Porous anodic aluminum oxide: anodization and templated synthesis of functional nanostructures.

Due to fast climate change and foreseen damage through global warming, access to clean and green energy has become very much essential for the sustainable development of the society, globally. Biomass based energy is one of the important renewable energy resources to meet the day to day energy requirements and is as old as the human civilization. Biomass gasification is among few important aspects of bioenergy for producing heat, power and biofuels for useful applications. Despite, the availability of vast literature, technological and material advancements, the dissemination of gasification technology could not overcome the critical barriers for the widespread acceptability over the conventional energy resources. This article presents a comprehensive review on the technical advancements, developments of biomass gasification technology and the barriers being faced by different stakeholders in the wide dissemination of the technology for day to day requirements of the society, followed by recommendations for policy makers to make this technology popular while serving the society.

Recent advances in the development of biomass gasification technology: A comprehensive review

The energy demand of the world is expected to reach 739 quadrillions BTU in 2040, which therefore demand for exploring more alternative source of renewable energy. Waste biomass though vast in reserve for generating renewable energy has its own downside. High moisture, fibrous nature, high bulk volume, hydrophilic nature and low calorific value are some of the inferior quality of waste biomass which creates bottleneck for easy renewable energy generation. Pre-treatment of biomass to overcome these challenges has created a new research interest. Among the treatment options available, the hydrothermal carbonization (HTC) method, which can process wet waste has become the most preferred choice among researchers recently. The HTC eliminates energy-intensive pre-drying process needed for other treatment methods such as pyrolysis, dry torrefaction and incineration. Through this article, we attempt to provide a detailed review of how renewable biomass can be effectively used to produce renewable energy by improving their inherent inferior characteristics. The review also highlights bottlenecks that constrain the deployment of renewable energy using HTC methods. The scope of further research direction is well identified in this review. The paper also present recent advancements which are filling the knowledge gap of HTC technology that were there earlier. Critical analysis of microwave assisted HTC and conventional heated HTC is also presented in this review. The analysis in this paper reveals that biomass is a valuable resource, and should be explored to take advantage of its renewable energy generation potential. The HTC method of biomass upgradation improves transport, storage and fuel characteristics by improving grindability, pellets durability, hydrophobicity, energy density, combustion behaviour and calorific value, and also helps in improving the environmental performance of solid fuel produced. Despite the fact that the technology is in the early stage of development and there still exist knowledge gap and shortcomings, the vast literature reviewed suggests that it has a potential of being future technology. Therefore, it needs further investigation which should fill existing shortcoming of the technology.

Hydrothermal carbonization of renewable waste biomass for solid biofuel production: A discussion on process mechanism, the influence of process parameters, environmental performance and fuel properties of hydrochar

Methane production through anaerobic digestion: Participation and digestion characteristics of cellulose, hemicellulose and lignin

Citrus is a major processed crop that results in large quantities of wastes and by-products rich in various bioactive compounds such as pectins, water soluble and insoluble antioxidants and essential oils. While some of those wastes are currently valorised by various technologies (yet most are discarded or used for feed), effective, non-toxic and profitable extraction strategies could further significantly promote the valorisation and provide both increased profits and high quality bioactives. The present review will describe and summarize the latest works concerning novel and greener methods for valorisation of citrus by-products. The outcomes and effectiveness of those technologies such as microwaves, ultrasound, pulsed electric fields and high pressure is compared both to conventional valorisation technologies and between the novel technologies themselves in order to highlight the advantages and potential scalability of these so-called “enabling technologies”. In many cases the reported novel technologies can enable a valorisation extraction process that is “greener” compared to the conventional technique due to a lower energy consumption and reduced utilization of toxic solvents.

https://www.mdpi.com/1420-3049/22/5/680/pdf

Innovative “Green” and Novel Strategies for the Extraction of Bioactive Added Value Compounds from Citrus Wastes—A Review

The present study investigates the use of hydrothermal carbonization (HTC) to upgrade agro-waste into solid biofuels and the use of citric acid (CA) as a catalyst capable of enhancing energy properties of hydrochars. HTC of pineapple waste (PA) was carried out at 180, 220, and 250 °C at a fixed 1-h residence time with and without the addition of CA. Contrarily to the current understanding with regard to the use of an acid catalyst during HTC, CA addition shows to appreciably increase hydrochar mass yields with HTC temperature, while increasing their degree of coalification and carbon retention. PA hydrochars produced with the addition of CA exhibit higher heating values (HHV) up to 29.7 MJ/kg dry basis (db), low residual ash (between 0.53 and 0.75 wt% db), and better combustion properties when compared to those of hydrochars obtained without CA addition. We show that the increase in mass yields and energy properties observed for hydrochars is due to CA catalytic effect toward back-polymerization of organics in the liquid phase to form secondary char. Secondary char formation and its role in influencing the hydrochar properties as solid biofuels are demonstrated by scanning electron microscopy, proximate, elemental analysis, and combustion reactivity.

Enhancement of energy and combustion properties of hydrochar via citric acid catalysed secondary char production

A procedure based on the high-field mechanism of the growth of anodic oxides was developed in order to evaluate the morphological features of porous layers. Since the thickness of the barrier film, separating the porous layer from the metal, does not change during the steady-state growth of an anodic porous layer, the rate of displacement of the metal-oxide interface to the metal direction must be equal to the rate of displacement of the pore base to the oxide direction. As a consequence, porosity can be expressed in terms of the ratio i
 diss/i
 ion, where i
 diss is the dissolution current density at the pore base, and i
 ion is the ionic current density at the metal-oxide interface. Pore diameter can be determined from geometrical considerations, while average pore population can be obtained from the ratio of porosity to the average surface area of a single pore. This procedure was checked by comparison with experimental results relative to membranes prepared in various conditions. The satisfactory agreement between theoretical and experimental findings indicates that porosity can be evaluated by current density data and vice-versa. Therefore, anodic alumina membranes may be tailored for different applications by choosing operative conditions giving the desired value of i
 diss/i
 ion.

Maurizio Volpe

Papers

Enhancement of energy and combustion properties of hydrochar via citric acid catalysed secondary char production

Porosity of anodic alumina membranes from electrochemical measurements

On the suitability of thermogravimetric balances for the study of biomass pyrolysis

Environmental assessment of a waste-to-energy practice: The pyrolysis of agro-industrial biomass residues

Developing a procedure to optimize electroless deposition of thin palladium layer on anodic alumina membranes