Propylene product distribution

Figure 4. Propylene product distribution at zero contact time (Reproduced from Ref. 1. Copyright 1964, American Chemical Society.)...

All lene Oxides and Aziridines. Alkyleneamines react readily with epoxides, such as ethylene oxide [75-21-8] (EO) or propylene oxide [75-56-9] (PO), to form mixtures of hydroxyalkyl derivatives. Product distribution is controlled by the amine to epoxide mole ratio. If EDA, which has four reactive amine hydrogens, reacts at an EDA to EO mole ratio which is greater than 1 4, a mixture of mono-, di-, tri,-, and tetrahydroxyethyl derivatives of EDA are formed. A 10 1 EDA EO feed mole ratio gives predominandy 2-hydroxyethylethylenediamine [111-41-1], the remainder is a mixture of bis-(2-hydroxyethyl)ethylenediamines (7). If the reactive NH to epoxide feed mole ratio is less than one and, additionally, a strong basic catalyst is used, then oxyalkyl derivatives, like those shown for EDA and excess PO result (8,9). 

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 volumetric expansion parameter S may thus be taken as 0.9675. The product distribution will vary somewhat with temperature, but the stoichiometry indicated above is sufficient for preliminary design purposes. (We should also indicate that if one s primary goal is the production of ethylene, the obvious thing to do is to recycle the propylene and ethane and any unreacted propane after separation from the lighter components. In such cases the reactor feed would consist of a mixture of propane, propylene, and ethane, and the design analysis that we will present would have to be modified. For our purposes, however, the use of a mixed feed would involve significantly more computation without serving sufficient educational purpose.)... 

Figure 7 Effect of propylene pressure on the product distribution of encapsulated 4,4 - and 3,4 -DIPB inside the pores and of the bulk products in the isopropylation of biphenyl. Reaction conditions biphenyl, 200 mmol HM(206), 1 g propylene pressure, 0.1-0.8 MPa temperature, 250 °C period, 4 h.

The major industrial source of ethylene and propylene is the pyrolysis (thermal cracking) of hydrocarbons.137-139 Since there is an increase in the number of moles during cracking, low partial pressure favors alkene formation. Pyrolysis, therefore, is carried out in the presence of steam (steam cracking), which also reduces coke formation. Cracking temperature and residence time are used to control product distribution. 

The main products formed by the catalytic alkylation of isobutane with ethylene (HC1—AICI3, 25-35°C) are 2,3-dimethylbutane and 2-methylpentane with smaller amounts of ethane and trimethylpentanes.13 Alkylation of isobutane with propylene (HC1—AICI3, — 30°C) yields 2,3- and 2,4-dimethylpentane as the main products and propane and trimethylpentanes as byproducts.14 This is in sharp contrast with product distributions of thermal alkylation that gives mainly 2,2-dimethylbutane (alkylation with ethylene)15 and 2,2-dimethylpentane (alkylation with propylene).16... 

Dimerization of propylene leads to the formation of isomeric methylpentenes in the presence of alkali metals.34 The product distribution strongly depends on the metal used. 4-Methyl-1-pentene is formed with high selectivity in the presence of potassium and cesium. Because of extensive isomerization, an equilibrium mixture of the isomers with 4-methyl-2-pentene and 2-methyl-2-pentene as the main products was isolated in a reaction catalyzed with sodium. 

Even though n-hexane is a minority hydrogenolysis product, it is a reliable measure of the degree of hydrogenolysis because of its ease of mass spectro-metric detection and it is not formed in a background reaction with the walls of the reaction chamber. Besides the saturated hydrogenolysis products and benzene, we found the olefinic products cyclohexene, ethylene, and propylene. Cyclohexene is an intermediate in the dehydrogenation to benzene and its various reactions will be discussed separately in the next section. The olefinic product distribution of ethylene propylene cyclohexene benzene is 10 1 0.5 1. 

Further evidence supporting the bismuth center as a site of propylene activation comes from the analysis of the rates of formation and product distribution of propylene oxidation over bismuth oxide, bismuth molybdate, and molybdenum oxide. Bismuth molybdate is highly active and selective for the conversion of propylene to acrolein. However, the interaction of propylene with its component oxides yields very different results. Haber and Grzybowska (//. ), Swift et al. 114), and Solymosi and Bozso 115) showed that in the absence of oxygen, propylene is converted to 1,5-hexadiene over bismuth oxide with good selectivity and at a high rate, whereas molybdenum oxide is known to be a fairly selective but a nonactive catalyst for acrolein formation. The formation of 1,5-hexadiene over bismuth oxide can be explained if the adsorption of propylene on a bismuth site yields a ir-allylic species. Two of these allylic intermediates can then combine to give 1,5-hexadiene. 

Fig. 1. Relation of product distribution to calculated contact time in propylene disproportionation. Data obtained in tests at 163 C and 450 p.s.i.g. with C0O-M0O3-AI2O3 catalyst and 60 propylene-40 propane feed (Ref. 1)...

Table II. Comparison between the pore size of catalysts and the product distributions of meta-diisopropylbenzene alkylation with propylene at...

The conditions needed to catalyze the reaction are very severe pressure = 3000-4500 psig and 150°C. The high pressure maintains the propylene in solution, ensures sufficient solubility of the H2 and CO and maintains the Co-carbonyl complex stable against decomposition. The product distribution is 4 1 linear to branch. 

Also given in Table 9.5 is the effect of distributing the cost of carbon emissions across only the olefins (ethylene and propylene) versus distributing this cost over all of the saleable products, i.e. that pyrolysis gasoline and other products should receive some of the carbon charge. The cost curves for the various scenarios are shown in Figure 9.15. 

Table II shows the yields and product distribution in a Dimersol Unit charging 3803 BPSD of mixed C3 s containing 2700 BPSD propylene. The conversion level on propylene is 957o.

The effects of inhibitors such as NO and propylene are rather interesting. There have been a large number of papers on the effects of these inhibitors. Crawford and Steacie, working with NO + w-butane, found a maximal inhibition by NO at about 10 mole per cent. The rates under these conditions were not, however, very reproducible, and contrary to earlier reports gave a different product distribution from the uninhibited reactions. ... 

The catalytic activity of silicoaluminophosphate molecular sieves (SAPO-5, SAPO-11, SAPO-34) has been studied during propylene conversion. During die reaction, SAPO-34 and SAPO-5 yielded C2-C7 hydrocarbons but both catalysts deactivated severely during reaction. The initial activity of SAPO-34 which contained sites of stronger acidity was higher than SAPO-5. SAPO-11, showing lower activity than SAPO-5 and SAPO-34 as well as rapid deactivation, yielded only C6 hydrocarbons. Differences in the product distribution observed during both reaction studies arise from the different acidity, pore structure and pore size of the S APO molecular sieves. 

In addition to the rates of olefin reactions, mass transfer also plays an important role in determining the extent of propylene conversion and the product distribution from SAPO molecular sieves. Restrictions on molecular movement may be severe in the SAPO catalysts, due to pore diameters (4.3 A for SAPO-34) and structure (one-dimensional pores in SAPO-5 and SAPO-11). The deactivation of SAPO-5 and SAPO-11 catalysts may be more directly related to mass transfer than the coking of SAPO-34. Synthesis of large or highly-branched products, having low diffusivities, inside the pores of SAPO-5 or SAPO-11 essentially block internal acid... 

Figure 6. Influence of Catalysts Deactivation on Product Distribution over SAPO Catalysts (Propylene Inlet Pressure- 16.2 kPA, Temp.= 650 K) (a) SAPO-5 (b) SAPO-34...

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