Alkylation Kinetics of Isobutane by C4 Olefins Using Sulfuric Acid as Catalyst

Abstract

The alkylation kinetics of isobutane with butene using sulfuric acid as catalyst was investigated by batch experiments in the conditions of industrial interest. More than 16 alkylates were identified and quantified by GC-MS. On the basis of the classic carbonium ion mechanism, the kinetic model was established, which can predict the concentration change of three groups of key alkylates including trimethylpentanes (TMPs), undesirable dimethylhexanes (DMHs), and heavy ends (HEs). The agreement between experimental and model calculated data was quite satisfactory. The rate constants were found to be constant with the varied temperatures (276.2 to 285.2 K) except those accounting for the addition of H+ to isobutene and its reversible reaction. An anti-Arrhenius behavior was observed for the addition reaction of H+ to isobutene, in which the corresponding rate constant falls with the increasing temperatures. The kinetic model was confirmed by the simulation of the industrial alkylation reactor. Hopefully, the kinetic model developed in this work will be useful to the design and optimization of novel alkylation reactors.

Understanding interfacial behaviors of isobutane alkylation with C4 olefin catalyzed by sulfuric acid or ionic liquids

“…Besides the solubility of isobutane, the diffusion of isobutane at the interface in acid/hydrocarbon dispersions is another important factor that affects the quality of alkylate. It is believed that the diffusion of isobutane across the hydrocarbon‐acid interface is the rate‐limiting step for the whole isobutane alkylation . The self‐diffusion coefficients D z of 2‐butene and isobutane at the interface for all systems are calculated using the modified Langevin equation, as shown in Figure .…”

“…Those ILs were prepared according to the previous article . The alkylation experimental procedure is similar to our previous work, and it is briefly introduced here.…”

“…The agitator started to work to ensure a good dispersing of the hydrocarbon mixture with the sulfuric acid and ILs, when the mixture of isobutane and olefin with the molar ratio of 8:1 was quickly introduced into the reactor. Finally, the alkylate was analyzed by the gas chromatography‐mass spectrometry (GC‐MS) using the same method introduced in our previous work …”

“…Correspondingly, the solubility of isobutane in the acid phase, or at least at the interface of the two phases, to a large extent determines the quality of alkylate . In addition, the mass transfer of isobutane across the hydrocarbon/acid interface is the rate‐controlling step for the alkylation reaction, considering the low solubility of isobutane combined with the rapid reaction rate of olefins . In view of the aforementioned points, the interfacial properties between two phases, such as interfacial area, interfacial concentration and diffusion of the reactants (particularly isobutane), are of significant importance to the quality of alkylate from the macroscopic perspective .…”

Intensification of the Sulfuric Acid Alkylation Process with Trifluoroacetic Acid

“…The mechanism of the H 2 SO 4 alkylation reaction is more complex than that of the HF alkylation reaction . In the H 2 SO 4 alkylation reaction, butene is first protonated by H 2 SO 4 to form a carbocation, which subsequently reacts with another butene to form trimethylpentane (TMP + ) or dimethylhexane (DMH + ); finally, a hydrogen transfer reaction between TMP + or DMH + and isobutane results in the formation of TMP or DMH, respectively, as the main products.…”