Ionic Liquids For Valorisation Of Lignocellulosic Biomass

This thesis explores novel applications which utilize ionic liquids and electrolyte solutions in treatment of biomass for obtaining high-quality value-added products, such as cellulose, hemicelluloses and lignin as relatively pure fractions, which can be further processed into useful materials and chemicals. Albeit ionic liquids have been described as chemically and thermally highly stable solvents, the potential drawbacks of ionic liquids and electrolyte solutions regarding to their possible degradation in common processing temperatures are discussed in detail in this thesis. The potential of a highly hydrophilic aqueous organic electrolyte solution tetra-n-butylphosphonium hydroxide [P4444][OH] was studied in fractionation of wheat straw. Lignin from the biomass was extracted with varying concentations of [P4444][OH] in water. The carbohydrate rich fractions were isolated and finally all collected fractions were analyzed. The results showed that 40 w/w% aqueous solutions of [P4444][OH] were found stable. The irreversible decomposition kinetics were assessed at for 60 w/w% solution and it was not possible to obtain 70 w/w% concentrations or higher because of the decomposition at during evaporation at 25 °C. The next project was to assess the hydrolytic stability of 1,5-diazabicyclo[4.3.0]non-5-enium acetate [DBNH][OAc] using HPLC. The [DBNH][OAc] can rapidly dissolve large quantities of cellulose and can be utilized in the IONCELL-F process to convert cellulose pulp into strong cellulosic man-made fibers. In addition, synthesis routes were studied for the superbase precursors 9-methyl-1,5-diazabicyclo(4.3.0)non-5-ene (9-mDBN) which was assumed to lead to increased hydrolytic stabilities of the final ionic liquid. In the last research, aqueous solution of triethylammonium hydrogensulphate [TEAH][HSO4] was studied for fractionation of wheat straw and aspen in comparison with non-sulfate NaOH pulping and various recently discovered pulping methods utilizing a microwave reactor in all procedures. All fractions were analyzed with GPC and spectroscopic methods in order to evaluate their potential for further refining.Ioniset nesteet ovat ruokasuolan tapaan suoloja, mutta niiden kemiallisen rakenteen takia ne muodostavat huonosti kiteitä, ja siksi niillä on matala sulamispiste. Sulamispiste voi olla jopa niin matala, että suola on sulaa huoneenlämpötilassa, ja siksi niitä voidaan käyttää liuottimina. Koska ioniset nesteet ovat suoloja, ne käyttäytyvät eri tavoin kuin perinteiset liuottimet, esimerkiksi asetoni tai tolueeni. Väitöskirjassani tutkin biopolymeerien uuttoa biomassoista, kuten puista ja kasveista, käyttäen ionisia nesteitä. Näistä biopolymeereistä tunnetuin on selluloosa, jota paperiteollisuus hyödyntää tuotteissaan. Muita merkittäviä biopolymeerejä biomassoissa ovat ligniini ja hemiselluloosat. Ligniini yleensä poltetaan, koska perinteisissä uuttoprosesseissa sen kemiallinen rakenne muuttuu sellaiseksi, että sen hyödyntäminen on hankalaa. Ionisten nesteiden käyttö voisi mahdollistaa ligniinin rakenteen pysymisen mahdollisimman muuttumattomana, jolloin ligniiniä voitaisiin tulevaisuudessa käyttää tuotteiden valmistuksessa. Toisena laajana kokonaisuutena tutkimuksessa tarkastellaan ionisten nesteiden stabiilisuutta uuttoprosessissa. Tällä tarkoitetaan ionisten nesteiden kemiallisen muuttumattomuuden tutkimista kuumennettaessa niitä esimerkiksi vesiliuoksessa, mikä on tärkeää siksi, että ioniseen nesteeseen liuenneet biopolymeerit saostetaan ulos lisäämällä siihen vettä. Ionisen nesteen käyttäminen uudelleen vaatii veden tislaamista pois korkeassa lämpötilassa. Korkea lämpötila mahdollistaa ei-haluttujen kemiallisten reaktioiden tapahtumisen veden ja ionisen nesteen välillä. Tutkittaessa fosforipitoisen ionisen nesteen stabiilisuutta osoittautui ydinmagneettinen resonanssispektroskopia hyväksi työkaluksi, sillä ioninen neste ja muodostunut hajoamistuote antoivat selvästi toisistaan erillään olevat signaalit, ja siten tulosten tulkinta oli suoraviivaista. Erästä toista ionista nestettä tutkittin hyödyntäen nestekromatografiaa, mutta tulosten tulkinta oli monimutkaista, sillä ei-haluttuja sivutuotteita muodostuikin kaksi, ja signaalit peittivät osittain toisiaan. Ongelma ratkaistiin matemaattisella mallilla, jolla laskennallisesti erotettiin signaalit toisistaan. Tulosten avulla pystyttiin havainnollistamaan, kuinka nopeasti ionisesta nesteestä tulisi käyttökelvotonta, koska sen puhdistamista hajoamistuotteista ei pidetty vaihtoehtona

On the Effect of Hot-Water Pretreatment in Sulfur-Free Pulping of Aspen and Wheat Straw

Published under an ACS AuthorChoice LicenseIn modern biorefineries, low value lignin and hemicellulose fractions are produced as side streams. New extraction methods for their purification are needed in order to utilize the whole biomass more efficiently and to produce special target products. In several new applications using plant based biomaterials, the native-type chemical and polymeric properties are desired. Especially, production of high-quality native-type lignin enables valorization of biomass entirely, thus making novel processes sustainable and economically viable. To investigate sulfur-free possibilities for so-called "lignin first" technologies, we compared alkaline organosolv, formic acid organosolv, and ionic liquid processes to simple soda "cooking" using wheat straw and aspen as raw materials. All experiments were carried out using microwave-assisted pulping approach toy enable rapid heat transfer and convenient control of temperature and pressure. The main target was to evaluate the advantage of a brief hot water extraction as a pretreatment for the pulping process. Most of these novel pulping methods resulted in high-quality lignin, which may be valorized more diversely than kraft lignin. Lignin fractions were thoroughly analyzed with NMR (C-13 and HSQC) and gel permeation chromatography to study the quality of the collected lignin. The cellulose fractions were analyzed by determining their lignin contents and carbohydrate profiles for further utilization in cellulose-based products or biofuels.Peer reviewe

Extraction of Wheat Straw with Aqueous Tetra-n-Butylphosphonium Hydroxide

Peer reviewe

Extraction of Wheat Straw with Aqueous Tetra-n-Butylphosphonium Hydroxide

The stability of tetra-n-butylphosphonium hydroxide ([P4444][OH](aq)) solutions and their potential for wheat straw extraction are investigated. Under certain concentration ranges, aqueous [P4444][OH](aq) is known to rapidly dissolve up to 20 wt% of cellulose at 25 ºC. However, at elevated temperatures and at the high concentration ranges required for cellulose dissolution, [P4444][OH](aq) irreversibly decomposes. This was determined by following the kinetics of decomposition at different temperatures and concentrations, using 31P NMR analysis of the solutions. A lower concentration range of 40 wt% [P4444][OH](aq) was observed for fractionation of wheat straw, avoiding significant decomposition of the expensive phosphonium component. Herein, the possibilities for producing cellulose-rich fractions with reduced lignin contents and hemicellulose-rich extracts are discussed. A proposal is given for a full process cycle using [P4444][OH](aq), where the phosphonium salt is used in fractionation and recovered by anion metathesis as a chloride salt. Although not demonstrated in this article, the chloride salt may be converted back to the hydroxide by means of, e.g., ion exchange

Effect of hot water pretreatment in simple pulping utilizing a laboratory scale microwave reactor

Meeting abstract: 135201

Feasibility of thermal separation in recycling of the distillable ionic liquid [DBNH][OAc] in cellulose fiber production

The objective of this work was to explore the feasibility of 1,5-diazabicyclo[4.3.0]non-5-enium acetate ([DBNH][OAc]) recovery from water solution by thermal separation. The evaporation behavior of pure [DBNH][OAc] was first studied using low pressure distillation in the pressure range of 0.5–2 kPa. The dew points of the distillation products from [DBNH][OAc] were measured in the pressure range of 0.5–15 kPa and modeled using an Antoine equation. Measurements for vapor liquid equilibrium (VLE) of water + [DBNH][OAc] system were carried out using a static total pressure method. The temperature range for the VLE measurement was 303–353 K. The results showed negative deviation from the Raoult's law. The NRTL activity coefficient model was used to correlate the VLE data. The experiments of [DBNH][OAc] product recovery from a solution containing 80 wt.% water were performed using a pilot-scale agitated thin-film evaporator. The performance of the evaporation system was analyzed as a function of the feed flow rate, the evaporator jacket temperature and the operating pressure. The analyses results indicated that the [DBNH][OAc] product with small water content (5–11.7 wt.%) was achieved by low pressure evaporation in a single stage.</p