Polyol processing continuous process

In this work, the novel polyol process was developed to support highly dispersed Pt particles on carbon support with more than 60 wt% in a single reduction step. The synthesis parameters were controlled to optimize the preparation method. Further the continuous polyol process was investigated to obtain an ultra high loading (> 75 wt %), where the reduction steps were repeated two or three times in the polyol process. Thus prepared highly dispersed Pt catalysts were applied to the cathode catalyst of DMFC. The relationship between the structure of R in the catalyst and performance of the DMFC was suggested. 

Following these batch experiments which showed the feasibility of millimeter-wave polyol processing, analysis indicated diat a continuous polyol process might be feasible, and might have significant advantages over the batch process. Conceptually, a continuous process should have much higher... 

Fig, 3. Schematic of continuous polyol process using 83 GHz millimeter-wave beam system and silica reaction tube... 

Propylene oxide [75-56-9] (methyloxirane, 1,2-epoxypropane) is a significant organic chemical used primarily as a reaction intermediate for production of polyether polyols, propylene glycol, alkanolamines (qv), glycol ethers, and many other useful products (see Glycols). Propylene oxide was first prepared in 1861 by Oser and first polymerized by Levene and Walti in 1927 (1). Propylene oxide is manufactured by two basic processes the traditional chlorohydrin process (see Chlorohydrins) and the hydroperoxide process, where either / fZ-butanol (see Butyl alcohols) or styrene (qv) is a co-product. Research continues in an effort to develop a direct oxidation process to be used commercially. 

In 1976, Meluch and Campbell at General Motors obtained a patent10 for a steam hydrolysis depolymerization of PUR. High-pressure steam hydrolyzes flexible PUR foams rapidly at temperatures of 232-316°C to form diamines and polyols. The diamines are distilled and extracted from the steam and the polyols are obtained from the hydrolysis residue. In 1977, Bayer AG obtained a patent for a continuous PUR hydrolysis process using a specially designed extruder.11... 

Gyttorp [Named after a small Swedish town] A continuous process for nitrating polyols to form nitrate esters, used as explosives. Similar to the Biazzi process. 

A number of issues related to this reaction should be discussed. First, a polymer is rarely isolated in this form. In the early 1950s a technology was developed that has since come to be known as the one-shot process. While the technique certainly produces a capped polyol, it immediately reacts further to achieve its ultimate form (Figure 2.6, bottom). You will notice that the capped polyol still has isocyanate functionalities as end groups. Regardless of the process, these end groups must continue to react (by the addition of water and/or a catalyst) to complete the process. While this reaction produces one of the most commonly constructed polyurethanes, it is rarely isolated as an end product. 

Figure 11.36 By extending the polyol reaction for a ven time period, various polyhedral shapes capped with 100 and 111 faces can be obtained in high yield, a) A schematic of the nucleation and growth process, in which silver continuously deposits onto the 100 faces to eventually result in a completely 111 -bound octahedron, b to f) SEM images of cubes, truncated cubes, cuboctahedra, truncated octahedra, and octahedra, respectively (scale bar 100 nm). Reproduced with permission from reference [91]. (2006) Wiley-VCH Verlag GmbH Co. KGaA.

In the prepolymer method for one-shot polyether flexible urethane foams the primary role of the silicone surfactant is to lower surface tension and to provide film (cell-wall) resilience. Resilient films prevent the collapse of the foam during foam rise and continue to stabilize it until the foam is self-supporting. A secondary, but nevertheless important role of the silicone surfactant is cell-size control. The silicones can be added to the formulation in any of the 2 to 6 streams usually fed to the mixing head in the one-shot process. Usually, however, the silicone is metered separately, in combination with the polyol, or added as a wa-ter/amine/silicone mixture. It can also be added in the fluorocarbon blowing agent (52). 

This operation can be described by a specific example, such as that of the production of an adduct with glycerin (Fig. 14.9). Although the manufacture of this polyether-polyol can be conducted continuously, most manufacturers operate with a batch process, in an inert atmosphere to prevent oxidation, which is responsible for staining the product, and in the absence of any trace of moisture that could lead to the formation of undesirable secondary derivatives. 

The polyether triols are the most important class of polyether polyols and they are used in flexible PU foam fabrication. The majority of polyether triols used in flexible foams are copolymers of PO-EO. Random copolymers are used in continuous slabstock flexible foams and block copolymers (PO-EO), with terminal poly[EO] block, are used in moulded foams (hot moulding and cold cure moulding processes). 

In the history of PU, some continuous processes for polyether polyol synthesis by anionic polymerisation were developed, but only at small scale (i.e., pilot plant). Tubular reactors with static mixing systems or a column with plate reactor types were used, but these technologies were not extended to industrial scale levels. The first continuous process for high MW polyether synthesis was developed by Bayer (IMPACT Technology) and is based on the very rapid coordinative polymerisation of alkylene oxides, especially PO, with dimetallic catalysts (DMC catalysts - see Chapter 5). A principle technological scheme of a polyether polyol fabrication plant is presented in Figure 4.30. 

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