In-Situ Catalytic Pyrolysis of Spirulina platensis residue (SPR): Effect of Temperature and Amount of C12-4 Catalyst on Product Yield

Currently, dependence on fossil energy, especially petroleum, is still high at 96% of the total consumption. One solution to overcome fossil energy consumption is processing alternative energy sources derived from microalgae biomass. This study aims to study the pyrolysis of microalgae with the addition of the C12-4 (Cr2O3+Fe2O3+C+CuO+promoter) catalyst. The biomass used in this study was Spirulina platensis residue (SPR). This study used a fixed bed reactor with an outer diameter of 44 mm, an inner diameter of 40 mm, and a total reactor height of 600 mm. The C12-4 was mixed fifty grams of SPR with a particle size of 100 mesh with a ratio variation of 5, 10, and 15 wt.%. The feed mixture was placed in the reactor (in-situ), and the reactor was tightly closed. The nickel-wire heater wrapped around the reactor wall was employed. The pyrolysis heating rate was 24.33 °C/min on average, and the temperatures were varied as 300, 400, 500, 550, and 600 °C. The research found that the optimum temperature conditions without and with the catalyst to produce bio-oil were different. The pyrolysis without any catalyst (500 0C), with a catalyst of 5 wt.% (500 0C), 10 wt.% (400 0C), and 15 wt.% (550 0C) produced the bio-oil yield of 15.00, 17.92, 16.78 and 16.54, respectively. The use of 5, 10, and 15 wt.% catalysts increased the water phase yield. The char yield was influenced by the amount of catalyst only at 300 0C; i.e., the more catalysts, the less char yield. The pyrolysis without any catalysts produced the highest gas product. A catalyst significantly increased the pyrolysis conversion from 48.69 (without catalyst) to 62.46% (15. wt.% catalyst) at a temperature of 300 0C. The optimum conditions for producing the best bio-oil were at 600 °C and 10 wt.% of catalysts, which resulted in an O/C ratio of 0.14.

Kata kunci: C12-4 catalyst, in-situ catalytic pyrolysis, Spirulina platensis residue, yield bio-oil 1. Introduction Dependence on fossil energy, especially petroleum in Indonesia, is still high, reaching 96% of the total consumption (BPPT−OEI, 2019). Fossil energy is detrimental to the environment because the waste from combustion produces harmful substances such as NOx, CO, SOx, and particulates that pollute the environment (Yang et al., 2019 (Basu, 2010).
Biomass pyrolysis is carried out by heating in oxygen-free conditions and produces liquid (bio-oil), solid (biochar), and gas products (Hu and Gholizadeh, 2019). Pyrolysis products are very dependent on several parameters, such as biomass composition, heating rate, pyrolysis temperature, residence time, biomass grain size, and catalyst (Jamilatun et al., 2018;Jamilatun et al., 2019).
Microalgae bio-oil is a dark-colored liquid fuel that smells like smoke and has a more excellent heating value than bio-oil from lignocellulosic biomass (Maity et al., 2014).
Still, it has a slightly lower calorific value than diesel oil and other fuel oils. In addition, Biooil still contains many oxygenate compounds that can cause corrosion in machines if directly used. Catalytic pyrolysis is one way to improve the quality (upgrading) of bio-oil by reducing the oxygen content. The lower the oxygenate content or O/C ratio, the better the bio-oil quality (Hu et al., 2018). In general, the use of catalysts in biomass pyrolysis can lower pyrolysis temperature, reduce equipment and energy costs, increase biomass conversion, and change product distribution (Zang et al., 2018).
The opportunity to utilize solid residue from SP microalgae extraction for the manufacture of liquid fuels is auspicious. In this study, the pyrolysis of Spirulina platensis residue (SPR) was studied using a solid C12-4 (Cr2O3+Fe2O3+C+CuO+promoter) catalyst.
Pyrolysis was carried out using a fixed bed reactor by mixing SPR without and with a catalyst (in-situ pyrolysis) at a temperature variation of 300-600 ⁰C and using a catalyst 5,    The microstructure test with SEM at magnifications of 100, 1000, 5000, and 10,000 times is presented in Figure 2. Figure 2d shows that Fe2O3 oxide is black iron to steel gray mixed with reddish CrO3 and CuO.

Procedures
The research was conducted in several stages of the process: (1) preparation of materials, (2) preparation of pyrolysis equipment, and (3) pyrolysis process.

Preparation of materials
Spirulina platensis residue (SPR) was crushed, then sieved with -80 + 100 mesh and -100 mesh. SPR used a grain size of -100 mesh. SPR was sun-dried for ten (10) days to reduce moisture content.

Preparation of Pyrolysis Equipment
The pyrolysis reactor is a vertical cylinder operated as a fixed bed reactor with an inner diameter of 40 mm, an outer diameter of 44 mm, and 600 mm. The complete setup of the pyrolysis equipment is shown in Figure 3. In addition, the reactor was equipped with the instruments necessary to study the reactor characteristics, namely temperature and time on the heating rate.  The effect of temperature and use of catalyst C12-4 wt.% on bio-oil yield in SPR pyrolysis with 100 mesh grain size is presented in Figure 5; the calculation follows Equation 2. Figure 5 shows the effect of temperature and the amount of catalyst on the bio-oil yield. Overall pyrolysis of 300-600 ⁰C with catalysts 0, 5, 10, and 15 wt.%, the result is the bio-oil yields in the range of 4. 61-15, 7.84-17.92, 13.17-16.78, and 14.47-16.54%, respectively. The use of 15 wt.% catalysts gave the best results, namely the highest amount of bio-oil at a temperature of 300-600 ⁰C. In general, the higher the pyrolysis temperature, the more active the decomposition is so that more bio-oil is formed. However, at 400-600

Results and Discussion
⁰C, the effect of secondary cracking is very dominant where the tar produced from primary cracking will decompose into gas and char (Jamilatun et al., 2017), the decomposition will cause the gas yield to increase, on the other hand, the bio-oil yield will decrease. This is because the formation of char in secondary cracking is minimal so that it does not affect the formation of char (Jamilatun et al., 2018). Therefore, the optimum conditions for pyrolysis without and with a catalyst have different values. For example, pyrolysis without a catalyst at 500 ⁰C, the yield of bio-oil is obtained 15.00%.

Water Phase Yield
The effect of temperature and the amount of C12-4 catalyst is presented in Figure 6, with the calculation using Equation 3. Based on Pyrolysis at a temperature lower than 400 °C produces higher char. The higher the pyrolysis temperature, the more the decomposition increases so that the liquid and gas products increase; this causes the char yield to decrease. The high heating rate and longer residence time also cause the secondary cracking reaction to being more active so that the char yield will drop (Jafarian et al., 2018).
Pyrolysis variables which are temperature, type and amount of catalyst, heating rate, residence time, and size of biomass grains affect the distribution of product yield composition. These variables will affect the amount of bio-oil yield, water phase, tar (biooil and water phase), char, and gas. The amount of char resulting from pyrolysis will decrease with increasing pyrolysis temperature-the rate at which the amount of char decreases is greatly influenced by the heating rate (Hu et al., 2019, Jamilatun et al., 2019.

Yield of Gas
Based on Figure 8, it can be seen that the gas yield of SPR pyrolysis with a catalyst weight of 0, 5, 10, and 15 wt.%, the calculation follows Equation 5. Pyrolysis without and with a catalyst of 5, 10, and 15 wt.% at a temperature of 300-600 ⁰C yielded a product gas of 30. 08-38.94, 20.31-42.61, 13.21-25.82, and 12.71-23.95%, respectively. Figure 8 shows that non-catalytic pyrolysis. Generally, it produces higher gas than pyrolysis with a catalyst because the catalyst causes more active hydrogenation and hydrodeoxygenation reactions. More water is formed. The formation of gaseous products is strongly influenced by temperature; the higher it is, the higher it is. At temperatures above 300 ⁰C, secondary cracking generally starts to occur, where the tar formed in the primary cracking will decompose into gas and char. For this reason, each pyrolysis variable will affect the distribution of product composition.  the O/C ratio compared to bio-oil products without a catalyst shows the results in Figure   10.

Conclusions
Catalytic pyrolysis of residual Spirulina platensis (SPR) with the particle size of 100 mesh was carried out in a fixed bed reactor at the temperature range of 300-600 ⁰C. The