Liquefaction of palm kernel shell to bio-oil using sub- and supercritical water: An overall kinetic study

Palm kernel shell was liquefied using sub- and supercritical water at 330–390 °C and 25 MPa for different reaction times. The overall kinetics of the liquefaction based on the conversion of biomass was analyzed using kinetic equation adopted from the literature, and the kinetic parameters were estimated from the evaluation of the kinetic equation. In this study, the rate constant (k) increased from 0.43 to 0.49 s^?1 with reaction temperature from 330 to 390 °C. The relationship of rate constant (k) and temperature agreed reasonably well with the Arrhenius equation. The activation energy (E) and pre-exponential factor (A) values for the liquefaction process were estimated to be 6.70 kJ/mol and 1.65 s^?1, respectively. In addition, the experimental bio-oil yields with respect to reaction time were well-fitted using the modified Reverchon-Sesti Osseo equation.     

Production and detailed characterization of bio-oil from fast pyrolysis of palm kernel shell

Bio-oil has been produced from palm kernel shell in a fluidized bed reactor. The process conditions were optimized and the detailed characteristics of bio-oil were carried out. The higher feeding rate and higher gas flow rate attributed to higher bio-oil yield. The maximum mass fraction of biomass (57%) converted to bio-oil at 550 °C when 2 L min⁻¹ of gas and 10 g min⁻¹ of biomass were fed. The bio-oil produced up to 500 °C existed in two distinct phases, while it formed one homogeneous phase when it was produced above 500 °C. The higher heating value of bio-oil produced at 550 °C was found to be 23.48 MJ kg⁻¹. As GC–MS data shows, the area ratio of phenol is the maximum among the area ratio of identified compounds in 550 °C bio-oil. The UV–Fluorescence absorption, which is the indication of aromatic content, is also the highest in 550 °C bio-oil.     

Optimization study of sub/supercritical water liquefication of lignite: Fast liquefaction for high bio-oil yield

Sub/supercritical water liquefication (SCWL) is a water-based thermochemical technology as well as an environmentally friendly treatment by converting wet feedstock into bioenergy. In the present study, a systematic investigation of SCWL of lignite was carried out covering a temperature range between 320 and 440 °C when residence time increased from 5 min to 40 min. The highest bio-oil oil yield of 34.3% with solid residue of 52.7% was obtained at 440 °C for 5 min. Phenol derivatives, carboxylic acids, long chain hydrocarbons, ketones, and naphthalene were the main bio-oil composition through FTIR and GC-MS analysis. Gas yields and their exact compositions were also determined and CO₂ was the dominate gas product but the percentage of CH₄ became significant at severe SCWL conditions. A conclusion was drawn that fast liquefaction (e.g. 5 min) at relative higher temperature (e.g. 400 °C) which avoid excessive gasification and repolymerization reactions was an optimization strategy for high yield bio-oil production from SCWL of lignite.     

Hydrothermal liquefaction of spent coffee grounds in water medium for bio-oil production

Spent coffee grounds (SCG) were liquefied in hot-compressed water to produce crude bio-oil via hydrothermal liquefaction (HTL) in a 100 cm³ stainless-steel autoclave reactor in N₂ atmosphere. We investigated the effects of operating parameters such as retention times (5 min, 10 min, 15 min, 20 min and 25 min), reaction temperatures (200 °C, 225 °C, 250 °C, 275 °C and 300 °C), and water/feedstock mass ratios (5:1, 10:1, 15:1 and 20:1) and initial pressure of process gas (2.0 MPa and 0.5 MPa) on the yield and properties of the resulting crude bio-oil. The highest yield of the crude bio-oil (47.3% mass fraction) was obtained at conditions of 275 °C, 10 min retention time and water/feedstock mass ratio of 20:1 with an initial pressure of 2.0 MPa. The elemental analysis of the produced crude bio-oil revealed that the oil product had a higher heating value (HHV) of 31.0 MJ kg⁻¹, much higher than that of the raw material (20.2 MJ kg⁻¹). GC–MS and FT-IR measurements showed that the main volatile compounds in the crude bio-oil were long chain aliphatic acids and esters.     

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.     

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.     

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.     

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.     

An overview of empty fruit bunch from oil palm as feedstock for bio-oil production

Empty fruit bunch (EFB) from oil palm is one of the potential biomass to produce biofuels like bio-oil due to its abundant supply and favorable physicochemical characteristics. Confirming the assertion, this paper presents an overview of EFB as a feedstock for bio-oil production. The fundamental characteristics of EFB in terms of proximate analysis, ultimate analysis and chemical composition, as well as the recent advances in EFB conversion processes for bio-oil production like pyrolysis and solvolysis are outlined and discussed. A comparison of properties in terms of proximate analysis, ultimate analysis and fuel properties between the bio-oil from EFB and petroleum fuel oil is included. The major challenges and future prospects towards the utilization of EFB as a useful resource for bio-oil production are also addressed.     

Utilization possibilities of palm shell as a source of biomass energy in Malaysia by producing bio-oil in pyrolysis process

Agriculture residues such as palm shell are one of the biomass categories that can be utilized for conversion to bio-oil by using pyrolysis process. Palm shells were pyrolyzed in a fluidized-bed reactor at 400, 500, 600, 700 and 800 °C with N₂ as carrier gas at flow rate 1, 2, 3, 4 and 5 L/min. The objective of the present work is to determine the effects of temperature, flow rate of N₂, particle size and reaction time on the optimization of production of renewable bio-oil from palm shell. According to this study the maximum yield of bio-oil (47.3 wt%) can be obtained, working at the medium level for the operation temperature (500 °C) and 2 L/min of N₂ flow rate at 60 min reaction time. Temperature is the most important factor, having a significant positive effect on yield product of bio-oil. The oil was characterized by Fourier Transform infra-red (FT-IR) spectroscopy and gas chromatography/mass spectrometry (GC-MS) techniques.     

Influence of reaction conditions on bio-oil production from pyrolysis of construction waste wood

The pyrolysis characteristics of construction waste wood were investigated for conversion into renewable liquid fuels. The activation energy of pyrolysis derived from thermogravimetric analysis increased gradually with temperature, from 149.41 kJ/mol to 590.22 kJ/mol, as the decomposition of cellulose and hemicellulose was completed and only lignin remained to be decomposed slowly. The yield and properties of pyrolysis oil were studied using two types of reactors, a batch reactor and a fluidized-bed reactor, for a temperature range of 400–550 °C. While both reactors revealed the maximum oil yield at 500 °C, the fluidized-bed reactor consistently gave larger and less temperature-dependent oil yields than the batch reactor. This type of reactor also reduced the moisture content of the oil and improved the oil quality by minimizing the secondary condensation and dehydration. The oil from the fluidized-bed reactor resulted in a larger phenolic content than from the batch reactor, indicating more effective decomposition of lignin. The catalytic pyrolysis over HZSM-5 in the batch reactor increased the proportion of light phenolics and aromatics, which was helpful in upgrading the oil quality.     

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.     

Comparison of pyrolysis and hydrothermal liquefaction of Chlamydomonas reinhardtii. Growth studies on the recovered hydrothermal aqueous phase

The production of bio-oil by pyrolysis with a high heating rate (500 K s⁻¹) and hydrothermal liquefaction (HTL) of Chlamydomonas reinhardtii was compared. HTL led to bio-oil yield decreasing from 67% mass fraction at 220 °C to 59% mass fraction at 310 °C whereas the bio-oil yield increased from 53% mass fraction at 400 °C to 60% mass fraction at 550 °C for pyrolysis. Energy ratios (energy produced in the form of bio-oil divided by the energy content of the initial microalgae) between 66% at 220 °C and 90% at 310 °C in HTL were obtained whereas it was in the range 73–83% at 400–550 °C for pyrolysis. The Higher Heating Value of the HTL bio-oil was increasing with the temperature while it was constant for pyrolysis. Microalgae cultivation in aqueous phase produced by HTL was also investigated and showed promising results.     

Pyrolysis of waste pomegranate peels for bio-oil production

In order to obtain bio-oil from the pomegranate peel which is a by-product of juice production process, the dried pomegranate peel was pyrolyzed at a heating rate of 10°C/min and different temperatures between 400 and 550°C. The highest pyrolytic oil yield of 40.47 wt% was obtained at the final temperature of 550°C. The oil product was characterized by various analysis techniques. The results showed that the oil product mostly contained fine chemicals with oxygen like phenols, furfural, and its derivatives with the carbon number in a range of C₃-C₁₀. The oil product had the potential for producing fine chemicals.     

Carbon deposition behavior in steam reforming of bio-oil model compound for hydrogen production

Catalyst deactivation caused by coke formation is a bottleneck in steam reforming of bio-oil for hydrogen production. The investigation of carbon deposition behavior can make a contribution to the improvement of catalyst and the knowledge of reaction mechanism. In this paper, m-cresol (C₇H₈O, one of the organic compounds present in bio-oil) was chosen as model compound. The experiment was carried out on a commercial Ni/MgO catalyst. As a comparative test, m-cresol decomposition showed carbon deposition can be formed more easily under higher temperature. In steam reforming process, for the competition of carbon deposition and carbon elimination, a peak value of coking formation rate was obtained in a broad range of temperature (575–900 °C). The increase of steam to carbon ratio can favor the carbon elimination. Final coking formation rate curve was determined under optimal reaction conditions and the results showed the severity of carbon deposition maintained a very low level during the entire reaction time. Based on the distribution of reforming products, high temperature and sufficient water feeding can favor the carbon conversion from solid and liquid phase to gaseous phase. Unreacted m-cresol is the main organic compound detected in liquid condensate. Some secondary reactions can be deduced through the other compounds detected. The carbon deposition state on catalyst surface can be in the form of nanofiber, but their concrete shapes can be different due to different reaction conditions.     

Conversion of black alder (Alnus glutinosa L.) in supercritical solvents

In this study, black alder (Alnus glutinosa L.) wood samples were subjected to supercritical fluid extraction (SFE) using acetone, methanol, and water as solvent. The highest yield (62.4%) of SFE was obtained from black alder with water solvent at 678 K. The supercritical fluid extracts were fractionated into water soluble, acetone soluble, phenolic, fatty acid, polar, and nonpolar fractions. The lowest and highest yields of phenolic fractions from the supercritical water extraction runs were 5.3% and 15.4%. The lowest and highest yields of polar fractions from the supercritical water extraction runs were 14.6% and 16.7%. Increases of higher heating values (HHVs) in the supercritical fluid extracts are range from 48.1% to 71.4%, from 41.7% to 67.2%, and from 34.4% to 61.9% for acetone, methanol, and water, respectively. Carbon and hydrogen contents in supercritical fluid extracts are higher than those of in the original black alder sample.     

Non-catalytic partial oxidation of bio-oil to synthesis gas for distributed hydrogen production

A system has been developed for the volatilization and conversion of a bio-oil mixed with methanol to synthesis gas via non-catalytic partial oxidation (NPOX) using an ultrasonic nozzle to feed the mixture. Such a process would be ideal for distributed H₂ production. The feedstock used was derived from poplar wood. The effects of both temperature (from 625 to 850 °C) and added oxygen (effective O:C ratio from 0.7 to 1.6) on the yields of CO and H₂ have been explored. High yields of CO (between 50% and 70% of the maximum possible from the bio-oil) have been observed. Hydrogen yields are much lower (∼25% of the maximum possible). However, the water formed during NPOX can be used to generate additional H₂. The bio-oil carbon to gas conversion is typically between 85% and 95% for optimal conditions. Due to this significant conversion, lower catalyst loadings are expected to be required for the downstream processing.     

Study of bio-oil and bio-char production from algae by slow pyrolysis

This study examined bio-oil and bio-char fuel produced from Spirulina Sp. by slow pyrolysis. A thermogravimetric analyser (TGA) was used to investigate the pyrolytic characteristics and essential components of algae. It was found that the temperature for the maximum degradation, 322 °C, is lower than that of other biomass. With our fixed-bed reactor, 125 g of dried Spirulina Sp. algae was fed under a nitrogen atmosphere until the temperature reached a set temperature between 450 and 600 °C. It was found that the suitable temperature to obtain bio-char and bio-oil were at approximately 500 and 550 °C respectively. The bio-oil components were identified by a gas chromatography/mass spectrometry (GC–MS). The saturated functional carbon of the bio-oil was in a range of heavy naphtha, kerosene and diesel oil. The energy consumption ratio (ECR) of bio-oil and bio-char was calculated, and the net energy output was positive. The ECR had an average value of 0.49.     

Review of catalytic supercritical water gasification for hydrogen production from biomass

Hydrogen is defined as an attractive energy carrier due to its potentially higher energy efficiency and low generation of pollutants, which can replace conventional fossil fuels in the future. The governments have invested huge funds and made great efforts on the research of hydrogen production. Among the various options, supercritical water gasification (SCWG) is a most promising method of hydrogen production from biomass. Supercritical water (SCW) has received a great deal of attention as a most suitable reaction medium for biomass gasification because it is safe, non-toxic, readily available, inexpensive and environmentally benign. However, high temperature and pressure are required to meet the minimum reaction condition. Therefore, the high operating cost has become the biggest obstacle to the development of this technology. To overcome this bottleneck, many researchers have carried out intensive research work on the catalytic supercritical water gasification (CSCWG). Based on the previous studies stated in the literature, the authors try to give an overview (but not an exhaustive review) on the recent investigations of CSCWG. Besides, the physicochemical properties of SCW and its contributions in subcritical and supercritical water reaction are also summarized.