Search

Roads play a crucial role in the economic development of nations; reconstruction, resurfacing, or rehabilitation of the current roads result in the milling of approximately 120 million tons of asphalt pavement every year. Due to the significant volume of resources involved, road agencies constantly trade-off among economic, performance and environmental challenges to maintain and build road assets. To address these challenges – such as reducing the dependency on non-renewable petroleum-based products and minimising waste and landfills – recycling of end of life road material through various organic binders has been evaluated. Bio-oil, obtained through recycling of different sources, contains lower molecular weight components that resemble fractions of the virgin asphalt binder used to make roads. This review article focuses on the recycling of bio-oil and its utilization in asphalt binders – as an alternative, extender, modifier and rejuvenator – and asphalt mixes. This review paper provides information on the production methodology used to produce bio-oil from various types of biomass, along with upgradation techniques adopted to upgrade the bio-oil before its addition into bitumen. The chemical and physical properties of bio-oils vary for each type of biomass. The production methodology to produce bio-binder from bio-oil is also specified. Simultaneously, the effect of bio-oil on the mechanical, rheological and chemical properties are compared with those of conventional bitumen. It is concluded that the performance of bio-binder varies with the type of bio-oil used for the modification, generally improving the intermediate and low-temperature viscoelastic behaviour but reducing the high-temperature performance. This review article provides a sketch of favourable and harmful aspects associated with the utilization of bio-oil to form bio-binders.

Major agricultural solid waste, rice husk (RH)-based mesoporous materials were prepared by potassium hydroxide (KOH) treatment of RH and RH hydrochar (RHH) produced at 180 °C with 20 min reaction time. In this study, RH was treated with three different methods: RH activation by KOH (KOH-RH), RH activation by KOH-aqueous silver (Ag)-shell nanoparticle (AgNP) incorporation followed calcination at 550 °C for 2 h (AgNP–KOH-RH) and hydrothermally carbonized RH activation by KOH (KOH-RHH). The main objective of this study was to determine the effect of KOH activation with different synthesis approaches and compare the characterization results of RH based porous material to identify the potential adsorbent application for wastewater treatment. Therefore, after activation in different methods, all interactive properties such as elemental, chemical, structural, morphological, and thermal analyses were investigated comprehensively for all samples. The crystallinity peak intensity around 22°λ at the angle of diffraction of 2θ confirmed the presence of silica, higher stability of the material, and removal of organic components during the KOH activation. AgNP–KOH-RH and KOH-RHH presented high porosity on the outer surface. The presence of negligible volatile matter in KOH-RHH by TGA demonstrated the decomposition of organic compound. Very high ratio of aromatic carbon and lignin content by FTIR and XPS analysis in both AgNP–KOH-RH and KOH-RHH showed these two samples have improved stability. Very high negative surface charge (zeta potential) in AgNP–KOH-RH (−43.9 mV) and KOH-RHH (−43.1 mV) indicated the enhanced water holding capacity. Surface area for all experimented porous materials has been enhanced after KOH activation, where KOH-RHH demonstrated the maximum surface area value, 27.87 m2/g. However, AgNP–KOH-RH presented maximum pore diameter, 18.16 nm, and pore volume, 0.12 cm3/g. Hence, it can be concluded that both KOH-RHH and AgNP–KOH-RH have the potential to be implemented as wastewater adsorbents.

Biosolids, the treated and stabilised sewage sludge, was pyrolysed in the presence of naturally occurring minerals in a Thermogravimetric Analyser (TGA). The results were then compared with a synthetic catalyst (i.e., 5% Co/Al2O3). Higher mass loss was observed in TGA in the presence of both minerals and the metal oxide based catalyst when compared to biosolids' alone pyrolysis. The scanning electron microscope (SEM) images confirmed significant morphological changes in the produced biochars while Fourier Transform Infrared (FTIR) spectra corroborated noticeable chemical changes in their structure. The kinetic analyses conducted using a hybrid approach consisting of model-fitting and model-free methods, suggested that there was a reduction in activation energy in the presence of minerals and the catalyst. Overall, it is concluded that minerals despite their low catalytic activity, offer various process and morphological advantages.

A qualitative and quantitative investigation on the formation of scale in mixing tanks was conducted. The fabrication of a purpose-built tank that could be disassembled into nine segments (including a base, four walls, and four baffles or four blanking pieces) allowed the measurement of scale thickness in critical regions such as the impeller zone. The scale grown on the walls of the tank was physically scanned using a coordinate measuring machine (CMM). The CMM readings were then used to plot 3-D graphs of scale thickness and distribution on the walls of the tank. Experiments conducted under unbaffled and baffled conditions showed that the bottom region of the reactor was almost free of scale while the top region near the liquid surface had noticeable scale formation under both configurations. The scale thickness and distribution were lower in the unbaffled tank compared to the baffled tank, which, in line with CFD simulations, can be attributed to the increased tangential liquid flow velocity near the tank wall under unbaffled condition.

Pavement recycling is actively applied on asphalt roads due to ageing problems associated with bituminous binders when exposed to weathering and trafficking during their service life. Recycling of asphalt occurs through rejuvenator agents. This study utilised bio-oil produced from hydrothermal liquefaction of waste plastic films (linear low-density polyethylene - LLDPE) to rejuvenate laboratory-aged bitumen. Initially, the neat bitumen was aged through thermal ageing (Pressure Ageing Vessel - PAV) and then the aged binder was mixed with bio-oil from waste plastics at 5% and 8% bio-oil (BO) by weight of aged binder. All four binders including neat bitumen, aged bitumen, aged bitumen/BO-5% and aged bitumen/BO-8% were analysed for thermogravimetric analysis, Fourier Transform Infra-Red analysis, rheology in the linear viscoelastic region, multiple stress creep and recovery analysis, and linear amplitude sweep analysis. The ageing of neat binder resulted in hardening of the binder; however, the bio-oil rejuvenator softened the aged binder significantly. The thermo-chemical and rheological performance of aged binder was significantly improved after the addition of bio-oil. The outcomes suggest how bio-oil produced from hydrothermal liquefaction of waste plastics (possibly non-recyclable) may serve as potential rejuvenator for aged asphalt binders in an effort to recycle more using non-recyclable material.

The design and synthesis of surface engineered functional inorganic nanomaterials for environmental applications is a long-standing goal of biomimetic research. Further developments in using nanomaterials for environmental engineering applications rely upon their surface modification, efficient sensing, stability under harsh conditions, biocompatibility, and less adverse environmental impact. Therefore, in this chapter, we review the amino acid functionalized inorganic nanomaterials, class of emerging materials that can address the afore-mentioned challenges to realize their environmental applications. These nanomaterials structurally mimic the characteristics of natural enzymes chirality, molecular recognition catalytic properties as well as possess the inherent electronic, optical, and catalytic properties of nanoparticles.

Australia has an advantage of having an abundant source of solar- and wind-based renewable energy. It can be utilized for renewable hydrogen production via liquid ammonia (NH3) pathway. Countries importing renewable ammonia can decompose it back to pure hydrogen using CSIRO (Commonwealth Scientific and Industrial Research Organization) metal membrane technology. The membrane separates ultrahigh pure hydrogen from ammonia while blocking all other gases. Re-cracked hydrogen can be used for fuel cell vehicles and other energy applications. The assessment of the economic viability of the abovementioned process chain requires a techno-economic evaluation (TEE) that involves process simulation, mass and energy balances, plant sizing, capital and operating cost estimations, and cash-flow and sensitivity analyses. This chapter presents the TEE methodology for a hydrogen energy system and it can be used in assessing engineering, research and development impact, scale-up, and the feasibility of the production system.

Accelerated growth of scale was studied in a baffled agitated reactor, which could be disassembled into nine sections, allowing quantitative determination of scale thickness. A coordinate measuring machine was used to determine the scale thickness on individual wall segments. The growth pattern of the scale was found to be nonuniform due to the variation of fluid velocity near the wall at various heights. Computational fluid dynamics (CFD) simulation showed that fluid flow is time-dependent and has two distinct flow zones, one involving recirculation through the impeller in the lower part of the vessel and the other involving lower velocities due to the flow separation at the wall in the upper part. CFD simulation also showed the presence of macroinstabilities, which manifest as asymmetrical and chaotic flow structures with relatively long-time scales. Scale growth is found to be prominent in regions where the fluid velocity and wall shear stresses are low.

The process parameters of microwave hydrothermal carbonization (MHTC) have significant effect on yield of hydrochar. This study discusses the effect of process parameters on hydrochar yield produced from MHTC of rice husk. Results revealed that, over the ranges tested, a lower temperature, lower reaction time, lower biomass to water ratio, and higher particle size produce more hydrochar. Maximum hydrochar yield of 62.8% was obtained at 1000 W, 220 °C, and 5 min. The higher heating value (HHV) was improved significantly from 6.80 MJ/kg of rice husk to 16.10 MJ/kg of hydrochar. Elemental analysis results showed that the carbon content increased and oxygen content decreased in hydrochar from 25.9 to 47.2% and 68.5 to 47.0%, respectively, improving the energy and combustion properties. SEM analysis exhibited modification in structure of rice husk and improvement in porosity after MHTC, which was further confirmed from BET surface analysis. The BET surface area increased from 25.0656 m2/g (rice husk) to 92.6832 m2/g (hydrochar). Thermal stability of hydrochar was improved from 340 °C for rice husk to 370 °C for hydrochar.

In this study, dewatered and raw paunch waste, with 15 and 3 wt% total solids respectively, generated at abattoirs was hydrothermally carbonised under subcritical water conditions. Higher solids content was found to produce higher hydrochar yield (i.e. 53% for 15 wt% compared to 33.5% for 3 wt%) at similar operating conditions of 10 bar and 240 °C for 5 min. The morphological differences were noted via Scanning Electron Microscopy (SEM) in the hydrochar samples, and the surface area for processing raw paunch waste was found to be 68.1 m2 g−1 compared to 10.8 m2 g−1 in case of dewatered paunch waste. The light bio-oil was mostly composed of phenolic compounds while the heavy bio-oil mainly contained long chain fatty acids and their esters. Following the experimental work, a full-scale ASPEN Plus process model was developed for a typical abattoir generating 27 tonne dry paunch waste per day. Pre-heater and hydrochar dryer contributed to 73% and 57% of the total energy for processing raw and dewatered paunch waste, respectively, because of the high moisture content of the feedstock and hydrochar. After the equipment sizing and estimation of capital and operating costs, the discounted cash flow analysis was performed using the Nth-Plant financing assumptions. It was concluded that treating dewatered paunch waste is preferable as it: needed a smaller reactor i.e. lower overall initial investment, was less sensitive to bio-oil price, and improved the net present value over a period of 30 years to $2.8 MM. Besides the liquid hourly speed velocity, its commercial viability is highly sensitive to internal rate of return and existence of hydrochar dryer.

There are several recent reviews published in the literature on hydrothermal carbonization, liquefaction and supercritical water gasification of lignocellulosic biomass and algae. The potential of hydrochar, bio-oil or synthesis gas production and applications have also been reviewed individually. The comprehensive review on the hydrothermal treatment of wet wastes (such as municipal solid waste, food waste, sewage sludge, algae) covering carbonization, liquefaction and supercritical water gasification, however, is missing in the literature which formed the basis of the current review paper. The current paper critically reviews the literature around the full spectrum of hydrothermal treatment for wet wastes and establishes a good comparison of the different hydrothermal treatment options for managing wet waste streams. Also, the role of catalysts as well as synthesis of catalysts using hydrothermal treatment of biomass has been critically reviewed. For the first time, efforts have also been made to summarize findings on modelling works as well as techno-economic assessments in the area of hydrothermal treatments of wet wastes. The study concludes with key findings, knowledge gaps and future recommendations to improve the productivity of hydrothermal treatment of wet wastes, helping improve the commercial viability and environmental sustainability.

The primary pathways by which nickel (Ni) and cobalt (Co) loss could occur from acidic sulfate solution during partial neutralisation of synthetic nickel laterite pressure acid leach solutions (to pH 4 at 85 °C) was investigated. Knowledge of the avenues by which Ni and Co loss occurs will enable minimisation of valuable metal losses through optimisation of the partial neutralisation process. Precipitation of Ni and Co as their hydroxides did not appear to be a pathway by which metal loss occurred during partial neutralisation. Additionally, co-precipitation of Ni and Co with either Fe(III) or Al was not found to be a significant route for valuable metal loss. Adsorption onto freshly precipitated hydrous oxides of Al and Fe(III), as well as haematite, a major component of nickel laterite pressure leach discharge solids, appeared to be the primary route by which Ni and Co loss occurs during partial neutralisation. There was a preference for Co to adsorb onto haematite and ferric iron precipitates whilst Ni preferentially adsorbed onto Al precipitates. The molar ratio of Al to Fe(III) in the synthetic feed liquor was found to be a key variable controlling Ni and Co loss during partial neutralisation. Final Ni losses initially increased with increasing Al/Fe molar ratio in the feed, being at their highest in the absence of Fe(III) (10.7% Ni loss), and when the Al/Fe molar ratio in solution was unity (11.9% Ni loss), then decreased significantly when the Al/Fe ratio in the feed liquor was greater than or equal to 2 (2% Ni loss). Cobalt losses generally decreased with increasing Al/Fe ratio in solution except for in the presence of haematite where Co losses were 3.30%, confirming that Co adsorption onto haematite is a significant route by which loss of this valuable metal occurs during partial neutralisation.

The behaviour of nickel (Ni), cobalt (Co) and major impurities such as aluminium (Al), trivalent chromium [Cr(III)] and ferric iron [Fe(III)] during the partial neutralisation of synthetic pressure acid leach (PAL) liquors and pulps was investigated. Ferric iron precipitation took place between pH85°C 2 to 3, and up to 54% of Cr(III) and 42% of Al were co-precipitated with Fe(III). Haematite appeared to act as a seed and promote the removal of Fe(III) from solution at a pH85°C as low as 2. Precipitation of the remaining Al and Cr(III) from solution did not commence until at or above pH85°C 3.5, and virtually went to completion at pH85°C 4 (96% precipitation extent). There was a linear correlation between the %Cr(III) precipitation and %Al precipitation from solution, which suggests that the behaviour of the two species is related and that Cr(III) is unlikely to behave independently in solution. Nickel and cobalt losses were strongly dependent on pulp pH, and valuable metal losses rapidly climbed above pH85°C 3 and further increased after 1 h of ageing; this behaviour appears to be consistent with adsorption processes. Cobalt losses were found to increase significantly in the presence of haematite whilst Ni losses were unchanged, suggesting that there is partitioning of Ni and Co during partial neutralisation of PAL pulps with Co preferentially adsorbing onto haematite. Final Ni losses were on average 1.95% and were unaffected by the presence of haematite; final Co losses were 0.38% in the absence of haematite and increased to 3.30% in the presence of haematite.

Introducing additional meso- or macroporosity into traditionally microporous metal-organic frameworks (MOFs) is a very promising way to improve the catalytic performance of these materials, mostly due to the resultant reductions of diffusional barriers during liquid-phase or gas-phase reactions. Here we show that HKUST-1 can be successfully synthesised either via post-synthetic treatment (etching prepared HKUST-1 samples in phosphoric acid, here called HKUST AE) or via in situ crystallisation (exposing the MOF precursor solution to supercritical CO2, here called HKUST CO2) to produce hierarchically porous structures that are highly beneficial for catalysis. These hierarchical MOFs were characterised by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM) and gas sorption to confirm the preservation of the microscopic structure and the appearance of macropores in the crystallites. More importantly, the benefits of introducing these hierarchical porous structures into this MOF for improving the diffusion accessibility of reagents to the sample in catalysed liquid- and gas-phase reactions were quantified for the first time. It was found that the hierarchical pore structure helped to increase the reaction conversion of styrene oxide methanolysis (by ~65 % using either HKUST AE and HKUST CO2, at 40 oC in 25 min) and CO oxidation (by 55 % using HKUST CO2 at 260 oC). These findings demonstrate the advantage of using hierarchical porous MOFs in catalysis.

Polymer composites are fabricated by incorporating fillers into a polymer matrix. The intent for addition of fillers is to improve the physical, mechanical, chemical and rheological properties of the composite. This study reports on a unique polymer composite using hydrochar, synthesised by microwave-assisted hydrothermal carbonization of rice husk, as filler in polylactide matrix. The polylactide/hydrochar composites were fabricated by incorporating hydrochar in polylactide at 5%, 10%, 15% and 20 wt% by melt processing in a Haake rheomix at 170 °C. Both the neat polylactide and polylactide/hydrochar composite were characterized for mechanical, structural, thermal and rheological properties. The tensile modulus of polylactide/hydrochar composites was improved from 2.63 GPa (neat polylactide) to 3.16 GPa, 3.33 GPa, 3.54 GPa, and 4.24 GPa after blending with hydrochar at 5%, 10%, 15%, and 20%, respectively. Further, the incorporation of hydrochar had little effect on storage modulus (G′) and loss modulus (G″). The findings of this study reported that addition of hydrochar improves some characteristics of polylactide composites suggesting the potential of hydrochar as filler for polymer/hydrochar composites.

The process parameters of microwave-induced hydrothermal carbonization (MIHTC) play an important role on the hydrothermal chars (hydrochar) yield. The effect of reaction temperature, reaction time, particle size and biomass to water ratio was optimized for hydrochar yield by modeling using the central composite design (CCD). Further, the rice straw and hydrochar at optimum conditions have been characterized for energy, chemical, structural and thermal properties. The optimum condition for hydrochar synthesis was found to be at a 180 &deg, C reaction temperature, a 20 min reaction time, a 1:15 weight per volume (w/v) biomass to water ratio and a 3 mm particle size, yielding 57.9% of hydrochar. The higher heating value (HHV), carbon content and fixed carbon values increased from 12.3 MJ/kg, 37.19% and 14.37% for rice straw to 17.6 MJ/kg, 48.8% and 35.4% for hydrochar. The porosity, crystallinity and thermal stability of the hydrochar were improved remarkably compared to rice straw after MIHTC. Two characteristic peaks from XRD were observed at 2&theta, of 15&deg, and 26&deg, whereas DTG peaks were observed at 50&ndash, 150 &deg, C and 300&ndash, 350 &deg, C for both the materials. Based on the results, it can be suggested that the hydrochar could be potentially used for adsorption, carbon sequestration, energy and agriculture applications.

Paunch waste is the wet waste generated from the cattle/sheep yard, paunch material, skin-shed, boning rooms, blood stream and rendering plant in an abattoir. It contains around 3% solids. It mainly consists of grass, grain, grease, fat, protein, blood, intestinal content, manure and cleaning products. In this study, paunch waste was treated under hydrothermal carbonisation conditions at different temperatures (160 to 240 ℃ ), residence time (5–150 min) and initial N2 pressure (10–30 bar) in a laboratory scale 600 mL Parr reactor system. The main objective of this study was to quantify the product distribution and further characterise the products produced from the hydrothermal carbonisation of paunch waste. The product distribution results reveal that higher bio-oil yield was obtained at relatively mild hydrothermal carbonisation conditions which is mainly attributed to fragile nature of paunch waste, higher water, volatile matter and carbohydrate content, and lower lignin and ash content. The resultant hydrochar was found to have higher HHV (∼24.48 M J k g - 1 ) and BET surface area (68.1 m 2 g - 1 ) which demonstrates their suitability as a coal substitute (in energy generation processes) or a porous medium (in soil conditioning, remediation or catalysts applications). Biodiesel-like compounds were found in the heavy bio-oil with the HHV of around 38 M J k g - 1 . Higher bio-oil production and excellent physico-chemical properties of hydrochar at milder hydrothermal carbonisation conditions have demonstrated significant improvement in the commercial viability of hydrothermal carbonisation of the paunch waste.

Roads serve as a backbone of developing economies; thousands of kilometres of new roads are built every year and old ones are continuously repaired. Due to the large areal extension, maintenance of asphalt pavements generates significant economic, energy, social, and environmental impacts. ‘Rejuvenation’ of reclaimed asphalt pavement (RAP) in roads helps minimize reliance on non-renewable resources; for this purpose, various organic-based rejuvenators have been used in recent times. Waste cooking oil (WCO), which contains light oil components analogous to those of the virgin bitumen, has been proposed as a sustainable product for improving recycling of aged asphalt. The present review study collects state-of-the-art information on asphalt rejuvenation using WCO. It provides insights on the correlations between plant production methods and laboratory studies to manufacture high content rejuvenated RAP mixes. In addition, WCO is comprehensively examined to provide more information about its chemical composition and the changes occurring in its chemical properties at various states of degradation (i.e. virgin and used cooking oil). The effect of WCO on the mechanical, rheological, chemical and microscopic characteristics of the asphalt binder and asphalt pavements behaviour was assessed. This review highlights that the addition of WCO to the asphalt binder improves fatigue and thermal cracking properties of the mix, but at the expense of rutting resistance unless further polymeric modification is achieved. The increase in the acid value of the oil and its moisture content negatively affect the asphalt binder properties. For the asphalt mixtures, an increment in WCO dosage generates an increase in the thermal cracking resistance but reduces rutting, fatigue, and moisture resistance of the pavement. Overall, this review article provides an overview of the positive and negative aspects of the applications of WCO as an eco-friendly asphalt rejuvenator.

Hierarchical assemblies are repeatedly encountered in nature, and when replicated in synthetic patterns and materials, can enhance their functionality or impart multifunctionality. In order to assemble a hierarchical superstructure that consists of components made up of multiple nanostructures, control over placement and stoichiometry is desirable. Macroscopic arrays that present up to three levels of hierarchy are demonstrated here and are achieved using the self-assembly of soft, collapsible block copolymer nanospheres for the first two levels, followed by directed self-assembly of metal nanospheres for the third. The fabrication approach combines advantages of soft sphere self-assembly to yield non-close-packed and variable array pitch values, with the inherent chemical functionality presented by the polymer-based soft spheres; these assemblies can then be transformed into a range of different materials, including metal or semiconductor nanostructures, or further tailored with an additional level of complexity. Structural investigation shows the superstructure formation to be governed by generic design rules that can be extended across different material combinations.