Background to Petroleum Chemicals

Introduction (History)

Chemical Industry : ancient origin founded on a wide variety of sources of raw materials

eg. coal, molasses, fats and oils, salt, metalliferous ores, water and the atmosphere

apperarance of petroleum as significant source of chemicals dates back to mid 1920’s

Petroleum : a mixture of hydrocarbons chemicals made from it are nearly all organic chemicals

but can also be inorganic for specific reasons Carbon black and hydrogen cyanide classed as

inorganic on arbitrary basis Sulphur present as undesirable impurity in crude oils

and natural gas can be recovered as element or sulphuric acid.

Hydrogen from petroleum is used in ammonia production

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Source of Typical organic chemicals

From petroleum From coal From fermentationFrom oils and fats

Ethylene and derivatives

Benzene*Toluene*

Ethyl alcohol*Food acids*

Fatty acidsFatty alcohols*

Propylene and derivatives

Naphtalene*Pyridine*

Monosodium glutamatePharmaceuticals*

SoapsGlycerine*

C4 hydrocarbons and derivatives

AnthraceneAcetylene*

Synthesis gas derivatives

Phenol*

Aromatics Cyclic compoundsAcetylene*

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Sources of typical inorganic chemicals

From petroleum From other sourcesHydrogen based :AmmoniaNitric acidNitrogen fertilizers

Chlorine/caustic sodaPotash and phosphate fertilizersSulphur/sulphuric acid*Titanium dioxideMetal salts

Sulphur based :Recovered sulphur *Sulphuric acid*

PyritesChalk/limeSoda ashBleaching powder

Carbon based :Hydrogen cyanideCarbon blackOxides of carbon

Fluorine/bromine/iodineBauxiteCalcium carbideSalt

Notes : The source indicated is predominant except for those marked * which have more than one significant source.

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Petroleum chemical manufacture is concerned to produce chemical products from raw materials of petroleum origin.

The chemical products made from petroleum do not differ in any significant way from those made using alternative raw materials. Differences relate to minor impurities present.

Petroleum industry original function – limited to separation of petroleum into its different fractions by distillation.

A stage was reached where gasoline fractions was required in large quantity and better quality than provided by simple separation resulting in introduction of thermal cracking and thermal reforming processes.

Cracking processes creates streams of olefinic gases of no immediate use to petroleum industry. After considerable research these olefinic gases were found suitable for a range of chemical products hence prompted the industry in 1920’s.

In the beginning, policy of petroleum industry was to establish the refinery capacity in close proximity to oil fields. Then policy was changed by locating the oil-refining capacity in regions of major consumption.

The production of petroleum chemicals no longer leans very heavily on refinery gas streams for its raw materials but the spread of refinery capacity tended to stimulate the development of chemical production from petroleum.

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European developments in petroleum chemical manufacture did not follow at all exactly the pattern set in the USA. The main difference was the use of liquid (usu. Naphtha) feedstocks for the production of the olefinic base materials, rather than the natural gas liquids and the major refinery sources available in the USA.

Feedstock trend in the US is towards liquids as raw materials for the lower olefins, whereas Europe make use of natural gas liquids from the North Sea.

Characteristics of Petrochemical Manufacture

As a general rule, the petroleum producers supply the chemical products companies with the raw materials, the latter manufacture finished products.

However, many exceptions to this rule and the integrating of petroleum and chemical activities is carried to greater or lesser degrees, depending on the case. The same company can also be engaged in several activities.1) some oil companies supply the chemical industry

with raw materials and intermediate products. 2) some chemical companies depend on the oil

industry for large quantities of raw materials and intermediates. They devote most of their efforts to manufacturing complex products and are specialized in organic chemistry products.

3) other oil companies extend their activities beyond basic products to include intermediate products and their derivatives and even end-products.

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4) some companies which do not make large-scale demands for raw materials and which usually make use of natural gas, liquefied petroleum gas, refinery gas and naphtha.

5) some chemical companies team up with oil companies to carry out joint activities.

6) chemical companies also have a tendency to buy up plastic manufacturing plants and the like. In this manner they guarantee themselves an outlet for some of their products at the same time as they acquire technological and practical experience in the field in question.

7) some companies pool their resources in order to create affiliates. The main advantages of such associations lie in the following points : possibility of building a large-capacity unit which

is competitive on the international market but which avoids harmful competition with small producers on the domestic market.

reduction of investments for each of the companies, thus enabling them to become involved in new fields of activity at the same time.

The petroleum industry has its own cherished traditions. A medium-size refinery is likely to consume at least 10 million tonnes of crude oil each year. The capacity of individual plant units is huge by the standards of most industries but will represent quite a modest proportion of the total market for the appropriate products in the market area serviced.

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Petroleum products : handled in a fluid form. very rarely identifiable chemical compounds commonly prepared as blended products, required to

meet a series of physical specifications, with occasional chemical interpolations as to impurities

provides oil-refining operations with a significant degree of flexibility

eg. blended products are prepared for markets whose standards of acceptance are well known and of long standing

Refineries present a spectacular array of pipe tracks and tank farms for the handling of raw material and finished products.

The chemical industry is rather more diverse. It ranges all the way from large-scale plants (still pretty small by petroleum standards) to small untidy batch-operated units.

Petroleum chemical manufacture commonly requires the application of typically petroleum processing techniques to typically chemical finished products.

Petroleum chemical units: usually continuous, elaborate, operating with catalytic

promotion and highly automated require large scale of operation to secure economic

advantage, otherwise little purpose in the development of petroleum raw materials to serve the chemical industry in any particular instance

subject to consideration of ‘min. economic size’

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Economics and Uses

Economic factors : Elements of operating cost of installations and manufacturing cost of products

These elements contribute in determining the operating cost of units and in calculating the manufacturing cost of products. They depend upon specific conditions prevailing in different industrialized or developing countries. Their analysis is of prime importance for it constitutes the basis for different studies to be undertaken when establishing new industrial projects.

They include : cost of raw materials cost of utilities (steam, electricity, fuel, etc.) cost of labor and supervision; cost of construction; taxes

Cost of raw materialsa) Natural GasThe price of natural gas is usually known at the well head. Its price when delivered as a raw material to a petrochemical plant depends on several factors such as : Location of consuming centers (which enables the

distance from the well to the plant to be evaluated) Amounts consumed (which enables the diameter of the

pipe line to be determined); thus making it possible to calculate the cost of transportation natural gas from the fields to consuming centers.

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This cost is quite low in the case of large quantities transported over rather small distances. It gets higher, when the rate of flow is low or when the distances are very long, and it becomes very high if special liquefaction facilities and liquid methane transportation in special refrigerated tankers. If adequate port facilities do not exist, their cost should be taken into account when calculating the transportation cost of natural gas.

b) Liquefied GasPrices of liquefied gas used as raw materials for petrochemicals depend mainly on the quantities consumed, that is on possible markets for petrochemical products based on LPG. In developing countries when LPG may be available in large quantities, possibilities of exporting propane and butane may help to lower cost of recuperation and of transportation from fields to the coast. This may be quite important because the petrochemical industry consumes rather small amounts of such feedstocks.

c) Liquid hydrocarbons : Naptha and CondensateNaptha is available in Europe and in many other countries such as India whose consumption of petroleum products is largely based on middle distillates such as kerosene and gas oil.Condensate is produced in association with natural gas.

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Cost of utilitiesThe petrochemical industry is a rather large consumer of electricity. The power consumed is about 15000 – 20000 kw for an ammonia or a butadiene unit of medium size.

In industrialized countries, power is often produced in very large thermal or hydro-electric power stations, and it can be purchased at different rates from one country to another depending on the power consumed and length of utilization.

If power is not available, it must be produced within the petrochemical plant itself. Its cost would then depend, for manufacturing units, on the cost of construction, price of fuel (natural gas, fuel gas, fuel oil), cost of labor, etc. and would change from one country to another. The same is valid for the cost of steam and cooling water which are usually produced in the plant itself.

Cost of Labor The cost of construction labor in developing countries is usually higher than industrialized countries, although wages are lower. This is due to factors such as lower productivity and lack of qualified technicians and skilled workmen (such specialists would have to be imported from abroad at very high cost).

It is difficult to specify the real maintenance and operational labor costs for the manufacturing units of a specific plant without going into details. Nevertheless, taking into account the following factors: training of local operators, foremen and engineers import of foreign technicians

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one may reasonably consider that there will be an increase of about 30-50% compared with industrialized countries, at least during the first years of operations.

Construction costs and financingThe cost of construction in different countries may vary considerably depending on different factors such as : cost and availability of equipment equipment specifications and construction standards cost of transporting equipment when it is not available

at the size cost and availability of labor cost of foreign labor when required productivity and duration of construction

When comparing construction costs in industrialized and developing countries, it can readily be seen that several factors intervene to make them higher in the latter countries.

Uses

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Raw materials

Notes on Petroleum and Natural gases

The basic raw materials for chemical manufacture are natural gas, refinery gases and liquid hydrocarbon fractions.

Secondary raw materials are derived from basic raw materials and their derivation are summarized below :Acetylene from cracking or partial oxidation, either of

methane in natural gas or higher paraffinsMethane Major constituent of natural gasHigher paraffins

Ethane, propane and butane separated from refinery gas streams or natural gas. Other raw materials in this category are paraffinic naphthas, and n-paraffins of varying carbon chain length

Ethylene Present to a limited extent in some refinery gas streams. Produced by cracking of ethane, propane or butane (derived from refinery streams or extracted from natural gas) or liquid hydrocarbons

Propylene From refinery gas streams or by thermal cracking of propane and liquid hydrocarbons

C4 hydrocarbon

From refinery gas streams or by thermal cracking of liquid hydrocarbons

Higher olefins

From wax cracking, n-paraffin dehydrogenation, or oligomerization of ethylene

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Refinery Gases

Refinery gases range from : hydrogen at the lower or more volatile end hydrocarbon with 4 carbon atoms in the molecule at the

less volatile end olefins (ethylene to butylenes) paraffins (methane to butanes) small proportions of components such as acetylene,

certain dienes (notablly butadiene) and, impurities such as hydrogen sulphide and nitrogen.

Refinery gases : originally used for petroleum chemical manufacture

came from the obsolete process of thermal cracking (eg. coking, viscosity breaking)

4 main sources are processes of crude oil distillation, catalytic cracking, catalytic reforming and hydrocracking

Crude oil distillation : Produces volatile fraction of paraffinic gases Minor component – gasoline Major component separated drg. Distillation, process –

stabilization of gasoline proportion of gas produced varied widely between one

crude oil and another

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Catalytic cracking : Replacing the old thermal cracking processes Provide more valuable range of products eg. higher

quality gasoline Modern fluid bed catalytic cracker uses catalyst in the

form of fine particles of controlled size Catalyst comprised combination of silica and

aluminium Molecular sieves introduced 15 years ago and become

predominant today Technique of passing feed and regenerated catalyst

through riser crackers become established High temperature (680 – 760oC) regeneration gives

more complete burn-off of coke deposited on the catalyst

Cracking reaction takes place at 475-550oC and about 2 atm press

Hydrocracking : Cracking operation carried out in a strong reducing

environment Represent an alternative to catalytic cracking as a

means of increasing the yield of gasoline from a barrel of oil

Cracking function – dual function catalyst comprises hydrogenation/dehydrogenation sites and acidic sites

Catalyst of zeolite type in combination with metal or metal oxide catalysts

Provides saturated gases including significant quantities of propane and butanes esp. isobutane

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Catalytic reforming : Replacing the older thermal reforming processes Design to improved the quality rather than the volume

of gasoline production Use for heavy gasoline fraction including naphthenes Catalyst comprises platinum and rhenium on an

alumina base Catalyst allow reaction to proceed at lower pressures,

greater throughput, higher yields or higher performance product

Main function of catalyst – isomerization and dehydrogenation of napthenes to produce aromatics

Most important reaction – cyclization and dehydrogenation of alkanes and dehydrogenation of naphthenes to aromatics

Other refinery processes. Some of the more intractable residues of refinery distillations are subjected to thermal coking to provide small amounts of gas/liquid fuels while producing a more readily handled ‘coke’ fuel.

Olefins from cat-cracker operations (or even steam cracking of natural gas liquids in the USA) may be used to alkylate branched alkanes, particularly isobutane. Alternatively, propylene and butenes may be oligomerized, and the resulting C6+ olefins hydrogenated to give ‘polygasoline’.

The term ‘hydrotreating’ tends to be used to cover all refinery hydrogenation processes. These may range from hydrogenation of olefinic mixtures (liquid cracker products for example) under mild conditions, to the hydrodesulphurization of heavy fractions and the hydrogenation of (poly-) aromatic components.

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The reasons behind the utilization of larger and larger quantities of oil and natural gas as raw materials in the chemical industry are as follows:1) Oil and natural gas can produce purer products

than those from carbochemistry.2) Petroleum refining can, by means of normal or

special processing, produce substances which are difficult to derive from other sources (xylenes)

3) Oil and natural gas can increase supplies of certain products which would not otherwise be available in sufficient quantities (glycerin).

4) Oil and natural gas can usually provide the required products at lower prices than can other sources (plastics).

Raw materials come from sources which are varied and adapted to local conditions. They are made up either of primary hydrocarbons obtained by simple separations from natural gas or oil, or of products which have already been transformed such as residual gas or petroleum cuts leftover from refining.

In the US use is made primarily of natural gas as well as ethane and the liquefied gas extracted from it. Gas from catalytic cracking, which is rich in olefins, is also an interesting source. Aromatics are extracted from reformed gasoline.

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Refinery operationsThe term ‘cracking’ and reforming’ are often used without qualification to describe a variety of refinery and primary petrochemical operations. It is hoped that Table 1 will provide a general guide to what is meant in a particular context.

Table 1 Petroleum fractionsMethaneEthane

Associated gas (Natural gas)

Propane Butanes

Liquefiedpetroleum gases (LPG)

Natural gas liquids (NGL)

C5(>0oC)-70oC Light gasoline or light naphtha

Feedstocks for motor spirit, also known as straight-run gasoline

70oC-170oC Naphtha (mid-range)

170oC-250oC Kerosene Vaporising oil, jet fuel

250oC-340oC Gas oil Diesel fuel, light fuel oil

340oC-500oC Heavy distillates

Feedstocks for lubricants and waxes or heavy fuel oils.

Fluid residues(from light crudes)Semi solid residues

Bitumen or asphalt

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Table 2 Refinery and petrochemical cracking and reforming operations

RefineryThermal cracking Obsolete, thermal decomposition of

middle/higher fractions to increase gasoline range hydrocarbons

Thermal cracking/coking (delayed coking etc.)

Thermal decomposition of very heavy fraction to give mainly gases and a high coke yield.

Catalytic cracking Accelerated decomposition, with some aromatization, of middle/higher fractions over solid acidic catalysts

Hydrocracking Accelerated hydrogenolysis/decomposition of heavy fractions to paraffinic hydrocarbons over metal/acid catalysts

Thermal reforming Obsolete, thermal rearrangement and aromatization of napthas under high pressure

Catalytic reforming (platforming)

Metal/acid-catalysed rearrangement and aromatization of napthas

PetrochemicalSteam cracking Thermal cracking of C2+ hydrocarbon

to olefins in the presence of steamThermal/autothermal cracking

More general term, including methane to acetylene autothermal, with partial combustion

Steam reforming Nickel-catalysed formation of synthesis gases from hydrocarbons

Natural Gas

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Natural gases : Dry gas consist largely of CH4

Sour gas containing impurities of sulphur compounds Associated gas – natural gas associated with oil recover Cracking technology of natural gas liquids does not

differ fr. Naphtha cracking

Acetylene from natural gasTraditional route – fr. Calcium carbide and indirectly fr. coal

CaO + 3C → CaC2 + COCaC2 + H2O → CaO + C2H2

Limitations : Carbide production concentrated in areas where coal

and power relatively economical Transportation of calcium carbide itself is a constraint –

3.3 ton CaC2 needed to prod. 1 ton C2H2

Production of acetylene fr. hydrocarbons2CH4 C2H2 + 3H2 Temp. ~ 1200oC

Problems/Disadvantages : Heat need to be introduced for reaction to proceed Reaction products must be cooled very rapidly to

prevent decomposition of acetylene Acetylene must be separated fr. other reaction products

Solutions : To achieve heat input by applying an electric arc to

feed, temp. rise to 1600oC

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Rapid quech by introduction of cold secondary HC feed

Processes : Wulff BASF SBA

Liquid Hydrocarbons

Acetylene fr. liquid HC’s (using this route usu. with problems)Hoechst HTP process : 2 stage flame process

Classification of Petrochemicals According to Source

Acetylene Derivatives1) Vinyl Chloride

The reaction of acetylene with hydrogen chlorideC2H2 + HCl → C2H3Cl

- advantage : no by-product hydrogen chloride was formed

- carried out in vap. phase using charcoal impregnated with 10% mercuric chloride as catalyst

- reagents pure and dry with slight Xs of hydrogen chloride

- press. atmospheric or slightly higher- temp : 100 to 210oC - exothermic reaction

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- rxn. conditions depends on age and cond. of catalyst

Nearly all vinyl chloride polymerized to PVC and small amount converted to vinylidene chloride.

The emergence of ethylene as a contender for vinyl chloride production arose from the development of the oxychlorination processes. The route pursued was the addition of chlorine to ethylene to give ethylene dichloride (EDC, 1,2-dichloroethane) and the thermal cracking of EDC (550oC) to vinyl chloride and HCl.

CH2=CH2 + Cl2 ClCH2CH2Cl CH2=CHCl + HCl

A snag was that these companies now had to dispose of hydrogen chloride. The most elegant solution was to react this with acetylene in a separate stage, to give what became known as the ‘Balanced Process’. This scheme became a driving force for naphtha cracking to mixtures of ethylene and acetylene, as exemplified by the Wulff process.

Nevertheless these special crackers proved expensive, and many gave serious operational problems. The final solution came with the development of the ethylene oxychlorination process. The reaction

CH2=CH2 + 2HCl + ½O2 ClCH2CH2Cl + H2O

is carried out at 250-300oC over supported copper chloride (melt) catalysts. This process may be combined with chlorine addition and EDC cracking to provide a balanced

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operation, if required; the overall stoichiometry then becomes

2CH2=CH2 + Cl2 + ½O2 2CH2=CHCl + H2O

The polymer referred to here is rigid PVC. The flexible material contains appreciable amounts of plasticizers (mainly phthalate esters), which obviously affects the overall energy utilization.

2) Vinyl AcetateThe reaction between acetylene and acetic acid

CH3COOH + HCCH CH3COOCH=CH2 vinyl acetate

- carried out in vap. phase using catalyst comprising zinc or cadmium acetate on charcoal

- temp. about 210oC- pressure slightly above atmospheric- Xs acetic acid to red. formation of ethylidene

diacetate by-product- exit gases cooled to 0oC - purified by distillation- polymerized rapidly either alone or with other vinyl

compds. - Applications : adhesives and emulsion paints

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Lower olefins (alkenes)and acetylene (alkynes)The paraffinic hydrocarbons in natural resources show very low reactivity under moderate conditions. Early petrochemical processes drew upon the greater reactivity of olefins, and when refinery supplies failed to meet demand means of converting alkanes to alkenes were developed. During the later period, low prices of naphtha (in Europe and Japan) and natural gas (in the USA and Europe) also promoted petrochemical routes to acetylene.

The resulting processes all require high temperatures and are, therefore, both energy-and capacity-intensive, so that very large scales of operation are desirable for efficiency and economic viability.

Cracking processes

Steam (thermal) cracking for lower olefins. A typical naphtha for cracking has a carbon number range from 4 to 12 or more. The uncatalysed cracking reaction is carried out within tubes in a furnace enclosure at near atmospheric pressure (less than 3 atm). Steam makes up 30-45% w/w of the total feed to improve heat transfer, reduce the partial pressure of hydrocarbons (thermodynamically desirable) and remove carbon by the reaction

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C + H20 CO + H2

Cracking temperatures were traditionally 750-850oC, but temperatures up to 900oC (high severity cracking) are becoming more common, in conjunction with shorter residence times (about 0.1 second).

Hydrocarbon dehydrogenation and cleavage reactions of the type

A B + C + D .....

are always strongly endothermic, with H values in the range 120-180 kJ for each additional molecule produced.

XXXXXXXXXXX

Cracking processes for acetylene (ethyne)

Minor amounts of acetylene are formed in steam cracking, but rarely justify separation. However, if cracking temperatures are increased to over 1100oC acetylene becomes a significant component, and a different approach to reactor design is necessary. The Wulff process furnaces contain stacks of tiles, and operate on 1-minute heating-cracking cycles. Fuel gas or oil burned in air to heat the tiles to about 1200oC, and the feed is then switched to naphtha and steam, the temperature falling to about 1000oC to complete the cycle.

At still higher temperatures (over 1500oC), methane can be partially converted into acetylene. An electric arc process has been operated, but the most successful and widespread approach is the BASF or Sachsse partial oxidation process. Typically methane (in excess) and oxygen are fed to a special burner, in which the temperature falls from a peak of about 2500oC to 1300oC in a very short time, at which point the gases enter a quench. A typical product stream (water-free basis) would contain some 8% (molar) acetylene, 25% carbon monoxide, 55% hydrogen and small amounts of methane, carbon dioxide and other gases. After acetylene extraction, the remaining gases may be integrated into a synthesis gas system.Finally, BASF have also developed a submerged flame autothermal cracking process for crude oil. Partial combustion raises the

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temperature locally, to the point at which cracking to both ethylene and acetylene occur.

Ethylene (ethene) and other olefins (alkenes)

We will start with the simpler cracking of ethane according to the following equation and theoretical energy balance (in MJ/mol ethylene), based on energy (fuel) values as defined above.

C2H6 (+heat) C2H4 + H2 1.428 + 0.137 1.323 + 0.242

Although absent from the equation, generation of the co-fed steam requires energy, and extra heat is necessary to raise the temperature of the reactants to over 800oC. Some of this extra energy is recovered (by steam generation) from the furnace flue gases and the reactor outlet gases, but, with additional steam required for product separation and purification, a net steam consumption results. The overall yield of ethylene on ethane in modern US plant is about 85% molar.

Acetylene (ethyne)

Before evaluating the petrochemical routes to acetylene, we should look first at the long-established process for producing acetylene via calcium carbide and water:

CaO + 3C CaC2 + COCaC2 + H2O C2H2 + CaO (or Ca(OH)2 with excess

water)

Essentially all the energy is consumed in calcium carbide manufacture. In the electrothermal process, the reaction is carried out at temperatures in excess of 1850oC.

If we ignore the lime (recovered), and convert other consumption/by-product figures to energy values, we obtain (per mol acetylene equivalent):

Coke (3.5g-atoms 1.4

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C/mol)Electricity-actual input 1.0Primary fuel value - 3.0

2.4 MJ/mol

4.4

General considerations. A number of organic products are potentially producible from either acetylene or a lower olefin, for example:

C2H2 + H2O CH3CHO C2H4 + ½ O2

C2H2 + CH3CO2H CH2=CHO2CCH3 C2H4 + ½ O2

+ CH3CO2HC2H2 + HCN CH2=CH.CN C3H6 + NH3 + 1½ O2

The reactions of acetylene are simpler, and were important early commercial routes to the products indicated, acetaldehyde, vinyl acetate and acrylonitrile.

The main driving force to discover and develop olefin based routes was the dramatic increase in scale of steam cracking operations in the post-war years. Early increases in demand for synthetic ethanol and ethylene oxide/glycol were followed by a rapid escalation in polyethylene production, now the major outlet for ethylene. In contrast, the group of products for which acetylene was the preferred feedstock grew more modestly, and a disparity in required production scales and prices developed. The steam cracking of naphtha in Europe and Japan also gave propylene in large quantities, for which new outlets had to be found. Thus acetylene was slowly squeezed out, including later displacement production to acetylene production is now 100-fold in USA if somewhat less elsewhere.

Vinyl Chloride (chloroethene).The production of vinyl chloride naturally attracted the

attention of those companies already involved in chlorination processes. The quantities of by-product hydrogen chloride available were often an embarrassment and the relatively facile production of vinyl chloride from acetylene and anhydrous HCl, over a supported mercuric chloride catalyst, provided a valuable outlet.

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As the market for vinyl chloride grew, major petrochemical companies without existing chlorination capabilities looked to other possible routes. With failing ethylene prices, the route pursued was the addition of chlorine to ethylene, to give ethylene dichloride (EDC, 1,2-dichloroethane), and the thermal cracking of EDC at about 550oC to vinyl chloride and HCl.

CH2=CH2 + Cl2 ClCH2CH2Cl CH2=CHCl + HCl

A snag was that these companies now had to dispose of hydrogen chloride. The most elegant solution was to react this with acetylene in a separate stage, to give what became known as the ‘Balanced Process’. This scheme became a driving force for naphtha cracking to mixtures of ethylene and acetylene, as exemplified by the Wulff process.

Polyethylene (polyethene) and polypropylene (polypropene)

Low-density polyethylene (LDPE) is produced by a free radical process, initiated with traces of oxygen or peroxides, at temperatures of 200oC to over 300oC and pressures up to 3000 atm. Over half of this low-melting point, flexible product is used for packaging film manufacture.

High density polyethylene (HDPE) is now produced mainly by polymer growth on microscopic particles of catalytic materials (chromium or Ziegler systems) suspended in a non-solvent or carried along in the gas-phase, at only 70-125oC and 15-40 atm. The product has a higher melting point and is more rigid, and finds major uses in containers, moulded items and pipes. Polypropylene, with both molding and fibre uses, ethylene-propylene copolymers and the newest product line, linear low-density polyethylene (LLDPE), are produced by similar methods. A C4/C6 terminal olefin co-monomer is used in the latter to provide a tough, flexible film forming product.

2.2 Methane Derivatives (C1 production)

For methanol and formaldehyde, see section 3.1

Formic (methanoic) acid and derivative

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The modest US requirements for formic acid (30 kilotonnes per annum) appear to be met mainly by co-product material from butane oxidation (when available) and imports. Outlets are into a variety of specialty areas.

In Europe, demand is swollen to over 100 kilotonnes per annum by use for the preservation of damp silage (grass) and other animal feedstuffs – a means of saving the energy otherwise required for drying. Co-product material from naptha oxidation is now exceeded by BASF’s recently expanded (200 kilotonnes per annum capacity) methyl formate (methyl methanoate) production from syn gas. The selective reaction

CH3OH + CO HCO2CH3

is catalysed by sodium methoxide at 80-100oC and 30-60 atm. BASF can hydrolyse about 2/3 of the ester directly to formic acid by a recently improved process. A Finnish plant is based on by-product CO.

N,N-dimethylformamide (DMF) is an important solvent for acrylic fibres and polyurethane leather production (and for separating acetylene from ethylene). Metyl formate reacts readily with dimethylamine.

HCO2CH3 + (CH3)2NH HCON(CH3)2 + CH3OH DMF

Alternatively the amine can be introduced directly into methanol/carbon monoxide reaction systems.

Mitsubishi have developed a process for methyl formate by the dehydrogenation of methanol. However, the major objective is the production of separate hydrogen and carbon monoxide streams for other uses from imported methanol.

2CH3OH HCO2CH3 + H2

HCO2CH3 CO + CH3OH

Hydrogen cyanide

The reported demand for hydrogen cyanide in the USA is 550 kt per annum. Possibly one quarter is by-product from acrylonitrile manufacturer; the remainder is produced by the oxidation of

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methane/ammonia mixtures over platinum at about 1100oC. The major use (40-45%) is in DuPont’s adiponitrile production, with some 30-35% used for methyl methacrylate (MMA) (methyl 2-methylpropenoate) manufacture and 10% sodium cyanide.

Chloromethanes

Passage of methanol and hydrogen chloride over a Lewis acid catalyst at about 350oC provides methyl chloride.

CH3OH + HCl CH3Cl + H2O

This product can be chlorinated to give the more highly substituted derivatives. However, more operations are now based on the oxychlorination of methane, over copper chloride catalysts, at temperatures of over 500oC.

2CH4 + Cl2 + ½O2 2CH3Cl + H2O2CH3Cl + Cl2 + ½O2 2CH2Cl2 + H2O

Mixtures are obtained with proportions dependent on the initial ratio of chlorine to methane. Some carbon tetrachloride is also produced by the chlorinolysis (C-C cleavage) of higher carbon number materials, and chlorination of carbon disulphide.

The total US production of chloromethanes is over 0.9 Mt per annum. Chloroform (trichloromethane) and carbon tetrachloride (tetrachloromethane) are precursors for fluorocarbons; their elimination from the aerosol can market has been partially offset by increased use as refrigerants and intermediates for fluoroplastics. Methylene dichloride (dichloromethane) has picked up some of the aerosol business, and is used in paint removal and degreasing. Methyl chloride (chloromethane) is used for silicones and the waning production of tetramethyl lead.

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