Hydrogenation

-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

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.

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.

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.

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.

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.

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.

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.

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

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.

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.

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.

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

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] •(+)
Ethane H3C–CH3 + Energy ——> [H3C–CH3] •(+)

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.

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.

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

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.

Hydrogenation

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