Processes Using Solid-State Acid Catalysts

Processes Using Solid-State Acid Catalysts 

Several solid acid catalysts were tested in the laboratory for the alkylation of ethylene with isobutane following the introduction of the sulfuric acid alkylation process. These were mostly derived from aluminum chloride or boron trifluoride and were never used in the full-scale production of alkylates. 

Snitable solid acids have been difficult to find. Those used for benzene alkylation ate not snfficiently acidic for economic operation and, also, the olefin can polymerize on the catalyst smface. This blocks the active sites and prevents adequate hydrogen transfer. Frequent regeneration of the catalyst is not economic. The use of antimony pentafluoride slurried with the hydrocarbons is one of the options that has been investigated in recent years.  

The best solution appears to be the use of an almost insoluble liquid catalyst held within the pores of a suitable inert support. Supported liquid catalysts are well known and can be used with a continuous catalytic regeneration system similar to that developed for catalytic reforming processes. Haldor Topsoe has successfully tested trifluoromethane sulfonic acid in this way since 1993 with a variety of olefin feeds. No formal regeneration was necessary apart from periodic removal of some catalyst for reimpregnation and the recovery of dissolved acid from the alkylate. Both catalyst and support are, therefore, recirculated. The small quantity of polymeric by-products formed (acid soluble oil) appears to be less tlm that formed in the sulfuric acid process, but slightly more than in the HF process. 

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Processes Using Solid-State Acid Catalysts... 

A method for the depolymerisation of PETP fibres using quarternary ammonium salt phase transfer catalysts in saponification processes at atmospheric pressure and temperatures as low as room temperature is reported. Terephthalic acid was produced in yields as high as 93%. Also reported are similar processes for the depolymerisation of nylon 66 and nylon 46 fibres. Nylon 46 oligomers produced were repolymerised using solid-state polymerisation to produce high molecular weight nylon 46. Nylon 66 was depolymerised to produce oligomers and adipic acid in reasonable yields. 11 refs. USA... 

Considering all we know up to now, the specific properties of zeolites can be summarized as follows. Zeolites are aluminosilicates with defined microporous channels or cages. They have excellent ion-exchange properties and can thus be used as water softeners and to remove heavy metal cations from solutions. Furthermore, zeolites have molecular sieve properties, making them very useful for gas separation and adsorption processes, e.g., they can be used as desiccants or for separation of product gas streams in chemical processes. Protonated zeolites are efficient solid-state acids, which are used in catalysis and metal-impregnated zeolites are useful catalysts as well. 

Low molecular weight PET and PBT resins are made by melt processes. For higher molecular weight resins, both melt processes or solid-state polymerization are used. Although terephthalic acid can be directly esterified, the most common process involves transesterification of dimethyl terephthalate with ethylene glycol or 1,4-butanediol in the presence of trace amounts of metal ion catalysts (67,68). 

Cumene manufacture consumed about 10 percent (2.2 billion lb) of the propylene used for chemicals in the United States in 1998. It is prepared in near stoichiometric yield from propylene and benzene with acidic catalysts (scheme below). Many catalysts have been used commercially, but most cumene is made using a solid phosphoric acid catalyst. Recently, there has been a major industry shift to zeolite-based catalyst. The new process has better catalyst productivity and also eliminates the environmental waste from spent phosphoric acid catalyst. It significantly improves the product yield and lowers the production cost. Cumene is used almost exclusively as feed to the cumene oxidation process, which has phenol and acetone as its coproducts. 

By using solid-state NMR, the hydrothermal stabilities (under 100% steam at 1073 K) of HZSM-5 zeolites modified by lanthanum and phosphorus have been studied. They are excellent zeolite catalysts for residual oil selective eatalytic cracking processes. It was indicated that the introduction of phosphorus to the zeolite via impregnation with orthophosphoric acid led to dealumination as well as formation of different A1 species, which were well distinguished by Al 3Q MAS NMR and P MAS NMR spectra. " ... 

Sulfonated EPDMs are formulated to form a number of rubbery products including adhesives for footwear, garden hoses, and in the formation of calendered sheets. Perfluori-nated ionomers marketed as Nation (DuPont) are used for membrane applications including chemical-processing separations, spent-acid regeneration, electrochemical fuel cells, ion-selective separations, electrodialysis, and in the production of chlorine. It is also employed as a solid -state catalyst in chemical synthesis and processing. lonomers are also used in blends with other polymers. 

In all cases, the solid-state NMR ( Si and C) spectra showed the presence of the organic fragment whatever the catalyst used (acid or base). Only T, C-Si(OSi)2(OR) and T, C-Si(OSi)3 are observed from Si NMR, proving the preserved Si-C bonds in the hybrid network after the hydrolysis-condensation process. 

A remarkable synthesis of oxalate salts using a supercritical mixture of CO2 and CO under very drastic conditions (400 bar, 380°C) in the presence of solid 082(003) was reported [71]. Friedel-Crafts-type alkylations on zeolites [72] or other solid acid catalysts [73] have been studied using SCCO2 as the medium. Performing the reaction in the supercritical state was found to be superior to either liquid or gas phase processes. Using scCOj lead to enhanced catalyst life-... 

An alkaline catalyst, such as sodium methoxide, or metallic sodium is normally used. The fat must be dry and free of fatty acids to prevent destruction of the catalyst. When the reaction is conducted at a temperature that maintains the fat in a molten state the process leads to "random" interesterification. "Directed" interesterification takes place when a portion of the fat is in a solid state. In a typical case of random interesterification the fat is heated in a closed tank under vacuum to 135°-150°C, 0.1% of catalyst is added, and mixed thoroughly for about 0.5 hr. A sample is taken for analysis and if the reaction is not complete an additional amount of catalyst is added and mixed for another 0.5 hr. When the interesterification is complete approximately 0.05% of phosphoric acid is added with agitation to neutralize the catalyst. The batch is then washed or bleached. 

Water and carbonated beverage bottles are made predominantly from poly(ethylene terephthalate) (PET). The polymer is made by condensation reaction of ethylene glycol with either terephthalic acid or its dimethyl ester. The process in practice includes three steps prepolymer formation, melt condensation to increase viscosity, and solid-state polymerization at 180-230°C to yield a resin with an average molecular weight that is high enough for use as bottle resins. Antimony trioxide is used as a catalyst in polymerization (Duh, 2002). 

Kim et al. [19] fabricated PET/clay composites using a two-step in-situ polymerization method. In the first step, a slurry mixture of monomer (purified tereph-thalic acid and ethylene glycol), polycondensation catalyst, clays, and some additives was kept at 250 °C for 5-6h in the esterification step. Then, it was transferred to a polycondensation reactor until the intrinsic viscosity (IV) value reached 0.6dlg" . Then, the materials were pelletized. Furthermore, a solid-state polymerization (SSP) process is carried out to conduct the polymerization process further. SSP was carried out at between 220 and 145 °C for around 8h until the IV reached 0.8dlg . ... 

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