Biocrude Yield Research Articles

Valorization of red macroalgae biomass via hydrothermal liquefaction using homogeneous catalysts

Hydrothermal liquefaction of red macroalgae species, Kappaphycus alvarezii (KA) and Eucheuma denticulatum (ED), was performed at 350 °C in the presence of 5 wt% neutral and alkali catalysts like Na2CO3, K2CO3, CaCO3, Na2SO4, NaOH, and KOH. The maximum bio-crude yield of 26.7 wt% and 18.5 wt%, on a dry ash-free basis, was obtained from Na2CO3 treatment of KA and KOH treatment of ED, respectively. The bio-crude from both feedstocks mainly consisted of cyclic oxygenates, whose selectivities were maximum in K2CO3 and CaCO3 treatments. The calorific value of the bio-crude was 38.5 MJ/kg from KA and 30.8 MJ/kg from ED, while that of biochars was 20–24 MJ/kg. A high degree of deoxygenation (64.2%) was observed in bio-crude produced from Na2SO4 treatment of KA biomass. Salts of Cl–, SO42– and K+ constituted the major inorganic portion of the aqueous phase. Maximum energy recovery (99%) was observed from the Na2CO3 treatment of ED.

Potential Use of Plant Biomass from Treatment Wetland Systems for Producing Biofuels through a Biocrude Green-Biorefining Platform

The potential of using the biomass of four wetland plant species (Iris pseudacorus, Juncus effusus, Phragmites australis and Typha latifolia) grown in treatment wetland systems and under natural conditions were tested to produce high-value materials using hydro-thermal liquefaction (HTL). The results show that the wetland plants biomass is suitable for biocrude and biochar production regardless of the origin. The hydrothermal liquefaction products’ (biocrude, biochar, aqueous and gaseous phase) yields vary according with the specific biomass composition of the species. Furthermore, the results show that the biomass composition can be affected by the growing condition (treatment wetland or natural unpolluted conditions) of the plants. None of the single components seems to have a determinant effect on the biocrude yields, which reached around 30% for all the analyzed plants. On the contrary, the biochar yields seem to be affected by the composition of the biomass, obtaining different yields for the different plant species, with biochar yields values from around 12% to 22%, being that Phragmites australis is the one with the highest average yield. The obtained aqueous phase from the different plant species produces homogeneous compounds for each plant species and each growing environment. The study shows that biomass from treatment wetlands is suitable for biocrude production. The environmental value of this biomass lies on the fact that it is considered a residual product with no aggregated value. The treatment wetland biomass is a potential sustainable source for biofuel production since these plants do not need extra land or nutrients for growing, and the biomass does not compete with other uses, offering new sources for enhancing the bioeconomy concepts.

Microwave co-pyrolysis of PET bottle waste and rice husk: effect of plastic waste loading on product formation

This research work is focused to understand the role of microwave susceptor-assisted pyrolysis on polyethylene terephthalate (PET) bottle waste with rice husk (RH) valorization. Microwave pyrolysis/co-pyrolysis experiments were conducted at 450 W microwave power using a graphite susceptor. Effects of PET: RH ratio and total mass of co-pyrolysis feed mixture were thoroughly investigated. Mass and energy yields of bio-crude, char, and gas were evaluated. Microwave energy consumption and energy efficiency of pyrolysis were also evaluated. Pyrolysis energy efficiency is higher at 40 g (73–76%) compared to 20 g (53–75%) of co-pyrolysis feed mixture. The heating value of bio-crude was high (34–36 MJ/kg) due to carbon (79–83 wt%) and hydrogen (5–6 wt%) rich compounds. Bio-crude composition significantly varied with PET: RH ratios. Co-pyrolysis promoted the formation of aromatic oxygenates and biphenyl hydrocarbons. The selectivity of biphenyl hydrocarbons (29.2%) is high at an equal PET: RH ratio. The selectivity of hydrocarbons obtained at the 20:20 (PET: RH) ratio is found to be 47.5%. The selectivity of aromatic hydrocarbons obtained in microwave pyrolysis (47.9%) of PET is higher compared to conventional pyrolysis (8%). In microwave pyrolysis of RH, the high selectivity of aromatic oxygenates (73%) was obtained. Whereas, in conventional pyrolysis, the formation of aliphatic oxygenates (36.5%) was observed. This research would provide an understanding of waste valorization using the co-pyrolysis platform.

Machine learning prediction of biocrude yields and higher heating values from hydrothermal liquefaction of wet biomass and wastes

Machine learning (ML) approach was applied for the prediction of biocrude yields (BY) and higher heating values (HHV) from hydrothermal liquefaction (HTL) of wet biomass and wastes using 17 input features from feedstock characteristics (biological and elemental properties) and operating conditions. Several novel ML algorithms were evaluated, based on 10-fold cross-validation, with 3 different sets of input features. An extreme gradient boosting (XGB) model proved to give the best prediction accuracy at nearly 0.9 R2 with normal root mean square error (NRMSE) of 0.16 for BY and about 0.87 R2 with NRMSE of about 0.04 for HHV. Temperature was found to be the most influential feature on the predictions for both BY and HHV. Meanwhile, feedstock characteristics contributed to the XGB model for more than 55%. Individual effects and interactions of most important features on the predictions were also exposed, leading to better understanding of the HTL system.

Py-GC-MS Study on Catalytic Pyrolysis of Biocrude Obtained via HTL of Fruit Pomace

Herein, we proposed new two-stage processing of blackcurrant pomace toward a value-added, hydrocarbon-rich biocrude fraction. The approach consisted of thermochemical liquefaction of a wet-type organic matter into liquid biocrude followed by its upgrade by thermal and catalytic pyrolysis. Particularly, we put effort into investigating the effect of selected catalysts (ZSM-5 and HY zeolite) on the composition of the volatiles released during the pyrolysis of the biocrude. The latter was obtained through liquefaction of the raw material in the binary solvent system of water and isopropanol. The biocrude yield accounted for ca. 45 wt.% of the initial dry biomass. It was a complex mixture of various component groups with an abundant share of oxygenates, especially carboxylic acids and esters. Thereafter, the biocrude was subjected to a pyrolysis study performed by means of the microscale coupled pyrolysis-gas chromatography-mass spectrometry technique (Py-GC-MS). The dominant components identified in the catalytic pyrolytic volatiles were unsaturated hydrocarbons (both cyclic and aliphatic ones) and, to a lesser extent, oxygen and nitrogen compounds. The addition of the ZSM-5 and HY zeolite allowed us to attain the relative total share of hydrocarbons in the volatile fraction equal to 66% and 73%, respectively (in relation to identified compounds). Thus, catalytic pyrolysis over zeolites seems to be particularly prospective due to the promotion of the deoxygenation reactions, which manifested in the noticeable decrease in the share of oxygen compounds in the evolved volatiles. The developed innovative two-stage processing of blackcurrant pomaces allows for obtaining value-added products that could serve as chemicals, biocomponents, and self-contained biofuels as well as bioplastic precursors. The presented contribution brings some new insights into the field of valorization of residuals generated by the food industry sector.

Hydrothermal co-liquefaction of rice straw and waste cooking-oil model compound for bio-crude production

This study aims to investigate the hydrothermal co-liquefaction of rice straw (RS) and waste cooking-oil model compound (WCOM) under sub-critical conditions for the optimum bio-crude yield and conversion. Effects of temperature, catalyst (K2CO3), residence time and mass ratios of RS to WCOM on products’ distribution were examined and the reaction mechanism for co-liquefaction of RS and WCOM was also explored. The highest bio-crude yield (88.77%) was obtained when mass ratio of RS to WCOM was 1:3 at 300 ℃, 10 min and in absence of K2CO3. When the mass ratio was 3:1, 1:1 and 1:3, the synergistic effect approached 14.38%, 11.38% and 12.84%, respectively. WCOM could improve the overall conversion rate of RS during co-liquefaction. GC-MS analysis suggested that the bio-crude contained large amounts of fatty acids and smaller amounts of phenols and ketone aldehydes. Co-liquefaction was found effective to improve the qualitative and quantitate features of products from biomass.

Hydrothermal co-liquefaction of rice straw and Nannochloropsis: The interaction effect on mechanism, product distribution and composition

Catalytic co-liquefaction of rice straw and Nannochloropsis has been investigated in this study, using alkali catalyst (K2CO3) in glycerol-water solvent at different temperature, residence time and raw material mass ratios. The distribution of co-liquefaction products was examined in relation to the main reaction conditions. The synergistic effect of rice straw and Nannochloropsis co-liquefaction was confirmed. The yield of bio-crude increased from 32.49% of pure rice straw to 42.22% of a mixture with rice straw/Nannochloropsis mass ratio 1:1 under reaction conditions of 350 °C for 10 min with K2CO3, resulting in a synergistic effect on encouraging bio-crude production of 8.86%. GC-MS results indicated that co-liquefaction affected the mechanism of bio-crude production. The formation of ketones and phenols in bio-crude were weakened but fatty acids, esters, and nitrogenous compounds were improved under co-liquefaction. Rice straw and Nannochloropsis co-liquefaction was beneficial to improve the quality of bio-crude. Co-liquefaction increased H/C and decreased N element content as compared to liquefaction of pure rice straw and Nannochloropsis, respectively. Meanwhile, co-liquefaction decreased the bio-crude O/C ratio. By recycling aqueous phase by-products in the co-liquefaction process, the yield and HHV of the bio-crude as well as the fractions of phenols and hydrocarbons were also increased.

Substituting microalgal biomass with faecal sludge for high-quality biocrude production through co-liquefaction: A sustainable biorefinery approach

Cultivation and harvesting of microalgal biomass are energy-intensive and expensive processes. Hence, this study explored the effect of substituting microalgal biomass with faecal sludge (wet-waste) at different ratios (100:0, 25:75, 50:50, 75:25, and 0:100) for biocrude production through hydrothermal liquefaction. Among the various ratios, the co-hydrothermal liquefaction of MA25FS75 (25% microalgae: 75% faecal sludge) sample showed the highest biocrude yield of 38% with a lighter hydrocarbon fraction of 43% (kerosene 15% and diesel 28%) and HHV of 33.8 MJ/Kg. In addition, the biocrude maturity and intensity analysis suggested higher A-factor and lower C-factor for MA25FS75, which indicated a high-quality crude property. Finally, the higher energy recovery of 85.6% and lower energy consumption ratio of 0.58 for MA25FS75 confirmed the net energy positivity system. So, this study suggested that the faecal sludge was an environment-friendly low-cost replacement of microalgae for high-quality biocrude production towards a sustainable biorefinery approach.

Catalytic hydrothermal liquefaction of microalgae cultivated in wastewater: Influence of ozone-air flotation on products, energy balance and carbon footprint

The use of ozone-air flotation for microalgae harvesting was investigated, in terms of its environmental feasibility and use in catalytic HTL. The environmental feasibility was determined by the Net Energy Ratio (NER) and carbon footprint metrics following a life cycle assessment (LCA). The effect of the variables in the catalytic HTL process (catalyst load, temperature, time), on the distribution of bio-crude and hydrocarbons, was experimentally evaluated using a mixed microalgae culture dominated by Scenedesmus sp. grown in wastewater and harvested by ozone-air flotation or gravity-sedimentation, respectively. Liquefaction was carried at three temperatures (325 °C, 350 °C and 370 °C), three reaction times (30, 60 and 120 min) and two HZSM-5 catalyst loads (0, 5 and 7 wt%). The bio-crude yields obtained (17 to 20%) were similar with both harvesting methods; however, the production of aliphatic compounds was doubled, when using ozone-air flotation, and further increased when using a HZMS-5 catalyst. The highest bio-crude quality (N: 3.0%, O: 5.6%, S: 0.1%) and high heat values (42.3 MJ/kg) were produced at 325 °C, 60 min and 5 wt%, in contrast with sedimented microalgae (6.0%, 7.0%, 1.0%, and 39.3 MJ/kg, respectively). Energy and carbon footprint were quantified with a LCA approach for a scenario using a functional unit (FU) of 1 GJ of bio-crude production and its possible bio-jet fuel conversion as a potential product. HTL microalgae conversion required the highest amount of energy among evaluated cultivation and harvesting processes. Harvesting via ozone-air flotation, gave a NER value and carbon footprint of 2.7 and 30.5 kg CO2 eq/GJ of bio-jet fuel, respectively. The proposed novel system had significantly lower greenhouse gas equivalent emissions (by 65%) and NER values (by 48%) than for conventional jet fuel.

Biocrude Production from Hydrothermal Liquefaction of Chlorella: Thermodynamic Modelling and Reactor Design

Hydrothermal liquefaction can directly and efficiently convert wet biomass into biocrude with a high heating value. We developed a continuous hydrothermal liquefaction model via Aspen Plus to explore the effects of moisture content of Chlorella, reaction pressure and temperature on thermodynamic equilibrium yields, and energy recoveries of biocrude. We also compared the simulated biocrude yield and energy recoveries with experiment values in literature. Furthermore, vertical and horizontal transportation characteristics of insoluble solids in Chlorella were analyzed to determine the critical diameters that could avoid the plugging of the reactor at different flow rates. The results showed that the optimum moisture content, reaction pressure, and reaction temperature were 70–90 wt%, 20 MPa, and 250–350 °C, respectively. At a thermodynamic equilibrium state, the yield and the energy recovery of biocrude could be higher than 56 wt% and 96%, respectively. When the capacity of the hydrothermal liquefaction system changed from 100 to 1000 kg·h−1, the critical diameter of the reactor increased from 9 to 25 mm.

Hydrothermal liquefaction of Spirulina platensis in post-carbonization wastewater from sewage sludge

Wet solid waste can achieve good dewaterability through hydrothermal carbonization. However, massive wastewater rich in organics is also generated during the process. Previous studies reported the anaerobic digestion potential of organic wastewater, but its inhibitors cause challenges. In our early work, the aqueous by-product from hydrothermal liquefaction of microalgae has been successfully recycled back into the liquefaction process, leading to an enhanced oil yield. Herein, this study addresses the possibility of wastewater from sewage sludge dewatering as a solvent to convert microalgae for biocrude production under temperature of 260-320 ° C . Results show that the wastewater owned a chemical oxygen demand value of 14 g/L and a total organic carbon value of 5.89 g/L with a nitrogen content of 10.34%. The biocrude yield in this wastewater was 31.3–38.7 wt%, higher than liquefaction in pure water (27–33 wt%). Over 10% increment was reached, demonstrating the potential of organic wastewater as a solvent for biocrude production. Following a slight decrease of the nitrogen content, the higher heating value of the biocrude from the wastewater solvent was close to that formed in pure water, suggesting a non-significant influence on fuel quality. Besides, the enhancing mechanism of wastewater stream on liquefaction was discussed based on various analytical approaches. Compound analysis indicates a reduction of nitrogenous chemicals in the wastewater during liquefaction, which are more likely to be transformed to oil phase forming amides. Therefore, this recycling strategy would help develop novel routes for utilization of organic wastewater, significant for sewage sludge treatment.

Hydrothermal liquefaction of sawdust in seawater and comparison between sodium chloride and sodium carbonate

Hydrothermal liquefaction (HTL) of biomass is a promising conversion technology for crude bio-oil (biocrude) production. This work is a continuation of our innovative exploration of using seawater in HTL and hereby the seawater effect is further investigated. Sawdust was chosen as feedstock of interest in this study. At the temperature of 270 °C, using seawater resulted in obvious decline in biocrude yield compared to using freshwater. An elevated temperature at 320 °C promoted the negative effect. Binary mixtures of sawdust’s model components, hemicellulose, cellulose and lignin were liquefied in seawater and freshwater respectively which verified that the negative seawater effect was mainly due to cellulose-lignin interaction. Cellulose-lignin interaction was sensitive to the presence of NaCl, led to severer repolymerization and eventually resulted in biocrude yield decline. A comparison of the performances of Na2CO3 and NaCl in HTL of sawdust found that Na2CO3 exhibited relatively mild negative effect than NaCl. Though increasing temperature enhanced the negative effect for both Na2CO3 and NaCl, Na2CO3 and NaCl affected biocrude formation differently. When adding Na2CO3 into the HTL of sawdust process, the biocrude yield was decreased via decomposing reaction intermediates to generate more aqueous and gaseous products. While the presence of NaCl not only led to the decomposition of intermediates into aqueous and gaseous products, but also induced the repolymerization of intermediates to form solid residue. Computational modelling (Density Functional Theory calculation) indicated that only 41.53 kcal/mol activation energy was required for Cl- to initiate the condensation/repolymerization as compared to that of 101.60 kcal/mol for CO32–, which was supportive for the different underlying pathways for Na2CO3 and NaCl.

Production of upgraded biocrude from hydrothermal liquefaction using clays as in situ catalysts

Hydrothermal liquefaction (HTL) is a thermochemical process that converts biomass into biocrude. HTL suffers from low yields of water-insoluble biocrude with high oxygen contents and low heating values. Inexpensive clay minerals including montmorillonite, dolomite, kaolinite and sand were used to upgrade HTL biocrude as in situ acid-base catalysts. Batch tests were performed using starch with 5 wt% clay minerals at 300 °C for 1 h. Bio-oil was fractionated into water-soluble and water-insoluble parts to explore potential catalytic mechanisms by analyzing the fractional distribution, elemental composition and chemical composition. Higher carbon recoveries in the bio-oil fraction (approaching 60%) occurred with clay-catalyzed HTL. Energy recovery of both bio-oil fractions increased by approximately 22% for all clays. A base-catalyzed pathway inhibits char formation from catalytic HTL, with dolomite approaching a char yield as low as 3%. Chromatographic analysis of heavy and light oils from both fractions showed that dolomite and montmorillonite play a catalytic effect via base and acid pathways on upgrading biocrude. Clay-catalyzed HTL modified the boiling point distributions by producing more 100–300 °C middle temperature distillates. Overall, catalytic HTL with clay minerals enhanced the heating value and energy recovery of bio-oils.

Effects of aqueous phase recirculation on product yields and quality from hydrothermal liquefaction of rice straw

Aqueous phase (AP) recirculation is a promising process intensification strategy to improve the yield and quality of the products and cost efficiency of the hydrothermal liquefaction (HTL) process by replacing the fresh water used in the experiments. The results demonstrate that AP recirculation in the HTL of rice straw decreases the bio-crude yield from 32.6 wt% to 9.1 wt% after the third recycle, while enhancing the bio-char yield up to 64.1 wt%. The bio-crude and bio-char show improved carbon and hydrogen content with AP recirculation. The decrease in selectivity to aliphatic hydrocarbons in the bio-crude and bio-char, coupled with increase in H2 content in the gaseous phase, suggests the prevalence of dehydrogenation reactions. The bio-char achieved better thermal stability, water retention and cation exchange capacity with AP recirculation. There was a significant accumulation of K+, Ca2+ and Cl– with a concomitant decrease in silicates, sulfate and phosphate in the AP.

MW‐assisted hydrothermal liquefaction of spent coffee grounds

AbstractHydrothermal liquefaction (HTL) is an attractive technology to process biomass to biocrude and hydrochar, and most studies have been using batch, tube, or continuous reactors with conventional heating. Attempts on microwave (MW)‐assisted HTL (MW‐HTL) is limited, and the effect of the heating rate on product distribution remains unexplored. There is also a lack of information on the MW effect in HTL processes. This study focused on the HTL of spent coffee grounds (SCG, most of which are currently disposed of in landfills) under MW irradiation. The investigation on the effect of heating rate revealed that increasing heating rate from 4.5 to 13.5°C/min promoted the biocrude formation and reduced the amount of solid residue. A low feedstock concentration of 8.3 wt.% was favourable for MW‐HTL of SCG compared to 14.3 wt.%. At a reaction temperature of 270°C, the biocrude yield gradually increased from 20.9 to 30.1 wt.% in response to an increase in reaction time from 0 to 20 min. In terms of the quality of products derived from MW‐HTL, the biocrude exhibited a satisfactory higher heating value (31.3 MJ/kg), and the solid residue, hydrochar, had a high specific surface area of 247.5 m2/g. As for the MW effect, MW and conventional heating resulted in comparable biocrude yield (27.8 vs. 25.7 wt.%, respectively). The characterization of biocrude, hydrochar, and aqueous phase also suggested that MW irradiation had no significant promotion effect on HTL under the experimental conditions in the study.

Hydrothermal liquefaction of municipal sewage sludge: Effect of red mud catalyst in ethylene and inert ambiences

In this study, ethylene and nitrogen(inert) reaction environments were applied into the hydrothermal liquefaction (HTL) process of municipal sewage sludge with red mud catalyst to evaluate the effects on biocrude and other byproducts. Red mud in three oxidation states was used: red mud calcined at 575 °C (CRM), reduced at 500 °C (RRM500), and 700 °C (RRM700). The RRM500 lowered the acidity by 14%; whereas, the RRM700 minimized the viscosity by 47% comparing to non-catalytic-inert biocrude samples. The ethylene ambience successfully maximized the biocrude yield by 41.6 wt% without any catalyst. The viscosity of the biocrudes produced under ethylene environment showed lower differences compared to nitrogen environment. The RRM500-ethylene reaction efficiently reduced the nitrogen content in the biocrude by 14%. These results suggested that the ethylene atmosphere has the potential for improved biocrude production during catalytic HTL treatment.

Biocrude oil production via hydrothermal liquefaction of food waste in a simplified high-throughput reactor

In this study, the hydrothermal liquefaction of food waste was investigated for generating bio-oils or biocrudes using a simplified high-throughput reactor. Different operating conditions were parametrically tested for obtaining maximum yield of biocrudes at temperatures from 280 to 340 °C and sample-to-water mixture ratios from 1:3 to 1:7, with 30 min residence time. The biocrude yields were found to increase significantly with increasing temperature and mixture ratio. A maximum biocrude yield of approximately 40% w/w dry basis (from a total liquid product yield of over 56% w/w) and energy recovery of over 70% were obtained at 340 °C and a mixture ratio of 1:7. High heating values of the resulting biocrude and solid residue were remarkably better than those of the raw material. Fatty acids, amides, N-containing compounds, and cyclic ketones were identified to be the main components of the biocrudes using advanced GCxGC/TOF-MS.

A probabilistic economic and environmental impact assessment of a cyanobacteria-based biorefinery

Microbial based biofuels represent a potential promising solution as an environmentally favorable transportation fuel. Cyanobacteria have many of the same advantages as microalgae: ability for rapid growth in otherwise non-arable regions, suitability for genetic engineering, and simple nutritional needs. Additionally, cyanobacteria can be engineered to secrete valuable co-products that can be harvested independent from the produced biomass. However, little work has been done to identify the processes and the economic and environmental impacts associated with a large-scale cyanobacteria-to-fuels facility. The present study is a concurrent techno-economic and life cycle assessment of a facility that generates fuels and methyl laurate, an oleochemical, from the cyanobacterial species Synechocystis sp. PCC 6803. The biorefinery model includes all aspects of cultivation, separation of the secreted methyl laurate, biomass harvesting and fuel processing via hydrothermal liquefaction (HTL) of the dewatered biomass. The assessments leverage Monte Carlo analysis (MCA) to address uncertainty and variability inherent in the most significant input parameters, replacing them with probabilistic functions. For the facility configuration producing both fuels and the oleochemical co-product, the MCA average minimum fuel selling price (MFSP) is $2.47 per decimeter (dm3) or $9.34 per gallon of gasoline equivalent (gge) with the corresponding average global warming potential determined to be 118 g CO2-eq-MJ−1. The case producing only fuels results in an MCA average MFSP of $2.01-(dm3)−1 ($7.60-gge−1) and an average environmental impact of 100 g CO2-eq-MJ−1. These results are compared to static optimistic and conservative scenario analysis estimates, illustrating the over- and under-estimation of outcomes associated with non-stochastic methods. Suggested facility improvements include increases in pond productivity of both the biomass and methyl laurate oil production, as well as improvements to carbon utilization and bio-crude yield from HTL processing.

Effect of Temperature on the Pilot-Scale Catalytic Pyrolysis of Loblolly Pine

A pilot-scale biomass catalytic pyrolysis unit with a nominal throughput of one tonne of biomass per day (1TPD) has been in operation since 2013 to investigate the process parameters that have the largest influence on biocrude yield, oxygen content, and chemical composition. A parametric study was conducted to investigate the effect of pyrolysis temperature, ranging from 433 to 581 °C, on biocrude yield and quality. A locally sourced loblolly pine feedstock and a commercially available, spray dried, nonzeolitic γ-Al2O3 catalyst were used in individual experiments conducted at each pyrolysis temperature to achieve a minimum of 4 h of steady-state continuous operation. Typically, 600–800 kg of biomass was fed over a 12-h period, with one experiment extended to almost 29 h (1144-kg biomass fed) and one experiment interrupted by a process upset after just 7 h (411-kg biomass fed). Comprehensive analysis of collected gas, liquid, and solid products were used to calculate carbon balances (77% to 107%) for each experiment. The biocrude yield ranged from 12 to 18 wt % C and, in general, decreased with increasing pyrolysis temperature. The average steady-state biocrude yield as a function of temperature translated to a biocrude production rate between 40 and 50 gallons per dry ton. The biocrude oxygen content varied between 21 and 31 wt %, on a dry basis, and as expected, decreased with increasing pyrolysis temperature. The identified components in the semivolatile biocrude products are mostly methoxyphenols and other multiphenolic compounds. The multiphenolic compounds are demethoxylated at pyrolysis temperatures above 500 °C, producing biocrudes with higher concentrations of monophenols and polycyclic aromatic hydrocarbons. The concentration of anhydrosugars, like levoglucosan in the biocrudes, decreased with increasing pyrolysis temperature from ∼15 to ∼1 vol %.

Pyrolysis of High-Ash Natural Microalgae from Water Blooms: Effects of Acid Pretreatment.

Natural microalgae (NA, cyanobacteria) collected from Taihu Lake (Jiangsu, China) were used for biofuel production through pyrolysis. The microalgae were de-ashed via pretreatment with deionized water and hydrochloric acid, and the samples obtained were noted as 0 M, 0.1 M, 1 M, 2 M, 4 M, 6 M, 8 M, respectively, according to the concentration of hydrochloric acid used in the pretreatment. Pyrolysis experiments were carried out at 500 °C for 2 h. The products were examined by various techniques to identify the influence of the ash on the pyrolysis behavior. The results showed that the ash inhibited the thermal transformation of microalgae. The 2 mol/L hydrochloric acid performed the best in removing ash and the liquid yield increased from 34.4% (NA) to 40.5% (2 M). Metal-oxides (mainly CaO, MgO, Al2O3) in ash promoted the reaction of hexadecanoic acid and NH3 to produce more hexadecanamide, which was further dehydrated to hexadecanenitrile. After acid pretreatment, significant improvement in the selectivity of hexadecanoic acid was observed, ranging from 22.4% (NA) to 58.8% (4 M). The hydrocarbon compounds in the liquid product increased from 12.90% (NA) to 26.67% (2 M). Furthermore, the acid pretreatment enhanced the content of C9–C16 compounds and the HHV values of bio-oil. For natural microalgae, the de-ashing pretreatment before pyrolysis was essential for improving the biocrude yield and quality, as well as the biomass conversion efficiency.