Wolfgang F. Hoelderich

Environmentally benign manufacturing of fine and intermediate chemicals

Environmental concerns and regulations are getting more and more severe. A lot of efforts and progress have been accomplished in the environmentally benign and sustainable industrial manufacture of fine and intermediate chemicals in recent years. Solid acid–base catalyzed commercialized processes as well as heterogeneously catalyzed oxidation processes and a dehydrogenation process are reviewed. The examples for acid catalyzed processes are the BASF-tert.-butylamine-process and the Beckmann-rearrangment to form ϵ-caprolactam. For solid base catalyzed processes, the Sumitomo-process for the production of 5-ethylidene-bicyclo [2.2.1] hepta-2-ene and other double bond isomerization processes have been chosen. In addition, short comments are given on side chain alkylation and transesterification reactions. Acid–base bifunctional heterogeneous catalysts are employed for the hydrogenation of aromatic and aliphatic carboxlic acids to the corresponding aldehydes. In oxidation processes, the oxidation of an unsaturated alcohol to the corresponding aldehyde will be demonstrated on the BASF-citral-process in which a silver catalyst is applied. For the oxidation of alkylaromatic compounds to the corresponding acids, the oxidation of β-picoline to nicotic acid in the presence of V2O5/TiO2-catalyst will be discussed. The oxidation of benzene to phenol using N2O as oxidant over a MFI-type zeolite is also described. The dehydrogenation of α-limonene to p-cymene over Pd/SiO2 catalyst is selected as an example for the environmentally benign use for a renewable feedstock.

ϵ-Caprolactam: new by-product free synthesis routes

The production of the nylon precursor ϵ-caprolactam via the Beckmann rearrangement is one of the large industrial processes worldwide. In this work, the state-of-the-art processes are summarized and the two main pathways for new production capacities (the butadiene-based and especially the heterogeneously catalyzed routes starting from benzene/cyclohexanone oxime) are described. Additionally, the new recycling processes to recover caprolactam from waste carpets and some new approaches are described.

Oxidation reactions in the synthesis of fine and intermediate chemicals using environmentally benign oxidants and the right reactor system

This review outlines several approaches for designing new and environmentally friendly heterogeneously catalyzed oxidation processes for the synthesis of fine and intermediate chemicals. Environmentally benign oxidants such as molecular oxygen, hydrogen peroxide or nitrous oxide can be activated on suitable heterogeneous catalysts showing high activity and selectivity toward the desired oxygenated products. Several examples illustrate that features known from the synthesis of bulk chemicals can successfully be applied for manufacturing intermediate and specialty chemicals applying conventional industrial reactor systems. Direct oxidation of isoprenol, b-picoline, and benzene are chosen as examples for continuous gas-phase processes, oxidation of pinene and propylene as examples for semi-continuous or batchwise processes in the liquid phase.

Direct oxidation of propylene and other olefins on precious metal containing Ti-catalysts

Abstract The properties and performance of an O2–H2 system used for the direct oxidation of olefins have been studied on the example of direct oxidation of propylene. Ti-catalysts modified by impregnation with palladium tetraminenitrate and platinum tetraminechloride and by followed reduction under various conditions were used as bifunctional catalysts. New investigations showed that the pre-impregnation of the catalyst with salt and the using of alcohols or ketones as solvent for the impregnation of the catalyst with precious metal improved the selectivity of propylene oxide (PO). Also the influence of other precious metals such as Ir or Au as promoters on titanium silicalite-1 (TS-1) has been studied. In addition to propylene, other olefins like styrene or terpenes were also tested in direct oxidation with an O2–H2 system by using Pd/Pt/TS-1 or Pd/Pt/Ti-MCM-41, respectively. The use of these olefins as substrate lead to low yields of the desired product and showed the limits of the O2–H2 oxidation system, so far.

‘One-pot’ reactions: a contribution to environmental protection

Abstract The direct oxidation of benzene, β-picoline and propylene, respectively, were carried out by ‘one-pot’ reactions. A steamed H-[Al]-ZSM-5 with strong Lewis acid sites yields the best results in the oxidation of benzene with N 2 O. β-picoline can be directly oxidized with O 2 in the gas-phase to nicotinic acid in the presence of a V 2 O 5 impregnated TiO 2 catalyst having Bronsted acid sites in addition to redox properties. Yields up to 98% can be achieved. The propylene oxide synthesis is based on the oxidation of propylene by using a O 2 –H 2 gas mixture over Pd/Pt-impregnated TS-1. Selectivities up to 85% are obtained at conversions between 15 and 20%.

Fries rearrangement in methane sulfonic acid, an environmental friendly acid

The Fries rearrangement of phenyl acetate for the paracetamol process is usually performed in hydrofluoric acid (HF). We have optimized this reaction with methane sulfonic acid (MSA), a strong, stable and biodegradable acid, to give para-hydroxyacetophenone with high conversion and selectivity (up to 92% of para-isomer and 8% of ortho-isomer at 100% conversion).

New Direct Hydroxylation of Benzene with Oxygen in the Presence of Hydrogen over Bifunctional Palladium/Platinum Catalysts

Benzene can be hydroxylated directly to phenol with oxygen in the presence of hydrogen over Pt/Pd containing acid catalysts such as zeolites (BEA, MOR, FER, MFI), acid resins such as Amberlyst, or Nafion/silica composites. The best results were obtained over Nafion/silica composites. As main side products hydroquinone and catechol were found. Various reaction parameters and catalyst preparation methods were optimised.

Preparation of superbases and their use as catalysts for double-bond isomerization

Abstract Solid superbases with basic strength up to H_≥37 can be prepared by a treatment of the carriers such as γ-alumina and MgO successively with alkali metal hydroxide and alkali metal under nitrogen or with cesium acetate followed by calcination at 700–750°C in vacuum. The catalytic activity of such superbases was studied in the double bond isomerization of β-pinene.

A Review of Mass Transfer Controlling the Reaction Rate in Heterogeneous Catalytic Systems

Mass transfer limitations play an important role on the rate of reaction; the rate of conversion and product formation, including in the catalytic systems. In a homogeneous catalytic reaction in which all substances (reactant(s), product(s), and catalyst) are in the same phase, the effect of mass transfer between phases is mostly negligible. In a heterogeneous catalytic reaction; however, the catalyst is usually in a different phase from the reactant(s). Commonly the catalyst is in the solid phase embedded in the reacting species which usually are in the liquid or gaseous phase. Consequently, the reaction rate is principally relied on the mass transfer or diffusion between these phases. A lot of efforts have been made, due to the important roles of mass transfer effects on the reaction rate. The main purpose for this chapter is to apply the basic restriction of mass transfer on the heterogeneous catalytic reaction. The illustrations based on the literature reviews in the heterogeneous catalytic processes are conducted for elucidation. Since the reaction catalyzed by solid catalysts occurs when the reactant molecules come in contact with the active sites, which are usually located inside the catalyst pores. In other words, the catalytic reaction is taken place after the reactant molecules diffuse through the fluid layer surrounding the catalyst particles (external diffusion or film diffusion), then through the pore with in the particle (internal diffusion). The internal diffusion of the molecules competes with the reaction; at the same time, the external mass transfer is dependent on the stagnant film thickness and the activity on the outer layer. Hence, the diffusion of molecules is not only hindered by the other molecules, but also by the physical hindrances. The classical seven steps for a catalytic reaction (Fig. 1), i.e. (1) diffusion of the reactants from the bulk phase (boundary layer) to the external surface of the catalyst pellet (film diffusion or interphase diffusion), (2) diffusion of the reactant from the pore mouth through the catalyst pores to the immediate vicinity of the internal catalytic surface; the point where the chemical transformation occurs, (pore diffusion or intraparticle diffusion), (3) adsorption of reactants on the inner catalytic surface, (4) reaction at specific active sites on the catalyst surface, (5) desorption of the products from the inner surface, (6) diffusion of the products from the interior of the pellet to the pore mouth at the external surface, and (7) diffusion of the products from the external pellet surface to the bulk fluid (interphase diffusion), are generally used as the key for explanation.

Transesterification of methyl benzoate and dimethyl terephthalate with ethylene glycol over basic zeolites

The transesterification of methyl benzoate and dimethyl terephthalate with ethylene glycol to 2-hydroxyethyl benzoate and 2-hydroxyethyl terephthalate, respectively, was investigated in the presence of various basic zeolites having different basic strengths. The reactions were carried out in the liquid phase at 150°C and 180°C under continuous removal of deliberated methanol. The dependence of conversion and selectivity is discussed upon temperature, various reactant/catalyst ratios and the starting material ratio.