Hydrogenation

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Hydrogenation
Chemical Industry Processes and Chemical Reactions

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Hydrogenation

  1. 1. -1-hydrogenation-140526162439-phpapp01.doc Suez Canal University Faculty Of Petroleum & Mining Engineering Prepared by/ Student/ Mohamed salah abou El_hamed Department/ petroleum refining Year/ third
  2. 2. -2-hydrogenation-140526162439-phpapp01.doc l ReactionsChemical Industry Processes and Chemica Chemical processes are used in the chemical industry to transform raw materials into more specialized products. The place where chemical products are produced is usually called chemical plant. The chemical industry relies on the knowledge and investigation of the chemical properties of different materials. Chemistry is the study of the matter and the transformations of it. While physics study matter from a more fundamental point of view, chemistry focuses on its composition, behavior, reactions, structure and properties. The study of the chemical reactions that affect matter gave humans the possibility to turn useless materials into more valuable and useful materials, through chemical transformations. Chemistry focuses on atoms, molecules, substances, crystals and other kind of aggregates. A chemical process is a method in which one or more chemicals or chemical compounds are changed in some way. Let's remember that a chemical is a substance with a constant chemical composition and characteristic properties, that cannot be separated into components by physical separation methods, and without breaking chemical bonds. The basic reactions used in the chemical industry are: Oxidation, Reduction, Hydrogenation, Dehydrogenation, Hydrolysis, Hydration reaction, Dehydration, Halogenation, Nitrification, Sulfonation, Ammoniation, Alkaline fusion, Alkylation, Dealkylation, Esterification, Polymerization, Polycondensation. Distillation is a separation technique that depends on boiling points. It is a physical separation process, not a chemical reaction. It is used to separate crude oil. Water is cleaned up by distillation to remove impurities like salt and other minerals. The air can be also put to distillation to separate it in components like oxygen, nitrogen and argon for their use in industry. The alcohol industry uses distillation to produce beverages with higher alcohol content. The place were alcohol is put to distillation is known as distillery. Fractional distillation is a more specialized process used to obtain specific chemical compounds. Precipitation is another separation method in which a solid is formatted in a solution or inside another solid during a chemical reaction or by diffusion in a solid. When this reaction occurs using a centrifuge, the solid formed is called pellet. When the reaction occurs in a liquid, the solid formed it is called precipitate.
  3. 3. -3-hydrogenation-140526162439-phpapp01.doc Chemical Industry in Modern Life Almost everything we use today needs chemical products to be manufactured or to function. The Chemical Industry is one of the most important industries in the modern world. Chemical products are involved in almost every industrial process and are essential in other industries. The Chemical industry is the one responsible of converting raw materials like water, oil, natural gas, air, metals, and minerals, into more valuable products. Around the 80% of the chemical industry production is centered in plastics and polymers. These products are fundamental for a very wide range of processes within other industries, like the automotive industry, medical instruments, food industry, space exploration, all manners of transport, and things of every day use like TVs, computers, pens, and even cloth. The chemical industry itself consumes around 26% of this chemical products. In a large scale, modern life depends on plastic and polymer products. The most important chemical companies are from the United States and European Union and chemicals is calculated to be a $3 trillion global enterprise. The chemical business sales can be divided in a few broad categories like basic chemicals with around 40% of output, life sciences 30%, specialty chemicals 20% and customer products 10%. Basic chemical include polymers, petrochemicals, reaction intermediates, inorganic chemicals and fertilizers. The polymers and plastics are used for construction pipes, tools, materials like acrylics, appliances, electronic devices, transportation, toys, games, packing, clothing and textiles like nylon and polyester, among many other products. Polymers come from petrochemical raw materials like liquefied petroleum gas (LPG), natural gas and crude oil or petroleum. Petrochemicals are also used for producing other organic chemicals and well as specialty chemicals. Other basic industrial chemicals include synthetic rubber, pigments, resins, explosives and rubber products. Inorganic chemicals belong to the oldest chemical categories, and include daily products like salt, chlorine, soda ash, acids like nitric, phosphoric and sulfuric acids, caustic soda and hydrogen peroxide, which are vital for several industries. Fertilizer belong to the smaller category of basic chemicals and include phosphates, ammonia and potash, which are used to supply the soil with nutrients for growing plants and agriculture.
  4. 4. -4-hydrogenation-140526162439-phpapp01.doc Life sciences industry use different chemicals and biological substances for manufacturing pharmaceuticals, animal health products, vitamins and pesticides. This industry produce a small volume compared to other chemical sectors, but their products are most commonly very expensive. These life science products are produced with very detailed specifications and have to be of the better quality. There is a lot of money invested in investigation even before making the first marketable product. This industry is very strictly scrutinized by governmental agencies and authorities. Specialty chemicals is a category of very high valued chemical products and is rapidly growing today thanks to scientific research and technology advances. This include the most innovative products valued more for what they do, than what chemicals they contain. This include electronic chemicals, industrial gases, adhesives and others. Finally, the consumer products are chemicals directly sold to the customers like soap, detergents and cosmetics.
  5. 5. -5-hydrogenation-140526162439-phpapp01.doc A Look at Common Industrial Chemicals Sulfuric Acid Probably the most common industrial acid. Used widely in mineral leaching and gas scrubbing (removing dangerous substances). Also used to neutralize alkaline substances. Ethylene Probably the most popular industrial precursor to polymer manufacturing . Ammonia Very popular scrubbing solvent to remove pollutants from fossil fuel combustion streams before they can be released to the atmosphere. Also a popular refrigerant. Phosphoric Acid Main use is in fertilizer production, other uses include soft drinks and other food products. Propylene Another industrial polymer precursor (polypropylene(. Chlorine Used in the manufacture of bleaching agents and titanium dioxide. Many of the bleaching agents based on chlorine are being replaced by hydrogen peroxide due to environmental restrictions placed on chlorine. Sodium Carbonate Most commonly known as soda ash, sodium carbonate is used in many cleaning agents and in glass making. Most soda ash is mined from trona ore, but it can be manufactured by reacting salt and sulfuric acid. Nitrobenzene Primary use is in the manufacture of aniline, which is in turn used as a rubber additive to prevent oxidation (antioxidant). Butyraldehyde Used to manufacture 2-ethylhexanol which is then used to manufacture hydraulic oils or synthetic lubricants. Aluminum Sulfate Widely used in the paper and wastewater treatment industries as a pH buffer. Ethylene Dichloride Nearly all ethylene dichloride produced is used to produce vinyl chloride which is then polymerized to polyvinyl chloride (PVC). Ammonium Nitrate Probably the most widely used solid fertilizer.
  6. 6. -6-hydrogenation-140526162439-phpapp01.doc Urea The majority of urea is used in fertilizer production. Some is also used in the manufacture of livestock feed. Vinyl Chloride As previously mentioned, this is the monomer form of polyvinyl chloride (PVC) which finds uses as a building material and other durable plastics. Ethylbenzene Used almost exclusivley as a reactant for the production of styrene. Methanol Used as a reactant to make methyl tertbutyl ether (MTBE), formaldeyde, and acetic acid. Typically produced from synthesis gases, namely carbon monoxide and hydrogen. Xylene – o-xylene (ortho) is used primarily to manufacture phthalic anhydride which is in turn used to make a variety of plasticizers and polymers. p-xylene is used to manufacture terephthalic acid, a polyester feedstock. Formaldehyde Commonly used as part of a copolymer series (Urea- formaldehyde resins) or as another polymer additive used to bring out desired characteristics. Terephthalic Acid Almost exclusively used in the manufacture of polyethylene terephthalate (PET) or polyester. Ethylene Oxide Majority of ethylene oxide is used to manufacture ethylene glycol which is described later. Ethylene Gylcol Most common use is as a reactant to form polyethylene terephthalate (PET). Also used a primary ingredient in antifreeze. Carbon Black Most common use is a rubber additive Isobutylene Most production is used to make butyl rubbers. Potash Used in agriculture as a crop fertilizer. Titanium Dioxide Used as a white pigment for many products ranging from paints and polymers to pharmaceuticals and food items. In short, if it’s white, it probably has titanium dioxide in it.
  7. 7. -7-hydrogenation-140526162439-phpapp01.doc Hydrogenation (to treat with hydrogen) is a chemical reaction between molecular hydrogen (H2) and another compound or element, usually in the presence of a catalyst. The process is commonly employed to reduce or saturate organic compounds. Hydrogenation typically constitutes the addition of pairs of hydrogen atoms to a molecule, generally an alkene. Catalysts are required for the reaction to be usable; non-catalytic hydrogenation takes place only at very high temperatures. Hydrogenation reduces double and triple bonds in hydrocarbons. Because of the importance of hydrogen, many related reactions have been developed for its use. Most hydrogenations use gaseous hydrogen (H2), but some involve the alternative sources of hydrogen, not H2: these processes are called transfer hydrogenations. The reverse reaction, removal of hydrogen from a molecule, is called dehydrogenation. A reaction where bonds are broken while hydrogen is added is called hydrogenolysis, a reaction that may occur to carbon-carbon and carbon-heteroatom (oxygen, nitrogen or halogen) bonds. Hydrogenation differs from protonation or hydride addition: in hydrogenation, the products have the same charge as the reactants. Hydrogenation of unsaturated fats produces saturated fats. In the case of partial hydrogenation, trans fats may be generated as well.
  8. 8. -8-hydrogenation-140526162439-phpapp01.doc Equipment used for hydrogenation Today's bench chemist has three main choices of hydrogenation equipment:  Batch hydrogenation under atmospheric conditions  Batch hydrogenation at elevated temperature and/or pressure  Flow hydrogenation Batch hydrogenation under atmospheric conditions The original and still a commonly practised form of hydrogenation in teaching laboratories, this process is usually effected by adding solid catalyst to a round bottom flask of dissolved reactant which has been evacuated using nitrogen or argon gas and sealing the mixture with a penetrable rubber seal. Hydrogen gas is then supplied from a H2-filled balloon. The resulting three phase mixture is agitated to promote mixing. Hydrogen uptake can be monitored, which can be useful for monitoring progress of a hydrogenation. This is achieved by either using a graduated tube containing a coloured liquid, usually aqueous copper sulfate or with gauges for each reaction vessel. Batch hydrogenation at elevated temperature and/or pressure Since many hydrogenation reactions such as hydrogenolysis of protecting groups and the reduction of aromatic systems proceed extremely sluggishly at atmospheric temperature and pressure, pressurised systems are popular. In these cases, catalyst is added to a solution of reactant under an inert atmosphere in a pressure vessel. Hydrogen is added directly from a cylinder or built in laboratory hydrogen source, and the pressurized slurry is mechanically rocked to provide agitation, or a spinning basket is used. Heat may also be used, as the pressure compensates for the associated reduction in gas solubility. Flow hydrogenation Flow hydrogenation has become a popular technique at the bench and increasingly the process scale. This technique involves continuously flowing a dilute stream of dissolved reactant over a fixed bed catalyst in the presence of hydrogen. Using established HPLC technology, this technique allows the application of pressures from atmospheric to 1,450 psi (100 bar). Elevated temperatures may also be used. At the bench scale, systems use a range of pre- packed catalysts which eliminates the need for weighing and filtering pyrophoric catalysts.
  9. 9. -9-hydrogenation-140526162439-phpapp01.doc Industrial reactors Catalytic hydrogenation is done in a tubular plug-flow reactor (PFR) packed with a supported catalyst. The pressures and temperatures are typically high, although this depends on the catalyst. Catalyst loading is typically much lower than in laboratory batch hydrogenation, and various promoters are added to the metal, or mixed metals are used, to improve activity, selectivity and catalyst stability. The use of nickel is common despite its low activity, due to its low cost compared to precious metals. Gas Liquid Induction Reactors (Hydrogenator) are also used for carrying out catalytic hydrogenation. FACTORS AFFECTING HYDROGENATION  Independent Variables 1. Pressure 2. Temperature 3. Agitation 4. Catalyst concentration  Dependent Variables 1. Trans fatty acids 2. Selectivity ratio 3. Hydrogenation rate
  10. 10. -10-hydrogenation-140526162439-phpapp01.doc Hydrogenation of hydrocarbons neseHydrogenation of Alk the reaction of the carbon-carbon double bond in alkenes with hydrogen in the presence of a metal catalyst. This is called hydrogenation. It includes the manufacture of margarine from animal or vegetable fats and oils. The hydrogenation of ethene Ethene reacts with hydrogen in the presence of a finely divided nickel catalyst at a temperature of about 150°C. Ethane is produced. This is a fairly pointless reaction because ethene is a far more useful compound than ethane! However, what is true of the reaction of the carbon-carbon double bond in ethene is equally true of it in much more complicated cases Heat of Hydrogenation Heat of hydrogenation (symbol: ΔHhydro, ΔHº) of an alkene is the standard enthalpy of catalytic hydrogenation of an alkene. Catalytic hydrogenation of an alkene is always exothermic. Therefore, heat of hydrogenation of alkenes is always negative. eg: Standard enthalpy of this reaction is -30.3 kcalmol-1. Thus, heat of hydrogenation of 1-butene is -30.3 kcalmol-1. Heat of hydrogenation of alkenes is a measure of the stability of carbon- carbon double bonds. All else being the same, the smaller the numerical value of heat of hydrogenation of an alkene, the more stable the double bond therein. Based on heats of hydrogenation of alkenes, the trend in the stability of carbon-carbon double bonds is tetrasubstituted > trisubstituted > disubstituted > monosubstituted > unsubstituted. Heat of hydrogenation of alkenes is additive, provided that the double bonds are not conjugated.
  11. 11. -11-hydrogenation-140526162439-phpapp01.doc eg: Common catalysts used are insoluble metals such as palladium in the form Pd- C, platinum in the form PtO2, and nickel in the form Ra-Ni. With the presence of a metal catalyst, the H-H bond in H2 cleaves, and each hydrogen attaches to the metal catalyst surface, forming metal-hydrogen bonds. The metal catalyst also absorbs the alkene onto its surface. A hydrogen atom is then transferred to the alkene, forming a new C-H bond. A second hydrogen atom is transferred forming another C-H bond. At this point, two hydrogens have added to the carbons across the double bond. Because of the physical arrangement of the alkene and the hydrogens on a flat metal catalyst surface, the two hydrogens must add to the same face of the double bond, displaying syn addition.
  12. 12. -12-hydrogenation-140526162439-phpapp01.doc Hydrogenation of Alkynes Reaction Type: Electrophilic Addition Summary  Alkynes can be partially reduced to cis-alkenes with H2 in the presence of poisoned catalysts. (eg. Pd / CaCO3 / quinoline which is also known as Lindlar's catalyst)  Alkynes can be reduced to alkanes with H2 in the presence of catalysts (Pt, Pd, Ni etc.)  The new C-H σ bonds are formed simultaneously from H atoms absorbed onto the metal surface.  The reaction is stereospecific giving only the syn addition product.  The "poisoned" catalyst prevents over-reduction, which would give the alkane by reducing the alkene Related reactions  Dissolving metal reduction of alkynes  Hydrogenation of alkenes CATALYTIC HYDROGENATION Step 1: Hydrogen gets absorbed onto the metal surface. Step 2: Alkyne approaches the H atoms absorbed on the metal surface. Step 3: C≡C reacts with the H atoms on the surface forming the two new C-H σ bonds generating the alkene.
  13. 13. -13-hydrogenation-140526162439-phpapp01.doc Addition Reactions of Alkynes A carbon-carbon triple bond may be located at any unbranched site within a carbon chain or at the end of a chain, in which case it is called terminal. Because of its linear configuration ( the bond angle of a sp-hybridized carbon is 180º ), a ten-membered carbon ring is the smallest that can accommodate this function without excessive strain. Since the most common chemical transformation of a carbon-carbon double bond is an addition reaction, we might expect the same to be true for carbon-carbon triple bonds. Indeed, most of the alkene addition reactions discussed earlier also take place with alkynes, and with similar regio- and stereoselectivity. 1. Catalytic Hydrogenation The catalytic addition of hydrogen to 2-butyne not only serves as an example of such an addition reaction, but also provides heat of reaction data that reflect the relative thermodynamic stabilities of these hydrocarbons, as shown in the diagram to the right. From the heats of hydrogenation, shown in blue in units of kcal/mole, it would appear that alkynes are thermodynamically less stable than alkenes to a greater degree than alkenes are less stable than alkanes. The standard bond energies for carbon-carbon bonds confirm this conclusion. Thus, a double bond is stronger than a single bond, but not twice as strong. The difference ( 63 kcal/mole ) may be regarded as the strength of the π-bond component. Similarly, a triple bond is stronger than a double bond, but not 50% stronger. Here the difference ( 54 kcal/mole ) may be taken as the strength of the second π-bond. The 9 kcal/mole weakening of this second π- bond is reflected in the heat of hydrogenation numbers ( 36.7 - 28.3 = 8.4 ). Since alkynes are thermodynamically less stable than alkenes, we might expect addition reactions of the former to be more exothermic and relatively faster than equivalent reactions of the latter. In the case of catalytic hydrogenation, the usual Pt and Pd hydrogenation catalysts are so effective in promoting addition of hydrogen to both double and triple carbon-carbon bonds that the alkene intermediate formed by hydrogen addition to an alkyne cannot be isolated. A less efficient catalyst, Lindlar's catalyst, prepared by deactivating (or poisoning) a conventional palladium catalyst by treating it with lead acetate
  14. 14. -14-hydrogenation-140526162439-phpapp01.doc and quinoline, permits alkynes to be converted to alkenes without further reduction to an alkane. The addition of hydrogen is stereoselectively syn (e.g. 2-butyne gives cis-2-butene). A complementary stereoselective reduction in the anti mode may be accomplished by a solution of sodium in liquid ammonia. This reaction will be discussed later in this section. R-C≡C-R + H2 & Lindlar catalyst ——> cis R-CH=CH-R R-C≡C-R + 2 Na in NH3 (liq) ——> trans R-CH=CH-R + 2 NaNH2 Alkenes and alkynes show a curious difference in behavior toward catalytic hydrogenation. Independent studies of hydrogenation rates for each class indicate that alkenes react more rapidly than alkynes. However, careful hydrogenation of an alkyne proceeds exclusively to the alkene until the former is consumed, at which point the product alkene is very rapidly hydrogenated to an alkane. This behavior is nicely explained by differences in the stages of the hydrogenation reaction. Before hydrogen can add to a multiple bond the alkene or alkyne must be adsorbed on the catalyst surface. In this respect, the formation of stable platinum (and palladium) complexes with alkenes has been described earlier. Since alkynes adsorb more strongly to such catalytic surfaces than do alkenes, they preferentially occupy reactive sites on the catalyst. Subsequent transfer of hydrogen to the adsorbed alkyne proceeds slowly, relative to the corresponding hydrogen transfer to an adsorbed alkene molecule. Acetylene HC≡CH + Energy ——> [HC≡CH •(+) + e(–) ΔH = +264 kcal/mole Ethylene H2C=CH2 + Energy ——> [H2C=CH2] •(+) + e(–) ΔH = +244 kcal/mole Ethane H3C–CH3 + Energy ——> [H3C–CH3] •(+) + e(–) ΔH = +296 kcal/mole
  15. 15. -15-hydrogenation-140526162439-phpapp01.doc Hydrogenation of Alkynes You almost invariably get incomplete combustion, and the arenes can be recognised by the smokiness of their flames. Hydrogenation Hydrogenation is an addition reaction in which hydrogen atoms are added all the way around the benzene ring. A cycloalkane is formed. For example: With benzene: . . . and methylbenzene: These reactions destroy the electron delocalisation in the original benzene ring, because those electrons are being used to form bonds with the new hydrogen atoms. Although the reactions are exothermic overall because of the strengths of all the new carbon-hydrogen bonds being made, there is a high activation barrier to the reaction. The reactions are done using the same finely divided nickel catalyst that is used in hydrogenating alkenes and at similar temperatures (around 150°C), but the pressures used tend to be higher.
  16. 16. -16-hydrogenation-140526162439-phpapp01.doc Hydrogenation of benzene to cyclohexane is an important case of the large- scale chemical processes. The reaction described by equation C6H6 + 3H2 → C6H6; ΔH298 = -206,2 [kJ/mol] is the first stage of a caprolactam production process according to the polish technology named CYCLOPOL. The industrial process is conducted in heterogeneous multitubular reactor at temperature in range 150-260°C on a commercial catalyst KUB-3 (manufacturer: Fertilizers Research Institute, Pulawy, POLAND). The main components of the KUB-3 catalyst are Ni, NiO, and Al2O3. Nickel is the active component of the catalyst while alumina is a structural promoter which provides the catalyst with high thermal stability. Physicochemical properties of the KUB-3 are as follows: • chemical composition, wt. % NiO min. 45 (NiO to Ni reduction degree min. 40%), Al2O3 as a support • balls of a diameter 4-6 mm • density 1.0 ± 0.1 kg/dm3 Hydrogenation of benzene is conducted in two stages. Partial hydrogenation takes place in the first stage, under pressure 0.3 MPa in a shortage of hydrogen,. In the second one, benzene is, in practice, completely hydrogenated to cyclohexane under pressure 1.0 MPa and an excess of hydrogen. In the catalyst bed there appears a reaction zone, which runs, step by step, along the reactor during its normal operation. The zone position change results from a progress of catalyst bed deactivation which is caused by sorption of sulphur compounds and coke deposition. Full deactivation process of the first catalyst bed lasts about 1-4 years. Nitrogen is the inert component of the reaction mixture.
  17. 17. -17-hydrogenation-140526162439-phpapp01.doc Hydrogenation of Unsaturated Fats and Trans Fat It has long been recognized that saturated fats tend to increase the blood level of the "bad" LDL cholesterol. Monounsaturated (one double bond) and polyunsaturated fats (two or more double bonds) found primarily in vegetable oils tend to lower "bad" LDL cholesterol. An elevated LDL-C increases the risk of developing coronary heart disease. Introduction Back in the 1950s, it was recognized that vegetable oils could be substituted for animal fats such as in butter, by making a product we know as margarine. But how do you make an oil into a solid? Recall that vegetable oils which contain more unsaturated fatty acids are liquids while saturated fatty acids are solids . Hydrogenation Reaction Unsaturated fatty acids may be converted to saturated fatty acids by the relatively simple hydrogenation reaction. Recall that the addition of hydrogen to an alkene (unsaturated) results in an alkane (saturated). A simple hydrogenation reaction is: H2C=CH2 + H2 → CH3CH3 (alkene plus hydrogen yields an alkane) Margarine Vegetable oils are commonly referred to as "polyunsaturated". This simply means that there are several double bonds present. Vegetable oils may be converted from liquids to solids by the hydrogenation reaction. Margarines and shortenings are "hardened" in this way to make them solid or semi-solids. Figure 1: Hydrogenation of a oleic fatty acid
  18. 18. -18-hydrogenation-140526162439-phpapp01.doc Vegetable oils which have been partially hydrogenated, are now partially saturated so the melting point increases to the point where a solid is present at room temperature. The degree of hydrogenation of unsaturated oils controls the final consistency of the product. What has happened to the healthfulness of the product which has been converted from unsaturated to saturated fats? There is still less saturated fat in a margarine when compared to butter. Trans Fat When naturally occurring unsaturated fatty acids are altered by partial hydrogenation, they are converted to saturated fatty acids, which have the effect of straightening the chains and changing the physical properties. Also during partial hydrogenation, some of the unsaturated fatty acids, which are normally found as the cis isomer about the double bonds, are changed to a trans double bond and remain unsaturated. Trans fatty acids of the same length and weight as the original cis fatty acids, still have the same number of carbons, hydrogens, and oxygens but they are now shaped in a more linear form, as opposed to the bent forms of the cis isomers. Although the trans fatty acids are chemically "monounsaturated" or "polyunsaturated" they are considered so different from the cis monounsaturated or polyunsaturated fatty acids that they can not be legally designated as unsaturated for purposes of labeling. Most of the trans fatty acids (although chemically still unsaturated) produced by the partial hydrogenation process are now classified in the same category as saturated fats.

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