Production of Dry Ice

If liquid CO2 is expanded from storage conditions (e.g. boiling fluid at 15 bara) to a pressure slightly above ambient pressure (e.g. 1.1 bara, -77.6 °C), about 52% of the CO2 occur as dry ice snow and the rest in gaseous form [6.29, 6.30]. This dry ice snow is pressed into blocks or into pellets. The remaining expansion gas is compressed to a little over the storage pressure by means of compressors and liquefied in a liquefaction unit so that it can be fed back into the storage tank. 

The required energy for the production of dry ice is about 170 to 210 kWh t including compression and re-liquefaction of the arising residual gas. 

Dry ice block weights can vary from 5 to 20 kg per block, with a density of about 1.4-1.6 kg dm .  

Pellets vary from 5 to 15 g per pellet, smaller pellets, 0.3 to 0.7 g are used for dry ice blasting, bulk density is about 0.8-1.0 kg dm  

Carbon dioxide has certain special properties (see Section 6.1.3) that must be 

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In the coal gasification, as well as in the FT process massive amounts of CO are inevitably produced. CO is the main component of the off-gas in the Sulphur recovery plarft (see above) and in the Benfield plant (which scrubs CO2 from the Synthol tailgas). The latter source is the purer of the two. CO is used in fire extinguishers and the production of "dry ice". 

The temperature is controlled throughout the reaction by intermittently adding additional pieces of dry ice to the dry ice-acetone bath. Strict temperature control throughout the bromination reaction is important to obtain high regioselectivity and purity of the product as the side products cannot be removed with ease. 

SFE of fruits and vegetables and meat products has been reported, but the sample preparation techniques necessary to obtain reproducible results are extremely time consuming. Solid absorbents such as Hydromatrix, Extrelut " anhydrous magnesium sulfate or absorbent polymers are required to control the level of water in the sample for the extraction of the nonpolar pesticides. Without the addition of Hydromatrix, nonpolar pesticides cannot penetrate the water barrier between the sample particles and the supercritical CO2. The sample is normally frozen and the addition of dry-ice may be required to reduce losses due to degradation and/or evaporation. Thorough reviews of the advantages and limitations of SFE in pesticide residues... 

Biological fluids such as urine should be collected from individuals with no known exposure to the active ingredient of the test product. These samples should be collected in tarred 2-4-L jars or vessels with nonleak lids and stored in a freezer or in a cooler of dry-ice away from any test product or treated samples until used for tield fortification. 

The reaction of Pt(C03)(dppp)] with a modest excess of vicinal diols in CH2C12 solution affords the corresponding [Pt(a,/3-diolato)(dppp)] species under equilibrium conditions, a reaction that is readily reversed by the addition of dry ice to the product. The reaction with triols such as glycerol and alditol carbohydrates also affords the corresponding diolato species, with the reaction exhibiting excellent equilibrium regioselectivities for a number of isomers, of which the 7, 6-threo diols are the most favored. 

Dried product resistance normally increases with increasing solute concentration and frequently decreases as the temperature of the frozen product approaches the eutectic temperature or T., . Production of larger ice crystals by a lower degree of water supercooling and/or an annealing process during freezing may also decrease the resistance. 

To a flask equipped with stirrer, condenser, and dropping funnel is added 40.0 gm (0.61 gm-atom) of zinc dust in 40 ml of absolute ethanol. After the condenser outlet is connected to a series of Dry Ice-acetone traps cooled to —80° to —70°C, the mixture is heated to gentle reflux while 20.3 gm (0.0852 mole) of l,2-dibromo-l,l-difluoropropene in 30 ml of 95% ethanol is added dropwise over a 2 hr period. The reaction mixture is heated for an additional hour, and then the gaseous products which are condensed in the Dry Ice traps are purified by several vaporization distillations to afford 3.6 gm (56 %) b.p. 

Allylic chlorides Actually the reaction of HOG with highly substituted alkenes is a convenient route to allylic chlorides if CH2G2 is used as the organic cosolvent. The reagent is prepared by addition of dry ice to calcium hypochlorite (70%) in water. The reaction of 1-methylcyclohexene is typical (equation I). Chlorohydrins arc the main products only in the case of 1-alkenes and 1,2-disubstituted alkenes. 

Amine 30 (108 mg, 0.50 mmol) was dissolved in 0.2 M NaOH (2.5 mL). Boc O (120 mg, 0.55 mmol), dissolved in dioxane (2.5 mL), was added to the soln in an ice bath. The mixture was stirred at rt for 2 h. H20 (15 mL) was added to the mixture, which was then addified with 10% citric acid and extracted with EtOAc (50 mL). The organic layer was washed with 10% citric acid and sat. NaCl, and dried (Na2S04). The soln was filtered and concentrated, affording an oily residue, which was then triturated with an EtOAc/pentane mixture in a strongly cooled bath of dry ice/EtOH. By pipetting off the supernatant, the product 31 was obtained yield 134mg (85%) mp 151-157°C [a]D24 -214 (c 1.0, MeOH). 

The same setup as in the previous example was used, but the trap which condensed the gaseous products was cooled with liquid N2 instead of dry ice/acetone. 

A 1-L, 3-necked, round-bottomed flask was equipped with magnetic stirrer, pressure-equalizing addition funnel with N2 inlet, low temperature thermometer, and a Friedrich condenser with N, outlet. The outlet was attached to two traps in series. The first was cooled in a Dewar of salt/ice water (- 15 C) and the second in a Dewar of dry ice/i-PrOH (— 78 C). 2-Bromo-3,3,3-trifluoropropene (50 g, 0.286 mol) and hexane (250 mL) were added to the flask. 1.6 M BuLi in hexane (190 mL, 0.304 mol, commercial) was added to the addition funnel. The flask was cooled with a hexane slush bath by addition of liquid N2 until the temperature of the solution inside the flask was - 85 °C. Then the BuLi soln was added over a period of 25 min at such a rate that the temperature remained below - 80 C. The slightly cloudy, yellowish solution was allowed to stir for an additional 10 min. Then, the hexane slush was removed, Upon reaching - 30 C, a gelatinous precipitate formed and the temperature rapidly rose to 28 "C. The volatile product was removed from solution by heating the mixture at reflux for 30 min with a slow flow of N2 through the system. The product was obtained from the dry ice trap yield 21 g (97%). 

Unfortunately, by focussing on the potential cooling aspects the operators did not understand that dry ice in water reacts to become carbonic acid. NaSH, a reaction product of H2S and sodium hydroxide, is stable at high pH, but liberates toxic H2S when acidified. As operators added pieces of dry ice, the pieces instantly created acidic pockets that reacted with the sodium hyrosulfide, and immediately liberated poisonous hydrogen sulfide gas. Events happened so quickly that the process operators were overcome by the toxic fumes before they were able to add all of the dry ice. They perished from acute hydrogen sulfide inhalation—while trying to be helpful. 

Carbon nanotubes and nested fullerenes were also prepared by reductive carbonization of CO2 with magnesium metal. Motiei et al. [104] reported on the production of nanotubes in ca. 0% yield and nested fullerenes in ca. 12% yield at 1000°C by the reaction of dry ice and magnesium. The reductive carbonization of CO2 is reminiscent of the HiPco process [105, 106], based on disproportionation of carbon monoxide (the Boudouard reaction) ... 

Along with natural gas, oil fields have other products. Hydrogen sulphide is the most abundant of the impurities. A small quantity in natural gas is desirable as a warning of leakage. When large quantities are present this sour gas is used to manufacture carbon black or is processed for sulphur recovery. Sometimes helium is present in useful quantities. Carbon dioxide is found in some fields. It is recovered and used in the manufacture of dry ice. 

Alternatively, a solution of crude product prepared at room temperature may be cooled to a low temperature. Filter stick filtration is again convenient for this procedure since it facilitates collection of the crystallized product at low temperature. It is common to cool the solvent to -78°C by slow addition of dry ice to an acetone cooling bath, but one convenient variation is to place the room temperature solution Inside a Dewar flask containing some isopropanol in a low temperature freezer (-80°C). The solution will then cool over a period of 6 - 12 hrs to -70°C. 

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