Abstract
A combined severity factor (RCSF) which is usually used to evaluate the effectiveness of hydrothermal pretreatment at above 100 °C had been developed to assess the influence of temperature, time, and alkali loading on pretreatment and enzymatic hydrolysis of lignocellulose. It is not suitable for evaluating alkaline pretreatment effectiveness at lower than 100 °C. According to the reported deducing process, this study modified the expression of [Formula: see text] as [Formula: see text] which is easier and more reasonable to assess the effectiveness of alkaline pretreatment. It showed that RCSF exhibited linear trend with lignin removal, and quadratic curve relation with enzymatic hydrolysis efficiency (EHE) at the same temperature. The EHE of alkali-treated SCB could attain the maximum value at lower RCSF, which indicated that it was not necessary to continuously enhance strength of alkaline pretreatment for improving EHE. Within a certain temperature range, the alkali loading was more important than temperature and time to influence pretreatment effectiveness and EHE. Furthermore, the contribution of temperature, time, and alkali loading to pretreatment cost which was seldom concerned was investigated in this work. The alkali loading contributed more than 70% to the pretreatment cost. This study laid the foundation of further optimizing alkaline pretreatment to reduce cost for its practical application.
Highlights
Various physical, chemical and biological tools have been adopted to pretreat lignocellulose like microwave, ultrasound, inorganic and organic solvents, microorganism, and so on
The maximum lignin removal of 77.94% reached at RCSF=1.122 (80 oC, 3% NaOH for 4 h) has little difference with that of 77.40% obtained at 180 oC, 10% NaOH/Ethanol for 30 min [23]
The close RCSF values obtained under different temperatures, different NaOH loadings for different times showed that NaOH loading was at the first place to influence lignin removal, followed by temperature (Table 1 and Fig. 1)
Summary
Chemical and biological tools have been adopted to pretreat lignocellulose like microwave, ultrasound, inorganic and organic solvents, microorganism, and so on. Based on the recycling technology of liquid wastes [13], the alkaline pretreatment cost investigated in this work is highly depended on energy consumption (relating to temperature and time), water consumption, and alkali loading. The effectiveness of alkaline pretreatment is related to temperature, time and alkali loading. The combined severity factor (RCSF) which is modified from hydrothermal pretreatment [14,15] had been used to describe the combined effects of temperature, time and alkali loading on alkaline pretreatment and enzymatic hydrolysis [16,17]. The equation [1] is deduced under the assumption that the reaction obeys to the first-order kinetics and the rate constant has relation to temperature via Arrhenius equation [14,15,18]. At the similar enzymatic hydrolysis efficiency, the alkali loading shared more cost
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