Propane oxidation, pressure

Propane. The VPO of propane [74-98-6] is the classic case (66,89,131—137). The low temperature oxidation (beginning at ca 300°C) readily produces oxygenated products. A prominent NTC region is encountered on raising the temperature (see Fig. 4) and cool flames and oscillations are extensively reported as compHcated functions of composition, pressure, and temperature (see Fig. 6) (96,128,138—140). There can be a marked induction period. Product distributions for propane oxidation are given in Table 1. 

In order to clarify the resistivity characteristics of the specimens, we obtained the relationship between an equilibrium oxygen partial pressure and the oxygen excess ratio from both theoretical calculations and measurements using the oxygen sensor. The complete propane oxidation can be described by the following reaction. 

Fig. 2. The variation with temperature of the maximum rate of oxidation of propane. Initial pressure of propane = 60 torr initial pressure of oxygen = 120 torr. (From ref. 17.)...

Heat release rate measurements from propane oxidation under stationary state conditions in a mechanically-stirred flow reactor were reported by Gray and Felton [12]. For the reactant composition [C3Hg] [02] = 1 2.2 at a pressure of 62.5 kPa (Fig. 6.6) there was a range of reactant temperatures at which the rate of heat release was virtually independent of temperature. However, a negative temperature dependence of the heat... 

Kinetic studies in a well-stirred flow reactor by Make and co-workers at the University of Washington [68-70] also apply to temperatures in excess of 1000 K. These studies provide information on the transition from the low-temperature combustion processes to those at normal flame temperatures, in the final stages of spontaneous ignition. These and related studies are summarized in the Appendix. A turbulent, high pressure, flow reactor has been developed by Koert et al. [14] for studies throughout the temperature range from 600 to 1000 K and at pressures up to 1.5 MPa. Results from it pertaining to propane oxidation are discussed in Section 6.4. 

The TPD/XPS results indicated that CO, propane and propene bind stronger to a reduced V-terminated 203(000 ) surface than to an oxidized V = 0 terminated surface. Nevertheless, vanadyl groups are probably required in the course of catalytic reactions. However, rates of propane oxidative dehydrogenation (ODH) to propene at atmospheric pressure are rather low and no reaction products were observed by gas chromatography, both for oxidized and reduced V Oj model surfaces at temperatures up to 500 K [12]. 

Propane oxidation experiments were generally carried out with 0.5g catalyst at atmospheric pressure, in the tenq)erature range 400-500°C, at a space velocity of 60 ml.min gcat. The gas feed composition was 10% C3H8, 10% O2 and 80% He (total flow rate 30 ml/min). Some experiments were also performed at a lower space velocity of 36 ml.min gcat, with a reactant mixture corresponding to 17% C3Hg, 17% O2 and 66% He (total flow rate 18 ml/min). 

Figure 3. Effects of 02 partial pressure on the propane oxidation over reduced H3PMol2O40(Py) at340°C. Symbols and reaction conditions except oxygen partial pressure are the same as those in Figure 2.

The high temperature propane oxidation by air, catalysed by prepared samples, was studied in the temperature range from 690 - 950°C in a flow fixed-bed quartz reactor on-line connected with an analytical system. In all the catalytic run almost equally amount of catalysts of about 40 g, and the catalyst fraction granulated from 2 to 3 mm were used. Propane and air mixture with a volume ratio of 1 7.14, were passed over the catalyst at a gas hourly spave velocity (GHSV) of 300 h and at atmospheric pressure. Before the catalytic tests the catalyst samples were carefully reduced in situ with propane and air mixture, at a volume ratio of 1 9.6, respeetively. 

Fig. 1. Maximum pressure jump d(Ap)/dt (reaction rate) during homogeneous propane oxidation vs. temperature (Vedeneev et al., 1997a, b). (1) experimental (2) calculated. Reaction conditions initial pressure P0 = 200Torr propane-to-oxygen ratio = 23.

Figure 2. XC2H4 vs. p°H p ( ) andp°co2 ( ) for T=463 K, Wcat=0.5 g, Ftot=5 mmol s. being most pronounced at low steam partial pressures. Marecot et al. [21] found inhibition due to steam of propane and propene oxidation over Pt/y-Al203. Bart et al. [22] found inhibition of the propane oxidation over a three-way catalyst for reducing conditions and rate enhancement for oxidizing conditions. The inhibition by steam is in contrast to the oxidation of CO by O2 over the same catalyst, where steam was found to strongly enhance the reaction rate [15]. Carbon dioxide also inhibits the reaction rate, although the inhibition is much smaller.

Catalytic study of propane oxidation was performed under atmospheric pressure in a stainless tube microreactor (2 cm o.d.) connected with a GC-MS apparatus, either at a temperature in the range 300-400 "C or at 340 C by varying the contact time. To better control the reaction temperature, the thermocouple was installed within the reactor. The gas feed consisted of 40 vol% propane, 20% oxygen and He as balance. Total flow rates were in the range 7.5 to 30 cm min and the mass of the catalyst was... 

In methane oxidation, a positive effect of methane partial pressure was measured in a wide range of feed composition the reaction order is 0.7 in CH4 and 0.1 in O2. In propane oxidation, the rise of fuel partial pressure promotes the reaction only at low reactant/oxygen ratio at higher values, surface saturation seems to take place (Figure 9). The oxygen dependence is 0.8, suggesting stronger competition by propane for surface sites, compared to methane. 

Vapor-phase reaction between ozone and olefins is quite rapid, the overall reactions become complicated, and stoichiometry varies with the reaction pressures. A 3 mole per cent mixture of OTOne in oxygen reacts with methane, propane, i -butane, and isobutane at 25-50 C. The reaction of ozone with isobutane resulted in formation of ferf-butanol plus one-third to one-half as much acetone, the combined yield being about equivalent to ozone reacted. Acetone was formed from propane oxidation. 

The composition of oxygenate mixture in the propane oxidation depends on the conditions (pressure and temperature of the process) [28d, 31b,c] (Table II.5). 

As for the products of the gas-phase oxidation of butane, pentane, and heavier hydrocarbons at high pressures, only disembodied data can be foimd. The authors of [26] studied the oxidation of normal butane, pentane, and heptane. Among the products of the interaction of n-butane with oxygen at pressures from 33 to 160 atm, along with the products characteristic of propane oxidation, butyl alcohols were found, their fraction increasing with the pressme. In [93], the oxidation of isobutane was reported to produce acetone, ferf-butanol, and tert-butyl hydroperoxide. 

Note that the data on the pressure dependence of the yield of propane oxidation products listed in Tables 10.4 and 10.5 were obtained at temperatures providing an approximately constant rate of the process rather than the maximum yield of alcohols. Since the same data show that a temperature rise increases the overall yield of normal alcohols (from 21% at 260 °C to 40% at 286 °C, both at P = 30 atm), optimum conditions are expected to provide a significantly higher )deld of alcohols. 

Badrian AS, Furman MS. Effect of pressure on the formation of intermediate propane oxidation products. Dokl Akad Nauk SSSR 1956 108 861-3 [in Russian]. 

Livshits VD, Sokolova NP, Beskova AP. Oxidation of propane under pressure. Tr GIAP 1959 (9) 223—37 [in Russian]. 

Petersen EL, Kalitan DM, Simmons S, Bourque G, Curran HJ, Simmie JM. Methane/ propane oxidation at high pressures experimental and detailed chemical kinetic modeling. Proc Combust Inst. 2007 31 447-454. 

Propane. Propane is difficult to oxidize in LPO because of its volatility and lack of reactivity. It can, however, be oxidized with a suitable solvent and sufficiently high pressures and temperatures (211). The principal products are acetone and isopropyl alcohol. 

Oxidation of Hydrocarbons. Ethanol is one of a variety of oxygen-containing compounds produced by the oxidation of hydrocarbons. Ethanol is reported to be obtained in a yield of 51% by the slow combustion of ethane (158,159). When propane is oxidi2ed at 350°C under a pressure of 17.2 MPa (170 atm) (160,161), 8% of the oxygen is converted to ethanol. Lower conversions to ethanol are obtained by oxidi2ing butane. Other oxidation systems used to produce ethanol and acetaldehyde (162—164) and methods for separating the products have been described in the patent Hterature. 

Like propane, n-hutane is mainly obtained from natural gas liquids. It is also a hy-product from different refinery operations. Currently, the major use of n-hutane is to control the vapor pressure of product gasoline. Due to new regulations restricting the vapor pressure of gasolines, this use is expected to he substantially reduced. Surplus n-butane could be isomerized to isobutane, which is currently in high demand for producing isobutene. Isobutene is a precursor for methyl and ethyl tertiary butyl ethers, which are important octane number boosters. Another alternative outlet for surplus n-butane is its oxidation to maleic anhydride. Almost all new maleic anhydride processes are based on butane oxidation. 

Some more recent processes have been developed which involve direct hydrogenation of the oil to the fatty acid and 1,2-propane diol. These high-temperature (>230 °C) and high-pressure processes generally use a copper chromium oxide catalyst. 

A similar system based on rhodium has been studied (123) and was found to be less active than the equivalent iridium catalysts. Selective hydrogenation of acetylenes to olefins and dienes to monoolefins can be performed using the rhodium system, and the authors note that although propan-2-ol is an effective source of hydrogen (via oxidation to acetone), mild pressures of hydrogen gas can also be employed. 

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