Severity Ethylene/Propylene Yield

Significant products from a typical steam cracker are ethylene, propylene, butadiene, and pyrolysis gasoline. Typical wt % yields for butylenes from a steam cracker for different feedstocks are ethane, 0.3 propane, 1.2 50% ethane/50% propane mixture, 0.8 butane, 2.8 hill-range naphtha, 7.3 light gas oil, 4.3. A typical steam cracking plant cracks a mixture of feedstocks that results in butylenes yields of about 1% to 4%. These yields can be increased by almost 50% if cracking severity is lowered to maximize propylene production instead of ethylene. 

Table 6 shows the effect of varying coil oudet pressure and steam-to-oil ratio for a typical naphtha feed on the product distribution. Although in these tables, the severity is defined as maximum, in a reaUstic sense they are not maximum. It is theoretically possible that one can further increase the severity and thus increase the ethylene yield. Based on experience, however, increasing the severity above these practical values produces significantly more fuel oil and methane with a severe reduction in propylene yield. The mn length of the heater is also significantly reduced. Therefore, this is an arbitrary maximum, and if economic conditions justify, one can operate the commercial coils above the so-called maximum severity. However, after a certain severity level, the ethylene yield drops further, and it is not advisable to operate near or beyond this point because of extremely severe coking. 

The reaction of toluene with propylene and higher olefins is similar to that of toluene with ethylene. In contrast to the acid-catalyzed alkylation of aromatics, the base-catalyzed reaction of toluene with propylene takes place less rapidly than the reaction with ethylene. With more severe conditions, such as temperatures of 225-250°, the reaction of toluene with propylene may be made to proceed satisfactorily, but butylenes yield only small amounts of products even at 300°, as reported by Pines and Mark 20). Such conditions result not only in more hydrogen transfer, but alkyl-group... 

Styrene, one of the world s major organic chemicals, is derived from ethylene via ethylbenzene. Several recent developments have occurred with respect to this use for ethylene. One is the production of styrene as a co-product of the propylene oxide process developed by Halcon International (12). In this process, benzene is alkylated with ethylene to ethylbenzene, and the latter is oxidized to ethylbenzene hydroperoxide. This hydroperoxide, in the presence of suitable catalysts, can convert a broad range of olefins to their corresponding oxirane compounds, of which propylene oxide presently has the greatest industrial importance. The ethylbenzene hydroperoxide is converted simultaneously to methylphenyl-carbinol which, upon dehydration, yields styrene. Commercial application of this new development in the use of ethylene will be demonstrated in a plant in Spain in the near future. 

Reactions of the recoil C1] with several olefins have been studied, including ethylene, propylene, cyclopentene, and cfs-butene-2, as well as with several paraffins. The type of products observed indicated the existence of several general modes of interaction, such as CH bond insertion, interactions with CC double bonds, formation of methylene-C11. The most important single product in all systems is acetylene, presumably formed by CH insertion and subsequent decomposition of the intermediate. Direct interaction with double bonds is shown by the fact that, for example, in the case of propylene, yields of stable carbon atom addition products were significantly higher than in the case of propane. The same was true for ethylene and ethane. 

As illustrated in Fig. 24, the addition of ethylene during the living polymerization of propylene resulted in rapid increases in both yield and Mn of the polymers. After the rapid increases which required several minutes, yield and lVln increased by a slower rate, identical with that of the propylene homopolymerization. The propylene content in the resulting polymers attained a minimum value several minutes after the addition of ethylene. These results indicate that the second stage of the polymerization with ethylene was complete within several minutes to afford a diblock copolymer, followed by the third stage of propylene homopolymerization leading to the formation of a triblock copolymer. The 13C NMR spectra of the diblock copolymers showed that the second block was composed of an ethylene-propylene random copolymer sequence. 

Again the production cost is sensitive to the relative price of propylene and ethylene which is illustrated in Figure 9.13. One of the features of heavy oil cracking is the high propylene yield at low severity. This serves to further reduce ethylene production cost as the relative value of propylene rises. 

Williams and Williams27 have studied the pyrolysis of both HDPE and LDPE in a fixed bed reactor. In each experiment the temperature was varied between 25 and 700 °C. The products were swept down through the bottom of the reactor by a nitrogen flow and separated into several fractions by condensation at different temperatures. Two main fractions were recovered as products from the HDPE and LDPE pyrolysis gases with a yield of 15-17 wt% and oils with yields in the range 80-84 wt%. The gases were rich in ethylene, propylene and butene, with lower proportions of saturated hydrocarbons (methane, ethane, propane and butane). The oils produced were analysed by FTIR and GPC,... 

To relate these ethylene statistics to propylene, consider the position of the older and therefore smaller ethylene producer. As his commitments for ethylene grow, with a fixed capacity unit he has no choice but to shift from propane to ethane feed or to operate at higher and higher severity with a heavier stock. All things being equal, this reduces propylene yield for either a given unit or for a given feedstock but does increase ethylene production by at least 10% in a plant. 

Table III also shows how propylene yield is reduced if ethylene production of a furnace is maximized by increasing severity for a given stock. Examples chosen are n-butane, straight run distillate, and gas oil.

Consider what has happened—we must have just gone from famine to feast in propylene. An over-capacity unit can operate at low severity to optimize propylene yield. Eventually, the new unit will operate at high severity, and then the old unit can be returned to operation. However, by-product demand is such that it is not unreasonable to contemplate the possibility of adapting in the interim some older units to n-butane feed. n-Butane is presently in oversupply (15), and more propylene can be made from it than from propane (see Table III). Table V presents data of Freiling et al. (22) for various feed stock requirements and by-product productions per pound of ethylene. If any existing ethylene units are not retired but are switched from ethane or propane to n-butane feed, one can immediately prorate feed rates and... 

Table 2.2 lists the pyrolysis product yields for different feedstocks treated at very high severity with recycle of the ethane produced or unconverted at the inlet of the reaction section. Indeed, ethane is an ideal raw material for the formation of the lower olefins. It may be observed that the relative production of ethylene decreases as the feedstock becomes heavier. Also worth noting is that the ratio of the ethylene and propylene yields (C2J CJ ratio) decreases steadily from ethane to the gas oils, whereas the percentage of pyrolysis gasoline (CS-20G°C cut) increases simultaneously. As to the butadiene yield, this varies slightly with the type of feedstock in the treatment of liquid petroleum fractions. 

Figure 1. Each sloped line represents the loci of all possible combinations of average residence times and hydrocarbon partial pressures which are consistent with a fixed pyrolysis yield pattern, i.e., constant pyrolysis selectivity lines. For liquid feedstocks, the methane-to-ethylene ratio found in the pyrolysis reactor effluent has been used as a good overall indicator of pyrolysis reactor selectivity. Low methane-to-ethylene ratios correspond to a high total yield of ethylene, propylene, butadiene and butylenes. Consequently, the yields of methane, ethane, aromatics and fuel oil are reduced. TL refore, each constant pyrolysis selectivity line shown in Figure 1 is identified with a fixed methane-to-ethylene ratio. This specific selectivity chart applies to a Kuwait heavy naphtha which is pyrolyzed to achieve a constant degree of feedstock dehydrogenation, i.e., a constant hydrogen content in the effluent liquid products, which in this case corresponds to the limiting cracking severity.

If we fix, for example, the ethylene/propylene ratio, however, we fix severity and - as with conventional cracking - the other product yields from a given feedstock are now determined. Exceptions to this are minor dependencies - especially of acetylene - on the partial pressure variables. 

Numerous organic reactions of sulfur monochloride are of practical and commercial importance. Of particular importance is the reaction of sulfur monochloride with olefins to yield various types of addition products (142). With ethylene, the severe vesicant bis(2-chloroethyl) sulfide [505-60-2] (mustard gas) forms with elemental sulfur and polysulfides (see Chemicals IN war). Propylene reacts similarly ... 

Polypyrocatechin borate has a higher inhibitive efficiency relative to the reactions of the radical R2 than to that of the radical Ri, since the latter exerts a more severe decrease in the yield of propane and propylene than in the yield of ethane and ethylene, and favors an insignificant growth of polyethylene nonsaturation in the pro-... 

Deep catalytic cracking (DCC) is a catalytic cracking process which selectively cracks a wide variety of feedstocks into light olefins. The reactor and the regenerator systems are similar to FCC. However, innovation in the catalyst development, severity, and process variable selection enables DCC to produce more olefins than FCC. In this mode of operation, propylene plus ethylene yields could reach over 25%. In addition, a high yield of amylenes (C5 olefins) is possible. Figure 3-7 shows the DCC process and Table 3-10 compares olefins produced from DCC and FCC processes. ... 

Propane cracking is similar to ethane except for the furnace temperature, which is relatively lower (longer chain hydrocarbons crack easier). However, more by-products are formed than with ethane, and the separation section is more complex. Propane gives lower ethylene yield, higher propylene and butadiene yields, and significantly more aromatic pyrolysis gasoline. Residual gas (mainly H2 and methane) is about two and half times that produced when ethane is used. Increasing the severity... 

A scandium complex, Cp ScH, also polymerizes ethylene, but does not polymerize propylene and isobutene [125]. On the other hand, a linked amidocyclo-pentadienyl complex [ Me2Si( / 5-C5 Me4)( /1 -NCMe3) Sc(H)(PMe3)] 2 slowly polymerizes propylene, 1-butene, and 1-pentene to yield atactic polymers with low molecular weight (Mn = 3000-7000) [126, 115]. A chiral, C2-symmetric ansa-metallocene complex of yttrium, [rac-Me2Si(C5H2SiMe3-2-Buf-4)2YH]2, polymerizes propylene, 1-butene, 1-pentene, and 1-hexene slowly over a period of several days at 25°C to afford isotactic polymers with modest molecular weight [114]. 

Meriting special comment on account of certain recent findings is the reagent o-aminothiophenol. This substance was reported, first in J 949 and again on several subsequent occasions,2 Bl B to yield 3.3-dihydrophenothiazine on condensation with ethylene oxide in base, Mid the corresponding substituted 2,3-dihydrophenothiazines with propylene oxide, cyclohexene oxide, and styrene oxido respectively. It Las now been established, however, in three laboratories,5 M that previous reports were in error. The products formed are in fact normal open-chain adducts, aa shown in Eqa. (670)-<672). Styrene... 

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