisation properties of refractory cordierite prepared from amorphous rice husk silica. J. Asian Ceram. Soc.; 2017; 5, pp. 186-192. [DOI: https://dx.doi.org/10.1016/j.jascer.2017.04.005]

46. Collie, R.L. Solar Heating System. U.S. Patent; 3955554, 11 May 1976.

47. Yazdani, A.; Hamid, R.; Hossein, G. Investigation Of Hydrothermal Synthesis of Wollastonite Using Silica and Nano Silica at Different Pressures. J. Ceram. Process. Res.; 2010; 11, pp. 348-353.

48. Saade, E.; Aslamyah, E. The Physical and Chemical Analysis of Tiger Prawn’s Feed Using Seaweeds as Binder. J. Torani; 2009; 19, pp. 107-115.

49. Masri, M.; Nazeri, M.M.; Ng, C.Y.; Mohamad, A.A. Tapioca binder for porous zinc anodes electrode in zinc–air batteries. J. King Saud Univ.—Eng. Sci.; 2015; 27, pp. 217-224. [DOI: https://dx.doi.org/10.1016/j.jksues.2013.06.001]

50. Pandiangan, K.; Simanjuntak, W.; Ilim, I.; Satria, H.; Jamarun, N. Catalytic Performance of CaO/SiO₂ Prepared from Local Limestone Industry and Rice Husk Silica. J. Pure App. Chem. Res.; 2019; 8, pp. 170-178. [DOI: https://dx.doi.org/10.21776/ub.jpacr.2019.008.02.459]

51. Chen, G.; Shan, R.; Li, S.; Shi, J. A biomimetic silicification approach to synthesize CaO·SiO₂ catalyst for the transesterification of palm oil into biodiesel. J. Fuel; 2015; 153, pp. 48-55. [DOI: https://dx.doi.org/10.1016/j.fuel.2015.02.109]

52. Gan, S.N.; Bakara, R.A.; Yahya, R. Production of High Purity Amorphous Silica from Rice Husk. Procedia Chem.; 2016; 19, pp. 189-195.

53. Sang, H.N.; Kim, S.H.; Lee, Y.W.; Yoo, M.J. Relation Between Density and Porosity in Sintered UO₂ Pellets. J. Korean Nucl. Soc.; 2022; 34, pp. 433-435.

54. Tabil, L.G.; Sokhansanj, S.; Tyler, R.T. Performance of Different Binders during Alfalfa Pelleting. Can. Agric. Eng.; 1997; 39, pp. 17-23.

55. Thomas, M.A.F.B.; van der Poel, A.F.B. Physical quality of pelleted animal feed. Criteria for pellet quality. Anim. Feed Sci. Technol.; 1996; 61, pp. 89-112. [DOI: https://dx.doi.org/10.1016/0377-8401(96)00949-2]

56. Mehdipour, I.; Khayat, K.H. Effect of Particle-Size Distribution and Specific Surface Area of Different Binder Systems on Packing Density and Flow Characteristics of Cement Paste. Cem. Concr. Compos.; 2017; 78, pp. 120-131. [DOI: https://dx.doi.org/10.1016/j.cemconcomp.2017.01.005]

57. Paraskevopoulou, P.; Chriti, D.; Raptopoulos, G.; Anyfantis, G.C. Synthetic Polymer Aerogels in Particulate Form. Materials; 2019; 12, 1543. [DOI: https://dx.doi.org/10.3390/ma12091543]

58. Setyawan, N.; Hoerudin,; Yuliani, S. Synthesis of silica from rice husk by sol-gel method. International Conference on Green Agro-industry and Bioeconomy. IOP Conf. Ser. Earth Environ. Sci.; 2021; 733, 12149. [DOI: https://dx.doi.org/10.1088/1755-1315/733/1/012149]

59. Jozefaciuk, G.; Bowanko, G. Effect of Acid and Alkali Treatments on Surface Areas and Adsorption Energies of Selected Minerals. J. Clays Clay Miner.; 2002; 50, pp. 771-783. [DOI: https://dx.doi.org/10.1346/000986002762090308]

60. Schall, K.; Kogel, J.E.; Trivedi, N.; Barker, J.; Krukowski, S. Industrial Minerals and Rock-Commodities, Markets and Uses; 7th ed. Society for Mining, Metallurgy and Exploration. Inc.: Englewood, CO, USA, 2006; pp. 1369-1374.

61. Karlsson, S.; Jonson, B.; Stålhandske, C. The technology of chemical glass strengthening-a review. Eur. J. Glass Sci.-Technol. A; 2010; 51, pp. 41-54.

62. Vallitu, P.K. Glass fiber in fiber-reinforced composites. Handbook of Oral Biomaterials; Matinlinna, J.P. Pan Stanford Publishing: Singapore, 2014; pp. 255-270.

63. Deng, Y.; Ma, R.; Yang, Z. Growth of centimetre-scale perovskite single-crystalline thin film via surface engineering. J. Nano Converg.; 2020; 7, 25. [DOI: https://dx.doi.org/10.1186/s40580-020-00236-5] [PubMed: https://www.ncbi.nlm.nih.gov/pubmed/32691332]

64. Mohd, N.; Amini, M.; Masri, M. Properties and Characterization of Starch as a Natural Binder: A Brief Overview. J. Trop. Resour. Sustain. Sci.; 2016; 4, pp. 117-121. [DOI: https://dx.doi.org/10.47253/jtrss.v4i2.619]

65. Gao, J.; Luo, Z.; Luo, F. Ionic Liquids as Solvents for Dissolution of Corn Starch and Homogeneous Synthesis of Fatty-Acid Starch Esters without Catalysts. J. Carbohydr. Polym.; 2012; 89, pp. 1215-1221. [DOI: https://dx.doi.org/10.1016/j.carbpol.2012.03.096]

66. Sangseethong, K.; Termvejsayanon, N.; Sriroth, K. Characterization of physicochemical properties of hypochlorite and peroxide-oxidized cassava starches. J. Carbohydr. Polym.; 2010; 82, pp. 446-453. [DOI: https://dx.doi.org/10.1016/j.carbpol.2010.05.003]

67. Klein, B.; Vanier, N.; Moomand, K.; Pinto, V.; Colussi, R.; Zavareze, E.; Dias, A. Ozone oxidation of cassava starch in aqueous solution at different pH. J. Food Chem.; 2015; 155, pp. 167-173. [DOI: https://dx.doi.org/10.1016/j.foodchem.2014.01.058] [PubMed: https://www.ncbi.nlm.nih.gov/pubmed/24594170]

68. Alfahed, B.; Alayad, A. The Effect of Sintering Temperature on Vickers Microhardness and Flexural Strength of Translucent Multi-Layered Zirconia Dental Materials. Coatings; 2023; 13, 688. [DOI: https://dx.doi.org/10.3390/coatings13040688]

69. Amat, N.F.; Muchtar, A.; Amril, M.S.; Ghazali, M.J.; Yahaya, N. Effect of Sintering Temperature on the Aging Resistance and Mechanical Properties of Monolithic Zirconia. J. Mater. Res. Technol.; 2019; 8, pp. 1092-1101. [DOI: https://dx.doi.org/10.1016/j.jmrt.2018.07.017]

70. Chai, Z.; Gao, Z.; Liu, H.; Zhang, X.; Glodan, G.; Xiao, P. Thermal conductivity of spark plasma sintered SiC ceramics with Alumina and Yttria. J. Eur. Ceram. Soc.; 2020; 41, pp. 3264-3273. [DOI: https://dx.doi.org/10.1016/j.jeurceramsoc.2020.12.020]

71. Kalapathy, C.; Protor, A.; Shultz, J. A Simple Method for Production of Pure Silica from Rice Husk Ash. Bioresour. Technol.; 2000; 73, pp. 257-264. [DOI: https://dx.doi.org/10.1016/S0960-8524(99)00127-3]

72. Callister, W.D.; Rethwisch, D.G. Materials Science and Engineering an Introduction; 9th ed. Wiley: Hoboken, NJ, USA, 2014; pp. 53-93.

73. Mohammadikish, M. Hydrothermal Synthesis, Characterization and Optical Properties of Ellipsoid Shape α-Fe₂O₃ Nanocrystals. Ceram. Int.; 2014; 40, pp. 1351-1358. [DOI: https://dx.doi.org/10.1016/j.ceramint.2013.07.016]

74. Clowutimon, W.; Prakob, K.; Pornsawan, A. Adsorption of Free Fatty Acid from Crude Palm Oil on Magnesium Silicate Derived from Rice Husk. J. Eng.; 2011; 15, pp. 15-25. [DOI: https://dx.doi.org/10.4186/ej.2011.15.3.15]

75. Hosseini, S.; Jashni, E.; Habibi, M.; Nemati, M.; Van der Bruggen, B. Evaluating the ion transport characteristics of novel graphene oxide nanoplates entrapped mixed matrix cation exchange membranes in water deionization. J. Membr. Sci.; 2017; 541, pp. 641-652. [DOI: https://dx.doi.org/10.1016/j.memsci.2017.07.022]

76. Adam, F.; Chew, T.S.; Andas, J. A Simple Template Free Sol-Gel Synthesis of Spherical Nanosilica from Agricultural Biomass. J. Sol-Gel Sci. Technol.; 2011; 59, pp. 580-583. [DOI: https://dx.doi.org/10.1007/s10971-011-2531-7]

77. Mourhly, M.; El, H. The Synthesis and Characterization of Low-Cost Mesoporous Silica SiO₂ from Local Pumice Rock. Nanomater. Nanotechnol.; 2015; 5, 35. [DOI: https://dx.doi.org/10.5772/62033]

78. Rosalia, R.; Asmi, D.; Suka, E.G. Preparasi dan Karakterisasi Keramik Silika (SiO₂) Sekam Padi dengan Suhu Kasinasi 800 °C–1000 °C. J. Teor. Apl. Fis.; 2015; 4, pp. 101-106.

79. Al-Surkhi, O.; Hamad, Z. Influence of Firing Temperature and Duration on the Hardness of Dental Zirconia for Optimum Selection of Sintering Conditions. J. Appl. Biomater. Funct. Mater.; 2022; 20, 22808000221114216. [DOI: https://dx.doi.org/10.1177/22808000221114218]

80. Naskar, M.; Chatterjee, M. A Novel Process for the Synthesis of Cordierite (Mg₂Al₄Si₅O₁₈) Powders from Rice Husk Ash and other Sources of Silica and their Comparative Study. J. Eur. Ceram. Soc.; 2001; 24, pp. 3499-3908. [DOI: https://dx.doi.org/10.1016/j.jeurceramsoc.2003.11.029]

81. Yu, Y.; Zhang, J.; Chen, C.W.; He, C.; Miao, J.; Li, H.; Chen, J. Effects of calcination temperature on physicochemical property and activity of CuSO₄/TiO₂ ammonia-selective catalytic reduction catalysts. J. Environ. Sci.; 2020; 91, pp. 237-245. [DOI: https://dx.doi.org/10.1016/j.jes.2020.01.010]

82. Iskandar, N.; Sulardjaka, S.; Syaiful, S.; Widayat, W. The Effect of Binder Concentration on Characteristic of Pellet Catalyst. AIP Conf. Proc.; 2023; 2667, 80007. [DOI: https://dx.doi.org/10.1063/5.0112560]

83. Freeman, D.C., Jr.; Tonawanda,; Stamires, D.N.; Buffalo, N.Y. Process for Compaction of Zeolite Powders. U.S. Patent; 3213164, 19 October 1965.

84. Abbaszadeh, H.; Masoudi, A.; Safabinesh, H.; Takestani, M. Investigation on the characteristics of micro-and nano-structured W–15 wt% Cu composite prepared by powder metallurgy route. Int. J. Refract. Met. Hard Mater.; 2012; 30, pp. 145-151. [DOI: https://dx.doi.org/10.1016/j.ijrmhm.2011.07.017]

85. Safrudin, M.; Yafiedan, W. Pengaruh variasi temperatur sintering dan waktu tahan sintering terhadap densitas dan kekerasan pada MMC W–Cu melalui proses metalurgi serbuk. J. Tek. Pomits; 2014; 3, pp. 2337-3539.

86. Setiawan, I.; Pramono, A.; Irawan, M.B. Analisa cacat pengaruh kompaksi proses metalurgi serbuk komposit Al/Al₂O₃ dari pemanfaatan limbah kaleng soft drink. Sainstek; 2012; 1, pp. 176-180.