Alkaline hydroxide activation

A. Linares-Solano, D. Lozano-Castello, M.A. Lillo-Rodenas and D. Cazorla-Amoros "Carbon Activation by Alkaline Hydroxides Preparation and Reactions, Porosity and Performance . In Ljubisa R. Radovic, editor. Chemistry and Physics of Carbon CRC Press, Taylor Francis Group, Boca Raton, FL (2008), ISBN 978-1-4200-4298-6. 

The next major theory of metal ammines was proposed by Carl Ernst Claus (1796—1864). In 1854, Claus rejected the ammonium theory and suggested a return to Berzelius view of complexes as conjugated compounds. He compared the platinum ammines not with ammonium salts nor with ammonium hydroxide but with metal oxides. He designated the coordinated ammonia molecule as passive, in contrast to the active, alkaline state in the ammonium salts, where it can easily be detected and replaced by other bases . 

When the diisocyanate and polyol are being reacted together, the diisocyanate is kept in excess as long as possible. The overall conditions are kept slightly acidic to reduce side reactions taking place. The acidity is a must when there is more polyol than diisocyanate present. The older-style PPG polyols may contain traces of potassium hydroxide (KOH). The KOH is a very active alkaline. Even small traces have a strong effect. 

This trend observed for chemically activated carbon fibers is very different from that obtained for the ACF prepared by physical activation of the same raw carbon fiber with C02 and steam, where the maximum scattering appears at the external zone of the fiber (see Figure 4.19). In the case of NaOH and KOH activation, the results indicate that the activating agents penetrate the fiber, which is a new interesting observation, which points out that alkaline hydroxides penetrate much better than C02 and steam. The different evolution of porosity obtained for the chemically activated carbon fibers compared to the physically activated carbon fibers could be explained considering the important differences between the mechanisms of both the activation methods. 

All oxidizing agents decompose it readily HaO and arsenic trioxid being formed by the less active oxidants, and HaO and arsenic acid by the more active. Solid potassium hydroxid decomposes the gas partially, and becomes coated with a dark deposit, which seems to be elementary arsenic. Solution of the alkaline, hydroxids absorb and decompose it H is given off and an alkaline-... 

Nature of catalyst. Of the active alkaline cata-lysts, which include the hydroxides of alkali and alkaline earth metals, alkali carbonates and bicarbonates, sodium methoxide, potassium phosphate and acetate, potassium carbonate proved to be the most effective catalyst. 

During the last 15 years our group has been researching carbon activation by alkaline hydroxides, analyzing its different aspects. Thus, we have compared both NaOH and KOH with other chemical agents [23], we have analyzed several variables of this activation process [21,23,42,43,70-72,77,88,98], we have studied the reactions taking place [99-101], we have worked on their porosity characterization [12,13,70,102-106], and, finally, we have studied these ACs in several applications [71,107-114]. From all these studies, which cover most of the aspects of carbon activation by alkaline hydroxides, we have been able to identify additional advantages to those mentioned earlier (1) the precursor ash content has no... 

Variables of the alkaline hydroxide activation method and suitability of... 

Singular characteristics of the AC prepared by alkaline hydroxide activation that can have both high MPV and narrow MPSD... 

As discussed in Section II, ACs with well-developed porosity can be prepared by activation with alkaline hydroxides by changing the experimental conditions. However, from an application point of view, the precise tailoring of porosity (not only pore volume and surface area but also pore size distribution) is the most important aspect of the carbon activation process. Thus, in the present section we will emphasize the type of microporosity that can be developed during hydroxide... 

Considering the importance of preparing adsorbents with high adsorption capacity and a homogeneous MPSD, alkaline hydroxide activation with a selection of the most suitable variables has been carried out. Variable selection has been based on the results discussed in Section II. 

As discussed in Section I, in this chapter we strive to simplify the study of reactions occurring during chemical activation with alkaline hydroxides by limiting our analysis to the activation of carbon materials. In other words, carbonaceous precursors that are not carbons are excluded. To identify the reaction products, to understand the types of reactions occurring, and to propose a main global reaction for hydroxide activation, a combination of different techniques has been used FTIR, in situ XRD, analysis of activation products followed by mass spectrometry, as well as thermodynamic data [99-101]. 

Thus, both FTIR and in situ XRD results lead to the same conclusion carbon activation with alkaline hydroxides involves a reaction in which the hydroxide (NaOH or KOH) is converted to a carbonate. In addition, XRD shows that the metal (Na or K) is also formed at the highest temperatme. 

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