Pitch ethylene tar

An important clue to the relevance of radical chemistry prior to mesophase formation comes from the study of Singer and Lewis (51) who observed that, in the carbonization of ethylene tar pitch (which leads to a smaller size of optical texture in resultant coke), both the concentration and rate of build-up of radicals are larger than for a petroleum-derived pitch. As discussed below, lower concentrations of radicals lead to larger sized optical textures. The relationships between transient and stable radicals have yet to be established. 

Miyazawa et al. (92) related rates of decrease of aliphatic hydrogen protons during pyrolysis of ethylene tar pitch to formation of mesophase. Yokono et al, (93) used the model compound anthracene to monitor the availability of transferable hydrogen. Co-carboniza-tions of pitches with anthracene suggested that extents of formation of 9,10-dihydroanthracene could be correlated with size of optical texture. The method was then applied to the carbonization behaviour of hydrogenated ethylene tar pitch (94). This pitch, hydrogenated at 573 K, had a pronounced proton donor ability and produced, on carbonization, a coke of flow-type anisotropy compared with the coarse-grained mosaics (<10 ym dia) of coke from untreated pitch. 

Figure 4 shows the relation between the Tj of ethylene tar pitch and the inverse of temperature. The Tj of ethylene tar pitch has the value of 400 msec at room temperature. It decreases with increasing temperature, and reaches its minimum value at about 420 K. As is shown in the figure, it has its maximum value of 190 msec at about 600 K, and the value decreases rapidly with increasing temperature. 

Resolved NMR Spectra and Hydrogen Aromaticity. Typical spectra for ethylene tar pitch are shown in Figure 5. On heating up to about 357 K, a broad resonance with no resolved structure becomes observable. At about 396 K the NMR spectrum shows two discrete lines, 200 Hz apart, which correspond to aromatic and aliphatic protons. 

Figure 4. Temperature dependence of proton spin-lattice relaxation time(Ti) of ethylene tar pitch during heating at 2 K-min ...

Figure 6 shows the relation between of ethylene tar pitch and the elevating temperature with the range of 1 K/min. It is clear that increases drastically after the temperature exceeds about 593 K. Hence Tq and to in Equation 4 can be taken as 593 K and 300 min, respectively. Based on Equation 6, observed values of In [(1 - /jjJ (df Jdt)] for ethylene tar pitch were plotted against t - to). A typical example of the results is shown in Figure 7, with q 4.17 x 10 K min, which corresponds to the heating rate of about 1 K/min. As expected, a... 

Figure 6. Temperature dependence of hydrogen aromaticity (fa J for ethylene tar pitch (heating rate is 1 K min )...

After the measurement of the NMR spectra of Kureha pitch at 723 K and ethylene tar pitch at 743 K, the samples were immediately quenched to room temperature and observed by polarized-light microscopy. It was confirmed that the bulk mesophase was produced. 

Figure 9. A NMR spectrum (a) from ethylene tar pitch at 743 K during heating at 1 K min and (h) a comparison of the experimentally observed spectrum with a computer-simulated spectrum (1) total simulated curve (2) Gaussian component with T2 = 30 Lsec (3) Gaussian component with T2 = 70 p ec (4) Lorentzian component with T2 = 260 pLsec and (5) Lorentzian component with T2 = 970 pisec.

Generally the sweep width of broad-line NMR is about 10 to 10 Hz, while that of high-resolution NMR is about 10 Hz at 36.4 MHz for a proton. But the H NMR spectra of the mesophase for Kureha pitch (Figure 8) and ethylene tar pitch (Figure 9) were swept over 2.5 x 10" Hz. Thus the sweep width of the H NMR spectrum for the carbonaceous mesophase is intermediate between those of broad-line H NMR... 

By means of computer simulation we found that the NMR lines for the mesophase include several components. The results with computer simulation are summarized in Table III. From the viev oint of general NMR behavior (20), Kureha pitch and ethylene tar pitch at the early stages of carbonization contain about 85% and 68% rigid structures, respectively. 

Use Coumarone resins solvent for asphalts, road tars, pitches, etc. cleansing compositions process engraving and lithography rubber cements (solvent) naphtha soaps manufacture of ethylene and acetic acid. 

Cracking of crude oil in the presence of steam superheated to 2000°C. with the formation, in addition to acetylene and ethylene, of various co-products (fuel gas, propylene, benzene, naphthalene, tars, pitches, etc.). This operation is followed by quenching and primary fractionation. 

The purpose of this subpart is to protect employees from exposure to toxic and hazardous substances in the workplace. It covers the Permissible Exposure Limits (PEL) for all air contaminants including all gases, vapors, and dusts. Some of the contaminants covered underthis subpart include asbestos, coal tar pitch volatiles, vinyl chloride, inorganic arsenic, lead, cadmium, benzene, coke-oven emissions, bloodborne pathogens, cotton dust, ethylene oxide, and formaldehyde. 

The unit Kureha operated at Nakoso to process 120,000 metric tons per year of naphtha produces a mix of acetylene and ethylene at a 1 1 ratio. Kureha s development work was directed toward producing ethylene from cmde oil. Their work showed that at extreme operating conditions, 2000°C and short residence time, appreciable acetylene production was possible. In the process, cmde oil or naphtha is sprayed with superheated steam into the specially designed reactor. The steam is superheated to 2000°C in refractory lined, pebble bed regenerative-type heaters. A pair of the heaters are used with countercurrent flows of combustion gas and steam to alternately heat the refractory and produce the superheated steam. In addition to the acetylene and ethylene products, the process produces a variety of by-products including pitch, tars, and oils rich in naphthalene. One of the important attributes of this type of reactor is its abiUty to produce variable quantities of ethylene as a coproduct by dropping the reaction temperature (20—22). 

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