Chemical technology notes

  • Chemical Technology
    1. Soda-Ash process

      • Solvay process is used in manufacture of soda ash.

solvay process for soda ash

CO2 is passed through a concentrated aqueous solution sodium chloride and ammonia. NaCl + CO2 + NH3 + H2O –> NaHCO3 + NH4Cl; ammonium bicarbonate is a precipitate. In a basic solution, NaHCO3 is less soluble than NaCl. The NH3 buffers the solution at a basic pH. Without NH3, a hydrochloric acid byproduct would render the solution acidic and arrest the precipitation.

The carbon dioxide required is produced by (calcination) heating limestone at 950oC – 1100oC.

solvay process for soda ash

NaHCO3 the precipitate in the reaction is filtered out from hot NH4Cl solution and solution is heated with quicklime.

solvay process for soda ash

Ammonia produced is recycled back. NaHCO3 is calcined (160oC – 230oC) to give Na2CO3, CO2 and H2O.

solvay process for soda ash

Calcium chloride sodium chloride liquor is used in soda ash industry.

      • Leblanc process for Na2CO3 (soda ash)
        Raw material: salt, H2SO4, limestone and coal

solvay process for soda ash

    1. Single superphosphate from phosphate rock

single superphosphate from phosphate rock

Single superphosphate contains P (7 – 9.5%), P2O5 (16 – 20%), Ca (18-21%), S (11 – 12%), pH < 2. Where soil is markedly acidic, i.e. rich in iron and aluminum content, mono-calcium phosphate gets converted into insoluble phosphate compounds.

single superphosphate not to  be used in acidic soil

Because iron and aluminum phosphates are insoluble, phosphate becomes unavailable in plants. That is why Single SuperPhosphate is not used in acidic soils until its limited.

    1. Triple superphosphate from phosphate rock

tripple super phosphate from phosphate rock

Triple superphosphate contains P2O5 (44 – 55%), Ca (15%), pH (1 – 3), water solubility of P > 90%

    1. Vinyl acetate from ethylene

vinyl acetate form ethylene

Ethylene and acetic acid with O2 in presence of Palladium catalyst

    1. Acrylonitrile (CH2CHCN vinyl nitrile) from propylene

Catalytic ammoxidation of propylene – SOHIO process

SOHIO process acrylonitrile from propylene

The reactants pass through reactor only once before being quenched in aqueous H2SO4. Excess propylene, CO, CO2 and N2 that do not dissolve are vented directly into atmosphere or incinerated. The aqueous solution consists of acrylonitrile, acetonitrile, hydrocyanic acid, and (NH4)2SO4 (excess NH3). Acetonitrile or acrylonitrile are separated by distillation.

    1. Urea (Bosch –Meiser process)

The composition to fresh feed to the high temperature high pressure urea autoclave is excess liquid ammonia and compressed CO2.

Consists of two equilibrium reactions

      • Carbamate formation

First is carbamate formation, fast exothermic reaction at high temperature and pressure

urea manufacture bosch meiser process

      • Decomposition of carbamate to urea

urea manufacture bosch meiser process

The overall conversion of NH3 and CO2 to urea is exothermic. The reaction heat from first drives the second. It follows Le Chatelier’s principle. The condition that favors carbamate formation have unfavorable effect on urea conversion equilibrium. The first reaction of high temperature (around 190oC) needed for second is compensated by conducting the process under high pressure (140 – 175 bar) which favors first reaction.

    1. Chlorobenzene – caustic process : For phenol

Raw material: – C6H6, NaOH, HCl. This process is competitive when low cost chlorine is available. This means that the process must be coupled to chlor-alkali plant. Steps involved:

      • Chlorination

chlorobenzene caustic process for phenol

      • Caustization

chlorobenzene caustic process for phenol

      • Hydrolysis

chlorobenzene caustic process for phenol

    1. Cumene process for phenol

Raw material: – Cumene, Air, H2SO4, NaOH

cumene process fot phenol

    1. H2 from natural gas

Following are the steps to produce hydrogen from natural gas

      • Steam methane reforming

steam methane reforming for hydrogen manufacturing from natural gas

      • Water gas shift reaction

High temperature (HT) followed by low temperature (LT)

steam methane reforming for hydrogen manufacturing from natural gas

      • PSA for H2 purification

This method produces large amount of greenhouse gases.

    1. Fisher-Trope synthesis

Converts CO+H2 to liquid HC

High temperature (150oC – 300oC), high pressure favors reaction; higher pressure favors longer chain.

      • High temperature fisher trope (HTFT)

330oC – 350oC, Fe as catalyst, used for coal to liquid.

      • Low temperature fisher trophe (LTFT)

Used for gas to liquid, Fe to Co catalyst.

Reaction steps:

fisher trope synthesis convert gases to liquid hydrocarbons

Reaction involves
a. Associative adsorption of CO 
b. Splitting of CO bond 
c. Dissociative adsorption of 2H2 
d. Transfer of 2H to oxygen to yield H2
e. Desorption of H2
f. Transfer of 2H to form CH2

Catalyst used are

a. Cobalt – best for natural gas feed stock 
b. Iron – low molecular weight product formed 
c. Ruthenium – active working at lowest reaction temperatures, highest molecular weight HC formed.

    1. Formaldehyde form methanol

Two methods

      • Dehydrogenation or oxidative dehydrogenation in presence of Ag or Cu catalyst

formaldehyde from methanol

      • Oxidation in presence of Fe containing MoO catalyst

formaldehyde from methanol

    1. Dehydrogenation of ethyl benzene

dehydrogenation of ethyl benzene

    1. Syntheis gas to methanol

synthesis gas to methanol

    1. Formation of Nylon 6,6

Nylon 6,6 (so called due to 6 C-atom between N atoms) is formed from condensation polymerization of hexamethylene diamine and adipic acid

formation of nylon 66

    1. Dehydration of Ethanol

Dehydration of ethanol is an exothermic reversible reaction conducted at high pressure in industry.

dehydration of ethanol

  • Chemical Technology
    1. Styrene

      • Styrene from benzene and ethylene

Styrene is manufactured from benzene and ethylene. Styrene-butadiene rubber used in tyre manufacturing. Catalyst used is Fe(III) Oxide promoted by K2O. Tertiary dodeceyl mercaptan is used as modifier and potassium pyrophosphate is used as a buffer.

    1. Paints

      • Oils with linolenic radical (three double bonds) are more suitable than oils with oleic radical (one double bond) as film forming paints for vehicles.

    2. Sodium hydroxide production

      • Decomposition efficiency

Decomposition efficiency (ηD) of an electrolyte cell used for producing NaOH is defined as 
ηD = Ratio of theoretical current to produce one gram equivalent to actual current to produce one gram equivalent.

      • Cauticizing method of production of sodium hydroxide

Historically NaOH was produced by treating Na2CO3 with Ca(OH)2 in an metathesis reaction. This process was called causticizing.

    1. Petroleum and its products

      • Low aniline point implies high aromatic content.

      • Hydrogen from light petroleum stock is manufactured by steam reforming of naphtha. Catalyst used in steam reforming of methane is Ni/Al2O3. High octane gasoline from naphtha is produced by platforming.

      • Electrostatic precipitator is used for separating particles from gases when particle size less than one micron.

      • The order of feedstock to a catalytic reformer is virgin naphtha –> coking naphtha –> catalytic naphtha.

      • Terylene is produced from dimethyl terephthalate and ethylene glycol.

    2. Biodiesel

      • Biodiesel is made by chemically reacting lipids (vegetable oil, soyabean oil, animal fat) with an alcohol producing fatty acid ester.

    3. General Polymer points

      • Propylene + 1-butene gives LLDPE

      • Terepthalic acid + ethylene glycol gives synthetic fibre

      • Terepthalic acid is manufactured by oxidation of xylene and is used as raw material for the manufacture of polyeaster.

      • In manufacture of Portland cement the major raw materials are limestone, clay, gypsum and coal.

      • Calcium ammonium nitrate is an inorganic fertilizer.

      • Pthallic anhydride is made by oxidation of naphthalene.

      • Ethylene oxidation is an auto thermal reaction.

      • Cellulose derivatives, polyamides and polyurethanes (mainly thermosetting) are polymers used for making fibres.

      • The preferred system for oxidation of O-xylene to Phthalic anhydride is jacketed steam heated multitubular reactor.

      • Raw material for grease is lithium stearate; Raw material for cosmetics is magnesium stearate; Aluminium sulphate is used in manufacture of paper.

    4. Sugar manufacturing

      • Calcium hydroxide is used in sugar manufacturing to maintain pH. Carbon dioxide is used to precipitate solid calcium compounds. Phosphoric acid is used to remove colour. Calcium hydroxide + Phosphoric acid is used for treatment of raw sugar to give final white sugar. Multieffect evaporator is used in manufacturing of paper and sugar.

    5. Paper manufacturing

      • Black liquor is by product of paper industry (kraft process Press mud is the compressed sugar industry waste produced from the filtration of the cane juice.

    6. Sulfite Process

      • In sulfite process, digester chemical used as sulfite or bisulfite depending upon pH along with SO2. The cooking liquor is magnesium sulfite and magnesium dicarbonate.
    7. Iron and Steel

      • As carbon percentage increases, steel has ability to become harder and stronger through heat treating. However it becomes less ductile. Regardless of heat treatment, a higher carbon content reduces weld ability. In carbon steel, the higher carbon content, lower melting point.

    8. Radical Polymerization

      • Radical polymerization works best on carbon-carbon double bond of vinyl monomers, and carbon-oxygen double bond in aldehyde and ketones. If longer chains are desired, the initiator concentration should be kept low, otherwise, many shorter chains will result. Oxygen is a common inhibitor. The growing chain will react with molecular oxygen producing an oxygen radical, which is much less reactive. Diphenyl picryl hydrazyl (DPPH) is another effective inhibitor due to resonance stabilization of the radical.

    9. Types of Polymerization

Based on method of formation

      • Bulk polymerization – reaction mixture contains only monomer and initiator, no solvent. Reaction is carried out by adding a soluble initiator to pure monomer. The reaction is initiated by heating or exposing to radiation. As reaction proceeds, the mixture becomes more viscous. The reaction is exothermic and a wide range of molecular masses are produced. Bulk polymerization is carried out in the absence of any solvent or dispersant and is thus simplest in terms of formulation. It is used for most step growth polymers and many types of chain growth polymers. Example – Nylon, polystyrene (by condensation polymerization), thermoplastic compounds

      • Solution polymerization – reaction mixture contains solvent, initiator and monomer. In this procedure, a monomer is dissolved in a non-reactive solvent that contains a catalyst. The reaction results in a polymer which is also soluble in the chosen solvent. Heat released by the reaction is absorbed by the solvent and so reaction rate is reduced. Moreover, the viscosity of the reaction mixture is reduced, not allowing auto acceleration at high monomer conversion. Once the desired conversion is reached, excess solvent has to be removed in order to obtain pure polymer. Hence, solution polymerization is mainly used for application where presence of solvent is desired anyway, as in case of varnish and adhesives. It is not useful for the production of dry polymers because of difficulty of complete solvent removal. For manufacturing of polyacryonitrile (PAN) and polyacrylic acid (PAA), sodium polyacrylate, phenol formaldehyde.

      • Suspension polymerization – reaction mixture contains an aqueous phase, water insoluble monomer, an initiator soluble in monomer (both monomer and initiator are hydrophobic). It is a heterogeneous radical polymerization process. It requires mechanical agitation to mix monomers in liquid phase such as water where monomers polymerize forming spheres of polymer. It is used for formation of resins, PVC (not produced by condensation polymerization), styrene resins including polystyrene, expanded polystyrene and high impact polystyrene, polystyrene-acrylonitrile, polymethyl methacrylate. It produces small uniform spheres.

      • Emulsion polymerization – it is similar to suspension polymerization except that the initiator is soluble in the aqueous phase rather than monomer droplets. The monomer is hydrophobic and initiator is hydrophilic. An emulsifying agent is also needed. Emulsion polymerization is a type of radical polymerization which starts with an emulsion incorporating water, monomer and surfactant. Advantages of emulsion polymerization includes
        1. High molecular weight polymers can be made at fast polymerization rates. By contrast, in bulk and solution free radical polymerization, there is a tradeoff between molecular weights and polymerization rate.
        2. Continuous water phase is excellent conductor of heat, enabling fast polymerization rate without loss of temperature control.
        3. Since polymer molecules are contained within the particles, the viscosity of the reaction medium remains close to that of water and is not dependent on molecular weight. Also used for manufacturing of synthetic rubber, SBR, polychloroprene (neoprene), flouroelastomer (FKM), dispersions (acetate co-polymers).

    1. Catalyst for various reactions

      • Catalyst for conversion of 
        methanol to gasoline – zeolite;
        edible oil hydrogenation – raney nickle, Sulphur is a catalyst poison.;
        methanation – nickle, ruthenium, iron, cobalt;
        catalyst for formation of butyl acetate – ion exchange resins;
        Catalyst for sulphuric acid – vanadium pentaoxide (V2O5);
        Catalyst used in catalytic reforming (platforming): Pt + Re;
        Catalyst used for formation of nitric acid is Platinum and Rhodium; 
        catalyst for formaldehyde formation is silver Oxide;
        Catalyst for ammonia synthesis is Fe/Al2O3.

    2. Preferred material of handling chemicals

      • Preferred material for 
        handling dilute H2SO4 is nickle; 
        for concentrated H2SO4 lead; 
        for concentrated HCl is lead;
        wet chlorine is titanium; 
        concentrated caustic soda is karbate; 
        for caustic soda is aluminium.

    3. Dust explosion

Coal forms an explosive mixture with air even at ambient temperatures if the particle size is very small (known as dust explosion). The possibility of dust explosion increases with decrease in size of particles.

  1. Crusher

    • Gyratory crusher applies compression force and buhrstone mill applies shear force to break materials.

  2. Sulphuric acid

    • In converter of the contact process for the manufacture of H2SO4, the equilibrium conversion of SOx decreases with increase in temperature and increases with increase in the mole ratio of SO2 to air.

    • For manufacture of H2SO4 from elemental Sulphur following sequence of major events is followed: Furnace –> Converter –> Absorber.

    • The catalytic converter for conversion of SO2 to SO3 by contact process should have feed with SO2 content between 7 – 10 %.