ethylene production

Pamantasan ng Lungsod ng Maynila College of Engineering and Technology

Department of Chemical Engineering

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ETHYLENE PRODUCTION

INTRODUCTION

Ethylene, is the lightest olefin. It is a colorless, flammable gas, which is produced mainly from petroleum-based feed stocks by thermal cracking in the presence of steam. It is the simplest alkene hydrocarbon, Consisting of 4 hydrogen atoms and 2 carbon atoms (C2H4), Connected by a double bond. Because of this double bond ethylene is called an unsaturated hydrocarbon, or olefin.

Ethylene is used primarily as an intermediate in the manufacture of other chemicals, especially plastics. It can be polymerized directly to produce polyethylene, the worlds most widely-used plastic. It can be chlorinated to make ethylene dichloride, a precursor to the plastic polyvinyl chloride. It can be combined with benzene to produce ethylbenzene, which is used in the manufacture of polystyrene, another important plastic. Smaller amounts of ethylene are oxidized to produce chemicals including ethylene oxide, ethanol, and polyvinyl acetate.

Other names Ethylene (compressed) Ethene (compressed)

Molecular formula C2H4

Physical properties Relative Vapor Density: 0.980 Flash Point: 135.0C Percent Volatile by volume: 100 Boiling point: 104C Melting Point: 169.2 C Explosive Limits: 2.7 mol%36 mol% Automatic Ignition Temperature: 543C in air at atmospheric pressure. ~ Slightly soluble in water, soluble in most organic solvents.



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HISTORY

1669

Ethylene have been discovered by Johann Joachim Becher, who obtained it by heating alcohol with sulfuric acid; he mentioned the gas in his Physica Subterranea. 1779 Joseph Priestley also mentions the gas in his Experiments and observations relating to the various branches of natural philosophy: with a continuation of the observations on air, where he reports that Jan Ingenhousz saw ethylene synthesized in the same way by a Mr. Ene in Amsterdam in 1777 and that Ingenhousz subsequently produced the gas himself.

1795 The properties of ethylene were studied by four Dutch chemists, Johann Rudolph Deimann, Adrien Paets van Troostwyck, Anthoni Lauwerenburgh and Nicolas Bondt, who found that it differed from hydrogen gas and that it contained both carbon and hydrogen. This group also discovered that ethylene could be combined with chlorine to produce the oil of the Dutch chemists, 1,2-dichloroethane; this discovery gave ethylene the name used for it at that time, olefiant gas (oil-making gas.) Mid-18th century The suffix -ene (an Ancient Greek root added to the end of female names meaning "daughter of") was widely used to refer to a molecule or part thereof that contained one fewer hydrogen atoms than the molecule being modified. Thus, ethylene (C2H4) was the "daughter of ethyl" (C2H5). The name ethylene was used in this sense as early as 1852. 1866 The German chemist August Wilhelm von Hofmann proposed a system of hydrocarbon nomenclature in which the suffixes -ane, -ene, -ine, -one, and -une were used to denote the hydrocarbons with 0, 2, 4, 6, and 8 fewer hydrogens than their parent alkane. In this system, ethylene became ethene. 1892 Hofmann's system eventually became the basis for the Geneva nomenclature approved by the International Congress of Chemists, which remains at the core of the IUPAC nomenclature. However, by that time, the name ethylene was deeply entrenched, and it remains in wide use today, especially in the chemical industry.

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1979 The IUPAC nomenclature rules made an exception for retaining the non-systematic name ethylene, however, this decision was reversed in the 1993 rules so the correct name is now ethene.

HISTORY IN PLANT BIOLOGY 1901 Dimitry Neljubov, using the triple response of pea seedlings, demonstrates that ethylene is the active component of illuminating gas, which had been shown to have profound effects on plants. He observed that the peas grown in the laboratory were abnormally short, thick and curled. He discovered that what was causing the abnormal morphology was the air in the laboratory. It turns out that the laboratory was using coal gas (aka illuminating gas) for lamp light. The active ingredient in the air that caused this growth response was ethylene, a byproduct of goal gas combustion. 1910

H.H. Cousins reported ethylene production in oranges. This would cause bananas to ripen prematurely if oranges and bananas were stored together. Later careful work showed that the oranges probably did not produce the ethylene, but that Penicillium mold on the oranges probably did.

1934 Ethylene was finally classified as a plant hormone. However, many people considered ethylene production a byproduct of excessive auxin content. 1935 Crocker proposed that ethylene was the plant hormone responsible for fruit ripening as well as inhibition of vegetative tissues (Crocker, 1935). Ethylene is now known to have many other functions as well.



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MANUFACTURING COMPANIES Shell Chemicals Inc.

Shell chemicals companies are among the leading producers of ethylene. We operate from a strong manufacturing technology and cost position, with world-scale manufacturing facilities in key locations. - Pandacan, Manila

Fluor Philippines

Fluor quickly built a reputation for applying innovative methods and performing precise engineering and construction work within the emerging petroleum industry. Today, Fluor continues to develop and implement innovative solutions for complex project issues in diverse industries,

including chemicals and petrochemicals, commercial and institutional (C&I), government services, life sciences, manufacturing, mining, oil and gas, power, renewable energy, telecommunications, and transportation infrastructure.

- Alabang Manila

JG Summit Petrochemicals Corp. The pre-eminent world-class manufacturer and supplier of polyolefin products in the Philippines. It started commercial operations in 1998, and is the first and only integrated Polyethylene and Polypropylene resin

manufacturer in the country, producing the Evalene brand of High Density Polyethylene (HDPE), Linear Low Density Polyethylene (LLDPE) and Polypropylene (PP).

-Brgy. Simlong, Batangas



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RAW MATERIALS Various feed stocks (liquid and gaseous) are used for the production of ethylene. The principal feedstocks are: Naphtas

A mixture of hydrocarbons in the boiling range of 30 to 200 C. Depending on the origin, naphta composition and quality can vary over a wide range requiring quality control of the feed mixtures.

Ethane Usually recovered from natural gas fields mainly USA.

Propane/butane Recovered from gas fields middle east, Texas etc. Kuwait has a large butane recovery system. Also can come from LNG plants

Gas oils (crude oil fractions)

Are also gaining importance as feedstocks in some areas of the world. Chemical analysis of the feedstock is important to ensure the required product specification and even more when the production is based on varying feed stocks.

MANUFACTURING PROCESS

1. Steam Cracker

Ethane Cracker



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The ethane, piped from Bass Strait via Long Island Point, is fed into five gas-fired

furnaces.

Steam is injected into the ethane feed immediately prior to entering each furnace.

Steam is added at controlled rates in order to increase the petrochemical yield and to minimize

carbon deposits (coke) forming in the furnace tubes. Coke deposits prevent the feedstock from

heating to the right temperature thereby reducing the effectiveness of the cracking reaction.

The ethane is subjected to a one second surge of extreme heat, between 750C900C, causing the splitting of the molecule into other hydrocarbons. Steam cracking refers therefore to the process whereby a hydrocarbon feedstockin this case ethanein the presence of steam and heat, changes to other hydrocarbons. The reaction is:

Over 60% of the ethane is reacted in the furnaces. The composition of the furnace

effluent (the gases coming from the furnace) is approximately 50% of ethylene, 35% of ethane

(by weight) with the remainder being hydrogen, methane, acetylene, propane, propylene and

some other hydrocarbons. The uncracked ethane is fed back into the furnaces later in the

process.

Steam crackers are designed to operate at conditions that make full use of the basic chemical and physical conditions favouring the formation of ethylene. The important conditions for successful operation of steam crackers include:

High temperatures

Short residence time The ethane is pumped through at a rapid rate as there is an optimum time for the cracking reaction to transpire. There has to be enough time or a high yield of ethylene to be produced but not too long so that the ethylene itself is cracked to form lower value by- products. Typical residence times for the molecules in the furnace tubes are less than one second.

Low hydrocarbon concentration Rapid quenching or cooling to minimize secondary reactions.



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2. Quench Tower

Quench Tower The effluent (the gases coming from the furnace) are immediately quenched or cooled

by water. This drops the temperature of the effluent from 840C to 700C. This is necessary to stop the cracking reaction from continuing and forming coke. The furnace effluents are combined and sent to the quench tower. Here cooling of the cracked gas to 30C is accomplished by direct contact with water. This quench water is then recovered and re-used.

Ethylene has been produced by the cracking reaction. However it is mixed in with many

different hydrocarbons. It needs to be separated out so that it can be sold as a product that is over 99% wt pure.

3. Gas Compressor

Multi-Stage Compression Train



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The conventional method of separating hydrocarbons is in distillation columns. This requires the furnace effluent to be liquefied. The way to liquefy a gas is to increase the pressure of the gas and then cool it down until a liquid is formed. Gas compression increases the pressure of the gas.

The cracked gas stream from the quench tower is compressed using a centrifugal

compressor. The gas compression in this section of the plant occurs in four stages. Heat

exchangers are used to cool the gas between each stage of compression.

This is necessary because when a gas is compressed it heats up. You therefore need to break up the compression steps to stop the gas becoming too hot. The gas is compressed to a pressure of approx. 3500 kPa.

4. Treating

Caustic Tower

The cracked gas stream contains impurities that need to be removed before the ethylene can be sold. These impurities include carbon dioxide, hydrogen sulphide and acetylene. Treatment of the cracked gas to remove impurities occurs between the third and fourth stages of the compressor. The hydrogen sulphide and carbon dioxide are removed in the caustic tower. The caustics towers purpose is to remove these unwanted chemicals from the ethylene. In this tower, the gas stream is contacted with dilute sodium hydroxide. the following reactions occur in the caustic tower:



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The waste sodium hydroxide stream is removed from the caustic tower. It is treated on site in the Spent Caustic Carbonation Unit which uses waste flue gas from a boiler to convert the stream into a benign baking soda solution prior to disposal. The carbonation unit is unique world first technology that does not require any acids or oxidisers to treat the sodium hydroxide waste stream. The acetylene is removed in a vessel called the acetylene converted. This is a large oval-shaped vessel filled with a nickel-iron catalyst. As the gas stream passes the catalyst the following reaction occurs:

(There are other different catalysts that can also be used). This catalyst is used to selectively promote only the hydrogenation of acetylene. Some of the other undesirable reactions include: This reaction is undesirable because it is a loss of valuable ethylene. The gas stream now needs to be dried. As the gas stream is going to be cooled to temperatures as low as 100C, any remaining water would form ice compounds thereby blocking pipes etc. The drying is achieved by passing the gas stream through an apparatus (the molecular sieve desiccant) that is designed to absorb water, it is now necessary to cool the gas stream.

5. Chilling Train

Ethylene Refrigerants

The chilling train is a series of three heat exchangers. On one side of the heat exchanger is the gas that needs to be cooled.



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On the other side of the heat exchanger is the refrigerant, liquid ethylene or propylene, which cools the gas. Neither stream comes into direct contact with the other. The gas is cooled and then it condenses or liquefies. The liquid stream can now go to the distillation columns to separate out the different chemical compounds.

6. Fractionation

Fractionation Process De-ethylenizer Column

There are three distillation columns. The way in which one of these columns works is shown in the figure. The first column is the de-methanizer. This separates out hydrogen and methane from the remaining components. The hydrogen and methane are used as fuel gas. The remaining heavy gas exits from the bottom of the de-methanizer (e.g. ethylene and ethane), and is then fed into the second distillation column. This is called the de-ethylenizer. This column separates ethylene from the heavier components of the de-methaniser bottom. It operates at a pressure of 1950 kPa, (nine times the pressure in your car tyre) and produces ethylene product at a purity greater than 99.85 %w. The third column, the de-ethanizer, separates ethane from the propylene and heavier components in the de-ethaniser bottoms. The overhead ethane stream is recycled back to the furnaces for cracking. The bottoms stream is sent to the gas oil cracker plant for further separation.



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INDUSTRIAL USES OF ETHYLENE Ethylene has two main industrial uses. It is used to accelerate the ripening of fruits and is most commonly used on bananas and also on citrus fruits. The other use of ethylene is in the manufacture of plastics, such as packing films, wire coatings, and squeeze bottles. Fruits

Ethylene occurs naturally in plants and stimulates the ripening of fruits. However by keeping the fruit in a chamber, such as a greenhouse, the amounts of ethylene present in the air can be controlled, and thus the degree of ripening of the fruit can also be controlled. The ethylene allows the fruit to mature in color and ripen. This process takes place over a few days, and the more ethylene that is used, the faster the fruit will ripen.

Plastics As for the industrial use of ethylene in plastics, the ethylene must first undergo polymerization. As briefly mentioned before, polymerization is the process where ethylene is converted to polyethylene through an addition reaction in the presence of a catalyst. Polymerization is an exothermic reaction as heat is given off and requires high temperatures and pressures for it to occur. Many examples of polyethylene that are commonly found in households include, milk bottles, bins and microwave wraps.

PVC and Polystyrene

While ethylene by itself is not particularly useful, it can be used to produce chemicals such as vinyl chloride (CH2=CHCl) and styrene (CH2=CH(C6H5)) which in turn can undergo polymerization to produce polyvinyl chloride (PVC) and polystyrene respectively. Traditional materials like rubber, steel, ceramics and glass are often replaced with PVC as it is a very versatile material and even simple modifications to the basic properties of the material can lead to a range of applications and different materials formed. One property of PVC is that it is thermoplastic and the material is usually mixed with additives which allows flexibility and strengthens it against UV rays. PVC is widely used and can be found as packaging and wire coatings while polystyrene is also used for packaging. The polymerization reactions of these monomers are illustrated below in the figure:



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* Polymerization of monomer vinyl chloride to form polymer polyvinyl chloride. Where n is the number of vinyl chloride molecules. Vinyl chloride is formed from the reaction between the chlorine from the electrolysis of sodium chloride and ethylene. * Polymerization of monomer styrene to form polymer polystyrene. Where n is the number of styrene molecules.

Antifreeze Ethylene glycol (CH2OH-CH2OH), also known as ethane-1,2-diol is a crucial component of antifreeze and is another chemical that is produced from ethylene. Ethylene glycol in its pure form is a colorless and viscous liquid. Since the molecule has two hydroxyl groups, it is readily soluble in water. Therefore in antifreeze solutions, ethylene glycol is mixed with water and since aqueous solutions of ethylene glycol have higher boiling and lower freezing temperatures than normal water and do not aid to the corrosion of iron, it is commonly used in car radiators.

Ethanol One application of ethylene is the production of ethanol, which is then used as a solvent in pharmaceuticals, inks and cosmetics and as a reagent for industrial applications. The production of ethanol occurs through the reaction between ethylene and water in the presence of phosphoric acid, the catalyst.



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SAFETY DATA

There is no evidence to indicate that prolonged exposure to low concentrations of ethylene can result in chronic effects. Prolonged exposure to high concentrations may cause permanent effects because of oxygen deprivation. Prolonged inhalation of about 85% in oxygen (a relatively high concentration) is also slightly toxic, resulting in a slow fall in blood pressure. At about 94% in oxygen, ethylene is acutely fatal.

It shows little or no carcinogenic or mutagenic properties. Although there may be moderate hyperglycemia, post operative nausea while higher than nitrous oxide is less than in the use of cyclopropane. During the induction and early phases, blood pressure may rise a little, but this effect may be due to patient anxiety, as blood pressure quickly returns to normal. Cardiac arrhythmias are infrequent and cardio-vascular effects are benign.

50%

15%

10%

5%

10%

10%

Uses of Ethylene

Polyethylene

PVC

Antifreeze

Fibres

Polystyrene & Copolymers

Miscellaneous (ethanol)

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ethylene production

Documents

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