Fossil fuels have been a major contributor to greenhouse gases, the amounts of which could be reduced if biofuels such as bioethanol and biodiesel were used for transportation. One of the most promising biofuels is ethyl alcohol. In 2015, the world production of ethanol was 25.6 billion gallons and the USA, Brazil, China, the European Union, and 28 other countries have set targets for blending ethanol with gasoline. The two major bio-source materials used for ethanol production are corn and sugarcane. For 1st generation biofuels, sugarcane and corn feedstocks are not able to fulfill the current demand for alcohol. Non-edible lignocellulosic biomass is an alternative bio-source for creating 2nd generation biofuels and algae biomass for 3rd and 4th generation biofuels. This review discusses the significance of biomass for the different generations of biofuels, and biochemical and thermochemical processes, and the significance of biorefinery products.
In light of the current concerns about environmental issues caused by the excessive use of fossil resources, more emphasis has been paid to the transition to a sustainable and circular economy. Bioplastics as eco-friendly products originating from biomass wastes have gained much attention to solve the problem of plastic pollution. Among them, polyhydroxyalkanoates (PHAs) are microbial polyesters produced using various feedstocks�renewable or recycled waste materials�contributing to a more sustainable commercial plastic life cycle by being a part of a circular bioeconomy. However, the scale-up of the PHA process cost effectively and sustainably remains challenging for large-scale industrial applications. This perspective provides a comprehensive overview of the current insights into lignocellulosic biomass's role in achieving a circular bioeconomy. Emerging greener biomass conversion technologies are discussed to characterize energy demand, cost, and sustainability within biorefinery PHA production. In addition, recent advances in synthetic biology and fermentation processes for PHA production are discussed. Technological challenges, i.e., bioreactor setup, downstream operation, and inconsistent properties to improve the sustainable production of PHAs and to help transfer this technology to real-world applications, are also addressed.
Renewable
biofuel will play a critical role in our energy future
by lowering our dependency on fossil fuel because energy shortage
is not a remote possibility but is on the horizon. Biofuels are a
valuable substitute due to the enormous transportation infrastructure
currently in place to support their use and distribution. Apparently,
efficient production processes are being developed for both drop-in
fuels and fuel additives. Hydrodeoxygenation (HDO) over heterogeneous
catalysts provides paths to platform compounds into a range of building
block chemicals; however, the selectivity of these reactions is limited
due to identical functional groups in intermediate compounds. HDO
reactions are complex, as they occur at multiple sites of solid catalysts.
Catalyst stability and selectivity toward desirable products are crucial
in the design of HDO catalysts. In addition, reduced surface area
and phase transformation of catalyst supports could occur with the
HDO process. In this review, the exact basis of heterogeneous catalysis
is introduced. After that, an insight into how the catalyst’s
size, porosity, facets, edges, and corners affect selectivity and
yields during HDO is provided. Recent strategies in developing heterogeneous
catalytic systems to overcome harsh reactions conditions associated
with HDO are discussed.
The combination of ball milling (BM), microwave irradiation (MI), and deep eutectic solvents (DES) results synergistic for an efficient, selective, and very rapid (10 min) delignification of materials with high lignin content (ca. 50 wt%) such as walnut shells (WS). Lignin is dissolved in the DES, whereas the polysaccharide fractions remain suspended with limited degradation, due to the rapid pretreatment. After ball milling procedure (3 h), biomass loadings in the range of 100–200 g L−1 are selectively delignified in 10 min at 150 °C by using choline chloride:formic acid DES (1:2 molar ratio), rendering lignin yields of 60–80% (ca. ~ 40–60 g lignin L−1). Ball milling, microwave irradiation, and DES systems are much more efficient than ball milling, conventional heating, and DES system. The obtained lignins exhibited similar Fourier-transform infrared spectroscopy (FTIR) profile to that of milled wood lignin (MWL), indicating minimal functional group changes.
Graphical abstract
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