Do you BET on routine? The reliability of N2 physisorption for the quantitative assessment of biochar’s surface area

A large specific surface area is one of the structural characteristics which makes biochar a promising material for novel applications in agriculture and environmental management. However, the high complexity and heterogeneity of biochar's physical and chemical structure can render routine surface area measurements unreliable. In this study, N-2 and CO2 characterization of twelve biochars from three feedstocks with production temperatures ranging from 400 degrees C to 900 degrees C were used to evaluate materials with varying structural properties. The results indicate that the frequently reported peak in the surface area of biochars around 650 degrees C is an artefact of N-2 measurements and not confirmed by CO2 analysis. Contradicting results indicate an influence of the structural rigidity of biochar on N-2 measurements due to pore deformation in certain biochars. Pore non-specific calculation models like the Brunauer-Emmett-Teller method do not allow for adjustments to these changes. Instead, the use of a pore specific model and the exclusion of pores smaller than 1.47 nm was found to achieve more representative results. The proposed calculation was validated on an external dataset to highlight the applicability of the method. Our results provide novel insights for understanding the structural evolution of biochar related to production temperature

Production and characterization of spruce wood and bark biochar

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A re-analysis of NH4+ sorption on biochar: Have expectations been too high?

Sorption of nutrients such as NH4+ is often quoted as a critical property of biochar, explaining its value as a soil amendment and a filter material. However, published values for NH4+ sorption to biochar vary by more than 3 orders of magnitude, without consensus as to the source of this variability. This lack of understanding greatly limits our ability to use quantitative sorption measurements towards product design. Here, our objective was to conduct a quantitative analysis of the sources of variability, and infer which biochar traits are more favourable to high sorption capacity. To do so, we conducted a standardized remodelling exercise of published batch sorption studies using Langmuir sorption isotherm. We excluded studies presenting datasets that either could not be reconciled with the standard Langmuir sorption isotherm or generated clear outliers. Our analysis indicates that the magnitude of sorption capacity of unmodified biochar for NH4+ is lower than previously reported, with a median of 4.2 mg NH4+ g−1 and a maximum reported sorption capacity of 22.8 mg NH4+ g−1. Activation resulted in a significant relative improvement in sorption capacity, but absolute improvements remain modest, with a maximum reported sorption of 27.56 mg NH4+ g−1 for an activated biochar. Methodology appeared to substantially impact sorption estimates, especially practices such as pH control of batch sorption solution and ash removal. Our results highlight some significant challenges in the quantification of NH4+ sorption by biochar and our curated data set provides a potentially valuable scale against which future estimates can be assessed.publishedVersio

Towards Biochar and Hydrochar Engineering—Influence of Process Conditions on Surface Physical and Chemical Properties, Thermal Stability, Nutrient Availability, Toxicity and Wettability

The impact of conversion process parameters in pyrolysis (maximum temperature, inert gas flow rate) and hydrothermal carbonization (maximum temperature, residence time and post-washing) on biochar and hydrochar properties is investigated. Pine wood (PW) and corn digestate (CD), with low and high inorganic species content respectively, are used as feedstock. CD biochars show lower H/C ratios, thermal recalcitrance and total specific surface area than PW biochars, but higher mesoporosity. CD and PW biochars present higher naphthalene and phenanthrene contents, respectively, which may indicate different reaction pathways. High temperatures (>500 °C) lead to lower PAH (polycyclic aromatic hydrocarbons) content (<12 mg/kg) and higher specific surface area. With increasing process severity the biochars carbon content is also enhanced, as well as the thermal stability. High inert gas flow rates increase the microporosity and wettability of biochars. In hydrochars the high inorganic content favor decarboxylation over dehydration reactions. Hydrochars show mainly mesoporosity, with a higher pore volume but generally lower specific surface area than biochars. Biochars present negligible availability of NO −3 and NH +4 , irrespective of the nitrogen content of the feedstock. For hydrochars, a potential increase in availability of NO −3 , NH +4 , PO 3−4 , and K + with respect to the feedstock is possible. The results from this work can be applied to “engineer” appropriate biochars with respect to soil demands and certification requirements

Molecular characterization of the thermally labile fraction of biochar by hydropyrolysis and pyrolysis-GC/MS

Agroenvironmental benefits and limitations of biochar in soil applications require a full understanding of the stability and fate of the various carbon fractions. Analytical hydropyrolysis (HyPy) enables the determination of the stable black carbon (BCHyPy) and thermally labile (semi-labile; non-BCHyPy) fractions in biochar and soil samples. The non-BCHyPy fraction can be analysed at a molecular level by gas chromatography-mass spectrometry (GC-MS). In the present study, HyPy was applied to the characterisation of biochars produced from pine wood, beech wood and corn digestate with the same pyrolysis unit at low (340–400 °C) and high (600 °C) temperatures. Results were compared with those from Py-GC-MS. HyPy provided consistent information concerning the thermal stability of biochar samples, with BCHyPy levels related with the relative abundance of the charred fraction estimated by Py-GC-MS and the hydrogen/carbon (H/C) ratios. The non-BCHyPy fractions were featured by the presence of polycyclic aromatic hydrocarbons (PAHs) from two to seven rings, including alkylated derivatives up to C4. Partially hydrogenated PAHs were also detected. The yields of non-BCHyPy were higher for those biochars produced at lower temperatures and always more abundant than the levels of solvent-extractable PAHs. The methylated/parent PAH ratios from HyPy and Py-GC-MS exhibited lower values for the most charred biochar. The observed differences in the abundance of the stable fraction and the molecular chemistry of the semi-labile fraction can be usefully utilised to drive the process conditions to the desired properties of the resulting biochars and to predict the impact of biochar amendment to soil organic pools. The concentrations of priority PAHs in the semi-labile fraction was evaluated in the mg g−1 level suggesting that it could be an important fraction of the polyaromatic carbon pool in soil

Mortality and pulmonary complications in patients undergoing surgery with perioperative SARS-CoV-2 infection: an international cohort study

Background: The impact of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) on postoperative recovery needs to be understood to inform clinical decision making during and after the COVID-19 pandemic. This study reports 30-day mortality and pulmonary complication rates in patients with perioperative SARS-CoV-2 infection. Methods: This international, multicentre, cohort study at 235 hospitals in 24 countries included all patients undergoing surgery who had SARS-CoV-2 infection confirmed within 7 days before or 30 days after surgery. The primary outcome measure was 30-day postoperative mortality and was assessed in all enrolled patients. The main secondary outcome measure was pulmonary complications, defined as pneumonia, acute respiratory distress syndrome, or unexpected postoperative ventilation. Findings: This analysis includes 1128 patients who had surgery between Jan 1 and March 31, 2020, of whom 835 (74·0%) had emergency surgery and 280 (24·8%) had elective surgery. SARS-CoV-2 infection was confirmed preoperatively in 294 (26·1%) patients. 30-day mortality was 23·8% (268 of 1128). Pulmonary complications occurred in 577 (51·2%) of 1128 patients; 30-day mortality in these patients was 38·0% (219 of 577), accounting for 81·7% (219 of 268) of all deaths. In adjusted analyses, 30-day mortality was associated with male sex (odds ratio 1·75 [95% CI 1·28–2·40], p\textless0·0001), age 70 years or older versus younger than 70 years (2·30 [1·65–3·22], p\textless0·0001), American Society of Anesthesiologists grades 3–5 versus grades 1–2 (2·35 [1·57–3·53], p\textless0·0001), malignant versus benign or obstetric diagnosis (1·55 [1·01–2·39], p=0·046), emergency versus elective surgery (1·67 [1·06–2·63], p=0·026), and major versus minor surgery (1·52 [1·01–2·31], p=0·047). Interpretation: Postoperative pulmonary complications occur in half of patients with perioperative SARS-CoV-2 infection and are associated with high mortality. Thresholds for surgery during the COVID-19 pandemic should be higher than during normal practice, particularly in men aged 70 years and older. Consideration should be given for postponing non-urgent procedures and promoting non-operative treatment to delay or avoid the need for surgery. Funding: National Institute for Health Research (NIHR), Association of Coloproctology of Great Britain and Ireland, Bowel and Cancer Research, Bowel Disease Research Foundation, Association of Upper Gastrointestinal Surgeons, British Association of Surgical Oncology, British Gynaecological Cancer Society, European Society of Coloproctology, NIHR Academy, Sarcoma UK, Vascular Society for Great Britain and Ireland, and Yorkshire Cancer Research

Die Festbettpyrolyse von Biomasse: Mechanismen und Biokohleerzeugung

The objective of this thesis is to gain a deeper understanding on the slow pyrolytic conversion of biomass in conditions similar to the ones present at industrial scale. The purpose of this is to contribute to two topics of significant relevance in the biomass thermochemical conversion community nowadays. Firstly, the need for further development of more detailed pyrolysis mechanisms, which account not only for chemical reactions pathways, but also for the influence of transport phenomena on these chemical reactions, enhanced in conditions typical of industrial scale, due to bigger particle and bed sizes. Secondly, the use of slow pyrolysis for production of biochar, in particular, the understanding of how pyrolysis conditions may affect biochar properties and consequently its behavior in soil. To this end, a technical-scale fixed bed reactor has been built, together with a novel combination of on-line characterization techniques, to perform an exhaustive on-line evaluation of the pyrolysis process. These techniques include temperature measurements inside the bed, characterization of permanent gas composition with gas chromatography - thermal conductivity detection (GC-TCD) and detection of fluorescence emitting compounds with laser-induced fluorescence spectroscopy (LIF). Differentiation between primary pyrolysis and secondary reactions of primary volatiles has been achieved, thanks to the selective detection of targeted species, products of these secondary reactions. Investigation on the source and production enhancement mechanisms of these species has been also carried out. In a second stage, several characterization methodologies have been developed and applied to get a deep characterization of the solid product (biochar), from two perspectives: structural properties and potential behavior in soil. The objective is to establish clear relations to "engineer" biochar, according to soil application demands and certification requirements. Besides, development of characterization techniques which may lead to a more complete evaluation and therefore better certification of this biochar has been considered, in particular for porosity characterization.Die Zielstellung dieser Dissertation ist es, ein tieferes Verständnis über die langsame pyrolytische Biomassenkonversion unter Bedingungen zu gewinnen, wie man sie im industriellen Maÿstab vor ndet. Hierdurch soll bezweckt werden, auf zwei Feldern von signi kanter Relevanz für die heutige Forschergemeinschaft der thermochemischen Biomassenkonversion einen Beitrag zu leisten. Denn zum einen besteht noch Entwicklungsbedarf für genauere Pyrolysemechanismen, welche nicht nur die chemischen Reaktionsabl äufe berücksichtigen, sondern auch den Ein uss durch Transportphänomene auf diese chemischen Reaktionsabläufe miteinbeziehen und angepasst an Bedingungen sind, wie man sie aufgrund von gröÿerer Partikel- und Bettgröÿe typischerweise im Industriemaÿstab vor ndet. Das zweite Feld beinhaltet die Produktion von Biochar durch eine langsame Pyrolyse und soll insbesondere klären, inwieweit die Pyrolysebedingungen die Eigenschaften des Biochars und konsequenterweise deren Reaktionen im Boden beein ussen. Um dieses Ziel zu erreichen wurde ein Festbettreaktor in Technikumsgröÿe errichtet und mit einer neuartigen Kombination von on-line Charakterisierungstechniken ausgestattet, welche es ermöglichen, den Pyrolysevorgang umfassend in-situ und on-line zu untersuchen. Diese Techniken umfassen die Temperaturerfassung im Reaktorbett, die Bestimmung der Permanentgaszusammensetzung durch Gaschromatographie-Wärmeleitfähigkeits detektor (GC-WLD) und der Nachweis von uoreszierenden Verbindungen durch laserinduzierte Fluoreszenzspektroskopie (LIF). Eine Unterscheidung zwischen der primären Pyrolyse und den Sekundärreaktionen der primär üchtigen Bestandteile war durchführbar, dank der selektiven Bestimmung von Schlüsselverbindungen, welche als Produkte der Sekundärreaktionen entstehen. Fernerhin wurde untersucht, welchen Ursprung diese Spezies haben und welche Mechanismen deren vermehrtes Auftreten fördern. In der zweiten Phase wurden mehrere Charakterisierungsmethoden entwickelt und angewendet, um das feste Produkt (Biochar) ausführlich in zweierlei Hinsicht zu charakterisieren. Zum einen Hinblick auf die strukturellen Eigenschaften, zum anderen auf das mögliche Verhalten im Boden. Zielstellung war es hier, klare Zusammenhänge herauszuarbeiten, um einen Biochar zu "konstruieren", welcher den Anforderungen bei Verwendung im Boden und Zerti zierungsvorgaben erfüllt. Auÿerdem wurde die Entwicklung weiterer Charakterisierungsmethoden geprüft, welche möglicherweise zu einer vollständigeren und daher auch besseren Zerti zierung von diesem Biochar führen, insbesondere in Hinsicht auf die Charakterisierung der Poren

Understanding the primary and secondary slow pyrolysis mechanisms of holocellulose, lignin and wood with laser-induced fluorescence

To understand the complex reaction mechanisms involved in biomass pyrolysis, volatile products are characterized on-line by laser-induced fluorescence (LIF), together with on-line measurements of permanent gases by GC-TCD (Gas Chromatograph-Thermal Conductivity Detector) and temperature evolutions in the bed. The focus is to determine the components that emit fluorescence and reactions involved in producing them from wood and from its two main macromolecular components, holocellulose and lignin. A technical-scale fixed-bed reactor is used to identify primary and secondary reactions involved in pyrolysis. The excitation wavelength used for the LIF measurements is 266 nm and the detected species are aromatic compounds (including one-ring phenolics and two-, three-or four-ring polycyclic aromatic hydrocarbons (PAHs)) and species containing carbonyl groups. Holocellulose volatiles show fluorescence that is attributed to the formation of carbonyl compounds and two-ring PAHs during heterogeneous secondary char-forming reactions, which also enhance the production of CO2. Volatiles from lignin show first fluorescence typical of one-ring phenolics and small (two-three rings) PAHs. Then, due to the enhancement of heterogeneous secondary reactions, fluorescence signal typical of bigger PAHs (three-four rings) is detected. These aromatic species are produced in parallel to gas species like CH4. The fluorescence that can be observed in pyrolysis of wood comes mainly from the lignin fraction, undergoing also heterogeneous secondary reactions resulting in the formation of bigger PAHs, although a contribution from cellulose is also present

Review of the use of additives to mitigate operational problems associated with the combustion of biomass with high content in ash-forming species

The impact of additives addition on the combustion behavior of biomass with high content in ash-forming species is evaluated in this review. Their influence on both emissions (particulate matter and gaseous emissions) and deposits formation (fouling and slagging) are here considered. The uncertainty in the availability, under current sustainability criteria, of good-quality woody biomass (i.e. woody biomass with low content in ash-forming species, mainly derived from stem wood), along with the growing demand for biomass fuels, has caused the pellet industry to attempt to diversify the sources of raw material. Other types of biomass such as bark, non-woody biomass (cereals and herbaceous materials), and residues from the agricultural industry are also potentially useful as raw materials due to the large volumes available. These fuels present however some challenges. They vary strongly in composition, impacting significantly their combustion behaviour. The high content in ash-forming species, such as alkali and alkaline-earth species, chlorine, phosphorous, nitrogen, and silicon can lead to an increase in gaseous (e.g. sulfur oxides and nitrogen oxides) and particulate matter (PM) emissions. They can also lead to operational problems, such as fouling, corrosion, slagging, and agglomeration during the combustion process. There are several routes to mitigate these ash-related problems, whose applicability depends on the technology and scale. In the present review, the use of additives to reduce emissions and deposits formation, as well as further operational problems these may trigger, is evaluated. However, the high heterogeneity in biomass composition and varying nature of the aforementioned combustion issues hinders the possibility to use a “one-size-fits-all” additive, resulting in the need for developing further understanding on the impact of different additives according to biomass composition and combustion conditions. For example, aluminosicates have proven to be effective to reduce fine particulate matter emissions, but they increase the gaseous emissions of HCl and SOx. The impact of Ca-based additives on PM and alkali-induced slagging is inconclusive, although they can capture gaseous emissions such as HCl and SOx. The additive application method and combustion conditions play on top a very significant role. For all this, reaching conclusions on the type of additive, amount, and application method is very challenging. With this work the authors aim at providing an overview of the state-of-art on the use of additives in biomass combustion, as well as to offer a framework to advance in the regulation on the use of additives