Determination of active hydrogen of ranny nickel by mannose method


There are many methods for the determination of the speech properties of Rainey nickel catalysts, and the determination of active hydrogen by mannose can meet the production requirements of most batch coping processes. The method is simple, accurate and fast.
  
The mannose method uses mannose and the catalyst's own active "linear hydrogen" after the quantitative reduction reaction, and uses Pei Lin's reagents A and B to determine the content of mannose in the reaction solution to calculate the amount of active hydrogen adsorbed by the catalyst per unit mass, and the activity of the catalyst is expressed by the amount of active hydrogen.
  
Accurately weigh 1.235 g of Raenenickel catalyst by pycnometer (in the presence of water) increment method on an electronic scale, remove water to basic dryness, transfer 250ml grind-mouth Erlenmeyer flask with 0.6000g of mannose and a small amount of reaction solvent accurately weighed in advance with reaction solvent, install a reflux condenser, reflux the water bath for 90min, filter with a sand core funnel while hot, and wash the Raney nickel catalyst with distilled water. Transfer the filtrate into a 250ml volumetric flask, cool to room temperature, add water to the scale, and take 25 ml sample in a 250ml Erlenmeyer flask with a pipette. The determination of reducing sugars according to GB7658-87 method is calculated as follows:

  

Active hydrogen (ml/g. Raininickel) =

W-W’

×1.2×100

G

 

Formula: W - mannose-like crystal mass (g);
      W' – unreacted exposed sugar mass (g);
      G - Rainey nickel catalyst mass (g);
      1.2×100 – the number of ml of active hydrogen per gram of mannose in the standard state
  
For catalysts of the same type, the mannose method measured very well reproducible. When the active hydrogen > measured was 42ml/g. Rainey nickel, it can be considered that the catalyst has high activity. In the production practice of hydrogenation of invert sugar to mannitol and sorbitol by Rainey nickel catalyst, it can be used as a reference index for the activity detection of Rainey nickel.

 

 

 

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Reni nickel catalyst science knowledge(1)

Physical and chemical properties: Reni nickel catalyst before activation is silver-gray amorphous powder (nickel-aluminum alloy powder), with a moderate degree of flammability, partial activation in the presence of water and the production of hydrogen easy agglomeration, long-term exposure to air is easy to weather. Nickel-aluminum alloy powder is activated into gray-black particles, accompanied by active hydrogen, extremely unstable, oxidative combustion in the air, must be immersed in water or ethanol for preservation. It was first used by American engineer Murray Rainey as a catalyst in the hydrogenation of vegetable oils. The preparation process is to treat nickel-aluminum alloy with concentrated sodium hydroxide solution, in this process, most of the aluminum will react with sodium hydroxide and dissolve, leaving a lot of micropores of different sizes. In this way, the surface of Raininickel is a fine gray powder, but from a microscopic point of view, each tiny particle in the powder is a three-dimensional porous structure, this porous structure greatly increases its surface area, and the large surface area brings high catalytic activity, which makes Raininickel widely used as a heterogeneous catalyst in organic synthesis and industrial hydrogenation reactions. Since "Rainey" is a registered trademark of Grace Chemicals, strictly speaking, only products manufactured by the company's Davidson Chemical Division can be called "Lanny Nickel". The term "metal backbone catalyst" or "sponge-metal catalyst" is used to refer to catalysts with a microporous structure and physical and chemical properties similar to Raney nickel.