Styrene from pyrolysis

STEX [Styrene extraction] A process for extracting styrene from pyrolysis gasoline. Developed by Toray. 

Sato, M., Extract styrene from pyrolysis gasoline . Hydrocarbon Processing, 52 (51 141-144 (1973). Morimoto, H., Tatsumi, M., Tbe Stex process. Extraction of styrene from pyrolysis gasoline Bull, of Japan FePtdeiim IRSL, 16 ( ) 38-42 (1974). 

All the styrene monomer (bpi.ou = 145-2°C, propylene oxide Some attempts have been made to extract styrene from pyrolysis Cj- gasolines (Stex process by Toray, described in Section 4.2.5), but they have not culminated in commercial plants. 

STEX [Siyrene Extraction] A process for extracting styrene from pyrolysis gasoline. Developed by Toray. Chem. Eng. News, 27 Aug 2001,79(35), 28-30. 

The p -substituted phenylcarbenes p-Me3MC6H4CH (M=Si, Ge, Sn) all give the substituted indane and styrene on pyrolysis, through isomerization to the ortho-substituted carbene (Scheme 3). The indane forms as more than 85% of the products for M = Si and Ge with styrene 5% at 400-500 °C, but only as half of the products of the decomposition for M = Sn, with about 25% styrene. This is formed exclusively at higher temperatures, but probably from the indane decomposing and not the stannirane (Scheme 4) (78TL5193). 

The SIMS spectrum of a 0.5 mm thick film of polystyrene cast on silver is shown in Figure 8. The characteristic ions, phenyl-type (m/z 77, 78, 79), benzyl (m/z 91), and protonated styrene (m/z 105) along with higher m/z ions resembling those from pyrolysis studies, are observed. 

Other methods, such as the direct reaction of benzene and ethylene (Fig. 2) or from pyrolysis gasoline (Fig. 3) are also used to manufacture styrene. 

Application To directly recover styrene from raw pyrolysis gasoline derived from steam cracking of naphtha, gas oils and NGLs using the GT-Styrene process. 

The extractive-distillation column overhead can be further processed to recover a high-quality mixed xylene stream. A typical world-scale cracker could produce approximately 25,000 tpy styrene and 75,000 tpy mixed xylenes from pyrolysis gasoline. 

Pyrolysis gas chromatography can be used to determine the acrylonitrile content of the SAN copolymer [7-9]. It is a method that heats the polymer above the decomposition temperature, then separates and identifies the low molecular weight compounds formed. The primary decomposition products are styrene, acrylonitrile, and propionitrile, and the styrene content of the copolymer is directly proportional to the styrene yield from pyrolysis [8]. 

Other main liquid components are dimeric, trimeric, and other oligomeric styrene components. The content reaches 14 wt% of these oligomers. Other components formed by the pyrolysis of polystyrene are toluene, a-methylstyrene, diphenylethane/propane, and other aromatics. The styrene oligomers show secondary isomerization reactions. These make it difficult to pyrolyze them in a following step into higher amounts of styrene. Mainly, other aromatics are obtained by the degradation of the styrene oligomers. This means that the optimum recovery of styrene from PS is about 77 wt% in an uncatalyzed fluidized-bed process. 

One of these studies evaluates the sequence distribution of dyads in styrene-m-chlorostyrene copolymer and in styrene-p-chlorostyrene copolymer [17]. The results are obtained using data from pyrolysis performed at 550° C and FID detection. In a similar study, the sequence distribution of dyads was evaluated for poly(acrylonitrile-co-m-chlorostyrene) and for poly(acrylonitrile-co-p-chlorostyrene) [18] (see also Section 4.3). 

Thermal cracking of ethane, propane, butane, naphthas, gas oils, and/or vacuum gas oils is the main process employed for the production of ethylene and propylene butadiene and benzene, toluene, and xylenes (BTX) are also produced. Thermal cracking of these hydrocarbons is also called pyrolysis of hydrocarbons. Ethylene is the organic chemical produced worldwide in the largest amoimts and has been called keystone to the petrochemical industry. This technology is well documented in the literature. Somewhat similar thermal cracking processes are used to produce vinyl chloride monomer (VCM) from ethylene dichloride (EDQ, styrene from ethylbenzene, and allyl chloride from propylene dichloride (PDC). Production of charcoal and coke from wood and coal is actually a pyrolysis process, but it is not discussed here. 

The BTX fraction shows a similar variability arising from pyrolysis severity and feedstock (Table III). In general, the aromatic content ranges upwards of 50% and may reach nearly 100% in high severity operation. BTX ratios vary widely, depending on feedstock. LPG-type feeds yield benzene predominantly among the aromatics, while the heavier feeds show increased yields of toluene and C8 aromatics. In all cases benzene appears to be synthesized predominantly from paraffin or naphthene chain fragments by condensation reactions. Toluene and the C8 aromatics appear to derive principally from aromatics in the feed with some pyrolytic side-chain dealkylation. In all cases styrene predominates in the C8 fraction (7). 

Application GT-Styrene is an extractive distillation process that directly recovers styrene from the raw pyrolysis gasoline derived from the steam cracking of naphtha, gasoils and natural gas liquids (NGLs). The produced styrene is high purity and suitable for polymerization at a very attractive cost compared to conventional styrene production routes. The process is economically attractive for pygas feeds containing more than 15,000 tpy of styrene. 

Description Raw pyrolysis gasoline is prefractionated into a heartcut Cg stream. The resulting styrene concentrate is fed to an extractive distillation column and mixed with a selective solvent, which extracts the styrene to the tower bottoms. The rich solvent mixture is routed to a solvent recovery column, which recycles the lean solvent back to the extractive distillation column and recovers the styrene overhead. A final purification step produces a 99.9% styrene product containing less than 50 ppm phenyl acetylene. The extractive distillation column overhead can be further processed to recover a high-quality mixed-xylene stream. A typical world-scale cracker can produce approximately 25,000 tpy of styrene and 75,000 tpy of mixed xylenes from pyrolysis gasoline. 

GTC Technology Styrene Pygas Cg cut Extractive distillation process that directly recovers styrene from the raw pyrolysis gasoline derived from the steam cracking of naphtha, gasoils and NGL 3 2009... 

Py-FIMS spectra of polystyrenes, from Ref. 30. (a) ordinary polystyrene, (b) poly(st)frene-b-styrene-dg). Pyrolysis heating rate 50 to 700°C at 1.2°C/sec. Sample size ca. 0.05 mg. 

FIGURE 1.16 Pyrolysis of pharmaceutical showing trace amounts of styrene from polystyrene. 

The commercial production of styrene nowadays is carried out almost exclusively by catalytic dehydrogenation of ethylbenzene. Toray has developed a process for recovery from pyrolysis gasoline, which contains 3 to 5% styrene. The method involves hydrogenation of the aliphatic diene components of a close-cut pyrolysis gasoline (130 to 140 °C) followed by extractive distillation with dimethyl-acetamide. 

Wang and Smith [46] applied Py-GC to determine the composition and microstructure of styrene-methylmethacrylate (MMA) copolymers. The composition of these copolymers was quantified by monomer peak intensities obtained from pyrolysis. Because of the poor stability of MMA oligomers, neither MMA dimers nor trimers... 

C, and styrene production was also more by 11 wt% in the case of waste expanded polystyrene. Oil yield increased from 24 to 98 wt% with increase in reaction temperature from 350 to 480 °C, while styrene selectivity, which was about 76 wt% up to 450 °C, decreased sharply to 49 wt% at 480 °C. This decrease in styrene selectivity takes place with increase in styrene dimer formation from 4 to 10 wt% and production of other chemicals. Also the production of toluene, ethylbenzene and methylstyrene decreased with the same rise in pyrolysis temperature. Thermal degradation of PS was reported to have started with random initiation to form polymer radicals, the main products being styrene and its corresponding dimers and trimers. These results were comparable with studies reported elsewhere on oil yield of 99 wt% with 60 wt% styrene monomer and 25 wt% for other aromatics. Another work has reported on recovery of 58 wt% styrene from thermal degradation of PS at 350 °C after a time of 60 min [a.379]. Furthermore, oil yields of 82 wt% with 70 wt% styrene selectivity and 77 wt% styrene recovery at 580 °C have been reported [a.380]. 

Figure 12.8 Mia ocolumn size exclusion chromatogram of a styrene-aaylonitrile copolymer sample fractions ti ansfeired to the pyrolysis system are indicated 1-6. Conditions fused-silica column (50 cm X 250 p.m i.d.) packed with Zorbax PSM-1000 (7p.m 4f) eluent, THF flow rate, 2.0 p.L/min detector, Jasco Uvidec V at 220 nm injection size, 20 nL. Reprinted from Analytical Chemistry, 61, H. J. Cortes et al, Multidimensional chromatography using on-line microcolumn liquid chromatography and pyrolysis gas chromatography for polymer characterization , pp. 961 -965, copyright 1989, with peimission from the American Chemical Society.

Figure 12.9 Typical pyrolysis chromatogram of fraction from a styrene-acTylonitiile copolymer sample obtained from a miciocolumn SEC system 1, acrylonitrile 2, styrene. Conditions 5 % Phenylmetliylsilicone (0.33 p.m df) column (50 m X 0.2 mm i.d.) oven temperature, 50 to 240 °C at 10 °C/min carrier, gas, helium at 60 cm/s flame-ionization detection at 320 °C make-up gas, nitrogen at a rate of 20 mL/min. P indicates tlie point at which pyrolysis was made. Reprinted from Analytical Chemistry, 61, H. J. Cortes et ai, Multidimensional cliromatography using on-line microcolumn liquid cliromatography and pyrolysis gas cliromatography for polymer characterization , pp. 961-965, copyright 1989, with permission from tlie American Chemical Society.

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