Characterization of Briquette from the Corncob Charcoal and Sago Stem Alloys

The briquettes fabricated from charcoal of corncob (zea mays,L) and sago stem (metroxilon sago rottb) have been produced and characterized. The samples were prepared step by step carefully. The charcoal powder filtered by strainer with mesh size of 70-80 to get the homogeneous particle size. Briquettes are made by mixing corncob charcoal powder, sago stem charcoal and sago adhesive with a mass ratio of 4:5:1, 4.5: 4.5: 1, 5:4:1. The materials are mixed with hot water and stirred to get homogeneous blend. Then they are compacted by pressure of 34.66kg/cm2, 69.32kg/cm2, and 103.98kg/cm2 to form a cylindrical shape with diameter of 4 cm. The cylindrical briquettes then were dried at temperature of 60°C for 48 hours. After dried, the samples where then characterized their density and water, ash, volatile matter, fixed carbon contents. The burning rate, combustion temperature, and ignition time were also determined. The experimental results show that the briquettes have average densities from 0.602 to 0.717gr/cm3. The density increase with the increasing of forming pressure. The increasing of pressure also result in the decreasing of moisture content from 2.669% to 0.842%. The ash content is found from 3.459% to 8.766%. Volatile matter and fixed carbon are varies from 13.658% and 21.168% and 67.667% to 80.758% respectively. The lowest burning rate is 0.0898gr/s and the optimum burning temperature is 499.2°C with the lowest ignition time of 1.58 minutes. These briquette’s parameters agree wit the quality standard of industrial briquette.


Introduction
Processing and utilization of biomass resources are being developed as more valuable material [1][2] as well as as alternatives to conventional energy source [3][4]. The biomass is a solid waste and it is commonly used as a fuel source. Biomass energy can be used as an alternative energy source to replace fossil fuels. The advantage of biomass is it does not contain sulfur and also did not caused the air pollution. It also improves the efficiency of utilization of forest and agriculture resources [5]. There are abundant biomass from agricultural wastes in Indonesia especially in southeast Sulawesi such as corncobs and sago stems. The corncob waste contains celluloses and lignins about 44.9% and 33.3%, respectively, while sago stem has celluloses of about 57% and lignins of 38% [6]. These facts indicate that the corncobs and sago stems can be used as material for producing the charcoal briquette. The charcoal briquette charcoal is charcoal which is made by changing the shape, the size and the density by applied a certain pressing to the mixture of charcoal powder with an adhesive. The manufacturing of briquette alloy of corncob charcoal and sago stem charcoal need an appropriate method to improve the briquette quality. Commonly, the production of briquettes are using conventional method, especially for drying is using electric furnace or fire. Recently, the use of microwave radiation or hot gases as a substitute for the conventional heating has been reported for processing materials. The applications have been reported in sintering ceramic [7][8][9][10], synthesizing organic materials [11][12][13] as well as speeding up a chemical reaction and drying [14][15]. The theoretical analysis were also reported [16][17]. Microwave radiation is believed to be able to increase the rate of a chemical reaction and may improve the microstructure of briquette and then result in increase their caloric energy. The use this technology for briquette is performing in our research group and will be reported soon in separated papers.
Chemically, sago stem contains 28% of amylose and 72% of amylopectin and can be used as adhesive [3]. Sago starch is potential as an adhesive of charcoal briquettes of the mixtures of charcoal corncob and sago stem. The ratio of the mass of charcoal corncob and sago stem is 9:1 which gives the optimum composition of charcoal briquette [18]. Briquette quality also depends on the particle size and pressure. Charcoal briquettes of corncobs with adhesive from sago is produced with the size of 80 mesh, and the pressure of 94,22kg/cm 2 . The resulting briquettes have a caloric value of 7607,4707 cal/g, the ash content of 5.3042%, moisture content of 2.2492% and the density of 0,7419gr/cm 3 [19]. The charcoal briquette of sago stem made with adhesive with composition of 9:1, particle size of 70 mesh, and pressure of 94,22kg/cm 2 produce the high burning temperature of 428,2 o C [20]. In this research, we study the effect of material composition and forming pressure to quality of briquette of corncob and sago stem alloy. The samples will characterize carefully such as their density, water content, ash content, volatile matter, fixed carbon, the burning rate, burning temperature, and burning time. By varying the composition there is expected to obtain the best composition of the charcoal briquettes for their optimum quality.

Briquette Fabrication
The material used in this research are the corncob wasted (Zea mays,L) and sago stem wasted (Metroxilon sagu Rottb). The corncob wasted is taken from Tikep, Muna, Indonesia. Sago stem waste is collected from Konda district of Konawe Selatan, Indonesia. Before carbonation, corncob and sago stem waste is dried in the oven with temperature of 110 o C for 120 minutes. The corncob is carbonated by using furnace for 60 minutes to achieve temperature's carbonation of 499 o C and sago stem is furnace about 160 minutes to reach the temperature of 530 o C. The charcoal of corncob and sago stem are then mashed to obtain the charcoal powder. The charcoal powder is then filtered by strainer with size of 80 mesh. The residue is the filtered again with the strainer of 70 mesh size. The resulted powder is then used as ingredient for making the charcoal briquette. The charcoal powder of corncob and sago stem are mixed with the adhesive from sago starch. The mass ratio composition are 4:5:1, 4.5:4.5:1, 5:4:1, respectively for total mass of the mixed material of 10g. The mixed material is then added with 2 ml of water and stirred until homogeneous.
The mixed samples with these composition were then formed to cylindrical shape with diameter of 4 cm with hole of 0.8 cm in the center. They were compressed with the pressure of 34.66kg/cm 2 , 69.32kg/cm 2 ,and 103.98kg/cm 2 , respectively. The resulted briquettes were then dried in oven at 60 o C for 48 hours.

Characterization of briquettes
After fabrication, the briquettes were then characterized. About one gram of sample heated in the oven with the temperature of 105 o C until the constant mass (no evaporation) is reached. The briquette was then cooled before weighted. The moisture content is calculated as the ratio of evaporated water's mass compared with sample's mass before heating. The volatile matter is determined in the same way but the sample is heated at temperature of 750 o C for 7 minutes. Volatile matter is evaporated mass during heating but water content. The ash content of the briquette is determined by burning the one gram briquette sample till all the sample become ash. The ash was then cooled and then weighted. The ash content is determined as presentation of the resulted ashes compared with the original sample. Fixed carbon is the carbon in the sample while the density is the mass ratio per unit volume of the sample. Burning testing is performed in the open space at temperature 25 o C. This is to obtain the ignition time, burning rate and the maximum temperature of the briquettes. The temperature were measured using infrared thermometer.

Density
The density of the briquette made from the charcoal of corncobs and sago stem alloys with different compositions is presented in Figure 1. The blue and the red lines are the density for the composition of charcoal corncob, the charcoal of sago stem and the adhesive of sago starch with ratio of 4 : 5: 1 and 4.5 : 4.5 : 1, respectively. While the green line is for the ratio of 5:4:1. It is shown that the density is increased with the increasing of the pressure. The briquette's density is from 0.602 g/cm 3 to 0.717g/cm 3 . The highest average density is found at the composition 4.5:4.5:1. The pressure applied during forming was not only to create material bonding and distance between atoms shorter but also to spread the adhesive thoroughly to whole charcoal body. The briquette with forming by suitable pressure will have a high density and high mechanical strength. However, if we applied not suitable pressure during fabrication, it may make briquette more fragile [20]. According the British standard, the value of the briquette density is more than 0.48g/cm 3 while the Japanese standard is lower than 1.2 g/cm 3 [21]. Based on this, the resulted briquette made from the charcoal of corncobs and sago stem alloys satisfy these standard.

Moisture content
Moisture content of charcoal from corncob and sago stem alloys with different composition is given in Figure 2. The blue and the red lines are the density for the composition of charcoal corncob, the charcoal of sago stem and the adhesive of sago starch with ratio of 4:5:1 and 4.5:4.5:1, respectively. The green line is for the ratio of 5:4:1. From the figure, we can see that the moisture content is decreased with the increment of the pressure. The moisture content of the briquettes are from 0.842% to 2.669%. The lowest average moisture content is obtained at composition of 5:4:1. Generally, the moisture content of the briquette is expected to be low because of the lower its moisture content the higher its burning power. The standard value of briquette moisture content is less than 3.6% for British standard and less than 8% for Japan standard [8]. Our briquettes meet to these standards.

Ash, volatile matter, and fixed carbon contents
The ash, volatile matter and fixed carbon contents of the briquettes made from the charcoal of corncob and sago stem alloys and adhesive for different composition ratio are presented in Table 1. From Table 1, we see that the highest fixed carbon content is the briquette made from the charcoal of corncob and sago stem alloys together with composition of 4.5:4.5:1. We also found that the charcoal of corncob contributed to the highest ash as well as volatile matter contents. According to the Japanese standard, the values for ash, volatile matters and the fixed carbon contents of briquettes are from 3% -6%, 15% -30%, and 60% -80 %, respectively [21]. Althought the values for ash content exceed the standard value, but for volatile matter and fixed carbon contents are in good agreement with the standard.

Burning rate, ignition time and maximum temperature
Burning rate is the rate of briquette's mass combusted in air at certain time. Figure 3 shown the average burning rate of the briquettes of three composition ratios. The blue and the red lines are for the composition of charcoal corncob, the charcoal of sago stem and the adhesive of sago starch of 4:5:1 and 4.5:4.5:1, respectively. While the green line is for the ratio of 5:4:1.The lowest burning rate of the briquette is found for the composition ratio of 5:4:1 while the highest one is for the composition ration of 4:5:1. The ignition time is time needed by the briquette for starting to blame. It determines how combustible the briquette. From Table 2, we found that the lowest iginition time is 1.58 minutes for briquette with the composition ratio of 5:4:1 and the the forming pressure of 103.98kg/cm 3 . The highest temperature is 499.2 o C for briquette with the composition ratio of 4.5:4.5:1 and the pressure of 34.66kg/cm 3 .

Conclusion
The fabrication the briquette from chorcoal of corncob and sago stem alloys was successfully performed. For adhesive, the sago strach was applied. The composition of corncob charcoal and sago stem charcoal alloys and an adhesive are 4:5:1, 4.5:4.5:1, and 5:4:1, rescpectively. And the corresponding forming pressure are 34.66 kg/cm 2 , 69.32 kg/cm 2 , and 103.98 kg/cm 2 . The briquete's characteristics are meet to the international standard for industrial briquette. The briquette with composition ratio of 5:4:1 and forming pressure of 34.66kg/cm 2 give the maximum temperature of 499.2 o C.