Isomalk-3 and Isomalk-3R in production of light paraffin hydrocarbons
One of the main trends in the oil refining and petrochemical world market in recent years has become an increase in the environmental friendliness of high-octane motor gasoline production and the creation of new petrochemicals production facilities.
Alexander N. Shakun, Marina L. Fedorova, Timofey V. Karpenko and Ekaterina V. Demidova
SIE Neftehim LLC
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The reduction in share of aromatic hydrocarbons and oxygen containing additives in motor gasolines at the legislative level has led to increase in demand for environmentally friendly high-octane components of the gasoline pool, such as alkylate and isomerate. New legislative initiatives focused on the promotion of hydrocarbon gases processing into petrochemical products have increased the attractiveness of investments in the industry.
The market transformation was expressed in appearance of new technologies and catalysts, the construction of new integrated aromatics and olefins production complexes for petrochemical synthesis.
Against this background, the value of butane fraction components has increased significantly. Isobutane is required as a feed for the production of alkylate, butyl rubber, oxygenates (MTBE and ETBE), isooctane. N-butane is a valuable feed of pyrolysis units, providing high yields of ethylene, propylene and n-butene used for the production of polymers.
N-butane and isobutane distribution in available butane fraction depends on its origin. The fraction obtained in the primary processing of hydrocarbon feed (gas condensate and crude oil) mainly contains n-butane.
In most oil refineries and petrochemical plants, the butane fraction can be recovered from liquefied petroleum gas (LPG), which is a by-product of secondary processing. The amount of produced LPG is relatively high and often exceeds the amount of LPG from primary processing. Thus, at diesel hydrotreating unit, LPG yield is approximately 1-2 wt. %, at hydrocracking unit – 6-8 wt. %, at reforming unit – 4-6 wt. %. In butane fraction of secondary origin, the isobutane share is high; it can reach 70-80 wt. % .
As a rule, companies focused on the motor fuels production have an increased demand for isobutane to obtain alkylate as one of the promising high-octane components of motor gasolines. The indisputable advantages of alkylate include a high octane number – 94-98 RON, a low vapour pressure – not more than 20 kPa, and absence of olefins, aromatics, sulphur and nitrogen-containing compounds.
The isobutane alkylation process with butylenes is carried out at a stoichiometric ratio of 1 mol/1 mol. However, in practice, to transfer the alkylation process from the diffusion area to the kinetic one, it is necessary to use an excess of isobutane, therefore, companies often meet with its deficit .
It is possible to obtain the additional amounts of isobutane using the technology for catalytic isomerisation of n-butane to isobutane. To address this issue, SIE Neftehim, LLC developed Isomalk-3 technology [3-5], which has been already proven in the industry as one of the most efficient solutions.
The isobutane fraction obtained by Isomalk-3 technology is characterised by high purity – the isobutane content may achieve 99 wt. % and above, there are no impurities of sulphur, nitrogen, chlorine and oxygen. The yield of by-products represented exclusively by С3 and С5 hydrocarbons is minimised in the process. The obtained products are also involved in petrochemical process feed. The pentane fraction contains 75-80 wt. % of isopentane and has an octane number in the range from 85 to 88 RON, which allows using it as a motor gasoline component .
For petrochemical companies, where butane fraction is used to produce ethylene, the situation is somewhat different.
The possibility of using the secondary butane fraction as a feed for the pyrolysis is sufficiently restricted. In this case, the increased content of isobutane is a significant disadvantage, since it helps to reduce the target ethylene yield during pyrolysis. The ethylene yield during n-butane pyrolysis achieves 35-40 wt. %, while during isobutane pyrolysis the ethylene formation does not occur.
In this regard, the economic efficiency of using LPG as ethylene production feed is low. The preliminary preparation of the feed is often not reasonable, since storage of excess isobutane is expensive and its sales are limited.
Ethylene and propylene are basic feed components for petrochemical and organic synthesis. Ethylene is an initial feed for the production of plastics, cosmetics, paints, solvents, and it is used to produce polyethylene, ethylene-propylene rubber, ethanol, ethylene glycol, ethylene oxide, ethylbenzene, polyvinyl chloride and many other products .
As of 2020, the total capacity of pyrolysis units for ethylene production in the Russian Federation went right up to the edge of 5 million tons/year. Table 1 shows the ethylene producing companies.
In the prospects for further ethylene production development in the Russian Federation, the commissioning of new pyrolysis units is expected, which allow increasing ethylene production by 7.6 million tons/year. Large projects announced for implementation at RusChemAlliance LLC – 3.1 million tons/year, Amur Gas Chemical Complex (GCC) LLC – 2.3 million tons/year, Irkutsk Polymer Plant (IPP) LLC – 0.67 million tons/year, PJSC Nizhnekamskneftekhim plans to double the ethylene production to 1.2 million tons/year .
In October 2020, Chapter 22 of the Russian Federation Tax Code was amended to stimulate the processing of ethane and liquefied petroleum gas to petrochemical products .
Due to demand for petrochemical companies, following n-butane isomerisation technology Isomalk-3, SIE Neftehim, LLC developed the reverse isomerisation technology Isomalk-3R, which allows converting excess isobutane into n-butane with high efficiency.
The butanes isomerisation reaction is equilibrium, while the thermodynamic equilibrium concentration in n-butane–isobutane pair depends exclusively on the reaction temperature. Low temperatures contribute to the equilibrium shift towards isobutane formation – the optimum temperature of n-butane isomerisation during catalyst operation is in the range of 130–160°C.
In turn, isobutane “normalisation” is appropriate at enhanced temperatures, at which thermodynamic equilibrium is more favourable for n-butane formation.
Thus, Isomalk-3R technology allows expanding the feed base of ethylene production due to the involvement of additional n-butane amount obtained by catalytic normalisation of isobutane. This approach allows increasing the volume of ethylene production without the involvement of additional amounts of fresh feed in processing.
Isobutane normalisation using Isomalk-3R technology allows increasing the ethylene production by more than twice compared to using the isobutane fraction as a pyrolysis feed.
Isomalk-3 and Isomalk-3R technologies do not provide a supply of chlorinating agents, and the highly active catalytic system is tolerant to poisons and impurities. These technologies have many significant advantages over technologies based on chlorinated alumina catalysts:
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