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Effect of heating rate on supercritical water gasification of glucose and guaiacol mixture Obie Farobie, Poomkawee Changkiendee, Shuhei Inoue, Takahito Inoue, Yoshifumi Kawai, Takashi Noguchi, Hiroaki Tanigawa, and Yukihiko Matsumura Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.7b00640 • Publication Date (Web): 01 May 2017 Downloaded from http://pubs.acs.org on May 23, 2017
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Industrial & Engineering Chemistry Research
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(1) Category of article
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Original Research Paper
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(2) Title
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Effect of heating rate on supercritical water gasification of glucose and guaiacol mixture
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(3) Authors’ names
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Obie FAROBIE1, Poomkawee CHANGKIENDEE1, Shuhei INOUE1, Takahito INOUE2,
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Yoshifumi KAWAI3, Takashi NOGUCHI4, Hiroaki TANIGAWA5, Yukihiko
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MATSUMURA1*
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(4) Affiliation, affiliation address
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Fukken Co., Ltd., 2-10-11 Hikarimachi, Higashi-ku, Hiroshima 732-0052 Japan.
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Chuden Plant Co., Ltd., 2-3-18 Deshio, Minamiku, Hiroshima 734-0001 Japan.
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Toyo Koatsu Co., Ltd., 2-1-22 Kusunoki-cho, Nishi-ku, Hiroshima 733-0002 Japan.
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Division of Energy and Environmental Engineering, Institute of Engineering, Hiroshima University, 1-4-1 Kagamiyama, Higashi-Hiroshima 739-8527 Japan.
The Chugoku Electric Power Co., Inc., 3-9-1 Kagamiyama, Higashi-hiroshima 7390046 Japan.
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Corresponding author
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*Prof. Yukihiko MATSUMURA,
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Division of Energy and Environmental Engineering, Institute of Engineering, Hiroshima University, 1-4-1 Kagamiyama, Higashi-Hiroshima, 739-8527 Japan
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Tel. +81-(0)82-424-7561, Fax: +81-(0)82-422-7193
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E-mail:
[email protected] 29
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Abstract
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We herein report the effect of feedstock heating rate on the supercritical water
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gasification of a glucose/guaiacol mixture. In the study, glucose was employed as a
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model compound for cellulose, and guaiacol was employed as a model compound for
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lignin. A mixture of glucose (0.34 wt%) and guaiacol (0.16 wt%) was fed into a
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laboratory scale continuous reactor at 600 °C and 25 MPa through a preheater, where
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the feedstock heating rate could be controlled. Feedstock flow rates of 1 and 2 g/min
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were employed along with preheaters of three different lengths (i.e., 0.45, 0.9, and
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1.8 m). We found that longer preheaters resulted in slower heating rates at the same
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feedstock flow rate. Studies into the effect of feedstock heating rate on the gasification
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efficiency indicated that a high heating rate enhanced the carbon gasification efficiency
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even for a glucose/guaiacol mixture. However, when the heating rate reached ~25 K/s, a
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decrease in the carbon gasification efficiency was observed. This may be due to glucose
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and guaiacol interacting in a similar manner to cellulose and lignin. Finally, the
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preheater length had no apparent effect on the product gas composition.
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Keywords: biomass; supercritical water; glucose; guaiacol; heating rate
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1. Introduction
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Growing concerns regarding climate change have led to an increase in studies
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examining the use of biomass as an alternative source of renewable energy. Indeed,
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biomass can be converted into useful secondary energy via various technologies,
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including thermochemical conversion methods such as pyrolysis, combustion,
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liquefaction, and solid fuel production. More specifically, thermochemical conversion
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employs high temperatures to chemically convert solid organic compounds into value-
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added products, including gaseous fuels and pyrolytic oils.1 However, biomass waste
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contains large quantities of water, which results in high drying costs when conventional
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gasification processes are employed. To address this issue, supercritical water
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gasification (SCWG) is considered a promising technology to convert biomass
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containing high-moisture compounds, since the gasification reaction takes place in
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supercritical water, and as such, it is not necessary to dry the biomass beforehand.2,3 In
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general, the SCWG reaction takes place at a water temperature and pressure above
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374 °C and 22.1 MPa, respectively. Under these conditions, water exhibits great
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potential as a solvent for organic components and gases, because all fluids are retained
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in a single phase.4–6 Water can therefore be considered a suitable reaction medium for
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biomass gasification.7–9
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Under SCWG conditions, biomass is easily decomposed into gaseous products
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over a short residence time; however, this decomposition is accompanied by
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polymerization reactions, which produce char and tar. These materials can cause serious
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problems in the SCWG process, as they not only reduce gasification efficiency, but can
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also plug the reactor. One possibility to suppress the production of such tarry materials
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is an increase in the feedstock heating rate, as high heating rates have been reported to
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improve carbon gasification efficiencies.10 As such, studies into the effect of heating
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rate on the SCWG reaction are of particular interest.
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In this context, Promdej and Matsumura examined the effect of temperature on
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the hydrothermal decomposition of glucose in sub- and supercritical water.11,12 They
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reported that char was only produced under subcritical water conditions, and was
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drastically suppressed under supercritical conditions. In addition, they found that the
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various reactions taking place during the SCWG of glucose could be classified into two
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main types, namely ionic and radical reactions. Furthermore, Chuntanapum and
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Matsumura
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hydroxymethylfurfuraldehyde (5-HMF) and furfural took place during glucose
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decomposition, thus leading to char formation.13,14
reported
that
the
polymerization
reactions
of
5-
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Meanwhile, Yong and Matsumura carried out a similar study using guaiacol in
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sub- and supercritical water.15 Unlike the hydrothermal decomposition of glucose,
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where solid yields were drastically suppressed, char formation from guaiacol was
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enhanced under supercritical conditions. In this case, char was generated exclusively in
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the supercritical region from the formation of compounds containing multiple benzene
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rings. In addition, several studies into the hydrothermal treatment of guaiacol16–20 have
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deduced that the quantities of guaiacol oligomers and low-molecular-weight products
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produced increased with longer residence times. Furthermore, the formation of char also
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occurs as a result of the dehydration of low-molecular-weight compounds. Interestingly,
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the SCWG of lignin compounds exhibits similar behavior to that of guaiacol, in which
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char formation was enhanced under supercritical conditions.21,22
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Due to the different behaviors of glucose and guaiacol under SCWG conditions
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in the context of char formation, studies into the behavior of a glucose/guaiacol mixture
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in supercritical water would be of particular interest. Studies concerning the interactions
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between glucose and phenols in SCWG have been reported earlier.23,24 However, to the
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best of our knowledge, no reports into the effects of heating rate on the supercritical
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water gasification of a glucose and guaiacol mixture have been published. Thus, we
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herein aim to investigate the effect of heating rate on the gasification characteristics of a
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mixture of glucose and guaiacol under supercritical water conditions.
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2. Materials and methods
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2.1 Experimental
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The supercritical water gasification of the glucose/guaiacol mixture was carried
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out using the flow reactor illustrated in Fig. 1, which was composed of SS 316 steel
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tubing (i.d. 2.17 mm, o.d. 3.18 mm, length 12 m). Meanwhile, three different lengths of
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pre-heater (i.e., 0.45, 0.9, and 1.8 m) with the same inner and outer diameter of 2.17 mm
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and 3.18 mm, respectively were employed. The pre-heater and reactor were placed
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inside the electric furnace for each. The length of the furnace for pre-heater was 17.5 cm
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with an internal diameter of 5 cm and external diameter of 30 cm. Meanwhile, the
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length of the furnace for the main reactor was 100 cm with an internal diameter of 15
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cm and external diameter of 40 cm. To start up the experimental setup, the water was
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fed into the reactor through a preheater, after which the pressure was adjusted to
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25 MPa using a back-pressure regulator. After achieving a constant pressure of 25 MPa,
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the reactor temperature was set at 600 °C, and the feedstock was fed into the system. To
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ensure steady-state conditions, the feedstock was fed into the system for 2 h prior to
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sample collection. All reaction products were cooled in a heat exchanger, and when a
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constant gas generation rate had been achieved, gas samples were collected in vials and
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their compositions were determined. Liquid samples were also collected to determine
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the total organic carbon (TOC) content. A summary of the experimental conditions is
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provided in Table 1.
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2.2 Analytical methods
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The liquid samples were analyzed using a TOC analyzer to quantify the total
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carbon present in the liquid compounds (non-purgeable organic carbon, NPOC) and in
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the dissolved gaseous products (inorganic carbon, IC). The gaseous products were
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analyzed using a gas chromatograph (GC) equipped with a thermal conductivity
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detector (TCD) and a flame ionization detector (FID). H2 was detected by GC-TCD
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with N2 as the carrier gas, CO2 and CO were detected by GC-TCD with He as the
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carrier gas, and CH4, C2H4, and C2H6 were detected by GC-FID with He as the carrier
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gas. The solid product particles trapped in the inline filter were removed, placed in a
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porcelain crucible, dried overnight in an oven, placed in a desiccator for 30 min, and
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then weighed until a constant weight was reached.
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The carbon gasification efficiency (CGE) for each experimental run was calculated based on the carbon content in the feedstock as indicated in Eq. (1): CGE =
Cgas + CIC
(1)
Cfeedstock
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where Cgas is the total amount of carbon present in the gaseous products [mol], CIC is the
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total amount of inorganic carbon present in the liquid effluent [mol], and Cfeedstock is the
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total amount of carbon present in the initial feedstock [mol].
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2.3 Reagents and materials
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All chemicals employed herein were used without further treatment or
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purification. ᴅ-glucose (>99.5%) was purchased from Sigma-Aldrich Co. (Japan) and
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guaiacol (98.0%) was purchased from Tokyo Chemical Industry Co., Ltd. (Japan).
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Deionized water (
