Proposal of Liquid Membrane-FTIR Spectroscopy to Quantify the Oxygen Content in Soluble Fraction of Degradative Solvent-Extraction

Abstract

A new technique for the structural analysis of biomass in the liquid phase processed by the degradative solvent extraction (DSE) method, called "liquid membrane-FTIR" is proposed. The technique has been applied to analyze the hydroxyl groups of the solvent-soluble of rice straws, which was extracted in 1-methylnaphthalene (1-MN) at 350 °C with DSE method. We found the liquid membrane-FTIR has several advantages to conventional solid membrane FTIR. 1) Easier to prepare and control the volume of the analyte, 2) Fewer chance of contamination of analyte, and 3) Sharper peaks in the spectra. A quantitative analysis of hydroxyl groups (including phenolic (C ar -OH) and alcoholic (C al -OH) hydroxyl) in soluble have been studied to validate the usage of the liquid membrane-FTIR technique. The result of quantification by this technique, 3.70% in weight percent of soluble on dry ash free basis, is reasonable with considering the existence of other kinds of oxygen-containing groups in soluble. The repeatability of the measurements was also examined and found that the mean difference (bias) between the measuring values of oxygen contained in hydroxyl groups by liquid membrane-FTIR and the average value of repeating measurement was very close to zero, 0.0024, in 5 measurements with the same sample.

Investigation on Conversion Pathways in Degradative Solvent Extraction of Rice Straw by Using Liquid Membrane-FTIR Spectroscopy

“…The suitability of liquid membrane-FTIR spectroscopy for use in analyzing the chemical structure of the RS Solvent-soluble was demonstrated previously through the quantitative measurement of the oxygen content in the OH-stretching region [42]. The oxygen content values that were obtained using liquid membrane-FTIR were in agreement with other published values for the DSE of RS [16].…”

“…The oxygen content values that were obtained using liquid membrane-FTIR were in agreement with other published values for the DSE of RS [16]. The reliability of the technique was also previously demonstrated, as the measured bias between measurement groups was found to be almost zero [42]. The technique has also been used in successfully identifying the overall process mechanism for RS DSE [43].…”

“…A lead metal sheet with a 0.05 mm thickness and a 22 × 10 mm 2 rectangular area was used as a spacer. The measurement procedure was similar to the study by Watcharakorn et al [42]. About 2.5 L/min of nitrogen gas was continuously purged through the measuring compartment in order to eliminate moisture.…”

“…The amount of hydroxyls contributing to each hydrogen bond, n OH,j , was estimated based on Beer's law by Equation 1, where A j is the peak area of OH for the jth peak, α OH,0 is the absorptivity of the stretching vibration of the free OH, and ∆ν OH,j is the wavenumber shift of OH in hydrogen bonds relative to the position of free OH groups (3611 cm −1 ). The α OH,0 value used to calculate the amount of OH was estimated referring to the slope of the free OH calibration curve with their concentrations, as in the previous study [42]. The total amount of OH, (n OH ) total , related to each absorption band can be calculated by Equation 2.…”

“…To acquire acceptable IR spectra of the analyte in the liquid state, special types of liquid cells were developed for this purpose. The technique, which uses liquid cells for absorption measurement, called liquid membrane-FTIR, has been shown to be a suitable and reproducible technique for the characterization and quantitative analysis of the Solvent-soluble of rice straw (RS) [42]. The use of liquid membrane-FTIR was proposed to interpret the main mechanism of the DSE of RS in a previous study [43].…”