Carbon dioxide filling limits

The composition of the gas mixture, which is introduced into the tube bundle reactor (tubes of 6-12 m length and 20-50 mm diameter, filled with the Ag catalyst) consists of 15-50 vol % ethylene, 5-9% oxygen, as much as 60% methane as dilution gas, and 10-15% carbon dioxide. The reaction therefore proceeds above the upper explosion limit. The ethylene conversion runs up to 10% per cycle through the reactor. The ethylene oxide selectivity amounts to 75-83 % maximum. The formed ethylene oxide is recovered by scrubbing with water and the newly formed carbon dioxide is separated from the cycle gas, e.g., by hot potash washing process. 

A straightforward way to measure air quality is to measure the carbon dioxide concentration, which is a natural biological metabolite and increases especially in rooms filled with people. An increase in C02 is mainly responsible for sleepiness and could therefore serve as a direct measure of poor air quality. The base concentration of C02 in the ambient air is around 400 ppm. In non-ventilated rooms the C02-concentration can amount to more than 1000 ppm. Some carbon dioxide concentrations and limits and their impact on human comfort are listed in Tab. 5.4. 

This method was used for the first time by Ray [6] to determine non-olefinic impurities in ethylene. The sample (10-25 ml) was first fed into a reactor (19 x 1.1 cm) filled with activated charcoal saturated with bromine (40%). The resulting liquid bromina-tion products of ethylene were securely retained on charcoal at room temperature. The zone of non-olefinic impurities (permanent and saturated hydrocarbon gases) moved in a flow of carbon dioxide (carrier gas) from the reactor into a chromatographic column (40 X 0.2 cm I.D.) packed with activated charcoal. A nitrometer was used as the detector [39, 40]. The method permitted the determination of trace concentrations of 10" -10" % in ethylene. The use of a more sensitive detector should substantially lower the detection limit. 

Syringe pumps can provide pulseless flow and can be easily filled with liquid carbon dioxide. Syringe pumps do not have to be cooled because the carbon dioxide is liquefied by pressure, not temperature. However, because the pumps have limited volume, the syringe must be filled and repressurized when the pump cylinder is emptied. Also, when changing modifiers, the pump head must be thoroughly flushed to prevent carryover. The pump should be able to... 

Although not recommended, processing requirements may occasionally necessitate storage in partially filled containers. Stainless steel or other containers that can be sealed effectively should be used in this case. After transfer, such containers should be topped with nitrogen gas and sealed. In this case, nitrogen, rather than carbon dioxide gassing, is recommended. The limited solubility of N2 (14 mg/L) compared with COg (1500 mg/L) in wine means that the former remains as a layer on and above the wine s surface for a longer period of time compared with CO2, which rapidly solubilizes. 

Suitable SCFs are not limited to carbon dioxide or other SCFs with low critical temperature. The SCFs may be used individually or in combination. Some examples of different SCFs used in the filling of CNTs are mentioned here. 

The same precautions for handling high pressure gas or liquid carbon dioxide apply equally to solid carbon dioxide converters. The only differences between liquid and solid storage are the method of filling and the amount of liquefied carbon dioxide contained. Dry ice converters are charged with dry ice, and the amount charged must not exceed the rated capacity of the converters. Do not overfill. When charging a dry ice converter, do not leave it open unnecessarily. This will minimize condensation within the converter and thus limit the possibility of corrosion. 

The grapes, completely destemmed, are transferred to the maceration tank with a must pump, the tank having been filled beforehand with a layer of carbon dioxide to avoid oxidation. Sulfiting is avoided, to limit the extraction of phenolic compounds. Different installations are possible. 

As with virtually all insulation materials and techniques, gas-filled powders have their limitations. First, the fill-gas must be unreactive and compatible with the powder material. Carbon dioxide has been widely used as a fill-gas. Second, a vapor barrier is necessary around the packing material to prevent diffusion of air or water into the insulation. 

Microparticles can be produced by a simple technique that consists of spraying a polymer, e.g., PLLA, solution in dichloromethane (or dimethylsulfoxide), through a nozzle into a reactor filled with supercritical carbon dioxide (Reverchon et al, 2000). This process is known as supercritical antisolvent precipitation (SAS). The experimental parameters have a limited influence on the particle size (1-4 /im). A modified version of the process, known as the SAS-EM process, allows nanoparticles of a controlled size (30-50 nm) to be produced (Chattopadhay et al., 2002). In order to restrict the use of an organic solvent. Pack and co-workers fed the SAS reactor with a solution of PLLA prepared by homogeneous ring-opening polymerisation in supercritical HCFC-22 (Pack et al, 2003a). 

---