Production of Light Olefins from Catalytic Cracking Bio-oil Model

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Biofuels and Biomass

Production of light olefins from catalytic cracking biooil model compounds over La2O3-modified ZSM-5 zeolite Fuwei Li, Shilei Ding, Zhaohe Wang, Zhixia Li, Lin Li, Chong Gao, Ze Zhong, Hongfei Lin, and Congjin Chen Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.7b04150 • Publication Date (Web): 26 Apr 2018 Downloaded from http://pubs.acs.org on May 3, 2018

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Production of light olefins from catalytic cracking bio-oil model compounds over La2O3-modified ZSM-5 zeolite Fuwei Li,† Shilei Ding,† Zhaohe Wang,a Zhixia Li,†,* Lin Li,† Chong Gao,† Ze Zhong,† Hongfei Lin,‡ and Congjin Chen† †

School of Chemistry and Chemical Engineering, Guangxi University, Nanning 530004, People’s

Republic of China ‡

Guangxi Bossco Environmental Protection Technology Co., Ltd., Nanning 530007, People’s

Republic of China

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ABSTRACT Diminishing fossil fuel reserve and the increasing consumption of light olefins are driving an intensive research to find new non-petrochemical substitute resource to produce light olefins. Biomass-derived bio-oil is a promising substitute resource because of its renewable, abundance and carbon neutral. In this study, three bio-oil models: oleic acid (OA), methyl laurate (ML) and waste cooking oil (WCO) were catalytically cracked over La2O3-modified ZSM-5(LaZ) aiming for production of light olefins. The content of La2O3 in catalysts was adjusted to optimize the structure and properties of catalysts. The maximal light olefin yield was 131 mL/g for OA, 120 mL/g for ML and 128 mL/g for WCO, which was obtained over LaZ catalyst containing 6% of La2O3 (6LaZ). The maximal light olefin selectivity was 36.1% for OA, 30.3% for ML and 33.8% for WCO. The obtained light olefins mainly contained propylene (13.6−17.1%), ethylene (10.7−15.4%) and butene (5.3−6.3%). Aromatic hydrocarbons and graphite were respectively the main components in the liquid product and solid product (coke). 6LaZ exhibited better catalytic activity and anti-coking ability than La-free ZSM-5, which was attributed to its appropriate porosity and acidity. The unsaturated molecular structure of feedstock was found helping to improve light olefin yield. Our investigations are useful for developing new process route to produce light olefins from the renewable biomass resources.

Key words: light olefin; bio-oil; catalytic cracking; oleic acid; methyl laurate; waste cooking oil;


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1. INTRODUCTION Light olefins such as ethylene and propylene often used to produce polymers and organic products are important chemicals and raw materials in the petrochemical industry.1 Light olefins, as the side production of crude oil refineries, were traditionally produced by steam cracking and/or catalytic cracking of naphtha, light diesel and other petroleum products.2,3 Oil resource's gradual depletion and the increasing consumption of light olefins bring the huge challenge to the light olefin production industry. To find new substitute resource to produce light olefins are drawing more attention of researchers. Recently, non-petrochemical routes such as methanol to olefins, ethanol to olefins, dimethyl ether to olefins, catalytic cracking of alkanes and biomass to olefins have been widely developed.4−8 Owing to being cheaply available everywhere and a renewable energy source, biomass and biomass-derived bio-oil becomes ideal candidates as materials to produce light olefins.8-12 Huang et al.8 performed catalytic cracking of different lignocellulosic biomass (rice husk, sawdust, sugarcane bagasse, cellulose, hemicellulose and lignin) over La/ZSM-5, finding that light olefin yields for different feedstocks decreased in the order: cellulose > hemicellulose > sugarcane bagasse > rice husk > sawdust > lignin. The sugarcane bagasse obtained the highest olefin yield of 0.12 kg olefins/(kg dry biomass). Gong et al.11 carried out catalytic cracking of biomass-pyrolytic bio-oil over La/ZSM-5 to produce light olefins. With a nearly complete conversion of bio-oil, the maximum yield reached 0.28 ± 0.02 kg olefins/(kg bio-oil). Dong et al.12 investigated cracking of microalga and microalga-derived lipids over the modified ZSM-5 zeolite, demonstrating that, in comparison to microalga, cracking of microalga-derived lipids achieved much higher light olefin yield and selectivity (the highest selectivity and olefin yield was 57.1 % and 36.7 %, respectively). Some researchers concerned about the catalytic cracking of the bio-oil model compounds such as ethanol, butanol, phenols, acetone etc.5,13 Overall, compared with solid biomass, liquid bio-oil shows enormous potential as the raw material for the production of light olefins.


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Lignocellulosic biomass is natural polymer material, and the components in its pyrolysis biooil are very complex. Compared with biomass pyrolysis bio-oil, the vegetable oil and waste cooking oil (WCO) have relatively defined and stable chemical structure, and are another kind of plentiful, cheap and renewable resource. Millions of tons of WCO are produced every year in China. These low-grade WCO cannot be used as raw materials for the production of light olefins because they contain a higher content of oxygen and a lower H/C ratio in chemical composition. WCO mainly consists of triglycerides and a small amount of free fatty acids. Triglycerides contain long fatty acid chains with C=C bonds and carbon atom number varying from 14 to 22. This leads to the complexity in the catalytic cracking reaction of WCO.14 Catalytic cracking is a simple and efficient way to convert triglycerides-rich bio-oil to valuable materials. During catalytic cracking process, oxygen atoms in bio-oil are removed by releasing H2O, CO2 and CO via dehydration, decarboxylation and decarbonylation mechanisms, while the light olefin-rich gaseous products and aromatic compound-rich liquid products are formed.15,16 These gaseous and liquid products are potential resources for obtaining chemistry raw materials such as ethylene, propylene, and benzene, toluene and xylene (BTX). A lot of researches had revealed that the product distributions from catalytic cracking process were dependent on the natures of feedstocks and catalysts used. When the conventional FCC catalyst based on large pore zeolite Y (pore opening size of 0.74 nm) was used to treat the unsaturated triglyceride-rich feedstock, the yield and quality of gasoline-range hydrocarbons and light olefins were poor.17,18 The medium pore zeolite ZSM-5 with pore opening size of 0.52−0.56 nm was proved to be effective to promote the formation of C5-C10 gasoline-range hydrocarbons while inhibit the formation of aromatic species.19,20 In another report, hierarchical ZSM-5 with a high fraction of mesoporosity was used for cracking of triolein and WCO, higher selectivity toward the desired products, i.e., gasoline-range hydrocarbons and light olefins, was achieved than with commercial ZSM-5.21 Comparative studies had evidenced that the relatively small pore size of ZSM-5 tended to give a high gas yield with low concentrations of light olefins, which was thought to occur undesired


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secondary reactions due to the diffusion constraints imposed by the small pore size of ZSM-5.19 To alleviate the diffusion inhibition, ZSM-5 zeolite was modified by La incorporation, demonstrating that La introduction adjusted the pore size distribution and the acidity of ZSM-5, and consequently facilitated the formation of light olefins during cracking of bio-oil.11 Although a lot of research on catalytically cracking of bio-oil and its model compounds have been performed to study the cracking reaction mechanism. However, the obtained theory is still not sufficient for understanding the reaction pathway for cracking bio-oil with triglycerides chemical structure. In this work, we comparatively studied the catalytic cracking properties of three bio-oil models: oleic acid (OA), methyl laurate (ML) and WCO, over La2O3-modified ZSM-5 catalysts for production of light olefins. The effects of La2O3-loading amount on catalytic cracking behaviors of three model oils were investigated. The gas, liquid and solid products (coke) were analyzed to understand the reaction mechanism of bio-oil with triglyceride chemical structure. 2. MATERIALS AND METHODS 2.1. Materials. Oleic acid (OA), methyl laurate (ML) and lanthanum nitrate salt (La2(NO3)3.6H2O) were of analytical grade and used as received, which were purchased from Macklin chemical reagent factory (Shanghai, China). H-type ZSM-5 zeolite (SiO2/Al2O3=16.3) was obtained from Nankai University Catalyst Plant (Tianjin, China). ZSM-5 zeolite was activated at 105 °C for 90 min before use. WCO was collected from a chophouse close to Student Apartment of Guangxi University, and pre-treated as follows: 50 g WCO was mixed with 100 mL saturated salt water, and heated at 80 °C for 3 h under stirring. After standing and layering for 12 h, the upper oil was collected, and mixed with 100 mL of deionized water and 2.0 g of activated carbon; the mixture was heated at 80 °C for 3 h under stirring. The mixture was then filtered to remove insoluble material, and the liquid fraction underwent standing and layering. The obtained oil layer was evaporated at 100 °C for 1h under less pressure condition to remove water. The obtained oil sample was then dried in oven at 105 °C for 12 h, and used in the following experiments. ACS Paragon Plus Environment 5

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2.2. Synthesis of the La/ZSM-5 catalysts. La2O3-modified ZSM-5 (LaZ) catalyst was prepared by impregnation method. As a typical run, La2(NO3)3·6H2O in its desired amounts was dissolved in deionized water to form La salt solution. A certain amount ZSM-5 was then dispersed in the La salt solution. The mixed suspension was stirred at 40 °C for 30 min and 80 °C for 3 h to remove the water. The obtained solid samples were dried, tableted, and calcined at 550 °C for 5 h. The resultant catalysts were sieved to collect the particles passing through 20−40 mesh screen, and kept for the subsequent experiments. The La2O3 content in the resulting catalysts was 2, 6, 10 and 14%, respectively. The corresponding catalyst was denoted as 2LaZ, 6LaZ, 10LaZ and 14LaZ, respectively. 2.3. Characterization of the catalysts. Crystalline structure of samples was determined by Xray powder diffraction (XRD) using a Rigaku SmartLab3 instrument in the range of 10−50° at a scanning rate of 2°/min. The data of 10LaZ catalyst was set as a reference, the relative crystallinity of other catalysts was calculated by the ratio of the area of the large peaks at 2θ=20°−25° in XRD pattern of catalyst to that of the reference sample which was assumed to have a crystallinity of 100%. Lattice constants were calculated from Bragg formula: 2dsinθ = nλ.22 The actual contents of SiO2 (CSi), Al2O3 (CAl) and La2O3 (CLa) were determined by inductively coupled plasma optical emission spectroscopy (ICP-OES, PE Optima8000). The surface morphology of the catalysts was observed on Hitachi SU8220 scanning electron microscopy (SEM). N2 adsorption-desorption isotherms were performed at −196 °C employing the Quantachrome NOVA 2200e instruments. Before nitrogen adsorption, the samples were outgassed at 300 °C for 5 h. Specific surface area (SBET) was obtained from the adsorption branch by the Brunauer Emmett Teller (BET) method. The total pore volume (VTotal) was estimated at P/P0=0.99. The micropore volume (VMicro) and external surface area (SExternal) were derived from the isotherms by the t-Plot method. The mesopore volume (VMeso) was estimated from the difference between the VTotal and VMicro. Pore size distribution was obtained using Non-Local Density Functional Theory


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(NLDFT) model. Particle sizes (PSize) of catalysts were also estimated by using an equation: particle size (nm) = 3216/SExternal, as reported elsewhere.23 The ammonia temperature-programmed desorption (NH3-TPD) were carried out using a quartz tube reactor equipped with a Residual Gas Analyzer (RGA200, Agilent). Prior to adsorption experiments, 500 mg of catalyst were pretreated at 300 °C for 1 h in a He flow. Upon cooling to 110 °C, the samples were saturated with a NH3 flow for 1h, and then the NH3 of physisorption were removed through purging with He gas for 1h. The samples were then heated to 800 °C at a heating rate of 15 °C/min in He at a flow rate of 75 mL/min. The desorbed NH3 was absorbed in 100 mL HCl (0.01 M), and NaOH solution (0.01 M) was used to titrate the NH3-absorbed HCl solution. The total acidity was calculated from the amount of HCl and NaOH consumed. The distribution of the weak acid, medium acid, and strong acid was calculated from the peak area from Gaussian Fitting of the NH3-TPD profiles. 2.4. Catalytic cracking of three kinds of bio-oil samples. The catalytic cracking experiments were carried out in a fixed bed reactor. The system was mainly composed of a quartz tube reactor (inner diameter: 20 mm; length 380 mm), an electric heating sleeve, a syringe pump located on the top of reactor and a condenser. As a typical run, the reactor packed with 1.0 g catalyst was heated to 600 °C in N2 stream at a flow rate of 40 mL/min. 2 mL of oil sample (1.75 g) was then injected into the reactor by the syringe pump at a constant speed of 1 mL/min, and reacted for another 2 min. Thus, the total reaction time was 4 min and weight hourly space velocity (WHSV, ratio of mass flow rate of oil sample to weight of the catalyst) was 52.5 h−1. After flowing out from reactor, the products were cooled at about −8 °C. The obtained gas was collected with gas collecting bag, and its volume was recorded. Liquid products were weighed and analyzed. The deposited carbon (coke) on catalyst was calculated from the increase in weight of catalyst after reaction. The total gas production (TGP), light olefin selectivity (SLO), light olefin yield (YLO), liquid yield (YLiquid), gas yield (YGas) and coke yield (YCoke) were calculated by the following equations, respectively. TGP (mL/g) = VTG/M0

(1)


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SLO (%) = x(C2=) + x(C3=) + x(C4=)

(2)

YLO (mL/g) = VTG × SLO/M0

(3)

YLiquid (%) = (ML/M0) × 100 %

(4)

YCoke (%) = (Mc1 − Mc0)/M0 × 100 %

(5)

YGas (%) = 1 − YLiquid − YCoke

(6)

where VTG: total volume of gas product excluding N2 (mL); x: mole fraction of light olefins in gas product (%); M0: mass of oil sample (g); ML: mass of liquid product (g); Mc1:mass of catalyst after reaction (g); Mc0: mass of catalyst before reaction (g). 2.5. Stability experiments of catalysts. The used catalyst was regenerated as follows: the used catalyst was packed in a quartz tube, and heated at 550 °C for 3 h in air airstream at a flow rate of 10 mL/min. The regenerated catalyst was then reused for catalytic cracking of three oil samples. Ten consecutive cracking-regeneration cycles were carried out to estimate the stability of catalysts. 2.6. Product analysis. The gaseous hydrocarbon products were analyzed using a gas chromatography (GC, FULI-9790II) equipped with a flame ionization detector (FID) and a capillary column of HP-PLOT/Q. Meanwhile, a GC equipped with a packed column (TDX-01) connected with a Residual Gas Analyzer (RGA, RGA200, Agilent) was used to separate and analyze CO, CO2, N2 and He (carrier gas). The following temperature program was used: hold at 25 °C for 4 min, heated to 240 °C at 15 °C/min, and hold at 240 °C for 15 min. The qualitative and quantitative analysis was performed using the standard gases (CH4, C2H4, C2H2, C2H6, C3H8, C3H4, C3H6, C4H8, C4H10, CO, CO2, and He). WCO sample and the liquid product was firstly methyl esterified according to the standard methods of GB/T 17376-2008. The components in products were analyzed by GC-MS (GC7820A, MS5977E, Agilent) equipped with HP-5MS (30 m × 250 µm × 0.25 µm) capillary column. The inlet and detector temperature was maintained at 290 °C. The oven temperature program was set as follows: hold at 60 °C for 5 min, heated to 280 °C at 10 °C/min, and hold at this temperature for 5 min.


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The thermal stability of coke was analyzed in a 30/70 (v/v) mixture of O2/N2 by Thermogravimetric Analysis (TGA, 209F3, Tarsus). Temperature-programmed oxidation (TPO) experiments were carried out to analyze the properties of coke on catalysts. In details, 0.2 g of the used catalysts was packed into a quartz tube reactor, treated at 300 °C for 1h and cooled to room temperature in He flow. Then, the quartz tube was temperature programmed at a rate of 10 °C/min from 100 °C to 800 °C in a 5% O2/He mixed atmosphere. The released CO, CO2 and H2O were online monitored by RGA. 3. RESULTS AND DISCUSSION 3.1. Characterization of the catalysts. The XRD spectra of LaZ catalysts along with La2O3free ZSM-5 are shown in Figure 1. Intense characteristic peaks designated as ZSM-5 (2θ at 23.1°, 23.4°, 23.8°, and 24.0°) are observed in all samples. Single peak at 24.5° indicates that all catalysts belonged to a typical orthorhombic phase. As La2O3 content increases from 0% to 14%, the XRD peaks due to ZSM-5 firstly enhance slightly and then decrease. The lattice parameters of catalysts were calculated and depicted in Table 1. Compared to ZSM-5, the 6LaZ has higher lattice constants and lattice volume. This might be because La3+ enters into the channels of ZSM-5 during the impregnation process, and the larger ion radius of La3+ (than H+) helps to enlarge the pore radius of ZSM-5 lattice.24 Besides, no obvious diffraction peaks of La2O3 are observed, indicating that La2O3 might be highly dispersed in ZSM-5 support.25 SEM micrographs of ZSM-5 and 6LaZ are shown in Figure 2. Both catalysts consists of irregular shaped particles with particle size of about 0.5−2 µm. Most of those larger particles are in fact the agglomerate of smaller particles. La-incorporation did not change the crystal shape of catalysts obviously. As shown in Figure 2(d), some tiny granules are observed on the surface of ZSM-5 support, which are likely due to the formation of nanosized La2O3.22 Some nanosized La2O3 particles could exist in the gap between micron-sized agglomerated particles as shown in the dark region of the images, and could not be observed in SEM images.26


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Figure 3 illustrates the pore size distribution and nitrogen adsorption−desorption isotherms for each catalysts. The major pore diameter is around 3 nm for all catalysts. All catalysts represent an isotherm type of IV with hysteresis loops at high relative pressure (P/P0=0.4−0.99), which indicate the existence of mesoporous structure. Table 2 summarizes the compositions and physicochemical properties of the catalysts. The actual Si/Al2 ratios of catalysts ranged from 15.5 to 16.3. The real La2O3 contents in 6LaZ, 10LaZ and 14LaZ were 3.26%, 7.46% and 12.79%, respectively, which were lower than the theoretical calculating value. The VMeso of La/ZSM-5 increased by 1.3%−3% compared to ZSM-5, probably owing to sight desilication of ZSM-5 skeleton structure during impregnation process.4,27 In addition, when La2O3 content increases from 0 to 14%, the VTotal, SBET and VMicro decreased significantly. This may be due to the fact that the small La2O3 particles could easily be deposited in the pores and subsequently block the pores in the supports. These results show that the textural properties of catalysts can be controlled by changing the La2O3 content. Besides, it should be noted that incorporation of La2O3 did not cause an obvious change in particle size. Figure 4 and Table 3 show the NH3-TPD results of catalysts. Several continuous NH3 desorption peaks are observed in the temperature range from 150 °C to 700 °C for all the catalysts, indicating the presence of different acid sites on catalysts due to different NH3 absorption intensity. The peaks appear the maximums in the following ranges: low temperature region (150−260°C), medium temperature region (260−430°C) and high temperature region (430−700°C). The low, medium and high temperature regions are assigned to desorption of NH3 from weak, medium and strong acid sites, respectively.28 It can be seen that increasing La2O3 content caused an increase in the acidities of weak acid and medium acid sites, and a decrease in the acidity of strong acid sites, but did not affect the total acidities of the catalysts significantly. 3.2. Catalyst performance. Three bio-oil models (OA, ML and WCO) were catalytically cracked at 600 °C in N2 stream over La2O3-free and La2O3-modified ZSM-5 catalysts. Total gas production (TGP), light olefin yield (YLO) and gaseous product distribution are summarized in ACS Paragon Plus Environment 10

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Table 4. The composition of liquid products obtained over 6LaZ is shown in Table 5. These data were further classified and the results are present in Figure 5. 3.2.1. Catalytic conversion of oleic acid (OA). The main gas products contained light olefins (C=2-4) such as ethylene (C2H4), propylene (C3H6) and butene (C4H8), and light alkanes (C1-4) such as methane (CH4), propane (C3H8) and butanes (C4H10). Some other gas compounds such as n-pentane, isobutylene and butadiene were also probably formed but could not be identified with the present standard gas.29 As shown in Table 4, the maximum TGP and YLO were 381 mL/g and 131 mL/g, respectively, which were obtained over 6LaZ. Meanwhile, the selectivity to C=2-4 increased from 28.3% to 36.1% with the rise of La2O3 content from 0 to 10% (Figure 5a). Besides, the C3H6 selectivity increased whereas C1-4 selectivity decreased with increasing the La2O3 content. This indicates that the catalytic activity of ZSM-5 was promoted by La2O3 incorporation. Among three oil samples, OA obtained the highest C=2-4 yield and selectivity over 6LaZ than ML and WCO, indicating that OA was better as feedstock to produce light olefins. As shown in Figure 5(d) and Table 5, liquid products from cracking OA contained 88.3−92.5% aromatic hydrocarbons (mainly indenes, naphthalenes, BTX and its derivatives), 3.2−6.4% esters (mainly methyl laurate), and a small amount of alkanes and other substances (2.6−5.3%). A higher selectivity to BTX (65%) was achieved on ZSM-5 and 6LaZ. Based on product analysis and previous reports, the proposed reaction pathway for OA conversion is given in Scheme 1. Since LaZ catalyst provided a lot of acid sites and metal sites, OA could be either directly decomposed to hydrocarbons on these active sites by releasing CO2 via decarboxylation mechanism (Scheme 1, R1.A),15 or firstly decomposed to long‐chain ketones and aldehydes (Scheme 1, R1.B), which were then converted to hydrocarbons through thermal and catalytic processes.14,30,31 The R1.A mainly represented the process: because of the high electron density C=C bond and –COOH in OA are easily activated by acidic active sites on the surface of catalysts. This leads to C–C bond breaking occurring at the β position of C=C and α position of – COOH in the chain.14 Consequently, short chain hydrocarbons and CO2 are formed. The R1.B ACS Paragon Plus Environment 11

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represented another possible process: the acidic protons (H+) provided by catalysts firstly interact with oxygen in –COOH (with the lone pair electrons), leading to the formation of aldehydes and ketenes (reduction and dehydration reaction), which are followed by C–C bond breaking at the β position of C=C and decarbonylation reaction of aldehyde and ketene functional groups. As a result, short chain hydrocarbons and CO are formed. These short chain hydrocarbons, in turn, could be cracked to light olefins and alkanes, while those products could further produce aromatic hydrocarbons through a series of reactions such as oligomerization, cyclization, and aromatization.31 It is noteworthy that propylene and ethylene are the predominant light olefin products. The formation of propylene on ZSM-5 catalyst is considered to follow carbonium mechanism.31 Compared to ZSM-5, propylene and butene selectivity in products from 6LaZ and 10LaZ increase, indicating that catalytic function of ZSM-5 zeolite is enhanced by La2O3 incorporation. As seen from Table 4, more CO2 and less CO is released with increasing La2O3loading amount, suggesting that decarboxylation reaction (Scheme 1, R1.A) is enhanced, whereas decarbonylation reaction (Scheme 1, R1.B) is weakened by La2O3 incorporation. 3.2.2. Catalytic conversion of methyl laurate (ML). Figure 5(b) shows gaseous product distribution for catalytic cracking of ML over LaZ catalysts with different La2O3 content. As seen in Table 4, the highest TGP and YLO were 407 mL/g and 120 mL/g, respectively, which were obtained over 6LaZ. 6LaZ catalyst achieved the highest C=2-4 selectivity (30.3%) and C3H6 selectivity (14.3%) within the tested catalysts. Compared with the La2O3-free ZSM-5, the YLO over 6LaZ increased by 56.8 %, indicating that the catalytic activity of ZSM-5 was markedly promoted by incorporation of La2O3. In addition, compared to OA, gas products from ML over all catalysts contained a higher content of CO and a lower content of CO2. This indicates that compared to –COOH group in OA, – COOCH3 group in ML tends to deoxygenate via decarbonylation mechanism. The high gas yield of ML is probably related to the shorter fatty acid carbon chain in its molecular structure. The C12 fatty acid chain in ML is easily broken from the C–C bond at the center of the chain to form gaseous hydrocarbons.


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As can be seen in Figure 5(d), compared to OA, less formation of aromatic compounds in liquid product is likely attributed to the saturated property of fatty acid chain in ML. Ordinarily it is more difficult to form light olefins through breaking a saturated carbon chain than an unsaturated one, and these light olefins are important precursors to produce aromatic compounds. For the same reason YLO from ML decreased and companied with an increase in the content of other gas compounds (Table 4). The LaZ catalysts provides acidic protons (H+), and thus light olefins and aromatic compounds can be produced through cracking ML according to the following pathways: ML could be either directly decomposed to hydrocarbons by releasing CO2 via decarboxylation reaction (Scheme 1, R2.A), or firstly decomposed to long-chain aldehydes and ketenes, which were then converted to hydrocarbons by releasing CO through decarbonylation reaction(Scheme 1, R2.C).12,14 ML could be decomposed to long-chain fatty acid and methanol (Scheme 1, R2.B) through breaking C–O bonds in the –COOCH3 group.12,14 Then the long‐chain fatty acid underwent further decomposition to produce short chain hydrocarbons according to a similar reaction pathway to R1.B. The methanol could be converted to methane and light olefins.23,32,33 These short hydrocarbons, afterwards, could be cracked to light olefins and alkanes, while those products could react further to produce aromatic hydrocarbons as discussed in previous section of OA. Compared with OA, cracking ML over all catalysts formed a higher content of CO, indicating that cracking reaction mainly followed the pathway of R2.B and R2.C. However, as seen in Table 5, a few of intermediates such as aldehydes and ketones are present in liquid products. It can be inferred that decarbonylation and subsequent cyclization of these intermediates are, under the experimental conditions, faster than the formation of these intermediates. 3.2.3. Catalytic conversion of WCO. After methyl esterification, WCO mainly contains methyl palmitate (C16:0, 29.3%), methyl oleate (C18:1, 45.1%), 9,12-octadecadienoic acid (Z,Z)-, methyl ester (C18:2, 14.5%), and methyl stearate (C18:0, 4.6%). It can be found that about 60% of fatty acid chain in WCO contain the unsaturated C=C bonds.


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As can be seen in Table 4, the maximum TGP and YLO from cracking WCO were 390 mL/g and 128 mL/g, respectively, which were obtained over 6LaZ catalyst. The highest C=2-4 selectivity (33.8%) and C3H6 selectivity (15.6%) were also obtained over the 6LaZ catalyst (Figure 5c). These results indicate the higher activity of 6LaZ. A similar C2H4 selectivity was obtained over all catalysts irrespective of La2O3 content, suggesting that La2O3 introduction mainly affected the formation of C3H6. In other words, instead of thermal decomposition, catalytic cracking activities of catalysts were significantly promoted by La2O3 incorporation.11,31 Besides, the selectivity to C1-4 was weakened while the formation of CO2 was enhanced with increasing La2O3 content. These trends were also observed for the other two oil samples. These results indicated that the incorporation of La2O3 in ZSM-5 suppressed the secondary cracking of light olefins, and also promoted the decarboxylation reaction. As can be seen from Table 5 and Figure 5(d), the liquid products mainly contain 77−87% aromatic hydrocarbons, 10−18% esters (including methyl laurate, methyl octadecadienoate, methyl hexadecanoate, methyl stearate), and a small amount of other components (1.4−4.4%). Compared to ML, more aromatic compounds are formed in liquid product from WCO, which is likely attributed to the unsaturated property of fatty acid chains in WCO. As previously analyzed, 60% of fatty acid chains in WCO contain C=C bonds, and the unsaturated carbon chain tends to break to form light olefins which are then converted to aromatic compounds. A considerable amount of esters exist in liquid products, indicating an incomplete conversion of WCO. The reaction condition needs to be further optimized for effective conversion. The possible reaction pathway of catalytic cracking of WCO is given in Scheme 2. Triglyceride could be thermally decomposed to monoglycerides and long-chain fatty acids via breaking C−O bonds at the position of backbone of triglycerides. The monoglycerides were subsequently converted to long-chain ketenes and acrolein. Acrolein could undergo further decarbonylation reaction to yield C2H4 and CO. The long-chain fatty acids followed a similar pathway to R1.A and R1.B (in Scheme 1) to form short chain hydrocarbons through


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decarbonylation, decraboxylation, dehydration and cracking reaction. The gaseous hydrocarbons (olefins and alkanes) and aromatic hydrocarbons were formed by further cracking of the short chain hydrocarbons.12 It was noticed that C2H6 was not detected in the gaseous products from cracking the three oil samples, which is likely due to the formed C2H6 reacting further with other intermediates from cracking process. Smaller hydrocarbon molecules, such as CH4 and C2H6, likely react with each other to generate active free radicals of ·C3H7, and furthermore, transferred to C6 or C6+ liquid hydrocarbons.34, 35 These light liquid and gaseous hydrocarbons (alkanes and olefins) could react to produce aromatic hydrocarbons in the pores of the zeolite catalysts through a series of reactions such as oligomerization, cyclization and aromatization.12,31 Among the tested catalysts, the 6LaZ catalyst achieved the highest YLO: 131 mL/g for OA, 120 mL/g for ML and 128 mL/g for WCO, respectively, indicating that 6LaZ was the optimized catalyst for three oil samples. As shown in Table 3, the increase in the active sites, including the medium acid sites and metal sites, was probably responsible for the high catalytic activity of 6LaZ. The obtained results were compared with those presented in literatures. The results are shown Table 6. The yield obtained in this study is 0.197∼0.209 kg olefins/(kg bio-oil), which are closed to those obtained from cracking of bio-oil11 and waste cooking oil,20 and much higher than those obtained from cracking of lignocellulosic biomass.8 The results show that it is more effective to convert biooil to light olefin than solid biomass as feedstock. The differences on yield and selectivity could be caused by different reaction conditions. 3.3. Coke analysis. The thermal stabilities of the used 6LaZ catalyst and La-free ZSM-5 were investigated by TGA and TPO to determine the potential carbon deposition (coke) and its composition. The mass loss accompanied with the corresponding DTG curves of the used catalysts from cracking three oil samples are shown in Figure 6. The mass loss below 300 °C belongs to sufficient removal of physically adsorbed water. The mass loss between 300 °C and 800 °C is attributed to the burning of coke. The amount of coke can be calculated accurately by the mass loss


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

of catalyst in the temperature range between 300 °C to 800 °C. As seen in Figure 6, the used 6LaZ shows a lower oxidative decomposition temperature than the used ZSM-5 regardless of oil samples, indicating that the coke deposited on 6LaZ can be easier oxidized than that deposited on ZSM-5. Besides, the amounts of coke deposited on 6LaZ from three oil samples is 7.2 mg for OA, 7.8 mg for ML and 12.0 mg for WCO, which is respectively 0.26%, 0.19% and 1.7% lower than those deposited on ZSM-5. This indicates that 6LaZ has better anti-coking ability. Furthermore, it can be seen that the mass loss of the used 6LaZ between 300−800 °C shows two stages: a slow decrease at temperature range of 300−500 °C, and a rapid decrease in 500−620 °C. The former is likely attribute to the oxidation of light coke in the form of cracking intermediates and the latter is probably due to the oxidation of heavy coke corresponding to the stable graphite.36, 37 By contrast, more heavy coke is formed on ZSM-5, which is likely owing to the strong acidity of ZSM-5. The strong acid sites trend to promote various secondary reactions, e.g., cyclization, oligomerization and hydrogen transfer.38 6LaZ has higher mesoporous volume and more medium acid sites. The mesoporous structure is helpful for the diffusion of bulkier molecules in pore and protects against forming coke on catalysts.39 The appropriate porous and acidic properties are responsible for less coke formation and the higher catalytic activity of 6LaZ. Figure 7 shows TPO profiles of the used ZSM-5 (UZSM-5) and used 6LaZ (U6LaZ) after cracking of the three oils: OA, ML and WCO. CO and CO2 are respectively detected due to incomplete and complete oxidation of the coke. H2O is not detected in TPO curves, indicating few H contained in coke. These results suggest that graphite is the main component in the coke deposited on present catalysts.37 If considering the peak areas, the order of the total peak area of CO and CO2 in TPO curves of three oil samples is: WCO > ML > OA. This suggests that more graphite-type carbon is formed in catalytic cracking process of WCO and ML. For three oil samples, the temperatures corresponding to peak height (Tp) in TPO curve of 6LaZ catalyst shift towards lower temperatures (565 °C), compared to that of ZSM-5 (600 °C), indicating some thermooxidative sensitive light compounds formed on 6LaZ.40 This is essentially in agreement with the


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result from previous TG-DTG analysis (the used 6LaZ has a lower oxidative decomposition temperature than the used ZSM-5). A much stronger CO peak than CO2 was observed on TPO curve of ZSM-5, but this did not be observed for 6LaZ. This suggests that the coke deposited on ZSM-5 is extremely stable, and is difficult to be oxidized completely. 3.4. Stability of the catalyst. Catalyst poisoning can be induced by CO gas evolved during reaction or adsorption of the compounds with C=C bond in molecular structure such as alkenes and aromatic compounds. The stability of catalyst was determined by repeating the cracking and regeneration experiments for ten times using three oil samples over the optimized 6LaZ catalyst. TGP, YLO and gaseous product distribution along with the cycle number are shown in Figure 8. As seen in Figure 8(a), TGP for three oil samples decreased less than 9%, while YLO decreased 18.7% for OA, 14.4% for ML and 14.5% for WCO after ten cycles. This could be since the coke was not completely removed by regeneration in air at 550°C, and a temperature about 565°C was required for the complete oxidation of the coke as indicated by TPO analysis. Besides, C =2-4 and C3H6 selectivity slightly decreased while C2H4 selectivity remained no obvious change with increasing cycle number for three oil samples. These results show that the present catalyst has good stability and reusability. 4. CONCLUSION Light olefins were produced from catalytic cracking OA, ML and WCO over La2O3-modified ZSM5. The mass fraction of La2O3 was optimized at a range from 2% to 14%. The maximal light olefin yield was 131 mL/g for OA, 120 mL/g for ML and 128 mL/g for WCO, which was obtained over 6LaZ catalyst. The maximal light olefin selectivity was 36.1% for OA, 30.3% for ML and 33.8% for WCO. The obtained light olefins mainly contained propylene (13.6−17.1%), ethylene (10.7−15.4%) and butene (5.3−6.3%). OA and WCO gained a higher light olefin yields, which was attributed to the unsaturated properties in chemical structure. 6LaZ exhibited better catalytic activity and anti-coking ability than La-free ZSM-5, which was associated with its appropriate porosity and acidity. A considerable of aromatic hydrocarbons were formed during cracking of three oil samples. ACS Paragon Plus Environment 17

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How to suppress the formation of aromatic hydrocarbons will become a key issue on improving light olefin yield. In the future research, the effects of process condition such as reaction temperature and liquid hourly space velocity will be investigated to further improve the conversion and light olefin yield.

AUTHOR INFORMATION Corresponding Author *Tel.: +86 771 3274209. E-mail: [email protected].

Notes The authors declare no competing financial interest.

■ACKNOWLEDGEMENT The authors are grateful for supports from the National Natural Science Foundation of China (21566004 and 21266002), the Guangxi Natural Science Foundation (2015GXNSFAA139036) and the Scientific Research Foundation of Guangxi University (XGZ120081, XTZ140787). ■REFERENCES (1) Corma, A.; Melo, F. V.; Sauvanaud, L.; Ortega F. Light cracked naphtha processing: controlling chemistry for maximum propylene production. Catal. Today 2005, 107−108, 699−706. (2) Park, Y. K.; Lee, C. W.; Kang, N. Y.; Choi, W. C.; Choi, S.; Oh, S. H.; Park, D. S. Catalytic cracking of lower-valued hydrocarbons for producing light olefins. Catal. Surv. Asia 2010, 14, 75−84. (3) Rahimi, N.; Karimzadeh, R. Catalytic cracking of hydrocarbons over modified ZSM-5 zeolites to produce light olefins: A review. Appl. Catal. A: Gen. 2011, 398, 1−17. (4) Wang, J.; Zhong, Z. P.; Ding, K.; Zhang, B.; Deng, A.; Min, M.; Chen, P.; Ruan, R. Successive desilication and dealumination of HZSM-5 in catalytic conversion of waste cooking oil to produce aromatics. Energ. Convers. Manage. 2017, 147, 100−107. (5) Sousaa, Z. S. B.; Veloso, C. O.; Henriques, C. A.; Teixeira da Silvaa, V. Ethanol Conversion into olefins and aromatics over HZSM-5 zeolite: Influence of reaction conditions and surface reaction studies. J. Mol. Catal. A: Chem. 2016, 422, 266−274. (6) Al-Dughaither, A. S.; De-Lasa, H. Neat dimethyl ether conversion to olefins (DTO) over ACS Paragon Plus Environment 18

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over MFI, BEA, and FAU. Appl. Catal. A: Gen. 2010, 384, 206−212. (20) Idem, R. O.; Katikaneni, S. P. R.; Bakhshi, N. N. Catalytic conversion of canola oil to fuels and chemicals: Roles of catalyst acidity, basicity and shape selectivity on product distribution. Fuel Process. Technol. 1997, 51, 101−125. (21) Vu, H. X.; Schneider, M.; Bentrup, U.; Dang, T. T.; Phan, B. M. Q.; Nguyen, D. A.; Armbruster, U.; Martin, A. Hierarchical ZSM-5 materials for an enhanced formation of gasoline-range hydrocarbons and light olefins in catalytic cracking of triglyceride-rich biomass. Ind. Eng. Chem. Res. 2015, 54, 1773−1782. (22) Liu, D. J.; Zhou, W. G.; Wu, J. La2CuO4/ZSM-5 sorbents for high-temperature desulphurization. Fuel 2016, 177, 251–259. (23) Losch, P.; Boltz, M.; Bernardon, C.; Louis, B.; Palčić, A.; Valtchev, V. Impact of external surface passivation of nano-ZSM-5 zeolites in the methanol-to-olefins reaction. Appl. Catal. A: Gen. 2016, 509, 30−37. (24) Tynjälä, P.; Pakkanen, T. T. Acidic properties of ZSM-5 zeolite modified with Ba2+, Al3+ and La3+ ion-exchange. J. Mol. Catal. A: Chem. 1996, 110, 153−161. (25) Liang, T.; Chen, J.; Qin, Z. F.; Li, J.; Wang, P.; Wang, S.; Wang, G. F.; Dong, M.; Fan, W. B.; Wang, J. G. Conversion of methanol to olefins over H-ZSM-5 zeolite: reaction pathway is related to the framework aluminum siting. ACS Catal. 2016, 6, 7311−7325. (26) Li, X.; Li, B. S.; Xu, J. Q.; Wang, Q.; Pang, X. M.; Gao, X. H.; Zhou, Z. Y.; Piao, J. R. Synthesis and characterization of Ln-ZSM-5/MCM-41 (Ln=La, Ce) by using kaolin as raw material. Appl. Clay Sci. 2010, 50, 81−86. (27) Cabral de Menezes, S. M.; Lam, Y. L.; Damodaran, K.; Pruski, M. Modification of HZSM-5 zeolites with phosphorus. 1. Identification of aluminum species by 27Al solid-state NMR and characterization of their catalytic properties. Micropor. Mesopor. Mat. 2006, 95, 286−295. (28) Huang, Z.; Ding, S.; Li, Z.; Lin, H.; Li, F.; Li, L.; Zong, Z.; Gao, C.; Chen, C.; Li, Y. Catalytic conversion of stearic acid to fuel oil in a hydrogen donor. Int. J. Hydrogen Energ. 2016, 41, 16402−16414. (29) Vu, X. H.; Nguyen, S.; Dang, T. T.; Phan, B. M. Q.; Nguyen, D. A.; Armbruster, U.; Martin, A. Catalytic cracking of triglyceride-rich biomass toward lower olefins over a Nano-ZSM-5/SBA15 analog composite. Catalysts 2015, 5, 1692−1703. (30) Yan, H.; Feng, X.; Liu, Y.B.; Yang, C.H.; Shan, H.H. Catalytic cracking of acetic acid and its ketene intermediate over HZSM-5 catalyst: A density functional theory study. Mol. Catal. 2017, 437, 11−17. (31) Dong, X. L.; Chen, Z. A.; Xue, S.; Zhang, J. L.; Zhou, J. N.; Liu, Y. A.; Xu, Y. P.; Liu, Z. M.


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Catalytic pyrolysis of microalga chlorella pyrenoidosa for production of ethylene, propylene and butene. RSC Adv. 2013, 3, 25780−25787. (32) Bjørgen, M.; Svelle, S.; Joensen, F.; Nerlov, J.; Kolboe, S.; Bonino, F.; Palumbo, L.; Bordiga, S.; Olsbye, U. Conversion of methanol to hydrocarbons over zeolite H-ZSM-5: On the origin of the olefinic species. J. Catal. 2007, 249, 195−207. (33) Hwang, A.; Kumar, M.; Rimer, J. D.; Bhan, A. Implications of methanol disproportionation on catalyst lifetime for methanol-to-olefins conversion by HSSZ-13. J. Catal. 2017, 346, 154−160. (34) Kubátová, A.; Št’ávová, J.; Seames, W. S.; Luo, Y.; Sadrameli, S. M.; Linnen, M. J.; Baglayeva, G. V.; Smoliakova, I. P.; Kozliak, E. I. Triacylglyceride thermal cracking: pathways to cyclic hydrocarbons. Energ. Fuel 2012, 26, 672−685. (35) Wang, C. M.; Wang, Y. D.; Xie, Z. K. Insights into the reaction mechanism of methanol-toolefins conversion in HSAPO-34 from first principles: Are olefins themselves the dominating hydrocarbon pool species? J. Catal. 2013, 301, 8−19. (36) Du, S. C.; Gamliel, D. P.; Giotto, M. V.; Valla, J. A.; Bollas, G. M. Coke formation of model compounds relevant to pyrolysis bio-oil over ZSM-5. Appl. Catal. A: Gen. 2016, 513, 67−81. (37) Kim, S.; Sasmaz, E.; Lauterbach, J. Effect of Pt and Gd on coke formation and regeneration during JP-8 cracking over ZSM-5 catalysts. Appl. Catal. B: Environ. 2015, 168−169, 212−219. (38) Bai, T.; Zhang, X.; Wang, F.; Qu, W. T.; Liu, X. L.; Duan, C. Coking behaviors and kinetics on HZSM-5/SAPO-34 catalysts for conversion of ethanol to propylene. J. Energ. Chem. 2016, 25, 545−552. (39) Ni, Y. M.; Sun, A. M.; Wu, X. L.; Hai, G. L.; Hu, J. L.; Li, T.; Li, G. X. Facile synthesis of hierarchical nanocrystalline ZSM-5 zeolite under mild conditions and its catalytic performance. J. Colloid Interface Sci. 2011, 361, 521−526. (40) Yaripour, F.; Shariatinia, Z.; Sahebdelfar, S.; Irandoukht, A. Effect of boron incorporation on the structure, products selectivities and lifetime of H-ZSM-5 nanocatalyst designed for application in methanol-to-olefins (MTO) reaction. Micropor. Mesopor. Mat. 2015, 203, 41−53.


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Table 1 Lattice parameters of La2O3-modified ZSM-5 catalysts. Catalyst

Lattice constants/nm

Crystallinity (%) a

b

c

Vcell /nm3

ZSM-5

98.6

1.98661

1.97222

1.32412

4.64983

2LaZ

99.03

1.98335

1.99161

1.31057

4.09233

6LaZ

99.58

1.98762

1.99301

1.32840

4.67081

10LaZ

100

1.99974

1.98100

1.31179

4.65286

14LaZ

99.26

1.99889

1.98267

1.31302

4.65168


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Energy & Fuels

Table 2 Compositions and physicochemical properties of catalysts. Catalysts

CSi

CAl

CLa

SBET

SExternal

2

2

PSize

VTotal

VMicro

(%)

(%)

(m /g)

(m /g)

(nm)

(cm /g)

(cm /g)

(cm3/g)

ZSM-5

82.96

5.09

0.015

496.5

293.8

10.95

0.4182

0.1024

0.3158

2LaZ

80.31

4.95

1.99

469.2

302.1

10.65

0.4085

0.0886

0.3199

6LaZ

79.9

4.89

3.26

450.3

294.5

10.92

0.3968

0.0759

0.3209

10LaZ

76.87

4.96

7.46

417.0

301.5

10.67

0.3841

0.0638

0.3203

14LaZ

73.19

4.64

12.79

402.6

284.6

11.30

0.3751

0.0497

0.3254

23

3

VMeso

(%)

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Table 3 Acidity and acid strength distribution of catalysts with different La2O3 contents. Catalysts

Total acid

Percentage of acid sites (% of total acidity)

(mmol/g)

Weak acid

Medium acid

Strong acid

ZSM-5

1.03 ± 0.015

12.75 ± 0.742

43.09 ± 0.235

44.16 ± 0.600

2LaZ

0.98 ± 0.020

13.29 ± 0.643

44.88 ± 0.386

41.83 ± 0.964

6LaZ

1.00 ± 0.010

15.42 ± 0.155

47.72 ± 0.280

36.86 ± 0.350

10LaZ

1.00 ± 0.012

18.01 ± 0.353

45.59 ± 0.375

36.40 ± 0.217

14LaZ

1.01 ± 0.006

19.20 ± 0.166

44.59 ± 0.402

36.21 ± 0.340

The data are shown as the mean ± standard deviation (n = 3).


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Energy & Fuels

Table 4 Total gas production (TGP), light olefin yield (YLO) and gaseous product distribution from cracking three oil samples over LaZ catalysts. OA

ML

WCO

ZSM-5

6LaZ

10LaZ

ZSM-5

6LaZ

14LaZ

ZSM-5

6LaZ

14LaZ

TGP (mL/g)

355 ± 5.29

381 ± 7.81

365 ± 6.08

384 ± 7.53

407 ± 5.18

404 ± 6.57

350 ± 4.36

390 ± 5.29

353 ± 5.57

YLO (mL/g)

98 ± 2.91

131 ± 2.18

128 ± 1.78

74 ± 2.71

120 ± 1.98

107 ± 3.75

95 ± 2.29

128 ± 3.01

106 ± 3.43

YLiquid (%)

35.6 ± 0.46

28.5 ± 0.63

30.6 ± 0.65

28.4 ± 0.52

22.7 ± 0.43

25.7 ± 0.67

32.6 ± 0.62

26.8 ± 0.49

29.7 ± 0.46

0.7 ± 0.12

0.4 ± 0.08

0.5 ± 0.15

0.6 ± 0.11

0.5 ± 0.10

0.6 ± 0.08

0.9 ± 0.16

0.7 ± 0.12

0.8 ± 0.11

63.7 ± 0.50

71.1 ± 0.72

68.9 ± 0.75

76.0 ± 0.64

76.9 ± 0.51

73.7 ± 0.69

66.5 ± 0.72

72.5 ± 0.58

69.6 ± 0.52

C2H4

12.5 ± 0.26

15.4 ± 0.210

13.1 ± 0.27

9.4 ± 0.18

10.7 ± 0.12

10.6 ± 0.12

12.4 ± 0.17

12.5 ± 0.25

11.6 ± 0.25

C3H6

12.1 ± 0.17

13.6 ± 0.18

17.1 ± 0.15

7.8 ± 0.10

14.3 ± 0.14

11.9 ± 0.15

11.6 ± 0.08

15.6 ± 0.09

13.6 ± 0.13

n-C4H8

3.7 ± 0.09

6.3 ± 0.19

5.9 ± 0.21

2.6 ± 0.13

5.3 ± 0.17

4.9 ± 0.38

4.1 ± 0.16

5.7 ± 0.15

5.8 ± 0.26

CH4

4.7 ± 0.09

4.0 ± 0.20

3.5 ± 0.14

6.6 ± 0.10

3.5 ± 0.09

3.1 ± 0.05

4.7 ± 0.15

3.2 ± 0.12

3.0 ± 0.13

C3H8

11.4 ± 0.11

9.0 ± 0.27

6.9 ± 0.21

11.9 ± 0.16

8.7 ± 0.15

8.1 ± 0.12

11.0 ± 0.17

8.0 ± 0.12

6.7 ± 0.21

n-C4H10

3.8 ± 0.06

4.9 ± 0.16

4.4 ± 0.09

3.2 ± 0.08

4.5 ± 0.14

4.7 ± 0.16

4.1 ± 0.22

4.9 ± 0.13

4.5 ± 0.19

C2H2

3.9 ± 0.16

3.6 ± 0.21

3.1 ± 0.17

4.4 ± 0.22

2.8 ± 0.17

2.6 ± 0.31

3.8 ± 0.16

2.9 ± 0.20

2.7 ± 0.24

CO2

3.4 ± 0.59

8.2 ± 0.95

8.7 ± 0.83

2.4 ± 0.35

3.9 ± 0.49

3.8 ± 0.40

3.1 ± 0.44

5.5 ± 0.57

7.0 ± 0.56

CO

8.0 ± 0.42

5.6 ± 0.61

5.4 ± 0.53

20.0 ± 0.57

13.7 ± 0.53

12.8 ± 0.45

8.9 ± 0.54

7.6 ± 0.34

7.4 ± 0.67

Others

36.5 ± 1.82

29.4 ± 2.67

31.9 ± 2.49

31.7 ± 1.54

32.6 ± 1.86

37.5 ± 1.92

36.3 ± 1.79

34.1 ± 1.93

37.7 ± 2.43

YCoke (%) YGas (%) Gas product (%)


25

ACS Paragon Plus Environment

Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Table 5 Compounds in liquid products from catalytic cracking three oil samples over 6LaZ catalyst. NO.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

RT (min)

2.072 3.055 4.821 5.156 5.713 6.521 6.528 7.285 7.501 7.928 8.257 8.357 8.955 9.202 9.392 9.481 9.489 9.513 9.521 9.608 10.129 10.137 10.138 10.208 10.213 10.327 10.397 11.231 11.239 11.428 11.531 11.65 12.001 12.055 12.207 12.83 13.168 13.343 13.346 13.816 14.064 15.377 15.38 15.577 16.781 21.208 22.91 22.964 23.121 26.133

Name of compound

Benzene Toluene Ethylbenzene p-Xylene o-Xylene Benzene, (1-methylethyl)Benzene, 1,2,3-trimethylBenzene, propylBenzene, 1-ethyl-3-methylBenzene, 1-ethyl-2-methylMesitylene Benzene, 1-ethenyl-4-methylo-Cymene Indane Indene Benzene, 1-propynylBenzene, 1,2-diethylBenzene, 1-methyl-3-propyl2-Indanol 2-Tolyloxirane Benzene, 2-butenyl(E)-1-Phenyl-1-butene Benzene, 1-methyl-2-(2-propenyl)1,3,8-p-Menthatriene Benzene, 4-ethyl-1,2-dimethyl4-Undecene, (Z)5-Un9decene Benzene, 2-ethenyl-1,4-dimethyl1H-Indene, 2,3-dihydro-5-methyl1H-Indene, 1-methyl2-Methylindene Naphthalene, 1,2,3,4-tetrahydroBenzene, (1,2-dimethyl-1Naphthalene Dodecane 2-Ethyl-2,3-dihydro-1H-indene 1H-Indene, 1,3-dimethyl(1-Methylbuta-1,3-dienyl)benzene 1H-Indene, 1,1-dimethylNaphthalene, 1-methylNaphthalene, 2-methylNaphthalene, 2,6-dimethylNaphthalene, 2,7-dimethylNaphthalene, 2,3-dimethylDodecanoic acid, methyl ester Hexadecanoic acid, methyl ester 8-Octadecenoic acid, methyl ester 9-Octadecenoic acid, methyl ester Methyl stearate 12-Tricosanone

Oil samples (area %) Molecular formula OA ML WCO C6H6 8.5 ± 1.2 9.67 ± 0.85 10.35 ± 1.03 C7H8 22.34 ± 1.72 17.97 ± 1.46 25.12 ± 1.65 C8H10 6.73 ± 0.87 5.21 ± 0.64 4.19 ± 0.38 C8H10 29.19 ± 1.87 28.93 ± 2.01 27.25 ± 1.62 C8H10 5.28 ± 0.62 3.41 ± 0.43 5.13 ± 0.71 C9H12 − 0.23 ± 0.04 0.19 C9H12 0.31 ± 0.16 − − C9H12 0.56 ± 0.95 0.44 ± 0.83 0.37 ± 0.27 C9H12 3.10 ± 0.05 0.05 1.60 ± 0.29 C9H12 0.24 ± 0.07 5.92 ± 0.11 0.19 ± 0.04 C9H12 1.82 ±0.25 1.61 ± 0.24 1.59 ± 1.98 C9H10 − − 0.13 ± 0.02 C10H14 − 0.09 − C9H10 2.11 ± 0.78 0.45 ± 0.22 1.81 ± 0.54 C9H10 0.91 ± 0.35 0.15 ± 0.02 1.02 ± 0.21 C9H8 − − 0.14 C10H14 0.27 ± 0.13 − − C10H14 − − 0.23 ± 0.11 C9H10O 0.43 ± 0.14 0.75 ± 0.17 − C9H10O 0.49 ± 0.08 0.45 ± 0.64 − C10H12 − − 0.48 ± 0.12 C10H12 0.46 ± 0.07 − − C10H12 − 0.18 ± 0.06 − C10H14 − 0.09 ± 0.03 − C10H14 0.16 ± 0.07 − − C11H22 − 0.38 ± 0.05 − C11H22 − 0.21 ± 0.10 − C10H12 − − 0.75 ± 0.05 C10H12 1.18 ± 0.04 0.29 ± 0.16 − C10H10 1.06 ± 0.32 0.17 0.86 ± 0.43 C10H10 0.47 ± 0.27 − 0.45 ± 0.19 C10H12 0.25 ± 0.13 − 0.19 ± 0.05 C11H14 0.31 ± 0.22 0.16 ± 0.03 0.17 ± 0.05 C10H8 2.11 ± 0.89 0.25 ± 0.08 1.48 ± 0.73 C12H26 − 0.10 − C11H14 − − 0.22 ± 0.04 C11H12 0.38 ± 0.14 − 0.16 ± 0.07 C11H12 − − 0.21 ± 0.11 C11H12 0.39 ± 0.08 0.05 − C11H10 3.09 ± 0.12 − − C11H10 0.20 ± 0.05 1.11 ± 0.03 1.95 ± 0.06 C12H12 0.58 ± 0.13 0.37 ± 0.17 − C12H12 − − 0.39 ± 0.11 C12H12 0.16 − − C13H26O2 4.87 ± 0.17 19.94 ± 0.24 1.15 ± 0.15 C17H34O2 − − 4.55 ± 1.14 C19H36O2 − − 2.80 ± 0.23 C19H36O2 − − 1.88 ± 0.65 C19H38O2 − − 0.75 ± 0.30 C23H46O − 0.10 −

−: Not detected.



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Energy & Fuels

Table 6 Comparison of catalytic cracking of different biomass and bio-oil to produce light olefins. Ref. No.

Feedstocks

Reactor

Reaction conditiona

Light olefin yield (Y) and selectivity (S)

8

Sugarcane bagasse

Fixed bed

6 wt% La/HZSM-5(Si/Al=23), 600 °C, catalyst/feed = 3

Y: 0.12 kg olefins/(kg dry biomass) S: 21.2% C- mol %

11

Bio-oil from fast pyrolysis of biomass

Fixed bed

6 wt% La/HZSM-5(Si/Al =23) 600 °C, 1.5h-1

Y: 0.23 kg olefins/(kg bio-oil) S: 50.6% C-mol %

12

Microalga

Fixed bed

PLa/ZSM-5 (Si/Al =45) 600 °C, catalyst/feed = 20

Y: 11 wt%, S: 24.6 wt%

12

the extracted lipids from microalga

Fixed bed

PLa/ZSM-5 (Si/Al =45) 600 °C, catalyst/feed = 20

Y: 36.7 wt%, S: 57.1 wt%

19

Canola oil

Fixed bed

ZSM-5 (Si/Al =50) 500 °C, 1.8h-1

Y: 1.1 % of canola oil feed

20

Waste cooking oil

Fixed bed

ZSM-5 (Si/Al =11) (450 °C, catalyst/feed = 0.4

Present work

Waste cooking oil

Fixed bed

6 wt% La/ZSM-5 (Si/Al =16) (600 °C, catalyst/feed = 0.6

Y: 20 wt % S: 83.8 % of total gas hydrocarbons Y: 0.205 kg olefins/(kg bio-oil) S: 33.8 mol% of total gas

Present work

Oleic acid

Fixed bed


Y: 0.209 kg olefins/(kg bio-oil) S: 35.3mol% of total gas

Present work

Methyl laurate

Fixed bed


Y: 0.197 kg olefins/(kg bio-oil) S: 30.3 mol% of total gas

Reaction condition mainly includes catalyst type, reaction temperature, weight hourly space velocity and catalyst/feed ratio.


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

FIGURE CAPTIONS Figure 1. XRD patterns of LaZ catalysts with different La2O3 contents. Figure 2. SEM images of ZSM-5 (a, b) and 6LaZ (c, d). Figure 3. (a) NLDFT pore size distribution and (b) N2 adsorption-desorption isotherms of the LaZ catalysts. Figure 4. NH3-TPD profiles of LaZ catalysts with different La2O3 contents. Figure 5. Gaseous product distribution from catalytic cracking of (a) OA, (b) ML and (c) WCO, and (d) liquid product distribution. Reaction conditions: T = 600 °C, WHSV = 52.5 h-1. Figure 6. TGA and DTG profiles of the used catalysts from cracking three oil samples, (a) OA, (b) ML and (c) WCO. Figure 7. TPO profiles of the used catalysts from cracking three oil samples, (a) OA, (b) ML and (c) WCO. Figure 8. The total gas production and light olefin yield (a); gaseous product selectivity with cycle number from cracking three oil samples over the 6LaZ catalyst, (b) OA, (c) ML and (d) WCO; Reaction conditions: T = 600 °C, WHSV = 52.5 h-1. Scheme 1 Postulated reaction pathways for catalytic cracking of OA and ML. Scheme 2 Postulated reaction pathways for catalytic cracking of WCO.


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Energy & Fuels

Figure 1. XRD patterns of LaZ catalysts with different La2O3 contents.


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(a)

(b)

(c)

(d)

Figure 2. SEM images of ZSM-5 (a, b) and 6LaZ (c, d).


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Energy & Fuels

Figure 3. (a) NLDFT pore size distribution and (b) N2 adsorption-desorption isotherms of the LaZ catalysts.


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 4. NH3-TPD profiles of LaZ catalysts with different La2O3 contents.


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Energy & Fuels

Figure 5. Gaseous product distribution from catalytic cracking of (a) OA, (b) ML and (c) WCO, and (d) liquid product distribution. Reaction conditions: T = 600 °C, WHSV = 52.5 h-1.


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 6. TGA and DTG profiles of the used catalysts from cracking three oil samples, (a) OA, (b) ML and (c) WCO.


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Energy & Fuels

Figure 7. TPO profiles of the used catalysts from cracking three oil samples, (a) OA, (b) ML and (c) WCO.


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 8. The total gas production and light olefin yield (a); gaseous product selectivity with cycle number from cracking three oil samples over the 6LaZ catalyst, (b) OA, (c) ML and (d) WCO; Reaction conditions: T = 600 °C, WHSV = 52.5 h-1.


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Energy & Fuels

Scheme 1 Postulated reaction pathways for catalytic cracking of OA and ML.


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Scheme 2 Postulated reaction pathways for catalytic cracking of WCO.


Page 38 of 38

Production of Light Olefins from Catalytic Cracking Bio-oil Model

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