Patent Application: US-201314391165-A

Abstract:
low transition temperature mixtures or solvents are provided that can be used in methods and systems to dissolve and bydrolyze certain components from lignin - containing biomass at mild conditions so that further degradation is prevented . the solvents , methods and systems according to the invention have various advantages over prior technology or approaches . for example , lttms are cheap solvents , renewable and / or non - toxic food ingredients . lttms dissolve lignin selectively from a lignin - containing biomass . a highly efficient lignin recovery can be achieved . the recovered lignin is of higher quality . the remaining cellulose is also of higher . much less water is needed , which means a tremendous reduction of the energy requirement in the recovery process , i . e . less energy needed for evaporating large quantities of water .

Description:
in the present invention , new low transition temperature mixtures ( lttms ) are provided by combining natural and renewable biomaterials as shown in fig1 . for the purposes of this invention , lttms are also referred to as deep eutectic solvents ( dess ). originally , these mixtures were called dess , but this name does not cover the complete class of solvents , because many mixtures do not show ( eutectic ) melting points , but glass transitions instead . the selection of starting materials was made on the basis of the available functional groups and the key interactions involved in lignocellulosic biomass dissolution . a set of representative natural amino acids with suitable structures and functional groups , some essential nutrients represented by choline chloride and nicotinic acid , as well as different natural acids present in fruits and vegetables were tested as liquid - phase promoters . in one example , the preparation of the new solvents was done by mixing both starting materials in the solid state , followed by melting them at 60 degrees celsius for mixtures containing lactic or oxalic acid , or at 130 degrees celsius for nicotinic and malic acid mixtures . it is noticeable that the melting temperature or glass transition temperature ( as some mixtures do not show a melting point ) was always found to be lower than the melting point of any of the starting materials . the higher the temperature during mixing and the better the mixing , the faster the melting was observed . nevertheless , higher thermal stability was found for mixtures obtained at lower temperatures for longer times . once a clear and transparent liquid was formed with no evidence of solid particles , the mixture was cooled down and differential scanning calorimetry ( dsc ) analysis was carried out to determine the phase transition temperature of the formed liquids . water content was always less than 1 wt %. a more detailed description of an example of an experimental procedure is included infra in the section supplemental information . tables 1a - c show the ‘ hydrogen bond donor ’—‘ hydrogen bond acceptor ’ combinations , which were resulting in clear liquids ( table 1a ), liquids at the set temperature but with formation of solid particles when cooling down ( table 1b ), and with no evidence of melting for the selected combination or ratio ( table 1c ). the building principles are not easy to generalize . unlike normal chemical bonds , hydrogen bonds present different contact distances and binding energies which do not depend only on the donor and acceptor nature . fig2 shows exemplary images of the evolution of the phase transition for the malic acid - choline chloride series shown in tables 1a - c . the proton affinity ( pa )/ pk a equalization plays a role in strengthening the h - bond , so the pk a slide rule was taken into account in the selection of the h - bonding counterparts . the pk a values for the main functional groups are included in fig1 . the acidity of the proton is also responsible for the formation of an lttm instead of an il . for instance , when lactic acid is combined with choline chloride , a liquid is formed at room temperature . however , the ionic liquid choline lactate is not produced as reflected in ir spectra ( not shown ). an il is a liquid below 100 ° c ., solely having ions . for the il to be formed , a stronger base with a higher pk a needs to be facing the h - bond donor or a stronger acid needs to be facing the acceptor . hydrogen bonding can be evidenced as well by the shifts in the representative peaks of the involved bonds in the fourier transform infrared spectroscopy ( ftir ) spectra . a shift in the resonance signal can also be noticed to lower field in 1 h - nmr ( spectra not shown ). these values are significantly lower compared with the melting point of the starting materials . some representative dsc curves can be found in fig3 showing unusual low glass transition temperatures . because for the selected mixtures no melting point was found , but most of the mixtures showed glass transitions instead , we named them lttms instead of dess . biomass processing faces two main challenges for a better exploitation of lignocellulosic biomass . the first challenge pertains to the recalcitrant nature of lignocellulosic biopolymers , making them difficult to dissolve . the second challenge is the efficient hydrolysis into sugars or high - valuable products . in both cases , the solvent plays a crucial role . in this context , 26 new mixtures , listed in table 2 , are screened as solvents for lignin , cellulose and starch . the importance of this screening lies in the evaluation of the potential ability of lttms to deconstruct the lignocellulosic biomass structure . high to selectivity is desirable for separating lignin from cellulose and hemicellulose , and high solubility leads to efficient hydrolysis . two different approaches can be considered for the hydrolysis with these solvents : catalytic or enzymatic hydrolysis . for catalytic hydrolysis , lttms are likely to act as solvents as well as catalysts or co - catalysts , considering their acid character . they can also be designed to be an enzyme - tolerant medium which allows the development of a one - pot process where both deconstruction and enzymatic hydrolysis occur . achieving good solubilities is a must for catalytic hydrolysis of cellulose or hemicellulose , while delignification and decrystallization are desirable for enzymes to perform better . in all cases , the biorenewable and natural character of the solvent constituents is of most importance . for further steps in the process , the recoverability of the solvent is considered . solvents that are able to form hydrogen bonding are very likely to phase separate when adding a non - hydrogen bonding solvent . as an example , acetone was proved to work as an anti - solvent for solvent recoverability . the experimental procedure is described infra in the section supplemental information . cellulose and lignin are the two most abundant renewable polymers in lignocellulosic biomass , and starch is chosen as the representative polysaccharide for this study . for a selection of 26 solvents , listed in table 3 , the solubility of these biopolymers was determined by using the cloud point method . vials containing 2 g of solvent were placed in an oil bath . the selected temperature ( t test ) was set constant for the whole experiment . consecutive additions of 0 . 2 - 1 mg of solute were done under vigorous stirring to ensure good contact between phases . once the turbidity or the presence of particles was noticeable by the cloud point method , the samples were equilibrated for at least 24 hours to check that the turbidity had not disappeared . zero solubility was considered when the addition of 0 . 1 wt % of solute showed turbidity . the dissolution temperature was set as 60 ° c . for less viscous mixtures and as 100 ° c . for the ones showing higher viscosity . from table 3 it can be observed that a high selectivity for the separation of lignin from a mixture of lignin and cellulose was found . furthermore , very different solubility values were obtained for the different combinations . choline chloride - lactic acid mixtures show high solubility for lignin , while cellulose was found to be immiscible with the whole series . lignin solubility shows in this case a clear trend when increasing the acid content ( lc1 . 3 : 1 & lt ; lc2 : 1 & lt ; lc3 : 1 & lt ; lc5 : 1 & lt ; lc9 : 1 ) however , the opposite trend was found when comparing with the malic acid - proline series ( mp1 : 1 & lt ;& lt ; mp1 : 2 & lt ; mp1 : 3 ). the malic acid combinations , in general , were found to show much higher solubilities for starch and lower solubilities for lignin when comparing with other hydrogen bond donors . but for the former series , an increase in solubility of cellulose ( also of lignin and starch ) was found when increasing the proline ratio . the role of the hydrogen bond acceptor opens room to further discussion . depending on the selected donor , the trend in solubilities can be inverted . for instance , lignin solubility shows the trend lb & gt ; lh & gt ; lc & gt ; lg & gt ; la & gt ; lp for the lactic acid sequence , while malic or oxalic acid follows mp & gt ; mc & gt ; mg & gt ;& gt ; mh ≈ mn ≈ mn ≈ mb and oc & gt ; op & gt ; ob & gt ; og ≈ ph ≈ on , respectively . even though cellulose solubility was found to be very poor or negligible for most of the studied solvents , there was a noticeable change in cellulose crystallinity in most cases , obtaining a turbid liquid after stirring overnight . in the case of lactic acid - choline chloride mixtures for example , the cellulose fibers were not dissolved , but for the mixtures containing proline , only a new turbid liquid phase was formed with no evidence of solid particles . experiments were done to test the solubility of real wheat straw biomass samples . for the first experiment , wheat straw biomass was suspended in the lc2 : 1 lttm . the lttm colored upon stirring the biomass suspension overnight , although biomass particles or fibers were still present ( fig4 and 5 ). after three washing cycles with ethanol , 90 . 5 wt % of the non - dissolved biomass could be recovered . direct separation of the suspended and dissolved biomass was done by centrifuging the lc2 : 1 with biomass without washing . fig4 shows the processed material after each one of the described steps . after washing , 81 . 6 % and 2 . 0 wt % of the added biomass was recovered from the separated precipitate and supernatant respectively , which means that 2 wt % of the biomass can be considered as being dissolved and composed entirely of lignin . a second experiment was done following the same procedure for mp1 : 3 . in this case , much less biomass particles can be noticed after the pretreatment ( fig4 and 5 ). this result is consistent with the higher values reported for the solubilities of cellulose and starch . lignin is soluble in higher extension , as reflected in the color change of the solvent . example of screening of lttms dl malic acid , was provided by merck chemicals (≧ 99 %), lactic acid was obtained at pharmaceutical grade from purac biochem bv , and the other chemicals were obtained from sigma - aldrich (≧ 98 %). choline chloride and lactic acid ( both hygroscopic ) were dried under vacuum before use . the required preparation temperature for the lttms depends on the lowest melting point of the constituents . both hydrogen bond donor and acceptor starting materials were added to a closed 25 ml flask provided with magnetic stirring , and which temperature was controlled by using a thermostatic oil bath set to 60 - 130 degrees celsius . both starting components where homogeneously mixed into the flask and set into the heating bath until the melting of the mixture provides enough liquid to initiate the magnetic stirring . the melting point of the mixture is always found to be much lower than the melting point of the starting materials . the better the mixing of the solid starting materials the less heating is required for melting . once the mixture forms a transparent liquid , it is cooled down and a tga analysis was carried out to check the thermal stability . the water content was measured with karl - fisher titration method on a metrohm 870 kf titrino plus . the glass transitions and melting points were analyzed by a q20 ta instruments differential scanning calorimeter ( dsc ). lignin ( 96 %, alkali lignin , low sulfonate content ), cellulose ( 90 %) and starch ( practical grade ) were purchased from sigma - aldrich . more details about the lignin used in these experiments are provided in table 4 . the solubility of the biopolymers was determined by cloud point method . vials containing 2 g of solvent were placed into an oil bath at constant temperature : 60 degrees celsius for less viscous mixtures and 80 or 100 degrees celsius for the ones showing higher viscosities . consecutive additions of 0 . 2 - 1 mg of solute were made while keeping vigorous stirring . once turbidity was noticeable , the samples were equilibrated for 24 hours . if the sample did not become clear , cloud point was registered ; below 0 . 1 wt % no solubility was considered . recoverability of the solvent after lignin subtraction is desirable ; therefore a screening for suitable anti - solvents was done . water and ethanol are likely to precipitate the lignin from the lttms . first , the miscibility of lttm with water and ethanol ( mixtures ) was tested , finding complete miscibility . then ethanol , water and their combinations ( 3 : 7 , 1 : 1 , 7 : 3 [ v : v ]) were added to saturated solutions of lc2 : 1 and lignin . precipitation occurred and after centrifuging the supernatant became colored but transparent . to get an overview of which antisolvent is working the best for each lttm and in which ratios , more experiments need to be done . solvents with strong hydrogen bonding are likely to separate from non hydrogen bonding solvents . for this reason lc2 : 1 and acetone were mixed . direct precipitation of the lttm occurred when adding lc2 : 1 to acetone , while a two liquid phase system appeared when adding acetone to pure lc2 : 1 . this implies that the pure lttm or its starting materials in principle are able to be ( partially ) recovered . as shown in fig6 , after dissolving the lignin from the biomass using a suitable lttm or des , the remaining solids are separated off with a suitable solid - liquid separation step ( such as filtration or sedimentation / centrifugation ). these solids are mainly long fibers of cellulose and hemicellulose ( a so - called ( hemi ) cellulose enriched phase ). these solids have value themselves as pulp , or could be further hydrolyzed to fermentable sugars . any traces of adhering lttm or des should not be a problem . in fact , lttms or dess can even act as solvents for both catalytic and enzymatic hydrolysis of the ( hemi ) cellulose enriched phase considering their acid character and the fact that they can be designed to be an enzyme - tolerant medium , which allows the development of a one - pot process where both deconstruction and enzymatic hydrolysis occur . the dissolved lignin can be recovered from the lttm or des phase by water addition . lignin is by definition not soluble in water , and therefore water acts as an anti - solvent for lignin . this means that lignin will precipitate out of the lttm or des solution by water addition . another solid - liquid separation step ( such filtration or sedimentation / centrifugation ) is needed to remove the solid lignin from the remaining des - water mixture or lttm - water mixture . this lignin has higher quality than the lignin from conventional pulping processes , and could be valorized in different ways . it can not only be thermally recycled ( the conventional way to get rid of the lignin ), but be converted to more valuable chemicals such as phenols . the remaining ( lttm or des )- water mixture can be disposed ( both water and des are generally cheap ). but , the process can even be more economical if the des is recycled in an energy - efficient way . there are several options available . evaporation of the water is a possibility if the amount of water to be distilled off is small . otherwise , the lttm or des can be recovered from the water by adding a nonhydrogen bonding solvent . as an example , acetone was proven to work as an anti - solvent for des recoverability . the lttm or des precipitated and could be separated off as a solid . after heating , the lttm or des turned liquid and could be reused . the only energy requirement was then the separation of acetone from water by distillation , allowing also for the water and the acetone to be reused . as a system the invention can be embodied with the following devices to perform the process steps : an extractor for lignin extraction / dissolution from biomass with an lttm or des . a filter or centrifuge for cellulose removal . a mixer for water addition to the des - lignin mixture . a filter or centrifuge for precipitated lignin removal . either an evaporator or distillation column for water removal from lttm or des , or ( i ) a mixer for acetone addition to ( lttm or des )- water mixture , ( ii ) a filter or centrifuge for lttm or des removal as solid , and ( iii ) a heater for lttm or des regeneration . an evaporator or distillation column for acetone removal from water . the present invention uses low transition temperature mixtures ( lttms ) and deep eutectic solvents ( dess ) in the process to dissolve lignin from a biomass . ionic liquids have been used as solvents in previous works but they are different in many ways . for example , ils dissolve all the biomass ( e . g . wood is completely dissolved , both the lignin and cellulose ). after the use of ils the process involves precipitation of cellulose so it can be filtered off . the lignin is then recovered by acetone evaporation ( not by precipitation followed by a solid - liquid separation step as taught in this invention ). in summary , prior art teachings using ils are different from the teachings of this invention when a lttm or des is used . for example : different solvents are used ( ils versus des or lttms ); there are different solubilities , i . e . cellulose dissolves when using ils , whereas it does not dissolve when using a des or lttm ); there is a different order of recovery ( first the lignin when using the process with lttms or dess or first the cellulose when using the process with ils ) there is a different way of recovering lignin ( by precipitation / solid - 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