Hydrocarbon Course UCD 1-4 sections PDF

The Chemistry and Processing of Hydrocarbons Section 1 Masters in Energy UCD, Dublin Prof. K.R. Thampi, Hydrocarbon Processing, Masters in Energy Relevance of hydrocarbons About 50% of the world’s energy is consumed by manufacturing. More than 90% of this is fossil fuel or Hydrocarbon based. When...

The Chemistry and Processing of Hydrocarbons Section 1 Masters in Energy UCD, Dublin Prof. K.R. Thampi, Hydrocarbon Processing, Masters in Energy Relevance of hydrocarbons About 50% of the world’s energy is consumed by manufacturing. More than 90% of this is fossil fuel or Hydrocarbon based. When the amount of hydrocarbon based feedstock, used as manufacturing raw material, is added to this quantity the importance of hydrocarbon chemistry and processes will be evident. This importance is not going to change very much even if we shift to an economy less dependent on fossil fuels, since hydrocarbons from renewables will move in instead. Prof. K.R. Thampi, Hydrocarbon Processing, Masters in Energy Fuel • What makes the fuel a fuel? • Fuel: a molecule • Fuel: Thermodynamic understanding • Fuel Molecule transformations Prof. K.R. Thampi, Hydrocarbon Processing, Masters in Energy Thermodynamics • • • • Gibbs and Helmholtz Free Energy Reversible transformations Useful work/energy Change in Free Energy, Enthalpy and Entropy • Activation Energy • Catalysis and Kinetics Prof. K.R. Thampi, Hydrocarbon Processing, Masters in Energy Thermodynamics vs Kinetics • Less stable Reactants • Stable Products • Driving Force and the Equilibrium of a reaction • Combustion • Oxidation • Reduction • Exo- and Endo- thermic Prof. K.R. Thampi, Hydrocarbon Processing, Masters in Energy Hydrocarbons • • • • • • CnH2n+2 alkanes (s two e- two centre bonds) CnH2n alkenes (olefins) CnH2n-2 alkynes Dienes two unsaturated bonds Polyenesmore unsaturated bonds Arenes aromatic (benzene parent, delocalized p system) • Cycloalkanes single, bridged, caged… Prof. K.R. Thampi, Hydrocarbon Processing, Masters in Energy Index of Unsaturation (2C + 2)- H i= 2 i = 0 for methane, 1 for ethene, 2 for ethyne H:C ratio highest for CH4, except for carbocations CH5+ and CH62+ For C60 or C70, H:C ratio can be as low as 0.03 Prof. K.R. Thampi, Hydrocarbon Processing, Masters in Energy H:C ratio of natural hydrocarbon sources • • • • • • CH4 Natural gas (NG)* Crude Petroleum Tar sand bitumen Raw shale oil Bituminous coal 4.0 3.8 1.8 1.5 1.5 0.8 * >80-90% CH4 + C2-C6 alkanes Prof. K.R. Thampi, Hydrocarbon Processing, Masters in Energy Hydrocarbon sources • NG • CH4.nH2O • Crude Petroleum biological origin (gas hydrates) sea beds, Siberia biological*, abiogenic process originating from deep CH4 dating back from earth’s origin** • Coal low H, biological origin, types: lignite, sub-bituminous, bituminous and anthracite, same order for increasing aromaticity and decreasing volatiles. H:C = 0.8 for bituminous and 0.2 for anthracite * Presence of V and Ni porphyrins, low level of oxygenates, anaerobic microbes acting on moderate temperatures **Gold’s theory, not yet proven Prof. K.R. Thampi, Hydrocarbon Processing, Masters in Energy Hydrocarbon sources (continued….) • Heavy oils, shale and tar sands Heavy (bitumenous) oils of California, Venezuela and Canada Shale oil and tar sands of Canada Heavy oils are viscous to semi-solids with high levels of N, O, S, and relatively less HC. Usually contain V (as VO2+), Fe and Ni organometallics. These elements make processing complex and poison catalysts. Superacid catalysis is one possible solution? Prof. K.R. Thampi, Hydrocarbon Processing, Masters in Energy Coal formation process* • *Coalification is a deoxygenationaromatization process. It is a continuum of chemical, microbial and thermal changes, in which cellulosic wood and peat are converted over many millions of years. Severe geologic conditions also play a role. Aging increases aromaticity and decreases O content in coals. Lignite (brown) is young and bituminous is older and so on… Prof. K.R. Thampi, Hydrocarbon Processing, Masters in Energy Schematic of structural groups and bridges in bituminous coal Scheme of W.H. Wiser, University of Utah Note (CH2)n, and ether linkages, as well as sulphide and biphenyl bonds. Prof. K.R. Thampi, Hydrocarbon Processing, Masters in Energy Coals to liquid Hydrocarbons (HC) Most bonds, except biphenyl, are readily scissible bonds. They undergo thermal and chemical cleavage reactions through which coals can be converted to liquid HC over a sequence of controlled reactions: - Breaking down of complex structures by hydrogenative cleavage reactions (increases solubility of organics) - Alkylation, hydrogenation and depolymerization, and their combinations - Extraction of products from reacted coals - Obtain clean liquid fuels, such as gasoline and heating oil Prof. K.R. Thampi, Hydrocarbon Processing, Masters in Energy Direct Coal liquefaction • High temperature solvent extraction - No catalyst, H donating solvent(s) H2 is added as a secondary H source • Catalytic liquefaction - a catalyst like ZnCl2, Friedel-Crafts catalysts like AlCl3, BF3-phenol catalyses depolymerizationhydrogenation of coals at 375 - 425 °C and 100-200 atmosphere pressure. Superacid HF-BF3 induced liquefaction involves depolymerization and ionic hydrogenation at 150 - 170°C. Prof. K.R. Thampi, Hydrocarbon Processing, Masters in Energy Direct Coal liquefaction (continued) • Direct catalytic hydrogenation - a catalyst is intimately mixed with coal - Usually no solvent - H2 gas Prof. K.R. Thampi, Hydrocarbon Processing, Masters in Energy Fischer-Tropsch (F-T) chemistry • (Coal + O2 + steam) at 1100 °C giving CO, CO2 and H2 • Water-Gas (WG) shift reaction then allows optmization of CO:H2 ratio in the syn-gas • Syn-gas is then catalytically hydrogenated by F-T to hydrocarbons, or used for methanol synthesis. Prof. K.R. Thampi, Hydrocarbon Processing, Masters in Energy C1 Reactions relevant to both the fossil fuel based and the future renewable technologies K.R. Thampi in ‘Recent developments in catalysis’ B. Viswanathan and C.N. Pillai,( eds) Narosa Publishers, 1990. Prof. K.R. Thampi, Hydrocarbon Processing, Masters in Energy Compositions (%) of typical crude petroleum types Fraction Light oil Heavy oil Saturates 78 17-21 Aromatics 18 36-38 Resins 4 26-28 Asphaltene Trace - 2 17 Prof. K.R. Thampi, Hydrocarbon Processing, Masters in Energy Petroleum Refining and Upgrading Crude petroleum is a dark viscous liquid, which contains hundreds of different HC. Distillation is used for separating the different fractions, which are used for different purposes. Prof. K.R. Thampi, Hydrocarbon Processing, Masters in Energy Refining Process Oil refining separates crude mineral oil into groups or fractions of substances. The following steps are useful: The most common way to separate fractions is to do fractional distillation. Then, some of the fractions are processed to refined products. This conversion process, for example, can break longer chains into shorter ones. This allows a refinery to turn diesel fuel into gasoline depending on the demand for gasoline. Refineries also treat the fractions to remove impurities. Refineries combine the various fractions (processed, unprocessed) into mixtures to make desired products. For example, different mixtures of chains can create gasolines with different octane ratings. Prof. K.R. Thampi, Hydrocarbon Processing, Masters in Energy Range of products from crude oil • • • • • Petroleum gas: for heating, cooking, feedstock for plastics, liquefied as LPG - C1 - C4 alkanes, b.p. = <40°C Naphtha or Ligroin: to be processed for gasoline - Mix of C5 - C9 alkanes, b.p. = 60 - 100°C Gasoline: liquid motor fuel - Mix of C5 - C12 alkanes and cycloalkanes; b.p. = 40 - 205°C Kerosene: fuel for jet engines and tractors, liquid, feedstock - Mix of C10 - C18 alkanes and aromatics; b.p. = 175 - 325°C Gas oil or diesel distillate: diesel fuel and heating oil; feedstock - Liquid > C12; b.p. = 250 - 350°C to continue…. Prof. K.R. Thampi, Hydrocarbon Processing, Masters in Energy Range of products from crude oil (contd..) • • • Lubricating oil: motor oil, grease, lubricants - mix of long chain liquids (C20-C50), alkanes, cycloalkanes, aromatics; b.p. = 300 - 370°C Heavy gas or fuel oil: industrial fuel, feedstock - mix of long chain liquids (C20-C70), alkanes, cycloalkanes, aromatics; b.p. = 370 - 600°C Residuals: coke, asphalt, tar, waxes, feedstock - mix of long chain solids (>C70); multiple ringed compounds; b.p. = >600°C Prof. K.R. Thampi, Hydrocarbon Processing, Masters in Energy Refining and Upgrading Most fuel sources, irrespective whether they are fossil based or renewable types, require chemical processing to upgrade their fuel value, suitability to the end use, adaptability to technology, pricing and distribution. For eg., - Distillation of crude petroleum - Refining - Cracking - Reforming, etc. In addition, fuel materials are also used as chemical building blocks, for example in polymers, resins, etc. They are studied as PETROCHEMICALS. This also involves a variety of processing methods. Examples: Isomerization, Metathesis, Oligomerization, etc. Prof. K.R. Thampi, Hydrocarbon Processing, Masters in Energy Petrochemicals Other uses Prof. K.R. Thampi, Hydrocarbon Processing, Masters in Energy A refinery Source: Prof. K.R. Thampi, Hydrocarbon Processing, Masters in Energy Oil Refining Source: Prof. K.R. Thampi, Hydrocarbon Processing, Masters in Energy Distillation of crude Source: Prof. K.R. Thampi, Hydrocarbon Processing, Masters in Energy HC refining and conversion processes - 1 - Cracking: to form lower Mol wt. Products and to supply alkenes for alkylation - Reforming (essentially dehydrogenation): increases Octane number of gasoline Prof. K.R. Thampi, Hydrocarbon Processing, Masters in Energy HC refining and conversion processes - 2 Isomerization of alkanes and alkylaromatics: also for increasing the octane number of gasoline an to produce xylenes and so on… Prof. K.R. Thampi, Hydrocarbon Processing, Masters in Energy HC refining and conversion processes - 3 • Alkylation: alkenes with alkanes and aromatics, to produce high octane gasoline, jet fuel, detergent alkylates, plastics, intermediates, etc. Prof. K.R. Thampi, Hydrocarbon Processing, Masters in Energy HC refining and conversion processes - 4 Metathesis Oligomerization and polymerization Prof. K.R. Thampi, Hydrocarbon Processing, Masters in Energy HC refining and conversion processes - 5 • • • • • • • Other conversions are mostly functionalizations: Additions Carbonylative conversions Acylations Substitutions Oxidations Reductions Prof. K.R. Thampi, Hydrocarbon Processing, Masters in Energy Mineral hydrocarbons Synthetic hydrocarbons • This may become necessary as the petroleum reserves are getting exhausted. Coal as such is not adaptable to an economy tuned for dealing with liquid and gaseous fuels. Prof. K.R. Thampi, Hydrocarbon Processing, Masters in Energy HC synthesis methods Prof. K.R. Thampi, Hydrocarbon Processing, Masters in Energy HC synthetic routes • Syngas based Fischer-Tropsch • CH3OH (MeOH) conversion - catalyst based, mainly zeolites - HBr based - Methyl halides based • CO2 conversion - photosynthetic, bacterial, catalytic, electrochemical • Direct CH4 conversion - condensation* - oxidative reactions, catalytic, superacids, halogens, Se, S, etc. Prof. K.R. Thampi, Hydrocarbon Processing, Masters in Energy Thermodynamic and kinetic issues 2 CH4 ® C2H6 + H2; DH = 16kcal/mol *Any condensation of CH4 to C2H6 and then to higher HCs must overcome unfavourable thermodynamics. This can be achieved in condensation processes of oxidative nature, where H2 is removed by the oxidant. Kinetically low yields and poor selectivity to favoured products. Superacids cleave also longer chain alkanes. Hence C3 - C6 products predominate. Prof. K.R. Thampi, Hydrocarbon Processing, Masters in Energy Nature of HC conversion reactions - 1 • Homolytic (free radical) reactions High temperature conversion processes of HCs fall in this category. Combustion of HCs itself is an example. Thermal cracking, cyclization, etc. are other examples. Low temperature examples are polymerization, and certain oxidation, substitution and addition reactions. Prof. K.R. Thampi, Hydrocarbon Processing, Masters in Energy Nature of HC conversion reactions - 2 • Heterolytic (ionic) reactions In acid catalysed reactions of unsaturated HCs, trivalent carbocations are responsible for electrophilic conversions. CH3+ is the parent. Carbocations with five CH5+ parent also occurs. They are initiated by protolytic reactions. Both C-H and C-C bonds are susceptible. Base catalysed HC conversions are less common. When occurs, by proton abstraction intermediate carbanions are formed. Prof. K.R. Thampi, Hydrocarbon Processing, Masters in Energy Heterolytic (ionic) reactions 1) 2) Prof. K.R. Thampi, Hydrocarbon Processing, Masters in Energy Heterolytic reactions (protolytic) 1) Not only C-H bonds but also C-C bonds…… 2) 3) Prof. K.R. Thampi, Hydrocarbon Processing, Masters in Energy Heterolytic reactions (acid catalyzed) Prof. K.R. Thampi, Hydrocarbon Processing, Masters in Energy Nature of HC conversion reactions - 3 • Base catalysed carbanionic alkylation, isomerization and polymerization are important. Base catalysed alkylation of alkylarenes, in contrast to acid catalyzed ring alkylation, leads to alkylation of the side chain in the benzylic position. An example is the alkylation of toluene to ethylbenzene required for styrene manufacture. Prof. K.R. Thampi, Hydrocarbon Processing, Masters in Energy Heterolytic reactions (base catalyzed) Through carbanions: 1) 2) 3) Prof. K.R. Thampi, Hydrocarbon Processing, Masters in Energy Use of Hydrocarbons • Refined Petroleum Products – Transportation fuels – Fuels for space heating – Fuels for power generation – Feedstock for chemicals and plastics – Components for lubricants Prof. K.R. Thampi, Hydrocarbon Processing, Masters in Energy Main references used in our lessons • • • • • • ‘Hydrocarbon Chemistry’ by G.A. Olah and A. Molnar, 2nd Edition, John Wiley, 2003. ‘Petrochemicals in non-technical language’ by D.L. Burdick and W.L. Leffler, Pennnwell books, 1990. ‘Chemistry of catalytic processes’ by B.C. gates, J.R. Katzer and G.C.A. Schuit, McGraw-Hill, 1979. ‘Fundamentals of Industrial Catalytic Processes’ by C.H. Bartholomew, Wiley-Interscience, 2006. ‘Sustainable Strategies for the upgrading of natural gas’, edited by E.G. Derouane, V. Parmon, F. Lemos and F.R. Ribeiro, Springer, 2005. Plus various other sources acknowledged in the slides. Prof. K.R. Thampi, Hydrocarbon Processing, Masters in Energy Exercise 1. Terms and names 1. Write down examples of: - Aliphatic, Cyclic, Saturated, Unsaturated, Alicyclic, Aromatic and Heterocyclic hydrocarbons. - Alkenes, arenes, n-alkane, i-alkane - Paraffins, Olefins, oxygenates, thiols, epoxides, cyclic oxides, anhydrides, ethers, nitriles, nitro-HC - O, m, p- xylenes, butylene Prof. K.R. Thampi, Hydrocarbon Processing, Masters in Energy Exercise 1 (contd…) 2. (CH3)2C=CH2 How do you call it? - isobutylene, 2-methyl propene or isobutene? 3. (CH3)3CH How do you call it? - isobutane, 2-methyl propane or butane? Prof. K.R. Thampi, Hydrocarbon Processing, Masters in Energy Exercise 1 (contd…) 3. What is: - a monomer, dimer, trimer, tetramer, oligomer, polymer and an isomer? - Give examples in each case. 4. What is Naphtha and Naphthene? Prof. K.R. Thampi, Hydrocarbon Processing, Masters in Energy Exercise 1 (contd…) 5. Why coal, tar sands and NG is less preferred (up till now) to crude oil? Give short answers. 6. Can you comment on why petroleum chemistry will still be very much relevant (or more) even if petroleum use is less favoured in future? Prof. K.R. Thampi, Hydrocarbon Processing, Masters in Energy Exercise 1 (contd…) 7. In petroleum processing, both thermal and catalytic conversions are widely used. For a given reaction and set of conditions, does the use of a catalyst change the equilibrium constant or heat of reaction compared to the situation in which no catalyst is used. Explain. (use your knowledge from other courses) Prof. K.R. Thampi, Hydrocarbon Processing, Masters in Energy Exercise 1 (contd…) 8. NH3 is an inorganic chemical. Then, why petroleum processing or C1 chemistry plays an important role in ammonia manufacture? (Hint: Answer lies in one of the slides covered in this class). Prof. K.R. Thampi, Hydrocarbon Processing, Masters in Energy Exercise 1 (contd…) 9. From coal to synthetic gasoline conversion, F-T reaction is an important route. Justify that this process is a depolymerization step followed by a polymerization reaction? Write relevant equations. Prof. K.R. Thampi, Hydrocarbon Processing, Masters in Energy Exercise 1 (contd…) 10. When buying gas appliances, why do you have to specify whether you are using LPG or NG? Prof. K.R. Thampi, Hydrocarbon Processing, Masters in Energy Exercise 1-11. Oil Refinery Disaster: What went wrong? Get the reading material from your teacher, if you are interested to know Prof. K.R. Thampi, Hydrocarbon the details Processing, Masters in Energy Excercise 1-12 Study and familiarize with distillation principles, vapour-liquid equilibrium (VLE) and McCabbe-Thiele method. Use these principles when studying other courses dealing with process design and separation. Document Title: DISTILLATION Base Document URL: http://lorien.ncl.ac.uk/ming/distil/distil0.htm Author: Ming T. Tham (Email:[email protected]) Date: Oct. 1997 Prof. K.R. Thampi, Hydrocarbon Processing, Masters in Energy Exercise 1-13 Refer to the slide, ‘HC refining and conversion processes - 2’. Use organic chemistry textbooks and references find out list a few examples of each of the reaction types given. List only hydrocarbon related transformations. Prof. K.R. Thampi, Hydrocarbon Processing, Masters in Energy The Chemistry and Processing of Hydrocarbons Energy Masters Section 2 Prof.K.R. Thampi, Hydrocarbon Processing, Masters in Energy Impossible without it…… • Processes based on H2 and syngas are one of the most basic processes involved in fuel, food and chemicals production and distribution. Prof.K.R. Thampi, Hydrocarbon Processing, Masters in Energy Syngas - Production and Reactions NH3 and Methanol are both high volume Early 20th Century F-T by mid 1920’s A combination of steam reforming and partial oxidation is called autothermal reforming. Prof.K.R. Thampi, Hydrocarbon Processing, Masters in Energy Syngas Reactions Prof.K.R. Thampi, Hydrocarbon Processing, Masters in Energy H2/CO ratios from various syngas processes Prof.K.R. Thampi, Hydrocarbon Processing, Masters in Energy Steam Reforming (SR) of HC: Process steps and catalysts HT & LT = High and Low temps. Prof.K.R. Thampi, Hydrocarbon Processing, Masters in Energy Reformer • A pre-reformer may be used when using higher HCs. This allows lower steam/carbon (S/C) ratio operation. Since SR and WGS are thermodynamically opposed, process is tuned for one or the other reaction. For NH3 synthesis, primary and secondary reforming are operated at high temperatures and WGS at low temperatures to favour the equilibrium yields. All stages operate in equilibrium. Prof.K.R. Thampi, Hydrocarbon Processing, Masters in Energy Process diagram for H2 production S/C = 2.5-4.0, Texit=900-1100°C, Pexit= 20-30 atm. Prof.K.R. Thampi, Hydrocarbon Processing, Masters in Energy Process stage 1 - Feedstock purification • S containing compounds: Reaction over CoMo/Al2O3 (to H2S) followed by scrubbing H2S by ZnO (BET area = 25m2/g) • To protect downstream Ni SMR catalyst, S should be below 0.01 ppm. • Chlorides cause corrosion in heat exchangers and poison catalysts (Cu-WGS). Cl- is scrubbed to below 5ppb with a alkaline-treated Al2O3. Prof.K.R. Thampi, Hydrocarbon Processing, Masters in Energy Primary steam reforming • Out of the three equations, the CO and H2 formation from CnHm are endothermic. WGS is exothermic. The combined reaction is either +ve or -ve, depending upon the process conditions. Most typically, it is strongly endothermic and heat must be supplied. • See the CH4 conversion as dependednt on temperatures and pressures in the next slide. Prof.K.R. Thampi, Hydrocarbon Processing, Masters in Energy CH4 conversion in SR of CH4 Prof.K.R. Thampi, Hydrocarbon Processing, Masters in Energy Compositional requirements for syngas • Stoichiometry, M = (H2-CO2)/(CO + CO2). • • This value should be 2. However, since H 2/CO is dependent on T °C, and of H2O/CH4 ratio, these two variables are adjusted to get the desired H2/CO ratio. However, syngas with M=2 cannot be produced directly by SMR of NG, although combined SMR and CMR* can provide the appropriate stoichiometry. For example, syngas used for methanol synthesis should conform to: • 0.75 CH4 + 0.25 CO2 + 0.5 H2O Û CO + 2H2 * CO2-CH4 reforming Prof.K.R. Thampi, Hydrocarbon Processing, Masters in Energy Industrial conditions for Reforming/ATR Prof.K.R. Thampi, Hydrocarbon Processing, Masters in Energy Combined steam/CO2 reforming for syngas with H2/CO = 2 P = 25 bar Texit = 950°C Prof.K.R. Thampi, Hydrocarbon Processing, Masters in Energy The Chemistry and Processing of Hydrocarbons Energy Masters Course Section 3 Prof.K.R. Thampi, Hydrocarbon Processing, Masters in Energy 71 An eye-view of important processes in crude oil processing Important catalytic processes are boxed or circled; rectangles denote base-metal catalysts; ovals denote noble metal catalysts Prof.K.R. Thampi, Hydrocarbon Processing, Masters in Energy 72 Cracking • Cracking is the breaking down of large petroleum molecules into smaller hydrocarbons, primarily in the gasoline range. • Cracking can be performed both catalytically and non-catalytically. The catalysts can decrease the severity of reaction conditions, increases selectivity and yield of desired products. • Innovative shift from SiO2-Al2O3 catalysts to modern zeolite catalysts enforced the redesign of cracking process practiced 5-6 decades ago. Prof.K.R. Thampi, Hydrocarbon Processing, Masters in Energy 73 Design Changes • Instead of a large fluidized bed, the cracker is now a small tube. Catalyst particles are conveyed through it by rapidly flowing oil vapours, which stay in contact with the catalyst only about 5 s. • Cracking chemistry is well understood. Prof.K.R. Thampi, Hydrocarbon Processing, Masters in Energy 74 Importance of FCC (fluidized catalytic cracking) • • • • • • • Thermal cracking possibility was recognized in 1913. Cracking to get high octane fuels: 1928 Commercial (cyclic) fixed bed plant: 1936 Continuous fluid-bed cracking:1942 Zeolite based modern process:1962 ZSM-5 octane enhancer: 1986 Now, >1600 tons/day of FCC catalyst is consumed to process > 14 million/barrels of gas oil (21% of refinery capacity) Prof.K.R. Thampi, Hydrocarbon Processing, Masters in Energy 75 Reactions •O = gas oil; G = gasoline; •X = undesired products (light over-cracked products) Prof.K.R. Thampi, Hydrocarbon Processing, Masters in Energy 76 Principle Reactions in FCC Prof.K.R. Thampi, Hydrocarbon Processing, Masters in Energy 77 Typical reactions in FCC Prof.K.R. Thampi, Hydrocarbon Processing, Masters in Energy 78 At equilibrium…… • The main cracking reactions are not limited by equilibrium under industrial conditions. • At equilibrium, HC would totally degrade to graphite and H2 • Isomerizations, alkyl group rearrangement and dealkylation of aromatics go to a moderate extent. • Paraffin-olefin alkylation, aromatic hydrogenation and olefin polymerization (except ethylene polymerization) go little. Prof.K.R. Thampi, Hydrocarbon Processing, Masters in Energy 79 Energetics • Cracking reactions are much endothermic. • Isomerizations have very small heats of reaction • H-transfer reactions are exothermic • In cracking process, the endothermic reactions predominate • Magnitude of heat effect depends on the feedstock, catalyst and reactor conditions Prof.K.R. Thampi, Hydrocarbon Processing, Masters in Energy 80 Prof.K.R. Thampi, Hydrocarbon Processing, Masters in Energy 81 Cracking:thermal or catalytic? High yields of ethylene indicates thermal cracking, whereas high yields of propylene indicates catalytic cracking. Prof.K.R. Thampi, Hydrocarbon Processing, Masters in Energy 82 FCC Catalyst deactivation Because of the stability of polynuclear aromatic carbonium ions, it can continue to grow on catalyst surface before a termination reaction occurs. Cyclisation, aromatisation and polyarenes formation can go up to coke and tar formation. This deactivate the FCC catalyst. Coke may be removed in a fluidised bed regenerator. Prof.K.R. Thampi, Hydrocarbon Processing, Masters in Energy 83 FCC reactor variables Single stage cracking: conversion to gas and coke high product flexibility low Two-stage cracking: low gas and coke, better product flexibility First stage: Riser reactor, short residence time, High T Separator: gas and gasoline products removal before stage II. Second stage: Fluidised bed reactor, low temperature. Regenerator: T= 650-760 °C, P = 3 atm., coke to be decreased from 2-5% to <0.1%. FCC catalyst is returned back to cracker along with fresh catalyst (< 1%/day). Prof.K.R. Thampi, Hydrocarbon Processing, Masters in Energy 84 FCC process flow diagram Prof.K.R. Thampi, Hydrocarbon Processing, Masters in Energy 85 Riser catalytic-cracking unit Prof.K.R. Thampi, Hydrocarbon Processing, Masters in Energy 86 FCC reaction sequence Reactor entrance: initiation, alkene desorption, isomerisation (leading mainly to C3 and C4 alkenes) Middle of the reactor: surface coverage of carbonium ions increases (H- transfer and oligomerisation becomes predominant; selectivity of alkene decreases, but that of alkane increases for a given C number) Reactor exit: C3=, iC4= and iC5 increased C4 products decreased Prof.K.R. Thampi, Hydrocarbon Processing, Masters in Energy 87 Operational Flow diagram of the CC process Prof.K.R. Thampi, Hydrocarbon Processing, Masters in Energy 88 Operating CC The refinery engineer should know: Quantitative comparisons of catalytic activity, selectivity and deactivation rate for various FCC catalysts to select 1) Best catalyst 2) Optimise the octane number 3) Model the effects of different catalysts using standard process models Prof.K.R. Thampi, Hydrocarbon Processing, Masters in Energy 89 FCC’s strategic importance FCC catalyst consumption per day (mostly for replenishment) : Processing per day : > 15 million barrels As a % of total refinery capacity : 21% Approx. Number of Refineries : 740 Prof.K.R. Thampi, Hydrocarbon Processing, Masters in Energy 1500 tons 90 Methanol Synthesis • • • • • Methanol is one of the top 10 most important sythetic organic chemicals. Methanol is a raw material for formaldehyde (40-50% of methanol production), chloromethanes, amines, acetic acid, methyl methacrylate and methyl-t-butyl ether (MTBE) manufacture. It is also a solvent. Until early 1900s, methanol was produced by destructive distillation of wood. In 1923, BASF developed catalytic methanol production using Zn/Cr2O3 catalyst (300-400°C, 300 bars) In 1966, ICI developed a better process (Cu/ZnO/Al2O3 catalysts, 220-300°C, 50-100 bars) Prof.K.R. Thampi, Hydrocarbon Processing, Masters in Energy ICI process advantages • Reduced compression power • Longer catalyst life • Larger capacity, single train converter designs • Productivity increase from 770 to 1120 tons of methanol per million M3 of NG • Globally > 30 million MT/year production • 50-2500 MT/day size plants • As MTBE is being phased out methanol demand is growing downwards from 1998. Prof.K.R. Thampi, Hydrocarbon Processing, Masters in Energy A combination of 2 exothermic equilibriums gives methanol • CO + H2O Þ H2 + CO2, DH298K = -41.2 kJ/mol • CO2 + 3H2 Þ CH3OH + H2O, DH298K = -49.5 kJ/mol • CO + 2H2 Þ CH3OH; • DH298K = -90.6 kJ/mol; DH600K = -100.5 kJ/mol • Note that in the final equation, CO2 is not shown. This has certain significance in the study of methanol synthesis. Reaction occurs at near equilibrium Conversion increases with decreasing temperature and increasing pressure • • Prof.K.R. Thampi, Hydrocarbon Processing, Masters in Energy Higher alcohol synthesis Because of their potential use as additives to gasoline and as chemical feedstocks, the synthesis of higher alcohols from NG via syngas is a promising technology. Na promoted Zn-Cr catalysts; 350-420°C, 1216 bars, GHSV 3000 - 15’000 h-1 Product composition: 68-72% methanol, 2-3% ethanol, 3-5% C3, 10-15% C4 and 7-12% C5 alcohols. Prof.K.R. Thampi, Hydrocarbon Processing, Masters in Energy F-T synthesis • Production of liquid HC from syn-gas • Possibility to use NG, biomass and coal • Enormous potential for this technology as we face dwindling oil reserves • Seen as a gas-to-liquid (GTL) technology suitable to beneficially use under-utilized or flared NG to a premium quality S-free diesel fuel. Prof.K.R. Thampi, Hydrocarbon Processing, Masters in Energy 4 steps in F-T synthesis • Starting from biomass, coal, NG (BTL, CTL and GTL, respectively) • 1) Production of syngas • 2) Syngas purification • 3) FTS • 4) Separation and upgrading of products Prof.K.R. Thampi, Hydrocarbon Processing, Masters in Energy From coal Prof.K.R. Thampi, Hydrocarbon Processing, Masters in Energy From NG Prof.K.R. Thampi, Hydrocarbon Processing, Masters in Energy Relevance of F-T synthesis • 1902-1928: Sabatier reaction leads to BASF’s Co-catalyzed liquid HC synthesis at severe conditions. Then, Fischer and Tropsch invented oxygenated hydrocarbon synthesis. This led them to perfect the presently known F-T synthesis over Co-Fe catalysts at <300°C and 1 bar pressure in 1925. The commercial development took place in Germany during WW II, due to lack of petroleum resources in Germany. USA and UK then keenly followed the technology and established F-T plants in USA. After 1957, due to cheap petroleum coming from the Middle-East F-T technology became redundant. However, it continued (1955 - 1994) in South Africa (SA) in a major way due to the apartheid embargo. The SA process is called SASOL. Prof.K.R. Thampi, Hydrocarbon Processing, Masters in Energy F-T technology today • The ‘oil embargo’ of 1973 stimulated interest in F-T synthesis again. Many process improvements happened in 1975-1990. SASOL and FTS Diesel processes resulted as a result. The modern GTL process (gas to liquid) is the latest in the F-T series. It is now gaining prominence due to the price rise of oil again….. Co and Fe catalysts are used along with tube-shell, fixed bed or fluidised bed reactors for GTL process. Prof.K.R. Thampi, Hydrocarbon Processing, Masters in Energy Exercise 3 1. What are the key differences you can observe between thermal and catalytic cracking? 2. What are the features of a reaction model governing thermal cracking? 3. In catalytic cracking, a tertiary carbon readily donates a H- to a primary or secondary carbonium ion; other transfers are slower. True or false? Prof.K.R. Thampi, Hydrocarbon Processing, Masters in Energy 101 Exercise 3 4. Formation of carbonium ions allow branching polymerisation reactions. Why? 5. Why FCC favours branched chain and isomerised products than thermal cracking? 6. What is the benefit of FCC when compared to thermal cracking process? Prof.K.R. Thampi, Hydrocarbon Processing, Masters in Energy 102 Exercise 3 7. Even though cracking reactions are endothermic, the equilibrium conversions in cracking may be high. What does this imply about the entropy changes in cracking reactions? 8. Examine the routes to the formation of carbonium ions from a long paraffin molecule. What are the most important routes to form carbonium ions in cracking reactions? 9. Why do we use low residence times in FCC process? 10. How FCC catalyst gets deactivated? Prof.K.R. Thampi, Hydrocarbon Processing, Masters in Energy 103 Exercise 3 11. What is the benefit in choosing zeolite based catalysts for FCC? 12. Why do we add ZSM-5 type additives to FCC catalysts? 13. What is b scission rule and why is it critical in cracking? 14. In zeolite based FCC catalysts, we find both Brønsted and Lewis acid sites. Which one is more important in FCC Reactions and why (from a reaction and molecular point of view? Prof.K.R. Thampi, Hydrocarbon Processing, Masters in Energy 104 The Chemistry and Processing of Hydrocarbons Energy Masters Section 4 Prof. K.R. Thampi, Hydrocarbon Processing, Masters in Energy 105 Two important refinery processes: 1. Hydro-cracking 2. Naphtha reforming* * Not to confuse with steam-reforming Prof. K.R. Thampi, Hydrocarbon Processing, Masters in Energy 106 1. Hydrocracking This is cracking and hydrogenation combined into a single process. Low value gas oil containing a high % of polynuclear aromatics is simultaneously cracked and hydrogenated to get high-value low and middle distillates including gasoline and diesel fuel. The catalyst MUST be bi-functional: - acid sites to catalyse cracking reactions - metal sites to catalyse hydrogenation Prof. K.R. Thampi, Hydrocarbon Processing, Masters in Energy 107 Advantages 1) This process can be designed to crack polyaromatics selectively to gasoline, diesel fuel or jet fuel. In contrast, FCC is not as selective as hydrocracking. 2) Processed in higher pressures over a much broader temperature range (290 - 525 °C) than in FCC. 3) Possible to hydrorefine heavier cuts from crude distillation. 4) It increases alkane content in aromatic rich fuels improves the Cetane number (a measure of combustion efficiency) of diesel fuel. Prof. K.R. Thampi, Hydrocarbon Processing, Masters in Energy 108 Typical Hydrocracking Reactions Prof. K.R. Thampi, Hydrocarbon Processing, Masters in Energy 109 Disadvantages The high pressure of H2 (80 - 200 atm) causes high consumption of H2 and energy. High pressures are required to crack heavier feeds and avoid coking. Mild hydrotreating at low pressures is still favoured for removing metals, sulfur and nitrogen compounds normally found in heavier oil feeds. This is often done in combination with HDM/HDS on Co-Mo or Ni-W catalysts. Prof. K.R. Thampi, Hydrocarbon Processing, Masters in Energy 110 Catalysts Selection of catalysts depend on the nature of feed and the desired selectivity to product composition. For producing lubricants, diesel and middle or heavy distillates: Base metal oxides of Co, Mo, Ni or W supported on either acid-treated Al2O3, Al2O3-SiO2 or a zeolite. For producing gasoline from S and N-free feeds: Pt or Pd supported on shape-selective zeolites (Faujasite : 0.74nm; 0.78nm for modernite; 0.55nm for ZSM-5) Prof. K.R. Thampi, Hydrocarbon Processing, Masters in Energy 111 Process Dual stage fixed bed reactors at 375 - 425 °C and 100 - 170 atm. LHSV (liquid hourly space velocity) = 0.5 - 2 h-1. High conversion causes large heat releases from hydrogenation reactions. Hence, product stream is cooled by injection of cold high pressure H2 between the two fixed bed reactors. Catalysts survive for 1-3 years. Replacement by fresh or re-generated catalysts. Prof. K.R. Thampi, Hydrocarbon Processing, Masters in Energy 112 Hydrocracking process scheme Prof. K.R. Thampi, Hydrocarbon Processing, Masters in Energy 113 2. Naphtha reforming Primarily done for: 1) Increasing octane number of naphtha cut boiling at 70 - 200 °C (C5 - C10) 2) As a source of aromatics for petrochemicals (eg., polyester) Prof. K.R. Thampi, Hydrocarbon Processing, Masters in Energy 114 Octane numbers of pure HC Prof. K.R. Thampi, Hydrocarbon Processing, Masters in Energy 115 Composition of a naphtha feed for BTX* production * BTX = Benzene, Toluene, Xylene Prof. K.R. Thampi, Hydrocarbon Processing, Masters in Energy 116 Thermodynamic data Major reforming reactions are endothermic. Prof. K.R. Thampi, Hydrocarbon Processing, Masters in Energy 117 Octane number vs C number for important groups in reforming Prof. K.R. Thampi, Hydrocarbon Processing, Masters in Energy 118 Prof. K.R. Thampi, Hydrocarbon Processing, Masters in Energy 119 Catalyst Typically, Pt or Pt-Re supported on g-Al2O3 (BET area = 200 m2/g) Pt - Re (0.35% Pt - 0.5% Re) g-Al2O3 is acidic. This is further improved by adding Cl- to it. Acididc function helps isomerisation reactions. Pt or Pt-Re helps hydrogenation and de-hydrogenation functions. Re is pre-sulfided using 10-20ppm H2S to improve the catalyst life. It breaks up Pt particles into smaller ensembles and prevent coking. Extrudates or pellets (1.5 - 6 mm dia) Prof. K.R. Thampi, Hydrocarbon Processing, Masters in Energy 120 Process - 1 Pre-treatment: hydrotreat to remove thiophene, pyridines, phenols Design should accommodate a variety of reactions with different relative activites and equilibrium limitations. Therefore, a series of separate reactors are used: The front end is preferentially dehydrogenation (endothermic and favours high operating temperatures). H2 is added in large excess to prevent excessive de-hydrogenation to coke). Prof. K.R. Thampi, Hydrocarbon Processing, Masters in Energy 121 Process - 2 Reforming processes are of three types: 1) Semi-regenerative (small units) - periodic shut down and catalyst regeneration 2) Cyclic (fully regenerative; large scale units) - swinging only one of 4-6 reactors off-line for catalyst regeneration 3) Continuously regenerative (moving bed) - small quantities of catalysts are withdrawn continuously, regenerated and returned to the top of the reactor system, which consists of 4-5 reactors stacked vertically. Prof. K.R. Thampi, Hydrocarbon Processing, Masters in Energy 122 Process - 3 1) Entry: 500 °C, 14-17 atm., LHSV = 1-3 h-1. 2) Reactor 1: 5% of the total catalyst, naphthenes to aromatics, high space velocity, kinetics easy, endothermic, exit cools to 420 °C. 3) Reactor 2: prior reheating to 500 °C, 15% of the total catalyst; slower kinetics, dehydrogenation + isomerization; Texit = 450 °C 4) Reactors 3 - 4: prior reheating to 500 °C, 20 & 60% bed volume; (smaller LHSV); dehydrocylisation. Overall process produces H2, a part of which is recycled to keep Prof. K.R. Thampi, Hydrocarbon 123 coke formation to a minimum. Processing, Masters in Energy Semi-regenerative reforming process Prof. K.R. Thampi, Hydrocarbon Processing, Masters in Energy 124 Cyclic regenerative reforming Prof. K.R. Thampi, Hydrocarbon Processing, Masters in Energy 125 Exercise 4 1. Compare briefly thermal cracking, FCC and hydrocracking. 2. What are the roles of H2 in hydrocracking and petroleum reforming? 3. What are the bi-functional characters of a (a) hydrocracking catalyst, (b) reforming catalyst? 4. What are the modes of deactivation of FCC, hydrocracking and Pt-reforming catalysts? 5. List important points in the re-activation of these catalysts. Prof. K.R. Thampi, Hydrocarbon Processing, Masters in Energy 126 Exercise 4 6. Why is hydrocracking activity greatly decreased by the presence of quinoline in higher amounts? How could the hydrocracking process be designed to minimise this effect? 7. Why acid sites and metal sites are provided for performing reforming reactions? 8. What are the main purposes of hydrocracking and catalytic reforming? 9. What is the role of Re in Pt-Re/Al2O3 catalyst used for reforming process? Prof. K.R. Thampi, Hydrocarbon Processing, Masters in Energy 127 Exercise 4 10. A refinery received a gas oil supply containing high amounts of metals, sulfur and nitrogen compounds. The refinery wants to maximise the production of gasoline and minimise the formation of light gases. As a refinery manager, what will you do? Prof. K.R. Thampi, Hydrocarbon Processing, Masters in Energy 128