Xylonic acid from sulfite spent liquor

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School of Chemical Engineering | Master's thesis
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Date

2010

Department

Kemian ja materiaalitieteiden tiedekunta

Major/Subject

Selluloosatekniikka

Mcode

Puu-23

Degree programme

Language

en

Pages

82 + [40]

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Abstract

The acid sulfite process is a very effective process for pulping. In this process the majority of hemicelluloses and lignin are dissolved into the sulfite spent liquor. Hemicelluloses appear as a monomeric form in the sulfite spent liquor. They also form aldonic acids and carboxylic acids. The fuel value of hemicelluloses approaches zero and therefore they should be removed and sold as a separate product. In this particular case, the majority of hemicelluloses consist of xylan, which poses the sulfite spent liquor to contain a vast amount of xylose. Harsh acid treatment causes these aldoses to form aldonic acids which lower the yield of the xylose recovery process drastically. The aim of this thesis was to clarify the properties of the aldonic acids present in spent liquor. Particularly xylonic acid was under investigation. Gluconic acid was used as a reference compound, since it has been studied prior in other contexts, such as the food industry. In the literature study the aim was to examine the formation of the acids and their chemical equilibrium especially in acidic conditions. Different analytical and separation methods were also investigated. The most interesting discovery was the lactone formation of acids in the low pH. Furthermore it was discovered that the ion exchange chromatography could be an effective method to separate these acids from the sulfite spent liquor. In the experimental part the equilibrium of the acids was the main target to investigate. It was obvious from the literature that the protonation reaction is much more rapid than the lactonization reaction. Therefore the NMR spectroscopy was used to analyze the samples. Protonation and lactonization were examined as a function of the pH. Results show that the gluconic and xylonic acids are almost identical concerning their protonation and lactonization nature. The acids were analyzed using the <sup>13</sup>C spectroscopy and examining the carbon shifts of the samples. The <sup>1</sup>H spectroscopy was used to compare the samples analyzed at different times. According to the results obtained from the NMR study the ion exchange chromatography separation was tested. These trials were carried out with three different ion exchange resins and in multiple pH: s. the goal was to separate the aldose and the corresponding aldonic acid from each other. However these tests concluded that acid and aldose could not be separated with these methods.

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Supervisor

Sixta, Herbert

Thesis advisor

Niemelä, Klaus

Keywords

xylonic acid, ksylonihappo, NMR, sulfiitti, sulfite, laktoni, lactone

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https://urn.fi/URN:NBN:fi:aalto-2020122356566

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[dipl] Kemian tekniikan korkeakoulu / CHEM