Propane catalyst deactivation

One obvious method of cleaning the feed is to remove asphaltic material (asphaltenes plus resins) using a solvent such as propane in a deasphalting unit. The resulting deasphalted oil has less metals than the original feedstock but coke formation and catalyst deactivation are not completely eliminated. The byproduct stream is usually only acceptable as a raw material for asphalt manufacture. Even then, the asphaltic by-product may be unsuitable for a specification grade asphalt and require disposal by other means. 

The H2-D2 equilibration reaction was shown to be useful as a probe for measuring the metal area not covered by coke, on Pt/Al203 and Pt-Sn/AL03 catalysts deactivated during propane dehydrogenation. Problems with the method are the effect that the repeated stops have on the dehydrogenation deactivation profile, and the difficulties in correlating the HD formation rate to free metal area. 

Catalyst deactivation by coke formation can occur through a more or less reversible mechanism. We have applied a transient approach to model the reversible behavior of the deactivation, and to separate the deactivation from the main reaction kinetics. The deactivation of a Pt-Sn/AbOs catalyst was studied during propane dehydrogenation. The gas composition and temperature were varied during the experiments, which allowed us to model the deactivation by assuming one reversible and one irreversible type of coke. It was found that the deactivation increased with the propene concentration but was independent of the partial pressure of propane. Hydrogen decreased the deactivation rate and could even activate the catalyst by removing reversible coke. 

A one-stage process for the manufacture of PO from propane instead of propene would have substantial economical advantages. In one patent, a catalyst composed of Ag/Cl/NaN03/La/Cr/BaC03 is claimed that gives 10% propane conversion with a PO selectivity of 8% at 480 °C, resulting in a PO space-time-yield of0.002 gpo gcat h however, this catalyst deactivates very rapidly [45a]. 

Propane aromatization reaction (at 550°C) was carried out at atmospheric pressure in a continuous flow quartz reactor (id 13 mm), using a propane-nitrogen mixture (33.3 mol-% propane) as a feed with a space velocity of 3100 cm g h". The catalytic activity and selectivity were measured as a function of time-on-stream (up to about 6.7 + 0.2 h). The reaction products were analyzed by an on-line GC with FID, using Poropak-Q (3 mm x 3 m) and Benton-34 (5%) and dinonylphthalate (5%) on Chromosorb-W (3 mm x 5 m) columns. The activity and selectivity data at different space velocities in the absence of catalyst deactivation (i.e. initial activity/selectivity) at 550°C were obtained by the square pulse technique by passing the reaction mixture at different space velocities over fresh catalyst for a short period (2-5 min) under steady state and then replacing the reactant mixture by pure Nj during the product analysis by the GC. 

Figure 2 shows the influence of time-on-stream on the selectivity for aromatics and undesired products (viz. methane and ethane). However, observed influence on the selectivity can be due to the catalyst deactivation and/or because of the decrease in the propane conversion with increasing the time-on-stream. 

Fig. 4.8-10 compares the durability results of the 2-methyl-propene and 2-methyl-propane reaction in the gas phase, liquid phase and supercritical phase. Very high initial activity, with yields of alkylate (2,2,4,-trimethylpen-tane) as high as 70%, was observed in the liquid phase reaction (50 °C, 35 bar). However, the activity decreased rapidly, and no activity was observed when the accumulated feed amount of olefin reached 20 mmol/g-cat. Similarly, rapid catalyst deactivation was observed in the gas phase reaction. Alkylate yield dropped to near zero at an accumulated alkene feed of 20 mmol/g-cat. For the supercritical-phase reaction, the catalyst deactivation was suppressed by the SCF. Even when the accumulated alkene feed reached 35 mmol/g-cat (after 5.6 h), the alkylate yield was still higher than 10%. Although the yield of alkylate decreased with time-on-stream, 2-methyl-propene conversion was almost 100%. If the reaction was carried out in the liquid phase at conditions (125 °C, 50 bar) only slightly different from those of the SCF reaction, the deactivation behavior was similar to that of the gas phase reaction. 

Fig. 4.8-12). After 2-methyl-butane was used to extract the spent catalyst for 1 h, the initial activity of alkylation reaction was restored to about 70%. A similar effect was observed upon extraction with 2-methyl-propane. However, if propane was used to regenerate the deactivated catalyst, no significant improvement was obtained and the catalyst still showed low alkylate yield and high oligomer yield. These results are in good accord with those reported in Fig. 4.8-11. It is clear that catalyst deactivation is closely related to the extraction capacity of the SCF. In situ extraction of catalyst poisons determines catalyst lifetime. Furthermore, failure of the extraction of these catalyst poisons favored the oligomerization reaction of the alkene. 

The monocyclic terpenes are easily disproportionated to the dehydrogenated p-cymene and the hydrogenated /7-menthane. For a short time on stream TOS (< 2 h), cracking of /)-cymene to toluene and propane/propene on the strongly acidic sites is the dominant reaction. With increasing TOS, these strong acid sites of the catalysts deactivate and, thus, the formation of products obtained by cracking decreases. 

Another important process in which catalyst deactivation by coke deposits plays an important role is propane dehydrogenation, which can be performed with a variety of materials, including metal and metal oxide catalysts. Different in situ and operando spectroscopies have been applied to these catalysts, including UV-vis, Raman, electron paramagnetic resonance (EPR), and X-ray absorption spectroscopies [4, 115, 140],... 

Alumina foams have been directly impregnated for propane CPO and OSR [13, 14, 40] to yield 0.01 wt.% rhodium. The catalyst on the foam body, which was 15 mm in diameter, 7 mm long and contained 400 cells per square inch (84% porosity), showed optimum performance at an oven temperature of700 °C and good stability under CPO conditions (C O = 0.8), even though a remaining hot spot of more than 200 K was observed in the foam. Under OSR conditions (C 0 = 0.5 and steam to carbon ratio = 1) only a 150 K hot spot was observed. However, the catalyst deactivated more rapidly, maybe due to the increase in byproduct formation. Complete homogeneous conversion was observed at an oven temperature of 800 °C... 

As a cheap alternative to noble metal and even nickel catalysts, Laosiripojana et al. proposed high surface area ceria [234]. Complete conversion of liquefied petroleum gas (prepared as a sulfur-free 60 wt.% propane/40 wt.% butane mixture) could be achieved above a reaction temperature of 800 °C. The S/C ratio was low at 1.45 and ethylene as a by-product could be suppressed at O/C ratios exceeding 0.6. The weight hourly space velocity was relatively low at 120 L (h gcat). however, catalyst deactivation was moderate within 70-h test duration, which is a promising result. 

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