Valorization of sorghum distillery residue to produce bioethanol for pollution mitigation and circular economy.

This research aims to study the wet torrefaction (WT) and saccharification of sorghum distillery residue (SDR) towards hydrochar and bioethanol production. The experiments are designed by Box-Behnken design from response surface methodology where the operating conditions include sulfuric acid concentration (0, 0.01, and 0.02 M), amyloglucosidase concentration (36, 51, and 66 IU), and saccharification time (120, 180, and 240 min). Compared to conventional dry torrefaction, the hydrochar yield is between 13.24 and 14.73%, which is much lower than dry torrefaction biochar (yield >50%). The calorific value of the raw SDR is 17.15 MJ/kg, which is significantly enhanced to 22.36-23.37 MJ/kg after WT. When the sulfuric acid concentration increases from 0 to 0.02 M, the glucose concentration in the product increases from 5.59 g/L to 13.05 g/L. The prediction of analysis of variance suggests that the best combination to maximum glucose production is 0.02 M H2SO4, 66 IU enzyme concentration, and 120 min saccharification time, and the glucose concentration is 30.85 g/L. The maximum bioethanol concentration of 19.21 g/L is obtained, which is higher than those from wheat straw (18.1 g/L) and sweet sorghum residue (16.2 g/L). A large amount of SDR is generated in the kaoliang liquor production process, which may cause environmental problems if it is not appropriately treated. This study fulfills SDR valorization for hydrochar and bioenergy to lower environmental pollution and even achieve a circular economy.

Gasification kinetics of raw and wet-torrefied microalgae Chlorella vulgaris ESP-31 in carbon dioxide.

This study aims at investigating the gasification behavior and kinetics of microalga Chlorella vulgaris ESP-31 before and after wet torrefaction. The raw and wet-torrefied microalgae were first gasified in a thermogravimetric analyzer under a continuous CO2 flow. Thereafter, the obtained thermogravimetric data were modeled for kinetic study, employing a seven-parallel-reaction mechanism. The decomposition of the microalgae in CO2 shows two reactive stages: devolatilization with two peaks and gasification with a peak accompanied by a shoulder, and the thermal decomposition of components in the samples can be clearly identified. Increasing wet torrefaction temperature lowers the height of the major devolatilization peak but enhances the height of the minor one. Moreover, the kinetic evaluation reveals that wet torrefaction affects most of the kinetic parameters of the microalgal components. Furthermore, wet torrefaction temperature influences the kinetic parameters of carbohydrate and lipid, but not on those of protein, "others", and chars.

Dilute sulfuric acid hydrolysis of red macroalgae Eucheuma denticulatum with microwave-assisted heating for biochar production and sugar recovery.

This study aims to produce biochar and sugars from a macroalga Eucheuma denticulatum using dilute sulfuric acid hydrolysis along with microwave-assisted heating. The reactions were operated at sulfuric acid concentrations of 0.1 and 0.2M, reaction temperatures of 150-170°C and a heating time of 10min. Compared to the raw macroalga, biochar qualities were improved with increased carbon content and lower ash and moisture contents. The calorific value of the biochar could be intensified up to 45%, and 39% of energy yield was recovered. Apart from producing biochar, the highest total reducing sugars were 51.47g/L (74.84% yield) along with a low by-product 5-HMF of 0.20g/L, when the biomass was treated under the optimum conditions at 160°C with 0.1M H2SO4. Thus, this study demonstrated that macroalgae could be potentially used as biomass feedstock under microwave-assisted acid hydrolysis for the production of biofuel and value-added products.

Hydrothermal carbonization of sugarcane bagasse via wet torrefaction in association with microwave heating.

Hydrothermal carbonization of sugarcane bagasse using wet torrefaction is studied. The biomass is torrefied in water or dilute sulfuric acid solution and microwaves are employed to heat the solutions where the reaction temperature is fixed at 180 °C. The effects of acid concentration, heating time and solid-to-liquid ratio on the performance of wet torrefaction are investigated. It is found that the addition of sulfuric acid and increasing heating time are conducive to carbonizing bagasse. The calorific value of bagasse can be increased up to 20.3% from wet torrefaction. With the same improvement in calorific value, the temperature of wet torrefaction is lower than that of dry torrefaction around 100 °C, revealing that wet torrefaction is a promising method to upgrade biomass as fuel. The calorific value of torrefied biomass can be predicted well based on proximate, elemental or fiber analysis, and the last one gives the best estimation.