Ethane and HigherParaffins-Based Chemicals

INTRODUCTION

• paraffinic hydrocarbons are less reactive than olefins• only a few chemicals are directly based on them. • Ethane is a major feedstock for steam crackers for the

production of ethylene. • Few chemicals could be obtained from the direct

reaction of ethane with other reagents. • The higher paraffins, propane, butanes, pentanes, and

heavier also have limited direct use in the chemical industry except for the production of light olefins through steam cracking.

• This chapter reviews the petrochemicals directly produced from ethane and higher paraffins.

ETHANE CHEMICALS• source for ethane is natural gas liquids. • Approximately 40% of the available ethane is recovered for

chemical use. • The only large consumer of ethane is the steam cracking

process for ethylene production.• A minor use of ethane is its chlorination to ethyl chloride:

CH3CH3 + Cl2 -CH3CH2C1 + HC1• By-product HC1 may be used for the hydrochlorination of

ethylene to produce more ethyl chloride. • Hydrochlorination of ethylene, however, is the main route

for the production of ethyl chloride"

CH2 = CH2 + HC1 CH3CH2C1

ETHANE CHEMICALS

• Major uses of ethyl chloride are – manufacture of tetraethyl lead – synthesis of insecticides. – alkylating agent and asa solvent for fats and wax.

• .

Vinyl chloride from ethane (Transcat process)

• A small portion of vinyl chloride is produced by this process• The process a combination of

– chlorination, oxychlorination, and dehydrochlorination reactions occur in a molten salt reactor.

– Catalyst: copper oxychloride catalyst – Temperature: 310-640OC

• During the reaction– copper oxychloride is converted to copper(I) and copper(II)

chlorides, – air oxidization regenerate the catalyst.

• Vinyl chloride is an important monomer for polyvinyl chloride (PVC).– The main route for obtaining this monomer is ethylene

Chemicals Based on Ethylene• More commercial chemicals are produced from

ethylene than from any other intermediate. • This unique position of ethylene among other

hydrocarbon intermediates is due to – Simple structure with high reactivity.

– Relatively inexpensive compound.

– Easily produced from any hydrocarbon source through steam cracking

– high yields.

– Less by-products generated from ethylene reactions with other compounds than from other olefins.

Chemicals Based on Ethylene (Cont.)

• Ethylene reacts by addition to many inexpensive reagents such as:- water, chlorine, hydrogen chloride, and oxygen to produce valuable chemicals.

• It can be initiated by free radicals or by coordination catalysts to produce polyethylene,

• It can also be copolymerized with other olefins producing polymers with improved properties. – For example, when ethylene is polymerized with

propylene, a thermoplastic elastomer is obtained.

Chemicals Based on Ethylene

• Global demand for ethylene is expected to increase from 79 million tons in 1997 to 114 million tons in 2005.

• In 1998, the U.S. consumption of ethylene was approximately 52 billion pounds.

OXIDATION OF ETHYLENE

• Can be oxidized to a variety of useful chemicals. • Oxidation products depend primarily on the catalyst

used and the reaction conditions.• Ethylene oxide is the most important oxidation product

of ethylene. • Acetaldehyde and vinyl acetate are also oxidation

products btained from ethylene under special catalytic conditions.

• Ethylene Oxide Ethylene oxide (EO) is a colorless gas that liquefies when cooled below 12OC.

• It is highly soluble in water and in organic solvents.

Ethylene Oxide • Ethylene oxide is a precursor for many chemicals of

great commercial importance, including:-• Ethylene glycols, • Ethanolamines, • and alcohol ethoxylates. • Ethylene glycol is one of the monomers for

polyesters, the• most widely-used synthetic fiber polymers. T• he current US production of EO is approximately

8.1 billion pounds.

Ethylene Oxide

• Side reaction

Ethylene Oxide• Production

– The main route to ethylene oxide is oxygen or air oxidation of ethylene over a silver catalyst.

– The reaction is exothermic; heat control is important:• The excessive temperature increase reduces ethylene oxide yield and

causes catalyst deterioration. • Over- oxidation can be minimized by using modifiers such as organic

chlorides.• It seems that silver is a unique epoxidation catalyst for ethylene. • All other catalysts are relatively ineffective, and the reaction to

ethylene is• limited among lower olefins. • Propylene and butylenes do not form epoxides through this route. • Using oxygen as the oxidant versus air is currently favored because it• is more economical.

Ethylene Oxide• Commercial EO production is conducted in a shell-

and-tube recycle reactor – Catalyst : silver catalyst supported on alumina– Contact time = 1 s – Reaction temperature = 230-290°C – Pressure = 10-30 bar.

• Processes are of two basic types according to whether oxygen or air is the oxidizing agent.

• The air process is used in older and larger plants (> 50,000-100,000 tons per year) based on lower capital costs,

• Oxygen process is preferred for new medium or small plants.

Oxygen process for production of ethylene oxide

Oxygen process for production of ethylene oxide

• Gaseous feed and recycle streams consisting of 19-28 mol% ethene, 5-9% O2, 5-6% CO2, and the remaining percentage of Ar, N2, and CH4 diluents,

• gas-hourly space velocity 2,000 to 7,000 = • Shell and tube reactor

– (7,000-10,000 per reactor) of 2.5-5.0 cm in diameter by 6-15 m in length.

• Each reactor tube is surrounded by boiling water to control the temperature, – necessary for high EO selectivity.

• Heat transfer from the catalyst bed is favored by the small reactor tube diameters and small catalyst particulates (3-10 mm in diameter).

• Inlet temperatures are between 240 and 280°C

Oxygen process for production of ethylene oxide (Cont.)

• single pass conversions of ethene are no more than 15% and typically 8-11 %,

• O2 conversion is 35-45%; • overall conversion in the process is above 97%. • The chief by-product is CO2, • The low conversion in the first pass and subsequent recycle

optimize the selectivity by minimizing excessive temperature rise in the reactor caused by the complete oxidation reaction.

• The recycle stream is periodically purged and continuously scrubbed of CO2 with K2CO3 before being returned to the reactor inlet.

• The EO product is condensed and absorbed in water followed by steam distillation to produce the separated liquid product of > 99.5% purity.

Oxygen process for production of ethylene oxide

– Advantages of O2 as oxidizing agent include– Increased yield and productivity of ethene oxide– Increased selectivity to ethene oxide (because of the higher

concentration of ethene on the feed)– Lower amount of vent gas and therefore reduced losses of

ethene– Possibility of choosing ideal ballast– Lower costs because of smaller equipment size– Disadvantages of O2 as oxidizing agent include– Costs for producing O2– Need for safety equipment– Need for more elaborate mixing devices– Costs for CO2 removal

Gas hourly space velocity

• GHSV (gas hourly space velocity) =(volumes of feed as gas at STP/hr)/(volume of the reactor or its content of catalyst)=

Derivative of EO Ethylene Glycol (EG)

Ethylene Glycol (CH2OHCH2OH)• EG is colorless syrupy liquid, • very soluble in water. • Boiling points of EG 197.2 C• Freezing points of EG -13.2 C• Current world production of EG =15 billion pounds (1999). • Most of that is used for producing

– polyethylene terephthalate– (PET) resins (for fiber, film, bottles), – Antifreeze (25%)– and other products.– 50% of the world EG was consumed in the manufacture of polyester fibers.

• EG consumption in the US was nearly 1/3 of the world's. – 50% of EG is consumed in antifreeze in US.– US production of ethylene glycol was 5.55 billion pounds in 1994,

• The main route for producing ethylene glycol is the hydration of ethylene• oxide in presence of dilute sulfuric acid

Process for EG Production Figure 7-4. The Scientific Design Co. process for producing ethylene glycols from ethylene oxide: (1) feed tank, (2) reactor, (3,4,5) multiple stage evaporators, #4 operates at lower pressure than #3, while #5 operates under vacuum, evaporated water is recycled to feed tank, (6) light ends stripper, (7,8) vacuum distillation columns

Ethylene Glycol (EG)

Ethylene Glycol (EG)

• The hydrolysis reaction occurs at a temperature range of 50-100C

• Contact time = 30 minutes.• Di- and triethylene glycols are coproducts with the

monoglycol. • Increasing the water/ethylene oxide ratio and

decreasing the contact time decreases the formation of higherglycols.

• A water/ethylene oxide = 10 is normally used to get approximately 90% yield of the monoglycol.

• di- and triglycols are not an economic burden, because of their commercial uses.

Ethanolamines

• A mixture of (MEA, DEA and TEA) by the reaction between ethylene oxide (EO) and aqueous ammonia.

• The reaction conditions – are approximately 30-40C – atmospheric pressure

• The relative ratios of the ethanolamines produced depend principally on the ethylene oxide/ammonia ratio. – A low EO/NH3 ratio increases MEA yield. – Increasing this ratio increases the yield of DEAand TEA

Ethanolamines (Cont.)

Ethanolamines Cont.)• Major uses of Ethanolamines• Ethanolamines are important absorbents of acid gases in

natural gas treatment processes. • production of surfactants. • The reaction between ethanolamines and fatty acids produces

ethanolamides (Fatty acids are merely carboxylic acids with long hydrocarbon chains. The hydrocarbon chain length may vary from 10-30 carbons). – lauric acid

– and MEA react to give N-(2hydroxyethyl)-lauramide– Lauric acid is the main fatty acid used for producing ethanolamides.

• Monoethanolamides are used primarily in heavy-duty powder detergents as foam stabilizers and rinse improvers.

Acetaldehyde productionWacker process

• Important intermediate (2 million t/a) for production of acetic acid• (40%) and ethyl acetate (60 %)• • Until the 1960: production from acetylene and water in diluted sulfuric• acid (yield around 98 %)• • Since the 1970ies: Wacker-Hoechst-process• • Single or two-step process with oxygen or air as oxidant and Pd/Cu• catalyst• • Two-step process: higher investment and energy costs; more• chlorinated hydrocarbons in waste stream, yet still preferred (costs for• air separation plant, as required for single step process, are even• higher)

• 85% of world acetaldehyde production by Wacker process

• Exothermic catalytic direct oxidation with two component catalyst

• PdCl2 and CuCl2

Reactions in the Wacker process

Single stage process Wacker process• Reaction of highly pure ethene and oxygen in a

bubble column– 120 – 130 °C, 3 bar, – conversion per pass: 35 - 45%

• Effluent gas is cooled, separated from catalyst and scrubbed with water for acetaldehyde recovery

• Excess ethene is recycled to the reactor.

• small part is purged to prevent inert gas accumulation

Single stage process Wacker process

Two stage Wacker process

• Ethene reaction and Cu+ reoxidation take place in different bubble columns.

• 105 – 110 °C,

• 10 bar,

• Almost complete conversion of ethene

• No loop gas required

• Acetaldehyde recovery by extractive distillation like in single stage process

Two stage Wacker process

Comparison of single stage and two stage Wacker Process

• Acetaldehyde yield almost equal (about 95%)

• Expensive construction materials required

• Lower investment costs in the single stage process, because of the need of only one reactor

• In two stage process air (less expensive) can be used for the reoxidation instead of pure oxygen

• No explosive ethene/O2 mixtures in two stage process.

Uses of Acetaldehyde

• compound with no direct use except for the synthesis of other compounds.

• For example, – it is oxidized to acetic acid and acetic anhydride.– It is a reactant in the production of 2-

ethylhexanol for the synthesis of plasticizers – production of pentaerithritol, a polyhydric com-

pound used in alkyd resins.

Important Chemicals from Acetaldehyde

Acetic Acid• Acetic acid is obtained from different sources.

– Carbonylation of methanol is currently the major route.

– Oxidation of butanes and butenes is an important source of acetic acid, especially in the U.S.

• It is also produced by the catalyzed oxidation of acetaldehyde:

• The reaction occurs in the liquid phase at approximately 65C using man ganese acetate as a catalyst.

Important Chemicals from Acetaldehyde (Cont.)n-Butanol

• n-Butanol is normally produced from propylene by the Oxo reaction.

• Aldol condensation of acetaldehyde in presence of a base produxes n-Butanol

• The formed 3-hydroxybutanal eliminates one mole of water in the presence of an acid producing crotonaldehyde.

• Hydrogenation of crotonaldehyde produces n-butanol"

• Hydrogenation of crotonaldehyde produces n-butanol"

Important Chemicals from Acetaldehyde (Cont.)

Vinyl Acetate•

• Vinyl acetate is a reactive colorless liquid that polymerizes easily if not stabilized.

• It is an important monomer for the production of – polyvinyl acetate,

– polyvinyl alcohol,

– and vinyl acetate copolymers.

• The U.S. production of vinyl acetate was approximately 3 billion pounds in 1994.

• Vinyl acetate was originally produced by the reaction of acetylene and acetic acid in the presence of mercury(II) acetate.

• Currently, it is produced by the catalytic oxidation of ethylene with oxygen, with acetic acid as a reactant and palladium as the catalyst:

Important Chemicals from Acetaldehyde (Cont.)

Vinyl Acetate (Cont.)

• The process is similar to the catalytic liquid-phase oxidation of ethylene to acetaldehyde.

• The difference between the two processes is the presence of acetic acid.

• Acetaldehyde is a major co-product.

• The mole ratio of acetaldehyde to vinyl acetate can be varied from 0.3:1 to 2.5:1.

• The liquid-phase process is not used extensively due to

– corrosion problems

– and the formation of a fairly wide variety of by-products.

Important Chemicals from Acetaldehyde (Cont.)

Vinyl Acetate (Cont.)

•vapor-phase process

•carried out in a tubular reactor

•at approximately 117OC

•5 atmospheres.

•The palladium acetate is supported on carriers resistant to attack by acetic acid.

•Conversions of about 10-15% based on ethylene are normally used to operate safely outside the explosion limits (approximately 10% O2).

•Selectivities of 91-94% based on ethylene are attainable.

CHLORINATION OF ETHYLENE•Chlorination of ethylene ethylene dichloride (1,2-dichloroethane).

•Ethylene dichloride vinyl chloride, • vinyl chloride which is an important monomer for polyvinyl chloride plastics and resins.

•Other uses of ethylene dichloride

– Formulation with tetraethyl and tetramethyl lead solutions

• degreasing agent,

– and as an intermediate in the synthesis of many ethylene derivatives.

•The reaction of ethylene with hydrogen chloride, ethyl chloride.

– Small-volume chemical

• alkylating agent,

• refrigerant,

• Solvent.

Vinyl chloride

VC from acetylene

•First commercial process for VC production (Griesheim-Elektron)• Catalyst: HgCl2 on activated carbon• High selectivity and low operating costs, but ethylene is cheaper than acetylene• There are still plants operating in countries with acetyleneproduction from coal (e.g. South Africa)

Vinyl chloride (Cont.)

EDC synthesisAlmost all VC produced today originates from the thermal cracking of 1,2-dichloro ethane (EDC).

• Two processes:

– addition of chlorine to ethylene

– newer route: oxychlorination of ethylene with HCl and O2 or air

Vinyl chloride (Cont.)

Direct chlorine addition to ethylene

Liquid phase reaction with solvated FeCl3, CuCl2 or SbCl3 as catalyst

•Reaction conditions: 40-70 °C, 4-5 bar

•Addition of 0.5% O2 to inhibit the radical reactions leading to 1,1,2-trichloroethane

•Reactor is liquid EDC - bubble column.

•Ethylene and chlorine dissolve in the liquid phase and combine in a homogeneous catalytic reaction to form EDC

Vinyl chloride (Cont.)Oxychlorination Oxychlorination

•Heterogeneous catalyzed gas phase reaction

•Catalyst: CuCl2 on different supports mainly Al2O3

•Reaction conditions: 220-240 °C, 2-4 bar

•Reaction byproducts: 1,1,2-trichloroethane, chloroform, chloral, carbon

•tetrachloride, ethyl chloride, 2-chloroethanol

vinyl chloride (Cont.)Heat management Heat management

• Heat removal for temperature control is essential

• Higher reactor temperatures lead to more by-products, mainly through increased ethylene oxidation to carbon oxides and increased EDC cracking

•High temperatures (>300°C) can also deactivate the catalyst through increased sublimation of CuCl2

• Staged oxygen or air admission in fixed bed •

• Packing of the reactor with catalysts with progressively higher CuCl2 loading.

Vinyl chloride (Cont.)Reactor types used

• Multitubular fixed bed

Compared with the fluidized bed process, fixed bed oxychlorination

generally operates at higher temperatures (230-300°C) and

pressures (150-1400 kPa).

• Fluidized bed

An operating temperature of 220-245°C

and gauge pressure of 150-500 kPa

(22-73 psig) are typical for oxychlorination

with a fluidized bed reactor.

vinyl chloride (Cont.)Oxychlorination air-based technology

• Ethylene and air are fed in slight excess of stoichiometric

requirements to ensure high conversion of hcl while minimizing the

loss of excess ethylene in the vent stream

• Conversions: 94-99 % for ethylene and 98.0-99.5 % for hcl

• EDC selectivities of 94-97 %

Vinyl chloride (Cont.)

Thermolytic cleavage of EDC

•Temperature 500-600 °C and pressure 25-35 bar

• EDC conversion per pass is normally maintained at 53-63%, with a residence time of 2-30 sec

• Selectivity to VC ~99%

• Radical chain mechanism

• In many cases usage of CCl4 or Cl2 as initiator

vinyl chloride (Cont.)

Mechanism of EDC cracking

vinyl chloride (Cont.)EDC Cracking & VCM purification process EDC Cracking & VCM purification process

•Quenching with cold EDC

•VC separation by distillation

•Recycle of HCl in oxychlorination process

vinyl chloride (Cont.)Balanced process