|Siti Jamilatun||Department of Chemical Engineering, Faculty of Industrial Technology, Universitas Ahmad Dahlan, Jalan Kapas 9, Yogyakarta 55166, Indonesia|
|Budhijanto budhijanto||Department of Chemical Engineering, Faculty of Engineering, Universitas Gadjah Mada, Jalan Grafika 2, Yogyakarta 55284, Indonesia|
|Rochmadi||Department of Chemical Engineering, Faculty of Engineering, Universitas Gadjah Mada, Jalan Grafika 2, Yogyakarta 55284, Indonesia|
|Avido Yuliestyan||Department of Chemical Engineering, Faculty of Industrial Technology, Universitas Pembangunan Nasional “Veteran” Yogyakarta, Jalan SWK 104, Yogyakarta 55283, Indonesia.|
|Arief Budiman||Department of Chemical Engineering, Faculty of Industrial Technology, Universitas Ahmad Dahlan, Jalan Kapas 9, Yogyakarta 55166, Indonesia|
Spirulina platensis microalgae is one of the feedstocks used in the production of the third generation of biofuel. The extraction of its lipid for biodiesel leaves behind a residue, which can be treated by pyrolysis to create certain other value-added products. This paper discusses the effects of Spirulina platensis residue (SPR) with respect to grain size (0.105, 0.149 and 0.177 mm), temperature (300 to 600°C) and amount of catalyst (0, 10, 20 and 40 wt.%) on the characteristics of products (bio-oil, water phase, char and gas) obtained from pyrolysis in a fixed-bed reactor. The results of the study show that the higher the pyrolysis temperature, the higher the conversion. For the bio-oil product, the optimum temperature is 500°C, which produces a peak yield of 35.99 wt.%. The larger the grain size, the lower the bio-oil yield, gas water and gas, for all of the tested temperatures (300–600°C). The amount of catalyst and the pyrolysis temperature greatly influence the quality of bio-oil products, grouping them into the fractions of LPG (C ? 4), gasoline (C5–C11), biodiesel (C12–C18) and heavy naphtha (C ? 19). The tendency for LPG-Gasoline formation at optimum conditions, considering the use of a 10 wt.% catalyst at a temperature of 400–500°C, was reported.
Alumina silica; Bio-oil pyrolysis; Fixed-bed; Spirulina platensis residue
The massive exploitation of non-renewable natural resources may pose a threat to lives in the future arising from an increase in associated health issues and the greater risk of environmental damage that stems from the lower energy reserves and greater release of emissions during their processing (Anggorowati et al., 2018; Setyawan et al., 2018). There is thus an urgent need to replace non-renewable energy sources with renewable ones. Biomass is one of the most potent renewable energy sources, with its development having now led to the third generation of biofuel (Purwanto et al., 2015; Supramono et al., 2015; Jamilatun et al., 2017a; Kusrini et al., 2018a).
The first-generation biofuels (Fatty Acid Methyl Esters (FAME) or biodiesel, corn ethanol and sugar alcohol) were produced from lignocellulosic sources in the form of vegetable oils, corn, sugar and others. Although safer from an environmental perspective, a negative impact on food security may have arisen due to competition with food for consumption (Naik et al., 2010; Maity et al., 2014). Different from their predecessors, second-generation biofuels (hydrotreating oil, bio-oil, ethanol from lignocellulose, butanol and alcohol mixtures) were developed to address the aforementioned issue on biofuel production by using non-food lignocellulosic sources such as agricultural residues, forests, grasses, aquatic biomass, etc. Despite not competing for resources with food production as they are derived from renewable resources, and with lower costs of production, the raw material resources used in the first and second generations did require extensive land; hence, biofuel production per area is relatively low (Pradana et al., 2017a; Sudibyo et al., 2017). To that end, microalgae, which requires less land to produce, offers the potential to be developed as a resource for use in the third generation of biofuels (Jamilatun et al., 2017b; Pradana et al., 2017b). Microalgae can be converted into biofuels through either a thermal or biological process. Pyrolysis technology can be utilized to process microalgae into third-generation biofuels (Yuliansyah et al., 2015). The initial process begins with the extraction of Spirulina platensis microalgae to leave behind a solid residue known as Spirulina platensis residue (SPR). The process of pyrolysis can then be applied to convert this low-value material into highly valuable fuel products and chemicals.
Microalgae pyrolysis is influenced by many parameters, such as the biomass type, temperature, heating rate, residence time, size and shape, catalyst, etc., as partly reported by Zheng et al. (2018). Temperature is the most significant of these operating parameters and has a tremendous effect on the product composition; indeed, pyrolysis is generally carried out at a temperature range of 400–600°C (Kusrini et al., 2018b). Within this temperature range, the liquid phase is mostly produced, which accounts for around 60–70 of the wt.%. However, further increasing the temperature beyond its optimum will lead to secondary cracking, whereby tar from the primary cracking product will be converted into gas and char. The effect of secondary cracking is a decline in bio-oil products and an increase in gas products (Dickerson & Soria, 2013).
In a fast pyrolysis process, it is generally assumed that the increase in grain size produces a greater temperature gradient in the particles. At any given time, the core temperature is lower than that of the surface of the biomass particles. This can lead to an increase in charcoal, while the amounts of gas and bio-oil decrease. Small particles have an adequate surface area via which to interact with pyrolysis media to form volatile products, thus enabling them to leave the biomass matrix without experiencing any secondary reactions. However, in the case of slow pyrolysis, particle size shows a less significant effect on product yield (Yang et al., 2019).
The presence of an additional catalyst significantly affects the product yield in catalytic pyrolysis. The gas yield increases and charcoal is initially produced, the amount of which is subsequently increased with the addition of the catalyst. In addition, charcoal yield reaches a minimum of 9 wt.% when the mass ratio of the raw material/catalyst is 1:3. The addition of further catalyst increases the catalytic cracking rate, thereby aiding in the formation of gas compounds. Furthermore, the oil yield decreases as the loading of the catalyst increases. This phenomenon occurs due to secondary steam cracks (Qi et al., 2018).
This paper aims to characterize the SPR pyrolysis products (bio-oil, water phase, char and gas) in fixed-bed reactors with various temperatures, SPR grain sizes and number of catalysts used. The ultimate, proximate and calorific values of the raw materials in the form of SPR are analyzed, while the components of the alumina-silica catalyst are analyzed by SEM-EDX (Scanning Electron Microscopy Energy-Dispersive X-Ray Analysis). The pyrolysis products in the form of bio-oil will be analyzed with GC-MS (Gas Chromatography-Mass Spectrometry), with the components then grouped into the fractions of LPG (C ? 4), gasoline (C5-C11), biodiesel (C12-C18) and heavy naphtha (C ? 19).
As a raw material source in the production of third-generation biofuel, Spirulina platensis residue offers the potential to be developed on a large scale due to its ease of cultivation, simple processing pyrolysis technology and low cost. Temperature and the grain size of SPR microalgae affect the composition of the product. Bio-oil yield will increase from 9.22 to 33.99 wt.% at a temperature of 300–500°C, then fall to 23.34 wt.% at 600°C with an SPR grain size of at least 0.105 mm. This positive-peak curvature trend also applies to the sizes of 0.149 and 0.177 mm. However, the larger the grain size, the lower the bio-oil yield. An increase in grain size seems to produce a fall in the water phase, gas and its total conversion, whereas the opposite is shown for the yield of char. This applies to all temperatures (300–600°C).
The use of a catalyst affects the composition of the product. A greater amount of catalysts (0–40 wt.%) appears likely to result in a lower yield of bio-oil and char, with greater amounts of converted product obtained in the gas phase and fairly constant amounts in the water phase.
Based on the grouping of the number of C atoms in the bio-oil constituent, the dominant fraction is the LPG-Gasoline fraction, with methanol being the most highly available component. In the optimum condition at temperatures of 400–500°C, pyrolysis with the use of 10 wt.% catalyst produced about 45.48–55.31 wt.% of LPG fraction and 35.70–28.95 wt.% of gasoline fraction.
The author is very grateful for the funding support from the Ministry of Research, Technology, and Higher Education, Republic of Indonesia. We also gratefully acknowledge the funding from USAID through the SHERA program – Centre for Development of Sustainable Region (CDSR) (077/Kontrak/TA/03/2018).
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