This article was downloaded by: [Universiti Putra Malaysia] On: 16 November 2011, At: 00:05 Publisher: Taylor & Francis Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK Energy Sources Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/ueso19 Biofuel Pro duction from Catalytic Cracking of Palm Oil OOI YEAN SANG a a School of Chemical Engineering, Universiti Sains Malaysia, Engineering Campus, Seberang Prai Selatan Penang, Malaysia Availa ble online: 24 Jun 2010 To cite this article: OOI YEAN SANG (2003): Biofuel Production from Catalytic Cracking of Palm Oil, Energy Sources, 25:9, 859-869 T o link to this ar ticle: http://dx.doi.org/10.1080/00908310390221309 PLEASE SCROLL DOWN FOR ARTICLE Full terms and conditions of use: http://www.tandfonline.com/page/terms-and-conditions This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply , or distribution in any form to anyone is expressly forbidden. The publisher does not give any warranty express or implied or make any representation that the contents will be complete or accurate or up to date. The accuracy of any instructions, formulae, and drug doses should be independently verified with primary sources. The publisher shall not be liable for any loss, actions, claims, proceedings, demand, or costs or damages whatsoever or howsoever caused arising directly or indirectly in connection with or arising out of the use of this material.
This article was downloaded by: [Universiti Putra Malaysia]On: 16 November 2011, At: 00:05Publisher: Taylor & FrancisInforma Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House37-41 Mortimer Street, London W1T 3JH, UK
Energy SourcesPublication details, including instructions for authors and subscription information:
http://www.tandfonline.com/loi/ueso19
Biofuel Production from Catalytic Cracking of Palm OiOOI YEAN SANG
a
aSchool of Chemical Engineering, Universiti Sains Malaysia, Engineering Campus, Seberan
Prai Selatan Penang, Malaysia
Available online: 24 Jun 2010
To cite this article: OOI YEAN SANG (2003): Biofuel Production from Catalytic Cracking of Palm Oil, Energy Sources, 25:9,
859-869
To link to this article: http://dx.doi.org/10.1080/00908310390221309
PLEASE SCROLL DOWN FOR ARTICLE
Full terms and conditions of use: http://www.tandfonline.com/page/terms-and-conditions
This article may be used for research, teaching, and private study purposes. Any substantial or systematicreproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form toanyone is expressly forbidden.
The publisher does not give any warranty express or implied or make any representation that the contentswill be complete or accurate or up to date. The accuracy of any instructions, formulae, and drug doses shouldbe independently verified with primary sources. The publisher shall not be liable for any loss, actions, claims,proceedings, demand, or costs or damages whatsoever or howsoever caused arising directly or indirectly inconnection with or arising out of the use of this material.
School of Chemical EngineeringUniversiti Sains Malaysia
Engineering CampusSeberang Prai Selatan Penang, Malaysia
Palm oil, a renewable source, has been cracked at atmospheric pressure, a reaction
temperature of 450◦C, and a weight hourly space velocity of 2.5 h−1 to producebiofuel in a fixed-bed microreactor. The reaction was carried out over microporous
HZSM-5 zeolite, mesoporous MCM-41, and composite micromesoporous zeolite ascatalysts in order to study the influence of catalyst pore size and acidity over biofuel
production. The products obtained were gas, organic liquid product, water, and coke.The organic liquid product was composed of hydrocarbons corresponding to gaso-line, kerosene, and diesel boiling point range. The maximum conversion of palm oil,99 wt%, and gasoline yield of 48 wt% was obtained with composite micromesoporous
As crude oil resources eventually begin to deplete, there are large investments in devel-oping alternative fuel engines such as fuel cell or methanol engine. However, insteadof converting engines to run on alternative fuels in the future, the marketplace is morewilling to convert the alternative energy resources into synthetic liquid fuels that aresimilar to gasoline or diesel (Piel, 2001). Recently, several studies have reported on theproduction of hydrocarbons from plant oils, such as canola oil, tall oil, and jojoba oil,carried out using cracking catalysts such as HZSM-5, silica alumina, and physical mix-tures of these catalysts (Katikaneni et al., 1995a, 1995b; Adjaye et al., 1996). Most of these studies are concentrating on developing alternative sources of hydrocarbons that
are needed in a wide range of industrial applications. Malaysia, as one of the larger
Received 13 June 2002; accepted 16 July 2002.The authors wish to express their thanks to The Universiti Sains Malaysia, Penang (Malaysia)
for an award of short term IRPA grant (Project: 073567) to carry out this research.Address correspondence to Subhash Bhatia, School of Chemical Engineering, Universiti Sains
Malaysia, Engineering Campus, 14300 Nibong Tebal, Seberang Prai Selatan Penang, Malaysia.E-mail: [email protected]
producers of palm oil, has attracted the attention of the researchers to develop an “envi-ronmentally friendly” and high-quality clean fuel since it is free of nitrogen and sulfur.Palm Oil Research Institute Malaysia (PORIM) has developed biodiesel using palm oilby converting it to methyl ester by reaction with methanol (Choo and Ma, 1996). There
is also a growing interest in studies involving catalytic conversion of palm oil to liquidhydrocarbons using various shape selective zeolite catalysts (Bhatia et al., 1998; Twaiqet al., 1999). The product distribution is governed by the characteristic of the catalysts,especially their pore size and acidity. In the present study, catalysts with different poresizes and Si/Al ratios were studied in order to investigate its effects on the productdistributions, especially bio-gasoline production.
The new family of mesostructured molecular sieves MCM-41 discovered in the early1990s (Beck et al., 1992) has a uniform, one-dimensional, and hexagonal pore structurein the range of 20 to 100 Å. Generally, large organic molecules are being hinderedin accessing zeolites micropore; the discovery of mesoporous molecular sieves is con-sidered to overcome this limitation. It bridges the gap between crystalline zeolites andamorphous silica in terms of pore size and pore size distribution. Incorporation of alu-minum into the MCM-41 structure to create acidity is one of the many efforts to fulfillthe requirements to catalyze large molecules (Kresage et al., 1995). Hence, MCM-41with different Si/Al ratios was prepared in order to study its ability in palm oil cracking.Composite mesomicroporous material was also synthesized to improve the conversion of palm oil as well as the selectivity of liquid hydrocarbon in the gasoline boiling range.The composite mesomicroporous material combines both the advantages of microporousand mesoporous properties and shows a better performance compared to mechanicallymixed micromesoporous material in acid catalysis (Kloetstra et al., 1996). The processstudies will be useful for catalytic cracking of the used vegetable/waste palm oil eas-ily obtained from fast food restaurants for the production of biofuel. The tunable poresize and acidity of the composite material are preferred catalysts for production of bio-fuel from waste palm oil due to their shorter chain length compared to crude palm oil.
Experimental
Catalysts
HZSM-5 zeolite with different Si/Al ratios of 50, 240, and 400 was obtained from Sud-Chemie AG., Katalys-Labor, Munich, Germany. The catalysts were coded as HZSM-5(X), where X is the Si/Al ratio. Prior to the activity test, the catalysts were subjectedto calcination at 500◦C for 6 h.
Aluminosilicate mesoporous material, Al-MCM-41, was prepared with different Si/Alratios according to the method suggested by Beck et al. (1992) and designated asAlMM(X), where X is the Si/Al ratio in the synthesis gel. Twenty-two ml of cetyl-trimethylammonium hydroxide C16TMA-OH (25% in methanol, Fluka) was dissolved in90 ml of deionized water, and 6 ml of tetraethylammonium hydroxide TEA-OH (20%
in water, Merck) was added to the solution. 0.2 g of NaOH and the desired amount of sodium aluminate (Al2O3.Na2O, Merck) were added to the solution with stirring. Fivegrams of cab-osil (M5, Fluka) was slowly added to the solution and stirred vigorously for1 h. The gel formed was transferred to the crystallizer (Parr autoclave) and stirred con-tinuously at 50 rpm for 24 h at 423 K for the crystallization process. The solid materialwas thoroughly washed, filtered, dried at room temperature overnight, and then calcinedat 813 K for 6 h.
A composite of mesoporous silicate material MCM-41 with microporous ZSM-5zeolite was also prepared in the laboratory (Kloetstra et al., 1996). All the sampleswere prepared having a silica-to-zeolite ratio of 0.2. Two grams of Na-ZSM-5 was ion-exchanged with 3 g of 25 wt% aqueous cetyltrimethylammonium chloride (Fluka) and
7 g of deionized water under mild mixing overnight. The mixture was subsequentlyadded to the freshly prepared MCM-41 gel. The MCM-41 gel was prepared by dilutingthe cetyltrimetylammonium chloride solution (25 wt% in water) with 3 g of deionizedwater. Then 0.62 g of tetramethylammonium silicate, TMA-SiO2, was added to 2.2 g of deionized water and poured into the mixture. The gel was enriched with 4.23 g of sodiumsilicate and 9.6 g of deionized water and was stirred vigorously for 15 min. The desiredamount of sodium aluminate was added and mixed for 5 min. The product gel of thesemixtures was introduced into the crystallizer and mixed at 50 rpm for 24 h at 423 Kunder hydrothermal conditions. The product was collected by filtration and washed thor-oughly by deionized water, dried at room temperature overnight, and then was followedby calcination at 813 K for 6 h. The resultant material (Na- form) was converted toH-form by refluxing with 0.1 N NH4Cl aqueous solution with a liquid:solid ratio of 20 at 353 K and continuous stirring overnight. The resultant product was consequentlyfiltered and washed with deionized water until a chloride-free solution was obtained.The sample was kept dry at room temperature overnight and then calcined at 823 Kfor 4 h.
Catalyst Characterization
The commercial catalyst as well as the catalysts synthesized in the laboratory werecharacterized for both physical and chemical properties. The surface area and pore sizedistribution measurements were carried out with Autosorb I (QuantaChrome Corporation,USA) using nitrogen adsorption. The samples were degassed overnight under vacuum at523 K prior to the analysis. The surface area and pore size calculations were performedby the software (Micropore version 2.46). The elemental analysis of the synthesized
catalyst was carried out using an inductive coupled plasma (ICP) spectrometer (Model;PE, Optima 3000). Temperature programmed desorption (TPD) of ammonia using aChembet 3000 TPD-TPR unit (Quantachrome) was performed for determination of theacidity of the samples. A 0.05 g sample was activated at 773 K for 1 h with helium(99.9% purity) flowing at 60 ml/min followed by adsorption of 1% ammonia in heliumfor 1 h at temperature. The ammonia was desorbed by heating the sample in flowinghelium from ambient to 973 K at 10 K/min. The desorption peak areas were normalizedusing the TPRWin version 1 software and used to calculate the acidity.
Activity Test
The palm oil cracking was carried out in the microcatalytic fixed-bed reactor setupshown in Figure 1. The reaction was performed at atmospheric pressure, with a reaction
temperature of 723 K with palm oil feed rate (weight hourly liquid space velocity)of 2.5 h−1. One g of calcined powder catalyst of particle size < 32 µm was loadedover 0.2 g quartz wool supported over a stainless steel mesh surface in a stainless steelreactor (150 mm long and 10 mm ID). The reactor was heated to the desired reactiontemperature using a vertical tube furnace under nitrogen gas at a rate of 100 ml/min. Palmoil was fed using a syringe pump (Cole-Parmer Model No. E-74900-05) once the reactiontemperature was stabilized. In order to prevent the solidification of the residual oil, the
Figure 1. Microreactor rig used for palm oil catalytic cracking.
products leaving the reactor were cooled to 313 K in the condenser system. The gaseousproducts were collected in a gas sampler, and the total gas evolved during the experiment
was monitored using water displacement. The condensed liquid products were collectedin a liquid sampler at room temperature once steady state was reached. The reactor wasthen flushed with nitrogen gas at 30 ml/min for 30 min to remove the remainder productsfrom the reactor. The aqueous phase was separated from the condensed liquid productsusing a syringe. The liquid product was distilled in a vacuum microdistillation unit at100 Pa and 473 K for 30 min. The distillate fraction was organic liquid product (OLP),and the pitch was assumed to be the residual oil. The catalyst was washed with acetoneand dried in an oven at 373 K for 1 h prior to coke analysis. The gaseous products wereanalyzed over gas chromatograph (Hewlett Packard, Model 5890 series II) using an HPPlot Q capillary column (Divinyl benzene/styrene porous polymer, 30 m long × 0.53 mmID × 40 µm film thickness) equipped with a thermal conductivity detector (TCD) andnitrogen as a carrier gas. The OLP was analyzed on a capillary glass column (Petrocol DH50.2, film thickness 0.5 micron, 50 m long × 0.2 mm ID) at a split ratio of 1:100 using
an FID detector. The oven temperature was programmed at a heating rate of 4 K/min inthe range of 333 to 523 K. The composition of OLP was defined according to the boilingrange of petroleum products such as gasoline (333–408 K), kerosene (408–433 K), anddiesel (433–523 K). The coke formed over the catalyst during the cracking reactionwas determined by a thermal gravimetric analyzer (Perkin Elmer TGA 7). About 5 mgof acetone-washed spent catalyst sample was subjected to thermal gravimetric analysis(TGA) at a temperature program of 20 K min−1. The sample was heated from ambient
to 373 K with a heating rate of 20 K min−1 under nitrogen gas flowing at 30 ml min−1.It was kept at 373 K for 10 min in order to remove the volatile materials. The samplewas then heated to 973 K at a heating rate of 10 K min−1 with oxygen gas flowing at30 ml min−1.
Results and Discussion
The catalysts with different Si/Al ratio and pore size were tested for palm oil catalyticcracking. The physicochemical properties of the commercially available zeolite HZSM-5and the calcined catalysts synthesized are presented in Table 1. The performance of eachcatalyst was evaluated in terms of conversion of palm oil and yield of liquid hydrocarbonproducts. The conversion, yield, and selectivity of the product obtained over differentcatalysts are defined as follows:
Conversion (wt%) =C
P × 100%, (1)
Yield (wt%) =Y
P × 100%, (2)
Selectivity (wt%) =Y
C× 100%, (3)
where C is total products = organic liquid product + gas + aqueous phase + coke (g),P is the palm oil feed (g), and Y is the product (gasoline, kerosene, etc.) (g). In order todetermine the extent of thermal cracking of palm oil, a blank run was performed in anempty reactor containing quartz-wool. Low conversion of palm oil was observed at 623 K(5%). The conversion of palm oil in an empty reactor at 723 K and WHSV of 2.5 h−1
was 40 wt%. The yield of gaseous product was about 5%, while the liquid product yieldwas < 10 wt%.
Table 1
Physicochemical properties of the catalyst used
AverageSurface Pore pore size
Si/Al area volume (BJH method) AcidityCatalyst ID ratio (m2 /g) (cc/g) (nm) (mmol H+ /g)
Figure 2. Selectivity of liquid products obtained from catalytic cracking of palm oil over HZSM-5catalysts having different Si/Al ratios.
HZSM-5 Microporous Material
Table 2 presents the conversion of the palm oil over HZSM-5 catalsyt and was almostconstant with different Si/Al ratios, but the product distributions were significantly dif-ferent. The acidity in HZSM-5 zeolite decreased as the Si/Al ratio was increased, hencethe yield of gaseous products was notably decreased with the increase of Si/Al ratio.The strength of the acid sites was found to play an important role in palm oil cracking.
The gasoline yield increased with the increase in the Si/Al ratio due to the decrease inthe secondary cracking reactions and the drop in the yield of gaseous products. Hencethe lower acidity of HZSM-5 has decreased the secondary cracking reactions resulting inhigher yield of liquid products. Figure 2 shows the effect of Si/Al ratio of HZSM-5 on
Table 2
Catalytic cracking of palm oil over HZSM-5 with different Si/Al ratios
the selectivity of liquid products including gasoline, kerosene, and diesel. The selectivityof gasoline and kerosene also increased with the Si/Al ratio, while diesel selectivity fol-lowed the opposite trend. This suggested that the expense of gaseous products and dieselyield were contributed to both gasoline and kerosene production.
Mesoporous Material
Table 3 presents the conversion of palm oil over mesoporous catalysts. It was found thatthe conversion increased with the increase in surface area from 650 to 1,150 m2 /g aswell as acid sites for the aluminum-containing sieve as shown in Table 1. The higheraluminum content did not show higher acidity as determined by TPD of ammonia due tothe low crystallinity and incorporation of aluminum in the framework of the mesoporousmaterial. The acidity was not the main factor in controlling the activity of mesoporousmaterial in palm oil cracking. It has been reported that the accessibility to the acid sitesin mesoporous materials (MCM-41) plays an important part in the cracking (Koch et al.,2000). Figure 3 shows the selectivity of AlMM(X) catalysts over liquid hydrocarbons in
the gasoline, kerosene, and diesel ranges. The selectivity for gasoline was higher over thematerial at a Si/Al ratio of 5, where even the mesoporous material had low crystallinity.Diesel was found to have an opposite trend to that of gasoline, showing that the effect of the secondary cracking reaction is more prominent for gasoline and kerosene production.The increase in acid sites increased the cracking activity, resulting in the conversion of 93 wt% with a gasoline yield of 31 wt%.
Micromesoporous Composite Material
The palm oil conversion and products distribution obtained from palm oil cracking overmicromesoporous composite material are presented in Table 4. The palm oil conversionwas increased more significantly from 95 wt% to 99 wt% with the presence of 5 wt% of alumina in the silica coating of 20 wt%. However, the conversion dropped to 88 wt% with
a further increase in the aluminum-containing coating to 15 wt%. The conversion wasdecreased because the BET surface area dropped from 504 to 141 m2 /g, probably due to
Table 3
Catalytic cracking of palm oil over aluminum-containing mesoporousmolecular sieve with different Si/Al ratios
Figure 3. Effect of Si/Al ratio of mesoporous molecular sieve materials on the selectivity of liquidproduct distribution.
the pore blockage during the coating of the ZSM-5 with mesoporous material, once thealumina content increased from 5 wt% to 15 wt%. The BET surface area was one of theimportant factors that influenced the catalytic cracking performance. The Si/Al ratio waslowered to produce catalysts with higher concentrations of active acid sites. As a result,CZM(5) with the lowest Si/Al ratio gave the highest yield and selectivity of gasoline.Therefore CZM(5) gave better performance compared to other composite materials. Theproduct distribution was also found to vary with an increase in the alumina content. Themaximum gasoline yield was 48 wt%. Even though the conversion was high, the yieldand selectivity of gasoline dropped notably with respect to the increase in alumina contentfrom 5 to 10 wt%, whereas the catalyst containing 15 wt% alumina in the coating gave
Table 4
Catalytic cracking of palm oil over composite micromesoporouswith different Si/Al ratios
a higher gasoline yield of 48 wt%. The kerosene-range hydrocarbon yield was decreasedfrom 20 wt% to 8 wt% when the alumina content increased. The diesel yield remainedconstant at 5 wt% over 5 to 10 wt% of alumina and increased to 7 wt% over 15 wt%alumina content. The gaseous products yield followed the opposite trend compared to that
of the gasoline yield. An increase in gaseous product yield reduced the gasoline yield. Theselectivity of the various organic liquid products is shown in Figure 4. The selectivity forgasoline and diesel was increased at higher alumina content in the coating. The selectivitywas higher than that obtained from HZSM-5 catalyst. However, the selectivity for thegaseous and kerosene products was decreased.
Figure 5 compares the performance of all the catalysts tested in the present studyfor the production of gasoline. The composite micromesoporous zeolite gave the highestselectivity toward gasoline although the conversion was only 82 wt%, while the HZSM-5(400) with the conversion as high as 94 wt% gave a lower selectivity of gasoline. Itis obvious that the decrease in kerosene selectivity for CZM(15) increased the gasolineselectivity. AlMM(5), with the lowest conversion of 78 wt%, gave the lowest selectivityof gasoline but the highest diesel selectivity and, hence, in order to increase the gasolineselectivity, the selectivity of diesel must be minimized.
A mechanism for the palm oil cracking is proposed in Figure 6. The palm oilcontains mainly palmitic, stearic, oleic, and linoleic acids. The composition (wt%) is asfollows: C16:0, 40.93; C18:0, 4.18; C18:1, 41.51; C18:2, 11.64. These fatty acids underwentvarious reactions, resulting in the formation of different types of hydrocarbons. Thekey steps involved in the hydrocarbon formation can be identified as deoxygenation,cracking, and aromatization with H-transfer reaction. The palm oil is converted by 2simultaneous reactions: condensation and cracking. The heavy hydrocarbons producedfrom deoxygenation and cracking to produce light alkenes and alkanes, water, carbondioxide, and carbon monoxide.
Figure 4. Effect of the aluminum content of mesoporous molecular sieve in the micromesoporouscomposite catalyst over the selectivity of hydrocarbon products.
The acidity and pore size of the catalysts showed significant effect in the conversionas well as product distributions in palm oil cracking. HZSM-5 with higher acidity gave
higher conversion, but for mesoporous material, acidity was not the major factor for palmoil cracking. Mesoporous material enhanced the accessibility of the bulky molecule anddecreased the gaseous production but increased the coke formation. Micromesoporouscomposite zeolite gave the highest conversion of 99 wt% and the highest gasoline selec-tivity. The composite catalyst combined the advantages of both micro- and mesoporousproperties for optimum performance in palm oil cracking, especially in gasoline produc-tion. A single step direct process for the production of biofuel from catalytic cracking of palm oil is a promising alternative route for environmentally friendly liquid fuels.
References
Adjaye, J. D., S. P. R. Katikaneneni, and N. N. Bakhshi. 1996. Catalytic conversion of a bio-fuel to hydrocarbons: Effect of mixtures of HZSM-5 and silica-alumina catalysts on product
distribution. Fuel Proc. Technol. 48:115–143.Beck, J. S., C. T.-W. Chu, I. D. Johanson, C. T. Kresge, M. E. Leonowicz, W. J. Roth, and J. C.Vartuli. 1992. Synthesis of mesoporous crystalline material. US Patent 5,108,725.
Bhatia, S., J. K. Heng, M. L. Lim, and A. R. Mohamed. 1998. Production of biofuel by catalyticcracking of palm oil: Performance of different catalyst. Proc. Biofuel, PORIM Intl. Biofuel
and Lubricant Conf ., Malaysia, pp. 107–112.Choo, Y. M., and A. N. Ma. 1996. Production technology of methyl esters from palm and palm
kernel oils. PORIM Technology Bulletin 18.Katikaneni, S. P. R., J. D. Adjaye, and N. N. Bakhshi. 1995a. Catalytic conversion of canola oil
to fuels and chemicals over various cracking catalysts. Can. J. Chem. Eng. 73:484–497.Katikaneni, S. P. R., J. D. Adjaye, and N. N. Bakhshi. 1995b. Performance of aluminophosphate
molecular sieve catalysts for production of hydrocarbons from wood-derived and vegetableoils. Energy Fuels 9:1065–1078.
Kloetstra, K. R., H. W. Zandbergen, J. C. Jansen, and H. V. Bekkum. 1996. Overgrowth of meso-
porous MCM-41 on faujasite. Microporous Materials 6:287–293.Koch, H., A. Klemt, A. Taouli, and W. Reschetilowski. 2000. Investigation of catalytic crackingof hydrocarbons on microporous and mesoporous catalysts with regards to selectivity on C3and C4 products. Private communications.
Kresage, C. T., J. C. Vartull, W. J. Roth, M. E. Leonowiez, J. C. Beck, K. D. Schmitt, C. T.-W.Chu, D. H. Olson, E. W. Shappard, S. B. McCullen, J. B. Higgins, and J. L. Schlenker. 1995.M41S: A new family of mesoporous molecular sieves prepared with liquid crystal templates.Proc. of the 2nd Tokyo Conf. on Advance Science and Technology. Science and Technology
in Catalysis 1994, edited by B. Delmon and J. T. Yates. pp. 11–19. Tokyo, Japan: KodanshaLtd.
Piel, W. J. 2001. Transportation fuels of the future. Fuel Proc. Technol. 71:167–179.Twaiq, F. A., N. A. M. Zabidi, and S. Bhatia. 1999. Catalytic conversion of palm oil to hydrocarbons
over potassium impregnated HZSM-5 catalyst and hybrid catalysts: Gasoline production. Proc.
of World Engineering Congress, Kuala Lumpur, Malaysia, pp. 255–260.
Twaiq, F. A., N. A. M. Zabidi, and S. Bhatia. 1999. Catalytic conversion of palm oil to hydrocar-bons: Performance of various zeolite catalysts. Industrial and Engineering Chemistry Research
