The authors like to thank Christoph Warth, Michael Russ, Carola Lepski, Julian Tejada and Dr. Rainer Kirchhof for their technical support. The study was funded by the BMBF (Project BiCoLim-Bio-Combustibles Limpios) under the grant number 01DN16036.

1. Preparation of sample material
<ol>
	<li>Harvest five year old willow, clone type &#8220;Tordes&#8221; ([Salix schwerinii x S. viminalis] x S. vim.), with a height of 12&#8722;14 m and a breast diameter of approximately 15 cm.</li>
	<li>Chip the wood and dry the chips in a kiln dryer for 24 h at 105 &#176;C.</li>
	<li>Cut the wood chips with a cutting mill and grind with a centrifugal mill to a particle size of 0.12 mm.</li>
</ol>
2. Microwave assisted hydrothermal carbonization
<ol>
	<li>Use a microwave oven with 850 W and a magnetron frequency of 2,455 MHz.</li>
	<li>Place 500 mg of raw material from step 1.3 in a 50 mL polytetrafluoroethylene (PTFE) reaction vessel with a spatula. Add 10 mL of demineralized water. Screw down the reaction vessel cap so that the pressure valve in the cap is on the same level as the cap brim.</li>
	<li>For each treatment temperature, put twelve reaction vessels with raw materials in the microwave oven and close the oven.</li>
	<li>Set up three temperature programs, with the microwave for the three temperatures: 150 &#176;C (ramp +12.5 &#176;C min-1, hold 60 min, peak power 50%), 170 &#176;C (ramp +9.6 &#176;C min-1, hold 60 min, peak power 80%), and 185 &#176;C (ramp +5.3 &#176;C min-1, hold 30 min, ramp -1.1 &#176;C min-1 to 150 &#176;C, peak power 100%). Start the microwave oven, for each single program.</li>
	<li>After the program is completed, remove the reaction vessels, allow them to cool and reactivate. Then open them under a fume cupboard after releasing the pressure inside.</li>
	<li>Add 35 mL of twice distilled water to each reaction vessel. Pour the solution in each vessel to a centrifuge cylinder and centrifuge at 1,714 x g for 10 min.</li>
	<li>The process water is drained into another tube and stored frozen at -5 &#176;C for pH and gas chromatography-mass spectrometry (GC-MS) analysis.</li>
	<li>Freeze the centrifuge cylinder with the remaining biocoal pellet at -5 &#176;C. Then take out the biocoal pellet and dry it at 105 &#176;C for 24 h. Weigh the biocoal pellet and calculate the weight loss induced by the MAHC treatment.</li>
	<li>Repeat steps 2.2&#8722;2.8 four times per temperature (48 reaction vessels per temperature) to produce enough biocoal (approximately 22 g) for the subsequent analysis.</li>
</ol>
3. Ash content determination
<ol>
	<li>Weigh 20 empty ceramic dishes individually. Add in each 1 g of sample (5 x 1 g of raw material, and 5 x 1 g of biocoal from each temperature treatment). 
	NOTE: Because the dishes cannot be labeled, a plan must be drawn for the arrangement of the vessels in the oven.</li>
	<li>Place the open ceramic dishes into a muffle furnace and close the furnace.</li>
	<li>Program a temperature program for the muffle furnace (+6 &#176;C min-1 from 25 &#176;C to 250 &#176;C, hold 60 min, +10 &#176;C min-1 to 550 &#176;C, hold 120 min) and start the program.</li>
	<li>After the program is completed, let the muffle furnace cool down to 105 &#176;C. Then open the furnace and take out the ceramic dishes.</li>
	<li>Place the ceramic dishes in an extractor (Table of Materials) filled with a drying agent consisting of silica gel. Close the desiccator and vacuum&#160;dry with the help of a vacuum pump.</li>
	<li>Take out the ceramic dishes after 24 h of cooling. Weigh the ceramic dish containing the ash and calculate the ash weight by subtracting the weight of the empty ceramic dish.</li>
	<li>Determine the ash content in percent by dividing the ash weight by the dry mass of the raw material or biocoal.</li>
</ol>
4. Determination of the higher and lower heating values
<ol>
	<li>Activate the water pump of the calorimeter and open the oxygen valve to supply 99.5% oxygen to the calorimeter.</li>
	<li>Weigh 1 g of glucose and place it into a plastic sample bag with a defined calorific value of 46,479 J/g. Put the sample bag into the combustion crucible of a calorimeter bomb.</li>
	<li>Add 5 mL of twice deionized water in the bottom of the bomb and screw down the bomb. Put the bomb into the calorimeter and close the calorimeter.</li>
	<li>Enter the weight of the sample and change settings to sample bag method. Start the calorimeter.</li>
	<li>After the measurement is completed, take out the bomb, turn it upside down and shake it slowly for 1 min.</li>
	<li>Unscrew the bomb, remove 5 mL of twice demineralized water and store it in a screw cap container for subsequent ion chromatography analysis.</li>
	<li>Repeat steps 4.2&#8722;4.6 three times to obtain the calibration standard.</li>
	<li>Repeat steps 4.2&#8722;4.6 five times with each MAHC biocoal (150 &#176;C, 170 &#176;C, 185 &#176;C) and the raw material.</li>
	<li>Calculate the lower heating value using the following equation40: 
	<img alt="Equation 2" src="/files/ftp_upload/58970/58970eq2.jpg" /> 
	where LHV is the lower heating value, HHV is the higher heating value obtained from the calorimeter in step 4.4, and &#969; is the hydrogen content [<img alt="Equation 3" src="/files/ftp_upload/58970/58970eq3.jpg" /> obtained from elemental analysis.</li>
</ol>
5. Ion chromatography for the quantification of chlorine
NOTE: Check the calibration of ion chromatograph before analysis.
<ol>
	<li>Take out the 5 mL of solution from step 4.8 and add 45 mL of twice demineralized water in a 50 mL volumetric mask.</li>
	<li>Insert the sample suction tube into a sample container and draw approximately 3 mL of the sample with a syringe into the pre-column. Start the analysis run.</li>
	<li>Carry out the measurements according to manufacturer&#8217;s instructions.</li>
	<li>Repeat steps 5.2 and 5.3 for each sample prepared in section 4.</li>
</ol>
6. Elemental analysis for the determination of the O/C and H/C ratios
<ol>
	<li>Select an appropriate method from the instrument manual for the samples to be measured.</li>
	<li>Make all the 20 mg sulfonamide standards and blanks required to calibrate the device.</li>
	<li>To prepare a material sample, put 20 mg of sample in tin foil on the micro balance. Weigh the sample on the tin foil, close the foil around the sample and press the package to contain as little air as possible. Afterwards repeat this 5x for each sample. 
	NOTE: In order to be able to analyze the biochar samples, the same amount of tungsten trioxide as the amount of the sample must be added in a ratio of 1:1. This is needed to compensate the missing oxygen in the biochar to ensure complete combustion in the elemental analyzer.</li>
	<li>Insert the prepared samples in the autosampler of the elemental analyzer.</li>
	<li>Open the oxygen and helium valve for the combustion chamber of the elemental analyzer.</li>
	<li>Start the analysis when the device has reached the temperature specified by the device. In this case, wait till the temperature reaches 900 &#176;C.</li>
	<li>Calculate the moles of each element in the sulfonamide standard by the sulfonamide standard weight (step 6.2), and the weight of 1 mole of the respective element.</li>
	<li>Calculate the relationship between moles of C, H, S, and N in sulfonamide, obtained from step 6.7, and the respective peak areas.</li>
	<li>Subtract the sample ash content, obtained from step 3.7, from the total sample weight.</li>
	<li>Compare the respective element peak area in the sulfonamide standard and the sample, and multiply by the mole of each element in sulfonamide to obtain the mole of the element in the sample.</li>
	<li>Calculate the weight of C, H, S, and N in the sample by multiplying the mole of the element, obtained from step 6.10, with the respective molar mass of the element from the periodic table.</li>
	<li>Calculate the weight of oxygen in the sample by using the ash free sample mass, obtained from step 6.9, and subtracting the weight of C, H, N, and S, obtained from step 6.11.</li>
	<li>Calculate the molar H/C and O/C ratios in the raw material and the MAHC biocoal samples.</li>
</ol>
7. Induced coupled plasma optical emission spectroscopy
<ol>
	<li>Weigh 400 mg of dried raw material or MAHC biocoal and put it into a 50 mL PTFE reaction vessel with a spatula. Add 3 mL of 69% nitric acid and 9 mL of 35% hydrochloric acid.</li>
	<li>Screw down the reaction vessel cap so that the pressure valve in the cap is on the same level as the cap brim.</li>
	<li>Put the reaction vessels of the samples to be analyzed in the microwave oven and close the oven.</li>
	<li>Program the temperature program for the complete degradation of the organic material: ramp +15.5 &#176;C min-1 to 200 &#176;C, hold 30 min, cool down to 180 &#176;C, hold for 5 min. Start the microwave oven.</li>
	<li>After the program is completed, remove the reaction vessels, allow them to cool and reactivate. Then open the vessels under a fume cupboard after releasing the pressure inside.</li>
	<li>Pour the samples into a 50 mL bulb cylinder. Then rinse the reaction vessel thoroughly with twice deionized water and transfer it to the bulb cylinder. Top up the cylinder to the 50 mL mark with twice deionized water to ensure even dilution of all samples.</li>
	<li>Filter the sample from step 7.6 with 150 &#181;m mesh filter paper. Fill the filtrate in 50 mL conical centrifuge tubes.</li>
	<li>Put the standard samples in the autoinjector of the ICP-OES. The standard samples are of the known concentrations (0.0001 ppm, 0.001 ppm, 0.1 ppm, 1 ppm 10 ppm, 20 ppm, 50 ppm) of the elements to be quantified (Ca, As, B, Be, Fe, Se, Zn, Ag, Al, Ba, Bi, Cd, Co, Cr, Cu, Ga, K, Li, Mg, Mn, Mo, Na, Ni, Pb, Rb, Sr, Te, Tl,V).</li>
	<li>Put the samples in the autoinjector of the ICP-OES and run the ICP-OES analysis with the same parameters.</li>
	<li>After the ICP-OES analysis, obtain the elemental concentration from the software, automatically calculated in mg/kg, based on the calibration curves obtained from standard samples in step 7.8.</li>
	<li>Calculate the elemental concentration reduction in the produced biocoal: 
	<img alt="Equation 4" src="/files/ftp_upload/58970/58970eq4.jpg" /> 
	where Conc. in biomass is the elemental concentration in the biomass and Conc. In coal is the elemental concentration in the biocoal.</li>
</ol>
8. Measuring the pH of the HTC process water
<ol>
	<li>Fill each liquid fraction from the MAHC treatment (step 2.7) of the raw material and the three biocoals in four respective beakers.</li>
	<li>Calibrate the pH probe with standard solutions.</li>
	<li>Measure the pH of the liquid fraction of the raw material and the three MAHC biocoals.</li>
</ol>
9. Gas chromatography-mass spectrometry
<ol>
	<li>Filter the liquid fractions from the MAHC treatment (step 2.7) with 150 &#181;m mesh filter paper. Add 20 mL of methanol to 1 mL of the filtered liquid fractions.</li>
	<li>Transfer 200 &#181;L to a GC-MS autosampler vial and put the vial in the GC-MS autosampler.</li>
	<li>Dilute pure standards of furfural and 5-methylfurfural (analytical grade) down to 10-2, 10-3, 10-4, and 10-5 with methanol.</li>
	<li>Put the standards in the GC-MS autosampler and analyze them with the parameters: 1 &#181;L injection volume at 230 &#176;C injector temperature and 1:40 split; 5MS non-polar column (Table of Materials) with 15 m length and 0.25 mm film thickness; temperature program 30 &#176;C, hold 2 min, ramp of +40 &#176;C/min to 250 &#176;C, hold 2 min; ionization with 70 mV and MS detector at the scan mode with a m/z range of 35&#8722;400, each scan in 0.3 s.</li>
	<li>Establish calibration curves by the total ion count (TIC) peak area and the compound concentration.</li>
	<li>Run the prepared HTC biocoal liquid phase samples with the same analytical parameters and identify furfural and 5-methylfurfural by means of retention time of the standard and the spectrum match in a spectra library.</li>
	<li>Determine the concentrations of furfural and 5-methylfurfural by using the calculated calibration curve (step 9.6) and inserting the sample peak areas of furfural and 5-methylfurfural.</li>
</ol>
10. Statistics
<ol>
	<li>Analyze the data with the Shapiro Wilks test for normal distribution.</li>
	<li>Use the Mann-Whitney U-test for non-normally distributed data sets and the t-test for normally distributed data sets to find significant differences between data sets. 
	NOTE: If one data set is normally distributed and the other not, use the Mann-Whitney U test.</li>
</ol>

The authors have nothing to disclose.

The MAHC allows the differentiation of the steps of the chemical degradation by applying different intensities of thermal treatment. Therefore, it is possible to assess the interactions between the mass loss, O/C-H/C ratio, heating value, ash component reduction, pH increase of the process water and accumulation of furans in the process water. The advantage of the MAHC method over the conventional HTC reactor method is based on the thermal conduction via microwaves that penetrate the whole reactor volume and conduct the ...

The application of microwaves for hydrothermal carbonization (MAHC) was used for the thermochemical transformation of biomass model compounds like fructose, glucose1,2 or cellulose3, and for organic substrates, preferably waste material4,5,6,7,8,9,10. The utilization of microwaves is advantageous as it allows an even heating of the treated biomass2,10 mainly through thermal losses of a dielectric solvent11,12, though the microwaves do not transfer enough energy to directly break chemical bonds and induce reactions13. The microwaves penetrate the whole reaction volume of the HTC reactor vessel and transfer the energy directly to the material, which is not possible with a conventional reactor that shows a slower heating rate due to the high heating capacity of the steel mantle and the sample itself14. The even excitation of the sample&#8217;s water molecules by microwaves allows an improved process control, as the temperature in the microwave reactor is evenly distributed11,14,15 and the cooldown after the reaction is much faster. Furthermore, conventional reactors heat up much slower and the chemical reactions occurring during the heating can bias the results that are usually assigned to the final temperature. The improved process control in an MAHC reactor enables a precise elaboration of the temperature dependency of selected HTC reactions (e.g., dehydration or decarboxylation). Another advantage of the even temperature distribution in the HTC-reactor volume is the lower adhesion of immobilized and completely carbonized particles on the inner reactor wall2. However, water is only an average microwave absorbing solvent that even shows decreasing microwave absorbance at higher temperatures, which limits the achievable maximum temperature. This negative effect is compensated when acids are produced during the HTC process or catalyzers (ionic or polar species) are added before the treatment. Microwave induced reactions show higher product yields in general11,15 and specifically of 5-hydroxymethylfurfural (5-HMF) from fructose in comparison to sand-bed catalyzed reactions12. They also have a much better energy balance then conventional heating methods15,16.
The fundamental chemical concept of hydrothermal carbonization is the degradation and successive polymerization of the biomass. In the course of these complex interacting reactions the tissue is depleted of oxygen, which increases the heating value. At first, the polymers hemicellulose and cellulose are hydrolyzed to sugar monomers17, though low temperatures mainly affect the hemicellulose18,19,20,21. In this early stage of the HTC reactions, organic acids are formed from the transformation of the sugar aldehydes and the deacetylation of hemicellulose. These acids can be acetic, lactic, levulinic,&#160; acrylic or formic acid20,21,22 and they decrease the pH of the reaction water in the reactor. Due to dissociation, they form free negative ions that increase the ion product in the process water. The increasing ion product allows the solving of cations, which are the major constituents of the ash in the biomass. By this mechanism, the tissue is depleted from emission precursors and slag formers (e.g., potassium, sodium, calcium, chlorine and heavy metals)23,24.
The formed organic acids can support the dehydration of sugar monomers to furans. A common sugar dehydration product is furfural and 5-hydroxymethylfurfural, which are feasible products for the chemical industry, as they serve as platform products (e.g., for the synthesis of biopolymers). 5-Methylfurfural can be formed by catalyzed reactions from cellulose25,26 or 5-hydroxymethylfurfural27. While the biopolymer synthesis is an artificial repolymerization under controlled conditions, the furans can also condense, polymerize and form high molecular weight aromatic structures in the complex chemical environment of the MAHC reactor. The interaction of the solubilized organic and inorganic compounds with the modified wood cell matrix add to the complexity of the reaction system20. The furan polymerization reaction pathways employ aldol condensation or/and intermolecular dehydration18,20 and yield hydrochar particles with a hydrophobic shell and a more hydrophilic core28. It is not yet revealed whether biomass particles are completely decomposed and then repolymerized or if the biomass particles serve as a template for the carbonization. However, the degradation and repolymerization reactions comprise dehydration and decarboxylation reactions, as well29,30, which induces the drop in the van Krevelen diagram towards the O/C and H/C ratios of black carbon.
While other studies proved the mineral reducing effect of conventional reactor based hydrothermal treatment31, of a water washing with combined mechanical leaching32 or water/ammonium acetate/hydrochloric acid washing33, our studies investigate the mineral leaching during low temperature carbonization with microwaves for the first time. As this study focuses on emission precursor leaching for fuel upgrading, it investigates the fate of potassium, sodium, magnesium, calcium, chlorine, sulfur, nitrogen and heavy metals. Fine dust precursors form volatile salts (e.g., KCl or K2SO4) at elevated temperatures in the gaseous phase. When these salts accumulate in the flue gas, heavy metals like zinc can scavenge them as nucleation particles, which leads to a particle growth chain reaction. At lower flue gas temperatures, salt condensation further triggers the particle growth and results in cancerogenous fine dust emission from the chimney. These emissions are at present the main factor that compromises the sustainability of biomass fuels. A sustainable energy supply relies on their reduction by expensive filters or their reduction in the fuels (e.g., by MAHC). As this study follows a practical approach, short rotation coppice (SRC) willow wood was chosen as a potential bioenergy feedstock with high growth rates. It can be grown by farmers on their fields for a self-sustainable power supply by gasification, but also for heat generation by direct combustion. A disadvantage of willow SRC is its high bark content due to a low stem:bark ratio at mature stage. The bark contains a lot of minerals in comparison to wood34,35,36,37 and yields higher quantities of gaseous or particle emissions38. Low temperature HTC can improve the combustion properties of SRC willow wood and, thereby, contribute to a sustainable heat and power supply. Another important parameter of the HTC biocoal investigated in this study is its energy density, its higher initial combustion temperature and its higher final combustion temperature39.

<table><tbody><tr><td>5MS non-polar cloumn</td><td>Thermo Fisher Scientific,Waltham, USA</td><td>TraceGOLD SQC</td><td>GCMS</td></tr><tr><td>9&amp;micro;m polyvinylalcohol particle column</td><td>Methrom AG, Filderstadt, Germany</td><td>Metrosep A Supp 4 -250/4.0</td><td>Ion chromatography</td></tr><tr><td>argon</td><td>Westfalen AG, M&amp;uuml;nster, Germany</td><td>UN 1006</td><td>ICP-OES</td></tr><tr><td>calorimeter</td><td>IKA-Werke GmbH &amp;amp; Co.KG, Stauffen, Germany</td><td>C6000</td><td>higher and lower heating value</td></tr><tr><td>centrifuge</td><td>Andreas Hettich GmbH &amp;amp; Co.KG, Germany</td><td>Rotofix 32 A</td><td></td></tr><tr><td>centrifuge mill</td><td>Retsch Technology GmbH, Haan,&lt;br/&gt; Germany</td><td>ZM 200</td><td></td></tr><tr><td>ceramic dishes</td><td>Carl Roth GmbH&amp;amp;Co.KG, Karlsruhe, Germany</td><td>XX83.1</td><td>Ash content</td></tr><tr><td>cutting mill</td><td>Fritsch GmbH, Markt Einersheim, Germany</td><td>pulverisette 19</td><td></td></tr><tr><td>D(+) Glucose</td><td>Carl Roth GmbH&amp;amp;Co.KG, Karlsruhe, Germany</td><td>X997.1</td><td>higher and lower heating value</td></tr><tr><td>elemental analyzer</td><td>elementar Analysesysteme GmbH, Langenselbold, Germany</td><td>varioMACRO cube</td><td>elemental analysis</td></tr><tr><td>exicator</td><td>DWK Life Sciences GmbH, Wertheim, Germany</td><td>DURAN DN300</td><td>Ash content</td></tr><tr><td>GC-MS system</td><td>Thermo Fisher Scientific,Waltham, USA</td><td>Trace 1300</td><td>GCMS</td></tr><tr><td>hydrochloric acid</td><td>Carl Roth GmbH&amp;amp;Co.KG, Karlsruhe, Germany</td><td>HN53.3</td><td>ICP-OES</td></tr><tr><td>ICP OES</td><td>Spectro Analytical Instruments GmbH, Kleve, Germany</td><td>Spectro Blue-EOP- TI</td><td>ICP-OES</td></tr><tr><td>Ion chromatograph</td><td>Methrom GmbH&amp;amp;Co.KG, Filderstadt, Germany</td><td>833 Basic IC plus</td><td>Ion chromatography</td></tr><tr><td>kiln dryer</td><td>Schellinger KG, Weingarten, Germany</td><td></td><td></td></tr><tr><td>kiln dryer</td><td>Schellinger KG, Weingarten, Germany</td><td></td><td>Ash content</td></tr><tr><td>mesh filter paper</td><td>Carl Roth GmbH&amp;amp;Co.KG, Karlsruhe, Germany</td><td>L874.1</td><td>ICP-OES</td></tr><tr><td>microwave oven</td><td>Anton Paar GmbH, Graz, Austria</td><td>Multiwave Go</td><td></td></tr><tr><td>muffel furnance</td><td>Carbolite Gero GmbH &amp;amp;Co.KG, Neuhausen, Germany</td><td>AAF 1100</td><td>Ash content</td></tr><tr><td>nitric acid</td><td>Carl Roth GmbH&amp;amp;Co.KG, Karlsruhe, Germany</td><td>4989.1</td><td>ICP-OES</td></tr><tr><td>oxygen</td><td>Westfalen AG, M&amp;uuml;nster, Germany</td><td>UN 1072</td><td>higher and lower heating value</td></tr><tr><td>pH-meter</td><td>ylem Analytics Germany Sales GmbH &amp;amp; Co. KG, Weilheim,Germany</td><td>pH 3310</td><td>pH</td></tr><tr><td>sample bag</td><td>IKA-Werke GmbH &amp;amp; Co.KG, Stauffen, Germany</td><td>C12a</td><td>higher and lower heating value</td></tr><tr><td>Standard Laboratory Vessels and Instruments</td><td></td><td></td><td></td></tr><tr><td>standard samples</td><td>Bernd Kraft GmbH, Duisburg, Germany</td><td></td><td>ICP-OES</td></tr><tr><td>sulfonamite</td><td>elementar Analysesysteme GmbH, Langenselbold, Germany</td><td>SLBS4782</td><td>elemental analysis</td></tr><tr><td>teflon reaction vessels</td><td>Anton Paar, Austria</td><td>HVT50</td><td></td></tr><tr><td>teflon reaction vessels</td><td>Anton Paar, Austria</td><td>HVT50</td><td>ICP-OES</td></tr><tr><td>tin foil</td><td>elementar Analysesysteme GmbH, Langenselbold, Germany</td><td>S12.01-0032</td><td>elemental analysis</td></tr><tr><td>tungstenVIoxide</td><td>elementar Analysesysteme GmbH, Langenselbold, Germany</td><td>11.02-0024</td><td>elemental analysis</td></tr><tr><td>twice deionized water</td><td>Carl Roth GmbH&amp;amp;Co.KG, Karlsruhe, Germany</td><td></td><td></td></tr><tr><td>twice deionized water</td><td>Carl Roth GmbH&amp;amp;Co.KG, Karlsruhe, Germany</td><td></td><td>higher and lower heating value</td></tr><tr><td>twice deionized water</td><td>Carl Roth GmbH&amp;amp;Co.KG, Karlsruhe, Germany</td><td></td><td>ICP-OES</td></tr></tbody></table>

reducing willow wood fuel emission by low temperature microwave assisted hydrothermal carbonization

Biomass is a sustainable fuel, as its CO2 emissions are reintegrated in biomass growth. However, the inorganic precursors in the biomass cause a negative environmental impact and slag formation. The selected short rotation coppice (SRC) willow wood has a high ash content (<img alt="Equation 1" src="/files/ftp_upload/58970/58970eq1.jpg" /> = 1.96%) and, therefore, a high content of emission and slag precursors. Therefore, the reduction of minerals from SRC willow wood by low temperature microwave assisted hydrothermal carbonization (MAHC) at 150 &#176;C, 170 &#176;C, and 185 &#176;C is investigated. An advantage of MAHC over conventional reactors is an even temperature conductance in the reaction medium, as microwaves penetrate the whole reactor volume. This allows a better temperature control and a faster cooldown. Therefore, a succession of depolymerization, transformation and repolymerization reactions can be analyzed effectively. In this study, the analysis of the mass loss, ash content and composition, heating values and molar O/C and H/C ratios of the treated and untreated SCR willow wood showed that the mineral content of the MAHC coal was reduced and the heating value increased. The process water showed a decreasing pH and contained furfural and 5-methylfurfural. A process temperature of 170 &#176;C showed the best combination of energy input and ash component reduction. The MAHC allows a better understanding of the hydrothermal carbonization process, while a large-scale industrial application is unlikely because of the high investment costs.

The results of the elemental analysis revealed differences between the O/C-H/C ratio of the willow wood and the MAHC biocoals (Figure 1). The raw material shows higher O/C-H/C ratios and a higher variation of the values. The MAHC treatment reduced the value variation due to homogenization in the microwave reactor. The precision of the microwave reactor allowed the differentiation of three stages of degradation. The H/C ratio was reduced at 150 &#176;C and the...

Watch this Scientific Journal Video about Reducing Willow Wood Fuel Emission by Low Temperature Microwave Assisted Hydrothermal Carbonization at JoVE.com

Reducing Willow Wood Fuel Emission by Low Temperature Microwave Assisted Hydrothermal Carbonization

A protocol for the emission precursor depletion from low quality biomass by low temperature microwave assisted hydrothermal carbonization treatment is presented. This protocol includes the microwave parameters and the analysis of the biocoal product and process water.

Biomass is a sustainable fuel, as its CO2 emissions are reintegrated in biomass growth. However, the inorganic precursors in the biomass cause a negative ...

reducing-willow-wood-fuel-emission-low-temperature-microwave-assisted

Research

JoVE Journal

Chemistry

8.1K Views.  University of Applied Science Rottenburg. In onze groep hebben we een lage temperatuur magnetronbehandeling toegepast om wilgenbiomassa van fijnstofprecursoren uit te putten. Dit kan helpen bij het upgraden van biomassa voor schone verbranding en daarmee het vergroten van het biomassa-brandstofpotentieel van een land. De microgolven zorgen voor een gelijkmatige en snelle biomassaverwarming omdat ze de watermoleculen in het hele reactorvolume opwekken.Water is een tussenliggende magnetron-absolving oplosmiddel en om hogere reac...

Video: Reducing Willow Wood Fuel Emission by Low Temperature Microwave Assisted Hydrothermal Carbonization

Biomass Conversion to Produce Hydrocarbon Liquid Fuel Via Hot-vapor Filtered Fast Pyrolysis and Catalytic Hydrotreating

Lignocellulosic biomass conversion to produce biofuels has received significant attention because of the quest for a replacement for fossil fuels. Among the various thermochemical and biochemical routes, fast pyrolysis followed by catalytic hydrotreating is considered to be a promising near-term opportunity. This paper reports on experimental methods used 1) at the National Renewable Energy Laboratory (NREL) for fast pyrolysis of lignocellulosic biomass to produce bio-oils in a fluidized-bed reactor and 2) at Pacific Northwest National Laboratory (PNNL) for catalytic hydrotreating of bio-oils in a two-stage, fixed-bed, continuous-flow catalytic reactor. The configurations of the reactor systems, the operating procedures, and the processing and analysis of feedstocks, bio-oils, and biofuels are described in detail in this paper. We also demonstrate hot-vapor filtration during fast pyrolysis to remove fine char particles and inorganic contaminants from bio-oil. Representative results showed successful conversion of biomass feedstocks to fuel-range hydrocarbon biofuels and, specifically, the effect of hot-vapor filtration on bio-oil production and upgrading. The protocols provided in this report could help to generate rigorous and reliable data for biomass pyrolysis and bio-oil hydrotreating research.

Experimental methods for fast pyrolysis of lignocellulosic biomass to produce bio-oils and for the catalytic hydrotreating of bio-oils to produce fuel range hydrocarbons are presented. Hot-vapor filtration during fast pyrolysis to remove fine char particles and inorganic contaminants from bio-oil was also assessed.

Lignocellulosic biomass conversion to produce biofuels has received significant attention because of the quest for a replacement for fossil fuels. Among ...

Biochemistry

Microwave-assisted Intramolecular Dehydrogenative Diels-Alder Reactions for the Synthesis of Functionalized Naphthalenes/Solvatochromic Dyes

Functionalized naphthalenes have applications in a variety of research fields ranging from the synthesis of natural or biologically active molecules to the preparation of new organic dyes. Although numerous strategies have been reported to access naphthalene scaffolds, many procedures still present limitations in terms of incorporating functionality, which in turn narrows the range of available substrates. The development of versatile methods for direct access to substituted naphthalenes is therefore highly desirable.
The Diels-Alder (DA) cycloaddition reaction is a powerful and attractive method for the formation of saturated and unsaturated ring systems from readily available starting materials. A new microwave-assisted intramolecular dehydrogenative DA reaction of styrenyl derivatives described herein generates a variety of functionalized cyclopenta[b]naphthalenes that could not be prepared using existing synthetic methods. When compared to conventional heating, microwave irradiation accelerates reaction rates, enhances yields, and limits the formation of undesired byproducts.
The utility of this protocol is further demonstrated by the conversion of a DA cycloadduct into a novel solvatochromic fluorescent dye via a Buchwald-Hartwig palladium-catalyzed cross-coupling reaction. Fluorescence spectroscopy, as an informative and sensitive analytical technique, plays a key role in research fields including environmental science, medicine, pharmacology, and cellular biology. Access to a variety of new organic fluorophores provided by the microwave-assisted dehydrogenative DA reaction allows for further advancement in these fields.

Microwave-assisted intramolecular dehydrogenative Diels-Alder (DA) reactions provide concise access to functionalized cyclopenta[b]naphthalene building blocks. The utility of this methodology is demonstrated by one-step conversion of the dehydrogenative DA cycloadducts into novel solvatochromic fluorescent dyes via Buchwald-Hartwig palladium-catalyzed cross-coupling reactions.

Functionalized naphthalenes have applications in a variety of research fields ranging from the synthesis of natural or biologically active molecules to ...

Evaluation of Integrated Anaerobic Digestion and Hydrothermal Carbonization for Bioenergy Production

Lignocellulosic biomass is one of the most abundant yet underutilized renewable energy resources. Both anaerobic digestion (AD) and hydrothermal carbonization (HTC) are promising technologies for bioenergy production from biomass in terms of biogas and HTC biochar, respectively. In this study, the combination of AD and HTC is proposed to increase overall bioenergy production. Wheat straw was anaerobically digested in a novel upflow anaerobic solid state reactor (UASS) in both mesophilic (37 &#176;C) and thermophilic (55 &#176;C) conditions. Wet digested from thermophilic AD was hydrothermally carbonized at 230 &#176;C for 6 hr for HTC biochar production. At thermophilic temperature, the UASS system yields an average of 165 LCH4/kgVS&#160;(VS: volatile solids) and 121 L CH4/kgVS&#160;at mesophilic AD over the continuous operation of 200 days. Meanwhile, 43.4 g of HTC biochar with 29.6 MJ/kgdry_biochar was obtained from HTC of 1 kg digestate (dry basis) from mesophilic AD. The combination of AD and HTC, in this particular set of experiment yield 13.2 MJ of energy per 1 kg of dry wheat straw, which is at least 20% higher than HTC alone and 60.2% higher than AD only.

A novel Upflow Anaerobic Solid State (UASS) reactor was used for biogas production from fibrous feedstock. Digestate from UASS reactor was hydrothermally carbonized into HTC biochar in a pressurized batch reactor. The integration of the two bioenergy concepts was applied in this study to increase overall bioenergy production.

Lignocellulosic biomass is one of the most abundant yet underutilized renewable energy resources. Both anaerobic digestion (AD) and hydrothermal ...

Environment

Microwave-assisted Functionalization of Poly(ethylene glycol) and On-resin Peptides for Use in Chain Polymerizations and Hydrogel Formation

One of the main benefits to using poly(ethylene glycol) (PEG) macromers in hydrogel formation is synthetic versatility. The ability to draw from a large variety of PEG molecular weights and configurations (arm number, arm length, and branching pattern) affords researchers tight control over resulting hydrogel structures and properties, including Young&#8217;s modulus and mesh size. This video will illustrate a rapid, efficient, solvent-free, microwave-assisted method to methacrylate PEG precursors into poly(ethylene glycol) dimethacrylate (PEGDM). This synthetic method provides much-needed starting materials for applications in drug delivery and regenerative medicine. The demonstrated method is superior to traditional methacrylation methods as it is significantly faster and simpler, as well as more economical and environmentally friendly, using smaller amounts of reagents and solvents. We will also demonstrate an adaptation of this technique for on-resin methacrylamide functionalization of peptides. This on-resin method allows the N-terminus of peptides to be functionalized with methacrylamide groups prior to deprotection and cleavage from resin. This allows for selective addition of methacrylamide groups to the N-termini of the peptides while amino acids with reactive side groups (e.g.&#160;primary amine of lysine, primary alcohol of serine, secondary alcohols of threonine, and phenol of tyrosine) remain protected, preventing functionalization at multiple sites. This article will detail common analytical methods (proton Nuclear Magnetic Resonance spectroscopy (;H-NMR) and Matrix Assisted Laser Desorption Ionization Time of Flight mass spectrometry (MALDI-ToF)) to assess the efficiency of the functionalizations. Common pitfalls and suggested troubleshooting methods will be addressed, as will modifications of the technique which can be used to further tune macromer functionality and resulting hydrogel physical and chemical properties. Use of synthesized products for the formation of hydrogels for drug delivery and cell-material interaction studies will be demonstrated, with particular attention paid to modifying hydrogel composition to affect mesh size, controlling hydrogel stiffness and drug release.

Microwave-assisted Functionalization of Polyethylene glycol and On-resin Peptides for Use in Chain Polymerizations and Hydrogel Formation

This video will illustrate a rapid, efficient method to methacrylate poly(ethylene glycol), enabling chain polymerizations and hydrogel synthesis. It will demonstrate how to similarly introduce methacrylamide functionalities into peptides, detail common analytical methods to assess functionalization efficiency, provide suggestions for troubleshooting and advanced modifications, and demonstrate typical hydrogel characterization techniques.

One of the main benefits to using poly(ethylene glycol) (PEG) macromers in hydrogel formation is synthetic versatility. The ability to draw from a large ...

Preparation of Silica Nanoparticles Through Microwave-assisted Acid-catalysis

Microwave-assisted synthetic techniques were used to quickly and reproducibly produce silica nanoparticle sols using an acid catalyst with nanoparticle diameters ranging from 30-250 nm by varying the reaction conditions. Through the selection of a microwave compatible solvent, silicic acid precursor, catalyst, and microwave irradiation time, these microwave-assisted methods were capable of overcoming the previously reported shortcomings associated with synthesis of silica nanoparticles using microwave reactors. The siloxane precursor was hydrolyzed using the acid catalyst, HCl. Acetone, a low-tan &#948; solvent, mediates the condensation reactions and has minimal interaction with the electromagnetic field. Condensation reactions begin when the silicic acid precursor couples with the microwave radiation, leading to silica nanoparticle sol formation. The silica nanoparticles were characterized by dynamic light scattering data and scanning electron microscopy, which show the materials&#39; morphology and size to be dependent on the reaction conditions. Microwave-assisted reactions produce silica nanoparticles with roughened textured surfaces that are atypical for silica sols produced by St&#246;ber&#39;s methods, which have smooth surfaces.

Silica nanoparticles were prepared using acid-catalysis of a siloxane precursor and microwave-assisted synthetic techniques resulting in the controlled growth of nanomaterials ranging from 30-250 nm in diameter. The growth dynamics can be controlled by varying the initial silicic acid concentration, time of the reaction, and temperature of reaction.

Microwave-assisted synthetic techniques were used to quickly and reproducibly produce silica nanoparticle sols using an acid catalyst with nanoparticle ...

Quantitative Detection of Trace Explosive Vapors by Programmed Temperature Desorption Gas Chromatography-Electron Capture Detector

The direct liquid deposition of solution standards onto sorbent-filled thermal desorption tubes is used for the quantitative analysis of trace explosive vapor samples. The direct liquid deposition method yields a higher fidelity between the analysis of vapor samples and the analysis of solution standards than using separate injection methods for vapors and solutions, i.e., samples collected on vapor collection tubes and standards prepared in solution vials. Additionally, the method can account for instrumentation losses, which makes it ideal for minimizing variability and quantitative trace chemical detection. Gas chromatography with an electron capture detector is an instrumentation configuration sensitive to nitro-energetics, such as TNT and RDX, due to their relatively high electron affinity. However, vapor quantitation of these compounds is difficult without viable vapor standards. Thus, we eliminate the requirement for vapor standards by combining the sensitivity of the instrumentation with a direct liquid deposition protocol to analyze trace explosive vapor samples.

Trace explosive vapors of TNT and RDX collected on sorbent-filled thermal desorption tubes were analyzed using a programmed temperature desorption system coupled to GC with an electron capture detector. The instrumental analysis is combined with direct liquid deposition method to reduce sample variability and account for instrumentation drift and losses.

The direct liquid deposition of solution standards onto sorbent-filled thermal desorption tubes is used for the quantitative analysis of trace explosive ...

Preparation of Biomass-based Mesoporous Carbon with Higher Nitrogen-/Oxygen-chelating Adsorption for Cu(II) Through Microwave Pre-Pyrolysis

An environment-friendly technique for synthesizing biomass-based mesoporous activated carbon with high nitrogen-/oxygen-chelating adsorption for Cu(II) is proposed. Bagasse impregnated with phosphoric acid is utilized as the precursor. To pyrolyze the precursor, two separate heating modes are used: microwave pyrolysis and conventional electric-heating pyrolysis. The resulting bagasse-derived carbon samples are modified with nitrification and reduction modification. Nitrogen (N)/oxygen (O) functional groups are simultaneously introduced to the surface of activated carbon, enhancing its adsorption of Cu(II) by complexing and ion-exchange. Characterization and copper adsorption experiments are performed to investigate the physicochemical properties of four prepared carbon samples and determine which heating method favors the subsequent modification for doping of N/O functional groups. In this technique, based on analyzing data of nitrogen adsorption, Fourier transform infrared spectroscopy, and batch adsorption experiments, it is proven that microwave-pyrolyzed carbon has more defect sites and, therefore, time-saving effective microwave pyrolysis contributes more N/O species to the carbon, although it leads to a lower specific surface area. This technique offers a promising route to synthesis adsorbents with higher nitrogen and oxygen content and a higher adsorption capacity of heavy-metal ions in wastewater remediation applications.

Preparation of Biomass-based Mesoporous Carbon with Higher Nitrogen-/Oxygen-chelating Adsorption for CuII Through Microwave Pre-Pyrolysis

Here, we present a protocol to synthesize nitrogen/oxygen dual-doped mesoporous carbon from biomass by chemical activation in different pyrolysis modes followed by modification. We demonstrate that the microwave pyrolysis benefits the subsequent modification process to simultaneously introduce more nitrogen and oxygen functional groups on the carbon.

An environment-friendly technique for synthesizing biomass-based mesoporous activated carbon with high nitrogen-/oxygen-chelating adsorption for Cu(II) is ...

Carbon Sequestration and Soil Enhancement Through Onsite Biochar Production

Producing, Characterizing and Quantifying Biochar in the Woods Using Portable Flame Cap Kilns

One of the biggest challenges in utilizing non-commercial forest biomass is its widely distributed nature. The best solution to the biomass problem, to avoid expensive and carbon-intensive processing (chipping) and transportation costs, is to process it onsite. However, conventional burn piles have destructive impacts on forest soil and provide no benefits other than fuel reduction. Converting forest slash to biochar onsite has many ecological advantages over the current practice of slash disposal by incineration in burn piles, including reduced soil heating and particulate emissions, along with multiple benefits of the biochar to forest soil health and water holding capacity when left in place. Making biochar onsite in the woods is a way to return a pyrogenic carbon component to forest soils that has been missing due to the recent history of fire suppression. Biochar is also a leading method of carbon removal and sequestration for climate change mitigation. In this study, we document a method for making biochar using a portable biochar kiln. This low-cost method utilizes hand crews equipped with water for quenching kilns before the biochar burns to ash. Simple techniques for quantifying and characterizing the biochar produced are incorporated into the method for the purpose of measuring impact and qualifying for carbon removal certificates to help pay for the cost of the work. We describe the CM002 Component Methodology that provides standardized procedures for the quantification of GHG benefits during three stages of the process: waste biomass sourcing, biochar production, and biochar soil application. The CM002 Methodology is based on international best practices, including the most recent VCS methodology VM0044 Standards and EBC C-Sink Artisan Standards. Reliable quantification methods utilizing appropriate safety factors are the first essential step toward eligibility for carbon removal finance.

Author Spotlight: On-Site Biochar Production for Woody Debris Incineration in Forestry 

New methods for disposing of forestry slash piles in place produce pyrogenic carbon for restoring forest soil health and for carbon removal and sequestration. Here, we present a biochar production method integrating a new carbon removal accounting methodology and a digital application.

One of the biggest challenges in utilizing non-commercial forest biomass is its widely distributed nature. The best solution to the biomass problem, to ...

Air Curtain Burners and Biochar &#8211; Advancing Forest Health and Carbon Capture

Continuous In-woods Production of Biochar Using a Trailer-Mounted Air Curtain Burner

Fuel treatments and other forest restoration thinning practices aim to reduce wildfire risk while building forest resilience to drought, insects, and diseases and increasing aboveground carbon (C) sequestration. However, fuel treatments generate large amounts of unmerchantable woody biomass residues that are often burned in open piles, releasing significant quantities of greenhouse gases and particulates, and potentially damaging the soil beneath the pile. Air curtain burners offer a solution to mitigate these issues, helping to reduce smoke and particulates from burning operations, more fully burn biomass residues compared to pile burning, and eliminate the direct and intense fire contact that can harm soil beneath the slash pile. In an air curtain burner, burning takes place in a controlled environment. Smoke is contained and recirculated by the air curtain, and therefore burning can be conducted under a variety of climatic conditions (e.g.,&#160;wind, rain, snow), lengthening the burning season for disposal of slash material. The mobile pyrolysis unit that continuously creates biochar was specifically designed to dispose of residual woody biomass at log landings, green wood at landfills, or salvaged logged materials and create biochar in the process. This high-carbon biochar output can be used to enhance soil resilience by improving its chemical, physical, and biological properties and has potential applications in remediating contaminated soils, including those at abandoned mine sites. Here, we describe the general use of this equipment, appropriate siting, loading methods, quenching requirements, and lessons learned about operating this new technology.

Author Spotlight: Advancing Place-Based Biochar Production for Ecosystem Restoration and Soil Health

We describe the use of a place-based mobile pyrolysis unit equipped with an air curtain to continuously create biochar. The technology reduces the need for open slash pile burning, which results in lower emissions and fewer soil impacts. The protocol includes guidelines for site selection, loading, and quenching.

Fuel treatments and other forest restoration thinning practices aim to reduce wildfire risk while building forest resilience to drought, insects, and ...

Transformation of Organic Household Leftovers into a Peat Substitute

A two-step procedure is described for the synthesis of a carbon material with a similar composition and properties as peat. The produced hydrochar is made suitable for agricultural applications by removing plant growing inhibitory substances. Wet household waste such as fruit peel, coffee grounds, inedible vegetable parts, or wet lignocellulosic material in general, are treated in presence of water at 215 &#x00B0;C and 21 bar in an autoclave, i.e., by hydrothermal carbonization. All these leftovers have a considerable water content of up to 90 weight % (wt%). Adding water extends the procedure to drier materials such as nutshells or even garden prunings and compostable polymers, i.e., the plastic bag for collection of the leftovers.
Usually, the resulting carbon material, called hydrochar, produces a negative effect on plant growth when added to soil. It is supposed that this effect is caused by adsorbed phytotoxic compounds. A simple post-treatment under inert atmosphere (absence of oxygen) at 275 &#x00B0;C removes these substances. Therefore, the raw hydrochar is placed on a glass frit of a vertical tubular quartz reactor. A nitrogen gas flow is applied in down-flow direction. The tube is heated to the desired temperature by means of a heating mantle for up to one hour.
The success of the thermal treatment is easily quantified by thermogravimetry (TG), carried out in air. A weight loss is determined when the temperature of 275 &#x00B0;C is reached, since volatile content is desorbed. Its amount is reduced in the final material, in comparison to the untreated hydrochar.
The two-step treatment converts household leftovers, including compostable bags employed for their collection, into a carbon material that may serve as plant growth promoter and, at the same time, as a carbon sink for climate change mitigation.

A protocol for hydrothermal carbonization of vegetable food waste in an autoclave is presented, with subsequent dry thermal treatment at 275 &#x00B0;C in a continuous flow reactor desorbing volatile organic substances. The aim is to produce a carbon material suitable as soil amendment product or substrate component.

A two-step procedure is described for the synthesis of a carbon material with a similar composition and properties as peat. The produced hydrochar is made ...

Reducing Willow Wood Fuel Emission by Low Temperature Microwave Assisted Hydrothermal Carbonization

Samenvatting

Meer video's verkennen