Typical Solid Acid Catalysts

Catalyst reaction temp./K Coversion/% Selectivity/% (ethanol basis)  

Shokubai Kouza, Vol. 8, p.285, Kodansha, Tokyo, 1985 (in Japanese). 

Murakami, T. Hattori, H. Uchida, Kogyo Kagaku Zasshi, 72, 1945, (1969) (in Japanese) Rhone-Poulenc, Jpn. Kokai, 1979-151905. 

Wakushima, T. Shimizu, H. Masumoto, T. Yashima, in Catalysis Acids and Bases, (B. Imelik et al., eds.), Elsevier, Amsterdam, 1985, p.205. 

1671 K. Arata, M. Hino, Shokubai (Catalyst), 25, 124(1983) 

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Under very mild conditions (0-20°C, 200 Torr ethylene pressure), ethylene was shown to be selectively dimerized to n-butenes over RhY (140). As shown in Fig. 14, 1-butene was formed initially but further isomerized to an equilibrium composition of -butenes with increasing reaction time. In a comparative experiment using HY as a typical solid-acid catalyst, no ethylene conversion was measurable up to 200°C, and at higher temperatures unselective polymerization and cracking reactions occurred. This provided good evidence that the selective dimerization over RhY did not proceed via a carbenium ion mechanism. 

Through this systematic study, Exelus was able to identify an optimal window of design parameter values that were then used to develop the catalyst. By judicious manipulation of the active material composition, researchers at Exelus developed a unique solid-acid catalytic system that has roughly 400% more active sites than a typical solid-acid catalyst. The catalyst activity was found to be higher than a typical liquid acid catalyst, which means that smaller amounts of catalyst are required, allowing one to design alkylation reactors with significantly lower volumes. 

HZSM-5 zeolite catalysts show high shape selectivity, because they have very fine micro pores within its crystallite [1], The pore diameter is almost equal to sizes of mono-aromatic molecules [2]. HZSM-5 catalysts are typical solid-acid catalysts, and their acid sites are distributed not only within but also on the outer surface of the crystallite [1,3]. Therefore, the shape selectivity of HZSM-5 zeolite is affected strongly by the size of the crystallite, the intracrystalline diffusivities of hydrocarbons and acidic properties within and on the outer surface of the crystallite [4-7],... 

Among a series of typical solid acid catalysts such as H-form zeolite, sulfated zirconia, sulfo-nated activated carbon, and Amberlyst polymer-based materials, sulfonated activated carbon showed a remarkably high yield of 40.5% of glucose [153]. 

The experimental results are presented for the esterification of dodecanoic acid (C12H24O2) with 2-ethylhexanol (CgHigO) and methanol (CH4O), in presence of solid acid catalysts (SAC). Reactions were performed using a system of six parallel reactors (Omni-Reacto Station 6100). In a typical reaction 1 eq of dodecanoic acid and 1 eq of 2-ethylhexanol were reacted at 160°C in the presence of 1 wt% SAC. Reaction progress was monitored by gas chromatography (GC). GC analysis was performed using an InterScience GC-8000 with a DB-1 capillary colunm (30 m x 0.21 mm). GC conditions isotherm at 40°C (2 ntin), ramp at 20°C min to 200°C, isotherm at 200°C (4 min). Injector and detector temperatures were set at 240°C. 

Traditionally, the production of LABs has been practiced commercially using either Lewis acid catalysts, or liquid hydrofluoric acid (HF).2 The HF catalysis typically gives 2-phenylalkane selectivities of only 17-18%. More recently, UOP/CEPSA have announced the DetalR process for LAB production that is reported to employ a solid acid catalyst.3 Within the same time frame, a number of papers and patents have been published describing LAB synthesis using a range of solid acid (sterically constrained) catalysts, including acidic clays,4 sulfated oxides,5 plus a variety of acidic zeolite structures.6"9 Many of these solid acids provide improved 2-phenylalkane selectivities. 

Acid catalysts are used to promote the alkylation of ethylene to benzene. Acid catalysts suitable for benzene alkylation include protonic acids (i.e., H2SO4, HF, and H3PO4), Friedel-Crafts catalysts (i.e., AICI3 and BF3), and more recently, solid acid catalysts. Solid acid catalysts used for the commercial manufacture of EB are typically zeolitic molecular sieves and materials such as ZSM-5, faujasite, MCM-22, and zeolite beta. Zeolites physical and chemical properties can be modified to optimize the activity, selectivity, and stability of the catalysts. This flexibility of zeolites has made them the preferred catalyst of choice. 

The activity of Nafion as a catalyst has been increased by applying it on silica by the sol-gel method using tetramethoxysilane20 or tetraethoxysilane and dimethyl-diethoxysilane.21 This increased its activity as a solid acid catalyst up to 100 times that of bulk Nafion. It performed better than Nafion on carbon in the dimerization of a methylstyrene. It was a much better catalyst (seven times on a weight basis) than Amberlyst 15, a typical sulfonic acid ion-exchange resin. It was more active in the benzyla-tion of benzene (6.6) than trifluoromethylsulfonic acid, a reaction in which Amberlyst 15 and p-toluenesulfonic acid... 

Dimethylether. Several strategies for the production of dimethyl ether (DME) are described, e.g. direct synthesis from syngas according to equation (8.5) or via dehydration of methanol according to equation (8.6). From a mechanistic point of view direct synthesis proceeds also via methanol formation and subsequent release of water but without procedural isolation of methanol. The process can also be designed to yield both methanol and DME. Established methanol catalysts are employed for methanol formation and typical dehydration catalysts are solid-acid catalysts, e.g. alumina, silica-, phosphorus- or boron-modified alumina, zeolite, (sili-co)aluminophosphates, tungsten-zirconia or sulfated-zirconia. " ... 

MTBE is commercially produced by the reaction of isobutylene with methanol in the presence of an acidic ion-exchange resin as catalyst, usually in the liquid phase and at temperatures below 100°C. A typical catalyst is sulfonated styrene/divinylbenzene resin catalyst. Other solid acid catalysts such as bentonites are also effective and other novel catalysts have recently been discovered. Isobutylene is obtained from field butane by initial isomerization of n-butane to isobutane, followed by dehydrogenation to isobutylene. Commercial preparations of MTBE are 95.03 to 98.93% pure. Impurities are methanol (<0.43%), t-butyl alcohol (<0.80%), and diisobutylene (<0.25%). 

Magnesium oxide, CaO, SrO, and BaO are typical solid base catalysts. In particular, MgO is a representative one and positioned as a sort of reference catalyst among solid base catalysts like Si02 — AI2O3 among solid acid catalysts. In contrast, very little investigation of BeO and RaO as catalysts has been done because of toxicity and radioactivity, respectively. 

Dehydrohalogenation was also indicated to be catalyzed by acid-base pair sites. Table 3.18 shows the product distribution from dehydrochlorination of 1,1,2-trichloroethane over alumina as well as over silica-alumina (a typical solid acid) and KOH —Si02 (a typical solid base). Silica-alumina and KOH —Si02 showed products typical of acid and base catalysts, respectively. On the other hand, the products from alumina are different from the others and well explained by a concerted mechanism catalyzed by both acid and base. 

Table I gives the compositions of alkylates produced with various acidic catalysts. The product distribution is similar for a variety of acidic catalysts, both solid and liquid, and over a wide range of process conditions. Typically, alkylate is a mixture of methyl-branched alkanes with a high content of isooctanes. Almost all the compounds have tertiary carbon atoms only very few have quaternary carbon atoms or are non-branched. Alkylate contains not only the primary products, trimethylpentanes, but also dimethylhexanes, sometimes methylheptanes, and a considerable amount of isopentane, isohexanes, isoheptanes and hydrocarbons with nine or more carbon atoms. The complexity of the product illustrates that no simple and straightforward single-step mechanism is operative rather, the reaction involves a set of parallel and consecutive reaction steps, with the importance of the individual steps differing markedly from one catalyst to another. To arrive at this complex product distribution from two simple molecules such as isobutane and butene, reaction steps such as isomerization, oligomerization, (3-scission, and hydride transfer have to be involved.

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