•Alternative aviation F–T fuel was compared with traditional RP-3 aviation fuel.•Qualitative relationship between atomization and TG properties were established.•Burnout index Bf and uniform parameter α were defined in this study.•Bf and α could reflect aviation fuels' atomization performance in some degree.As many potential alternative jet fuels would be used in the in-service engine, such as the most promising Fischer–Tropsch (F–T) jet fuel, it's necessary to test their performance in compared with petroleum derived jet fuel. In this study, atomization performance of F–T fuel and traditional RP-3 jet fuel were assessed based on three parameters including Sauter mean diameter, Spray cone angle, and Distribution index N. Thermogravimetric (TG) analysis is also conducted for kinetics analysis. TG experiments of F–T fuel and RP-3 were carried out in order to establish the relationship between atomization and TG characteristics. Burnout index Bf and uniform parameter α derived based on TG experiments were defined in this study. The qualitative relationship between Bf, α and atomization parameters were given for rapid evaluation of alternative jet fuel's atomization characteristics.

•Pretreatment decreased activation energy of microalgae pyrolysis process.•Acid treatment decreased initial decomposition temperature and increased intensity.•Acid treatment improved biocrude quality (N reduction and increase of esters and ethers).•Improved esterification reaction between carbohydrate derivative and lipid at acid condition.•Assessment of the pretreatment effect based on the energy conversion efficiency and LCA.Effects of three different cell pretreatment methods on microalgae Isochrysis sp. pyrolysis kinetics, biocrude yields and quality, energy conversion efficiency and life cycle assessment (LCA) were investigated. From derived thermogrametry (DTG) curves, the decomposition reaction was apparently enhanced for acid pretreatment sample at 200 °C. The activation energy of pretreated microalgae pyrolysis was lower than that without pretreatment. The biocrude yields for raw microalgae were higher than pretreated samples at 450–475 °C and lower at 400–425 °C. Carbon distributions of biocrude from microalgae pyrolysis with ultrasonication and microwave pretreatment were similar and mainly in C6-10, C16, C18, and C20, while carbon distribution of biocrude from acid pretreatment mainly located in C7, C16, C18, and C20. Acid heating pretreatment improved fuel quality including N compounds reduction and increase of esters and ethers content, which was likely due to esterification reaction between carbohydrate derivative and lipid at acid conditions. From the point of energy conversion efficiency, pretreatment decreased the energy ratio and energy efficiency and increased the energy consumption/output ratio ECR (except ECR of acid heating pretreatment) during microalgae pyrolysis process. Based on the LCA, pretreatment increased the GHG emissions in the production process of alternative biofuels. Co-use of pretreatment process during biofuel production and valuable chemicals extraction can be further researched to enhance energy efficiency and cost-efficiency for microalgae.

•High lipid content in microalgae increases energy conversion efficiency.•Indirect pathway has the highest mass ratio, energy ratio and energy efficiency.•The Isochrysis indirect pathway produces most kerosene component precursor.•The Isochrysis indirect pyrolysis pathway shows the best performance in LCA.Although the research of microalgae pyrolysis has been conducted for many years, there is a lack of investigations on energy efficiency and life cycle assessment. In this study, we investigated the biocrude yield and energy efficiency of direct pyrolysis, microalgae residue pyrolysis after lipid extraction (indirect pyrolysis), and different microalgae co-pyrolysis. This research also investigated the life cycle assessment of the three different pyrolysis pathways. A system boundary of Well-to-Wake (WTWa) was defined and included sub-process models, such as feedstock production, fuel production and pump-to-wheels (PTW) stages. The pathway of Isochrysis indirect pyrolysis shows the best performance in the mass ratio and energy ratio, produces the most kerosene component precursor, has the lowest WTWa total energy input, fossil fuel consumption and greenhouse gas emissions, and resultes in the best energy efficiency. All the evidence indicates that Isochrysis R2 pathway is a potential and optimal pyrolysis pathway to liquid biofuels. The mass ratio of pyrolysis biocrude is shown to be the decisive factor for different microalgae species. The sensitivity analysis results also indicates that the life cycle indicators are particularly sensitive to the mass ratio of pyrolysis biocrude for microalgae-based hydrotreated pyrolysis aviation fuel.

This study explored the effect of the Maillard reaction on the Co-Hydrothermal Liquefaction (HTL) of two different microalgae strains for bio-crude production. Model compounds, glucose and soya protein were mixed at different ratios and HTL was run at different temperatures to investigate the mechanism of the Maillard reaction. Pure Nannochloropsis (Nan), Spirulina (Spi) and the mixture of the two microalgae strains at the ratio of 1:1 (oven dry weight basis) were hydrothermally converted under the same reaction conditions for comparison. The mixtures of model compound and microalgae were also subjected to HTL to investigate the effects of chemical compounds on bio-crude yield. The Co-HTL for Nan and Spi exhibited lower bio-crude yield than that of HTL for individual microalgae. A high protein content has a negative effect on the fatty acid recovery. The dosage of glucose could enhance the bio-crude yield during HTL because of the Maillard reaction with protein. In addition, the results of elemental analysis indicated that the glucose dosage had promoted the energy recovery during HTL; FTIR and GC-MS spectra of bio-crudes revealing that tailoring the ratio between glucose and protein could elevate the quality of bio-crude from microalgae, especially for the microalgae with a low lipid content.

•A model of the PVE direct-coupling system is agreed with the experimental data.•The PVE direct-coupling system has been operated in Beijing for a year.•Optimization method is setup for the PVE direct-coupling system in practical use.•The interactions of the operation factors with the system efficiency are studied.•Annual analysis of the system operating in Beijing.Hydrogen as a clean energy carrier for solar energy can be produced by using photovoltaic-electrolyser (PVE) direct-coupling system that is well known as a kind of simple and low investment but unstable system for solar energy conversion. The key to improve hydrogen yield of a direct-coupling system is to keep its working points around maximum power point (MPP) of photovoltaic (PV) modules. The coupling of three different connection patterns of six PV modules with one electrolyser were investigated in summer, autumn and winter, three typical seasons in a year, to seek the optimum arrangement for higher system efficiency in Beijing (116°E, 40°N). A corresponding mathematics model of the system is applied to simulate and analyze the instantaneous efficiency of the system, which agreed well with the experimental results. The variation rate of the system instantaneous efficiency varies with the solar irradiation intensity, the ambient temperature and the resistance of the electrolyser. The working point that distinguishes the variation trends of the system efficiency is called the efficiency changing point (ECP). The author use a parameter V/Vm, the ratio between the voltage of the working point to the voltage of the maximum power point, to analyze the respective ECP of each factor above. It can be concluded that the variation rate of system instantaneous efficiency changes little with the above factors when the value of V/Vm of working point is smaller than that of the ECP and is sensitive to those factors when the value of V/Vm is larger than that of the ECP. Following the annual historical climate data in Beijing, the result of the annual analysis is that the best scheme for the experiment system with a 1 m2 PV panel covering 1.05 m2 areas of ground can convert 78.4 kWh of solar energy to hydrogen energy in 2012.

CuO/TiO2 photocatalysts were prepared and shown to enhance the rate of CO2 photoreduction and the production of total organic carbon (TOC), including HCOOH, HCHO and CH3OH. Resulting TOC could act as electron donors for enhancing visible light hydrogen evolution from Pt/TiO2 photocatalysts. The impacts on CO2 photoreduction were investigated including the effect of Cu dopant, pH, irradiation time and using Na2SO3 as a sacrificial agent, and those on hydrogen evolution was also studied including TOC concentration and Pt doping. The CO2 photoreduction mechanisms with respect to pH and CO2 reduction potentials were discussed. CuO/TiO2 and Pt/TiO2 photocatalysts were characterized by X-ray diffraction, Raman spectroscopy and diffuse reflection UV–vis spectrophotometry. Both photocatalysts showed a visible light response in comparison with pure TiO2. The photocatalytic experiments and FT-IR spectra indicated that photoproduct desorption was the rate-limiting step in the CO2 photoreduction.

•Quantitative relationship between nitrogen and lipid content/specific productivity.•Key issues for sustainable feedstock of microalgae strains in cultivation.•The quantitative changes of LCA results under different lipid contents.•Quantitative effects of the nitrogen nutrient on LCA results.The aim of this work is to compare the life cycle assessments of low-N and normal culture conditions for a balance between the lipid content and specific productivity. In order to achieve the potential contribution of lipid content to the life cycle assessment, this study established relationships between lipid content (nitrogen effect) and specific productivity based on three microalgae strains including Chlorella, Isochrysis and Nannochloropsis. For microalgae-based aviation fuel, the effects of the lipid content on fossil fuel consumption and greenhouse gas (GHG) emissions are similar. The fossil fuel consumption (0.32–0.68 MJ·MJ−1 MBAF) and GHG emissions (17.23–51.04 g CO2e·MJ−1 MBAF) increase (59.70–192.22%) with the increased lipid content. The total energy input decreases (2.13–3.08 MJ·MJ−1 MBAF, 14.91–27.95%) with the increased lipid content. The LCA indicators increased (0–47.10%) with the decreased nitrogen recovery efficiency (75–50%).

•Protein, lipid and carbohydrate were isolated for microalgal component pyrolysis.•Relationship between DTG curves of microalgae and their isolated components.•Experimental N was 0.6776, 0.3861 and 0.2856 for lipid, protein and carbohydrate.•Recommended pyrolysis pathways by biocrude composition of isolated algal components.•Steroids and lipopolysaccharides increased hydrocarbon content in bio-crude.Microalgal components were isolated gradually to get lipid-rich, protein-rich and carbohydrate-rich components. The aim of this work was to study pyrolysis mechanism of microalgae by real isolated real algae components. Thermogrametric analysis (DTG) curve of microalgae was fitted by single pyrolysis curves of protein, lipid and carbohydrate except special zones, which likely affected by cell disruption and hydrolysis mass loss. Experimental microalgae liquefaction without water index N was 0.6776, 0.3861 and 0.2856 for isolated lipid, protein and carbohydrate. Pyrolysis pathways of lipid are decarboxylation, decarbonylation, fragmentation of glycerin moieties and steroid to form hydrocarbons, carboxylic acids and esters. Pyrolysis pathways of protein are decarboxylation, deamination, hydrocarbon residue fragmentation, dimerization and fragmentation of peptide bonds to form amide/amines/nitriles, esters, hydrocarbons and N-heterocyclic compounds, especially diketopiperazines (DKPs). Pyrolysis pathways of carbohydrate are dehydrated reactions and further fragmentation to form ketones and aldehyde, decomposition of lignin to form phenols, and fragmentation of lipopolysaccharides.