Ethylene oxide history

The U.S. price history for merchant ethylene oxide sales is shown in Figure 4. It can be seen that ethylene oxide pricing generally reflects the cost of ethylene and, of course, supply/demand forces. In the late 1980s, several U.S. producers announced their withdrawal from the merchant ethylene oxide market. 

Hazards attendant on use of ethylene oxide in steriliser chambers arise from difficulties in its subsequent removal by evacuation procedures, owing to its ready absorption or adsorption by the treated material. Even after 2 evacuation cycles the oxide may still be present. Safety is ensured by using the oxide diluted with up to 90% of Freon or carbon dioxide. If high concentrations of oxide are used, an inert gas purge between cycles is essential [7]. The main factors in safe handling and use on laboratory or small pilot plant scales have been identified [8]. Safe operation of ethoxylation processes on industrial scale is discussed, with case histories [15],... 

In other words, the D-value is a function of the previous history of the monitor as well as of the sterilizer in which it was determined. The composition of the fluid from which the spores were dried may also influence D-values by coating the spores with a layer of material through which moisture or ethylene oxide may have restricted permeability. This also gives importance to the conditions in which the spores were grown (complex or defmed media) and washed. Graham [10] quotes D-values of 2.4 min and 3.S min for the same strain of B. subtilis var niger grown in different liquid media and exposed to ethylene oxide under identical conditions. 

Starting with the silicone elastomer hydrocephalus shunt in 1955, silicone elastomer has become widely used as a soft, flexible, elastomeric material of construction for artificial organs and implants for the human body. When prepared with controls to assure its duplication and freedom from contamination, specific formulations have excellent biocompatibility, biodurability, and a long history of clinical safety. Properties can be varied to meet the needs in many different implant applications. Silicone elastomer can be fabricated in a wide variety of forms and shapes by most all of the techniques used to fabricate thermosetting elastomers. Radiopacity can be increased by fillers such as barium sulfate or powdered metals. It can be sterilized by ethylene oxide, steam autoclave, dry heat, or radiation. Shelf-life at ambient conditions is indefinite. When implanted the host reaction is typically limited to encapsulation of... 

IV. Diagnosis is based on a history of exposure and typical upper-airway irritant effects. Detection of ethylene oxide odor indicates significant exposure. Industrial hygiene sampling is necessary to document air levels of exposure. 

Such large production capacities called for a very weU-developed, mature technology, particularly for PTA since the second ingredient, ethylene glycol, can be obtained by hydration of ethylene oxide made by a relatively straightforward and established vapor-phase oxidation of ethylene on a silver catalyst. In the following, a brief history and evolution of the PTA technology is presented (Landau and Saffer 1968 McIntyre 2003). 

The CL emission of poly(ethylene-C6>-1,4-cyclo-hexane-dimethylene terephthalate) (PECT) is highly dependent upon the thermal and UV oxidative history of the material [650]. Thermal oxidation of the polymer as measured by hydroperoxide concentration is directly related to CL intensity and can predict the behaviour of antioxidants. 

Kovacs AJ, Straupe C. Isothermal growth, thickening and melting of poly(ethylene oxide) single crystals in the bulk. Part 4—Dependence of pathological crystal habits on temperature and thermal history. Faraday Discuss 1979 68 225-238. 

For all metal reactors, the yields of ethylene and total coke were often found to vary significantly with the past history or pretreatment of the reactor. Pretreatments used were with either oxygen, steam, or hydrogen sulfide. Total coke is defined here as the sum of the CO, C02, and net coke it is postulated that CO and C02 were formed by oxidation of part of the coke which formed and that net coke is the amount of coke left on the reactor walls at the end of the run. The results for runs M01 and D44 are one example of the large differences in yields that can be obtained in reactors of the same material of construction (see Table I). Run M01 was made after a stainless steel 304 reactor had been treated with hydrogen sulfide. Hydrogen sulfide results in the formation of metal sulfides (8) and acts in most cases to passivate the surface so that coke formation is minimized. D44 was made using a new stainless steel 304 reactor, whose surface became very active when it was treated with steam. 

The Standard Oil process has the longest history. Working with ethylene pressures around 70 bar, it represents a medium-pressure process. The polymerization is started by one of the usual commercial hydroforming catalysts partially reduced M0O3 aluminum oxide, activated by sodium or lithium aluminum hydride. The ethylene is dissolved to 5-10% in xylene and polymerized to practically a 100% yield at temperatures below 200°C but still above the melting point of poly(ethylene). This solution polymerization enables the catalyst surfaces to be kept predominantly free and active. 

---