The study of the effect of the concentration of propylene in the PPF to the liquid yield of the reaction

The results of the study of the effect of the concentration of propylene to propane-propylene fraction to a liquid yield of the reaction depending on the feed space velocity are presented. The results in the presence of a chromia-alumina catalyst in oxides of Ni, Co, Cr are examined. The optimal reaction conditions (Т-280 0 С, V overall velocity 50-200 h -1 ), in which the liquid yield of the reaction was determined depending on the concentration of С 3 Н 8 and С 3 Н 6 in the raw feedstock, were set.

ISSN 2321-807X 3822 | P a g e A u g u s t 2 5 , 2 0 1 5 One of the most important tasks of oil refining from both the environmental as well as economic points of view is the effective use of hydrocarbon residue gas of refineries and the chemical industry for the production of light oil products and raw materials for the petrochemical industry. The problem of using gases of catalytic cracking can be solved to a great degree by the introduction of new processes of their alkylation over zeolite-containing catalysts in oil refining. In this regard, the problem of expansion of production of alkylation gasoline, which share now accounts for about one seventh of the total volume of the world's gasoline production, arises.
Most part of alkylation gasoline is produced by reacting isobutane with С2-С5 olefins in the presence of a catalyst. A drawback of these productions is the formation of acid sludge as well as the use of solely isoparaffins as a raw material. In this regard, the importance of developing new processes using heterogeneous catalysts is increasing. Development and implementation of recycling process of gases of oil refineries would allow production of an additional amount of automobile gasoline and drastic reduction of the amount of harmful emissions into the atmosphere.
Modern automobile gasoline is prepared by mixing the components obtained by direct distillation, catalytic cracking and reforming, alkylation, isomerization, polymerization and other refining processes [1]. Alkylate, obtained by alkylating isobutane with С3-С5 olefins, is one of the most promising components among them. Alkylate is a component satisfying the technical-operational and environmental requirements of modern European standards for fuel. This process significantly reduces manufacturing costs and provides high-quality gasoline [2].
Currently, one of the most important areas of modern petro chemistry is the development of new solid acid catalysts of alkylation over zeolites. Zeolites have sufficient activity, stability and the ability to regenerate, which is essential for the practical implementation of the process. It is commonly known, zeolites are multifunctional. They possess isomerizing, hydrogenating and dehydrogenating properties and can lead reaction to oligomerization of cracking, cyclization. Unlike mineral acids, zeolite catalysts may be modified and promoted. At that, there is no need to separate the catalyst from the reaction mixture, and it becomes possible to carry out the process in continuous conditions and the environmental conditions significantly improve [3,4,5].
Of all the existing methods for producing unsaturated hydrocarbons, the main share is accounted for the catalytic dehydrogenation of n-paraffins. This is due to the large number of studies conducted on the improvement and development of new catalysts [6,7].

EXPERIMENTAL PART
The purpose of this study is to investigate the activity of the chromia-alumina catalyst promoted with oxides of Ni, Co, Cr and study of the effect of the concentration of propylene to propane-propylene fraction to a liquid yield of the reaction depending on the feed space velocity.
One of the characteristics of the recommended process, developed in Institute of Petrochemical Processes of Azerbaijan National Academy of Sciences, is the involvement of paraffins contained in the gases of the catalytic cracking in the alkylation reaction via their dehydrogenation to the corresponding olefins. The resulting propylene С3-С4 participates in the alkylation reaction of paraffins. With this purpose, modifiers Ni, Cu, Co in an amount of 10% are added into composition of the industrial zeolite catalyst OMNIKAT-210П by applying them to a base, -Al2O3 in an amount of 10% is taken as the binder. The reactor was charged with the catalyst in an amount of 30 cm 3 . We have found that in the catalyst subjected to calcination under vacuum at a temperature 500-550 0 С, NiAl2O4 and CoAl2O4 are formed, presence of which leads to formation of olefins by dehydrogenation of the corresponding paraffins.
In order to study the effect of the concentration of С3Н6 in the initial fraction to yield liquid reaction products, artificial mixture of from pure propane and propylene was prepared (95-96% purity). The concentration of propylene in the artificial mixture was varied from 40 to 60% at a constant feed space velocity of PPF (50÷200 h -1 ). The volume of the loaded zeolite catalyst -30 cm 3 . Studies were carried out at a temperature of 280°C. The contact time at a feed space velocity of PPF 50 h -1 is 22.4 seconds ( Table 1).
As shown in Table 2, when changing the concentration of С3Н6 from 40 to 60% of volume concentration of С3Н8 changes from 60 to 40%. At a feed space velocity of PPF 50 h -1 , 100% conversion of С3Н6 is observed. Conversion of С3Н8 thus increases from 9.8% at its content in the initial fraction of 60% to 28.7% at its content of 50%. Then conversion of С3Н8 is somewhat reduced to 24.4% at 40 % concentration of С3Н8. With increasing concentrations of С3Н6 in the mixture of 40 to 60%, yield of liquid product per unit weight of the catalyst increases from 0.068 g/hr to 0.1 g/hr. The yield of liquid to the original PPF increased from 42.4 to 69.8%. The yield of liquid on С3Н6 increased from 117.3 wt% at a concentration of С3Н6 in the initial mixture in 40 wt% to 124.37 wt% at 50% concentration of С3Н6, and then liquid propylene yield decreased to 116.3% (Table 3).  From the above it follows that the С3Н6 is fully involved in the reaction and С3Н8 is alkylated, the maximum amount thereof that is involved in the reaction is achieved at 50% content in the original mixture. Further reduction of the concentration of С3Н8 in the original mixture leads to a reduction of alkylation reaction of С3Н8 by propylene and therefore the yield of liquid is reducing based on the initial С3Н6.
When the feed space velocity of 100 h -1 (process indicators are given in Table 4) yield of liquid per unit of weight of the catalyst increases from 0.105 to 0.257 g/h. at a 50%concentration of С3Н6, and then reduces to 0.1 g/h. The yield of liquid to original propylene is respectively changed from 84.8 to 152.46 wt% and then reduced to 58.5 wt%. The conversion of С3Н6 (wt%) thus varies from 70.2 to 99.2% and then reduced to 39.6 wt%. Conversion С3Н8 increases from 9.3 to 61.1% and then decreased to 27.3 wt% (Table 5). Consequently, in this case, there is a saturation of the catalyst with propylene and further increase of the concentration of С3Н6 in the feedstock does not lead to increase of the yield of liquid products (see Table 6). The yield of liquid product on feedstock from increase the concentration of С3Н6 in the feedstock increases from 33.02 to 80.9 wt% to 50% of С3Н6 content in the feedstock then is reduced to 34.6 wt% at the content of С3Н6 in 60% by volume.
By increasing the feed space velocity from 50 to 200 h -1 , conversion of С3Н8 increases from ~9.5 to 10.5 wt%, while reducing the yield of liquid products both to С3Н6 and all the feedstock, wherein the concentration of С3Н6 accounts for 40%, the rest is С3Н8. Consequently, with increasing of partial pressure of С3Н8, alkylation reaction of С3Н8 by propylene also increases.
With the content of С3H8 the feedstock in amount of 50%, the conversion of С3Н8 increases to feed space velocity of 100 h -1 . Then С3H8 conversion decreases from 61 to ~8%. As a consequence, the yield of liquid raw material initially increases and after 100 h -1 decreases. Decrease the concentration of С3Н8 in the feed to 40% leads to reduction the conversion of С3Н8, caused by the decrease of its partial pressure. This leads to a reduction of alkylation reaction of С3Н8 by propylene. The yield of liquid to the source С3Н8 decreases from ~120 to 15%. This decrease means a reduction of alkylation reaction of С3Н6 by propylene.   This is explained by the fact that with increase of the contact time, emerging dimers were further converted with emergence of trimers, cyclic hydrocarbons, etc. These compounds are adsorbing on the catalyst surface at the reaction temperature (280 0 С) and are not desorbing, thereby lowering the number of active centers and reducing the active surface, which leads to a decrease in the yield of liquid per unit weight of the catalyst. The yield of liquid to the source С3Н6 with increase of a contact time from 11.2 seconds to 22.4 seconds, which corresponds to the feed space velocity from 100 to 50 h -1 (Table. 1, 4), is reduced from 152.5 to 124.4 %.
With feed space velocity of 200 h -1 (Table 7), which corresponds to a contact time of 5.58 s, yield of liquids to introduced С3Н6 is also reduced from 152.5% at τк=11,2 s. (Table 4) to 40% at 5.58 s. Essentially doubly reducing the contact time results in fact that the residence time of С3Н6 on the surface is not enough for both dimerization like reaction and involving of С3Н8 in alkylation reaction. And increasing the contact time from 5.6 to 22.4 leads to increased conversion of С3Н8 from 6.8 to 61.1%. Thus, with 50% concentration of propane, increasing the contact time promotes the alkylation reaction of С3Н8 by propylene. Table 8 presents the value of the conversion of propane and propylene, depending on their initial concentration in the feedstock. Table 9 presents the value of the transformation rate of propane and propylene into yield liquid reaction products, depending on the concentration of propane and propylene in the feedstock.

CONCLUSION
Changes in the concentration of propylene in the PPF (propane propylene fraction) to the yield of liquid products are described in the proposed article: With the increase of space velocity (50-200 h -1 at a temperature of 280 0 С), conversion of С3Н8 increases from 28.7% to 61.1% and with a further increase in the space velocity decreases to 6.8%. At the same conditions С3Н6 reduces from 100% to 99.2% and, at higher space velocity with concentration of the components in the initial mixture (50/50 of С3Н8 и С3Н6), conversion decreases to 37.27%.
As it can be seen from Table 2, С3Н6 is fully involved in the reaction but С3Н8 is subjected to alkylation.
It is established that the yield of liquid products at the initial propylene (Voverall velocity, 50-200 h -1 ) increases from 124.37% to 152.46% and at higher feed space velocity reduces to 40%. The best option of experiment is =11.2sec, Voverall velocity=100 h -1 .