Propane from pyrolysis

As further comparison of propane and ethane pyrolyses, four different mixtures of propane and ethane were pyrolyzed In the Incoloy reactor employing a 800°C bath temperature and one atmosphere total pressure. These mixtures had propane-to-ethane ratios of 0.04 1, 0.29 1, 1 1, and 2.97 1 the last three mixtures were premixed with steam on a 1 1 basis. In estimating the conversions of both propane and ethane during pyrolysis of the mixture. It was assumed that no propane was formed as a result of the pyrolysis of ethane and that no ethane was formed from pyrolysis of propane these two assumptions are certainly not quite accurate since small amounts of both ethane and propane were formed during the pyrolysis of the pure paraffins. 

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. 

Of the many forms of carbon and graphite produced commercially, only pyrolytic graphite (8,9) is produced from the gas phase via the pyrolysis of hydrocarbons. The process for making pyrolytic graphite is referred to as the chemical vapor deposition (CVD) process. Deposition occurs on some suitable substrate, usually graphite, that is heated at high temperatures, usually in excess of 1000°C, in the presence of a hydrocarbon, eg, methane, propane, acetjiene, or benzene. 

Acetonitrile oxide was generated from 3,4-dimethylfuroxan oxide by flash vacuum pyrolysis and trapped at -40 °C where its and NMR spectra were examined. Warming to room temperature in the presence of propane produced 3,5-dimethyl-2-isoxazoline (Scheme 108) (79TL2443). The oxide could also be generated by photolysis of furoxan (68CC977). 

Methylsuccinic acid has been prepared by the pyrolysis of tartaric acid from 1,2-dibromopropane or allyl halides by the action of potassium cyanide followed by hydrolysis by reduction of itaconic, citraconic, and mesaconic acids by hydrolysis of ketovalerolactonecarboxylic acid by decarboxylation of 1,1,2-propane tricarboxylic acid by oxidation of /3-methylcyclo-hexanone by fusion of gamboge with alkali by hydrog. nation and condensation of sodium lactate over nickel oxide from acetoacetic ester by successive alkylation with a methyl halide and a monohaloacetic ester by hydrolysis of oi-methyl-o -oxalosuccinic ester or a-methyl-a -acetosuccinic ester by action of hot, concentrated potassium hydroxide upon methyl-succinaldehyde dioxime from the ammonium salt of a-methyl-butyric acid by oxidation with. hydrogen peroxide from /9-methyllevulinic acid by oxidation with dilute nitric acid or hypobromite from /J-methyladipic acid and from the decomposition products of glyceric acid and pyruvic acid. The method described above is a modification of that of Higginbotham and Lapworth. ... 

Chemical vapor deposition (CVD) of carbon from propane is the main reaction in the fabrication of the C/C composites [1,2] and the C-SiC functionally graded material [3,4,5]. The carbon deposition rate from propane is high compared with those from other aliphatic hydrocarbons [4]. Propane is rapidly decomposed in the gas phase and various hydrocarbons are formed independently of the film growth in the CVD reactor. The propane concentration distribution is determined by the gas-phase kinetics. The gas-phase reaction model, in addition to the film growth reaction model, is required for the numerical simulation of the CVD reactor for designing and controlling purposes. Therefore, a compact gas-phase reaction model is preferred. The authors proposed the procedure to reduce an elementary reaction model consisting of hundreds of reactions to a compact model objectively [6]. In this study, the procedure is applied to propane pyrolysis for carbon CVD and a compact gas-phase reaction model is built by the proposed procedure and the kinetic parameters are determined from the experimental results. 

Experiments of propane pyrolysis were carried out using a thin tubular CVD reactor as shown in Fig. 1 [4]. The inner diameter and heating length of the tube were 4.8 mm and 30 cm, respectively. Temperature was around 1000°C. Propane pressure was 0.1-6.7 kPa. Total pressure was 6.7 kPa. Helium was used as carrier gas. The product gas was analyzed by gas chromatography and the carbon deposition rate was calculated from the film thickness measured by electron microscopy. The effects of the residence time and the temperature... 

Product distribution for propane pyrolysis. [From Schutt, Chemical Engineering Progress, 50 (415), 1954. Used with permission.]... 

Table 8.1 shows the stochastic model solution for the petrochemical system. The solution indicated the selection of 22 processes with a slightly different configuration and production capacities from the deterministic case, Table 4.2 in Chapter 4. For example, acetic acid was produced by direct oxidation of n-butylenes instead of the air oxidation of acetaldehyde. Furthermore, ethylene was produced by pyrolysis of ethane instead of steam cracking of ethane-propane (50-50 wt%). These changes, as well as the different production capacities obtained, illustrate the effect of the uncertainty in process yield, raw material and product prices, and lower product... 

Above 300°C. the effective reaction of an alkyl radical with oxygen may be Reaction 3 rather than 2 because of the reversibility of Reaction 2. If it is assumed that Reaction 3 is important at about 450°C., its rate can be estimated from the competition between pyrolysis and oxidation of alkyl radicals. Falconer and Knox (21) observed that the ratio of (pro-pene)/(ethylene) from the oxidation of propane between 435° and 475°C. increased with oxygen concentration and decreased with temperature—the apparent activation energy difference for the two reactions forming the olefins being 27 =t 5 kcal. per mole. They interpreted this result in terms of a competition between Reactions 1 and 3. The observed ratio (propene)/(ethylene) was 3.5 at 435°C. and 10 mm. of Hg pressure. If log ki(propyl) = 13.2 — 30,000/2.30RT, the value for the n-propyl radical (34), then log k3 = 8.0. If the A factor is 109-3, we derive the Arrhenius equation... 

The U.S. ethylene industry has been based primarily on the cracking of ethane and propane derived from natural gas. The quantities and liquid contents of U.S. natural gases have been such as to permit substantial quantities of these light hydrocarbons to be recovered for use as economically attractive ethylene feedstocks. In Europe and Japan, however, naphthas have been generally the available and preferred feeds to pyrolysis. 

United States. The U.S. ethylene industry has been based mainly on pyrolysis of light hydrocarbons, predominately ethane and propane recovered from natural gas. Essentially all the ethane recovered is used as pyrolysis feed, whereas only about one quarter of the propane is used for this purpose. The remainder is mostly consumed in the LPG market. 

CARBENE. The name quite generally used for the methylene radical, CH,. It is formed during a number of reactions. Thus the flash photochemical decomposition of ketene (CH2=C=0) has been shown to proceed in two stages. The first yields carbon monoxide and CHj. the latter then reacting with more ketene to form ethylene and carbon monoxide. Carbcne reacts by insertion into a C- H bond to form a C-CH, bond. Thus carbene generated from ketene reacts with propane to form, i-butane and isobutane. Carbene generated by pyrolysis uf diazomethane reacts with diethyl ether to form ethylpropyl ether and ethylisopropyl ether. 

Feedstocks for various industrial pyrolysis units are natural gas liquids (ethane, propane, and n-butane) and heavier petroleum materials such as naphthas, gas oils, or even whole crude oils. In the United States, ethane and propane are the favored feedstocks due, in large part, to the availability of relatively cheap natural gas in Canada and the Arctic regions of North America this natural gas contains significant amounts of ethane and propane. Europe has lesser amounts of ethane and propane naphthas obtained from petroleum crude oil are favored in much of Europe. The prices of natural gas and crude oil influence the choice of the feedstock, operating conditions, and selection of a specific pyrolysis system. 

All this was later put on a sound basis as a result of more precise measurements of rate constants and of activation energies. However, it did not require precise measurements to predict which chlorinated hydrocarbons would decompose by a radical chain mechanism and which by the unimolecular mechanism. Clearly, if the chlorinated hydrocarbon, or the product from the pyrolysis of the chlorinated hydrocarbon reacted with chlorine atoms to break the chain then the chain mechanism would not exist. Such chlorinated hydrocarbons would decompose by the unimolecular mechanism. Mono-chlorinated derivatives of propane, butane, cyclohexane, etc. would afford propylene, butenes, cyclohexene, etc. All these olefins are inhibitors of chlorine radical chain reactions because of the attack of chlorine atoms at their allylic positions to give the corresponding stabilized allylic radicals which do not carry the chain. 

Traditionally, olefins in the United States have been produced from light hydrocarbon pyrolysis. Earlier publications on computer simulation and control of pyrolysis reactors were addressed primarily to pyrolysis furnaces using ethane, propane and butane as feedstocks (1,2,3). 

Olefin production is achieved by pyrolysis of various feedstocks, ranging from light hydrocarbons (ethane, propane) to naphthas, gas oils and even crude oils. The variety of and change in the nature of available feedstocks due to new sources (e.g. off-gas from the North Sea) or to political problems, and the marked variation in prices and... 

The cracked gases are cooled and fractionated to remove fuel oil and water (2-5) then compressed (6), processed for acid-gas removal (8) and dried (9). The C3 and lighter material is separated as an overhead product in the depropanizer (10) and acetylene is hydrogenated in the acetylene converter (11). The acetylene converter effluent is processed in the demethanizer system (12-14) to separate the fuel gas and hydrogen products. The demethanizer bottoms is sent to the deethanizer (15) from which the overhead flows to the C2-splitter (16), which produces the polymer-grade ethylene product and the ethane stream, which is recycled to the furnaces as a feedstock. The deethanizer bottoms flows to the C3-splitter (18) where the polymer-grade propylene is recovered as the overhead product. The C3-splitter bottoms product, propane, is typically recycled to the furnaces as a feedstock. The depropanizer bottoms product, C4S and heavier, flow to the debutanizer (19) for recovery of the mixed-C4 product and aromatic-rich pyrolysis gasoline. 

The fiwdstocks used for pyrolysis vary widely and range from light saturated hydrocarbons such as ethane, propane, and even ethane/propane blends, to heavier petroleum cuts such as petrochemical naphtha and light and heavy gas oils. In this respect, the situation is clearly in favor of fight hydrocarbons in the United States, a country that is rich in natural gases containing methane as well as ethane and propane, and vHiich still mainly uses the latter two to manufacture ethylene, hi Europe and Japan, by contrast, petroleum cuts traditionally supply the steam cracker feedstocl (Table Zl). 

---