281
Indonesian Journal of Science & Technology 8.
281-306 Indonesian Journal of Science & Technology Journal homepage: http://ejournal.
edu/index.
php/ijost/ Bifunctional CaCO3/HY Catalyst in the Simultaneous Cracking-Deoxygenation of Palm Oil to Diesel-Range Hydrocarbons Rosyad Adrian Febriansyar1.
Teguh Riyanto1,2.
Istadi1,2*.
Didi D.
Anggoro1.
Bunjerd Jongsomjit3 Department of Chemical Engineering.
Faculty of Engineering.
Universitas Diponegoro.
Semarang 50275.
Indonesia.
Laboratory of Plasma-Catalysis (R3.
Center of Research and Services - Diponegoro University (CORES-DU).
Integrated Laboratory.
Universitas Diponegoro.
Semarang.
Central Java 50275.
Indonesia.
Department of Chemical Engineering.
Faculty of Engineering.
Chulalongkorn University.
Bangkok 10330.
Thailand.
*Correspondence: E-mail: istadi@che.
ABSTRACT
Palm oil is a promising raw material for biofuel production using the simultaneous catalytic mechanism of the bifunctional crackingdeoxygenation reactions.
Through the cracking-deoxygenation process, the chains of palmitic acid and oleic acid in the palm oil were converted to diesel-range hydrocarbons.
The combination effects of CaCO3 and HY zeolite enhanced the bifunctional catalytic crackingdeoxygenation of palm oil into biofuel, because of the increasing acid and basic sites in the catalysts due to the synergistic roles of CaCO3 and HY.
The introduction of CaCO3 on HY zeolite generated both a strong acid and strong basic sites simultaneously on the designed catalyst, which supports the bifunctional mechanisms of hybrid cracking-deoxygenation, respectively.
The CaCO3 impregnated on the HY catalyst has a synergistic and bifunctional effect on the catalyst supporting cracking-deoxygenation reaction mechanisms as mentioned previously.
The deoxygenation reaction required the bifunctional strong acid and strong basic sites on the CaCO3/HY hydrodeoxygenation reaction mechanisms.
Meanwhile, the cracking reaction pathway was supported by the strong acid sites generated on the CaCO3/HY catalyst.
In other words, the high acidity strength promotes diesel selectivity, whereas the high strength of basicity leads to the deoxygenation reaction.
A 2023 Tim Pengembang Jurnal UPI
ARTICLE INFO
Article History:
Submitted/Received 18 Nov 2022
First Revised 19 Dec 2022
Accepted 03 Feb 2023
First Available Online 07 Feb 2023
Publication Date 01 Sep 2023
____________________
Keyword:
Bifunctional.
Biofuel.
Calcium carbonate.
Cracking.
Deoxygenation.
Palm oil.
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INTRODUCTION
Globally, the consumption of fossil fuelbased energy is predicted to grow, resulting in increased environmental pollution and limited fossil fuel supplies.
About 80% of global energy consumption comes from fossil fuels (Hancsyk et al.
, 2.
The use of renewable fuels is one of the essential aspects of reducing carbon dioxide emissions.
Therefore, renewable fuels have the potential to be suitable replacements for fossil fuels.
Vegetable oils-derived renewable fuels have recently attracted the attention of researchers seeking solutions to the difficulties provided by decreasing oil reserves, oil supply issues, and the growing usage of non-renewable fuels.
Palm oil is a vegetable oil that is often utilized as a raw material in the production of biofuels due to its high long-chain hydrocarbon content, relatively equal saturated and unsaturated oil content, widespread availability around the world, and abundant availability particularly in Indonesia (Istadi et al.
, 2020a.
Xu et al.
Palm oil is mainly composed of triglyceride containing three fatty acid chains, which are connected by a carboxyl group to glycerol, with a molecular structure that is like hydrocarbon (Seifi & Sadrameli, 2.
Additionally, it may be utilized to produce biofuels through catalytic cracking processes.
Thermal and catalytic cracking can be used to produce biofuels (Xu et al.
, 2017.
Zhao et al.
Istadi et al.
, 2020.
The catalytic cracking process of palm oil is driven by a chain reaction mechanism that includes initiation, propagation, and termination, which is a simple and effective method for biofuel production from palm oil (Corma & Orchilles, 2000.
Riyanto et al.
, 2020.
Yigezu & Muthukumar, 2.
Kwon et al.
reported that removing the oxygen content of used palm oil is required to improve biofuel quality by increasing energy density, decreasing viscosity, and stabilizing biofuels.
However, the high amount of oxygen in palm oil cannot be used directly as a fuel and causes engine compatibility issues, such as corrosion, carbon deposition, and thickening of engine Therefore, palm oil must be improved through the deoxygenation process by using specific catalysts to be utilized as a biofuel (Ooi et al.
, 2.
Typically, the triglyceride catalytic cracking reaction pathway is controlled mainly by catalyst properties, such as strength, type and many acid sites, and pore shape (Wang et al.
Zhao et al.
explained that by using a proper catalyst, catalytic cracking breaks the triglyceride double bonds and removes triglyceride oxygen from palm oil.
Research by Kubiska et al.
showed that the catalytic cracking of palm oil at 300 AC using Si-15NiMo catalyst resulted in a deoxygenation rate of 95% because SiO2 supports the NiMo catalyst, causing a decarboxylation reaction in the catalytic Papageridis et al.
also reported that the catalytic cracking of palm oil using Ni/Al catalyst showed a deoxygenation rate of 77%.
Co-CaO catalyst has bifunctional properties and strong acidic sites on the catalyst generate fatty acid cracking as reported by Asikin-Mijan et al.
, whilst strong basicity influences deoxygenation pathway in the conversion process of palm oil into hydrocarbons with a deoxygenation rate of 75%.
Deoxygenation of triglyceride is a method of removing oxygen atoms contained by fatty acids through decarboxylation (-CO.
(-CO) hydrodeoxygenation (-H2O) reactions (AsikinMijan et al.
, 2.
However, the pathways lose each carbon atom to byproducts in the form of CO and CO2 gases, resulting in the reduction of carbon in the liquid products.
The acid-basic bifunctional catalysts are solid heterogeneous catalysts consisting of both acidic and basic active sites on the The advantages of the bifunctional heterogeneous catalysts include their ability to be recycled, reused, and regenerated with minimal energy consumption (Elias et al.
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Carbon and hydrogen may also be converted into aromatics and olefins (Istadi et al.
, 2021a.
Shakirova et al.
, 1.
Sartipi et al.
explained that HY zeolites have more acid sites, which produce stronger acid sites to accelerate cracking.
Sugiyama et al.
also explained that CaCO3 is used as a catalyst support with a basic site.
Suyrez et al.
reported that metal impregnation on HY zeolite could enhance the number of Lewis acid sites due to the presence of unpaired electrons in the metals.
Metals, such as CaCO3, may be used to modify the characteristics of zeolites to generate Lewis acid sites.
Several pathways of hybrid cracking-deoxygenation may occur on CaCO3modified These processes may produce carbon dioxide, carbon monoxide, and water as byproducts, respectively.
In biofuel production, oxygen content in the cracking product becomes a problem for fuel cases that must be reduced in the cracking process.
According to Kianfar et al.
, the use of ZSM-5/CaCO3 as a catalytic cracking catalyst improves the production of heavy hydrocarbons by 38.
Istadi et al.
also found that Ni-Co/HY catalyst supported cracking and deoxygenation mechanisms in the production of biofuels from palm oil reaching a yield of hydrocarbons and oxygenated by 98.
46% and 1.
Meanwhile, cracking palm oil using a bifunctional Zn/ZSM-5 catalyst to produce hydrocarbon fuel and oxygen content by 71.
78% and 4.
07%, respectively, was reported by Zhao et al.
Cheng et hydrodeoxygenation and hydrogenation on the bifunctional Fe-Ni/HZSM-5 catalysts producing the highest biofuel yield of 28.
wt% and the highest hydrocarbon content of Although many researchers have reported on many types of suitable bifunctional catalysts for the cracking and deoxygenation of palm oil to biofuels, the specific studies on the design and roles of bifunctional catalysts deoxygenation of triglyceride to biofuels are Therefore, it is necessary to develop a simultaneous cracking-deoxygenation of triglyceride to biofuels.
The combination of CaCO3 and HY zeolite is expected to increase the acid sites (Lewis and Brynsted acid.
and basic sites on the catalysts simultaneously.
However, further detailed testing of the designed CaCO3-modified HY catalyst is required for the catalytic crackingdeoxygenation process of triglyceride into To the best of our knowledge, studies on the influence of the bifunctional CaCO3modified HY catalyst on the simultaneous cracking-deoxygenation reaction pathways were limited.
Therefore, this research focused on emphasizing the role of bifunctional the strong acid and strong basic sites generated on the catalyst supporting the simultaneous cracking-deoxygenation of palm oil into diesel-range hydrocarbons.
MATERIALS AND METHODS
Materials This research used commercial HY zeolite from Zeolyst International (CBV.
as a catalyst support and calcium carbonate (CaCO.
Merc.
as a precursor.
Palm oil, as a raw material of triglyceride, was used to test the activity of the catalyst in the cracking-deoxygenation reactions (Table .
In addition, nitrogen gas .
UHP) was used to remove/flush oxygen content in the pipelines and reactor DOI: https://doi.
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Table 1.
Fatty acids composition of triglyceride in the palm oil raw material.
Component Palmitic acid Stearic acid Oleic acid 1-Tridecene 2,6,10,14,18-Penta methyl eicosa Total Preparation of Catalysts HY zeolite powder was dried for 1 h at 110 AC in an electric oven (Memmer.
and labeled as HY.
Then, 20 g of the HY was immersed in a CaCO3 solution .
25 M).
Thus, the targeted impregnated CaCO3 were 5, 10, and 20 wt%.
The resulting slurry was stirred at a stirring speed of 600 rpm for 1 h.
After that, the slurry was aged The mixture was filtered and dried overnight at a temperature of 65AC in an electric oven (Memmer.
Thus, the targeted CaCO3 content was only physically and chemically adsorbed on the HY catalyst.
The catalyst was then calcined at 550AC for 3 h in a furnace (ThermoLyn.
and was labeled as xCaCO3/HY catalyst, where x is %wt of CaCO3.
Catalyst Characterizations Crystal Structure Phase Identification of Catalyst Using X-Ray Diffraction (XRD) Determination of the crystal structure and phase identification of the CaCO3/HY catalyst was conducted using an XRD analysis (Shimadzu 7.
operating at 30 kV and 30 mA with Cu-K The catalyst was scanned at an angle of 2 from 5-90A at a scanning speed of 3A/min.
Determination of Particle Surface Area and Pore Size Distribution of Catalyst The adsorption-desorption of the N2 method (Micromeritics TriStar II 3.
was used to determine the catalysts surface area and pore size distribution.
The adsorption of N2 was conducted at bath temperature of 77 K.
Before the adsorption process, catalysts were degassed Chemical Formula
C16:0
C18:0
C18:1
Composition .
t%) at 200AC for 2 h.
The Brunauer-Emmett-Teller (BET) method was used to determine the specific surface area, while the pore size distribution was determined using the BarrettAe JoynerAeHalenda (BJH) method.
Catalyst Morphology using Scanning Electron Microscopy Ae Energy Dispersive X-Ray (SEM-EDX) SEM-EDX (JEOL JSM-6510LA), 10 AAm resolution, and 3,000 to 10,000x magnification were used to examine the morphology of HY, 5CaCO3/HY, 10CaCO3/HY, and 20CaCO3/HY At 20 kV, a 1 g powder sample was mounted on a platform and examined for 51.
Secondary electrons are used to obtain high-resolution SEM images.
The elemental composition of solids was determined via EDX analysis by scanning the sample at a precise spot on the specimen.
Acidity Strength NH3Temperature Programmed Desorption (NH3-TPD) The catalysts of HY, 5CaCO3/HY, 10CaCO3/HY, and 20CaCO3/HY were weighed as much as 1 g.
Samples were pretreated by heating at 350AC for 60 min under He gas .
Then.
NH3 adsorption .
% in He, v/.
was carried out at 100 AC for 30 min, then purged with He gas .
at the same temperature, for 30 min to remove the physisorbed NH3.
NH3 desorption was carried out at a temperature of 100Ae650AC with a temperature increase of 10 AC/min.
The entire flow rate of gas is 40 mL/min.
The desorbed NH3 was measured using a thermal conductivity detector (TCD).
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Basicity Strength
CO2
Temperature Programmed Desorption (CO2-TPD) Each catalyst of HY, 5CaCO3/HY, 10CaCO3/HY, and 20CaCO3/HY was weighed as much as 1 g.
Samples were pretreated by heating at 350AC for 60 min under He gas .
The CO2 adsorption .
% CO2 in He, v/.
was carried out at room temperature for 30 min, then purged with He gas .
at the same temperature for 30 min to remove the physisorbed CO2.
The CO2 desorption was carried out at room temperature to 650AC with a temperature increase of 10 AC/min.
The flow rate of gas is 40 mL/min.
The desorbed CO2 was measured using a thermal conductivity detector (TCD).
Catalyst Performance Testing and Biofuel Product Analysis The catalysts were tested for the catalytic cracking-deoxygenation reactions of palm oil over a fixed-bed catalytic reactor .
ee Figure .
to produce liquid fuels.
The reactor was constructed with a stainless-steel tube with a diameter of 1 inch.
An electric heating furnace was installed outside the tubing before entering the reactor called a tube line preheating process.
The catalyst was loaded into the reactor for an amount of 5 g of each run.
Then, 100 mL/min of N2 gas was flowed into the tubing and reactor system for 15 min to flush oxygen gas content within the system.
The reactor was heated up to reaction temperature .
AC) until reach the targeted reactor temperature.
After the reactor temperature was steady, palm oil was fed into the reactor at a weight hourly space velocity (WHSV) of 0.
288 minOe1 in which the flow rate was controlled using a peristaltic pump (RZ1030-BX).
The product of the reaction was condensed in a condenser equipped with a chiller (CCA-.
and collected as an organic liquid product (OLP) during the cracking Figure 1.
Scheme of continuous catalytic cracking experimental setup: .
Palm oil tank, .
Peristaltic pump, .
Pre-Heater, .
Fixed-bed reactor, .
Catalyst bed, .
Electric Tube Furnace, .
Glass wool, .
Condenser, .
Chiller, .
Organic liquid product, .
N 2 gas tank, .
Flowmeter.
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Product Characterization Quantification The organic liquid product (OLP), as a cracking product composed of hydrocarbons and oxygenates, was condensed and The collected liquid product was analyzed using gas chromatography-mass spectrometry (GC-MS).
Determination of components identification and compositions of liquid biofuels product was conducted Gas Chromatography-Mass Spectrometry (GC-MS) (QP2010S SHIMADZU.
DB-1 colum.
The samples were analyzed at 50 oC oven temperature .
old for 5 mi.
and ramped 10 AC/min to 260 oC and held for 33 The liquid reaction product was taken at the first 3 h after a steady state was achieved for GC-MS analysis purposes.
Regarding this matter, an assumption was then taken that the steady state condition was achieved after 30 minutes on stream.
To calculate yield and selectivity, the OLP is distilled fractionally based on the temperature range of diesel fraction of 300 Ae 370 AC (CAS 68334-30-.
using a batch distillation to determine the yield of diesel fraction product.
The yield and selectivity were calculated Equations .
Ae .
Yield of OLP (%) = OLP C100 m feed Yield of gas (%) = Intensity .
EE E E E E E
C100
m feed
Yield of coke (%) = coke C100
m feed
C100
m feed Selectivity of diesel (%) = diesel C100 mOLP Yield of water (%) = .
RESULTS AND DISCUSSION Phase Identification and Crystal Structure Analysis using the XRD The crystal structure of the catalysts (HY, 5CaCO3/HY, 10CaCO3/HY, and 20CaCO3/HY) was determined by utilizing diffraction patterns of XRD analysis.
The resulting diffraction peaks were then compared with the ICDD (International Center for Diffraction Dat.
Figure 2 and Table 2 show the diffraction patterns and the analysis of the peak, according to the ICDD3.
E Faujasite C CaCO3
C C CC
20CaCO3/HY 10CaCO3/HY 5CaCO3/HY 2 (A) Figure 2.
X-ray diffraction patterns of catalysts (HY, 5CaCO 3/HY, 10CaCO3/HY, and 20CaCO3/HY).
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Detected phases of catalysts by ICDD compound data of XRD.
Data ICDD File 5CaCO3/HY 10CaCO3/HY 20CaCO3/HY Compound CaCO3a Faujasiteb Faujasite CaCO3 Faujasite CaCO3 Faujasite CaCO3 Faujasite 2 (A) a COD Database no.
96-900-9668
b COD Database no.
96-154-5416
Based on Figure 2, the HY catalyst shows the diffraction peaks with cubic structure (Faujasit.
at 2 of 6.
6, 10.
6, 12.
4, 16.
2, and 3A concerning hkl of .
, .
, .
, .
, and .
, respectively.
These peaks are in line with the result of Choo et al.
which identified the diffractogram of the HY These peaks were also found in all catalysts (HY, 5CaCO3/HY, 10CaCO3/HY, and 20CaCO3/HY), indicating that the Faujasite structure is found in all catalysts.
The diffraction peaks of CaCO3 with a hexagonal structure are detected at 2 of 23.
3, 29.
2, 39.
6, 43.
4, 47.
4, and 48.
7A concerning hkl of .
, .
, .
, .
, .
, .
, respectively.
The presence of these diffraction peaks indicates that the CaCO 3 has been impregnated successfully on the HY As shown in Figure 2, the diffraction pattern of CaCO3 increases as the rising amount of impregnated CaCO3.
It indicates that the presence of the hexagonal structure of the CaCO3 phase increases.
However, the peak of the Faujasite structure decreases with the increase in CaCO3 concentration.
The decreases in the peaksAo intensity could be caused by the decrease in the relative crystallinity and/or the X-ray absorption by the metals (Huang et al.
, 2.
In addition, the phase interpretation of the detected XRD peaks also indicates that the CaCO3 was not converted to CaO during the calcination process .
alcination temperature of 550oC).
Table 2 shows the peaks analysis of HY, 5CaCO3/HY, 10CaCO3/HY, and 20CaCO3/HY catalysts and compares them with ICDD (International Center for Diffraction Dat.
Surface Area.
Pore Volume, and Pore Size Properties of Catalysts The catalysts were characterized by their surface area and pore size distribution using the N2 adsorption method and estimated using procedures of Brunauer-Emmett-Teller (BET) and Barret-Joyner-Halenda (BJH).
The characterization method was performed on HY, 5CaCO3/HY, 10CaCO3/HY, 20CaCO3/HY catalysts to determine their surface area, pore volume size, and pore size Figure 3(A) shows that all catalysts have the type IV isotherm profile of an N2 isothermadsorption, indicating the presence of microporous and mesoporous structures (AlOthman, 2.
In Figure 3(A), all catalysts tend to dip upwards at low p/po .
/po < 0.
which is attributed to the micropores filling.
However, this dip upward is significantly decreased as the increase in the CaCO3 It indicates that the micropores composition is decreased.
It is true since the micropore volume (Vmicr.
is significantly decreased after CaCO3 addition (Table .
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Figure 3.
(A) N2-sorption isotherm and (B) pore size distribution of the catalysts.
Table 3.
Characterization of surface area, pore volume, and pore size of the catalysts.
Catalysts 5CaCO3/HY 10CaCO3/HY 20CaCO3/HY SBET .
Smicro* .
Sext* .
dpA .
Vmicro* .
Vtotal .
*Based on t-plot method.
AAverage pore size using BJH-desorption data From Table 3, the effect of adding CaCO3 to the HY zeolite catalyst is indicated, which causes a decrease in surface area and pore volume by 226 m2/g and 0.
262 cm3/g.
The decreased surface area is caused by the metal agglomeration of CaCO3, while the decrease in the pore volume of the catalyst was caused by the micropore filling by CaCO3 particles during the impregnation process (Liu & Corma, 2.
According to research by Wang et al.
the addition of CaCO3 results in a reduction in surface area and pore volume, which is consistent with the results in this investigation.
It is conceivable for an uneven metal distribution on the catalyst surface to occur during the impregnation process when a relatively high metal concentration causes ion competition near the pore opening (Anggoro et al.
, 2.
Tsai .
also explained that CaCO3 particles have poorer pore properties than nitrogen probes and porous materials such as zeolites.
They suggested that the addition of CaCO3 into HY zeolite decreases the surface area and pore volume because of the pore filling.
Figure 3(B) shows the pore size distribution of HY, 5CaCO3/HY, 10CaCO3/HY, and 20CaCO3/HY catalysts.
The higher content of CaCO3 added to the HY catalyst decreases the catalyst surface area, because some micropores were blocked by CaCO3.
However.
Cheng et al.
explained that the size of the pores can be controlled by applying CaCO3.
Catalysts with mesoporous pore sizes have the advantage of adjusting the hydrocarbon distribution's porosity and acidity (Jun et al.
, 2.
Therefore, the addition of CaCO3 can increase the acidity (Lewis acid sit.
of the catalyst to produce the desired liquid fuel product (Kianfar et al.
Lewis acid site is provided by empty orbitals which can accept electron pairs.
Introducing transition metal on zeolite provides orbital which consists of a single electron in d orbital as active sites to homolytically dissociate hydrogen gas in a DOI: https://doi.
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Munnik et al.
found that the catalyst impregnation process mixture produced an aggregation on the catalyst surface.
Based on this finding related to the aforementioned literature, during the impregnation process with CaCO3, the macropore structure fills up on the catalyst's surface, which makes the mesoporous structure bigger.
Therefore, the addition of CaCO3 to the HY impregnation caused a decrease in the surface area and pore volume (Table .
, which was caused by covering the pores of HY zeolite with CaCO3 particles.
addition, the impregnation process causes the formation of agglomerations of metal particles on the catalyst surface which can increase the pore sizes.
Morphology Analysis of Catalysts Using SEM-EDX The SEM characterization was used to analyze the surface morphology and pore size distribution of the catalysts, while the elemental composition in the catalysts was analyzed using EDX.
Figure 4 shows the findings of SEM characterization for HY, 5CaCO3/HY, 10CaCO3/HY, and 20CaCO3/HY Figure 4(A) shows the SEM morphology of the original HY catalyst, which looks homogeneous, the crystallinity is sharper, and the morphological structure is cubic crystals with a particle size of 800A175 Oyebanji et al.
identified zeolite-Y with a similar particle size distribution as this Research by Oenema et al.
also suggested that zeolite-Y crystal size is between 200-1000 nm.
Figure 4(B-D) shows the catalysts of 5CaCO3/HY, 10CaCO3/HY, and 20CaCO3/HY with a hexagonal structure that produces an average particle size of 673A190 nm, 654A160 nm, and 770A211 nm.
Because of the covering catalyst surface by aggregate, the addition of more CaCO3 causes an increase in the particle size of the catalyst, leading to an uneven particle size distribution on the catalyst (Table .
Doyle et al.
postulated that contaminants in HY zeolite may have contributed to the agglomeration.
The aggregate particles on CaCO3/HY are formed from interconnected cubic and hexagonal This was also confirmed by XRD analysis results (Figure .
, which revealed the formation of HY with a cubic structure and CaCO3 with a hexagonal structure.
The energy dispersive X-ray (EDX) was used to determine the elemental composition of catalysts (HY, 5CaCO3/HY, 10CaCO3/HY, and 20CaCO3/HY), after being calcined at a temperature of 550 AC for 3 hours, while the composition results are tabulated in Table 4.
Based on Figure 5, the EDX results of the HY catalyst contains the elements of Si.
Al.
Cu, and O, while the 5CaCO3/HY, 10CaCO3/HY, and 20CaCO3/HY catalysts contain Si.
Al.
Ca.
Cu, and O.
The presence of calcium in CaCO3/HY catalysts suggests that CaCO3 was successfully impregnated on the HY catalyst, owing to the distribution of Ca metal inside the HY zeolite structure which is also confirmed by XRD Furthermore, the Si/Al ratios of HY, 5CaCO3/HY, 10CaCO3/HY, and 20CaCO3/HY catalysts are 26.
08, 29.
76, 20.
78, respectively.
The increased Si/Al ratio changes the acidic zeolite characteristics, resulting in a reduction in the concentration of Brynsted acid sites (Golubev et al.
, 2.
However.
Doyle et al.
stated that the increase in the Si/Al ratio of zeolite over 2.
5Ae10.
0 increased the strength of Brynsted acid, the hydrophobicity of the catalyst, and the number of acid sites.
Meanwhile, the Lewis acid site also increases with increasing Si/Al ratio (Hartanto et al.
Table 4 clearly shows that an increase in Al content during the CaCO3 impregnation on HY zeolite caused a lower Si/Al ratio, especially for 10CaCO3/HY and 20CaCO3/HY However, the CaCO3-modified catalysts had a higher Si/Al ratio than the original HY zeolite, because some Brynsted acid site protons of HY zeolite were substituted by Ca2 or the aluminum species is moved to extra-framework, resulting in a larger concentration of Lewis acid sites.
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(A)
Count (%) Diameter .
(B) Count (%) Diameter .
(C) Count (%) Diameter .
(D) Count (%) Diameter .
Figure 4.
SEM characterization results of catalysts: (A) HY, (B) 5CaCO 3/HY, (C) 10CaCO3/HY, dan (D) 20CaCO3/HY.
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Elemental composition of catalysts analyzed by EDX.
Elemental Composition Si/Al Ratio (% mas.
5CaCO3/HY (% mas.
10CaCO3/HY (% mas.
20CaCO3/HY (% mas.
(A) (B) (C) (D) Figure 5.
Elemental composition of catalysts: (A) HY, (B) 5CaCO 3/HY, (C) 10CaCO3/HY, and (D) 20CaCO3/H.
Analysis of Acidity and Basicity Strengths NH3and CO2probed Temperature Programmed Desorption (TPD) The acid and basic strengths of catalysts were determined using NH3-TPD and CO2-TPD methods, respectively, because of CaCO3 impregnation on HY zeolite (Figure 6 and Table .
According to Yi et al.
, there were three kinds of adsorbed species on alkaline metal oxide basic sites through CO 2TPD, including unidentate carbonate forms on surface O2Oe ions, bidentate carbonate forms on Lewis-acidAeBrynsted-basic pairs (Ca2 Ae O2O.
, and bicarbonate species on weak basic Concerning the cracking process, the Brynsted acid site is important according to Meng et al.
suggestion that the reaction conversion and product distribution of the cracking process may be controlled by adjusting the Brynsted acidity of zeolite HY.
general, a strong acid catalyst with a high concentration of Brynsted and/or Lewis acids sites of original or modified zeolite HY is needed for cracking hydrocarbon, while deoxygenation reaction pathway is tailored by strong basicity adjusted by CaCO3.
Based on the desorption temperature of NH3, the acid strength of NH3-TPD is classified as weak .
Ae300 AC), moderate .
Ae500 AC), and strong (>500 AC) acid sites (Suprun et al.
Meanwhile.
CO2-TPD-based basic strength is classified as weak .
Ae200 AC), moderate .
Ae400 AC), and strong (>400 AC) basic sites (Ezeh et al.
, 2.
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20CaCO3/HY 10CaCO3/HY 5CaCO3/HY 20CaCO3/HY 10CaCO3/HY 5CaCO3/HY (B) TCD Signal .
TCD Signal .
(A)
Temperature (AC) Temperature (AC) Figure 6.
Catalysts characterization results of acid and basic strengths using: (A) NH3-TPD and (B) CO2-TPD of catalysts.
Table 5.
Concentration distribution of acid and basic sites of catalysts based on the range of acidity and basicity strengths.
NH3-TPD .
Catalyst 5CaCO3/HY 10CaCO3/HY 20CaCO3/HY Weak Moderate Strong Total Acid Sites .
Figure 6 and Table 5 present the results of the NH3-TPD and CO2-TPD analysis of the Figure 6(A) shows that the total acid site concentrations of the HY, 5CaCO3/HY, 10CaCO3/HY, and 20CaCO3/HY catalysts are 558, 998, 875, and 833 mol/g, respectively.
The NH3-TPD results suggest that adding CaCO3 to the HY catalyst changes the acid strength of the catalyst, especially the strong acid site.
As presented in Table 5, the addition of CaCO3 increases the formation of strong acid sites, but it slightly appears in Figure 6(A).
It suggested that this acidity comes from the Lewis acid site of Ca2 from the bidentate carbonate which is in line with the results of Yi et al.
Furthermore, the change in the acid strength of catalysts affects the surface catalytic activity, especially for the cracking reaction pathway.
Zheng et al.
and Putluru et al.
explained that the weak acidity of zeolite-based materials is mainly attributed to the Brynsted acid site, while moderate and strong acidities are attributed to the Lewis acid site.
In addition.
Huang et al.
also explained that calcium carbonate on the catalyst surface is the dominating surface site and acts as a Lewis acid site.
Based CO2-TPD .
Weak Moderate Strong Total Basic Sites .
on these understandings, it is suggested that the strong acidity after CaCO3 addition to HY catalyst is attributed to the formation of the Lewis acid site.
Moreover, the addition of CaCO3 on zeolite enhances Lewis acid sites rather than Brynsted acid sites from HY.
Table 5 shows that the total basic sites of the catalysts of HY, 5CaCO3/HY, 10CaCO3/HY, and 20CaCO3/HY are 200, 402, 541, and 619 mol/g, respectively.
In the catalysts, the adsorbed CO2, which is desorbed at a lowtemperature range, indicates weak basicity, while the adsorbed CO2, which is desorbed at higher temperature ranges, indicates moderate and strong basicity (Charisiou et al.
Concerning the CaCO3 doped on HY catalyst characterization results.
Dias & Assaf .
also explained that Ca2 ions may enhance the ion density of the basic site of the catalyst leading to increased CO2 adsorption, which can support the decarboxylation reaction pathway of fatty acids.
In addition, the strong basic site plays a role in maintaining the stability of the catalyst and causes an increase in the activity of the catalyst concerning the deoxygenation reaction (Asikin-Mijan et al.
, 2020.
Wei et al.
, 2.
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The presence of CaCO3 on the surface of the HY zeolite modifies the zeolite's surface structure which in turn has an impact on the acidity and basicity of the catalyst.
After physically interacting with the neighboring Ca2 ion, the CO32Oe ion gets polarized and forms monodentate carbonate.
Monodentate carbonate attacks the oxygen atom that binds aluminum and silicon, puncturing the aluminum-oxygen bond and forming Lewis acid sites.
Additionally, the O 2Oe ions that are neighboring the Ca2 ions are polarized and fill the aluminum structure's lone pair.
Furthermore.
Ca2 ions attack the electrons of aluminum, resulting in the formation of Brynsted acid sites (Bonenfant et al.
, 2008.
Gallei & Stumpf, 1.
Moreover, the basic site which is adsorbed through the Lewis acid - Brynsted basic pair (Ca2 Ae O2O.
produces a weak basic site (Yi et al.
, 2019.
Puriwat et al.
specially diesel-range hydrocarbon.
The blank test at 450 AC was also included.
The blank test was conducted at the same feed flow rate as the catalytic test.
As presented in Figure 7, the utilization of catalysts slightly increases the yield of organic liquid product (OLP).
In addition, the yield of OLP as the addition of CaCO3 on HY catalysts is Using the catalysts of HY, 5CaCO3/HY, 10CaCO3/HY, and 20CaCO3/HY, the OLP yields were found to be 77.
41, 79.
53, and 76.
53%, respectively.
Higher CaCO3 concentration in the catalysts enhances the mesoporous structure by covering the micropore pores with CaCO3 aggregates which reduces surface area and pore volume, which results in the filling and blocking of micropores in the HY zeolite.
This is due to the addition of calcium carbonate producing more mesopore .
ee Table .
According to Twaiq et al.
, the increase in concentrations and strengths of acidic sites might result in over-cracking, resulting in a decrease in OLP production.
contrast, increasing the concentration of CaCO3 in the catalysts enhances the acidity and basicity of the catalyst (Figure .
As seen in Figure 7, the production of gas as calculated from mass balance increases as the CaCO 3 concentration increases.
The gas yields for the usage of HY, 5CaCO3/HY, 10CaCO3/HY, and 20CaCO3/HY catalysts are 18.
46, 17.
57, 16.
03%, respectively.
Catalyst Performance Testing for Cracking Palm Oil Process to DieselRange Hydrocarbons The HY, 5CaCO3/HY, 10CaCO3/HY, and 20CaCO3/HY catalysts were tested for cracking palm oil to produce liquid fuels Yield of OLP Yield of Coke Yield of Gas Yield of Water Yield (%) Blank 5CaCO3/HY 10CaCO3/HY 20CaCO3/HY Catalysts Figure 7.
Catalyst testing results for cracking palm oil to biofuels.
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Concerning coke formation during the cracking-deoxygenation process, the yields of coke formed on the catalysts of HY, 5CaCO3/HY, 10CaCO3/HY, and 20CaCO3/HY 17, 2.
21, 2.
39, and 2.
86%, respectively.
It shows that the highest coke yield is found by the 20CaCO3/HY catalyst.
It was reported that the optimum reaction temperature for chain scission of C=O in free fatty acids is between 350 and 375AC.
Thus, the reaction temperature above 400 AC results in the creation of coke due to the enhanced cracking process (Ramesh et al.
, 2019.
Khan et al.
In addition, as shown in Table 3, the surface area of the catalysts decreases and the average pore size increases as the increases of CaCO3 amount.
The CaCO3 aggregates cover the macropore size on the catalyst surface, increasing the mesopore structure and coke in the catalytic cracking process.
Therefore, the surface area and pore size of the catalyst could affect coke In addition, the highest strong acid site is shown on the 20CaCO3/HY catalyst (Figure .
It is well-known that the strong acid site enhances the cracking reaction pathway performance as well as coking formation.
was reported that coke increased due to the strong acidity of the catalyst, especially Lewis acid, which caused the cracking reaction (Istadi et al.
, 2021.
Therefore, the coke formation is affected by both surface area and acid site amount.
Furthermore, the yield of water over the usage of the 5CaCO3/HY, 10CaCO3/HY, and 20CaCO3/HY catalysts, which are 1.
96%, 2.
21%, 1.
80%, and 2.
25 %,
reaction as also supported by Hermida et al.
in which water yield is due to the water-gas shift reaction (WGSR) during the deoxygenation process.
However, the blank test does not produce water.
It indicates that the deoxygenation reaction might not occur.
Indeed, the catalyst performance test results presented show that increasing CaCO 3 concentration from 5% to 20% .
doped on the HY zeolite catalyst slightly increases the yield of gaseous products, coke, and water, but slightly decreased the yield of OLP or biofuel product.
Overall, this indicated that the cracking activity of the HY zeolite is slightly higher than that of the CaCO3/HY.
The triglyceride molecules are catalytically cracked at the catalyst surface, resulting in heavier hydrocarbons and oxygenated chemicals, such as fatty acids, ketones.
Additionally, secondary cracking converts the intermediate compounds into gaseous products (CO.
CO 2.
, paraffin, and olefins with long and short chains, water, and alcohols.
Effect of CaCO3 Modification of HY Catalyst on Hydrocarbons Composition Distribution of Biofuels in the OLP Product The hydrocarbon composition distribution in the OLP biofuel product is analyzed using Gas Chromatography-Mass Spectrophotometer (GC-MS) and reported in Figure 8.
Figure 8 explains the results of the catalyst performance test over the catalytic cracking-deoxygenation of palm oil.
In this catalytic reaction test, hydrocarbons-based fuel product is increased from 91.
14% to 56% because of the introduction of CaCO3 on the HY catalyst .
CaCO3/HY), while the composition of an oxygenated compound of biofuel decreased from 8.
85 to 5.
The detailed components of the OLP are presented in Table 6 based on GC-MS analysis.
The oxygen atom content of the liquid biofuel product decreases significantly when using 20CaCO3/HY catalyst from 0.
91 to 0.
This acid site supports the cracking and deoxygenation reaction pathways, while the high basic strength (Figure 6(B)) enhances the deoxygenation reaction mechanism including decarboxylation and decarbonylation.
These bifunctional roles of catalyst remove more oxygen atoms from palm oil as CO2 and CO molecules through the decarboxylation and DOI: https://doi.
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Composition distribution of hydrocarbon products .
t%) of Organic Liquid Product.
Table 6.
Composition of OLP by GC-MS analysis.
Components Molecular Formula Hydrocarbons Cyclopentene Cyclohexene 1-Hexene Hexane 1-Heptene Heptane 1-Octene Octane 3-Octyne, 2-methyl Cyclohexene, 3-propyl 1-Nonene Heptane, 2-4 Dimethyl Nonane Benzene, 2-ethenyl-1,4-dimethyl Cyclohexene, 3-.
-methylpropy.
Cyclopentene, 1-.
-Methylbuty.
1-Decene Cis-3-Decene Decane Benzene, pentyl Cyclohexene, 1-Pentyl Cyclopropane, 1-pentyl-2-propyl 5-Undecene Undecane Cyclopropane.
Nonyl
1-Dodecene 2-Dodecene 3-Dodecene Dodecane Benzene, heptyl
1-Tridecene C5H8
C6H10
C6H12
C6H14
C7H14
C7H16
C8H16
C8H18
C9H16
C9H16
C9H18
C9H20
C9H20
C10H12
C10H18
C10H18
C10H20
C10H20
C10H22
C11H16
C11H20
C11H22
C11H22
C11H24
C12H24
C12H24
C12H24
C12H24
C12H26
C13H20
C13H26
Composition .
t%) HY Catalyst 20CaCO3/HY Catalyst DOI: https://doi.
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Table 6 (Continu.
Composition of OLP by GC-MS analysis.
Components Tridecane Cyclotetradecane Tetradecane Cyclopentane, decyl 1-Pentadecene Cyclopentadecane Cyclohexene, 1-Decyl 3-Hexadecene Cyclohexadecane Hexadecane Cyclohexane, undecyl 1-Heptadecene 8-Heptadecene Heptadecene 1-Octadecene 9-Octadecene 1-Nonadecene Aldehyde 2-Propenal Ketone Tetracyclo .
]decan-10-one 2-Decanone Acids Decanoic Acid
Propandioic acid, dicyclohexyl ester
Alcohol
1-Tridecanol
1-Tetradecanol
1-Pentadecanol
1-Hexadecanol
1-Eicosanol
Molecular
Formula
C13H28
C14H28
C14H30
C15H30
C15H30
C15H30
C16H30
C16H32
C16H32
C16H34
C17H34
C17H34
C17H34
C17H36
C18H36
C18H36
C19H38
C3H4O
C10H12O
C10H20O
C10H20O2
C15H24O4
C13H28O
C14H30O
C15H32O
C16H34O
C20H42O
Concerning the HY and 20CaCO3/HY catalysts showing 91.
14 and 94.
hydrocarbon contents, respectively, although the catalyst surface area decreases (Table .
significantly, the pore size of catalysts increases from 2.
86 to 4.
62 nm due to CaCO3 introduction shifting to the heavier hydrocarbons range products .
iesel range rather than gasoline rang.
However, the CaCO3 introduction on the HY catalyst may affect the Lewis acid sites in improving the hydrocarbon yield (Phung et al.
, 2.
Based on Kianfar et al.
results, the addition of CaCO3 into ZSM-5 zeolite caused a decrease in surface area and increased heavy hydrocarbons by 38.
65%, which is in line with Composition .
t%) HY Catalyst 20CaCO3/HY Catalyst this study's results.
Asikin-Mijan et al.
also found that the Co-CaO catalyst has high catalytic activity in the deoxygenation reaction, resulting in a hydrocarbon product with a C15 C17 chain of 54%.
The presence of palm oil short-chain hydrocarbons (C3AeC.
suggests a hybrid role of cracking-deoxygenation reaction pathways.
The deoxygenation reaction pathway eliminated the carboxyl and carbonyl groups in the fatty acid, resulting in a hydrocarbon with one atom less carbon than the parent structure (C16 and C.
The crackingdeoxygenation reaction requires more Brynsted and Lewis acids sites .
igher acidity strengt.
, while the deoxygenation reaction DOI: https://doi.
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Therefore, these designed catalysts (CaCO3/HY) have the bifunctional roles required in cracking-deoxygenation reaction mechanisms.
From the crackingdeoxygenation reaction mechanisms, some gases were also formed in these findings, i.
(CO.
decarboxylation reaction pathway, carbon monoxide (CO) from the decarbonylation reaction pathway, and H2O from the hydrodeoxygenation reaction pathway due to role of self-produced hydrogen (H.
rom WGS reaction or dehydrogenation from fatty acids or hydrocarbon.
in the reaction.
Based on the GC-MS results (Figure .
, it is possible to shift cracking performance to lower chain (C16 hydrocarbo.
product when using the 20CaCO3/HY catalyst through scission of COeC as also suggested by SantillanJimenez & Crocker .
In this case, the oxygenated compounds, formed by catalytic cracking, diffuse into the pores of the CaCO 3modified HY catalysts and react with protons at the active sites through multiple reaction decarbonylation, and hydrodeoxygenation.
Therefore, the CaCO3 impregnated on the HY catalyst has bifunctional effects of the catalyst supporting cracking-deoxygenation reaction mechanisms as mentioned previously.
The role of 20CaCO3/HY as a bifunctional acidbasic catalyst is attributed to its higher activity in deoxygenation and cracking reaction Effect of CaCO3 Modification of HY Zeolite Catalyst on Hydrocarbons Product Selectivity The effect of CaCO3-modified catalysts on hydrocarbon .
fuel product selectivity is presented in Figure 9.
In the blank test, the selectivity of the diesel fraction was different, which was much lower than in a catalytic test.
However, the obtained diesel fraction is dominated by fatty acid because it is coagulated rapidly at room temperature.
The utilization of catalysts significantly increases the selectivity of diesel fraction.
addition, according to Figure 9, the doping CaCO3 on the HY catalyst increases dieselrange hydrocarbon product selectivity from 4 to 31.
88 %.
Compared to the other previous research on palm oil cracking, this study produces more diesel hydrocarbon fraction (Table .
This result demonstrates a synergistic effect of CaCO3 introduction and HY roles, which results in good selectivity in the shortchain hydrocarbons fraction and high activity in the cracking and deoxygenation reactions mechanism simultaneously.
Furthermore, the significant activities of cracking and .
ecarboxylation, decarbonylation, and hydrodeoxygenatio.
were enhanced by the high-strength acidity and basicity effects on the catalyst (Figure .
In this case, the high acidity strength promotes the diesel selectivity, whereas the high strength of basicity leads to the deoxygenation reaction.
The improvement in selectivity to diesel range hydrocarbons was caused by a larger pore size (Table .
Fathi et al.
also reported that the addition of CaCO3 on the HZSM-5 improved selectivity to gasoline.
They also reported that high selectivity of diesel towards short-chain hydrocarbon fraction was observed when using HY and modifiedCaCO3.
It was also reported that the diesel range hydrocarbon selectivity can be affected by the mesoporous distribution of the catalyst (Peng et al.
, 2.
Based on Figure 3(B), the 20CaCO3/HY has a larger pore size than the HY zeolite, which means that the impregnation of CaCO3 on the HY catalysts enhances the average pore size of the catalysts, although the surface area decreases.
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Selectivity of Diesel (%) Blank 5CaCO3/HY 10CaCO3/HY 20CaCO3/HY Catalysts Figure 9.
Effect of CaCO3-modified catalysts on diesel range hydrocarbons product selectivity.
Table 7.
Comparison of previous research on the cracking of palm oil into biofuel.
Temp.
(AC)
ZSM-5
HZSM-5
Ni/HY 5CaCO3/HY 10CaCO3/HY 20CaCO3/HY *n.
a : not available Catalyst Yield of OLP (%) Selectivity (%) Gasoline Kerosene Diesel The decreased catalyst surface area .
ompared to original HY catalys.
causes slight improvement of OLP or biofuel yield although the acidity strength of catalysts increased, while the increased catalyst average pore size leads to diesel hydrocarbon range selectivity.
Because of the catalyst pore selectivity point of view, the CaCO3/HY catalyst with high pore sizes may release the cracking product of long-chain hydrocarbons.
Furthermore, the CaCO3/HY catalyst has higher diesel selectivity than the HY catalyst due to pore size selectivity, as CaCO3/HY has larger pore size than HY catalyst, and the pore structure may affect the catalyst activity in the cracking reaction (Li et al.
, 2.
Li et al.
also reported that the large pore size causes the liquid product to be quickly released from the surface.
These findings may support improving catalyst stability of the Reference (Riyanto et al.
, 2.
(Bhatia et al.
, 2.
(Li et al.
, 2.
This study This study This study This study CaCO3/HY toward cracking deoxygenation of triglycerides due to its strong resistance to coke formation.
Proposed Reaction Mechanism of Catalytic Bifunctional CrackingDeoxygenation using CaCO3/HY Catalyst Figure 10 illustrates a proposed reaction mechanism of catalytic bifunctional crackingdeoxygenation over CaCO3/HY catalysts.
this reaction mechanism, the triglycerides are cracked through -elimination and formed into a long-chain fatty acid.
The COeC carbon chains of long-chain fatty acids are cracked through catalytic cracking reactions due to the roles of the high acid strength of acid sites (Brynsted and Lewi.
As a result of the breakage of the double bonds in unsaturated acids, smaller chains of the hydrocarbon product are formed.
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September 2023 Hal 281-306 Figure 10.
Proposed reaction mechanisms of catalytic cracking-deoxygenation over CaCO3/HY Concerning pathways.
Srihanun et al.
also reported that the deoxygenation process produces carbon dioxide (CO.
, carbon monoxide (CO), and water (H2O) as byproducts.
In the case of continuing cracking of the fatty acids after elimination, the deoxygenation reaction mechanism forms hydrocarbon chains containing C16-C18 carbon atoms, while the hydrocarbon chains below C15 are formed by the cracking (-scissio.
reactions (Istadi et , 2021.
Gosselink et al.
also explained that decreased C17 chain length and increased short hydrocarbon chains (C1AeC.
lead to stronger cracking activity due to the high strength of acidity catalyst properties, which is also confirmed in this study.
The main components of palm oil raw material are palmitic acid (C16:.
and oleic acid (C18:.
(Table .
, so it is possible to produce C15 and C17 hydrocarbons through cracking, decarboxylation, decarbonylation, and/or Furthermore, the long fatty acids, as intermediates after -elimination of triglyceride, are cracked via -scission, as well as decarboxylation, decarbonylation, and/or hydrodeoxygenation reaction to form shorter chain hydrocarbons with lower oxygen Moreover, the C O hydrogenolytic cleavage of the triglyceride molecule can also occur (Istadi et al.
, 2021.
According to these findings, a strong acid base also plays important role in controlling the reactivity of the deoxygenation reaction.
The CaCO3modified HY with high strong acid sites may convert the carboxylic acid groups to aldehydes and H2O by chemisorption of the oxygen, bound in the carboxylic acid, on the catalyst surface.
Catalyst Stability Test Catalyst stability is a critical issue in the palm oil cracking process, especially in the DOI: https://doi.
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CONCLUSION
Yield of OLP (%) Therefore, the designed catalysts (CaCO3modified HY) have the bifunctional roles required in cracking-deoxygenation reaction mechanisms, including carbon dioxide (CO .
removal through the decarboxylation reaction pathway, carbon monoxide (CO) removal through decarbonylation reaction pathway, and H2O removal from hydrodeoxygenation reaction pathway.
The significant activities of cracking and deoxygenation .
ecarboxylation, decarbonylation, and hydrodeoxygenatio.
were enhanced by the high strength of acidity .
ue to Lewis and Brynsted acid site roles of a combination of CaCO3 and HY) and basicity .
ue to CaCO3 rol.
affected on the catalyst.
the proposed reaction mechanism, the triglycerides are cracked through elimination forming long-chain fatty acid.
The COeC carbon chains of long-chain fatty acids are cracked through catalytic cracking reactions due to the roles of the high acid strength of acid sites (Brynsted and Lewi.
Furthermore, the long fatty acids, as intermediates after elimination of triglyceride, are cracked via scission, as well as decarboxylation, decarbonylation, and/or hydrodeoxygenation reaction to form shorter chain hydrocarbons with lower oxygen content.
Selectivity of Diesel (%) continuous catalytic cracking process.
In this study, the stability test was conducted to investigate the stability performance of 20CaCO3/HY catalyst to convert palm oil to biofuel as a function of time on stream (TOS).
The analysis was conducted for 23 h at 450 AC and WHSV of 0.
288 minOe1.
The yield of OLP and the selectivity of diesel fraction were monitored every 2 h of the continuous cracking process.
The profiles of the yield of OLP and the selectivity of diesel are presented in Figure 11.
The 20CaCO3/HY catalyst showed good catalyst stability.
The profile of the yield of OLP seems to be constant over the TOS of 23 h.
In addition, the catalyst has also good stability for diesel production.
As can be observed, the selectivity of diesel fraction decreases in a neglectable value over 23 h.
Therefore, it can be concluded that the 20CaCO3/HY catalyst has good stability for the palm oil cracking process to produce biofuel, especially in the diesel range.
Yield of OLP Selectivity of Diesel Time on Stream .
Figure 11.
Stability test result of 20CaCO3/HY catalyst for palm oil cracking process.
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ACKNOWLEDGMENT
The authors would like to express their sincere gratitude to Research Institution and Community Service.
Universitas Diponegoro.
Indonesia, for the financial support through the World Class Research Universitas Diponegoro (WCRU) research project category A with contract number: 11822/UN7.
1/PP/2021.
AUTHORSAo NOTE The author.
that there is no conflict of interest regarding the publication of this article.
The authors confirmed that the data and the paper are free of plagiarism.
REFERENCES