Ethylene Gas C2H4
A flammable, colorless, Gas with a characteristic sweet odor
Mol. Wt.: 28.05
Sp. Volume: 13.8 cf/lb
Flammability Limits: 13.1-32% in Air
Toxicity: Simple asphyxiant
Valve outlet: CGA 350, LB CGA 170
DOT Name: Ethylene, Compressed
Hazard Class: 2.1
DOT No.: UN 1962
DOT Label: Flammable Gas
CAS No.: 74-85-1
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 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 by-product 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. Within the industry, it is estimated that losses directly related to ethylene run into the billions of dollars annually. Removal of ethylene from the storage and shipping environment retards spoilage, reduces loss and increases profit.
source: http://www.marathonproducts.com/products/ethyover.html 27jul01
Ethylene Sensitivity Chart
N=None H=High L=Low M=Medium VH=Very High VL=Very Low Perishable Temperature Ethylene Ethylene Commodities C / F Production Sensitivity Fruits & Vegetables Apple (non-chilled) 1.1 / 30 VH H Apple (chilled) 4.4 / 40 VH H Apricot -0.5 / 31 H H Artichoke 0 / 32 VL L Asian Pear 1.1 / 34 H H Asparagus 2.2 / 36 VL M (Toughness) Avocado (California) 3.3 / 38 H H Avocado (Tropical) 10.0 / 50 H H Banana 14.4 / 58 M H Beans (Lima) 0 / 32 L M Beans (Snap/Green) 7.2 / 45 L M Belgian Endive 2.2 / 36 VL M Berries (Blackberry) -0.5 / 31 L L (Mold) Berries (Blueberry) -0.5 / 31 L L (Mold) Berries (Cranberry) 2.2 / 36 L L (Mold) Berries (Currants) -0.5 / 31 L L (Mold) Berries (Dewberry) -0.5 / 31 L L (Mold) Berries (Elderberry) -0.5 / 31 L L (Mold) Berries (Gooseberry) -0.5 / 31 L L (Mold) Berries (Loganberry) -0.5 / 31 L L (Mold) Berries (Raspberry) -0.5 / 31 L L (Mold) Berries (Strawberry) -0.5 / 31 L L (Mold) Breadfruit 13.3 / 56 M M Broccoli 0 / 32 VL H (Yellowing) Brussel Sprouts 0 / 32 VL H Cabbage 0 / 32 VL H Cantalope 4.4 / 40 H M Cape Gooseberry 12.2 / 54 L L Carrots (Topped) 0 / 32 VL L (Bitterness) Casaba Melon 10.0 / 50 L L Cauliflower 0 / 32 VL H Celery 0 / 32 VL M Chard 0 / 32 VL H Cherimoya 12.8 / 55 VH H Cherry (Sour) -0.5 / 31 VL L (Softening) Cherry (Sweet) -1.1 / 30 VL L (Softening) Chicory 0 / 32 VL H Chinese Gooseberry 0 / 32 L H Collards 0 / 32 VL M Crenshaw Melon 10.0 / 50 M H Cucumbers 10.0 / 50 L H (Yellowing) Eggplant 10.0 / 50 L L Endive (Escarole) 0 / 32 VL M Feijoa 5.0 / 41 M L Figs 0 / 32 M L Garlic 0 / 32 VL L (Odor) Ginger 13.3 / 56 VL L Grapefruit (AZ,CA,FL,TX) 13.3 / 56 VL M (Mold) Grapes -1.1 / 30 VL L (Mold) Greens (Leafy) 0 / 32 VL H (Russet Spotting) Guava 10 / 50 L M Honeydew 10 / 50 M H Horseradish 0 / 32 VL L Jack Fruit 13.3 / 56 M M Kale 0 / 32 VL M Kiwi Fruit 0 / 32 L H Kohlrabi 0 / 32 VL L Leeks 0 / 32 VL M Lemons 12.2 / 54 VL M (Mold) Lettuce (Butterhead) 0 / 32 L M (Russet Spotting) Lettuce (Head/Iceberg) 0 / 32 VL H (Russet Spotting) Lime 12.2 / 54 VL M (Mold Degreen) Lychee 1.7 /35 M M Mandarine 7.2 / 45 VL M Mango 13.3 / 56 M H Mangosteen 13.3 / 56 M H Mineola 3.3 / 38 L L Mushrooms 0 / 32 L M Nectarine -0.5 / 31 H H Okra 10.0 / 50 L M Olive 7.2 / 45 L M Onions (Dry) 0 / 32 VL L (Odor) Onions (Green) 0 / 32 VL M Orange (CA,AZ) 7.2 / 45 VL M Orange (FL,TX) 2.2 / 36 VL M Papaya 12.2 / 54 H H Paprika 10.0 / 50 L L Parsnip 0 / 32 VL L Parsley 0 / 32 VL H Passion Fruit 12.2 / 54 VH H Peach -0.5 / 31 H H Pear (Anjou,Bartlett/Bosc) 1.1 / 30 H H Pear (Prickley) 5.0 / 41 N L Peas 0 / 32 VL M Pepper (Bell) 10.0 / 50 L L Pepper (Chile) 10.0 / 50 L L Persian Melon 10.0 / 50 M H Persimmon (Fuyu) 10.0 / 50 L H Persimmon (Hachiya) 0.5 / 41 L H Pineapple 10.0 / 50 L L Pineapple (Guava) 5.0 / 41 M L Plantain 14.4 / 58 L H Plum/Prune -0.5 / 31 M H Pomegranate 5.0 / 41 L L Potato (Processing) 10.0 / 50 VL M (Sprouting) Potato (Seed) 4.4 / 40 VL M Potato (Table) 7.2 / 45 VL M Pumpkin 12.2 / 54 L L Quince -0.5 / 31 L H Radishes 0 / 32 VL L Red Beet 2.8 / 37 VL L Rambutan 12.2 / 54 H H Rhubard 0 / 32 VL L Rutabaga 0 / 32 VL L Sapota 12.2 / 54 VH H Spinach 0 / 32 VL H Squash (Hard Skin) 12.2 / 54 L L Squash (Soft Skin) 10.0 / 50 L M Squash (Summer) 7.2 / 45 L M Squash (Zucchini) 7.2 / 45 N N Star Fruit 8.9 / 48 L L Swede (Rhutabaga) 0 / 32 VL L Sweet Corn 0 / 32 VL L Sweet Potato 13.3 / 56 VL L Tamarillo 0 / 32 L M Tangerine 7.2 / 45 VL M Taro Root 7.2 / 45 N N Tomato (Mature/Green) 13.3 / 56 VL H Tomato (Brkr/Lt Pink) 10.0 / 50 M H Tree-Tomato 3.9 / 39 H M Turnip (Roots) 0 / 32 VL L Turnip (Greens) 0 / 32 VL H Watercress 0 / 32 VL H Watermelon 10,0 / 50 L H Yam 13.3 / 56 VL L Live Plants Cut Flowers (Carnations) 0 / 32 VL H (Sleepiness) Cut Flowers (Chrysanthemums) 0 / 32 VL H Cut Flowers (Gladioli) 2.2 / 36 VL H Cut Flowers (Roses) 0 / 32 VL H (Open Sooner) Potted Plants -2.8-18.3 / 27-65 VL H Nursery Stock -1.1-4.4 / 30-40 VL H (Slower Start) Christmas Trees 0 / 32 N N Flowers Bulbs (Bulbs/ 7.2-15 / 45-59 VL H Corms/Rhizomes/Tubers)
Ethylene is a plant hormone that differs from other plant hormones in being a gas. It has the molecular structure: H2C=CH2 When fruits approach maturity, they release ethylene. Ethylene promotes the ripening of fruit. Among the many changes that ethylene causes is the destruction of chlorophyll. With the breakdown of chlorophyll, the red and/or yellow pigments in the cells of the fruit are unmasked and the fruit assumes its ripened color. The presence of ethylene is probably detected by transmembrane receptors (protein that passes one or more times through the lipid bilayer of a cell membrane) in the surface of the plasma membrane of the cells.
How the role of ethylene was discovered.
As is so often the case in science, the discovery of the role of ethylene was made by accident. When first harvested, lemons are often too green to be acceptable in the market. In order to hasten the development of a uniform yellow color, lemon growers used to store newly-harvested lemons in sheds kept warm with kerosene stoves. When one grower tried a more modern heating system, he found that his lemons no longer turned yellow on time. Following this clue, it was soon found that
1901 Neljubow in St. Petersburg Russia:
Coal gas = illuminating gas in cities (gas lights)1910 Oranges cause bananas to ripen prematurely (natural ethylene?)
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)
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
What is ethylene?Simplest olefin hydrocarbon: C2H4
Gas at room temperature
Oxidizes to ethylene oxide C2H4O and ultimately ethylene glycol OH-C2H4-OH
Controlling the Pool Size
Pathway elucidated completely in 1979 (Adams & S. F. Yang)
ACC synthase (usually limiting enzyme in path)
Ethylene Forming Enzyme (sometimes limiting, esp fruit senescence)
Degradation:Ethylene -> Ethylene oxide C2H4O -> oxalic acid HOOC-COOH -> 2 CO2
Transport:Gas generally diffuses rapidly but not under waterlogging immersion.
ACC is transported in nonpolar way
Adsorption on charcoal and KMnO4 (potassium permanganate)
Conjugation:ACC ---> Malonyl ACC--NOT STORAGE...irreversible
Pool Size:1 uL/L (= 1 ppm) is active in most responses
Stress and IAA stimulate ethylene biosynthesis at ACC synthase
Receptors: Bind Ag+ ions and CO2 as well as C2H4 and contains Cu cofactor
Abscission; leaf flower fruits (thinning, harvesting)
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. The degree of damage depends upon the concentration of ethylene, length of exposure time, and product temperature. One of the following methods should be used to ensure that ethylene-sensitive produce is not exposed: a) Ethylene producing items (such as apples, avocados, bananas, melons, peaches, pears, and tomatoes) should be stored separately from ethylene-sensitive ones (broccoli, cabbage, cauliflower, leafy greens, lettuce, etc.). Also, ethylene is emitted by engines. Propane, diesel, and gasoline powered engines all produce ethylene in amounts large enough to cause damage to the ethylene-sensitive produce items mentioned; b) Ventilate the storage area, preferably to the outside of the warehouse, on a continuous or regular basis to purge the air of any ethylene; c) Remove ethylene with ethylene absorbing filters. These have been proven in reducing and maintaining low ethylene levels. If ethylene damage is suspected, a quick and easy way to detect ethylene levels is with hand held sensor tubes. This will indicate if the above steps should be followed.
Ethylene is explosive at high temperatures. When using as directed the products of Catalytic Generators, reaching the explosive level is not possible. The explosive level is about 200 times greater than that found in ripening rooms. As a matter of fact, it would take 20 - 30 of the Easy-Ripe Generators on the highest setting in a one-load room to reach this level.
Ethylene was used historically as an important anesthetic until less flammable compounds were developed. It is a colorless gas with a sweet ether-like odor. As an anesthetic, it was used as a concentration of 85% with 15% oxygen. Ethylene is a hydrocarbon gas and quite flammable and explosive at concentrations above about 3%. Remember, a non-toxic anesthetic for humans at a concentration of 85% or higher, yet as a fruit ripening hormone, ethylene gas is effective at 0.1 to 1 ppm. One part of ethylene per million parts of air that's one cupful of ethylene gas in 62,000 gallons of air - is enough to promote the ripening process in fruits.
Using tomatoes as an example, the life of a tomato fruit begins with fertilization of the flower ovules. After fertilization, the young fruit goes through a short period of cell division which is then followed by a rapid period of growth as these cells enlarge. During the final stages of growth and development, the tomato fruit reaches its full size and is now mature. This period of growth and development, from fertilization to development of the mature fruit, requires about 45-55 days, depending on the cultivar and the season. During the growth and development period, there are many chemical and physical changes occurring that have an impact on fruit quality and ripening behavior after harvest. Ripening is the final stage of the maturation process when the fruit changes color, and develops the flavor, texture and aroma that makes up what we define as optimum eating quality. The biological agent that initiates this ripening process after the fruit is mature is naturally produced ethylene - this simple plant hormone described and understood over 40years ago. While there are other factors involved in this "triggering" of the ripening process by ethylene, it is essentially a universal ripening hormone. When this internal concentration of naturally produced ethylene increases to about 0.1 - 1.0 ppm, the ripening process is irreversibly initiated. The process may be glowed, but it cannot be reversed once it is truly under way. So, here is the key point: additional and externally applied ethylene, provided prior to the time that the naturally produced internal concentration reaches the required 0.1 - 1.0 ppm level, will trigger or initiate - "promote" if you will - this natural ripening process at an earlier time.
The additional externally applied ethylene (the "gassing" so frequently referred to in the popular press) merely accelerates the normal ripening process. Numerous studies have shown that there are no important biochemical, chemical, or physiological differences between fruit ripened where the naturally produced ethylene has been the triggering mechanism or where additionally externally applied ethylene has triggered the process in the mature but unripe fruit.
For example, tomato fruit are not and cannot be "artificially
reddened" by ethylene. The normal tomato ripening process, which includes
pigment changes - the loss of green chlorophyll and conversion of carotenoids
into red lycopene pigments - can be accelerated and brought about earlier by
externally applied ethylene, but this is a normal process. In fact, some of the
components of nutritional quality, such as Vitamin C content, benefit because of
the fact that the fruits will be consumed after a shorter time interval from
harvest as a result of ethylene treatments and hence, the initial level will not
have degraded as far as the longer, unaccelcratcd process. Ethylene is actually
used commercially on only a few crops, including: (a) bananas, (b) for removing
the green color from citrus fruits, (e) almost all honeydew melons, and (d) to a
limited extent, with tomatoes.
Although many factors could be listed, there are four which play the dominant role in determining the quality of tomato fruits presented to the customer in the retail store: (1) variety; (2) maturity at time of harvest; (3) storage temperature during shipping and handling, and (4) physical damage.
Source: California Fresh Market Advisory Board, Informational Bulletin No. 12, June 1, 1976.
Ethylene use in the Ripening of Organic Bananas
Ethylene is a permitted material under Council Regulation (EEC) No. 2092/91 for use in 'degreening bananas'. The Soil Association permits the use of ethylene as a trigger in the ripening process for organic bananas being imported into Europe.
The UK organic banana market
Approximately £80,000 worth of organic bananas are brought into the UK each week. The vast majority of these imports are derived from small scale individually owned holdings predominantly in the Carribean. Contrastingly, commercial conventional banana production has drifted towards very large scale monocultural production in order to compete on a global scale. These conventional systems may be relying on up to 50 pesticide sprays per year which is both hazardous to the producer and to the environment.
The 'natural' process of ripening Natural release of small amounts of ethylene is caused by temperature increase or invasion of the fruit by pests and pathogens This initial ethylene release triggers the fruits own ethylene production In turn, the ethylene produced by the fruit will initiate ripening (and further ethylene production) in neighbouring fruit.
This positive feed-back system results in more and more ethylene being produced. However, stages of ripeness will vary from tree to tree and bunch to bunch depending on localised ethylene concentrations. The window of ripeness for human consumption of bananas is also very small compared to many other fruit.
Ripening of bananas for export
In order for the fruit to survive the transit time from source to origin it must be picked at 3/4 maturity when the bananas appear green. After arrival in the destination country a very small controlled release of ethylene, approximately 10-50 parts per million (ppm), is used to trigger the natural ripening process. This treatment, combined with control of ventilation and temperature, ensures uniform development of maturity in both the pulp and the peel. The source of the ethylene used is ethanol i.e. alchohol most of which is produced by fermentation of fruit and vegetables.
Consequences of not using ethylene
Without a controlled release of ethylene bananas could potentially ripen in storage due to triggers from pathogen invasion and increased temperature. However, this uncontrolled process would lead to post-harvest losses of up to 50% and increased labour costs due to the following:
- Uneven ripening - soft over-ripe and green fruit unsuitable for sale.
- Requirement for daily sorting after approximately 5 days of storage, leading to bruising of the fruit
- Increased pest and disease susceptibility
- Soft and dull ripe fruit tends which is not appealing to the consumer
- Fruit selected for sale would go over-ripe in approximately 1-2 days after leaving storage.
These factors would make volume sales of bananas prohibitively expensive and as a result would impact heavily on an expanding base of small-holder producers currently supplying the UK market.
Ethylene is a natural compound used at low controlled doses to trigger the ripening process of bananas in storage. The even and controlled ripeness that ethylene initiates prevents post-harvest losses of up to 50% which might otherwise occur.
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The PURASPEC 320 Ethylene Purification Process is designed for the purification of ethylene feed streams to high density polyethylene and linear low density polyethylene plants, HDPE and LLDPE respectively. The ethylene feed to these plants contains a number of impurities that would interfere with the polymerization reaction and reduce the yield and quality of the final product.
The PURASPEC 320 Process consists of a three-stage system and uses a range of catalysts, absorbents and regenerable adsorbents.
Stage 1: Comprises two beds, the top bed containing PURASPEC 3020 low temperature absorbent for the removal of H2S and the bottom bed containing PURASPEC 3410 high activity acetylene/hydrogen removal catalyst. Hydrogen is added to the stream to provide a 3:1 molar ratio with acetylene for the hydrogenation reaction over the PURASPEC 3410.
Stage 2: Contains two identically sized reactors in series for the removal of CO and O2, the first reactor oxidises CO over oxidised PURASPEC 3450 and the second reactor adsorbs O2 over reduced PURASPEC 3450. In reality the CO and O2 will work against each other, the CO reducing the catalyst to give CO2 followed by the O2 reoxidising the catalyst.
Stage 3: The Temperature Swing Adsorption system consists of two downflow reactors in parallel. Each reactor comprises from top to bottom, 3A molecular sieve (PURASPEC 3487 adsorbent) for water removal and activated alumina absorbents, PURASPEC 3482 (for oxygenate removal), PURASPEC 3484 (for carbon dioxide removal), and for some duties PURASPEC 3480 (to act as a guard bed and bed support).
NOx and Ammonia Removal: Removal of the various components of the inlet NOx occurs at different stages in the process. Some of the NOx is reduced to NH3 and H2O in the 1st Stage. In the second stage, some of the NOx is reduced to N2 and H2O. NH3 is absorbed in the final stage.
see also: Intro to Polyolefins http://www.synetix.com/polymers/polyolefins.htm
Ethylene CAS No. 74-85-1
Synonym. Acetene; Elayl; Ethene.
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.
Acute Toxicity. Mice tolerate administration of 0.5 ml of a solution with a concentration of 150 mg E./l without changes in their behavior.
Repeated Exposure. Accumulation is impossible because of the rapid excretion of E. from the body.
Short-term Toxicity. Mice were dosed by gavage with 3.75 mg/kg BW for 4 month. The treated animals displayed no changes in behavior or in BW gain and oxygen consumption. Gross pathological examination revealed no changes in the relative weights or in the histological structure of the visceral organs.1
Long-term Toxicity. Rats were given 0.05 mg/kg BW for 6 month. The treatment produced little abnormalities in behavior, BW gain, leukocyte phagocytic activity, or in cholinesterase anal conditioned reflex activity.'
Genotoxicity and Carcinogenicity. Experiments proved E. to be converted in certain species notably mice and rats, into the carcinogenic and mutagenic ethylene oxide.2 Carcinogenic effect of E. of endogenous origin is suggested.3 Whether such an effect is possible with oral administration is not clear. No toxic or carcinogenic effects were found after inhalation of 300 to 3000 ppm.4
Carcinogenicity Classification. IARC: Group 3.
Chemobiokinetics. It is unlikely that there is a direct chemical interaction between E. and bio logical media. 1:. is not broken down in the body. It seems to he rapidly excreted via the lungs
Standards. Russia (1988) MAU and PML: 0.5 mg/l (organolept., odor).
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.
source: Sheftel, VO. Handbook of Toxic Properties of Monomers and Additives. 1995
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