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European Journal of Applied Sciences – Vol. 12, No. 3

Publication Date: June 25, 2024

DOI:10.14738/aivp.123.17039

Vamvuka, D., Panagiotidou, S., & Orfanoudaki, A. (2024). Hydrogen-rich Syngas from Steam Gasification of Waste Biomass

Materials through CO2 Capture and Use of Catalysts. European Journal of Applied Sciences, Vol - 12(3). 233-246.

Services for Science and Education – United Kingdom

Hydrogen-rich Syngas from Steam Gasification of Waste Biomass

Materials through CO2 Capture and Use of Catalysts

Despina Vamvuka

School of Mineral Resources Engineering,

Technical University of Crete, Chania, Greece

Stavroula Panagiotidou

School of Mineral Resources Engineering,

Technical University of Crete, Chania, Greece

Agapi Orfanoudaki

School of Mineral Resources Engineering,

Technical University of Crete, Chania, Greece

ABSTRACT

The exploitation of some abundant and low-cost waste materials was investigated

for production of clean energy carriers rich in hydrogen, in line with low-carbon

and circular economy policies. Waste concrete fines were used together with CeO2

and Na2CO3 as catalysts in order to achieve an improved system performance at

lower temperatures. The study focused on the effects of sorbent/biomass ratio,

type and catalyst loading, as well as temperature on fuel conversion, product gas

composition and heating value, syngas and hydrogen yield and energy recovery

from the solid waste materials used. The experiments were conducted in a fixed

bed system, following a two-step process for eliminating tar and increasing the

reactivity of generated biosolid. Gas analysis was performed by a

thermogravimetric-mass spectrometry unit. At a molar ratio Ca/C=1, the amount

of CO2 captured between 700°C and 750°C was 83-95% and the concentration of

hydrogen in the product gas increased by about 40%, achieving values 69.5% mol

for winery waste fuel and 59.6% for helianthus waste at 750°C. CeO2 and Na2CO3

catalysts improved conversion, which was raised up to 91-100% on a daf basis.

Na2CO3 catalyst presented a better overall performance at a loading of 20% wt. At

750°C the molar fraction of hydrogen in the gas mixture ranged between 73% and

96% for the two fuels, whereas the higher heating value of gas and syngas yield

varied between 12.4-13.1 MJ/m3 and 1.86-4.94 m3/kg, respectively.

Keywords: Waste biomass, Steam gasification, Waste concrete, CO2 capture, Catalysts

INTRODUCTION

Global energy crisis nowadays, rising costs of fossil fuels and environmental pollution from

their use demand an urgent transition to renewable and clean energy sources. Biomass

materials, covering a wide range of agricultural, forest, industrial and urban wastes, are

generated in huge quantities worldwide at low or no cost possessing a high energy potential

[1]. Their great availability and neutral carbon footprint to the environment make them very

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European Journal of Applied Sciences (EJAS) Vol. 12, Issue 3, June-2024

attractive as energy carriers, meeting the policies for decarbonized energy and circular

economy [2].

Many countries, especially those of South Europe, produce a large amount of wastes from

wine/spirit making factories. Energy recovery from these could be a promising solution to the

high energy requirements in these countries, due to developed tourism industry. However,

the seasonal availability of such wastes needs the use of a variety of feedstocks, to ensure

sustainability of energy resources. Among these feedstocks, energy crops with high yield

potential are being widely established in recent years, especially on pasture or abandoned

agricultural land [3,4]. Helianthus annuus L., a short rotation coppice crop, is widely

cultivated in Europe not only for biodiesel production, but also as an agricultural plant for oil

production leaving great quantities of solid residues [4,5]. As an alternative to combustion

emitting toxic gases responsible for acid rain, gasification of biomass materials with steam is

an environmentally friendly technology, offering high efficiency and flexibility of generated

gas. This gas, consisting of H2, CO, CO2 and small amounts of CH4 and hydrocarbons, is suitable

not only for heat, power, or biofuels production, but also due to its elevated content in highly

marketable H2 in transport and other industrial applications [6-9]. However, the gasification

process is limited to some drawbacks, the principal of which are its endothermic nature and

the greenhouse gas by-product CO2. Calcium-based sorbents, being abundantly found at low

cost, have been quite successfully used for CO2 capture, providing also heat through the

exothermic carbonation reaction, as well as an increase in hydrogen yield [10,11]. However,

most sorbents decompose at temperatures where gasification efficiency is quite low

(~700°C), so that addition of catalysts is necessary to improve the process.

In previous investigations, calcined limestone or dolomite were principally used as CO2

sorbents, in combination with catalysts mostly based on Ni, such as Ni/Fe, NiO, NiO/γ-Al2O3,

NiO/NiAl2O4 [11-13]. A concentration of hydrogen in product gas ranging between 68% and

90% mol was achieved from the gasification of some agricultural and forest wastes and stalk

from energy crop corn [12]. Also, alkali salts of K and Na have been used by several studies to

improve the quality of syngas produced from the steam gasification of woody and corncob

chars, but at high temperatures 900-950°C, reporting total gas yield up to 3 m3/kg [7,14]. The

catalytic effect of K was also confirmed during the gasification of Erianthus crop and corncob

chars using CO2 as the gasifying agent [15,16]. There is very limited research on the effect of

CeO2 as catalyst during the steam gasification of materials similar to the ones under study.

Gasification of a woody residue at 900°C in presence of Ca-Al-Ce bifunctional catalyst

exhibited a 81% H2 concentration in the syngas mixture [17], whereas gasification of cellulose

with Ce/Fe catalyst at 800°C produced a gas with 28.6% H2 [18].

The innovative idea of current work was to investigate the exploitation of some abundant and

low-cost waste materials for production of clean energy carriers rich in hydrogen, in line with

low-carbon and circular economy policies. To enhance hydrogen yield and minimize carbon

dioxide greenhouse gas emissions, waste concrete fines, generated in vast quantities from

construction activities, were used together with CeO2 and Na2CO3 as catalysts, in order to

achieve an improved system performance at lower temperatures. The steam gasification of

agro-industrial wastes or energy crops, the biomass materials under study, integrated with in

situ carbon dioxide sorbent from waste concrete fines and CeO2/Na2CO3 catalysts has not

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235

Vamvuka, D., Panagiotidou, S., & Orfanoudaki, A. (2024). Hydrogen-rich Syngas from Steam Gasification of Waste Biomass Materials through CO2

Capture and Use of Catalysts. European Journal of Applied Sciences, Vol - 12(3). 233-246.

URL: http://dx.doi.org/10.14738/aivp.123.17039

been reported so far. Some previous experimental work by the authors examined the effect of

several factors on process efficiency, such as the physical and chemical characteristics of the

fuels, the steam/biomass ratio and operating conditions. This study focused on the effects of

sorbent/biomass ratio, type and catalyst loading, as well as temperature on fuel conversion,

product gas composition and heating value, syngas and hydrogen yield and energy recovery

from the solid waste materials used. The experiments were conducted in a fixed bed system,

following a two-step process for eliminating tar and increasing the reactivity of generated

biosolid. Gas analysis was performed by a thermogravimetric-mass spectrometry unit.

EXPERIMENTAL SECTION

Preparation of Materials and Feedstocks

The biomass materials selected for current work were a solid winery waste (WW) provided

by a private industry in West Crete and a helianthus waste (HW) from an oil company in

Central Greece. After air drying the materials were ground in a cutting mill, sieved to a

particle size below 1 mm and riffled to obtain representative samples for analysis and further

processing. Waste concrete fines (WCF), provided by Finomix AE company, were employed as

CO2 adsorbent from gasification tests. The material with particle size lower than 100 μm was

calcined at 950°C for 2 h in a muffle furnace and then it was placed in a glass vessel under a

water saturated atmosphere, for at least one week before use, so that its calcium oxide

components would be transformed to the active CO2 adsorbent Ca (OH)2 [11].

Cerium oxide catalyst was prepared from calcium acetate and cerium nitrate hexahydrate Ce

(NO3)3.6H2O, as described in a previous report [19]. Mass ratios of CeO2 to CaO used for the

tests were 10:90, 20:80 and 30:70.

Sodium carbonate catalyst was purchased by Sigma-Aldrich. Mixtures with solid feedstocks at

weight ratios 10:90, 20:80 and 30:70 were prepared, according to the incipient wetness

method. After 24 h stirring at room temperature, the mixtures were dried in the oven at

110°C.

Gasification feedstocks were generated in a high temperature fixed bed system, schematically

presented in Figure A1. The reactor was equipped with a grid sample holder, a Ni-Cr-Ni

thermocouple in contact with the bed and a furnace controller of ±3°C accuracy. Each biomass

material was pyrolyzed in nitrogen of flow rate 200 mL/min, with a heating rate of 10°C/min,

up to 600°C and kept at the final temperature for 30 min. Following system cooling under

nitrogen, pyrolysis products were collected, weighed and stored for analysis and subsequent

tests.

Gasification Experiments

Each char produced from the previous pyrolysis step was introduced into the reactor, either

sole or mixed with waste concrete fines (at Ca/C molar ratios 1 and 2 according to the

stoichiometry of each fuel and the adsorbent material) and catalyst at specific ratios and

heated in nitrogen up to 600°C. At this point, distilled water of flow rate corresponding to

steam/biochar=3 (maximizing hydrogen production according to our previous findings [20])

was injected automatically through a syringe pump, while the nitrogen flow was stopped. A

uniform flow of steam was achieved by a 2 m pipe surrounding the reactor. The unit was