Alkylation Kinetics of Isobutane by C4 Olefins Using Sulfuric Acid as Catalyst Weizhen Sun, Yi Shi, Jie Chen, Zhenhao Xi, and Ling Zhao* State-Key Laboratory of Chemical Engineering, East China University of Science and Technology, Shanghai 200237, China * S Supporting Information 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. 1. INTRODUCTION In early 1990s, the USA refiners had to start changing their strategy on gasoline composition to meet the mandatory CAA (Clean Air Act) specifications. 1 Since that time, gasoline was forced to move in a more environmentally friendly direction, such as reducing volatility, limitations in the aromatic content, increased amount of oxygenates, reduction of olefins and sulfur, and elimination of lead. As a desirable blending component, without olefins or aromatics, alkylate exclusively contains isoalkanes with high octane number. Since its commercial production in the last century, alkylate had been the most ideal blending component for a typical refinery gasoline pool. Nearly 70% of the world’s alkylate production is from North America, and over 20% is produced from Europe. 2 It was believed that alkylate will continue to be a desirable blending component as long as cars are operated on high octane gasoline. 3 The alkylation reaction producing alkylates combines isobutane with light C3-C5 olefins in the presence of a strong acid catalyst. Currently, the only processes of commercial importance use either sulfuric or hydrofluoric acid as catalysts. 4 Although the number of established alkylation units using sulfuric acid is almost as much as that using hydrofluoric acid, more new alkylation plants built worldwide chose sulfuric acid as catalyst in the recent past years. 5 One of the reasons is that hydrofluoric acid is a highly toxic liquid, and released into the atmosphere, it forms aerosol, which drifts downwind for several kilometers. 6 Actually, both acids suffer from certain drawbacks, but it is not the intent of this work to review in detail the pros and cons of sulfuric acid versus hydrofluoric acid but to address the alkylation kinetics using sulfuric acid as a catalyst. It is well-known that the study on reaction kinetics is of fundamental importance not only to the design and optimization of a ripe chemical reactor but also to the development of a novel one. Also, it is helpful in understanding the reaction mechanism. As to the alkylation mechanism of isobutane with olefins, much classical literature had been published, 7-11 in which the formation pathway of the majority of key components and intermediates in alkylate were well formulated although different publications would have different descriptions regarding some specific steps. However, to the best of our knowledge, there was little literature focusing on the alkylation kinetics of isobutane with butene in sulfuric acid to address the formation of several key alkylates such as trimethylpentanes (TMPs), dimethylhexanes (DMHs), and heavy ends (HEs). Using uniform hydrocarbon drops and short contact time, the sulfuric acid catalyzed reaction of isobutane with 1-butene, as well as the oligomerization of 1-butene, was investigated, in which only two key reactions were consid- ered, 12 but other important reaction steps in view of the presence of several dozen isoparaffins in commercial produced alkylates are far from being understood. 13 The two-step process for the alkylation of isobutane with C4 olefins was investigated, but the rate constants were not given. 10 In this work, the alkylation kinetics of isobutane with butene using sulfuric acid as catalyst was measured under the condition of industrial interest. The kinetic model was established on the basis of the carbonium ion mechanism, in which three families of key isoparaffins were considered including TMPs, DMHs, and HEs. 2. EXPERIMENTAL SECTION The experiments were carried out in a batch setup with a glass reactor with the volume of 1 L. To keep isobutane and olefin in Special Issue: NASCRE 3 Received: February 4, 2013 Revised: April 2, 2013 Accepted: April 3, 2013 Published: April 3, 2013 Article pubs.acs.org/IECR © 2013 American Chemical Society 15262 dx.doi.org/10.1021/ie400415p | Ind. Eng. Chem. Res. 2013, 52, 15262-15269