Acetylene, absorption

Acetylene Recovery Process. A process to recover coproduct acetylene developed by Linde AG (Fig. 11), and reduced to practice in 11 commercial plants, comprises three sections acetylene absorption, ethylene stripper, and acetylene stripper. 

Fig. 11. Linde AG acetylene recovery unit for acetylene absorption, ethylene stripping, and acetylene stripping. CW = cooling water.

Acetylene Absorption. The gaseous feedstock containing the hydrocarbons is introduced into the acetylene absorption tower at a pressure... 

Other laboratories have used FTIR spectroscopy to determine the kinetics of reactions on different polymer supports39 and to enumerate factors regulating site interactions in different types of supports (see Chapter 7, p. 219).40 A major weak point of the procedure is the need for IR diagnostic functions or changes in hybridization to be involved in the transformation to be investigated. For phenylacetylene oligomers, however, the TMS and terminal acetylene absorptions are ideal. 

Acetylene. The existence of a continuum in the acetylene absorption spectrum suggests that dissociation occurs at 1849 A.lM... 

The liquid linear polymer 1 was found to readily convert into a thermoset under thermal conditions by the crosslinking of diacetylene units as observed by the disappearance of the acetylenic absorption at 2,175 cm and the appearance of a new, weak peak centered at 1,600 (C=C) cm indicative of a 1,4-addition reaction... 

Condensation of the phenylethynyl-tetraamine with m-bis (p -phenoxyphenylglyoxalyl)benzene in m-cresol, afforded prepolymer A. The prepolymer exhibited a Tg of 215 C by TMA and a strong DTA exotherm maximizing at 2 5°C. Thermal treatment of the prepolymer at 2U5°C overnight resulted in its conversion to the fused benzanthracene polymer B as evidenced by absence of the DTA exotherm and the acetylene absorption band in the infrared. Polymer B, after the 2 5 C cure, showed a Tg of 365 C which represents a 120 C advancement in Tg over the cure temperature. 

Vibrational spectroscopy has been, and will continue to be, one of the most important teclmiques in physical chemistry. In fact, the vibrational absorption of a single acetylene molecule on a Cu(lOO) surface was recently reported [ ]. Its endurance is due to the fact that it provides detailed infonnation on structure, dynamics and enviromnent. It is employed in a wide variety of circumstances, from routine analytical applications, to identifying novel (often transient) species, to providing some of the most important data for advancing the understanding of intramolecular and intemiolecular interactions. 

Bromine. Slip the glass cover of a jar momentarily aside, add 2-3 ml. of bromine water, replace the cover and shake the contents of the jar vigorously. Note that the bromine is absorbed only very slowly, in marked contrast to the rapid absorption by ethylene. This slow reaction with bromine water is also in marked contrast to the action of chlorine water, which unites with acetylene with explosive violence. (Therefore do not attempt this test with chlorine or chlorine water.)... 

Conjugation with olefinic or acetylenic groups lowers the frequency and raises the intensity. Conjugation with carbonyl groups usually has little effect on the position of absorption. 

Description of Method. Copper and zinc are isolated by digesting tissue samples after extracting any fatty tissue. The concentration of copper and zinc in the supernatant are determined by atomic absorption using an air-acetylene flame. 

M HNO3. The concentration of Cu and Zn in the diluted supernatant is determined by atomic absorption spectroscopy using an air-acetylene flame and external standards. Copper is analyzed at a wavelength of 324.8 nm with a slit width of 0.5 nm, and zinc is analyzed at 213.9 nm with a slit width of 1.0 nm. Background correction is used for zinc. Results are reported as micrograms of Cu or Zn per gram of FFDT. 

Similarly, the acetylenic group, —C=C—, shows an intense absorption system at about... 

Another use is in various extraction and absorption processes for the purification of acetylene or butadiene and for separation of aHphatic hydrocarbons, which have limited solubiHty in DMF, from aromatic hydrocarbons. DMF has also been used to recover CO2 from flue gases. Because of the high solubiHty of SO2 iu DMF, this method can even be used for exhaust streams from processes using high sulfur fuels. The CO2 is not contaminated with sulfur-containing impurities, which are recovered from the DMF in a separate step (29). 

Acetylene can be deterrnined volumetricaHy by absorption in Aiming sulfuric acid (or more conveniently in sulfuric acid activated with silver sulfate) or by reaction with silver nitrate in solution and titration of the nitric acid formed ... 

The BASF process uses /V-methy1pyrro1idinone as the solvent to purify acetylene in the cracked gas effluent. Alow pressure prescmbbing is used to remove naphthalenes and higher acetylenes. The cracked gas is then compressed to 1 MPa (10 atm) and fed to the main absorption tower for acetylene removal. Light gases are removed from the top of this tower. 

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. 

Most by-product acetylene from ethylene production is hydrogenated to ethylene in the course of separation and purification of ethylene. In this process, however, acetylene can be recovered economically by solvent absorption instead of hydrogenation. Commercial recovery processes based on acetone, dimetbylform amide, or /V-metby1pyrro1idinone have a long history of successfiil operation. The difficulty in using this relatively low cost acetylene is that each 450, 000 t/yr world-scale ethylene plant only produces from 7000 9000 t/yr of acetylene. This is a small volume for an economically scaled derivatives unit. 

Quantitative aluminum deterrninations in aluminum and aluminum base alloys is rarely done. The aluminum content is generally inferred as the balance after determining alloying additions and tramp elements. When aluminum is present as an alloying component in alternative alloy systems it is commonly deterrnined by some form of spectroscopy (qv) spark source emission, x-ray fluorescence, plasma emission (both inductively coupled and d-c plasmas), or atomic absorption using a nitrous oxide acetylene flame. 

Atomic absorption spectroscopy is more suited to samples where the number of metals is small, because it is essentially a single-element technique. The conventional air—acetylene flame is used for most metals however, elements that form refractory compounds, eg, Al, Si, V, etc, require the hotter nitrous oxide—acetylene flame. The use of a graphite furnace provides detection limits much lower than either of the flames. A cold-vapor-generation technique combined with atomic absorption is considered the most suitable method for mercury analysis (34). 

Atomic absorption spectroscopy is an alternative to the colorimetric method. Arsine is stiU generated but is purged into a heated open-end tube furnace or an argon—hydrogen flame for atomi2ation of the arsenic and measurement. Arsenic can also be measured by direct sample injection into the graphite furnace. The detection limit with the air—acetylene flame is too high to be useful for most water analysis. 

Acetylene black is very pure with a carbon content of 99.7%. It has a surface area of about 65 m /g, an average particle diameter of 40 nm, and a very high but rather weak stmcture with a DBPA value of 250 mL/100 g. It is the most crystalline or graphitic of the commercial blacks. These unique features result in high electrical and thermal conductivity, low moisture absorption, and high Hquid absorption. 

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. 

Endo 3a,4,S,6,7,7a-Hexahydro-4,7-methano-2-lndene-l-one (2). A solution ol octacaibonyidcobalt (1.0 g, 3 mmol) and bicycio [2 2.1) hepi-2-ene 1 (3.0 g, 32 mmol) in Isooctane (100 mL) was stirred first with acetylene and then under a mixture of 1.1 of acetylene and carbon monoxyde at 60-70°C until gas absorption ceased (total 1550 mL). The mixture was concentrated and the residue chromatographed on neutral alumina. Petroleum ether PhH (1 1) eluted acetylene hexacaibonyl dicobalt 70 mg, PhH CHCla (1.1) eluted a yellow oil which after distillation afforded 3 54 g of 2 (74%), bp 101-102°C (15 mm) Colorless crystals from pentane, mp32°C. 

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