Alkylation liquid acid processes

Liquid acid-catalyzed processes are mature technologies, which are not expected to undergo dramatic changes in the near future. Solid acid-catalyzed alkylation now has been developed to a point where the technology can compete with the existing processes. Catalyst regeneration by hydrogen treatment is the method of choice in all the process developments. Some of the process developments eliminate most if not all the drawbacks of the liquid acid processes. The verdict about whether solid acid-catalyzed processes will be applied in the near future will be determined primarily by economic issues. 

Other observations of this test work, with respect to key alkylate product properties, were that neither the Reid vapor pressure (RVP) nor density deviated significantly from values that would be obtained via liquid acid alkylation. Further, acid-soluble oils (ASO), formed as contaminant side products in the case of liquid acid processes, could not be detected among the reaction products in our SAC testing. Compared with the liquid acid technologies, this effect results in both lower feed consumption per unit of alkylate production and eliminates generation of a by-product that can be difficult to dispose of. 

A RON value of 96 is claimed for the alkylate obtained through the Allqr-Clean process. AlkyClean has been presented as a very versatile option to retrofit liquid acid processes, having up to 20% lower inside-battery-limits cost than for a H2SO4 unit and comparable to that for a HF plant. The process is also shown as attractive to revamp gasoline polymerization units, offering a short time for payback (252). 

Either a liquid or a gas-phase process is used for the alkylation reaction. In the liquid-phase process, low temperatures and pressures (approximately 50°C and 5 atmospheres ) are used with sulfuric acid as a catalyst. 

Rhodium catalyzed carbonylations of olefins and methanol can be operated in the absence of an alkyl iodide or hydrogen iodide if the carbonylation is operated in the presence of iodide-based ionic liquids. In this chapter, we will describe the historical development of these non-alkyl halide containing processes beginning with the carbonylation of ethylene to propionic acid in which the omission of alkyl hahde led to an improvement in the selectivity. We will further describe extension of the nonalkyl halide based carbonylation to the carbonylation of MeOH (producing acetic acid) in both a batch and continuous mode of operation. In the continuous mode, the best ionic liquids for carbonylation of MeOH were based on pyridinium and polyalkylated pyridinium iodide derivatives. Removing the highly toxic alkyl halide represents safer, potentially lower cost, process with less complex product purification. 

In this manuscript, we will chronicle the discoveiy and development of these non-alkyl halide containing processes for the rhodium catalyzed carbonylation of ethylene to propionic acid and methanol to acetic acid when using ionic liquids as solvent. 

This contribution is an in-depth review of chemical and technological aspects of the alkylation of isobutane with lightalkenes, focused on the mechanisms operative with both liquid and solid acid catalysts. The differences in importance of the individual mechanistic steps are discussed in terms of the physical-chemical properties of specific catalysts. The impact of important process parameters on alkylation performance is deduced from the mechanism. The established industrial processes based on the application of liquid acids and recent process developments involving solid acid catalysts are described briefly. 2004 Elsevier Inc. 

The technology and chemistry of isoalkane-alkene alkylation have been thoroughly reviewed for both liquid and solid acid catalysts (15) and for solid acid catalysts alone (16). The intention of this review is to provide an up-to-date overview of the alkylation reaction with both liquid and solid acids as catalysts. The focus is on the similarities and differences between the liquid acid catalysts on one hand and solid acid catalysts, especially zeolites, on the other. Thus, the reaction mechanism, the physical properties of the individual catalysts, and their consequences for successful operation are reviewed. The final section is an overview of existing processes and new process developments utilizing solid acids. 

In the liquid acid-catalyzed processes, the hydrocarbon phase and the acid phase are only slightly soluble in each other in the two-phase stirred reactor, the hydrocarbon phase is dispersed as droplets in the continuous acid phase. The reaction takes place at or close to the interface between the hydrocarbon and the acid phase. The overall reaction rate depends on the area of the interface. Larger interfacial areas promote more rapid alkylation reactions and generally result in higher quality products. The alkene is transported through the hydrocarbon phase to the interface, and, upon contact with the acid, forms an acid-soluble ester, which slowly decomposes in the acid phase to give a solvated... 

The numbers for the liquid acids are taken from Refs. (12,23,221). As zeolites are not used in industrial alkylation process, the given values represent the judgment of the authors extracted from laboratory and pilot scale data obtained in a slurry reactor. 

This section is a review of alkylation process technology. The processes in which liquid acids are used are all mature technologies and described briefly here. Information about process developments with solid acid catalysts is also presented. 

The catalyst is reported to be a true solid acid without halogen ion addition. In the patent describing the process (239), a Pt/USY zeolite with an alumina binder is employed. It was claimed that the catalyst is rather insensitive to feed impurities and feedstock composition, so that feed pretreatment can be less stringent than in conventional liquid acid-catalyzed processes. The process is operated at temperatures of 323-363 K, so that the cooling requirements are less than those of lower temperature processes. The molar isobutane/alkene feed ratio is kept between 8 and 10. Alkene space velocities are not reported. Akzo claims that the alkylate quality is identical to or higher than that attained with the liquid acid-catalyzed processes. 

Several metal oxides could be used as acid catalysts, although zeolites and zeo-types are mainly preferred as an alternative to liquid acids (Figure 13.1). This is a consequence of the possibility of tuning the acidity of microporous materials as well as the shape selectivity observed with zeolites that have favored their use in new catalytic processes. However, a solid with similar or higher acid strength than 100% sulfuric acid (the so-called superacid materials) could be preferred in some processes. From these solid catalysts, nation, heteropolyoxometalates, or sulfated metal oxides have been extensively studied in the last ten years (Figure 13.2). Their so-called superacid character has favored their use in a large number of acid reactions alkane isomerization, alkylation of isobutene, or aromatic hydrocarbons with olefins, acylation, nitrations, and so forth. 

Concentrated sulfuric acid and hydrogen fluoride are still mainly used in commercial isoalkane-alkene alkylation processes.353 Because of the difficulties associated with these liquid acid catalysts (see Section 5.1.1), considerable research efforts are still devoted to find suitable solid acid catalysts for replacement.354-356 Various large-pore zeolites, mainly X and Y, and more recently zeolite Beta were studied in this reaction. Considering the reaction scheme [(Eqs (5.3)—(5.5) and Scheme 5.1)] it is obvious that the large-pore zeolitic structure is a prerequisite, since many of the reaction steps involve bimolecular bulky intermediates. In addition, the fast and easy desorption of highly branched bulky products, such as trimethylpentanes, also requires sufficient and adequate pore size. Experiments showed that even with large-pore zeolite Y, alkylation is severely diffusion limited under liquid-phase conditions.357... 

In 1999, Akzo Nobel (which later sold its catalyst division to Albemarle) patented a new technology for alkylating hydrocarbons based on a zeolite acid catalyst [193]. This new process, AlkyClean, was then designed by ABB Lummus and Albemarle, and a 10 barrels per stream day (BPSD) demonstration unit came online in Finland in 2002. AlkyClean produces a high-quality sulfur-free alkylate (96 octane), eliminating all the drawbacks of the liquid acid catalyst technologies. There are no add-soluble oil waste streams, the reactor operates at 50-90 °C, and the catalyst is a solid, noncorrosive material, which is easily transported and stored. 

The pioneer work in this field was carried out on polystyrene-supported acid catalysts [161]. Thereafter, several works on the use of sulfonic, strong acidic cation exchangers as acid catalysts were reported for alkylation, hydration, etherification, esterification, cleavage of ether bonds, dehydration, and aldol condensation [162,168-171], Besides, industrial applications of these materials were evaluated with reactions related to the chemistry of alkenes, that is, alkylation, isomerization, oligomerization, and acylation. [163,169], Also, Nation, an acid resin which has an acid strength equivalent to concentrated sulfuric acid, can be applied as an acid catalyst. It is used for the alkylation of aromatics with olefins in the liquid or gas phases and other reactions however, due to its low surface area, the Nation resin has relatively low catalytic activity in gas-phase reactions or liquid-phase processes where a nonpolar reactant or solvent is employed [166],... 

Beside isopropyl benzene (IPB) a substantial amount of polyalkylates is formed by consecutive reactions, mostly as C6H5-(C3H7)2 (DIPB) with some C6H5-(C3H7)3 (TPB). The main reaction has a large exothermal effect, of-113kJ/mol in standard conditions. The alkylation reaction is promoted by acid-type catalysts. The synthesis can be performed in gas or liquid phase. Before 1990 gas-phase alkylation processes dominated, but today liquid-phase processes with zeolite catalysts prevail. Recent developments make use of reactive distillation. 

In industrial practice, two liquid acids are employed as catalysts for isobutane/ butene alkylation, namely sulfuric acid and hydrofluoric acid [3, 19, 20]. Both processes deliver a high-quality gasoline component. The catalyst consumption in the H2S04 process is high, typically 70-100kg/t The spent sulfuric acid contains tarry hydrocarbons and water and has to be processed externally. On the other hand, corrosiveness and toxicity of HF are reasons of concern that require use of additives that lower the HF vapor pressure and minimize the amount of HF released in the case of an accident. However, in many industrialized countries, new HF alkylation processes are no longer approved by authorities. 

Liquid-phase processes such as oxidation, hydrogenation, sulfonation, nitration, halogenation, hydrohalogenation, alkylation, sulfonation, polycondensation, polymerization, etc. Examples oxidation of acetaldehyde to acetic acid... 

UOP LLC has developed two alternate processes for liquid-acid alkylation. The... 

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