Ethylene

Ethylene (IUPAC name: ethene) is an organic compound, a hydrocarbon with the formula C2H4 or H2C=CH2. It is a colorless flammable gas with a faint "sweet and musky" odor when pure. It is the simplest alkene (a hydrocarbon with carbon-carbon double bonds), and the simplest unsaturated hydrocarbon after acetylene (C2H2). Ethylene is widely used in chemical industry, and its worldwide production (over 109 million tonnes in 2006) exceeds that of any other organic compound.[4] Ethylene is also an important natural plant hormone, used in agriculture to force the ripening of fruits

Ethylene Glycol (MEG)

Ethylene gas (C2H4) is an odorless, colorless gas that exists in nature and is also created by man-made sources. Not easily detectable, it exists where produce is stored. In nature, the largest producers

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are plant and plant products (ie. fruits, vegetables and floral products) which produce ethylene within their tissues and release it into the surrounding atmosphere. It is also a byproduct of man-made processes, such as combustion. As is often the case, the role of ethylene and its effects on produce was discovered by accident. Lemon growers would store newly harvested green lemons in sheds kept warm by kerosene heaters until they turned yellow and ripened enough to market. When new modern heating systems were tried, the lemons no longer turned yellow on time. Research soon found that the important factor in the ripening process was small amounts of ethylene gas given off by the burning kerosene in the heaters. Ethylene, also known as the 'death' or 'ripening hormone' plays a regulatory role in many processes of plant growth, development and eventually death. Fruits, vegetables and flowers contain receptors which serve as bonding sites to absorb free atmospheric ethylene molecules. The common practice of placing a

tomato, avocado or banana in a paper bag to hasten ripening is an example of the action of ethylene on produce. Increased levels of ethylene contained within the bag, released by the produce itself, serves as a stimulant after reabsorption to initiate the production of more ethylene. The overall effect is to hasten ripening, aging and eventually spoilage. A refrigerator acts in much the same way. Kept closed to retain the desired temperature, it also enables an increased concentration of ethylene to accumulate. Any closed environment, such as a truck trailer, shipping container or warehouse, will have a similar effect. Storage of produce items is of economic importance to the food and floral industry. Storage allows producers, handlers and sellers to spread availability over periods of strong and weak demand, maintaining supply and stabilizing cost

Production Global ethylene production was 107 million tonnes in 200514] and 109 million tonnes in 2006.’ By 2010 ethylene was produced by at least 117 companies in 55 countries.141 To meet the ever increasing demand for ethylene, sharp increases in production facilities are added globally, particularly in the Persian Gulf countries and in China.141 Ethylene is produced in the petrochemical industry by steam cracking. In this process, gaseous or light liquid hydrocarbons are heated to 750—950 “C, inducing numerous free radical reactions followed by immediate quench to stop these reactions. This process converts large hydrocarbons into smaller ones and introduces unsaturation. Ethylene is separated from the resulting complex mixture by repeated compression and distillation. In a related process used in oil refineries, high molecular weight hydrocarbons are cracked over zeolite catalysts. Heavier feedstocks. such as naphtha and gas oils require at least two “quench towers” downstream of the cracking furnaces to recirculate pyrolysisderived gasoline and process

water. When cracking a mixture of ethane and propane, only one water quench tower is requiredJ The areas of an ethylene plant are: 1.

steam

cracking

furnaces:

2. primary and secondary heat recovery with quench: 3. a dilution steam recycle system between the furnaces and the quench system; 4. primary compression of the cracked gas (3 stages of compression); 5. hydrogen sulfide and carbon dioxide removal (acid gas removal); 6. secondary compression (1 or 2 stages); 7. drying of the cracked gas: 8.

cryogenic

treatment:

9. all of the cold cracked gas stream goes to the demethanizer tower. The overhead stream from the demethanizer tower consists of all the hydrogen and methane that was in the cracked gas stream. Cryogenically (—250 F (—157 “C)) treating this overhead stream separates hydrogen from methane. Methane recovery is critical to the economical operation of an ethylene plant.

10. the bottom stream from the demethanizer tower goes to the deethanizer tower. The overhead stream from the deethanizer tower consists of all the C2,s that were in the cracked gas stream. The C2 stream contains acetylene. which is explosive above 200 kPa (29 psi).t1] If the partial pressure of acetylene is expected to exceed these values, the C2 stream is partially hydrogenated. The C2s then proceed to a C2 splitter. The product ethylene is taken from the overhead of the tower and the ethane coming from the bottom of the splitter is recyded to the furnaces to be cracked again: 11. the bottom stream from the de-ethanizer tower goes to the depropanizer tower. The overhead stream from the depropanizer tower consists of all the C3’s that were in the cracked gas stream. Before feeding the C3’s to the C3 splitter, the stream is hydrogenated to convert the methylacetylene and propadiene (alIene) mix. This stream is then sent to the C3 splitter. The overhead stream from the C3 splitter is product propylene and the bottom stream is propane which is sent back to the furnaces for cracking or used as fuel. 12. The bottom stream from the

depropanizer tower is fed to the debutanizer tower. The overhead stream from the debutanizer is all of the C4s that were in the cracked gas stream. The bottom stream from the debutanizer (light pyrolysis gasoline) consists of everything in the cracked gas stream that is C5 or heavier.1

Since ethylene production is energy intensive, much effort has been dedicated to recovering heat from the

cracked

gas

is

(1200 psig) steam. This steam is in turn used to drive the turbines for compressing cracked gas, the propylene refrigeration compressor, and the ethylene refrigeration compressor. An ethylene plant, once wnning,

gas leaving the furnaces. Most of the energy recovered from the used to make high pressure

does not need to import steam to drive its steam turbines. A typical world scale ethylene plant (about 1.5 billion pounds of ethylene per year) uses a 45,000 horsepower (34,000 kW) cracked gas compressor, a 30.000 hp (22,000 kW) propylene compressor, and a 15,000 hp (11.000 kW) ethylene compressor.

Discovery 1901 Neljubow in St. Petersburg Russia: Coal gas = illuminating gas in cities (gas lights) Causes triple response: dwarf stem, fat stem, agravitropism in stem in peas also leaf abscission in nearby trees Identified ethylene from the gas as the causative agent. (OLDEST IDENTIFIED GROWTH REGULATOR) 1910 Oranges cause bananas to ripen prematurely (natural ethylene?) 1934 Ethylene is a natural product (plant hormone?) Forgotten for many years as possible hormone.... 1959 Burg & Thimann

rediscover old research and begin studies showing ethylene as possible hormone

EFFECTS Fruit Ripening Abscission; leaf flower fruits (thinning, harvesting) Epinasty Triple Resonses Hook Closure Maintenance Initiates Germination in Grains Activates dormant buds (potatoes in storage) Stem elongation in deep-water rice Induces Flowering in Pineapple Promotes Female Expression in Flowers Flower and Leaf Senescence: Ag preventative (vase life)

Ethylene was used medically as a anesthetic in concentrations significantly greater than that found in a ripening room. However, ethylene is often targeted as the reason for difficulty in breathing in ripening rooms; what can affect some people is usually either: a) Carbon Dioxide (CO2,) levels: CO2, is produced by the ripening fruit in the room and

levels increase over time, or b) Oxygen levels: The oxygen in the room when loaded is taken in by the ripening fruit. This sometimes will make breathing in a ripening room difficult. The increased CO2, and decreased oxygen levels are the main reasons for venting the ripening room. It will permeate through produce cardboard shipping boxes, wood and even concrete walls. While ethylene is invaluable due to its ability to initiate the ripening process in several fruits, it can also be very harmful to many fruits, vegetables, flowers, and plants by accelerating the aging process and decreasing the product quality and shelf life Ethylene is explosive at high concentrations. When using as directed, reaching the explosive level is not possible. The explosive level is about 200 times greater than that found in ripening rooms.

Properties. Colorless gas with a faint odor of ether. Solubility in water is 20 mg/1 (20°C) and 250 mg/l (0°C). Rapidly volatilizes from the open surface of water. Odor perception threshold is reported to be 0.039 mg/l,02 = 0.5 mg/l,010 or even 260 mg/l.010 Does not affect the color or clarity of water. References: 1. See BUTYLENE, 28. 2. Filser. J. G. and Bold, HM, Exhalation of ethylene oxide by rats on exposure to ethylene. Mutat. Res. 120, 57, 1983. 3. Kokonov, M. T., Ethylene -- an endogenous substance in tumor-carrier, in Problems of Medical Chemistry, Vol. 58. 1960, p.158 (in Russian). 4. Rostron C ., Ethylene metabolism and carcinogenicity Food Chem. Toxicol., 24, 70, 1987