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

Summary

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.

Abstract

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 ( = 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 °C, 170 °C, and 185 °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 °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.

Introduction

The application of microwaves for hydrothermal carbonization (MAHC) was used for the thermochemical transformation of biomass model compounds like fructose, glucose^1,2 or cellulose³, and for organic substrates, preferably waste material^{4,5,6,7,8,9,10}. The utilization of microwaves is advantageous as it allows an even heating of the treated biomass

Protocol

1. Preparation of sample material

1. Harvest five year old willow, clone type “Tordes” ([Salix schwerinii x S. viminalis] x S. vim.), with a height of 12−14 m and a breast diameter of approximately 15 cm.
2. Chip the wood and dry the chips in a kiln dryer for 24 h at 105 °C.
3. Cut the wood chips with a cutting mill and grind with a centrifugal mill to a particle size of 0.12 mm.

2. Microwave assisted hydrothermal carbonization

1. Use a microwave oven with 850 W and a magnetron frequency of 2,455 MHz.
2. Place 500 mg of raw material from step 1.3 in a 50 mL polytetrafluoroethyl....

Results

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 °C and the vari.......

Discussion

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 .......

Materials

List of materials used in this article

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