Handbook Of Green Chemistry

.5.1Low-Temperature CO Oxidation and VOC Combustion 265NOx Abatement 273Conclusion 277Application of High-Throughput Screening to EmissionsControl 277Future Trends in Combinatorial Catalysis 278References 278Catalytic Conversion of High-Moisture Biomass to SyntheticNatural Gas in Supercritical Water 281Frédéric VogelIntroduction 281Heterogeneous Catalysis in Hydrothermal Medium at theOrigin of Life? 281Biomethane – a Green and Sustainable Fuel 282Energetic Potentials 283Nutrient Cycles 284Survey of Different Technologies for the Production of Methanefrom Carbonaceous Feedstocks 285Anaerobic Digestion 285Thermal Processes 286Water as Solvent and Reactant 288Solubility of Organic compounds and Gases 289Solubility of Salts 290The Role of Heterogeneous Catalysis 290Experimental Methods 290Thermodynamic Stability of Methane under HydrothermalConditions 291Main Reactions of Biomass Gasification 293Homogeneous, Non-catalyzed Pathways in HotCompressed Water 294Heterogeneously Catalyzed Pathways in Hot CompressedWater 297Active Metals Suited to Hydrothermal Conditions 298Methanation and Steam Reforming Catalysts 299Nickel 302Ruthenium 305Catalyst Supports Suited to Hydrothermal Conditions 306Deactivation Mechanisms in a Hydrothermal Environment 312Coke Formation 312Sintering 314Poisoning 314Continuous Catalytic Hydrothermal Process for the Productionof Methane 315Overview of Processes 315XI

XIIContents12.5.212.5.2.112.5.2.212.612.712.7.1PSI s Catalytic Hydrothermal Gasification Process 315Continuous Salt Precipitation and Separation 316Status 318Summary and Conclusions 318Outlook for Future Developments 319A Self-sustaining Biomass Vision (SunCHem) 319References 320Index325

XIIIAbout the EditorsSeries EditorPaul T. Anastas joined Yale University as Professor and servesas the Director of the Center for Green Chemistry and GreenEngineering there. From 2004–2006, Paul was the Director ofthe Green Chemistry Institute in Washington, D.C. UntilJune 2004 he served as Assistant Director for Environmentat the White House Office of Science and Technology Policywhere his responsibilities included a wide range of environmental science issues including furthering internationalpublic-private cooperation in areas of Science for Sustainability such as Green Chemistry. In 1991, he established the industry-governmentuniversity partnership Green Chemistry Program, which was expanded to includebasic research, and the Presidential Green Chemistry Challenge Awards. He haspublished and edited several books in the field of Green Chemistry and developedthe 12 Principles of Green Chemistry.Volume EditorRobert Crabtree took his first degree at Oxford, did his Ph.D.at Sussex and spent four years in Paris at the CNRS. He hasbeen at Yale since 1977. He has chaired the Inorganic Divisionat ACS, and won the ACS and RSC organometallic chemistryprizes. He is the author of an organometallic textbook, and isthe editor-in-chief of the Encyclopedia of Inorganic Chemistryand Comprehensive Organometallic Chemistry. He has contributed to C-H activation, H2 complexes, dihydrogen bonding, and his homogeneous tritiation and hydrogenationcatalyst is in wide use. More recently, he has combined molecular recognitionwith CH hydroxylation to obtain high selectivity with a biomimetic strategy.Handbook of Green Chemistry, Volume 2: Heterogeneous Catalysis. Edited by Robert H. CrabtreeCopyright Ó 2009 WILEY-VCH Verlag GmbH & Co. KGaA, WeinheimISBN: 978-3-527-32497-2

XVList of ContributorsMasakazu AnpoOsaka Prefecture UniversityGraduate School of EngineeringDepartment of Applied ChemistryGakuen-chi, 1-1SakaiOsaka 599-8531JapanStephen H. BrownEMRE CSR1545 Route 22 EastAnnandale, NJ 08801USAJoel CizeronSymyx Technologies, Inc.3100 Central ExpresswaySanta Clara, CA 95051USAChristophe CopéretUniversité de LyonInstitut de Chimie de LyonLaboratoire C2P2 – ESCPE Lyon43 boulevard du 11 Novembre 191869616 VilleurbanneFranceStephen CypesSymyx Technologies, Inc.3100 Central ExpresswaySanta Clara, CA 95051USARobert J. FarrautoBASF Catalysts25 Middlesex–Essex TurnpikeIselin, NJ 08830USAAnthony G. FitchCalifornia Institute of TechnologyDivision of Chemistry and ChemicalEngineeringBeckman Institute and KavliNanoscience Institute210 Noyes Laboratory, 127–72Pasadena, CA 91125USAAlfred HagemeyerSüd-Chemie AGWaldheimer Strasse 1383052 BruckmühlGermanyJeffrey HokeBASF Catalysts25 Middlesex–Essex TurnpikeIselin, NJ 08830USAHandbook of Green Chemistry, Volume 2: Heterogeneous Catalysis. Edited by Robert H. CrabtreeCopyright Ó 2009 WILEY-VCH Verlag GmbH & Co. KGaA, WeinheimISBN: 978-3-527-32497-2

XVIList of ContributorsHicham IdrissUniversity of AberdeenDepartment of ChemistryMeston WalkAberdeen, AB24 3EUUKHeiko JacobsenKemKom1215 Ursulines AvenueNew Orleans, LA 70116USAMazaahir KidwaiUniversity of DelhiDepartment of ChemistryGreen Chemistry Research LaboratoryDelhi 110007IndiaIvan KozhevnikovDepartment of ChemistryUniversity of LiverpoolLiverpool L69 7ZDUKAdam F. LeeUniversity of YorkDepartment of ChemistrySurface Chemistry and Catalysis GroupHeslingtonYork YO10 5DDUKNathan S. LewisCalifornia Institute of TechnologyDivision of Chemistry and ChemicalEngineeringBeckman Institute and KavliNanoscience Institute210 Noyes Laboratory, 127–72Pasadena, CA 91125USAMasaya MatsuokaOsaka Prefecture UniversityGraduate School of EngineeringDepartment of Applied ChemistryGakuen-chi, 1-1SakaiOsaka 599-8531JapanMorgan S. ScottUniversity of AucklandDepartment of ChemistryPrivate Bag 92019AucklandNew ZealandFrédéric VogelPaul Scherrer InstitutLaboratory for Energy and MaterialsCycles5232 Villigen PSISwitzerlandAnthony Volpe JrSymyx Technologies Inc.3100 Central ExpresswaySanta Clara, CA 95051USADon WalkerCalifornia Institute of TechnologyDivision of Chemistry and ChemicalEngineeringBeckman Institute and KavliNanoscience Institute210 Noyes Laboratory, 127–72Pasadena, CA 91125USA

List of ContributorsKaren WilsonUniversity of YorkDepartment of ChemistrySurface Chemistry and Catalysis GroupHeslingtonYork YO10 5DDUKXVII

j11Zeolites in CatalysisStephen H. Brown1.1IntroductionAcid catalysis as a modern science is less than 150 years old. From its inception, acidcatalysis has been explored as a means of producing fuels, lubes and petrochemicals.Ordinary homogeneous acids, both inorganic and organic, never proved industriallyuseful at temperatures much above 150 C. The first reports of aluminosilicate solidacid catalysts involved the use of clays after the turn of the century. The inspiration forthe first commercial synthetic aluminosilicate catalysts came from work done coprecipitating silicon and aluminum salts during WWI by a Sun Oil chemist [1]. TheBrønsted acid site in these materials is most often represented as in Scheme 1.1.Useful features of this novel type of acid versus homogeneous liquid acids were theirhigh temperature stability, moderate acidity (roughly equivalent to a 50% sulfuricacid solution), solid and non-corrosive character and regenerability by air oxidation.These features enabled acid catalyzed reactions of chemicals to be contemplated at agreatly extended range of temperatures (up to 600 C) and metallurgies.Scheme 1.1 The Brønsted acid site of an aluminosilicate.The first embodiments of many modern refining processes including heavy oilcracking, naphtha reforming and light gas oligomerization did not use catalysts [2].As soon as these thermal processes commercialized, exploration of the use of solidacid catalysts ensued naturally.Because of the key role played in the development of the automotive industry, heavyoil cracking to gasoline provided a focal point for the early development of heterogeneous acid catalysis. Temperatures above 400 C and pressures below 3 atmospheresare thermodynamically favorable for the conversion of heavy oils to light hydrocarbons rich in olefins. Acceptable heavy oil cracking rates are achieved without aHandbook of Green Chemistry, Volume 2: Heterogeneous Catalysis. Edited by Robert H. CrabtreeCopyright 2009 WILEY-VCH Verlag GmbH & Co. KGaA, WeinheimISBN: 978-3-527-32497-2

j 1 Zeolites in Catalysis2catalyst at temperatures above 600 C. This was the basis of the thermal crackingprocess. Thermal cracking produces high yields of methane and aromatic hydrocarbons. The goal of researchers was to find a catalyst that could crack heavyhydrocarbons selectively to gasoline with only minimal formation of gases withmolecular weights of less than 30. Due to thermodynamic constraints, the catalysthad to be effective at a temperature above 400 C. In order to avoid unselectivethermal cracking, the catalyst had to be effective below 550 C.The discovery in the early 1920s by Houdry that acid activated clays were active andselective in this temperature window was a breakthrough [2]. In the 1930s and 1940smethods were developed and commercialized to produce high surface area manmade aluminosilicates that were significantly improved catalysts. Examination of thealuminosilicate catalysts led to the understanding that the active site was a Brønstedacid [3].At the time of the discovery of synthetic zeolites in the early 1950s, only two classesof solid Brønsted acids (solid phosphoric acid and aluminosilicates) were being usedcommercially to produce commodity fuels or petrochemicals [4]. The commercialization of silica-rich synthetic zeolites in their hydrogen form represented a breakthrough for scientists and organizations interested in the production of fuels, lubesand petrochemicals at temperatures above 200 C. Like amorphous aluminosilicates,zeolite Brønsted acid sites are active and stable up to 600 C. Shortly after UnionCarbide s discovery of synthetic zeolites in the late 1940s, Mobil Oil researchers incatalytic cracking of heavy oil investigated zeolites as potential catalysts [5]. Thezeolite known as faujasite (FAU) was found to be three to five orders of magnitudemore active than amorphous aluminosilicates. Unmodified, FAU was too active tobe useful. When the activity of FAU was tuned by ion exchange with rare earth cationsand/or by reducing aluminum content, it was found to have a dramatically differentselectivity to cracked products. Optimized samples of FAU zeolites produced almost5% less C2-gases and coke and increased gasoline yields by more than 10 wt%. Overthe course of the past 50 years, evolving heavy oil cracking catalysts and hardwarehave been continuously decreasing coke and C2-gas yields while increasing the yieldof gasoline.The commercialization of zeolite catalysts for heavy oil cracking unleashed thecreative abilities of every organization interested in producing fuels and petrochemicals using acid catalysts between 250 and 600 C. Close to 23 processes have beencommercialized (Table 1.1). About two-thirds of the processes had no real precedenceusing homogeneous acids. The other third involved displacement of homogeneousand amorphous acid catalysts. Introduction of zeolite catalysts for the production ofcommodities has proceeded at a steady pace. Each commercialization has providedan opportunity for zeolite scientists to find improved catalysts.1.1.1The Environmental Benefits of Zeolite-enabled ProcessesThe petroleum industry has been subject to environmental drivers for manydecades [6]. Innovations in technology, some driven by more restrictive regulations,

1.1 IntroductionTable 1.1 List of zeolite processes.ProcessReactor typeTemperature range, CToluene þ C9 þ aromaticsMSTDPCumene via transalkylationEthylbenzene via transalkylationEthylbenzeneCumeneFluid catalytic cracking (FCC)ZSM-5 in FCCGasoil hydrocrackingDistillate hydrocrackingDistillate dewaxingWax hydrocrackingWax hydroisomerizationGasoline octane enhancementReformate upgradingLight paraffin isomerizationButene isomerizationXylene isomerizationLight paraffin aromatizationMethanol to gasolineMethanol to olefinsAromatics feed –550300–400400–500150–250350–450have continuously increased the efficiency of refining processes. The trend is toproduce fuels having lower concentrations of heteroatoms and polynuclear aromatics(often referred to as clean fuels) that can be burned to carbon dioxide and water withincreasingly lower emissions of NOx, SOx and particulate byproducts.For decades, nearly the entire hydrocarbon content of a barrel of oil feeding arefinery or petrochemical complex has been converted to salable products or used forfuel at the manufacturing site. Distillation of crude oil largely splits it into streamswith the boiling ranges of the fuels sold to consumers and businesses (gasoline,diesel, fuel oil, etc.). The quantities of the streams produced by distillation rarelymatch market demand. Processes using zeolite catalysts have reduced the effortrequired to convert streams that are oversupplied by simple crude oil distillation intoundersupplied products. Optimized zeolite catalyzed processes are often hightechnology operations. Performance can be sensitive to the performance of neighboring units. Operating multiple zeolite-catalyzed processes can provide refinerswith an incentive to continuously work to bring the refinery closer to steady stateoperation. Adoption of these high technology processes and work practices hashelped refiners to steadily increase the amount of clean fuel products produced fromeach barrel of oil, thereby reducing emissions of CO2, NOx, SOx and particulates andincreasing energy efficiency.j3

j 1 Zeolites in Catalysis4Zeolite catalysts are remarkably efficient. Each weight unit of zeolite producesbetween 3000 and 500 000 weight units of fuel or petrochemical product before itslifetime ends and it is removed from catalyst service. As a result, relatively smallvolumes of spent zeolite catalysts are produced. There are often other uses for spentcatalysts, such as an ingredient for cement. In the many cases where reuse is anoption, there are little/no catalyst waste disposal costs.Catalytic cracking (also known as fluid catalytic cracking or FCC) is by far the mosteconomically important process in the refining and petrochemicals industry and willbe described in some detail to allow the green aspects to be highlighted. World wide,FCC units process almost 20 million bbl/day of feedstock (almost 30% of the crude oilproduced) and FCC catalysts generate 1 billion in sales [7]. The remarkableperformance of the FCC process is achieved by both optimizing the zeolite catalystand the reactor design. A schematic of an FCC unit is provided in Figure 1.1.The FCC catalyst spends most of its time in a large, cylindrical regeneration vesseltypically 15 meters in diameter and 40 meters tall holding 300 tons of a coarse powdercatalyst comprised of a bell-shaped distribution of spheres between 15 and 120microns in diameter. The vessel is typically held at 15–25 psig and 620 to 700 C. Air iscontinuously blown up from the bottom of the vessel and is carefully distributed toprovide uniform contacting with the solids. When properly engineered, up flowinggases mix with the coarse catalyst powder to form a mixture which behaves like afluid. The reaction carried out in the regeneration vessel is the combustion of thesolid carbonaceous reaction byproducts that accumulate on the catalyst during thecracking reaction. The FCC catalyst enters the isothermal, back-mixed regenerator atthe reaction temperature (about 550 C) and is heated to the regenerator temperatureby the heat of combustion of the coke.Because of its fluid-like properties in the presence of a flowing gas stream, thecatalyst will flow smoothly out of the bottom of the regenerator, up a 2 meter diameterFigure 1.1 FCC reactor process flow diagram.

1.2 General Process Considerationspipe (called a riser) where it contacts the heavy oil feedstock and then back into the topof the regeneration vessel. A typical catalyst circulation rate for a unit filled with 300tons of catalyst would be 3000 tons/hour. An average catalyst particle travels throughthe riser once every 5 or 6 minutes. Heavy oil feedstock is heated to about 300 C andsprayed into the circulating catalyst (620 to 700 C) at the bottom of the riser. Feedvaporization is accomplished by direct contact with the hot zeolite catalyst. Thegaseous product is removed utilizing cyclones at the top of the riser. Feedstock istypically fed into the riser at twice the total catalyst inventory and one fifth the catalystcirculation rate (e.g. catalyst circulation of 3000 tons/h and a feed throughput of600 tons/h). The total time of feedstock and catalyst contact is several seconds. About5 wt% of the feedstock (no more, no less) must be converted to the carbonaceoussolids (coke) that are required to provide the energy input needed to drive thefeedstock vaporization and the endothermic reaction. A typical catalyst particlecontains about 1 wt% coke on catalyst upon entering the regenerator.Thirty to fifty percent of a barrel of crude oil boils above the endpoint of gasolineand automotive diesel fuels. The FCC unit converts much of this material intogasoline and diesel fuels with roughly 80 wt% selectivity. Another 5 to 10% of the C4products are easily converted into high quality gasoline in a second step, resulting inan overall selectivity to gasoline and diesel fuels of 85 to 90%. Five wt% of the feed isconverted to coke which is used to supply most of the fuel for the unit (regenerat

Handbook of Green Chemistry ISBN (12 volumes): 978-3-527-31404-1 Set 1 Green Catalysis 978-3-527-31577-2 Volume 1: Homogeneous Catalysis Set 2 Green Solvents 978-3-527-31574-1 Volume 2: Heterogeneous Catalysis Set 3 Green Processes 978-3-527-31576-5 Volume 3: Biocatalysis Set 4 Green Product