Thermo-Catalytic Reforming of spent coffee grounds

Value-Added Bio-carbon Production through the Slow Pyrolysis of Waste Bio-oil: Fundamental Studies on Their Structure-Property-Processing Co-relation

The present work addresses the transformation of bio-oil into valuable biocarbon through slow pyrolysis. The biocarbons produced at three different temperatures (400, 600, and 900 °C), 10 °C min^-1 heating rate, and 30 min holding time were tested for their surface morphology, thermal stability, elemental composition, functionality, particle size, and thermal and electrical conductivity. The physicochemical study of bio-oil showed substantial carbon content, higher heating value, and lower nitrogen content. Also, the Thermogravimetric analyzer-FourierTransform Infrared Spectroscopy (TGA-FTIR) study of bio-oil confirmed that the majority of gases released were hydrocarbons, carbonyl products, ethers, CO, and CO_2, with a minor percentage of water and alcohol. Overall, it was found that the pyrolysis temperature has the dominant role in the yield and properties of biocarbon. The physicochemical characterization of biocarbon showed that the higher temperature based pyrolyzed biocarbon (600 and 900 °C) improved the properties in terms of thermal stability, thermal conductivity, graphitic content, ash content, and carbon content. Furthermore, the elemental and Energy-Dispersive Spectroscopy study of biocarbon confirmed the substantial depletion in oxygen and hydrogen at a higher temperature (600 and 900 °C) than the lower temperature based pyrolyzed biocarbon (400 °C). Additionally, the purest form of the biocarbon is found at a higher temperature (900 °C) with higher thermal stability and carbon content. The study of the surface morphology of biocarbon revealed that the higher temperature (600 and 900 °C) biocarbon showed larger and harder particles than the lower temperature biocarbon (400 °C); however, the electrical conductivity of biocarbon decreased, whereas thermal conductivity increased, with an increase in the pyrolysis temperatures. Moreover, the particle size analysis of biocarbon confirmed that most of the particles were found in the range of 1 μm. The increased thermal stability, carbon content, and graphitic content and the lower ash content endorse biocarbon as an excellent feedstock for carbon-based energy storage materials.

Statistical Optimization of Alkali Pretreatment to Improve Sugars Recovery from Spent Coffee Grounds and Utilization in Lactic Acid Fermentation

Biorefinery, which utilizes carbon-neutral biomass as a resource, is attracting attention as a significant alternative in a modern society confronted with climate change. In this study, spent coffee grounds (SCGs) were used as the feedstock for lactic acid fermentation. In order to improve sugar conversion, alkali pretreatment was optimized by a statistical method, namely response surface methodology (RSM). The optimum conditions for the alkali pretreatment of SCGs were determined as follows: 75 °C, 3% potassium hydroxide (KOH) and a time of 2.8 h. The optimum conditions for enzymatic hydrolysis of pretreated SCGs were determined as follows: enzyme complex loading of 30-unit cellulase, 15-unit cellobiase and 50-unit mannanase per g biomass and a reaction time of 96 h. SCG hydrolysates were used as the carbon source for Lactobacillus cultivation, and the conversions of lactic acid by L. brevis ATCC 8287 and L. parabuchneri ATCC 49374 were 40.1% and 55.8%, respectively. Finally, the maximum lactic acid production by L. parabuchneri ATCC 49374 was estimated to be 101.2 g based on 1000 g of SCGs through the optimization of alkali pretreatment and enzymatic hydrolysis.

Progress in waste valorization using advanced pyrolysis techniques for hydrogen and gaseous fuel production

Hydrogen and gaseous fuel derived from wastes have opened up promising alternative pathways for the production of renewable and sustainable fuels to substitute classical fossil energy resources that cause global warming and pollution. Existing review articles focus mostly on gasification, reforming and pyrolysis processes, with limited information on particularly gaseous fuel production via pyrolysis of various waste products. This review provides an overview on the recent advanced pyrolysis technology used in hydrogen and gaseous fuel production. The key parameters to maximize the production of specific compounds were discussed. More studies are needed to optimize the process parameters and improve the understanding of reaction mechanisms and co-relationship between these advanced techniques. These advanced techniques provide novel environmentally sustainable and commercially procedures for waste-based production of hydrogen and gaseous fuels.

Biorefinery of spent coffee grounds waste: Viable pathway towards circular bioeconomy

The circular bioeconomy plan is an innovative research based scheme intended for augmenting the complete utilization and management of bio-based resources in a sustainable biorefinery route. Spent coffee grounds based biorefinery is the emerging aspect promoting circular bioeconomy. The sustainable circular bioeconomy by utilizing SCG is achieved by cascade approaches and the inclusion of many biorefinery approaches to obtain many bio-products. The maximum energy recovery can be obtained by process integration. The economic analysis of the biofuel production from SCG is dependent on the cost of raw material, transportation, the need of labor and energy, oil extraction operations and biofuel production. The inclusion of new products from already established product can minimize the investment cost when related to the production cost. A positive net present value can be achieved via SCG biorefinery which indicates the profitability of the process.