Peter J. Ashman

Graphene-based nitrogen-doped carbon sandwich nanosheets: a new capacitive process controlled anode material for high-performance sodium-ion batteries

Anode materials with capacitive charge storage (CCS) are highly desirable for the development of high-performance sodium-ion batteries (SIBs), because the capacitive process usually shows kinetically high ion diffusion and superior structural stability. Here, we report a new CCS anode material of graphene-based nitrogen-doped carbon sandwich nanosheets (G-NCs). The as-prepared G-NCs show a high capacitive contribution during the discharge/charge processes. As expected, the G-NCs exhibit excellent rate performance with a reversible capacity of 110 mA h g−1, even at a current as high as 10000 mA g−1, and outstanding cycle stability (a retention of 154 mA h g−1 after 10000 cycles at 5000 mA g−1). This represents the best cycle stability among all reported carbon anode materials for SIBs, thereby showing great potential as a commercial anode material for SIBs.

Effect of operating conditions on yield and quality of biocrude during hydrothermal liquefaction of halophytic microalga Tetraselmis sp.

The biomass of halophytic microalga Tetraselmis sp. with 16%w/w solids was converted into biocrude by a hydrothermal liquefaction (HTL) process in a batch reactor at different temperatures (310, 330, 350 and 370°C) and reaction times (5, 15, 30, 45 and 60min). The biocrude yield, elemental composition, energy density and severity parameter obtained at various reaction conditions were used to predict the optimum condition for maximum recovery of biocrude with improved quality. This study clearly indicated that the operating condition for obtaining maximum biocrude yield and ideal quality biocrude for refining were different. A maximum biocrude yield of ∼65wt% ash free dry weight (AFDW) was obtained at 350°C and 5min, with a severity parameter and energy density of 5.21 and ∼35MJ/kg, respectively. The treatment with 45min reaction time recorded ∼62wt% (AFDW) yield of biocrude with and energy density of ∼39MJ/kg and higher severity parameter of 7.53.

Harvesting, Thickening and Dewatering Microalgae Biomass

The recovery and processing of microalgae biomass from a culture media is an essential component for the production of almost all microalgae products. Microalgae recovery techniques can be used individually (single-stage) or in combination (multi-stage) and the choice is often dependent on the species of microalgae, desired product concentration and product quality. A wide range of solid-liquid separation techniques is available and this chapter compares the technologies and assess the technical and economic considerations for each option. The major challenge in selecting an appropriate technology for biofuels production from microalgae is that traditional microalgae concentration processes have generally used energy-intensive unit operations that are expensive.

Force and energy requirement for microalgal cell disruption: an atomic force microscope evaluation.

Cell disruption is an essential step in the release of cellular contents but mechanical cell disruption processes are highly energy intensive. This energy requirement may become a critical issue for the sustainability of low valued commodities such as microalgal biofuels derived from extracted lipids. By the use of an atomic force microscope (AFM), this study evaluated the force and energy required to indent and disrupt individual cells of the marine microalga, Tetraselmis suecica. It was found that the force and energy required for the indentation and disruption varies according to the location of the cell with the average being 17.43 pJ. This amount is the equivalent of 673 J kg(-1) of the dry microalgal biomass. In comparison, the most energy efficient mechanical cell disruption process, hydrodynamic cavitation, has specific energy requirement that is approx. 5 orders of magnitude greater than that measured by AFM. The result clearly shows that existing mechanical cell disruption processes are highly energy inefficient and further research and innovation is required for sustainable microalgal biofuels production.

Hydrothermal liquefaction of microalgae for biocrude production: improving the biocrude properties with vacuum distillation

This paper proposes a two-part process for producing biocrude with reduced impurities. The biocrude was produced from hydrothermal liquefaction (HTL) of Spirulina sp. and Tetraselmis sp. in a batch reactor at both 300 and 350°C, 5min, and 16%w/w solid feed composition. The resultant biocrudes were vacuum distilled at a maximum temperature of 360°C. It was shown that biocrude quality could be enhanced without using catalyst by vacuum distillation (VD). The biocrude yield for Spirulina sp. was 36wt% at 300°C, 42wt% at 350°C, and for Tetraselmis sp. was 34wt% at 300°C, and 58wt% at 350°C. VD of Spirulina sp. biocrude obtained at 300 and 350°C led to 62 and 67wt% distilled biocrudes yield, respectively. VD of Tetraselmis sp. biocrude obtained at 300°C was 70wt%, and 73wt% at 350°C. The higher heating values (HHV) increased from 32MJ/kg to 40MJ/kg. There were substantial reductions in oxygen, metallic content, and boiling point ranges in distilled biocrudes.

The fate of char-nitrogen in low-temperature oxidation

Nitrogen release during the oxidation of coal char has been studied in a thermogravimetric analyzer (TGA) at 873 K with 2% O2 in He. Species profiles are determined using Fourier transform infrared (FTIR) spectroscopy (NO, NO2, CO, CO2, N2O, and HCN) and high-speed gas chromatography (N2), which allows all of the char-N to be accounted for in the gas phase. Char-N is released predominantly as N2 with smaller amounts of NO and HCN also present. The proportion of char-N released to the gas phase as N2, NO, and HCN is relatively constant throughout burnout. At the low-temperature conditions of this study, N2O is not produced and the results suggest that HCN is a primary product formed via heterogeneous oxidation and not by slow or secondary devolatilization. The gaseous product species profiles suggest that nitrogen is preferentially retained in the char as the carbon is oxidized and this is confirmed directly by X-ray photoelectron spectroscopy (XPS) and elemental analysis of partially oxidized char samples. Analysis of the XPS results also shows that enrichment of the char in nitrogen is a surface effect that occurs with an increase in the pyridinic N content of the char relative to pyrrolic N. At low temperatures, the enrichment of the char in nitrogen as burnout proceeds is the major contributing factor to the increase in the [NO]/([CO2]+[CO]) ratio.

Interactions of gaseous no with char during the low-temperature oxidation of coal chars

The role of nitric oxide (NO) during the low-temperature oxidation (873 K, ca. 2% O2/He) of subbituminous and bituminous coal chars was studied experimentally in fixed-bed reactor systems. Analysis of the gas-phase products by gas chromatography (GC) and Fourier transform infrared spectroscopy (FTIR) identified nitrogenous products with typical abundance N2(54%), NO (22%), HNCO (12%), HCN (6%), and N2O (1%). Significant retention of char nitrogen (char N) occurred within the char during the early stages of burnout. This may be explained via the following mechanism: NO + 2C() → C(N) + C(O) (1) C(N) + NO → N2 + C(O) or CO (2) C(N) + O2 → NO + C(O) or CO (3) The observed extent of nitrogen enrichment of the char during burnout requires that up to 90% of the NO formed by oxidation of char N (3) is reincorporated into the char (1) in the burnout. Experiments also were conducted using a dispersed-bed reactor in which isotopically labeled 15NO (0–1000 ppm) was added to the reactant gases (2% O2 in He) during the oxidation of coal char. The concentrations of labeled HC15N and H15NCO that were observed by FTIR indicated a significant interaction between gaseous NO and the char surface. The ratios of isotopes present in the HCN and HNCO product distributions were similar, suggesting that these species may be formed by related processes.

Rate coefficient of H+O2+M→HO2+M (M=H2O, N2, Ar, CO2)

The oxidation of H 2 , in the presence of NO, has been studied using a laminar flow reactor for the temperature range 750–900 K with residence times of the order of 1–2 s. Product species concentrations are determined using a chemiluminescent NO x analyzer (NO x and NO), FTIR spectrometer (H 2 O), and a micro-gas chromatograph (H 2 ). The chemical-kinetic model prediction for NO 2 is sensitive to only a small number of rate constants of which only the value of k 5 (H+O 2 +M→HO 2 +M) is uncertain. Matching of the experimental and predicted NO 2 profiles is then performed using the value of k 5 as an adjustable parameter, leading to an experimental determination of k 5 . The effect of different third bodies (N 2 , CO 2 , Ar, and H 2 O) on the rate of k 5 is investigated by the use of N 2 , CO 2 , Ar, and moist N 2 carrier gases. The value of k 5 (M=N 2 ) has been determined as k 5,N 2 =2.25×10 15 exp(+680/ T ) cm 6 mol −2 s −1 (±30%) in the temperature range 750–900 K. Comparison of this value for k 5 (M=N 2 ) with values determined for M =H 2 O, CO 2 , and Ar lead to third-body efficiencies (relative to N 2 ) for these species of 10.6, 2.4, and 0.56, respectively, throughout the temperature range studied.

Technical issues in the large-scale hydrothermal liquefaction of microalgal biomass to biocrude

Much of the current knowledge on the hydrothermic liquefaction of biomass to biocrude is on the basis of laboratory benchtop findings, and the step up to industrial scale reactors will require a range of information that is currently either unavailable or insufficient. This work highlights a number of these issues such as the heat of reaction, process heat recovery, optimal reaction time and waste product treatment. Effects of these knowledge gaps on the reactor design, process economics, and impacts on the environment are discussed. Although technologies do exist to deal with some of these issues, their applications are often limited by economic considerations and further studies are required.

Influence of process conditions on pretreatment of microalgae for protein extraction and production of biocrude during hydrothermal liquefaction of pretreated Tetraselmis sp.

Direct conversion of microalgae to advanced biofuels with hydrothermal liquefaction (HTL) is an attractive option which has drawn attention in recent years. The presence of heteroatoms in the resultant biocrude, energy input and the process water has been a long-term concern. In this study, the pretreatment of microalgae biomass for protein extraction was conducted prior to HTL for biocrude production. The impact of operating conditions on both the pretreatment and hydrothermal liquefaction steps was investigated. Following HTL using the pretreated algae with an initial solid content of 16% w/w for 30 min at 310 °C, the biocrude yield was 65 wt%, which was more than a 50% improvement in yield as compared to HTL of untreated algae under the same reaction conditions. To achieve a similar biocrude yield using the untreated algae required a much higher reaction temperature of 350 °C. Using recycled process water as reaction media led to a 25 wt% higher biocrude yield. HTL of pretreated algae led to 32–46% nitrogen reduction in resultant biocrude. The biocrude had a higher heating value (HHV) of 28 MJ kg−1 to 34 MJ kg−1. A maximum of 15 wt% protein extract was obtained during pretreatment at 150 °C, 20 min. A similar energy input was required in biocrude production from the untreated route and the combined pretreatment and HTL.