Production of petroleum-like synthetic fuel by hydrocracking
of crude soybean oil over ZSM5 zeolite – Improvement of catalyst
lifetime by ion exchange
Cassio Henrique Zandonai
a,⇑, Patricia Hissae Yassue-Cordeiro
a, Sibele Berenice Castellã-Pergher
b,
Mara Heloisa Neves Olsen Scaliante
a, Nádia Regina Camargo Fernandes-Machado
aaDepartamento de Engenharia Química, Universidade Estadual de Maringá, Avenida Colombo, 5790, Bl D-90, Maringá, PR, Brazil b
Departamento de Química, Universidade Federal do Rio Grande do Norte, Av. Salgado Filho, 3000, Lagoa Nova, 59078970 Natal, RN, Brazil
a r t i c l e i n f o
Article history: Received 16 July 2015
Received in revised form 29 November 2015 Accepted 29 December 2015
Available online 4 January 2016 Keywords: Biofuel Catalytic cracking vegetable oil Hydrodeoxygenation Ion exchange Zeolite
a b s t r a c t
It is possible to produce hydrocarbons by hydrocracking of biomass, such as those produced by crude oil cracking. This product can be incorporated as raw material in petrochemical industry and used as petro-leum fractions without any changes on engines. The hydrocracking process was performed over NaZSM5 and HZSM5, where the improvement of this acidity was carried out by ion exchange with ammonia fol-lowed by calcination. The reactions were performed on a stainless steel fixed bed reactor. The catalyst was evaluated at 723 K and 138 kPa, under flow of hydrogen gas, with weight hourly space velocity (WHSV) of 4 h1. Products are analysed by gas chromatography with mass spectra detector (GC–MS) and by nuclear magnetic resonance (NMR) of1H. For the fresh catalyst, all triglyceride was converted to hydrocarbon by the process. For NaZSM5, the catalyst activity is high but has a high decrease over the time of reaction. It was changed for HZSM5, where the catalyst maintained a high activity even after 90 min of reaction. This treatment improved also the product, where a high yield of gaseous hydrocarbon was changed to a high yield of liquid hydrocarbon, especially by the presence of aromatics molecules.
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1. Introduction
The growing demand of liquid fuel for transportation has led to increase the production of petroleum that is a fuel fossil. Because of pollution problems to fauna and flora around the world, this source of energy is being gradually substituted by renewable source of liq-uid fuel. Many sources of renewable liqliq-uid fuel were available, where vegetable oil is extensively used.
It is possible to produce liquid fuel similar to liquid fuel derived from petroleum by a catalytic cracking of vegetable oil process. This technology allows using a lot of vegetable oil as raw material [1], food or not. Cracking of vegetable oil consist in the fragmenta-tion of triglycerides of the oil in free fatty acids, which take place
above 500 K, with complete volatilization above 600 K [2] and
maximum decomposition rate at 685 K[3]for soybean oil. After
the decomposition, two groups of reactions take place by thermal effects: the scission of CA C bonds and the deoxygenation of the free fatty acids. The deoxygenation could be by: decarboxylation,
decarbonylation or hydrodeoxygenation[4]. In case of cracking, an acid site may accelerate the cracking of the CAC bonds.
The most used catalyst on cracking process is those based on zeolites, which are materials with acid sites. These sites have dif-ferent intensity of acidy according to zeolite types. ZSM5 zeolite has strong acid sites and it is extensively applied on cracking pro-cess of petroleum and vegetable oils. The vegetable oil nature affects the cracking process. Over HZSM5, Buzetski et al.[5] evalu-ated the cracking of rapeseed and sunflower oil. They also tested used oil from frying. They used a stirred batch reactor and temper-ature between 623 and 713 K. They calculated and compared the unsaturation index[6]. The results showed that the most saturated oil (rapeseed, 7.3) produced more cracking residue and the most unsaturated (sunflower, 8.4) produced more gaseous products. In a fixed-bed flow reactor, at 723 K, Doronin et al.[6] performed the cracking with HZSM5 of coconut, rapeseed, mustard and sun-flower oil, with 1.2, 4.7, 6.4 and 9.0 of unsaturation indexes respec-tively. The results showed that the most unsaturated oil has produced more aromatics compounds than the saturated oils; which produced more paraffin and olefin hydrocarbons.
Looking for an optimal condition on cracking of waste cooking palm oil over ZSM5, Taufiqurrahmi et al.[7]evaluated the effects
http://dx.doi.org/10.1016/j.fuel.2015.12.059
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Fuel
of variables of process on conversion and yield of products. They used a fixed bed reactor with space velocity (WHSV) of 2.5 h1. For this catalyst, the optimal condition was at 728 K, with an oil/-catalyst ratio of 6.22 (m/m), which resulted on 92.29% of conver-sion, with 53.40% of organic liquid product (OLP) and 37.05% of gasoline. In a similar experiment Sang et al.[8]evaluated the opti-mal condition for a fatty acid mixture cracking over HZSM5 with acidity of 0.25 mmol NH3/gcat. They studied the ranging of
temper-ature, WHSV and oil/catalyst ratio. The results showed that the
optimal gasoline yield occurred at 713 K, WHSV of 3.66 h1and
9.64 g oil/catalyst ratio. An increase of the temperature promotes an increase on conversion. However, the yield of gasoline decreases and yield of gaseous product increase. In the range of WHSV from 2.5 h1to 4.5 h1, the minimal value led to the maximal conver-sion, showing an inverse effect of the temperature.
Tamunaidu and Bhatia [9]evaluated the cracking of palm oil
over rare earth Y zeolite and evaluated the aromatics produced. The results showed that an increase on temperature led to an increase on aromatics produced and the relative content of xylene and toluene reduced by the increase of benzene. Production of aro-matic hydrocarbons was observed on cracking of sunflower over a composite catalyst[6]. The increase of the amount of HZSM5 zeo-lite results on an increase of aromatics production, mono and di-aromatics.
The acidity of the catalyst is an important characteristic on the cracking process. On the ZSM5, the Si/Al ratio of the framework directly influences the acidity value and the characteristics of acid sites. Twaiq et al.[10]using HZSM5 of 50, 90, 240 and 400 Si/Al ratio, found 0.63, 0.29, 0.24 and 0.19 mmol H+/gcat respectively.
In a closer analysis of acidity of ZSM5 looking at the temperature
of ammonium desorption peaks [11,12], the result showed that
this material has a low and a high temperature peak. Ranging the Si/Al ratio, an increase reduces the total amount of acidity and change the peaks profile. At low Si/Al ratio, the predominance is for low temperature peaks, however with the increase of the ratio an inversion occurs, where the high temperature peak becomes predominant. The acidity of HZSM5 catalyst influenced the product distribution obtained from palm cracking. The gaseous yield was reduced and gasoline production increased with the Si/Al ratio increase.
For cracking process, catalyst acidity is an important factor; the acid sites interact with the hydrocarbons accelerating the crack reactions. The interference of this factor was availed on cracking of from food waste oil[13]by comparing different catalyst with different acidity profile. It was produced more liquid hydrocarbons with fewer aromatics and more cyclic molecules with higher num-ber of acid sites. Gaseous hydrocarbons, aromatics and oxygenated molecules were produced with higher value of strong acid sites (HA). Gas and gasoline were produced in more quantities, with less content of liquid organic product when it was used fatty acid mix-ture over HZSM5[8,14], as the acid increased at 723 K and WHSV of 2.5 h1.
The results on cracking of soybean oil show different product distribution with different Si/Al ratio on HZSM5[3], which leads to a different distribution of acidity. Conversion was higher than higher the acidity, which led to a higher production of gas and organic liquid. The lowest content of coke was found for the cata-lyst with the lowest acidity content.
Comparing the type of cracking reactor used, the results show that for continuous tubular fixed bed reactor produce a large
amount of gaseous product 28%[15], when under low pressure.
At a closed reactor, at an approximated temperature, which have an increase on pressure over the reaction time, the production of gaseous products was lower for all oils tested over HZSM5[5]
In this work, the catalytic cracking of crude soybean oil was realized, in a fixed bed reactor, with H2flow in order to evaluate
de activity and selectivity of ZSM5 and the ion exchanged with ammonium zeolite HZSM5.
2. Experimental 2.1. Materials
Crude soybean oil was used, that means no treatment of degumming or clarification was performed after the solvent remove. The distribution of fatty in triglycerides of crude soybean oil is palmitic acid (16:0) 12.93%; linoleic acid (16:1) 36.81%; oleic acid (16:2) 45.38% and stearic acid (18:0) 4.88%, with an unsatura-tion index of 7.97.
Hydrocracking transformation of vegetable oil was performed under optimal conditions as shown on literature for cracking of vegetable oil [7–9]. It was 723 K; weight hourly space velocity
(WHSV) of 4 h1 under flux of hydrogen gas; low pressure of
127 kPa, on a stainless steel reactor. The test conducted during 120 min drawing samples each 30 min. Before the test, the catalyst was preheated at 10 K/min from room to the reaction temperature on N2flow, for 1 h. Then the N2flow was substituted by H2flow at
30 ml/min and after 30 min, the reaction was started. At 5 min of reaction, the gaseous product was sampled and analysed, that pro-cedure was repeated each 15 min until the end of the 120 min test. After each 30 min of reaction, the liquid product was sampled and analysed. Before CG analysis, liquid product was treated with methylation of free fat acids and triglycerides.
2.2. Ion exchange procedure
The acidity of catalyst was modified, by mean of ion exchange,
using adapted methodology from literature [16]. It was used
1 mol/L ammonium chloride solution, pH 4.5 and 10% solids content, under stirring at 348 K for 2 h. Before this process, the material was stirred over than 10 h for better dispersion of solids in solution. After filtration, it was rinsed and dried at 373 K, the material was calcined at 773 K for 6 h, with a heating rate of 2 K/min with isothermal steps by1 h at 393 K and 473 K, in oxidative atmosphere.
2.3. Catalyst characterization
27Si and29Al NMR analysis on solid state was realized on
Mer-cury Plus 300, Varian, with solid-state probe CP/MAS 7 mm. The analysis was carried out at 59.6132 MHz for27Si nucleus and at
79.186 MHz for29Al nucleus. For aluminium, a silicon nitride rotor
(7 mm) was used, with Kel-F cover and 6.5 kHz of rotation. For silicon, a zirconia rotor (7 mm) was used, with Kel-F cover and 3.5 kHz of rotation. The MAS technology was used, with acquisition time of 0.05 s and pulses of 90°, at 293 K and recycling waiting time of 20 s. For reference, the kaolin signal was used (91.16 ppm).
The quantification of the catalyst acidity was held by TPD, on quartz microrreator on ChemBet 3000, Quantachrome. Before this process, all catalyst was calcined at 773 K on oxidative atmo-sphere. A prior degasification, at 573 K with nitrogen gas flux, was performed to remove the water content in pore. The chemisorption occurs at 373 K with a gas mixture of 5% mass/mass
(m/m) of NH3 in Ar mixture, until no more chemisorption was
observed. After this process, the flux of nitrogen was re-established and with a heating of 10 K/min, desorption process starts until a final temperature of 973 K. A thermal conductivity detector (TCD) performed the quantification, where the areas were related with the areas of known NH3/Ar concentration mixtures.
physisorption of nitrogen at 77 K under pressure, on NOVA1000 of QUANTACHROME equipment.
2.4. Product characterization
The gas product was analysed by gas chromatography with TCD detector, on a Varian 1420 equipped with a Porapak Q column (3.15 mm in diameter and 90 cm in length). Identification of com-pounds of the peaks was performed by injecting standard gas mix-tures of carbon monoxide, carbon dioxide, methane, ethane, ethene, propane, propene, butane, pentane, N2and H2O. The
anal-ysis was performed with the following program: an initial temper-ature of 403 K for 4 min, followed by a heating rate of 20 K/min, until 433 K, maintained for 9 min.
To quantify liquid product, gas chromatography with mass spectra detector was carried out, on CG-MS Thermo-Finigan
equip-ment, equipped with a 60 m–0.25 mm–0.25
l
m DB-5 capillarycol-umn. It was used initial temperature of 323 K, followed by a heating of 10 K/min until a final temperature of 533 K, on a
methodology adapted from literature [17]. The data processing
was done by equipment software, Xcalibur Data System Version 1.4. The software has a NIST library (National Institute of Standards and Technology) from compound identification.
A DB-5 Column has a relative polar phase with has high interac-tion with polar compounds. A free acid is a compound that is pre-sent in oil cracking product. It is necessary a previous treatment. An esterification with methanol (methylation) was carried out for turn less polar these molecules, in form of ester. It was used an adapted procedure[18]: 100 mg of liquid product react with 2 ml of NaOH solution (0.5 mol/L) at 90°C for 4 min; after cooled, 3 ml of a solution (3:5 g of NH4Cl:H2SO4 per litter of methanol) was
added. The methylation occurred at 90°C by 3 min; after cooled
a saturated NaCl solution, 2 ml, was added for phase separation and (as solvent) 3 ml of isopentane was added.
1H NMR analysis was used in order to classify species by
func-tional group in liquid products. In the analysis, the samples were prepared at 5% v/v solvent CDCl3/CCl41: 1 (v/v) so that the peak
of chloroform not interferes with the sample peaks. The following parameters were used: d1 = 1; nT = 16; Pw = 25°. For identification of peaks, their chemical shift was classified by the type of hydrogen in its composition, which was grouped by the review on literature [19–25]. It is shown onTable 1.
The TPO (Temperature Programmed Oxidation) tests was per-formed in CHEMBET 3000 Quanta-chrome equipment coupled to
a mass spectrometer Pfeiffer Vacuum THERMOSTARTM, using a
quartz reactor. In order to quantify the oxidations products, CO2
and CO, it was carried out a series of injections of known amounts of these substances. Quantification of CO (m/e = 28) was
per-formed, discounting the amount of CO fragmentation of CO2
(m/e = 44), since the CO species is preferably detected as m/e = 28
and only 11.4% of the CO2molecules are fragmented in this ion
[26]. Samples of catalyst with coke were preheated at 523 K for 1 h with nitrogen flow of 75 ml/min, in order to remove water con-tent. Then, the reaction was carried out under flow of a mixture of 3% O2/Ar at 75 ml/min, with a heating rate of 10 K/min from 373 K
to 973 K, which was maintained at the final temperature until
complete oxidation, until the CO and CO2species have not been
detected any more. 3. Results analysis
The main objective of the process is deoxygenation of the organic acids in the oil, and conversion of all oxygenated molecules is hard to evaluate. The parameter degree of deoxygenation (DOD) [27], Eq. (1), was an important information about the extent of reaction, correlating the weight of oxygenates in the product with reagent. For analysing the cracking extent of reaction, the degree of cracking (DOC), Eq.(2), was used, which is the relation of the num-ber of carbons in the mean chain of organic molecules in products (MC(c in products)) and in feed (MC(c in feed)). Both parameters are:
DOD¼ ð1 wto:in:product=wto:in:feedÞ:100 ð1Þ
DCO¼ ð1 MCc:in:product=MCc:in:feedÞ:100 ð2Þ
With these parameters is possible to evaluate the extensions of deoxygenation and cracking. Both processes occur separately, by the cracking of large carbon chain organic acids to short carbon chain organic acids, without any deoxygenation occur, and by the deoxy-genation of free fatty acids with no fragmentation of carbon chain.
To evaluate the quality of product an analysis of its selectivity (SEL), Eq.(3), was realized, taking into account the relation of the molar amount of hydrocarbon produced (Hy), desired products, and the organic oxygenated compounds produced (Ox), undesired products[28].
SEL¼ ðFHy=FOxÞ ð3Þ
This quantification carried out as described on literature[29]. In addition, for analysis of the aromatization capacity a degree of aromatization (DOA), Eq.(4), was evaluated relating the number of non-aromatics hydrocarbons (NNA) with the total number of hydrocarbons aromatics (THP) on product.
DOA¼ ðNNA=THPÞ 100 ð4Þ
4. Results and discussion 4.1. Catalyst characterization
The N2physisorption analysis of catalyst sowed a high porous
media for ZSM5 material. The specific surface area was 318 m2/g,
Table 1
Regions of chemical shift for1H NMR spectra.
Regions Chemical shift (ppm) Hydrogen (H) Source
1 9.00–7.60 Polyaromatic [21–23]
2 7.60–7.20 Diaromatic [21–23]
3 7.20–6.00 Monoaromatic [21–23]
4 6.00–5.20 Olefin (ACH@CHA) [21,23,25]
5 5.15–5.00 Methine group of glyceride (ACHOCOR) [19,20,25]
6 4.90–4.00 Methylene group of glyceride (ACH2OCOR) [19,20,25]
7 4.00–2.70 a-methylene between double-bound (@CHACH2ACH@) [19,20]
8 2.70–2.35 Hydrogen ona-position on aromatic rings [21,23]
9 2.35–2.15 a-methylene group carboxyl (ACH2COOH) [19,20,24,25]
10 2.15–1.80 Methylene of double bound (@CHACH2A) [19,20]
11 1.80–1.50 b-carboxyl group (AC2HCH2COOH) [19,20,24]
12 1.50–1.15 Methylene group (CH2)n [19–21,23]
with 264.42 m2/g of micropore area and 53.35 m2/g of external
area. The pore volume 0.17 cm3/g, with 0.135 cm3/g of micropore
and 0.015 cm3/g of mesopore, associated with mesoporosity
gener-ated by crystal agglomeration.
The27Si NMR revealed two kinds of coordination peaks in
sili-con atoms in the zeolite framework. As showed inFig. 1, a charac-teristic peak of coordination with silicon atom with no aluminium, Si(0Al), was found in111.77 ppm, and a peak of silicon
coordi-nated with one aluminium atom, Si(1Al), was found at
104.90 ppm. The intensity was measured and the revealed a Si/Al ratio of 20, which was relative low[11,30].
The acidity profile of catalyst was determined with temperature programmed desorption (TPD) of ammonia. A set of overlapping peaks was observed on all analysis and a deconvolution of these graphic showed the hidden peaks, which are the acid sites of the material with different acidity strength. The quantification of these peaks is inTable 2, with results.
A TPD analysis of NaZSM5 found three categories of peaks, Fig. 2. The peaks 01 and 02, at 496.22 and 548.32 K respectively, represent the low acidity sites (LA), because of the relative low temperature of ammonia desorption. The peak 03 at 619.60 K, rep-resents the mean acidity peak (MA), and the last peak, at 764.91 K, represent the strong acid sites of the material (HA), which has the strongest chemical interaction with the ammonium molecule. This material has a large amount of acidity, even with a low Si/Al ratio. The total acidity found for this Si/Al ratio is at range of literature [31], for a ratio of 15.6 a higher amount of HA acid sites, for a ratio of 30 a total of 1.16 mmol of NH3/gcatalystwas absorbed, with a
higher amount of LA acid sites. For Si/Al = 15.8, the relation HA/LA > 1 and for Si/Al = 30 is HA/LA < 1. That result indicates the predominance of HA on zeolites with low Si/Al ration.
With the treatment, an increase on acidity of the material was
observed, Fig. 3. For HZSM5 the result showed a peak of LA at
545 K, which suffers a contraction on its amount of 10%. MA peak
at 614 K, which suffers a decrease on its maximum of 5 K, indicat-ing a slight change of acidity strength; however, the amount of acidity of this peak has an increase of 51.15%. For the last peak the HA, the maximum was on 754 K, which is a reduction of 10 K, however that peak has and increase on its area of 49.06%. After the ion exchange, the total acidity has an increase of 25%, which occur by the substitution of the compensation cation, from Na+, to H+. The ion exchange promotes an increase of strong acid
sites and a reduction of weaker acid sites.
4.2. Products
As result of cracking process, a mixture of organic and inorganic molecules is produced. For gaseous phase, this mixture involves carbon oxides, water and hydrocarbons. The liquid phase is a com-plex mixture, with water phase and an organic phase, which was a mixture of hydrocarbon, oxygenated products and triglycerides that did not react.
Analysing the production of fuel is possible to group the result as the correspondent GLP (C1–C4), and liquid hydrocarbons from
boiling points, gasoline (310–450 K), kerosene (450–519 K) and diesel (519–618 K), as we can see onTable 3.
Looking for raw material as petrochemical, the organic liquid products are grouped by the chemical structure as aliphatic,
Fig. 1.29
Si NMR spectra of ZSM5.
Table 2
Acid sites profile of catalyst. Acidity (mmol NH3/gcat)
Catalyst Low (LA) Mean (MA) High (HA) Total NaZSM-5 0.5595 0.1951 0.5864 1.3412 HZSM-5 0.5077 0.2957 0.8742 1.6778
Fig. 2. Ammonium temperature programed desorption of NaZSM5.
aromatic and cyclic hydrocarbons, acids and oxygenated radicals, Table 4.
4.3. Products from NaZSM5
The result of cracking for the NaZSM5,Table 3, show that the cracking of soybean oil triglycerides was successful, with high selectivity for hydrocarbons for the first period of 30 min. Until this time, the catalyst was fresh and its acid sites was available, the production of gaseous products was the greater, 57.89%, indicating
a high DOC,Fig. 4. Those amount were greater than which were
produced on another triglyceride cracking over ZSM5 [3,14,32],
and comparing with another zeolites, the ZSM5 is that produces more gas[13]. Palm oil[8]in the same conditions of this soybean oil cracking, the gas yield was around of 15% lower, what could be attributed for the higher unsaturation index of soybean oil.
The ZSM5 have a high amount of acid sites with strong acidity, what benefits cracking and deoxygenation processes, by the
production of more gaseous products. The increase in acidity by ion exchange led to an improvement in the cracking capability of catalyst. With ZSM5 with different Si/Al ratios[3], the catalyst with higher acidity led more gaseous product, showing the higher cracking capability, with higher acidity.
For subsequent period of 60, 90 and 120 min, the gas produc-tion decreases, from 30.98%, to 20.31% and 4.15% at the end of pro-cess, which indicates catalyst deactivation, what is common for cracking process over acid catalyst, mainly by coking.
The high cracking capacity of this material affects also the liquid product distribution. For HZSM5, the fresh catalyst produced low liquid content. The gasoline and diesel content was low because of the large amount of cracking reactions. The kerosene fraction was higher because of the high amount of aromatics, what includes naphthenic hydrocarbons. That low content of diesel was found also on palm oil cracking over HZSM5[33].
It is valuable to observe the diesel fraction on product over the time. At the fresh catalyst, the content was low 2.08%. After 60 min of reaction, the product contained 0.89% of diesel fraction. After 90 min, the content rise for 2.53%, rising again after 120 min of reaction. 9.01%. It means that occur a change on cracking capability by deactivation.
On theTable 4, the fresh catalyst produced mainly aromatics compounds, as the time go on. There are reduction, indicating a decrease on frequency of fragmentation and aromatization reac-tions. That change is followed by the increase on aliphatic
hydro-carbon content. At the third period, after 90 min, the
aromatization frequency was low and the mainly content of hydro-carbon was gas. For the partially deactivated catalyst, after 120 min of reaction, was found an increase on diesel content, fol-lowed by an increase on aliphatic hydrocarbon content. The change
Table 3
Product distribution of crude soybean oil cracking.
Catalyst Time (min) Gas Hydrocarbon products (% m/m) Oxygenated products (% m/m) Inorganic (% m/m) Selectivity Gasoline Kerosene Diesel Trig. acid Frag. acid. R–O COX H2O
NaZSM5 30 56.25 10.43 9.51 7.46 0.00 0.00 0.40 4.85 11.09 1,018.58 60 52.59 15.46 9.85 3.24 6.48 0.12 0.00 6.32 5.94 79.00 90 31.55 20.57 2.40 2.53 26.03 0.76 3.86 6.13 6.18 12.91 120 6.40 12.43 5.94 9.01 45.30 5.69 4.56 2.36 8.31 3.74 HZSM5 30 58.17 21.38 3.20 0.73 0.00 0.00 0.00 4.33 12.20 – 60 39.43 36.66 7.54 0.94 0.00 0.00 0.04 4.84 10.55 6,582.74 90 28.85 50.77 7.00 0.59 0.11 0.09 0.14 5.50 6.94 947.72 120 6.09 37.05 6.25 1.23 26.33 12.49 1.72 3.82 5.02 4.89 Table 4
Organic products distribution and DOA. Time
(min)
Organic chemical structures (% mass/mass) Aromatics Cyclic Aliphatic Acid R–O DOA NaZSM5 30 25.95 0.00 1.46 0.00 0.40 31.82 60 27.05 0.30 1.20 6.60 0.00 34.58 90 2.72 1.39 20.70 26.79 3.86 5.17 120 3.58 1.68 22.12 50.99 4.56 10.88 HZSM5 30 18.68 0.02 6.61 0.00 0.00 22.38 60 37.71 0.41 7.01 0.00 0.04 44.59 90 46.35 0.76 11.26 0.19 0.14 54.75 120 36.85 0.18 7.51 38.82 1.72 72.80
on hydrocarbon composition is more evident observing the DOA over the time,Fig. 5.
These results indicate that the diesel produced after 60 min of reaction is rich on aromatic compounds. On the order hand, after 120 min it is rich on aliphatic hydrocarbons. It indicates that after 120 min of reaction, the cracking capability was compromised and the hydrocarbon is produced by deoxygenation of free acids, keep-ing its chain length.
In general, as the time goes on, the content of liquid hydrocar-bon on products increases, following by decrease on DOC. In conse-quence, the hydrocarbon produced by deoxygenation maintains its chain length, producing long-chain hydrocarbon. The DOD also is reduced over the time (Fig. 6), as result of non-deoxygenated acids on product. These two effects occur because of the catalyst deacti-vation, which reduces the cracking and the deoxygenation capabil-ity of the material. This deactivation is mainly by coke deposition over the acid sites[34].
The high DOD indicates an almost complete conversion of the oxygenated compounds for the NaZSM5 fresh catalyst, reflected in the high selectivity to hydrocarbons (1018.58). This
deoxygena-tion process occurred by hydrodeoxygenadeoxygena-tion (HDO), decarboxyla-tion (DCX) and decarbonyladecarboxyla-tion (DCN).
The occurrence of those reactions was sustained by presence of carbon oxides and water on liquid and gaseous products by the presence of specific hydrocarbons. For the fresh catalyst, a major quantity of water on products indicates a predominance of HDO reaction, which lead to production of C18hydrocarbon by HDO of
stearic acid (18:0) and of C15 hydrocarbon by HDO of C16fatty
acids. For fresh catalyst, only the C15and C16hydrocarbons are
pre-sent, and this occurrence was for the thermal stability of saturated C16fatty acid (palmitic acid).
The products distributions change as the deactivation advance. It was clear in the results onFig. 3and is evident onFig. 7, which summarizes the results by carbon atom number of molecules by time, grouping hydrocarbons from 1 to 18 carbons, water and car-bon oxydes, also oxygenated from 6 to 18 carcar-bons, the sibscrite x indicates that all oxygenate wit the respective chain length. The Fig. 7highlight the product distribution changed, occurred mainly by coke deposition, which affected the crack and deoxygenation capability of material. Over the time was a visible reduction on gas product and an increase on long chain hydrocarbons.
The deactivation reduces not only the DOC, also the DOD was greatly reduced by time on cracking over NaZSM5. In consequence of deactivation, the production of fatty acid increase, observed in Fig. 7by C16Oxand C18Ox,which compose the triglycerides of
soy-bean oil. The decrease on degrees DOD and DOC, together led to the production of free fatty acids, which are not present on the raw material. These molecules were originated by the cracking of the chain of fatty acid, without a deoxygenation, reaction have been happened. The effect was a high acid content on product, which increases as the deactivation goes on. The sum of these effects led to an inversion of products with a high production of gaseous hydrocarbon at the beginning of the reaction, to a high production of fatty acids after 120 min of reaction because of deactivation.
The dehydrogenation, cyclization and aromatization were also strongly affected by deactivation on cracking over NaZSM5. The results onTable 4show that the aromatic content was higher for the first 90 min of reaction but it decreases over time. The high amount of aromatic compounds of liquid product indicates a high occurrence of dehydrogenation reactions, which produces unsatu-ration of the carbon chain, cyclization and aromatic formation.
Fig. 6. Degree of Deoxygenation for ZSM5 catalyst.
Because of deactivation, the HDO process was incomplete for some acids, which led to production of oxygenated radicals (R– O). For NaZSM5, the amount of these radicals has a great increase after 90 min of reaction. These molecules include alcohols, ethers, aldehydes, and cyclic ketones. The longer chain species at 90 and 120 min was Octadecadecen-1-ol and Cyclopenten-1-one, 2-pentyl, on a less than 3% amount. That kind of molecules was found on a study of cracking on myristic acid over NaZSM5 and HZSM5
[35], the results show compounds like 1-Octanol and Octanal.
The incomplete hydrodeoxygenation is a strong evidence of
occur-rence of this reaction, and the presence of COx an evidence of
decarbonyl and decarboxylation. The results onTable 3show that for the fresh catalyst the higher amount of H2O indicates the
pref-erence for hydrodeoxygenation. On the second period, 60 min, the major content was of carbon oxides, indicating that the hydrodeoxygenation is not the preferred reaction, which continues until 120 min of reaction. The result shows an inversion of deoxy-genation process over the time, which occurs by cocking of catalyst.
4.4. Products from HZSM5
The HZSM5 products, shown onTable 3 and summarized by
chain length onFig. 8, by the same criteria forFig. 7, show that this catalyst produced a greater amount of gaseous products, for the fresh catalyst, than the NaZSM5. That occurred because of the increase on catalyst acidity led to an increase of cracking[36]. In this period, this catalyst produced gasoline, less kerosene and very low content of diesel. The low content of heavy hydrocarbons like diesel on product of HZSM5 is because its high cracking capability. In this period, no oxygenated organic compound was found, indicating complete triglyceride conversion, and how none of undesirable products was produced, the selectivity do not fit on discussion,Table 3. After 60 min of reaction only 0.04% of oxy-genated radical (R–O) was produced, which a selectivity greater than the fresh NaZSM5. Even after 90 min, the selectivity of proton zeolite is greater than the Na. Only after 120 min, the selectivity have a low value of 4.89, however the amount of hydrocarbon are greater than the oxygenated. It is clear that H+on zeolite on
zeolite instead of Na+and in consequence, increases of acidity
pro-motes deoxygenation reaction.
The liquid hydrocarbon content produced on reaction with HZSM5 changes with reaction time. For fresh catalyst, the mainly content was gasoline (21.38%) and kerosene (3.20%), with insignif-icant diesel content. In this situation, the fresh catalyst fragments organic chains, producing more light hydrocarbons, because of its high activity. After 60 min, the gasoline and kerosene content rises to 36.66% and 7.54%, respectively. That occurs by the decrease on fragmentation frequency and by an increase on aromatization reactions, shown on DOA (Fig. 5).
At 90 min, the catalyst activity is still high; however, the profile of liquid is changing. The gasoline content continues to rise to 50.77%, with 7.0% of kerosene. With low diesel content and only 0.09% of oxygenated compounds on product. That result indicates a decrease on deoxygenation and cracking reactions, by the rise of mean hydrocarbon molecular weight and by the increase on organic oxygenated molecules.
After 120 min, gasoline content strongly decreases and kero-sene has a weak decrease, with a production of 1.23% of diesel, this increase was also accompanied by an increase in the content of organic acid to 38.82%, and an increase to 1.72% to oxygenated rad-icals. At this period, the result show strong signs of deactivation, by the decrease of deoxygenation and cracking reactions. However, the hydrocarbon produced has a high DOA value,Fig. 5, indicating that the aromatization reactions have less interference on deacti-vation process.
For HZSM5 the higher amount of aromatics compounds could be mainly by the presence of a higher acidity and by the availabil-ity of a high content of H+. This could interact with the organic
compounds, capturing hydrogen and generating gas H2. On
crack-ing of soybean oil over HZSM5 the mainly component of liquid pro-duct was aromatic hydrocarbons (74%)[3].
By the degree of aromatization,Fig. 5, is evident the great differ-ence on hydrocarbon products between the treated material and the non-treated. Over the time, for HZSM5, the DOA increase, showing that the percentage of hydrocarbon that turn into aro-matic form by aromatization reactions is being higher. The deacti-vation effect change mainly on deoxygenation and cracking reactions, with the aromatization reactions, being less affected.
This result indicates that the lifetime on cracking was raised by the ion exchange process. That interfered on global distribution of products. Joining the products after 90 min on reaction, for NaZSM5 the total of hydrocarbon represent 58% of the total pro-duct, whereas for the HZSM5 this represents 85%. Also, is possible to observe the change on product characteristics by the reaction time, because of deactivation. It indicates that with different resi-dence times, on a continuous catalyst-fed reactor, is possible to control the type of product obtained, producing the raw material of interest.
The protonated catalyst, also changes the deoxygenation pro-cess. During all period the amount of H2O was higher than CO2,
which indicates that the main process of deoxygenation was is hydrodeoxygenation. That result was different that found for NaZSM5, which only at the first period the hydrodeoxygenation was the principal deoxygenation mechanism.
5.1H NMR analysis
Looking into results,Fig. 9, is possible to see the change on the products profile over the time. For the fresh catalyst, as found on the result from CG-MS, the product was rich on aromatic hydrogen, with a relative high content of phenyl and naphthyl groups with a saturated chain as the radical, identified as propyl-benzene and propenyl-naphthalene. That contributed for the relative high con-tent of saturated hydrogen. The concentration of aromatics hydro-carbon reduces as the reaction goes on and the effects of deactivation take place. At the 120 min, less than 5% of all hydro-gen was aromatic.
The olefin hydrogen is from of unsaturations on organic mole-cules, which includes hydrocarbon and oxygenated molecules. That hydrogen content reduces over the time,Fig. 10, being nearly constant from the second period of cracking. Showing that the fre-quency of triglyceride fragmentation and cracking of free fatty acids reactions was reducing as the deactivation occur.
The content of hydrogen from glyceride species on triglyceride decomposition show that the conversion for triglyceride was com-plete for the fresh catalyst. After 60 min, the triglyceride hydrogen content was still on product, growing with reaction time. That ris-ing, was followed by the rising of the saturated hydrocarbon con-tent, which was from the long chains of fatty acid on triglycerides. 5.1. Coke produced
As yet discussed, it was observed a change of liquid and gaseous products distribution over time. After the reaction, the catalyst
sur-face was visible covered with a black compound, which is common for cracking process.
Coke analysis and quantification by TPO test showed the amount of carbon material at the used catalyst. TheTable 5 pre-sents the amount and type of coke quantified by hydrogen con-sumption. It shows a great difference on carbon deposited over the both catalyst.
The amount of coke deposed over NaZSM5 after 120 min of reaction was significant, 140.25 mg/gcatalyst.Fig. 11show the TPO
oxidation peaks for NaZSM5, where the two firsts peaks, at 677 K and 770 K, is relative to heavy liquid hydrocarbon trapped on the porous structure of material. The light coke oxidation peak, at 863 K, is the solid hydrocarbon easier to oxidize than the heavy hydrocarbon in the last oxidation peak, at 967 K. The light hydro-carbon could be associated with amorphous coke deposited over the catalyst surface and the heavy hydrocarbon with graphitic car-bon like that found over La2NiO4/ZSM5[37]and Ga-MA/ZSM5[38]
for different reaction times.
The amount of deposited carbon on HZSM5 was inferior, 59.95 mg/gcatalyst, after 120 min of reaction. TheFig. 12shows the
oxidation peak distribution for this catalyst. At 767 K, a hydrocar-bon peak was evident, showing a slight on its amount. The light coke peak suffer an increase on its maxima of 30 K, however the amount of this carbon was 900% lower than NaZSM5. For the heavy coke, the amount was slight inferior and the peak maximum has an increase.
The TPO results shown that the ion exchange move peaks to higher temperature. They are more fixed on catalytic surface. Com-paring with a coke combustion study for ZSM5 by a thermogravi-metric analysis, the acidification process increase the coke amount[39], however, as higher the Si/Al ratio was as higher is the coke yield, indicating that the stronger acid catalyst produced less coke. The acidification by ammonium rise the acidity of mate-rial, reducing the coke amount.
The increased strength of strong acid sites, after the exchange with ammonia, led to less coke formation in quantity; however, the coke formed is harder to oxidize than that formed by catalyst
Fig. 9.1
H NMR spectra result for soybean cracking over NaZSM5.
Fig. 10.1
H NMR hydrogen distribution for soybean cracking over NaZSM5.
Table 5
Amount of carbon by TPO of used catalyst. Carbon amount (mgcarbon/gcatalyst)
Catalyst Total Hydrocarbon Light coke Heavy coke NaZSM5 140.25 40.32 79.95 19.96 HZSM5 56.95 30.66 8.68 17.59
with no ion exchange. This result is similar from that found in the literature[3], where with a higher acidity of the catalyst, led to less coke production.
6. Conclusions
Cracking of soybean oil produces a large variety of compounds, which change which catalytic acidity and time of reaction. Using ZSM5, it was possible observed big difference between protonic, HZSM5, and non-protonic form, NaZSM5. Using NaZSM5, the main produced from fresh catalyst was gaseous hydrocarbon and aro-matics. The hydrodeoxygenation was the main deoxygenation pro-cess. The deactivation changes strongly the products and the deoxygenation mechanism.
The acidity increases when HZSM5 was used which changes the product distribution over the reaction time. The improvement of acidity increases the hydrocarbon production and the aromatic content. Even after 90 min of reaction, the hydrocarbon selectivity was higher than for NaZSM5
The results of 1H NMR show a complete conversion of the
triglycerides for the fresh NaZSM5, reducing with the reaction time. That indicates also a complete conversion of the triglycerides even after 90 min of reaction for HZSM5, indicating a great improvement on catalyst lifetime.
Acknowledgments
Thanks to the CAPES – Brazil (Coordenação de Aperfeiçoamento de Pessoal de Nível Superior) for financial support. Thanks to PhD Valmir Calsavara for the support on this research.
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