PROCESS FOR THE ISOLATION OF MONOSACCHARIDES
20170342511 · 2017-11-30
Assignee
Inventors
Cpc classification
C13K13/007
CHEMISTRY; METALLURGY
International classification
Abstract
A process for the separation of a monosaccharide from an aqueous solution comprising the monosaccharide, in particular a hydrolysate of a polysaccharide containing biomass, characterized in that a) the solution comprises one or more salts or mineral acids, b) the solution is contacted with a zeolite adsorbent preferably of BEA zeotype for adsorbing the monosaccharide on the zeolite, c) the zeolite with the adsorbed monosaccharide is separated from the solution, d) the monosaccharide is separated from the zeolite absorbent. The process in a chromatographic process, in particular SMB, produces relatively highly concentrated and pure monosaccharide solution in water.
Claims
1. A process for the separation of a monosaccharide from an aqueous solution comprising the monosaccharide and one or more salts and/or mineral acids characterized in that a. the solution is contacted with a zeolite adsorbent for adsorbing the monosaccharide on the zeolite, b. one or more salts and/or mineral acids present in the solution improve the adsorbtion process, c. the zeolite with the adsorbed monosaccharide is separated from the solution, d. the monosaccharide is separated from the zeolite absorbent.
2. The process according to claim 1, wherein the zeolite is characterised by pore opening with at least 12 T atoms, preferably having a cavity size of less than 1 nm and preferably having a high porosity defined as BET surface area more than 400, preferably more than 450, 500 or even 550 m.sup.2/g and preferably has a silica to alumina ratio between 5 and infinite, more preferably between 10 and 150, most preferably between 10 and 50.
3. The process according to anyone of claims 1-2, wherein the zeolite is selected from the group of BEA, MOR or FAU zeolites, preferably the zeolite is BEA zeolite.
4. The process according to anyone of claims 1-3, wherein the salt comprises a cation selected from the group of Na, Li, Ca, Zn, Cu, Fe, Mg and an anion, preferably chloride and the mineral acid preferably is HCl or H.sub.2SO.sub.4.
5. The process according to anyone of claims 1-4, wherein the amount of salt or mineral acid in the aqueous solution is between 1 and 70 wt %, preferably between 5 and 65 wt %, more preferably between 10, 15, 20, 25, 30 or 35 wt % and 65 wt % relative to the total amount of water, salt and mineral acid and, in particular for monovalent cations, most preferably close to the saturation concentration.
6. The process according to anyone of claims 1-5 wherein aqueous solution comprises a salt chosen from the group of ZnCl.sub.2, CaCl.sub.2, LiCl or mixtures thereof, preferably substantially only ZnCl.sub.2, wherein preferably the amount of ZnCl.sub.2, in the aqueous solvent is between 30 and 70 wt %, preferably 40-60 wt % and most preferably 45-55 wt % relative to the total amount of water and salt.
7. The process according to anyone of claims 1-6, wherein the aqueous solution is a hydrolysate of a polysaccharide containing bio-mass.
8. The process according to anyone of claims 1-7, wherein the aqueous solution comprises less than 30, preferably less than 25, 20, 15, 10 or 5 wt % of mono-saccharide derived side products, in particular polyols or anhydro-saccharides and preferably the amount of monosaccharide in the aqueous solution relative to the total amount of polysaccharide hydrolysate (i.e. only saccharide components; not including water and salt) is at least 50 wt %.
9. The process according to anyone of claims 7-8, wherein the aqueous solution is obtained by a process for the conversion of a polysaccharide containing bio-mass, preferably ligno-cellulosic bio-mass, wherein the polysaccharide containing biomass is contacted with an inorganic molten salt hydrate and preferably also a mineral acid and the polysaccharide is dissolved and hydrolysed in the inorganic molten salt hydrate.
10. The process according to claims 7-9 wherein the inorganic molten salt hydrate is chosen from the group of ZnCl.sub.2, CaCl.sub.2, LiCl hydrates or mixtures thereof, preferably at least 60% of the salt in the inorganic molten salt hydrate is ZnCl.sub.2 and most preferably the inorganic molten salt hydrate substantially consists of ZnCl.sub.2 hydrate.
11. The process according to claims 7-10 wherein hemicellulose is selectively hydrolysed in molten ZnCl.sub.2 hydrate wherein the ZnCl.sub.2 salt is present in an amount between 30 and 50 wt %, preferably in presence of a mineral acid, preferably HCl, followed by separation of monosaccharides xylose, glucose and arabinose or wherein cellulose is hydrolysed in molten ZnCl.sub.2 hydrate wherein the ZnCl.sub.2 salt is present in an amount between 62 and 78, more preferably between 65 and 75 and most preferably between 67.5 and 72.5 wt %, preferably in presence of a mineral acid, preferably HCl, followed by separation of monosaccharide glucose or wherein cellulose and hemicellulose are both simultaneously hydrolysed in molten ZnCl.sub.2 hydrate wherein the ZnCl.sub.2 salt is present in an amount between 62 and 78, more preferably between 65 and 75 and most preferably between 67.5 and 72.5 wt % relative to the total amount of water and salt, preferably in presence of a mineral acid, preferably HCl, followed by separation of obtained monosaccharides.
12. The process according to claims 7-11 wherein after the hydrolisation step and before contacting with the zeolite adsorbent, the obtained hydrolysate is diluted to reduce the ZnCl.sub.2 content such that the aqueous solution comprises between 30 and 70 wt %, preferably 40-60 wt % and most preferably 45-55 wt % ZnCl.sub.2 relative to the total amount of water and salt.
13. The process according to anyone of claims 7-12 wherein oligomeric polysaccharides are separated by precipitation with an anti-solvent before or after the separation of the monosaccharides.
14. The process according to anyone of claims 1-13 wherein separation is done in a chromatographic process wherein the zeolite adsorbent is the stationary phase and the eluent is water, preferably at temperatures between 20 and 120° C., wherein the chromatographic process preferably is batch, recycling batch, multi-column or simulated-moving-bed-type process.
15. The process according to claim 14 resulting in an extract comprising between 3 and 40 wt % of the monosaccharide in water and preferably with a yield of preferably more than 90, preferably 95 wt % and a monosaccharide purity of at least 90, preferably 95 wt %.
Description
EXAMPLE 1
Glucose and Cellobiose Adsorption on Various Zeolites
[0045] Various sorbents were added in a weight ratio of 1:10 to a solution (=feed solution) containing 6 wt % Glucose, 2 wt % Cellobiose, 50 wt % ZnCl.sub.2 and 42 wt % water. The samples were shaken regularly and left standing for 24 h at room temperature. The fraction of glucose and cellobiose remaining in solution after contact with the sorbent (xw,Fin) was measured using Agilent Infinity HPLC equipped with RID and UV-VIS detectors using a Biorad Aminex HPX-87H Column. The Glucose and Cellobiose loadings (q) were calculated from the composition of the feed solution (xw,Feed), the solution after contact with the sorbent (xw,Fin), solution mass (msol) and sorbent mass (msorb) added:
[0046] Note that the volume of the liquid phase is assumed to be constant. In case of preferential water adsorption, the weight fraction of ZnCl.sub.2 and sugars could increase and the calculated loading becomes negative.
[0047] Note that due to the high ZnCl.sub.2 concentration it is difficult to calculate the ZnCl.sub.2 loading if this loading is very low because small errors in the concentration can lead to large errors in the calculated loading (xw,Feed˜xw,Fin). These adsorption equilibrium experiments therefore reveal the capacity for the sorbent for the sugars, but is a poor indication of the ZnCl.sub.2 co-adsorption. The ZnCl.sub.2 loading is not reported for this reason.
[0048] The results of the Adsorption equilibrium screening of different sorbents for the ZnCl.sub.2/Glucose/Cellobiose system (model for a cellulose hydrolysate) are presented in table 3.
TABLE-US-00003 TABLE 3 Loading, g/g sorbent Zeotype SAR Cellobiose Glucose CP811C-300 BEA 300 0.001 0.029 CP-814C BEA 38 0.003 0.057 CP-814E BEA 25 0.006 0.055 RT-12/015A MFI 26 −0.001 −0.002 RT-12/015C FAU 5 0.003 0.011 RT13-016C MFI 41 −0.002 −0.001 RT13/016A BEA 38 0.009 0.056 RT13/016B FAU 80 0.012 −0.003 CBV-28014 MFI 280 −0.001 0.001 CBV-400 FAU 5.1 0.002 0.017 PP1519 MOR 0.008 0.026 MP2101 MOR 0.003 0.014 AM1787 BEA 38 0.006 0.058 AM1291 FER 0.000 0.000 CBV90A MOR 90 −0.001 0.015
[0049] The results show that zeolite BEA yields the highest Glucose loading. From the other zeolytes that were studied only MOR and FAU showed some Glucose adsorption, but the loadings are low and zeolite MFI and FER do not significantly adsorb.
[0050] Without wishing to be bound by theory, it is assumed that MFI and FER do not adsorb because of their pore size: the 10-membered-window zeolites have apparently too narrow pores for Glucose to access. The 12-membered-window zeolites BEA, FAU and MOR are accessible. Interestingly, Cellobiose adsorption is low, but most significant in FAU, which has the largest cavity. Moreover, this is zeolite shows Cellobiose and Glucose adsorption selectivity. This could be an indication that pore size selectivity plays a role: FAU has a large cavity in which Cellobiose nicely fits, but is too big for Glucose and MOR and BEA which have smaller cavities with a size large enough able to adsorb glucose, but too small to adsorb Cellobiose. The lower Glucose loading of MOR as compared to BEA may be explained from its lower porosity and lower BET area.
[0051] The BEA and MOR adsorption data suggest that a too high SAR (high hydrophobicity) is not preferred since it leads to a lower Glucose loading. The MOR data also indicate a maximum Glucose loading at intermediate SAR. An explanation can be that at low SAR (high hydrophilicity) water adsorption is dominant and inhibiting Glucose adsorption.
EXAMPLE 2
Xylose Adsorbtion on Various Zeolites
[0052] In this experiment an aqueous solution of xylose was prepared as a model for a hemicellulose hydrolysate. The aqueous solution contains 6 wt % Xylose, 1.5 wt % Acetic Acid, 50 wt % ZnCl.sub.2 and 42.5 wt % water. The adsorption equilibrium experiments are executed according to the procedure as described in Example 1. The results of the sorbent screening test are listed in Table 4.
TABLE-US-00004 TABLE 4 Sorbent screening results for a model Hemicellulose hydrolysate. Loading, g/g sorbent Acetic Sorbent Zeotype SAR Xylose acid CP811C-300 BEA 300 0.015 0.052 CP-814C BEA 38 0.035 0.043 CP-814E BEA 25 0.038 0.039 RT-12/015A MFI 26 0.004 0.057 RT-12/015C FAU 5 0.011 0.028 RT13/016A BEA 38 0.034 0.050 RT13/016B FAU 80 0.001 0.028 RT13-016C MFI 41 0.006 0.064 CBV-28014 MFI 280 0.000 0.115 CBV-400 FAU 5.1 0.016 0.044 PP1519 MOR 0.020 0.024 MP2101 MOR 0.004 0.004 AM1787 BEA 38 0.038 0.041 AM1291 FER −0.001 0.034 CBV90A MOR 90 0.011 0.053
[0053] This table shows that only BEA yields Xylose loading of more than 0.03 g/g sorbent. Acetic Acid has a lower concentration in the solution compared to Xylose, but it is clearly more strongly adsorbed. Acetic Acid can be adsorbed well with all zeotypes. A higher SAR (more hydrophobic sorbent) appears to promote adsorption of acetic acid, but this is not critical.
[0054] The adsorption results show that zeolites can adsorb Xylose similarly as found for Glucose in Example 1. Also here the 10-membered pore zeolites (MFI and FER) do not show significant Xylose adsorption. MOR, FAU and BEA do show adsorption and BEA shows a superior loading compared to MOR and FAU. The adsorption of Xylose on FAU appears higher compared to Glucose. The MOR, FAU and BEA data suggest that an intermediate SAR (about 10-50) yields the highest Xylose loading.
EXAMPLE 3
[0055] An adsorption isotherm of Glucose on RT13/016A (BEA) was measured in an aqueous and in a 50% ZnCl.sub.2 solution at room temperature (FIG. 1). For details on these adsorption equilibrium measurements and calculation methods see Example 1.
[0056] This example demonstrates that Glucose adsorption on RT13/016A (BEA) follows a Langmuir type isotherm and that the adsorption is strongly enhanced by the presence of 50% ZnCl.sub.2.
EXAMPLE 4
[0057] Aqueous solutions with varying amount of ZnCl.sub.2 were prepared as model compound for a hydrolysate of a cellulose containing biomass which is dissolved and hydrolised in molten salt hydrate ZnCl.sub.2.
[0058] Adsorption data of Glucose on zeolite BEA (‘Microspheres’) from solutions containing 8% w Glucose, 0 to 70 wt % ZnCl.sub.2 and 1 wt % HCl is shown in Table 5. The same method as described in Example 1 is used.
TABLE-US-00005 TABLE 5 Glucose loading on BEA as a function of ZnCl.sub.2 content with and without addition of 1% HCl. ZnCl.sub.2 mass ZnCl.sub.2 percentage in Glucose Loading mass percentage solvent*** with HCl No HCl 0 0 0.008 0.022 5 5 0.009 0.020 10 11 0.020 0.027 30 33 0.030 0.053 40 43 0.067 45 49 0.073 50 54 0.044 0.061 55 60 0.059 60 65 0.046 70 76 0.015 −0.003 *Solvent is considered as ZnCl.sub.2 and water, excluding sugars and HCl
**Note that in all other cases in the examples the mass fractions or percentages are expressed as part of the solution, i.e. including the sugars, HCl and other components.
[0059] Aqueous solutions with varying amount of NaCl were prepared. The same method as described in Example 1 is used to determine adsorption data of Glucose on zeolite BEA (‘Microspheres’) from solutions containing 8% w Glucose, 0-25% w NaCl, and no HCl. The results are shown in Table 6.
TABLE-US-00006 TABLE 6 Glucose loading on ‘Microspheres’ (BEA) as a function of NaCl content. NaCl mass Glucose fraction loading 0 0.021 5 0.026 10 0.048 15 0.045 20 0.055 24 0.066
[0060] The examples show that with increasing ZnCl.sub.2 content the Glucose loading first increases, has a maximum value around 45 wt % and then decrease strongly to very low loadings. With increasing NaCl a continuously increasing Glucose loading is found. The highest NaCl concentration was close to its solubility (saturation) limit.
[0061] The presence of 1% HCl appears to have a significant negative effect on the Glucose loading and in view of the separation it is therefore not preferred to have mineral acid present in the aqueous solution. Although the data also show that it is possible to achieve separation in the presence of an acid, the process of the invention is particularly useful in a process wherein the polysaccharide is hydrolised in the substantial absence of mineral acid.
[0062] Without wishing to be bound by theory it is assumed that ZnCl.sub.2 shows a decrease in Glucose loading at concentration higher than 45 wt % due to the fact that with increasing ZnCl.sub.2 content the ion distribution in the solution shifts from C.sup.1− and Zn.sup.2+ to multi-ion complexes like ZnCl.sub.3.sup.− and ZnCl.sub.4.sup.2− and less ions and less effective ions are available to promote adsorption.
EXAMPLE 5
[0063] As described in more detail in Example 1, adsorption equilibrium data of Glucose was measured on zeolite ‘Microspheres’ BEA with different types of salts. The initial Glucose content was always 8 wt %. The results are shown in Table 7. A reference measurement without salt is performed (indicated as salt n.a.: non available). The table also shows the Ionic Strength of the solution, which can be calculated from the ion molality (b) and charge number (z) of all species in the solution:
TABLE-US-00007 TABLE 7 Effect of different salts on the Glucose loading on ‘Microspheres’ (zeolite BEA) Glucose loading, Salt type Salt content, % w Ionic strength, M g/g zeolite n.a. n.a. 0.00 0.021 ZnCl.sub.2 10.0 5.24 0.027 ZnCl.sub.2 50.0 26.20 0.063 NaCl 10.0 2.09 0.048 NaCl 20.0 4.75 0.055 MgCl.sub.2 10.0 3.84 0.034 MgCl.sub.2 25.0 11.75 0.081 CaCl.sub.2 15.0 5.27 0.044 CaCl.sub.2 30.0 13.08 0.072 CuCl.sub.2 15.0 4.35 0.024 CuCl.sub.2 30.0 10.80 0.050 BMIM—Cl* 30.0 2.77 −0.014 BMIM—Cl 50.0 6.82 −0.010 HCl 5.0 1.58 0.009 HCl 10.0 3.34 0.025 H.sub.2SO.sub.4 5.0 1.76 0.004 H.sub.2SO.sub.4 20.0 8.50 0.028 FeCl.sub.2 15.0 4.61 0.043 FeCl.sub.2 30.0 11.45 0.058 Ca(NO.sub.3).sub.2 20.0 2.54 −0.008 Ca(NO.sub.3).sub.2 40.0 7.03 0.000 MgSO.sub.4 7.5 2.95 −0.008 MgSO.sub.4 15.0 6.47 −0.005 NaI 25.0 2.49 0.001 NaI 50.0 7.94 −0.009 NaNO.sub.3 17.5 2.76 0.007 NaNO.sub.3 35.0 7.22 −0.001 Na.sub.2CO.sub.3 7.5 1.26 −0.003 Na.sub.2CO.sub.3 15.0 2.76 0.022 NH.sub.4Cl 10.0 2.28 0.009 NH.sub.4Cl 20.0 5.19 −0.001 *BMIM—Cl = 1-Butyl-3-methylimidazolium Chloride
[0064] It is clear that the Glucose adsorption is increased by many different salts and is not specific for ZnCl.sub.2 or NaCl. However, for many salts also a reduced Glucose adsorption is found.
[0065] In Table 8 the effect of the different salts on the glucose loading are compared at similar Ionic strength (for a type of ion with different counter ions)
TABLE-US-00008 TABLE 8 Order in adsorption effect for different ions. Ion Order in loading increasing effect of the counter ion Na.sup.+ Cl.sup.− > CO.sub.3.sup.2− > NO.sub.3.sup.− > I.sup.− Mg.sup.2+ Cl.sup.− > SO.sub.4.sup.2− Cl.sup.− Na.sup.+ > Mg.sup.2+, Ca.sup.2+, Fe.sup.2+ > Cu.sup.2+, H.sup.+, Zn.sup.2+ >> NH.sup.4+, BMIM SO.sub.4.sup.2− H.sup.+ > Mg.sup.2+
[0066] It appears that Na+ is better than Zn.sup.2+, Ca.sup.2+ and Mg.sup.2+ and halogenides, in particular Cl are best in increasing glucose loading. It is envisaged that adding monovalent cation salts can further improve the loading increasing effect beyond the maximum effect of bivalent cations like Zn.sup.2+.
EXAMPLE 6
[0067] As described in more detail in Example 1, adsorption equilibrium data were measured on ‘Microspheres’ BEA with different sugars and acetic acid in an aqueous and 50% w ZnCl.sub.2 solution. The initial content of the organic component was always 8% w. The results are shown in Table 9.
TABLE-US-00009 TABLE 9 Loading of Sugars and Acetic Acid on BEA in water and 50% ZnCl.sub.2 solution. Component loading, g/g sorbent Water 50% ZnCl.sub.2 Arabinose 0.049 0.069 Xylose 0.034 0.072 Fructose 0.029 0.073 Glucose 0.022 0.061 Cellobiose 0.017 0.017 Sucrose −0.008 0.002 Acetic Acid 0.051 0.096
[0068] The monosugars (Glucose, Xylose, Arabinose, Fructose) have a relative low loading in the presence of water, but the loading strongly increases when 50% ZnCl.sub.2 is present in the solution. Clearly a positive effect of ZnCl.sub.2 on 5 and 6 carbon-membered sugars is found. The studied sugar dimers (Sucrose, Cellobiose) have a low loading both in water and in a 50% ZnCl.sub.2 solution. The Acetic Acid loading is also strongly increased by the presence of ZnCl.sub.2.
EXAMPLE 7
[0069] 3 Columns with 1 cm diameter were loaded with Microspheres (BEA) to end up with a total column length of 2.55 m. For 5 minutes a synthetic feed representing a cellulose hydrolysate (50% ZnCl.sub.2, 2% Cellobiose, 6% w Glucose) was injected and eluted with water. The flow was in all steps 5 ml min−1 and the temperature was 20° C. The product fractions collected at the column exit were analyzed in the HPLC to calculate the concentrations. A plot of the concentrations as a function of the elution volume is shown in FIG. 2.
[0070] This Example demonstrates that Glucose can be separated from both ZnCl.sub.2 and Cellobiose by column chromatography using zeolite BEA (Microspheres). Moreover, separation of cellobiose from ZnCl.sub.2 can be done, albeit much more difficult than Glucose.
EXAMPLE 8
[0071] A solution containing 30% ZnCl.sub.2, 70% water and 0.4 M HCl was prepared. Dried bagasse was contacted with this solution in a mass ratio of 1:10. This mixture was heated to 90° C. for 90 minutes. After the reaction, this mixture was filtered over a 50 micron filter. Then, the filtrate was contacted with fresh bagasse for for 90 minutes at 90° C. After the reaction, this mixture was filtered over a 50 micron filter. The remaining solid was washed thoroughly with water and dried producing a lignocellulosic residue. HCl was removed from the filtered liquid by addition of ZnO and stirring overnight. The liquid was concentrated by water evaporation in a rotavapor up to a ZnCl.sub.2 content of about 50% w. This hydrolysate product was filtered over a 0.2 micron Teflon membrane filter in a Buchner funnel and 16 bed volumes were passed over a column filled with Amberlite XAD.sub.4 at 1 bed volume per hour to remove a large part of the so-called Acid Soluble Lignin (ASL). This treated hemicellulose hydrolysate had the following composition: 45% ZnCl.sub.2, 0.66% Acetic Acid, 4.33% w Xylose, 0.341% Oligomers, 0.42% Glucose, 0.437% Arabinose, 0.054% Acid Soluble Lignin (ASL) and traces of furfural. Note that ASL is measured by UV-vis at 240 nm. This hydrolysate was used in a column experiment as described Example 7. FIG. 3 shows that Xylose can be separated together with Glucose, Arabinose and Acetic from ZnCl.sub.2 and oligomers by column chromatography using zeolite BEA (Microspheres). Part of the oligomer fraction was more strongly adsorbed and was after some time desorbed with a 50% MeOH/water mixture. A large part of the ASL fraction remains with the ZnCl.sub.2/oligomer fraction and part of the ASL is relatively strongly adsorbed and requires a 50% MeOH/water mixture to be desorbed.
EXAMPLE 9
[0072] A break through column experiment was carried out as described Example 7 with the following differences: 1) the injection time was 45 minutes 2) the sorbent was RT13/016A. A plot of the concentrations as a function of the elution volume is shown in FIG. 4.
[0073] This example confirms the separation of Glucose from both ZnCl.sub.2 and Cellobiose and more particularly shows that when the Glucose is separated from the ZnCl.sub.2, its separation becomes more difficult because the Glucose loading in the absence of ZnCl.sub.2 is much lower. Now water acts actually as a desorbent for Glucose, leading to a strongly concentrated Glucose peak. For this reason full peak separation of Glucose and ZnCl.sub.2 is difficult and the choice of technology to perform this chromatographic step is very important. Simulated Moving Bed (SMB) technology, for example, would be very suitable to perform this separation since people skilled in the art know that full peak separation on the column is with this technology not required to work at high glucose purity and yield. This is further demonstrated in Example 11. An advantage of the strong desorption of Glucose is that very concentrated product streams can be obtained, whereas typically in chromatography product streams are diluted compared to the original feed.
EXAMPLE 10
[0074] The lignocellulosic residue prepared in example 8 is contacted with a solution of 70% w ZnCl.sub.2 and 0.4 M HCl for 90 minutes at 80° C. After the reaction, this mixture is diluted with water to 50% w ZnCl.sub.2 and filtered over a 50 micron filter.
[0075] This filtered hydrolysate product was further filtered over a 0.2 micron Teflon membrane filter in a Buchner funnel and 5 L was fed to a 250 ml column filled with Amberlite XAD7HP at 5 ml min−1 to remove a large part of the so-called Acid Soluble Lignin (ASL). The HCl was neutralized by addition of ZnO and stirring the solution overnight at room temperature.
[0076] From HPLC analysis (Biorad Aminex HPX 87H) the following composition was determined of the feed: 47.3% ZnCl.sub.2, 1.7% Oligomers (including Cellobiose), 3.4% Glucose, 0.34% Xylose, 0.017% Arabinose, 0.046% Anhydroglucose and 0.008% Acetic Acid. HMF and furfural were present only in very low concentrations (<0.1%). The solution also contains Acid Soluble Lignin (0.023%) and is light brownish of colour.
[0077] A column experiment was carried out as described Example 7, with the following differences: 1) The injected feed was prepared starting from sugar cane bagasse as described above, 2) 30 minutes after the feed injection a 50%/50% MeOH/water was fed to the column. A plot of the concentrations as a function of the elution volume is shown in FIG. 5.
[0078] The separation of mono-sugars and acetic acid from ZnCl.sub.2 and cellobiose is confirmed for a real hydrolysate sample. Anhydro-glusose is much stronger adsorbed than the other sugars and can be effectively separated by using an organic desorbent (e.g. 50% MeOH in water in this case) to desorb the anhydro-glucose. The ASL is partly eluted with water, but the largest part is retained on the column and is removed by eluting with 50% MeOH. Organic residues accumulating on the column, like part of the ASL, could be removed by elution with organic solvent like acetone. In case of an SMB configuration an extra regeneration zone can be added. Also using an eluent containing a certain level of organic solvent could be used to prevent accumulation of strongly adsorbing components. People skilled in the art will realize that regeneration will be more efficient at higher temperatures.
EXAMPLE 11
[0079] The separation of a mixture of 50% ZnCl.sub.2, 6% Glucose and 2% w Cellobiose was studied in SMB configuration. The SMB setup was custom made by Knauer/Separations. A schematic drawing is given in FIG. 6.
[0080] The SMB configuration consists of 8 columns (0.01×0.85 cm each) divided in 4 zones in a 2-2-2-2 configuration. 4 pumps control the flows in each zone. To simulate the bed movement, the liquid inlet and outlet points are switched in time by 16 7-(6/1)-port valves. The columns were loaded with ‘Microspheres’ and the system was operated at 20° C. In the current experiment the system is operated in open-loop configuration (FIG. 6). The Feed, Extract, Raffinate, Eluent and Waste flows were set to 0.84, 1.92, 2.0, 7.0 and 3.92 ml min−1, respectively. The valve switching time was set to 11.22 min−1. The waste stream contained only traces of the products (<0.01% w).
[0081] The yield (Y) and purity (P) in the different product flows (f, f=extract or raffinate) were calculated based on the extract and raffinate volumetric flows (F), density (ρ) and compositions (in weight fractions: xw) according to:
[0082] Note that in the purity calculation water is excluded.
[0083] The results are summarized in Table 10. The results show that Glucose and ZnCl.sub.2 can be separated at high yield and high purity using the SMB technique. The Glucose purity is compromised mainly by the presence Cellobiose, which adsorbs more than ZnCl.sub.2.
[0084] Note that the current data are an example and should not be considered representative for an optimized system. Further experiments showed for instance that the productivity could easily increased by a factor 5 without compromising yield and purity, for example in SMB by lowering the switching time and at the same time increasing the flow rates and preferably also increasing the feed flow. Moreover, it was found that the eluent flow used to desorb the Glucose could be reduced at least by a factor 5. This resulted in an extract with more than 15% w Glucose combined with a similar sugar purity as in the current example and further optimization is possible.
TABLE-US-00010 TABLE 10 Experimental settings and results of a typical SMB experiment. Feed Eluent Extract Raffinate Flow rate, ml min.sup.−1 0.84 7.0 (3.08**) 1.92 2.0 Density, kg m.sup.−3 1614 1000 1015 1244 Glucose, % w 6 0 3.7 0.09 Cellobiose, % w 2 0 0.16 0.99 ZnCl.sub.2, % w 50 0 0.14 27.6 Glucose yield, % 97.0 3.0 Cellobiose yield, % 12.0 88.0 ZnCl.sub.2 yield, % 0.5 99.5 Glucose purity, % 92.4 Total sugar purity, %* 96.4 *Total sugar purity considers the sum of Glucose and Cellobiose as desired product. **Since the system is operated in open loop with a waste flow of 3.92 ml min.sup.−1, the effective eluent flow in a closed loop would be 3.08 ml min.sup.−1.
EXAMPLE 12
[0085] The experiment described in Example 11 was repeated at 50° C. The data are presented in FIG. 7, together with the results from Example 7, which were measured at 20° C. This example shows that increasing the temperature leads to narrower, more intense peaks with less tailing. The peak separation of Glucose/ZnCl.sub.2 decreases with increasing temperature. Glucose can still be effectively separated at higher temperatures, which is an advantage because the aqueous solution obtained by hydrolysis does not need to be cooled to room temperature.
[0086] Thus, the invention has been described by reference to certain embodiments discussed above. It will be recognized that these embodiments are susceptible to various modifications and alternative forms well known to those of skill in the art. Further modifications in addition to those described above may be made to the structures and techniques described herein without departing from the spirit and scope of the invention. Accordingly, although specific embodiments have been described, these are examples only and are not limiting upon the scope of the invention.