Influence of Mineral Composition of Chars Derived by Hydrothermal Carbonization on Sorption Behavior of CO2, CH4, and O2.

Carsten Wedler,Markus Richter,Gongkui Xiao,Eric F May,Martin Muhler,Arash Arami-Niya,Katrin Lotz,Roland Span

doi:10.1021/acsomega.9b04370

Abstract

The doping of SiO2 and Fe2O3 into hydrochars that were produced by the hydrothermal carbonization of cellulose was studied with respect to its impact on the resulting surface characteristics and sorption behavior of CO2, CH4, and O2. During pyrolysis, the structural order of the Fe-doped char changed, as the fraction of highly ordered domains increased, which was not observed for the undoped and Si-doped chars. The Si doping had no apparent influence on the oxidation temperature of the hydrochar in contrast to the Fe-doped char where the oxidation temperature was reduced because of the catalytic effect of Fe. Both dopants reduced the micro-, meso- and macroporous surface areas of the chars, although the Fe-doped chars had larger meso- and macroporosity than the Si-doped char. However, the increased degree in the structural order of the carbon matrix of the Fe-doped char reduced its microporosity relative to the Si-doped char. The adsorption of CO2 and CH4 on the chars at temperatures between 273.15 and 423.15 K and at pressures up to 115 kPa was slightly inhibited by the Si doping but strongly suppressed by the Fe doping. For O2, however, the Si doping promoted the observed adsorption capacity, while Fe doping also showed an inhibiting effect.

Highlights

Hydrothermal carbonization (HTC) chars, which are pyrolyzed hydrochars derived via hydrothermal carbonization under high pressure from lignocellulosic biomass and water, have aroused interest in many fields of science and application over recent years.[1]
Depending on different raw plants, woods, or agricultural wastes, the mineral content of, e.g., iron, silica, or potassium can vary significantly, which can have a catalytic effect on morphology, pyrolysis, gasification, and combustion.[5−8] Trubetskaya et al.[6] have shown for two biomasses with different silica and potassium content that the high silica content of rice husk leads to a preserved shape of the char particles during pyrolysis, whereby the low silica and high potassium content of wheat straw lead to a broader deviation of particle shapes
The X-ray Diffraction (XRD) patterns and TEM images show that the Fe doping increases the structural ordering of the char during pyrolysis while the Si doping had no apparent effect on the char structure

Summary

Introduction

Hydrothermal carbonization (HTC) chars, which are pyrolyzed hydrochars derived via hydrothermal carbonization under high pressure from lignocellulosic biomass and water, have aroused interest in many fields of science and application over recent years.[1]. The higher potassium content of the wheat straw resulted in a higher reactivity of the char, which was confirmed by various studies for different biomasses.[5,9,10] Khelfa et al.[7] have shown the catalytic effect of Fe2O3 on pyrolysis and gasification of miscanthus chars. For these studies, the catalytic effect was shown using different natural biomasses with different mineral compositions[6] by the addition of further mineral particles to the biomass particles[7] or by acid leaching of most of the original mineral content with additional doping of the investigated mineral.[5,8−10] interactions between the different mineral components or influences of the acid leaching cannot be distinguished clearly

Methods

Results

Conclusion