3230
Ind. Eng. Chem. Res. 1999, 38, 3230-3237
Catalytic Conversion of Palm Oil to Hydrocarbons: Performance of Various Zeolite Catalysts Farouq A. Twaiq, Noor A. M. Zabidi, and Subhash Bhatia* School of Chemical Engineering, Perak Branch Campus, Universiti Sains Malaysia, 31750 Tronoh, Perak, Malaysia
The catalytic cracking of palm oil to fuels was studied in a fixed bed microreactor operated at atmospheric pressure, a reaction temperature of 350-450 °C and weight hourly space velocities (WHSVs) of 1-4 h-1. HZSM-5, zeolite β, and ultrastable Y (USY) zeolites with different pore sizes were used to study the effects of reaction temperature and WHSV on the conversion of palm oil and yields of gasoline. The performances of HZSM-5-USY and HZSM-5-zeolite β hybrid catalysts containing 10, 20, and 30 wt % HZSM-5 were investegated. Potassium-impregnated K-HZSM-5 catalysts with different potassium loadings were used to study the effect of acidity on the selectivity for gasoline formation. The major products obtained were organic liquid product (OLP), hydrocarbon gases, and water. HZSM-5 catalyst gave conversion of 99 wt % and a gasoline yield of 28 wt % at a reaction temperature of 350 °C and WHSV of 1 h-1 and was the best among the three zeolites tested. The HZSM-5-USY hybrid catalyst performed better than USY catalyst as it resulted in a higher gasoline yield, whereas HZSM-5-zeolite β hybrid catalyst gave lower conversion compared to that of zeolite β. The selectivity for gasoline decreased from 45 to 10 wt % with an increase in potassium concentration from 0 to 1.5 wt %. Introduction Currently some researchers are concentrating on developing alternative and renewable sources of liquid fuels that are “environmental friendly”.1 Vegetable oils are attracting increased interest in this respect.2 Many researchers improved the production of hydrocarbons and chemicals from plant oils using catalytic cracking processes.3 The vegetable oils that have been investigated as alternative fuels are canola oil, tall oil, and jajoba oil. These plant oils were converted to hydrocarbons over many types of catalysts such as HZSM-5, hydrogen-zeolite Y, silica-alumina, H-mordenite, and silica-alumina-pillared clay, at a temperature range of 300-500 °C.4 Over 95 wt % of the plant oils were converted to liquid hydrocarbons in the gasoline boiling range, light gases, and water.4,5 Oil palm is widely grown in Malaysia, and the palm oil has a triglyceride composition (wt %) as follows: C44, 0.07; C46, 1.18; C48, 8.08; C50, 39.88; C52, 38.77; C54, 11.35; C56, 0.59.6 Palm oil has been converted into a more compatible form of methyl ester known as biodiesel, by the Palm Oil Research Institute Malaysia (PORIM). The biodiesel was developed to substitute the diesel for engines. Rapeseed, sunflower, and soybean oils are examples of oils used in methyl ester production. There is a need for a direct conversion process for converting palm oil to clean premium transportation fuels and chemicals. In the literature, the shape selective zeolite catalysts have been used for catalytic cracking and the medium pore size catalyst such as HZSM-5 was found to be more efficient in the cracking process and in the organic liquid production.7,8 Prasad and coworkers reported that HZSM-5 catalyst gave mainly aromatic hydrocarbons.9,10 The properties of shape selective catalysts control the product distribution in the process, and therefore, the * To whom correspondence should be addressed. Fax: 60 5 3677055. E-mail:
[email protected].
choice of the shape selective zeolite catalyst is an important factor.11 Activity and selectivity of these catalysts are governed by several factors, such as acidity, pore size and its distribution, and also the shape of the pores. Hybrid catalysts were used to improve the shape selectivity of the catalyst.10 Katikaneni and coworkers reported cracking of canola oil over hybrid catalysts using the mixture of HZSM-5 with silicaalumina and H-Y with silica-alumina.8 The addition of zeolite catalysts to silica-alumina increased the cracking of canola oil and aromatic hydrocarbon contents. Acidity of a catalyst was determined to be one of the important factors in the cracking process. The conversion was found to decrease with a decrease in catalyst acidity. The acidity of the catalyst influences selectivity of the catalyst. Katikaneni and co-workers reported that potassium impregnation of HZSM-5 catalysts affects the aromatization and oligomerization reactions.12 The objectives of the present investigation are (a) to study the effects of zeolite catalyst pore size on the conversion of palm oil and selectivity for gasoline, (b) to determine the performance of hybrid catalysts, and (c) to study the effects of the catalyst acidity on the selectivity for aromatic hydrocarbons and liquid hydrocarbons in the gasoline boiling point range. Experimental Section Catalysts. The HZSM-5 (CBU 8070) and zeolite β (811BL-25) were supplied by P. Q. Corp., Kansas City, MO. The USY zeolite was obtained from W. R. Grace (s) Ltd., Grace Division, Asia Pacific, Singapore. These powder zeolites were calcined in a muffle furnace for 6 h prior to use. The calcination temperature was 400 °C for zeolite β, and it was 500 °C for HZSM-5 and USY zeolites. Hybrid catalysts were prepared in order to increase the selectivity of aromatics and gasoline range hydro-
10.1021/ie980758f CCC: $18.00 © 1999 American Chemical Society Published on Web 08/19/1999
Ind. Eng. Chem. Res., Vol. 38, No. 9, 1999 3231
carbons over the USY and zeolite β catalysts. The HZSM-5-zeolite β hybrid catalysts were prepared by physical mixing of the HZSM-5 with zeolite β powders. The same method was used to prepare HZSM-5-USY hybrid catalysts. The compositions of both types of hybrid catalysts were 10, 20, and 30 wt % HZSM-5. To investigate the effects of catalyst acidity on the conversion of palm oil and yields of product, a series of potassium-impregnated HZSM-5 was prepared. The potassium-impregnated K-HZSM-5 catalysts were prepared via the wet impregnation technique by using different concentrations of potassium carbonate aqueous solutions. Catalysts were dried in the oven at 100 °C for 2 h, followed by calcination in a muffle furnace for 6 h at 500 °C. The HZSM-5 loaded with 0.5 wt % potassium was coded as K1; the 1 and 1.5 wt % potassium ones were labeled as K2 and K3, respectively. The nonimpregnated HZSM-5 catalyst was coded as K0. Catalyst Characterization. The impregnated catalysts were characterized using different techniques. (a) X-ray Diffraction Measurements. Powder Xray diffraction (XRD) measurements were carried out to identify component phases as well as to determine the degree of the crystallinity of the catalysts,13 after potassium impregnation. The XRD analysis was performed on the catalysts using a Philips diffractometer (Model PW 1820) with a graphite-monochromated Cu KR source operated at 40 kV and 40 mA. The XRD patterns were obtained using scanning angle (2θ) in the range of 5-80° at a scanning speed of 2°/min. The search software (JCPDS) that was available in the computer was used to identify the various phases in the potassium-impregnated samples and to compare them with those of the nonimpregnated catalyst. (b) Nitrogen Adsorption. Surface area and pore size measurements of catalysts were conducted on the Autosorb I, Quantachrome Automated Gas Sorption System supplied by Quantachrome Corp. The powder samples were degassed overnight under vacuum at a temperature of 250 °C. Multipoint adsorption isotherms were obtained on the samples using nitrogen as adsorbate. The Autosorb I setup is capable of measuring surface area down to 1 m2 as nitrogen is used as an adsorbent. The software (Micropore version 2.46) was used to calculate the surface area and pore size from nitrogen adsorption isotherm. (c) Acid Strength Measurements. Thermal gravimetric analysis (TGA) was used to determine the strength of the acid sites formed over the catalyst.14 The thermal gravimetric analyzer (TGA 7) was supplied by Perkin-Elmer, and it was coupled with a TG controller (TAC 7/DX). The TGA was used to determine the concentration of acid sites through adsorption-desorption of isopropylamine (an organic base) by monitoring the weight changes that occur. The amount of weight change and the energy (temperature) required to desorb the isopropylamine provides an indication of the density and the strength of the acid sites, respectively. The sample was heated to 500 °C, at a heating rate of 10 °C/min in an argon gas stream, flowing at 40 mL/min for 30 min for isotherm activation.15 The sample was cooled to 100 °C and equilibrated at this temperature. A pulse of isopropylamine in argon was introduced for 5-10 min; the excess isopropylamine was physically desorbed under the argon purge for 80-85 min. The sample was heated to 750 °C at a heating rate of 10 °C/min to desorb the chemisorbed isopropylamine. The
chemisorption curve reveals the density and acid strength of the catalyst sample. The results obtained from this method were reliable, and the accuracy of the measurement was within the range of (5%. (d) FT-IR Studies. FT-IR technique was employed to determine the nature of acid sites (Lewis and Bronsted types) present on the zeolite catalyst.16 The procedure of preparing the catalyst samples for FT-IR analysis was based on the method described by Corma and co-workers.17 The catalyst samples were degassed overnight at 300 °C under vacuum. Excess pyridine was admitted to the catalyst for adsorption for 1 h, followed by desorption of physically adsorbed pyridine at 200 °C under vacuum. The IR spectra of the catalysts were scanned using a Perkin-Elmer FTIR (Model 2000). The FT-IR measurements were made on pellets (5% catalyst in KBr) to record the band of framework of O-H bonds in the region of 3500-4000 cm-1. The attenuated total reflectance (ATR) accessory (Model 1600) with ZnSe crystal was employed for recording bands in the region of 1400-1650 cm-1. (e) XRF Measurements. X-ray fluorescence (XRF) was used to identify the elements in the impregnated catalysts13 and to determine the exact percentage of potassium incorporated into the catalyst through the impregnation. The XRF measurements were carried out with the X-ray spectrometer RIX3000 supplied by Rigaku. The spectrometer was equipped with an Rh X-ray tube operated at 50 kV and 50 mA. The XRF measurements were carried out on fusion beads (10% catalyst in Li2B4O7) at the scanning speed of 120 deg min-1. Experimental Procedure The palm oil cracking was performed over the zeolite catalyst at atmospheric pressure, a reaction temperature ranging from 350 to 450 °C, and a palm oil feed rate (weight hour space velocity(WHSV)) in the range of 1-4 h-1. Figure 1 shows the experimental setup used for the present study. A 1 g amount of calcined catalyst was used in the powder form (particle size less than 32 µm) in order to minimize mass-transfer effect. The catalyst was loaded over 0.2 g of quartz wool supported over a stainless steel mesh surface supported over the pin. The reactor was heated to the desired reaction temperature using a vertical tube furnace under argon gas flowing at a rate of 1 L h-1. After temperature stabilization, the flow of argon gas was stopped. The palm oil was fed using a syringe pump (Model No. E-74900-05, Cole-Parmer) at the desired WHSV. The products leaving the reactor were cooled to 40 °C in the condenser system in order to prevent solidification of residual oil. The condensed liquid products were collected in a glass liquid sampler at room temperature, and the gaseous products were collected in a gassampling bag. The sample was collected once the steady state was reached. The reactor was flushed by passing argon gas at the rate of 0.1 L h-1 to remove the remainding products from the reactor. The catalyst was washed with n-hexane solvent in order to determine the products that remained in the system. The washed catalyst was dried in an oven for 1 h prior to coke analysis. The aqueous phase was separated from the condensed liquid products using a syringe. The liquid product was distilled in a vacuum microdistillation unit (G-Seal Sdn. Bhd., Penang, Malaysia) under a vacuum of 5 × 10-3 kPa, at 200 °C for 30 min. The distillate
3232 Ind. Eng. Chem. Res., Vol. 38, No. 9, 1999
kerosene, and diesel were separated in the temperature ranges of 60-135, 135-160, and 160-200 °C, respectively. Other important peaks of aromatic hydrocarbons were determined by injecting pure samples of aromatics (benzene, toluene, and xylenes) and were separated in the temperature range of 90-135 °C. (c) Coke Analysis. The coke formed over the catalyst during the cracking reaction was determined by two methods: (1) Spent HZSM-5 catalyst was regenerated in a muffle furnace at 600 °C for 1 h, whereas zeolite β and USY zeolite catalysts required 2 h for regeneration. The difference in weight between hexane-washed catalyst and regenerated catalyst was equivalent to the coke formed from the cracking reaction. (2) Thermal gravimetric analysis (TGA) was used to determine the type of coke deposit over the catalyst. About 5 mg of hexane-washed spent catalyst sample was subjected to TGA at a temperature program of 20 °C min-1. The heating started from ambient temperature to 700 °C in an argon gas stream of 100 mL min-1. The low-temperature peaks correspond to soft coke, whereas the higher temperature peak was related to the hard coke. Results and Discussion (1) HZSM-5, Zeolite β, and USY Catalysts. The performance of three zeolite catalysts having different pore sizes was studied in terms of conversion, yield of gasoline, and selectivity for OLP products. The conversion, yield, and selectivity are defined as follows: Figure 1. Microreactor rig used in the catalytic conversion of palm oil.
fraction was the organic liquid product (OLP), and the pitch was assumed to be residual oil. The amount of residual oil was weighed after each run. Analysis of Products. (a) Gaseous Products. The gaseous products were analyzed using a gas chromatograph (Hewlett-Packard, Model No. 5890 series II) using a Porapak Q column of 3.15 mm diameter × 90 cm length. The chromatograph was equipped with both flame ionization (FID) and thermal conductivity detectors (TCD). Helium was used as a carrier gas for both detectors. The FID was used to detect the hydrocarbon components (C1-C5) present in the gaseous product, and the TCD was used to determine other gaseous products such as CO2. The weight of the gaseous product was determined from the average molecular weight determined from gas analysis. The total gas evolved during the experiment was monitored using a gas flow meter. (b) Organic Liquid Product. Organic liquid products were analyzed using a capillary glass column (Petrocol DH 50.2, film thickness, 0.5 µm; 50 m length × 0.2 mm id) at a split ratio of 1:100. The oven temperature was programmed at a heating rate of 4 °C/ min in the range of 60-200 °C. The analysis of OLP included a wide variety of hydrocarbon components. The composition of OLP was defined according to the boiling point range of the petroleum products. Gasoline, kerosene, and diesel were identified by injecting a commercial sample of the respective component. Light hydrocarbons were separated in the column at the temperature of 60 °C for 6 min, whereas, gasoline,
conversion (wt %) ) yield (wt %) ) selectivity (wt %) )
P-R × 100% P
Y × 100% P
Y × 100% P-R-Y
(1) (2) (3)
where P is the palm oil feed weight (kg), R is the residual oil weight, (kg), and Y is the product weight (gasoline, kerosene, etc.) (kg). Tables 1-3 show the conversions and yield of various products obtained using HZSM-5, zeolite β, and USY catalysts, respectively. The performance of these catalysts was compared only in terms of their pore sizes. The three zeolite catalysts having different pore sizes gave different amounts of gasoline yield. HZSM-5 with a pore size of 0.54 × 0.56 nm and a 10 ring pore system gave the highest conversion of 99 wt % and a maximum gasoline yield at low WHSV of 1 h-1. The conversion remained almost constant with the change in reaction temperature from 350 to 450 °C at WHSV of 1 h-1. Zeolite β has a pore size of 0.56 × 0.74 nm with an interconnecting 12 ring pore system and chiral pore sections. In the presence of zeolite β, the conversion of palm oil increased with reaction temperature and decreased with WHSV. The external surface area of zeolite β is relatively high compared to that of HZSM5. It is possible that acid sites associated with an aluminum framework lie closely to the outer surface and contribute to the overall catalytic activity of the zeolite. This may adversely affect the shape selectivity of the reaction.18 USY zeolite has a pore opening of 0.8 nm and
Ind. Eng. Chem. Res., Vol. 38, No. 9, 1999 3233 Table 1. Cracking of Palm Oil over HZSM-5 Catalyst 350 °C
400 °C
450 °C
WHSV ) 1 h-1
WHSV ) 2.5 h-1
WHSV ) 4 h-1
WHSV ) 1 h-1
WHSV ) 2.5 h-1
WHSV ) 4 h-1
WHSV ) 1 h-1
WHSV ) 2.5 h-1
WHSV ) 4 h-1
conversion
99.0
80.3
77.4
96.9
89.6
78.7
97.2
91.6
86.1
residual oil aqueous phase yield coke yield gas yield OLP yield
1.0 7.5 6.1 41.8 43.6
19.7 5.9 1.4 20.0 53.0
21.3 8.9 2.3 36.4 31.1
2.8 5.7 5.3 46.1 40.1
8.4 2.7 1.0 44.4 43.5
13.9 2.6 2.5 34.8 46.2
methane ethylene and ethane propylene and propane C4+ C5+
1.6 6.0 17.6 13.0 3.6
Yields of Gaseous Composition (wt % Palm Oil Fed) 0.7 0.5 0.6 0.5 0.5 2.9 2.4 4.0 2.3 2.3 8.4 5.8 22.6 15.6 18.5 6.4 4.8 16.6 11.4 12.7 1.6 1.0 3.5 2.8 2.4
1.2 4.2 20.5 15.8 4.4
2.2 6.1 17.4 14.3 4.4
3.1 9.5 10.4 7.7 4.1
light hydrocarbons gasoline kerosene diesel
1.2 28.3 9.1 5.0
Yields of OLP Composition (wt % Palm Oil Fed) 6.4 5.1 4.3 4.2 1.2 26.6 23.5 20.5 25.8 17.3 15.8 15.4 11.4 14.2 8.7 4.2 3.3 4.0 4.8 3.9
3.2 24.2 9.3 3.4
5.1 22.9 12.6 2.9
4.1 24.4 15.8 1.9
benzene toluene xylene
3.8 11.8 11.5
2.5 7.1 8.5
2.0 6.5 8.7
1.9 7.4 11.0
Product Distribution (wt % Palm Oil Fed) 22.6 3.1 10.4 5.6 3.7 3.1 10.0 5.7 4.7 14.5 47.3 32.6 47.3 40.2 49.0
Yields of Aromatic Hydrocarbons in OLP (wt % Palm Oil Fed) 1.8 1.1 2.0 2.1 1.5 7.6 5.7 6.0 8.2 5.0 11.7 9.8 8.1 11.6 6.6
Table 2. Cracking of Palm Oil over Zeolite β Catalyst 350 °C
conversion residual oil aqueous phase yield coke yield gas yield OLP yield methane ethylene and ethane propylene and propane C4+ C5+ light hydrocarbons gasoline kerosene diesel benzene toluene xylene
400 °C
450 °C
WHSV ) 1 h-1
WHSV ) 2.5 h-1
WHSV ) 4 h-1
WHSV ) 1 h-1
WHSV ) 2.5 h-1
WHSV ) 4 h-1
WHSV ) 1 h-1
WHSV ) 2.5 h-1
WHSV ) 4 h-1
82.2
65.0
51.3
86.0
76.6
64.1
95.7
88.2
77.2
Product Distribution (wt % Palm Oil Fed) 48.7 14.0 23.4 35.9 1.4 5.3 4.2 4.8 7.3 8.2 7.3 8.4 6.0 18.8 17.3 11.1 36.6 53.7 47.8 39.8
4.3 4.4 8.0 45.2 38.1
11.8 2.5 6.2 26.5 53.0
22.8 1.8 5.0 31.0 39.4
1.0 3.2 4.5 4.6 0.7
Yields of Gaseous Composition (wt % Palm Oil Fed) 0.5 0.1 1.5 1.0 0.3 1.6 0.9 5.0 3.7 1.4 2.6 2.3 5.5 5.3 3.5 2.5 2.4 5.4 5.7 4.3 0.4 0.3 1.4 1.6 1.6
2.9 9.4 16.0 15.5 1.4
0.6 2.6 8.5 11.8 3.0
1.0 5.4 9.5 10.0 4.1
7.5 22.0 9.4 9.2
Yields of OLP Composition (wt % Palm Oil Fed) 7.5 7.0 8.8 10.6 7.3 19.1 15.6 22.1 19.6 16.4 8.6 6.9 12.1 9.2 8.5 7.7 7.1 10.7 8.4 7.6
4.3 18.4 8.7 7.0
6.5 26.3 11.1 9.1
0.7 16.3 12.8 9.6
0.5 0.9 2.1
Yields of Aromatic Hydrocarbons in OLP (wt % Palm Oil Fed) 0.9 0.6 0.7 0.7 0./6 1.0 2.9 2.1 1.5 1.2 2.6 4.9 3.8 2.5 2.6
0.5 2.2 3.9
1.1 2.0 3.6
0.4 2.4 6.3
17.8 9.7 10.4 14.0 48.1
35.0 6.0 8.5 7.6 42.9
a 12 ring pore system. The conversion increased more sharply within the temperature range of 400-450 °C in the presence of USY zeolite. The product distribution was also found to vary with the change in pore size of different zeolites. Based on the palm oil feed, the gasoline yields were between 17 and 28 wt % over HZSM-5, 15-26 wt % for zeolite β, and 4-17 wt % for USY zeolite catalyst. The gasoline yields decreased with an increase of WHSV and a decrease of reaction temperature for zeolite β and USY zeolite catalysts. The maximum gasoline yield was obtained with HZSM-5, indicating high shape selectivity of a catalyst. The shape selectivity played an important role in secondary cracking, resulting in a high yield of organic liquid product. USY zeolite gave high selectivity for kerosene and diesel-range hydrocarbons. The selec-
tivity for aromatic hydrocarbons was 20-38 wt % with HZSM-5 catalyst, 4-16 wt % in zeolite β, and 3-13 wt % in USY zeolite, respectively. The gas yield increased with temperature and decreased with an increase of WHSV. Ethylene, ethane, propylene, propane and butane were some of the major components of the gaseous products. The performance of each catalyst in terms of the coke formation was also examined. Different zeolite catalysts gave different weight percent coke, showing their shape selectivity in the coke formation. At 400 °C and WHSV of 2.5 h-1, HZSM-5 gave 10 wt % coke, whereas zeolite β and USY gave 30 and 15 wt % coke, respectively, based on the weight of spent catalyst. Based on the conversion and yield of products from palm oil cracking with each catalyst, the relative
3234 Ind. Eng. Chem. Res., Vol. 38, No. 9, 1999 Table 3. Cracking of Palm Oil over Ultrastable Y (USY) Catalyst 350 °C
400 °C
450 °C
WHSV )1 h-1
WHSV ) 2.5 h-1
WHSV ) 4 h-1
WHSV ) 1 h-1
WHSV ) 2.5 h-1
WHSV ) 4 h-1
WHSV ) 1 h-1
WHSV ) 2.5 h-1
WHSV ) 4 h-1
conversion
53.2
45.4
28.3
61.5
51.1
29.6
93.2
70.7
57.6
residual oil aqueous phase yield coke yield gas yield OLP yield
46.8 5.4 12.2 6.4 29.2
54.6 1.6 9.5 9.9 24.4
70.4 4.4 5.0 8.5 11.7
6.8 4.5 4.3 39.3 45.1
29.3 4.3 5.0 36.3 25.1
42.4 0.0 3.0 28.3 26.3
Yields of Gaseous Composition (wt % Palm Oil Fed) 1.2 0.3 1.4 0.4 0.4 3.0 0.7 5.0 1.1 2.4 3.6 0.6 4.5 2.2 3.4 1.6 0.3 2.5 3.0 2.0 0.5 0.1 0.7 0.4 0.3
1.8 6.2 15.7 10.2 5.4
1.0 8.0 13.0 11.3 3.0
0.8 2.1 14.4 9.1 1.9
Yields of OLP Composition (wt % Palm Oil Fed) 1.8 8.1 2.7 2.6 5.2 3.8 13.0 13.0 3.0 2.9 13.8 6.6 14.4 5.7 0.8 5.7
5.7 17.5 11.5 10.4
3.5 14.3 5.0 2.3
1.6 11.7 7.2 5.8
0.9 1.7 2.6
1.3 1.8 2.0
0.1 0.4 1.4
methane ethylene and ethane propylene and propane C4+ C5+ light hydrocarbons gasoline kerosene diesel benzene toluene xylene
0.8 2.4 1.9 1.0 0.3 2.3 7.3 9.0 10.6 0.2 0.5 1.5
Product Distribution (wt % Palm Oil Fed) 71.7 38.5 48.9 3.6 7.6 3.0 2.2 9.5 13.1 2.0 14.1 7.1 20.5 30.3 27.9
0.8 4.3 3.1 3.5
Yields of Aromatic Hydrocarbons in OLP (wt % Palm Oil Fed) 0.1 0.7 0.7 0.6 0.1 0.3 0.2 0.3 0.3 0.1 0.8 0.9 1.4 1.6 0.8
performance of the catalysts for the production of hydrocarbons can be presented as follows: (1) Yield of gaseous hydrocarbons: HZSM-5 > zeolite β > USY. The highest value obtained was 47.3 wt % over HZSM-5 at 400 °C and WHSV of 1 h-1. (2) Yield of OLP: HZSM-5 ) zeolite β > USY. The optimum value was 53.0 wt % over HZSM-5 at 350 °C and WHSV of 2.5 h-1 and 53.7 wt % over zeolite β at 400 °C and WHSV of 1 h-1. (3) Yield of gasoline: HZSM-5 > zeolite β > USY. The highest value was 28.3 wt % over HZSM-5 at 350 °C and WHSV of 1 h-1. (4) Yield of aromatic hydrocarbons: HZSM-5 > zeolite β > USY. The highest value found was 27.0 wt % over HZSM-5 at 350 °C and WHSV of 1 h-1. (5) Yield of kerosene: HZSM-5 > zeolite β > USY. The optimum value found was 15.9 wt % over HZSM-5 at 350 °C and WHSV of 2.5 h-1. (6) Yield of diesel: USY > zeolite β > HZSM-5. The highest value found was 14.35 wt % over USY at 350 °C and WHSV of 2.5 h-1. (2) Hybrid Catalysts. Tables 4 and 5 show the overall material balance for catalytic cracking of palm oil over HZSM-5-USY and HZSM-5-zeolite β hybrid catalysts containing 10, 20, and 30 wt % HZSM-5. All experiments involving hybrid catalysts were conducted at 400 °C and WHSV of 2.5 h-1. (a) HZSM-5-USY Hybrid Catalysts. HZSM-5zeolite catalyst was highly selective for aromatics and hydrocarbons in the gasoline boiling point range, whereas USY was less selective for aromatics but more selective for hydrocarbons in the diesel boiling range. The results show that the conversion and gas production increased with increasing HZSM-5 content, whereas the production of OLP decreased slightly with increasing HZSM-5 content in the hybrid catalyst. The hybrid catalysts improved the ability for palm oil conversion at lower reaction temperatures. The increase in conversion resulted from the synergetic effect of the pore size of the two catalysts. The USY catalyst, with a pore size of 0.8 nm, was highly selective for long-chain hydrocarbons such as palm oil and ease of desorption of the hydro-
Table 4. Cracking of Palm Oil over Different HZSM-5-USY Hybrid Catalysts catalyst conversion
10 wt % HZSM-5
20 wt % HZSM-5
30 wt % HZSM-5
62.9
64.9
76.5
Product Distribution (wt % Palm Oil Fed) residual oil 37.1 35.1 aqueous phase yield 1.5 3.0 coke yield 6.9 4.6 gas yield 17.0 17.7 OLP yield 37.5 39.6
23.5 3.0 4.1 22.6 46.8
Yields of OLP Composition (wt % of Palm Oil Fed) light hydrocarbons 5.0 0.3 5.9 gasoline 15.5 19.0 22.7 kerosene 10.0 10.3 12.6 diesel 7.0 4.0 5.6 Yields of Aromatic Hydrocarbons in OLP (wt % of Palm Oil Fed) benzene 0.6 0.9 1.1 toluene 2.1 3.7 4.5 xylene 3.3 5.9 7.8
carbon products from its pores. The role of HZSM-5 was in the second stage of the cracking, resulting in an increase of conversion and selectivity for aromatic hydrocarbons. The selectivity for liquid hydrocarbon products, especially gasoline, increased with increasing HZSM-5 content in the range of 20 and 30 wt %. The selectivity for aromatics and hydrocarbons in the kerosene boiling range were found to increase with an increase in HZSM-5 content. However, the selectivity for the hydrocarbons in the diesel boiling range was found to decrease with an increase in HZSM-5. It is clear from the results that improvements of USY selectivity and cracking ability were achieved with the addition of HZSM-5 to the USY catalyst. (b) HZSM-5-Zeolite β Hybrid Catalysts. It was found in the present study that HZSM-5 and zeolite β were both highly selective for formation of hydrocarbons in the gasoline boiling range. Zeolite β has been proven to be an active and shape selective catalyst for alkylation of benzene with propane.18 HZSM-5 had higher cracking ability and selectivity for aromatic hydrocar-
Ind. Eng. Chem. Res., Vol. 38, No. 9, 1999 3235 Table 5. Cracking of Palm Oil over Different HZSM-5-Zeolite β Catalysts catalyst conversion
Table 6. Cracking of Palm Oil over Potassium-Impregnated Catalysts
10 wt % HZSM-5
20 wt % HZSM-5
30 wt % HZSM-5
59.9
48.4
50.0
conversion
50.0 4.5 6.4 18.4 20.7
Product Distribution (wt % Palm Oil Fed) residual oil 9.6 25.4 aqueous phase yield 3.0 2.0 coke yield 2.8 2.5 gas yield 30.1 23.0 OLP yield 54.5 47.1
Products Distribution (wt % Palm Oil Fed) residual oil 40.1 51.6 aqueous phase yield 4.2 4.5 coke yield 8.9 6.7 gas yield 26.4 18.1 OLP yield 20.4 18.9 Yields of OLP Composition (wt % Palm Oil Fed) light hydrocarbons 2.6 2.0 gasoline 9.4 8.5 kerosene 5.4 5.4 diesel 3.0 2.8
3.8 8.8 5.2 2.9
catalyst
0.5 wt % K-HZSM-5
1.0 wt % K-HZSM-5
1.5 wt % K-HZSM-5
90.4
74.6
39.2 60.8 0.0 3.7 20.0 15.5
Yields of OLP Composition (wt % of Palm Oil Fed) light hydrocarbons 5.2 7.5 2.1 gasoline 27.9 22.2 3.3 kerosene 17.3 13.0 4.5 diesel 4.1 4.4 5.6
Yields of Aromatic Hydrocarbons in OLP (wt % Palm Oil Fed) benzene 0.3 1.3 2.8 toluene 0.2 0.9 1.4 xylene 0.3 1.2 1.8
Yields of Aromatic Hydrocarbons in OLP (wt % Palm Oil Fed) benzene 1.6 0.6 0.1 toluene 6.7 2.7 0.2 xylene 9.1 4.8 0.1
bons. The results show that conversion of palm oil and production for OLP did not vary significantly in hybrid catalysts with the addition of HZSM-5-zeolite (0-30 wt %). These results indicate that the addition of HZSM-5 to zeolite β did not make any positive contribution. Experiments conducted with zeolite β alone gave higher conversion and yield of organic product compared to the hybrid catalyst. The selectivity for hydrocarbons in the gasoline boiling range decreased with the addition of HZSM-5-zeolite to the hybrid catalyst. Zeolite β gave higher coke formation due to the polymerization reaction that occurred inside the pores of the zeolite β catalyst. This polymerization reaction decreased the chance of the second cracking reactions over HZSM-5 catalyst. Therefore, the presence of HZSM-5 catalyst did not improve conversion and selectivity. On the other hand, zeolite β has been widely studied as a Bronsted acid catalyst and shown to be highly active for reactions such as alkylation and acylation, which makes the catalyst highly selective for branch hydrocarbons.19 The branch hydrocarbons have restriction in diffusion in medium pores of HZSM-5-zeolites. Thus, the addition of HZSM-5 resulted in the dilution of zeolite β in the hybrid catalyst, which gave lower conversion and hydrocarbon selectivity. Thus, addition of HZSM-5 in HZSM-5-zeolite β hybrid catalyst was not beneficial in getting higher palm oil conversion and selectivity of hydrocarbon products. (3) Potassium-Impregnated HZSM-5 Catalysts. The palm oil conversion, material balance, and products distribution obtained from the cracking reaction of palm oil over potassium-impregnated HZSM-5 catalyst are presented in Table 6. The results show that the conversion of palm oil did not vary significantly at 0.5 wt. % potassium but decreased sharply as the potassium concentration increased to 1.5 wt %. The BrunauerEmmett-Teller (BET) surface areas of catalysts having different loading of potassium are presented in Table 7. It can be seen that the BET surface area of potassiumimpregnated HZSM-5 catalysts did not change appreciably with the loading of potassium up to 1 wt %. However, the 1.5 wt % potassium-impregnated HZSM-5 catalyst showed a marked drop in surface area (nearly 14%). Thus, the decrease in surface area is related to the blockage of the micropores. At low potassium loading, potassium is probably located at the outside zeolite surface, thus not reflecting the drop in the
Table 7. Surface Characteristics of Potassium-Impregnated HZSM-5 Catalysts
catalyst HZSM-5 0.5 wt % K-HZSM-5 1.0 wt % K-HZSM-5 1.5 wt % K-HZSM-5
acid BET method surface area, pore vol, density, cm3/g mm2 catalyst (m2/(g of catalyst) (t-method) g/m2 identity K0 K1 K2 K3
394.4 387.7 386.9 337.0
0.1717 0.1700 0.1645 0.1406
0.0984 0.0872 0.0904 0.0510
surface area. At a higher concentration of potassium, pore blockage has occurred and a drop in surface area has been observed due to the accumulation of the potassium in the pores. Pore size measurements from N2 adsorption data indicated that the micropore volume is higher than the mesopore volume. OLP, gasoline, and kerosene yields followed the same trend as that of the conversion. The yields of diesel product decreased with increasing potassium concentration. The gaseous yields also decreased with an increase of potassium concentration. Coke formation over the catalyst increased with increasing potassium concentration. The selectivity for gasoline and kerosene is highest at 0.5 wt % potassium and then decreased with a further increase in potassium concentration. The decrease in Bronsted acid sites due to impregnation by potassium ions increased the selectivity for diesel production. The selectivity for aromatic hydrocarbons decreased with increasing potassium concentration and dropped to about zero at 1.5 wt % potassium. The coke formation increased with increasing potassium from 0.5 to 1.5 wt %. The percentage of coke formed was found to be similar for K0 and K1 catalysts, but the type of coke present in each catalyst was different. The increase in coke formation with increasing potassium concentration indicates that the decrease in catalyst acidity favored the formation of coke on the surface of the catalyst. The results of acidity measurements for the four catalysts, HZSM-5 (K0) and KHZSM-5 catalysts (K1, K2, and K3), following isopropylamine adsorption using thermal gravimetric analysis are presented in Figure 2. Two types of peaks were present in the desorption temperature range of 100420 °C. The peak in the temperature range of 100-320 °C was associated with the weak acid site. The second peak that was found in the range of 320-420 °C represented the strong acid sites. The presence of
3236 Ind. Eng. Chem. Res., Vol. 38, No. 9, 1999
Conclusions (1) Among the three zeolite catalysts (HZSM-5, zeolite β, and USY), HZSM-5 gave the best performance in terms of conversion, gasoline yield, higher selectivity for aromatics, and lower coke formation. (2) USY and zeolite β catalysts gave higher selectivity for hydrocarbons in the diesel range and lower production of gaseous products. (3) Potassium-impregnated HZSM-5 catalyst gave lower selectivity for aromatics production compared to HZSM-5 catalyst. (4) The gasoline yield increased with the addition of HZSM-5 catalyst to HZSM-5-USY hybrid catalyst. (5) The addition of HZSM-5 to HZSM-5-zeolite β did not improve the conversion of palm oil or the yields of hydrocarbon products. Acknowledgment Figure 2. TGA spectra of HZSM-5 and potassium impregnated HZSM-5 catalysts: K0, HZSM-5; K1, 0.5 wt % K-HZSM-5; K2, 1 wt % K-HZSM-5; K3, 1.5 wt % K-HZSM-5.
The financial support by the Universiti Sains Malaysia under long-term IRPA grant (Project 03-02-05-7005) is gratefully acknowledged. The authors would like to express their gratitude to P. Q. Corp., Kansas city, MO, and W. R. Grace & Co., Singapore, for providing free samples of zeolites for the research. Literature Cited
Figure 3. IR spectra of HZSM-5 and potassium-impregnated HZSM-5 catalysts for the pyridine region: K0, HZSM-5; K1, 0.5 wt % K-HZSM-5; K2, 1 wt % K-HZSM-5; K3, 1.5 wt % K-HZSM5.
potassium affected the strong acid sites more than the weak acid sites. At 0.5 wt % potassium, the strong acid sites decreased by about 30%, whereas the weak acid sites decreased around 10%. The acid density was calculated by dividing the total peak area by the surface area of the catalyst, and the values obtained are shown in Table 6. In addition to the TGA analysis, infrared spectroscopy was also used to identify the acid sites on the catalyst. The two types of acid sites present in the zeolite catalysts were as follows: (1) Lewis type and (2) Bronsted type. The IR spectra of fresh and pyridineadsorbed catalyst in the pyridine wavenumbers range (1410-1575 cm-1) for HZSM-5 (K0) and K-HZSM-5 catalysts (K1, K2, and K3) are presented in Figure 3. The HZSM-5 catalyst exhibited bands at wavenumbers of 1545, 1490, and 1450 cm-1. The band at 1545 cm-1 represents the pyridinium ion (Bronsted-bound pyridine), whereas the band at 1490 cm-1 shows the presence of a mixture of Bronsted and Lewis acid sites bonded to the pyridine. The band at 1450 cm-1, which was observed to be broader than the other bands, is a characteristic of Lewis acid sites. Figure 3 shows that the intensity of the band at 1545 cm-1 (Bronsted acid sites) decreased with increasing potassium content.
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Received for review November 30, 1998 Revised manuscript received June 17, 1999 Accepted June 24, 1999 IE980758F
