Bulk chemical production, aqueous

Hydroformylation comprises the state-of-the-art of bulk chemical production via aqueous-biphasic processes. At present five plants produce worldwide some 800,000 tpy of oxo products [1], Another bulk process - the hydrodimerization of butadiene and water, a variant of telomerization - is mn by Kururay with a capacity of 5000 tpy (Equation 5.2 [3 lb,36]). 

Biocatalysts are most often employed in aqueous solution and offer the chemist exquisite selectivity. It is therefore not surprising that they are now being employed at the industrial level, and of course water is the solvent. The application of biocatalysts to industrial chemical synthesis was recently reviewed, and two examples will be highlighted here. However, enzymes in water have found use in all sectors of the chemical manufacturing industry from pharmaceuticals through fine chemicals and materials to bulk chemical production. 

Table I. Bulk chemical production in aqueous two-phase systems...

Even though aqueous two-phase sytems hold promise for bulk chemical production, their applicability on a large scale is not assured unless the phase components, at least, the fractionated dextran, are replaced by cheaper polymers, or technology is developed permitting full recycling of the polymers. These aspects are discussed later in the paper. 

Production of fine chemicals. Inspite of the interest shown in the production of bulk chemicals in aqueous two-phase systems, the potential of these systems for fine chemical production has not yet been exploited. The only bioconversion reported has been the deacylation of benzyl penicillin to 6-amino penicillanic acid (15). Today, industrial deacylation is performed by penicillin acylase in an immobilized form. The productivity of the reaction in a... 

The synthesis of aldehydes via hydroformylation of alkenes is an important industrial process used to produce in the region of 6 million tonnes a year of aldehydes. These compounds are used as intermediates in the manufacture of plasticizers, soaps, detergents and pharmaceutical products [7], While the majority of aldehydes prepared from alkene hydroformylation are done so in organic solvents, some research in 1975 showed that rhodium complexes with sulfonated phosphine ligands immobilized in water were able to hydroformylate propene with virtually complete retention of rhodium in the aqueous phase [8], Since catalyst loss is a major problem in the production of bulk chemicals of this nature, the process was scaled up, culminating in the Ruhrchemie-Rhone-Poulenc process for hydroformylation of propene, initially on a 120000 tonne per year scale [9], The development of this biphasic process represents one of the major transitions since the discovery of the hydroformylation reaction. The key transitions in this field include [10] ... 

The influence of process variables such as the temperature, pressure of H2 and CO on the hydroformylation reaction is well recognized by all researchers. However, other aspects, such as stirring speed, the shape and size of the stirrer, relative amounts of the aqueous and organic phases, etc. are usually overlooked by people working in laboratories far from the actual chemicals production. A few papers in the open literature deal with these questions, of which perhaps the most important concerns the location of the chemical reaction. Does it takes place in the bulk phases or at the interphase region ... 

Likewise, a thermoregulated phase transfer process within the aqueous/organic two-phase system has been reported by Jin and co-workers (cf. Section 3.1.1.1) [290]. A water-soluble supramolecular Rh catalyst based on functionalized /1-cyclodextrin was also described [291]. In a two-phase system this catalyst may function as a carrier for the transfer of both the starting material and the product between the different phases. As an alternative to polar media for biphasic hydroformylation, Chauvin et al., used ionic liquids based on imidazolium salts which are well known for dimerization reactions (cf. Sections 2.3.1.4 and 3.1.1.2.2) [270, 271, 292]. For introduction into technical processes the currently availability and price of ionic liquids could be a drawback, especially for bulk chemicals such as 0x0 products. 

Production of bulk chemicals. The production of solvents is normally characterized by a general inhibition phenomenon which has been mainly attributed to the changes in membrane permeability, or to the toxic effects on the metabolic pathway. Aqueous two-phase systems have been shown to be effective as media for the extractive fermentation of a number of solvents which include ethanol, acetone-butanol and acetic acid (3). Improved productivity has been achieved in most of the cases as compared to the conventional fermentations, which is significantly due to the elimination of product inhibition. However, there is an indication that changes in the microenvironment of the microbial cells due to the presence of non-metabolizable polymers could also contribute, in the initial phases, to the increased production. The addition of PEG and dextran to a growth medium, for instance, was shown to give increased initial ethanol yields, as a result of decrease in the chemical potential of water (8). 

Due to the large-scale production of urea as a bulk commodity, it is readily available in large quantities. Since the involved reactants CO2 and NH3 needed for urea synthesis are bulk chemicals that are produced directly from air and natural gas, using the well-known industrial Haber-Bosch process, urea can be produced at a low price [8]. Also, urea is nontoxic, noncorrosive and can easily be handled as aqueous solutions, such as a 32.5 wt % solution with the trade name AdBlue . 

For more than a century, a number of different aluminum alloys have been commonly used in the aircraft industry These substrates mainly contain several alloying elements, such as copper, chromium, iron, nickel, cobalt, magnesium, manganese, silicon, titanium and zinc. It is known that these metals and alloys can be dissolved as oxides or other compounds in an aqueous medium due to the chemical or electrochemical reactions between their metal surfaces and the environment (solution). The rate of the dissolution from anode to cathode phases at the metal surfaces can be influenced by the electrical conductivity of electrolytic solutions. Thus, anodic and cathodic electron transfer reactions readily exist with bulk electrolytes in water and, hence, produce corrosive products and ions. It is known that pure water has poor electrical conductivity, which in turn lowers the corrosion rate of materials however, natural environmental solutions (e g. sea water, acid rains, emissions or pollutants, chemical products and industrial waste) are highly corrosive and the environment s temperature, humidity, UV light and pressure continuously vary depending on time and the type of process involved. ... 

It is common practice to refer to the molecular species HX and also the pure (anhydrous) compounds as hydrogen halides, and to call their aqueous solutions hydrohalic acids. Both the anhydrous compounds and their aqueous solutions will be considered in this section. HCl and hydrochloric acid are major industrial chemicals and there is also a substantial production of HF and hydrofluoric acid. HBr and hydrobromic acid are made on a much smaller scale and there seems to be little industrial demand for HI and hydriodic acid. It will be convenient to discuss first the preparation and industrial uses of the compounds and then to consider their molecular and bulk physical properties. The chemical reactivity of the anhydrous compounds and their acidic aqueous solutions will then be reviewed, and the section concludes with a discussion of the anhydrous compounds as nonaqueous solvents. 

Aqueous environments will range from very thin condensed films of moisture to bulk solutions, and will include natural environments such as the atmosphere, natural waters, soils, body fluids, etc. as well as chemicals and food products. However, since environments are dealt with fully in Chapter 2, this discussion will be confined to simple chemical solutions, whose behaviour can be more readily interpreted in terms of fundamental physicochemical principles, and additional factors will have to be considered in interpreting the behaviour of metals in more complex environments. For example, iron will corrode rapidly in oxygenated water, but only very slowly when oxygen is absent however, in an anaerobic water containing sulphate-reducing bacteria, rapid corrosion occurs, and the mechanism of the process clearly involves the specific action of the bacteria see Section 2.6). 

Jang, J.S., Li, W., Oh, S.H., and Lee, J.S. (2006) Fabrication of CdS/Ti02 nano-bulk composite photocatalysts for hydrogen production from aqueous H2S solution under visible light. Chemical Physics Letters, 425 (4-6), 278-282. 

An example of different domains in a copper corrosion problem is shown schematically in Fig. 11.2. Four of the domains domains are volumetric. That is, they are three-dimensional, so concentrations of species within these domains might have units of mol/m3, for example. The volumetric domains shown correspond to the gas (G), bulk copper that is being corroded (B), an aqueous layer (A), and a layer in which corrosion products have formed (C). The list of species that can exist in one domain may be (and surely is) different from the species present in another domain. Chemical reaction rates-of-progress within a volumetric domain have units like mol/m3-s. 

The interface between two volumetric domains is designated a surface domain, and its dimensionality is one less than a volumetric domain. Concentrations of species in a surface domain have dimensions of mol/m2, for example. The four types of surface domains shown in Fig. 11.2 are A-G, the interface between the aqueous domain and the gas A-C, the interface between the aqueous domain and the corrosion-product layer C-G, the interface between the corrosion layer and the gas and C-B, the interface between the corrosion layer and the bulk copper layer. Chemical reactions of species residing in one volumetric domain with species in another volumetric domain have to occur at an interface, namely a surface... 

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