Acetylene Specifications

In Europe fom or five of the more modem 1950s steam crackers, based on naphtha feed, replaced the fused iron or nickel front-end catalysts with a new palladium catalyst using an a-alumina support. Success in meeting the strict new acetylene specifications, while hydrogenating 95% of the methyl acetylene and forming no green oil, led to the use of this catalyst in many new ethylene plant desigrts. 

The concentration of is determined by measurement of the specific P-activity. Usually, the carbon from the sample is converted into a gas, eg, carbon dioxide, methane, or acetylene, and introduced into a gas-proportional counter. Alternatively, Hquid-scintiHation counting is used after a benzene synthesis. The limit of the technique, ca 50,000 yr, is determined largely by the signal to background ratio and counting statistics. 

The specifications set the maximum vol % of solvent that may be added to the cylinder shell (measured by its water capacity). The volume of solvent also varies with the capacity of the cylinder. Cylinders in the 90—92% porosity range with a capacity above 9.1 kg of water may contain a maximum acetone charge of 43.4%, whereas those with 9.1 kg or less water capacity may contain up to 41.8 vol %. The first category of cylinders are normally referred to as welding cylinders and the latter as small tanks (those with 0.28 and 1.12 m acetylene capacity). 

Purification of Carbide Acetylene. The purity of carbide acetylene depends largely on the quaUty of carbide employed and, to a much lesser degree, on the type of generator and its operation. Carbide quahty in turn is affected by the impurities in the raw materials used in carbide production, specifically, the purity of the metallurgical coke and the limestone from which the lime is produced. The nature and amounts of impurities in carbide acetylene are shown in Table 4. 

To extend the study of the apparent decomposition recombination reaction, and specifically to determine if the carbon atoms exchange with other atoms in other acetylene molecules, tests using carbon isotopes were conducted. A mixture of 50% regular acetylene, C2H2, and 50% heavy acetylene. 

Ethylene Stripping. The acetylene absorber bottom product is routed to the ethylene stripper, which operates at low pressure. In the bottom part of this tower the loaded solvent is stripped by heat input according to the purity specifications of the acetylene product. A lean DMF fraction is routed to the top of the upper part for selective absorption of acetylene. This feature reduces the acetylene content in the recycle gas to its minimum (typically 1%). The overhead gas fraction is recycled to the cracked gas compression of the olefin plant for the recovery of the ethylene. 

Based on the bench-scale data, two coal-to-acetylene processes were taken to the pilot-plant level. These were the AVCO and Hbls arc-coal processes. The Avco process development centered on identifying fundamental process relationships (29). Preliminary data analysis was simplified by first combining two of three independent variables, power and gas flow, into a single enthalpy term. The variation of the important criteria, specific energy requirements (SER), concentration, and yield with enthalpy are indicated in Figure 12. As the plots show, minimum SER is achieved at an enthalpy of about 5300 kW/(m /s) (2.5 kW/cfm), whereas maximum acetylene concentrations and yield are obtained at about 7400 kW/(m /s) (3.5 kW/cfm). An operating enthalpy between these two values should, therefore, be optimum. Based on the results of this work and the need to demonstrate the process at... 

Table 3 provides typical specifications for isoprene that are suitable for Al—Ti polymerization (89). Traditional purification techniques including superfractionation and extractive distillation are used to provide an isoprene that is practically free of catalyst poisons. Acetylenes and 1,3-cyclopentadiene are the most difficult to remove, and distillation can be supplemented with chemical removal or partial hydrogenation. Generally speaking distillation is the preferred approach. Purity is not the main consideration because high quaUty polymer can be produced from monomer with relatively high levels of olefins and / -pentane. On the other hand, there must be less than 1 ppm of 1,3-cyclopentadiene. 

Gas yield, the most impoitant specification for acetylene-giade carbide, is determined by slaking the carbide in water, collecting and measuring the volume... 

When acetylene is recovered, absorption—desorption towers are used. In the first tower, acetylene is absorbed in acetone, dimethylformarnide, or methylpyroUidinone (66,67). In the second tower, absorbed ethylene and ethane are rejected. In the third tower, acetylene is desorbed. Since acetylene decomposition can result at certain conditions of temperature, pressure, and composition, for safety reasons, the design of this unit is critical. The handling of pure acetylene streams requires specific design considerations such as the use of flame arrestors. 

Tower bottoms-ACN, butadiene, with some butenes and acetylenes - are fed to a recovery/stripping column. The hydrocarbons are taken overhead and then rerun to meet product specifications. The stripping column bottoms, (ACN) is then remrned near the top of the extractive distillation tower. A small slipstream goes to the ACN recovery tower, where solvent is also recovered from the water wash streams. 

A very obvious way to change die measurement range and sensitivity of a fluid manometer is by using fluids of different densities. There are only a few suitable liquids with specific gravit> between that of water and mercury. Ethylene bromide has a specific gravity of 2.2 and acetylene tetrabromide 3.0., but they are corrosive. 

Type and specifications on fan driver, gear types, pow er voltage, phase, cycles. Motors should at least meet specifications equivalent to totally enclosed, fan cooled, or if in explosive hazardous area, TEFC Class I, Group D (except this not acceptable in hydrogen or acetylene atmosphere). Due to moisture conditions around this equipment, it should be protected against moisture penetration and corrosion. 

A related preparation of specific stabilized phosphonium yUdes corresponds to the reaction of triarylphosphines with acetylene dicarboxylic esters in presence of fullerene, which affords a cyclopropanyl-fullerene substituted stabilized phosphonium ylide [9] or the corresponding evolution products [10]. 

Over the last decade, the chemistry of the carbon-carbon triple bond has experienced a vigorous resurgence [1]. Whereas construction of alkyne-con-taining systems had previously been a laborious process, the advent of new synthetic methodology based on organotransition metal complexes has revolutionized the field [2]. Specifically, palladium-catalyzed cross-coupling reactions between alkyne sp-carbon atoms and sp -carbon atoms of arenes and alkenes have allowed for rapid assembly of relatively complex structures [3]. In particular, the preparation of alkyne-rich macrocycles, the subject of this report, has benefited enormously from these recent advances. For the purpose of this review, we Emit the discussion to cychc systems which contain benzene and acetylene moieties only, henceforth referred to as phenylacetylene and phenyldiacetylene macrocycles (PAMs and PDMs, respectively). Not only have a wide... 

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