Pyrolysis 1-butene

Earlier workers have identified some of the products of 1-butene pyrolysis (3,4). In this work, several previously unreported products were found along with many of those previously noted. Acetylene was observed among the products from 1-butene as well as 2-butene in yields that paralleled the formation of ethylene. Yields varied from a trace at low temperatures to between 5%-10% of the total C2 product at the highest temperatures. Methylacetylene + propadiene (MAP) yield varied in a similar manner for 1-butene pyrolysis ranging between 2% and 20% of the C3 product. In 2-butene pyrolysis, the MAP yield comprised approximately 10% of the C3 product in all of the runs. 

Tabulations of yields of all identified products from runs in the 80-wt % conversion range are given in Tables III and IV for 1-butene and mixed 2-butene pyrolysis, respectively. These product distributions are typical of those observed in all of the high conversion runs. 

The rate of decomposition of 1-butene was found to be much faster than that of cis-2-butene. Pyrolysis of 1-butene was studied in the temperature range of 530 to 605 C, whereas the temperatures used for the pyrolysis of cis-2-butene were 575 to 620 C. As can be seen in Figure 1 and Tables I and II, the product distribution for these two pyrolyses were very different. Cracking is the main course of the reaction for 1-butene, but isomerization is the main result of cis-2-butene pyrolysis. 

Step 1 is for the initiation of cis-2-butene pyrolysis, step 2 for trans-2-butene, and steps 3 to 5 for 1-butene. Step 3 is known to be the principle initiation step for 1-butene (17). Step 4 is expected to have an activation energy of 12.5 kcal/mole higher than step 3, and step 5 is 20 kcal/mole higher than step 3. 

Most Important Elementary Steps for Cis-2-Butene Pyrolysis... 

Figure 3 shows the selectivity diagram for the major products from 1-butene pyrolysis. This shows that molecular hydrogen is not an initial product of decomposition. Initial products appear to be (in mol/100 mol) butadiene, 25 methane, 30 ethylene, 15 propylene, 40 C5 products, 10 and isomerization products as cis- and trans-2-butene, 25. 

For 1-butene pyrolysis, the calculated first-order rate constants decreased significantly with increasing conversion at each temperature. Reduction of the data by using the integrated form of the second-order rate law provided specific rate constants that were satisfactorily independent of conversion. 

Figures 7 and 8 show the Arrhenius plots for pyrolysis of 1-butene and 2-butene, respectively. An apparent activation energy of 57.2 kcal/ mol is indicated for 1-butene pyrolysis. This compares favorably with values reported by Kerr, Spencer, and Trotman-Dickenson (8) and by Shibatani (3) but differs from those reported by Molera and Stubbs (13), by Kunugi (12), by Sehon and Swarc (10), and by Bryce and Kebarle...

Figure 7. Temperature dependence of the rate for 1-butene pyrolysis...

Figure 6.1.22. Pyrogram of poly(propylene-co-1-butene) 14 % wt. butene. Pyrolysis done on 0.4 mg material at 60Cf C in He, with the separation on a Carbowax type column.

Investigation of pyrolysis of the butenes was chosen here as a complement to previous work in this laboratory on pyrolysis and partial oxidation of n-butane (1)(2)(3). Previous investigations of butene pyrolysis typically have employed static systems and/or high conversions (4)(5)(6)(7)(8)(9). 

The mechanism of butene pyrolysis is obviously more complex than the mechanism operative in butane pyrolysis. The complexity of butene pyrolysis is emphasized by the larger number of products and the larger nuinber of possible free radicals. 

An Important feature of butene pyrolysis Is the existence of free radicals with resonant stabilization energy. The allyl and the 2-butenyl (methylallyl) radicals are stabilized by the fact that they have delocalized electrons. Added stability of these free radicals Is about 10 to 13 kcal/mole (16), which significantly increases the rate of their production and decreases the rate of their consumption. 

The pattern of commercial production of 1,3-butadiene parallels the overall development of the petrochemical industry. Since its discovery via pyrolysis of various organic materials, butadiene has been manufactured from acetylene as weU as ethanol, both via butanediols (1,3- and 1,4-) as intermediates (see Acetylene-DERIVED chemicals). On a global basis, the importance of these processes has decreased substantially because of the increasing production of butadiene from petroleum sources. China and India stiU convert ethanol to butadiene using the two-step process while Poland and the former USSR use a one-step process (229,230). In the past butadiene also was produced by the dehydrogenation of / -butane and oxydehydrogenation of / -butenes. However, butadiene is now primarily produced as a by-product in the steam cracking of hydrocarbon streams to produce ethylene. Except under market dislocation situations, butadiene is almost exclusively manufactured by this process in the United States, Western Europe, and Japan. 

Because of the high pyrolysis temperature, the C4-fraction contains quantities of vinyl acetylene and ethyl acetylene, the removal of which prior to the recovery of butadiene is necessary in certain cases, particularly if butadiene of low acetylene content is desired. Similar considerations apply to effractions obtained by the dehydrogenation of n-butane and n-butenes. 

Sampling in inverse coannular diffusion flames [62] in which propene was the fuel has shown the presence of large quantities of allene. Schalla et al. [57] also have shown that propene is second to butene as the most prolific sooter of the n-olefins. Indeed, this result is consistent with the data for propene and allene in Ref. 72. Allene and its isomer methylacetylene exhibit what at first glance appears to be an unusually high tendency to soot. However, Wu and Kem [111] have shown that both pyrolyze relatively rapidly to form benzene. This pyrolysis step is represented as alternate route C in Fig. 8.23. 

The primary products obtained from 2-butanol are of mechanistic. significance and may be compared with other eliminations in the sec-butyl system 87). The direction of elimination does not follow the Hofmann rule 88) nor is it governed by statistical factors. The latter would predict 60% 1-butene and 40% 2-butene. The greater amount of 2-alkene and especially the unusual predominance of the cis-olefin over the trans isomer rules out a concerted cis elimination, in which steric factors invariably hinder the formation of cis-olefin. For example, the following ratios oicisjtrans 2-butene are obtained on pyrolysis of 2-butyl compounds acetate, 0.53 89, 90) xanthate, 0.45 (S7) and amine oxide, 0.57 86) whereas dehydration of 2-butanol over the alkali-free alumina (P) gave a cisjtrans ratio of 4.3 (Fig. 3). 

Neither the thermal nor the cobalt-catalyzed decomposition of 3-butene-2-hydroperoxide in benzene at 100 °C. produced any acetaldehyde or propionaldehyde. In the presence of a trace of sulfuric acid, a small amount of acetaldehyde along with a large number of other products were produced on mixing. Furthermore, on heating at 100°C., polymerization is apparently the major reaction no volatile products were detected, and only a slight increase in acetaldehyde was observed. Pyrolysis of a benzene or carbon tetrachloride solution at 200°C. in the injection block of the gas chromatograph gave no acetaldehyde or propionaldehyde, and none was detected in any experiments conducted in methanol. 

One synthetic route to the damascones starts with an appropriate cyclogeranic acid derivative (halide, ester, etc.). This is reacted with an allyl magnesium halide to give 2,6,6-trimethylcyclohexenyl diallyl carbinol, which on pyrolysis yields the desired l-(2,6,6-trimethylcyclohexenyl)-3-buten-l-one. Damascone is obtained by rearrangement of the double bond in the side-chain [98]. 

N 13 59% oxygen-rich monomer no props are reported except 1R spectrum was prepd by reaction of ethyl methyl ketone with formaldehyde, hydrogenation of the product with Gi chromite catalyst, acetylation to the triacetate, pyrolysis, deacerylation, and nitration of 3,3"bis(hydroxymethyl) -butene-1. The subject compd was synthesized as a binder constituent, which might be polymer-... 

Decreased deactivation efficiency may also account for changing product ratios, such as increased formation of 3-methylbutene-l. Although Frey found no 3-methylbutene-l in photolysis experiments without added argon, this product was reported by Setser and Rabinovitch in pyrolysis of CH2N2-butene-2 mixtures and is also found to some extent in the thermal decomposition of 1,2-dimethylcyclopropane. It appears, therefore, that the formation of 3-methylbutene-l depends more on reaction conditions than on the electronic state of CH2. 

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