Influences of “Neutral” Salts on Thermochemical Conversion of Cellulose and of Sucrose

Abstract

The term biomass conventionally refers to plant cell wall material, usually in the form of agricultural “wastes”. This type of biomass is the material normally studied and used in attempts to derive economically viable thermochemical conversions. Cellulose is the major component in such biomass (typically 40–70% of the dry matter). Sucrose is the world’s most abundant pure organic chemical and its thermochemistry is of importance in its production and also its use in food processes (cooking). In both types of thermochemistry, in practice the raw material is not in a completely pure form, but is accompanied by impurities, commonly salts. We have studied both systems and find many similarities and correlations in their respective chemistry.

This paper is concerned with effects of salts such as sodium chloride which are not normally considered to be either acidic or basic and which are used at very low concentrations. The pyrolysis is channeled by sodium chloride to increasing char and to low molecular weight products, especially glycolaldehyde, hydroxyacetone, and formic acid. The possible mechanisms of this phenomenon will be discussed.

In the case of sucrose, both impurities and crystallinity are major factors in thermal degradation. Pure crystalline sucrose is relatively stable (e.g. no significant degradation in several hours at 150°C). These processes are dramatically catalyzed by traces of sodium chloride (e.g. 0.05 mole/mole sucrose). Similar effects of salts on hydrolysis of sucrose are observed in concentrated, neutral aqueous solutions of sucrose. These effects are related to the extent of hydration of the cation component of the salt.

The mechanisms of catalysis of pyrolysis of pure cellulose and of pure sucrose by traces of sodium chloride will be discussed in relation to thermochemical biomass conversion and to food process operations.