Mechanism and kinetics of cellobiose decomposition in hot-compressed water

This thesis reports some insight into fundamental chemistry of cellobiose decomposition in hot-compressed water (HCW). This includes the effect of mild temperature, initial cellobiose concentration, weakly acidic condition and AAEM chlorides on decomposition behaviour of cellobiose. The new knowledge provides fundamental understanding on decomposition mechanisms of sugar oligomers into monomers and other products. Such knowledge is also essential to understanding the decomposition behaviour of more complex cellulose and biomass conversion in HCW

Effect of grater position on the size of grated sago (Metroxylon spp.)

The natural arrangement of sago palm’s fiber orientation is parallel to the vertical axis of the trunk. Extraction of the sago starch requires breaking of the trunk into fine sizes. The sago size is affected by the grater position which affects the of starch recovery. This study was conducted to evaluate grating efficiency through sago size produced at the different direction of grating (0° and 90° to roller teeth rotation). Sago palm trunks without outer layer were cut into square blocks of 100 mm3. Each trunk block was placed on roller grater platform at a different position where the cutting spike was parallel to the vertical axis of sago trunk fiber orientation (grating at 0° direction) and perpendicular (grating at 90° direction). 100 g of dry grated sago was sifted to determine the size distribution with different sieve sizes i.e. 2.80 mm, 2.00 mm, 1.00 mm, 0.85 mm and 0.425 mm. A total weight of 1 kg of grated sago was mixed with water and squeezed to be extracted. The starch recovery produced by the grating process at 0° directions was 10.30% higher than 90 0 directions. The present study showed that the direction of grating at 0° was able to produce finer grated sago with maximum starch recovery

Effect of Alkali and Alkaline Earth Metal Chlorides on Cellobiose Decomposition in Hot-Compressed Water

This paper reports a systematic study on the catalytic effect of alkali and alkaline earth metal (AAEM) chlorides on cellobiose decomposition in hot-compressed water (HCW) at 200–275 °C. The AAEM chlorides catalyze the cellobiose decomposition in HCW in the order of MgCl2 > CaCl2 > KCl > NaCl. The presence of AAEM chlorides not only increases the reaction rate but also alters the selectivities of primary reactions of cellobiose decomposition. The isomerization reactions to cellobiulose and glucosyl-mannose are strongly promoted by these cations due to their interactions with cellobiose. The hydrolysis reaction to glucose is also promoted as the hydrolysis of hydrated metal complexes generates H3O+. However, the promotion effect on hydrolysis reaction is much weaker, resulting in reduced glucose selectivity in AAEM chloride solutions. Depending on the AAEM species, the secondary decomposition reactions of those primary products are selectively catalyzed in AAEM chloride solutions, thus greatly influencing the product distribution of cellobiose decomposition in HCW

Effect of initial pH on hydrothermal decomposition of cellobiose under weakly acidic conditions

The paper reports the cellobiose hydrothermal decomposition at 200–250 °C under non-catalytic (with an initial pH close to 7) and weakly acidic conditions (with an initial pH of 4–6). It was found cellobiose decomposition under both non-catalytic and weakly acidic conditions follows similar primary decomposition pathways, i.e., isomerization and hydrolysis reactions being the main primary reactions. However, cellobiose decomposition under acidic conditions decreases the selectivities of isomerization reactions but increases the selectivity of hydrolysis reaction. While the rate constants of isomerization reactions under various pH conditions are found to be similar, that of hydrolysis reaction increases significantly with reducing the initial pH of the solution. Therefore, the acceleration of cellobiose decomposition under acidic conditions is mainly due to the increased contribution of hydrolysis reaction. Further analysis suggests that the rate constant of hydrolysis reaction is dependent on the hydrogen ion concentration of the solution at reaction temperature. A kinetic model was then developed, considering the isomerization and hydrolysis reactions. The model can well predict the cellobiose hydrothermal decomposition under various initial pH conditions at low temperatures (i.e., <225 °C). However, the model underestimates the rate constant of cellobiose hydrothermal decomposition at higher temperatures (i.e., 250 °C), suggesting the increased contribution of other reactions (e.g., reversion reactions) under the conditions

Study of machines performance in producing different sizes of grated sago

Sago starch is a product from sago palm. In order to extract the sago starch, certain process is needed to break the bonding of the pith either mechanically or manually by grating the pith into small sizes. Water is widely used as a solvent medium in the extraction process of sago starch. The more refined that grated sago, the more sago starch can be dissolved from the grated sago. Different machines were used to produce grated sago for machine capability test. The machines are handheld chainsaw, coconut husk decorticator, commercial coconut grater and in-house roller grating prototype. Sago palm trunk was cut into three parts with length of 50 cm long each. The outer layer of each sago palm trunks was peeled off and split into 8 pieces. All sago trunks were grated using four different machines as stated above. Each 100 gram of the grated sago trunk produced by each machine were sifted according to the grading size of 2.80 mm, 2.00 mm, 1.00 mm, 0.85 mm and 0.425 mm. The weights of sago starch from the sieving process were recorded according to their respected grading size. Based on results of the sieve experiments, the most finest grated sago trunk was produced from the handheld chainsaw with a weight percentage ratio of 13.028% (X < 0.3 mm), 10.682% (0.3 ≤ X < 0.425 mm), 28.361% (0.425 ≤ X <0.85 mm), 28.821% (0.85 ≤ X <1.0 mm), 4.728% (1.0 ≤ X <2.0 mm), 7.877% (2.0 ≤ X <2.8 mm), and 4.868% (X ≥2.8 mm) where X value refer to sieve mesh size

Cellobiose Decomposition in Hot-Compressed Water: Importance of Isomerization Reactions

This paper reports an investigation on the fundamental reaction mechanism of cellobiose decomposition in hotcompressed water (HCW) using a continuous reactor system at 225-275 °C. The importance of isomerization reactions to form two cellobiose isomers (i.e., cellobiulose and glucosyl-mannose) as the primary reaction products is clearly demonstrated under the reaction conditions, using a high-performance anion exchange chromatography with pulsed amperometric detection and mass spectrometry (HPAEC-PAD-MS). The results also confirm another two primary reactions take place during cellobiose decomposition in HCW: retro-aldol condensation reaction to produce glucosyl-erythrose (GE) and glycolaldehyde, and hydrolysis reaction to produce glucose. The data show that isomerization and retro-aldol condensation are the dominant primary reactions while hydrolysis of cellobiose is only a minor primary reaction (accounting for ~10-20% of cellobiose decomposition depending on reaction temperature). The results indicate that the reaction solution becomes acidic at the early stage of cellobiose decomposition, most likely due to the formation of organic acids, resulting in the subsequent reactions exhibiting more characteristics of acid-catalyzed reactions. The results further suggest that the formed acidic condition has little catalytic effects onthe primary reactions of cellobiose decomposition, but is effective in catalyzing secondary reactions of various reaction intermediates such as hydrolysis and dehydration reactions to form glucose and 5-HMF, respectively