CELLULOSE DECOMPOSITION IN ELECTROLYTIC SOLUTION USING IN-LIQUID PLASMA METHOD

Transcription

1 Proceedings of the Asian Conference on Thermal Sciences 2017, 1st ACTS March 26-30, 2017, Jeju Island, Korea ACTS-P00699 CELLULOSE DECOMPOSITION IN ELECTROLYTIC SOLUTION USING IN-LIQUID PLASMA METHOD Kazuki Tange 1 *, Shinfuku Nomura. 1, Shinobu Mukasa 1, Fadhli Syahrial 1,2 1 The University of Ehime, Dogo-Himata 10-13, Matsuyama-shi, Ehime , Japan 2 University of Teknikal Malaysia Melaka, Hang Tuah Jaya, Durian Tunggal, Melaka, Malaysia. * Presenting and Corresponding Author: c840017u@mails.cc.ehime-u.ac.jp ABSTRACT Hydrogen is the most promising energy for source future sustainable development. The decomposition of cellulose in an electrolytic solution by 27.12MHz radio frequency in-liquid plasma is carried out to produce hydrogen. In-liquid plasma decomposition, using the electrolyte solution, Na2SO4, improves the efficiency of hydrogen production. While hydrogen is the main gas generated by the plasma breakdown, carbon monoxide, carbon dioxide, and other low-grade flammable gases are also produced. The size of plasma increases when using concentrated Na2SO4 because Na + ions and SO4 2- ions collide with the copper electrode generating the plasma which facilitates plasma generation. The emission intensity of OH decreases with increased electrolyte concentration, and the quantity of H2O2 also decreases. The cellulose can directly enter the plasma as a particle, where the plasma decomposes the cellulose directly, significantly increasing the amount of gas generated. KEYWORDS: Hydrogen, Radio-frequency, In-liquid plasma, Cellulose, electrolyte 1. INTRODUCTION Biomass is one of the most abundant renewable resources in the world, providing about 10 to 15% of today s world energy demand.[1] Biomass is a versatile fuel that can be the source of biogas, liquid fuels and electricity. Biomass energy is carbon neutral in that it is derived from plants, a stored source of solar energy in the form of chemical energy through the process of photosynthesis.[2] Cellulose is expected to be a major component of renewable resources because, as an inedible biomass, it is not being utilized as a food source so it is quite abundant. However, the molecular structure of cellulose, β-(1 4)-D-glucan, causes chain-packing by strong inter- and intramolecular hydrogen-bonding, which makes any efforts to process or modify the material exceeding difficult.[3] The purpose of this research is to convert cellulose into fuel. One effective method of treating waste materials is using the highly active energy field of plasma. The authors have developed the "in-liquid plasma method" in which gas bubbles are formed in liquids under high pressure, creating a chemical reaction field that reaches 3500K.[4] This enables liquids to be directly decomposed by plasma, making it possible to decompose harmful substances without a catalyst. Some electrolytic solutions such as NaOH, H2SO4, and Na2SO4 have been found to enhance the gas production rate by in-liquid plasma from a cellulose solution. However, the reason for this is still incompletely understood. Decomposition of a cellulose suspension in liquids, such as 0.01~1 mol/dm3 Na2SO4 and pure water, is carried out using 27.12MHz in-liquid plasma and the gas production rates are measured. This experiment will provide useful knowledge about the electrolyte effect on the decomposition of cellulose by in-liquid plasma. 2. EXPERIMENTAL APPARATUS 1

2 A schematic diagram of apparatus for decomposition of a cellulose suspension is shown in Fig. 1. A 3.0 mm diameter copper electrode was inserted vertically from the bottom of the reactor. A quartz glass tube, used as a dielectric substance to avoid energy loss, enveloped the electrode. The bottom of the reactor, which is made of copper, is the counter electrode. In this experiment, mol/dm 3 Na2SO4 and pure water were used as a reagent. Na2SO4 was used to enhance the gas production rate from the decomposition of the cellulose suspension by RF in-liquid plasma. Cellulose powder passed through a 38.0 μm mesh (catalogue number Wako Pure Chemical Industries, Japan) was employed as the source material. The experiments were performed at initial cellulose contents of 0.0 and 20.0 wt%. The experimental procedures are as follows. Initially, the pressure of the reactor was reduced to MPa using an aspirator. Under this condition, power input from a MHz radio-frequency (RF) generator and impedance were simultaneously adjusted by a matching box. The discharge power was 200 W, and the AC voltage was 200 V, as calculated by subtraction of the reflected power from the input power. Subsequently, the reactor valve was opened to raise the reactor pressure to atmospheric pressure. The produced gases were drawn out of the apparatus by an air-tight glass syringe. Fig. 1 Experimental set-up. 3. RESULTS AND DISCUSSION The gas production rate from the solution decomposed by RF in-liquid plasma is shown in Fig. 2. Fig. 2 shows Na2SO4 increases the gasification efficiency of the solution. The gas production rate increased with an increase in the concentration of Na2SO4. A comparison between a solution with a cellulose suspension versus that of one without cellulose showed that the gas production rate of the cellulose suspension was higher than that of only the solution. The types of gas produced and their percentages are shown in Fig. 3. Fig. 3(a) shows O2 and H2 were generated for the case without cellulose suspension. The O2 percentage increased with an increase in the concentration of Na2SO4. Fig. 3(b) shows O2, H2, CO, CO2 and CH4 were generated for the case with cellulose suspension. The production of CO, CO2 and CH4 gases suggests that gasification of the cellulose occurred. The CO, CO2, and CH4 percentages increased with an increase in the concentration of Na2SO4. This suggests that Na2SO4 concentration influence the efficiency of cellulose gasification. To estimate the plasma size, photographs were taken. The bright shine of Na might lead to overexposure, resulting in an overestimation of the discharge size. To avoid this, the photographs were taken through an H-alpha pass filter (Baader Planetarium, FWHM = 35nm centered at 656 nm). The filtered photographs are shown in Fig. 4(c) and (d), 2

3 Fig. 2 Gas production rate versus Na2SO4 concentration. Fig. 3 Gas production types and percentages for (a) without cellulose and (b) cellulose 20 wt%. Fig. 4 Image of RF plasma generated in (a), (c) pure water and (b), (d) 1 mol/dm 3 Na2SO4 obtained using a CCD camera. (a) and (b) were taken through an ND filter. (c) and (d) were taken through an H-alpha pass filter (FWHM = 35nm centered at 656 nm). which show that the plasma sizes correspond to plasmas in pure water and 1 mol/dm3 Na2SO4 solution, respectively. The size of the plasma can be evaluated by comparison with a quartz glass tube (OD: 6 mm). In pure water, plasma with a width of 2.1 mm and height of 3.0 mm was formed just on the surface of the electrode. In 1 mol/dm 3 Na2SO4 solution, the plasma was 4.3 mm in width and 4.3 mm in height. With an increase in the Na2SO4 concentration, the size of the plasma increased. Na2SO4 solution contains Na + ions and SO4 2- ions. It is assumed that the electric field 3

4 causes these ions collide with the copper electrode which generates greater electron emission. Consequently, it facilitates plasma generation. Spectrometry measurements were taken in order to investigate the types of radical formations in the plasma. Fig. 5 shows the average intensity of IOH versus Na2SO4 concentration. The average intensity was taken from 309 nm. The intensity of the OH line decreased with an increase in Na2SO4 concentration. Hydrogen peroxide is produced by the generation of RF plasma in water. Hydrogen peroxide is produced in the bubbles surrounding the plasma or in the aqueous neighborhood of the bubbles by the following recombination process: 2OH H₂O₂ After the solutions were exposed to the RF plasma for 8 min, the density of hydrogen peroxide was determined using a colorimetric method, in which 4-aminoantipyrine with an enzyme was used as a reagent for coloring (DPM-H2O2, Kyoritsu Chemical-Check Lab). Fig. 5 shows the concentration of hydrogen peroxide versus Na2SO4 concentration. A comparison between the solution with cellulose suspension versus that without cellulose suspension showed that the hydrogen peroxide density of the cellulose suspension was less than for the solution with no cellulose suspension. The concentration of hydrogen peroxide decreased with an increase in Na2SO4 concentration. Fig. 5 suggests that the intensity of OH influences the production rate of hydrogen peroxide. OH radicals have a strong oxidizing power that indirectly decomposes the cellulose. However, the gas production rate increased with an increase in Na2SO4 concentration, which is in contradiction of Fig. 5. Although the reason is not clear, this may suggest that Na2SO4 increases production of OH radicals even as it blocks the OH excited state and generation of H2O2. After exposure, the solutions were filtered by Advantec Quantitative Filter Paper No.3. An absorbance spectrum of the solutions was measured. The absorbance A is defined as A(λ) log I0(λ)/I (λ), where I0(λ) and I (λ) are the intensities before and after the transmission of light through the solutions, at wavelength λ. After the solutions was exposed to the RF plasma for 8 min, the intensity of the peak was increased. The addition of Na2SO4 to cellulose suspension increased the intensity of the peak in 400 nm. This suggests that cellulose is broken into smaller molecular units. In addition, Na2SO4 may change the cellulose into a soluble substance by replacing hydroxy groups of the cellulose. Fig. 5 Average Intensity of OH line, IOH, (orange line) versus Na2SO4 concentration. The blue and gray bars denote the concentration of hydrogen peroxide 4

5 Fig. 6 Absorbance spectra of cellulose solutions before and after exposure. The solutions were exposed to plasma for 8 min. CONCLUSION Decomposition of cellulose suspension in liquids, such as mol/dm 3 Na2SO4 and pure water, was carried out using 27.12MHz in-liquid plasma and the gas production rates were measured. Na2SO4 increased the gasification efficiency of the solutions. The gas percentages of CO, CO2 and CH4 were increased with increasing the Na2SO4 concentration. The size of the plasma was increased with an increased Na2SO4 concentration. The intensity of the OH and the generation of hydrogen peroxide decreased with an increased Na2SO4 concentration. Detection of hydrogen peroxide generation was minimal in a cellulose suspension. An absorbance spectrum of the solutions increased with Na2SO4 concentration. ACKNOWLEDGMENT The present works was partially supported by a JKA and its promotion funds (No ) from Auto Race. REFERENCE [1] R. Saidur, E.A. Abdelaziz, A. Demirbas, M.S. Hossain, S. Mekhilef, A review on biomass as a fuel for boilers, Renew. Sustain. Energy Rev. 15 (2011) [2] A. Demirbaş, Biomass resource facilities and biomass conversion processing for fuels and chemicals, Energy Convers. Manag. 42 (2001) [3] J. ZHOU, L. ZHANGT, Solubility of cellulose in NaOH / urea aqueous solution, Polym. J. 32 (2000) [4] S. Nomura, S. Mukasa, H. Toyota, H. Miyake, H. Yamashita, T. Maehara, A. Kawashima, F. Abe, Characteristics of in-liquid plasma in water under higher pressure than atmospheric pressure, Plasma Sources Sci. Technol. 20 (2011)