Reutilization potential of antibiotic wastes via hydrothermal liquefaction (HTL): Bio-oil and aqueous phase characteristics

Hydrothermal liquefaction (HTL) technology was employed to investigate the feasibility of recovering energy from penicillin mycelial waste (PMW) with the help of TG, Py-GC/MS and GC-MS techniques; meanwhile, the nutrients in aqueous phase were also analyzed by spectrophotometry methods. The effects of operating conditions, including hydrothermal temperature (240–300 °C), duration time (20–60 min), total solid ratio (5–15%) and their interactive reactions were concurrently evaluated via response surface methodology. Results demonstrated that operating temperature was found to be the dominant variable affecting the HTL of PMW. Based on the optimal conditions of 298 °C, 60 min and 14.85%, heavy oil derived from PMW was comparable with algal-derived bio-oil as it possessed the highest energy recovery efficiency (42.95%) with a calorie value of 32.84 MJ/kg and a yield of 24.93%. GC/MS results indicated that heavy oil mainly consisted of N-containing compounds (36.73%) and aromatic compounds (31.07%), which might be contributed to the hydrolysis of protein and the aromatization of intermediates, respectively. Besides, more than 65% of nitrogen and 40% of carbon were enriched in aqueous phase, suggesting the possibility of further recycling for algae cultivation, fermentation and anaerobic digestion.     

Catalytic supercritical water gasification of aqueous phase directly derived from microalgae hydrothermal liquefaction

Microalgae (N. chlorella) hydrothermal liquefaction (HTL) was conducted at 320 °C for 30 min to directly obtain original aqueous phase with a solvent-free separation method, and then the supercritical water gasification (SCWG) experiments of the aqueous phase were performed at 450 and 500 °C for 10 min with different catalysts (i.e., Pt-Pd/C, Ru/C, Pd/C, Na₂CO₃ and NaOH). The results show that increasing temperature from 450 to 500 °C could improve H₂ yield and TGE (total gasification efficiency), CGE (carbon gasification efficiency), HGE (hydrogen gasification efficiency), TOC (total organic carbon) removal efficiency and tar removal efficiency. The catalytic activity order in improving the H₂ yield was NaOH > Na₂CO₃ > None > Pd/C > Pt-Pd/C > Ru/C. Ru/C produced the highest CH₄ mole fraction, TGE, CGE, TOC removal efficiency and tar removal efficiency, while NaOH led to the highest H₂ mole fraction, H₂ yield and HGE at 500 °C. Increasing temperature and adding proper catalyst could remarkably improve the SCWG process above, but some N-containing compounds were difficult to be gasified. This information is valuable for guiding the treatment of the aqueous phase derived from microalgae HTL.     

Bio-oil production from hydrothermal liquefaction of waste Cyanophyta biomass: Influence of process variables and their interactions on the product distributions

Hydrothermal liquefaction (HTL) of waste Cyanophyta biomass at different temperatures (factor A, 260–420 °C), times (factor B, 5–75 min) and algae/water (a/w) ratios (factor C, 0.02–0.3) by single reaction condition and Response Surface Method (RSM) experiments was investigated. By single reaction condition runs, maximum total bio-oil yield (29.24%) was obtained at 350 °C, 60 min and 0.25 a/w ratio. Maximum bio-oil HHV of 40.04 MJ/kg and energy recovery of 51.09% was achieved at 350 °C, 30 min, 0.1 a/w ratio and 350 °C, 60 min, 0.25 a/w ratio, respectively. RSM results indicate that effect of AB interaction was significant on light bio-oil yield. Both AC and AB had more remarkable influence than BC on heavy bio-oil yield and aqueous total organic carbon (TOC) recovery whereas BC was noticeable on ammonia nitrogen (NH₃N) recovery in aqueous products. By model-based optimization of highest bio-oil yield, the highest bio-oil yield reached 31.79%, increasing by 8.72% after RSM optimization, and light and heavy bio-oil yield was 17.44% and 14.35%, respectively. Long-chain alkanes, alkenes, ketones, fatty acids, phenols, benzenes, amides, naphthalenes were the main components in light bio-oil. Some alcohols, phenols and aromatics were primarily found in heavy bio-oil. Solid residue after HTL consisted of numerous microparticles (～5 μm) observed by Scanning Electron Microscopy (SEM). Energy Dispersive Spectrometer (EDS) analysis shows these particles primarily contained C, O, Mg, P and microelements, derived from Cyanophyta cells.     

Characterization of bio-oil and its sub-fractions from pyrolysis of Scenedesmus dimorphus

In the present study, microalgae Scenedesmus dimorphus was reported for pyrolysis in a fixed-bed reactor to determine the effects of temperature on products yield and the chemical compositions of the liquid and solid products. Experiments were carried out at a temperature range of 300–600 °C with heating rate of 40 °C/min and nitrogen flow rate of 100 ml/min. The yield of bio-oil was found to be maximum (39.6%) at the temperature of 500 °C and was further fractionated into n-hexane, toluene, ethyl acetate and methanol sub-fractions by using liquid column chromatography. Various characteristics of bio-oil and its sub-fractions were determined by ¹H NMR, FTIR and GC–MS. The biochar produced as a co-product can be a potential soil amendment with multiple benefits including soil fertility and C-sequestration. The present investigation suggests the suitability of Scenedesmus dimorphus as a potential feedstock for exploitation of energy and biomaterials through pyrolytic conversion.     

Comparative studies of thermochemical liquefaction characteristics of microalgae using different organic solvents

The effect of different organic solvents, such as methanol, ethanol and 1,4-dioxane, on thermochemical liquefaction characteristics of Spirulina (a kind of high-protein microalgae) was systematically studied. The liquefaction experiments were conducted in a 1000 mL autoclave at different temperatures from 573 to 653 K with a fixed solid/liquid ratio. Liquefaction of Spirulina processed in methanol and ethanol favored the conversion rate and bio-oil yield compared with that in 1,4-dioxane solvent. The bio-oil generated in methanol contained higher C and H concentrations but a lower O content, resulting in a higher caloric value (39.83 MJ/kg). The results of FT-IR (Fourier Transform Infrared Spectroscopy) and GC-MS (Gas Chromatography-Mass Spectroscopy) analyses indicated that the compositions of bio-oil products were greatly affected by the type of solvent used for the liquefaction process. The major component of bio-oil produced with methanol was hexadecanoic acid methyl ester (C₁₇H₃₄O₂, 35.53%). However, ethanol favored the formation of hexadecanoic acid ethyl ester (C₁₈H₃₆O₂, 26.27%). When Spirulina were operated with 1,4-dioxane, the bio-oil was dominated by hexadecanenitrile (C₁₆H₃₁N, 22.7%). The presence of methanol and ethanol might promote the formation of esters. Low-boiling-points compounds with phenol ring structure or heterocyclics can be generated when 1,4-dioxane was employed as solvent.     

Hydrothermal liquefaction of biomass: A review of subcritical water technologies

This article reviews the hydrothermal liquefaction of biomass with the aim of describing the current status of the technology. Hydrothermal liquefaction is a medium-temperature, high-pressure thermochemical process, which produces a liquid product, often called bio-oil or bi-crude. During the hydrothermal liquefaction process, the macromolecules of the biomass are first hydrolyzed and/or degraded into smaller molecules. Many of the produced molecules are unstable and reactive and can recombine into larger ones. During this process, a substantial part of the oxygen in the biomass is removed by dehydration or decarboxylation. The chemical properties of bio-oil are highly dependent of the biomass substrate composition. Biomass constitutes of various components such as protein; carbohydrates, lignin and fat, and each of them produce distinct spectra of compounds during hydrothermal liquefaction. In spite of the potential for hydrothermal production of renewable fuels, only a few hydrothermal technologies have so far gone beyond lab- or bench-scale.     

A comparative study on the quality of bioproducts derived from catalytic pyrolysis of green microalgae Spirulina (Arthrospira) plantensis over transition metals supported on HMS-ZSM5 composite

This study investigated three different types of catalysts: Ni/HMS-ZSM5, Fe/HMS-ZSM5, and Ce/HMS-ZSM5 in the thermochemical decomposition of green microalgae Spirulina (Arthrospira) plantensis. First, non-catalytic pyrolysis tests were conducted in a temperature ranges of 400–700 °C in a dual-bed pyrolysis reactor. The optimum temperature for maximized liquid yield was determined as 500 °C. Then, the influence of acid washing on bio-products upgrading was studied at the optimum temperature. Compared to the product yields from the pyrolysis of raw spirulina, a higher bio-oil yield (from 34.488 to 37.778 %wt.) and a lower bio-char yield (from 37 to 35 %wt.) were observed for pretreated spirulina, indicating that pretreatment promoted the formation of bio-oil, while it inhibited the formation of biochar from biomass pyrolysis. Finally, catalytic pyrolysis experiments of pretreated-spirulina resulted that Fe as an active phase in catalyst exhibited excellent catalytic activity, toward producing hydrocarbons and the highest hydrogen yield (3.81 mmol/gr spirulina).     

Hydrophobic organic compounds from hydrothermal liquefaction of bacterial biomass

The residual biomass of Cupriavidus necator, a biopolyester-producing bacterium, was liquefied in subcritical water at 300 °C. The hydrophobic organic compounds, accounting for about 45% carbon of the original biomass, were recovered with methylene dichloride for analysis. The organic compounds included hydrocarbons such as long chain alkane and benzene, and nitrogen-containing heterocycles such as pyrroles and indoles. The liquid had the similar elemental composition (C, H, O, N) and high heating value (34 MJ kg⁻¹ HHV) of the bio-oils derived from microalgae biomass.     

Catalytic hydrothermal liquefaction of Spirulina platensis: Focusing on aqueous phase characterization

Hydrothermal liquefaction of microalgae under alkaline and acidic conditions has been widely investigated. However, limited data are available on the mechanism of aqueous phase formation during liquefaction. In the present work, we conducted a detailed characterization of the aqueous phase from hydrothermal liquefaction of Spirulina platensis using acetic acid and potassium hydroxide as the catalyst. GC‐MS analysis revealed that a large proportion of nitrogen‐based heteroatom compounds and few oxygen‐based heterocycle compounds were presented in all the aqueous phase. All the aqueous phase displayed alkalescence and a high level of total organic carbon. Whereas, the addition of potassium hydroxide reduced the total organic carbon and the average molecular weight of the aqueous phase. The conventional liquefaction converted the Spirulina platensis to plenty of water‐soluble amides, while these compounds were apt to form acids under both the alkaline and acidic catalysts. Based on the analyses, the general reaction frameworks for the catalytic liquefaction were also proposed.     

Hydrothermal liquefaction of macroalgae: Influence of zeolites based catalyst on products

Hydrothermal liquefaction (HTL) of Ulva prolifera macroalgae (UP) was carried out in the presence of three zeolites based catalysts (ZSM-5, Y-Zeolite and Mordenite) with the different weight percentage (10–20 wt%) at 260–300 °C for 15–45 min. A comparison between non-catalytic and catalytic behavior of ZSM-5, Y-Zeolite, and Mordenite in the conversion of Ulva prolifera showed that is affected by properties of zeolites. Maximum bio-oil yield for non-catalytic liquefaction was 16.6 wt% at 280 °C for 15 min. The bio-oil yield increased to 29.3 wt% with ZSM-5 catalyst (15.0 wt%) at 280 °C. The chemical components and functional groups present in the bio-oils are identified by GC-MS, FT-IR, ¹H-NMR, and elemental analysis techniques. Higher heating value (HHV) of bio-oil (32.2–34.8 MJ/kg) obtained when catalyst was used compared to the non-catalytic reaction (21.2 MJ/kg). The higher de-oxygenation occurred in the case of ZSM-5 catalytic liquefaction reaction compared to the other catalyst such as Y-zeolite and mordenite. The maximum percentage of the aromatic proton was observed in bio-oil of ZSM-5 (29.7%) catalyzed reaction and minimum (1.4%) was observed in the non-catalyst reaction bio-oil. The use of zeolites catalyst during the liquefaction, the oxygen content in the bio-oil reduced to 17.7%. Aqueous phase analysis exposed that presence of valuables nutrients.     

Optimisation of bio-oil production by hydrothermal liquefaction of agro-industrial residues: Blackcurrant pomace (Ribes nigrum L.) as an example

This work reports bio-oil production by hydrothermal liquefaction of blackcurrant pomace (Ribes nigrum L.), a fruit residue obtained after berry pressing. The bio-oil has a higher heating value of 35.9 MJ kg⁻¹ and low ash content, which makes it suitable for energy applications. We report the influence of process parameters on yields and carbon distribution between products: temperature (563–608 K), holding time (0–240 min), mass fraction of dry biomass in the slurry (0.05–0.29), and initial pH (3.1–12.8) by adding sodium hydroxide (NaOH). Depending on the experiments, the bio-oil accounts for at least 24% mass fraction of the initial dry biomass, while char yields ranges from 24 to 40%. A temperature of 583 K enhances the bio-oil yield, up to 30%, while holding time does not have a significant influence on the results. Increasing biomass concentrations decreases bio-oil yields from 29% to 24%. Adding sodium hydroxide decreases the char yield from 35% at pH = 3.1 (without NaOH) to 24% at pH = 12.8. It also increases the bio-oil yield and carbon transfer to the aqueous phase. Thermogravimetric analysis shows that a 43% mass fraction of the bio-oil boils in the medium naphtha petroleum fraction range. The bio-oil is highly acidic and unsaturated, and its dynamic viscosity is high (1.7 Pa s at 298 K), underlining the need for further upgrading before any use for fuel applications.     

Biocrude production by catalytic hydrothermal liquefaction of wood chips using NiMo series catalysts

In this work, hydrothermal liquefaction of wood chips was studied for biocrude production using a mix of Ni–Mo nitrides and carbides. The catalytic materials were synthesized by a temperature-programmed reaction method at 800 °C under a hydrogen atmosphere with nickel loads from 0 to 20 wt%. Lignin contained in the lignocellulosic biomass was successfully release via Kraft process. Hydrothermal liquefaction was carried out in a batch reactor at 320 °C with an initial pressure of 1000 psi of H₂. According to characterization results, nanostructured catalysts with a mix of Ni₂Mo₃N/Mo₂C compo4unds were obtained. NiMo series catalysts composition varies with nickel loads. The catalytic activity shows a reduction in the amount of solid products and an increase in the production of gaseous products as a function of the increase Ni loadings on the catalyst. The most optimal production of biocrude was obtained with the NiMo-10 catalyst, since 81.43% of the total product corresponded to water soluble products (WPS) fraction and the oil fraction, while the solids fraction represented the 6.43% of the total product. Hydrothermal liquefaction catalytic processes were selective towards WSP fraction, improving biocrude quality and favoring biocrude conversion into advanced biofuels.     

Chemometric analysis of composition of bio-crude and aqueous phase from hydrothermal liquefaction of thermally and chemically pretreated Miscanthus x giganteus

Bio-crude from hydrothermal liquefaction (HTL) of lignocellulosic biomass is a potential alternative to conventional fossil fuels. Continuous HTL of lignocellulosic biomass requires feedstock pretreatment to obtain pumpable slurries. This work extends upon previous evaluations of pretreatment methods for obtaining stable slurries of Miscanthus х giganteus. In the current study, extensive characterization of the bio-crude and aqueous phase from HTL of thermally and chemically pretreated M. х giganteus is reported and molecular differences of these samples are evaluated. The bio-crude and aqueous phase is characterized with gas chromatography coupled to mass spectrometry using pre-derivatization with silylating reagent and methyl chloroformate, respectively. Principal component analysis shows that bio-crudes of untreated and slurry stabilized samples have higher concentrations of small organic acids and fatty acids, samples pretreated at mild alkali conditions have higher concentrations of alcohols, polyaromatics, and methylated phenolics, and samples pretreated with strong alkali conditions have higher concentrations of cyclic oxygenates and ketonized aromatics. Aqueous phases are separated based on the addition of slurry stabilizer which has higher concentrations of dicarboxylic acids and phenol. The detailed exploration of both bio-crude and aqueous phase will be of interest for other investigations of the pretreatment effects on biomass for hydrothermal liquefaction.     

In-situ hydrodeoxygenation of lignin via hydrothermal liquefaction with water splitting metals: Comparison between autocatalytic and non-autocatalytic processes

In this study, various water splitting metals (Mg, Al, Zn, and Fe) were investigated for lignin HDO-HTL. Their behaviors during autocatalyzed hydrogenation and interactions with Al–Ni alloy catalyst during non-autocatalyzed hydrogenation were studied. The relationships between Mg, Zn, and Fe with Al–Ni catalyst were synergistic in HTL for bio-oils generation, leading to higher bio-oil yields in non-autocatalytic process than in autocatalytic process and Al–Ni catalytic HDO process. In contrast, because the effect of γ-AlO(OH) was strengthened when Al was used, the coking phenomenon was induced, leading to an antagonistic effect towards bio-oil production. Additionally, although the production of hydrogen was the lowest when Fe was applied, the bio-oil yields reached the highest (44.53 wt% in non-autocatalytic process and 49.83 wt% in autocatalytic process, respectively) with the deoxygenation degrees of 8.41% in non-autocatalytic process and 9.75% in autocatalytic process. Accordingly, Fe exhibited significant potential in lignin in-situ HDO-HTL.     

Production of fuel range oxygenates by supercritical hydrothermal liquefaction of lignocellulosic model systems

Lignocellulosic model compounds and aspen wood are processed at supercritical hydrothermal conditions to study and understand feedstock impact on biocrude formation and characteristics. Glucose and xylose demonstrate similar yield of biocrude and biochar, similar biocrude characteristics, and it is hypothesized that reaction mechanisms for the two model compounds are indistinguishable. Glucose and xylose are main sources of substituted cyclopentenones and substantial contributors to oxygenated aromatics mainly in the range of C₆–C₉ number of carbon atoms, and potential, sustainable biogasoline candidates. Lignin yields predominantly aromatic biocrudes having similar C₆–C₉ number of carbon atoms. Model mixtures show good predictability in the distribution of substituted cyclopentenones and oxygenated aromatics, but aspen wood-derived biocrude is more aromatic than predicted by model mixtures. The work extends previous work on the understanding of the chemical mechanisms of lignocellulose liquefaction and the biocrude formation. Potential applications for the biocrudes are identified, where significant sustainability issues for the transport sector can be addressed.     

Hydrogen from aqueous fraction of biomass pyrolysis liquids by catalytic steam reforming in fluidized bed

Sustainable pathways for producing hydrogen as a synthesis intermediate or as a clean energetic vector will be needed in the future. Renewable biomass resources should be taken into account in this new scenario. Processing through a pyrolysis step, optimized to high liquid production (bio-oil), increases the energy bulk density of biomass for transportation. Steam reforming of the aqueous fraction is an alternative process that increases the hydrogen content of the syngas. However, the thermochemical conversion of organic compounds derived from biomass involves drawbacks such as coke formation on the catalysts. This work studies the performance of Ni-Al catalysts modified with Ca or Mg in the steam reforming of the aqueous fraction of pyrolysis liquids and the resulting coke deposits. The catalyst composition influenced the quantity and type of coke deposits. Calcium improved the formation of carbonaceous products leading to lower H₂/CO ratios while magnesium improved the WGS (water gas shift) reaction. The strategy of reducing the space velocity resulted in a low coke removal although the addition of small quantities of oxygen decreased the coke content of the catalyst by more than 50% weight. Greater efficiency and further catalyst development are needed to improve the energetic requirements of the process.     

Optimization and characterization studies on bio-oil production from palm shell by pyrolysis using response surface methodology

In this work palm shell waste was pyrolyzed to produces bio-oil. The effects of several parameters on the pyrolysis efficiency were tested to identify the optimal bio-oil production conditions. The tested parameters include temperature, N₂ flow rate, feed-stock particle size, and reaction time. The experiments were conducted using a fix-bed reactor. The efficient response surface methodology (RSM), with a central composite design (CCD), were used for modeling and optimization the process parameters. The results showed that the second-order polynomial equation explains adequately the non-linear nature of the modeled response. An R² value of 0.9337 indicates a sufficient adjustment of the model with the experimental data. The optimal conditions found to be at the temperature of 500 °C, N₂ flow rate of 2 L/min, particle size of 2 mm and reaction time of 60 min and yield of bio-oil was approximately obtained 46.4 wt %. In addition, Fourier Transform infra-red (FT-IR) spectroscopy and gas chromatography/mass spectrometry (GC-MS) were used to characterize the gained bio-oil under the optimum condition.     

Growth and hydrogen production by three Chlamydomonas strains cultivated in a commercial fertilizer

In the present investigation, we report the growth and hydrogen production of two wild type Chlamydomonas reinhardtii strains isolated from a tropical oxidation pond in Costa Rica. The performance of these two new isolates was compared to that of Chlamydomonas reinhardtii CC124. All the strains were grown both in conventional Tris-Acetate-Phosphate medium (TAP) and in a commercial fertilizer medium (NPK 20-20-20). The growth of the new two isolates in medium formulated with fertilizer was higher than that attained with the reference strain (CC124). However, the hydrogen production performance of the strain CC124 in TAP-S and fertilizer were comparable, while the two new strains performed better in fertilizer, although the total hydrogen production was lower than that achieved with CC124. By using fertilizer it is possible to reduce the cost of chemical reagents by about 63% compared to TAP. Another advantage of the fertilizer is that it does not contain sulfur, therefore it can be directly used for hydrogen production using the Melis protocol.     

Pyrolysis of Alternanthera philoxeroides (alligator weed): Effect of pyrolysis parameter on product yield and characterization of liquid product and bio char

In the present work, fast pyrolysis of Alternanthera philoxeroides was evaluated with a focus to study the chemical and physical characteristics of bio-oil produced and to determine its practicability as a transportation fuel. Pyrolysis of A.philoxeroides was conducted inside a semi batch quartz glass reactor to determine the effect of different operating conditions on the pyrolysis product yield. The thermal pyrolysis of A. philoxeroides were performed at a temperature range from 350 to 550 °C at a constant heating rate of 25 °C/min & under nitrogen atmosphere at a flow rate of 0.1 L/min, which yielded a total 40.10 wt.% of bio-oil at 450 °C. Later, some more sets of experiments were also performed to see the effect on pyrolysis product yield with change in operating conditions like varying heating rates (50 °C/min, 75 °C/min & 100 °C/min) and different flow rates of nitrogen (0.2, 0.3, 0.4 & 0.5 L/min). The yield of bio-oil during different heating rate (25, 50, 75 and 100 °C/min) was found to be more (43.15 wt.%) at a constant heating rate of 50 °C/min with 0.2 L/min N₂ gas flow rate and at a fixed pyrolysis temperature of 450 °C. The High Heating Value (HHV) value of bio-oil (8.88 MJ/kg) was very less due to presence of oxygen in the biomass. However, the high heating value of bio-char (20.41 MJ/kg) was more, and has the potential to be used as a solid fuel. The thermal degradation of A. philoxeroides was studied in TGA under inert atmosphere. The characterization of bio-oil was done by elemental analyser (CHNS/O analyser), FT-IR, & GC/MS. The char was characterized by elemental analyser (CHNS/O analysis), SEM, BET and FT-IR techniques. The chemical characterization showed that the bio-oil could be used as a transportation fuel if upgraded or blended with other fuels. The bio-oil can also be used as feedstock for different chemicals. The bio-char obtained from A. philoxeroides can be used for adsorption purposes because of its high surface area.     

Assessment of liquefaction and pyrolysis systems

A summary is presented on the developments in the state of the art of experimental direct liquefaction of biomass, and the technoeconomic studies carried out within the IEA Biomass Agreement liquefaction activities from 1983 to 1991. The objectives of the study are: to identify potential improvements in developing process concepts, and to evaluate technically and economically the processes in direct thermal liquefaction. The principal instrument utilized in assessing the new technologies was a technoeconomic assessment. A standard procedure was constructed. Balances were calculated for a 1000 dry t/d plant size. Feedstocks included wood, peat, and straw. The thermal efficiency in the fuel oil substitute and gasoline production from woody biomass is above 60 % and 50 %, respectively. At a wood cost of US$ 30/wet t (US$ 3.4/GJ), and with a capital recovery factor of 0.12, a fuel oil substitute could be produced at US$ 8/GJ. The estimated cost for the least expensive transportation fuel process would be US$ 12/GJ. Areas where more research is needed are highlighted.