Classifications

• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B11/00—Electrodes; Manufacture thereof not otherwise provided for
  • C25B11/04—Electrodes; Manufacture thereof not otherwise provided for characterised by the material
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B3/00—Electrolytic production of organic compounds
  • C25B3/20—Processes
  • C25B3/23—Oxidation

Definitions

• the invention relates to a process for the preparation of vanillin, which comprises an electrolysis of an aqueous, alkaline lignin-containing suspension or solution.
• Lignin as well as lignin-containing substances such as alkali lignin, lignin sulfate or lignin sulfonate, fall as waste or by-products of wood processing into pulp.
• the total production of lignocellulosic substances is estimated at about 20 billion tons per year. Lignin thus represents a valuable raw material. Parts of this lignin are still used.
• alkali lignin which can be prepared by alkaline treatment of the black liquor obtained in papermaking, used in North America as a binder for wood-based and cellulose-based press plates, as a dispersant, for clarification of sugar solutions, stabilization of asphalt emulsions and foam stabilization.
• waste lignin is produced by combustion as an energy source, e.g. used for the pulp process.
• the biopolymer lignin is a group of three-dimensional, occurring in the cell wall of plants macromolecules, which are composed of various phenolic monomer units such as p -Cumarylalkohol, coniferyl alcohol and Sinapylalkohol. Due to its composition, it is the only significant aromatic source of nature dar. The use of this renewable natural material also does not compete with a use as food.
• Vanillin 4-hydroxy-3-methoxybenzaldehyde
• Vanillin is a synthetic flavoring agent widely used as a flavoring for foods, as a fragrance in deodorants and perfumes, and as a flavor enhancer for pharmaceuticals and vitamin supplements instead of the expensive natural vanilla.
• Vanillin is also an intermediate in the synthesis of various drugs, e.g. L-dopa, methyldopa and papaverine.
• lignin should be suitable as a starting material for the production of vanillin.
• the oxidative cleavage of lignin to vanillin and other aromatic aldehydes is therefore since the 1940s the subject of numerous investigations.
• the most commonly used conversions of lignin are the chemical oxidation with copper oxide (see JM Pepper, BW Casselman, JC Karapally, Can. J. Chem. 1967, 45, 3009-3012 ) or nitrobenzene (see B. Leopold, Acta. Chem. Scand. 1950, 4, 1523-1537 ; B.
• WO 87/03014 describes a process for the electrochemical oxidation of lignin at temperatures of preferably 170 to 190 ° C in aqueous, strongly alkaline solutions. Above all, electrodes made of copper or nickel are used as anodes.
• a complex mixture is obtained, which inter alia vanillic acid (4-hydroxy-3-methoxybenzoic acid), vanillin, 4-hydroxybenzaldehyde, 4-hydroxyacetophenone and acetovanillon (4-hydroxy-3-methoxyacetophenone) and optionally phenol, syringic acid (4 Hydroxy-3,5-dimethoxybenzoic acid) and syringaldehyde (4-hydroxy-3,5-dimethoxybenzaldehyde).
• 4-hydroxybenzoic acid is the major product.
• the selectivity to vanillin formation is low and reasonably satisfactory only at high temperatures.
• a strong corrosion of the electrode materials takes place. This corrosion is also problematic in terms of contaminating the vanillin with heavy metals.
• the high temperatures are unfavorable from an energetic point of view. However, lowering the temperature leads to a significant loss of selectivity.
• the electrolysis cell used is a circulating cell in which the lignosulfate-containing electrolyte is circulated continuously through a cylindrical electrode arrangement with a central cylindrical nickel network as the cathode and a nickel net surrounding the cathode as an anode. The selectivity problem and corrosion problems are not solved by this.
• the WO 2009/138368 describes a process for the electrolytic degradation of lignin, in which an aqueous lignin-containing electrolyte is oxidized on a diamond electrode.
• a low molecular weight product which contains about equal parts vanillin together with other hydroxybenzaldehyde derivatives such as acetovanillon or guaiacol.
• the selectivity of lignin oxidation with respect to vanillin is low.
• corrosion of the diamond electrode takes place under the reaction conditions.
• the EP 0 882 814 A1 deals with the electrochemical delignification of aqueous pulp with lignin-containing material.
• the WO 2013/021040 describes for the production of vanillin, the electrolysis of lignin-containing solutions or suspensions, being used as the anode material silver or silver-containing alloys.
• the object of the present invention is to provide a process which allows the production of vanillin from lignin or lignin-containing substances in good yields and with high selectivity with regard to vanillin formation. Furthermore, the method should be feasible under milder conditions than the methods of the prior art. The task is also to improve the corrosion problem. In particular, the vanillin is to be obtained in a form which does not preclude use as a flavoring agent.
• aqueous, alkaline lignin-containing suspension or solution is electrolyzed, wherein a base alloy is used as the anode material, which is based on Co base alloys, Fe base alloys, Cu base alloys and Ni. Base alloys is selected.
• the present invention thus relates to a process for the production of vanillin comprising electrolysis of an aqueous alkaline lignin-containing suspension or solution, using as the anode material a base alloy selected from Co-base alloys, Fe-base alloys, Cu-base alloys and Ni-base alloys is.
• the process according to the invention has a number of advantages.
• the electrode materials used lead to a significant increase in selectivity.
• This high selectivity can surprisingly be achieved even at a comparatively low temperature of up to 100 ° C.
• the anode materials used in the invention prove to be extremely resistant to the corrosive reaction conditions and, unlike the methods of the prior art, no or no appreciable corrosion takes place.
• an aqueous lignin-containing electrolyte containing lignin or a lignin-containing substance which is in the form of an aqueous suspension or solution is subjected to electrolysis under alkaline conditions.
• the oxidation of the lignin contained or the lignin derivative takes place at the anode.
• a reduction of the aqueous electrolyte e.g. with formation of hydrogen.
• one or more base alloy anodes are used as the anode material, and the base alloy is selected from Co base alloys, Fe base alloys, Cu base alloys, and Ni base alloys.
• a base alloy an alloy containing at least 50% by weight, in particular at least 55% by weight, especially at least 58% by weight, e.g. 50 to 99 wt .-%, preferably 50 to 95 wt .-%, in particular 55 to 95 wt .-%, particularly preferably 55 to 90 wt .-% and especially 58 to 90 wt .-% of the respective base metal (in the case a Co-base alloy Co, in the case of a Cu-based alloy Cu, in the case of a Ni-base alloy Ni and in the case of an Fe-based alloy Fe) and at least one further alloying constituent, the total amount of all other alloy constituents other than the base metal typically being at least 1 Wt .-%, in particular at least 5 wt .-% and especially at least 10 wt .-% is and, for example in the range of 1 to 50 wt .-%, preferably in the range of 5 to 50 wt .-%, in particular in the range
• Typical other alloying constituents are, in particular, Cu, Fe, Co, Ni, Mn, Cr, Mo, V, Nb, Ti, Ag, Pb and Zn, but also Si, C, P and S. Accordingly, base alloys which are at least one other of the aforementioned, different from the base metal alloy components.
• Ni-base alloys Ni-base alloys, Fe base alloys and Co base alloys, in particular Ni base alloys and Co base alloys.
• Ni-base alloys the total amount of Al, Si, C and S will preferably not exceed 5 wt%.
• Typical proportions of the further alloying constituents which may be contained in Ni-base alloys in a quantity significant for the alloy are given in the following Table 1: Table 1: Further alloy components of Ni-base alloys Alloy component Amount [wt%] Cu 5 to 35 Fe 0.5 to 18 Co 5 to 42 Mn 0.5 to 5 Cr 5 to 40 Not a word 5 to 35 W 0.5 to 5 V 1 to 22 Nb 1 to 20 Ti 0.5 to 7 al 0.1 to 3 Si 0.1 to 3 C 0.1 to 3 S 0.1 to 3
• the Ni base alloys of the first embodiment those containing 5 to 35% by weight, especially 10 to 30% by weight of Cu as a further alloying ingredient are particularly preferred. These alloys are referred to below as group 1.1.
• the Group 1.1 base alloys may contain one or more of the following alloying ingredients in an amount of up to 45% by weight, in particular up to 40 wt .-%: Fe, Co, Mn, Cr, Mo, W, V, Nb, Ti, Si, Al, C and S.
• the further alloying ingredient if present, in one in Table 1 given quantity.
• Ni-base alloys of group 1.1 are alloys of the EN-abbreviations NiCu30Fe (Monel 400) and NiCu30Al as well as the nickel-copper alloy of the following composition: 63% by weight Ni, 30% by weight Cu, 2% by weight. % Fe, 1.5 wt% Mn, 0.5 wt% Ti (Monel 500K).
• the Ni-base alloys of the first embodiment those which contain 5 to 40% by weight, in particular 15 to 30% by weight of Cr as a further alloying constituent are particularly preferred. These alloys are referred to below as group 1.2.
• the base alloys of group 1.2 may contain one or more of the following alloying ingredients in an amount of up to 40% by weight, in particular up to 35% by weight: Fe, Co, Mn, Cu, Mo, W, V, Nb, Ti, Si, Al, C and S.
• the further alloying ingredient, if present will be present in an amount shown in Table 1.
• the Ni-base alloys of group 1.2 particular preference is given to those which contain Mo, Nb and / or Fe as further alloying constituent, in particular in a total amount of from 1 to 30% by weight.
• Ni base alloys are alloys of the EN abbreviations NiCr19NbMo (Inconel® alloy 718) and NiCr15Fe (Inconel® alloy 600), NiCr22Mo19Fe5 (Inconel® 625), NiMo17Cr16 FeWMn (Hastelloy® C276), a Ni-Cr Fe Alloy having a nickel content of 72 to 76% by weight, a Cr content of 18 to 21% by weight, a C content of 0.08 to 0.13% by weight and an Fe content of 5 Wt .-% and a Ni-Cr-Co-Mo alloy having a nickel content of 48 to 60 wt .-%, a Cr content of 19 wt .-%, a Co content of 13.5 wt .-% and a Mo content of 4.3% by weight (Waspaloy®).
• the base alloys of group 1.3 may contain one or more of the following alloying ingredients in an amount of up to 40% by weight, in particular up to 35% by weight: Fe, Co, Mn, Cu, Cr, W, V, Nb, Ti, Si, Al, C and S.
• the further alloying ingredient, if present will be present in an amount shown in Table 1.
• those which are particularly preferred are Cr, Nb and / or Fe as a further alloying ingredient, in particular in an amount of 1 to 30 wt .-%, in total.
• Ni base alloys are alloys of the EN short names NiMo28 (Hastelloy® B and Hastelloy® B-2) and NiMo29Cr (Hastelloy® B-3).
• Ni base alloys of the first embodiment those of Groups 1.2 and 1.3 are particularly preferred in view of high stability with high selectivity.
• the total amount of Si, C and P will preferably not exceed 5 wt%.
• Typical proportions of the further alloying constituents that may be present in Co-base alloys in a quantity significant for the alloy are given in the following Table 2: Table 2: Other alloying constituents of Co base alloys Alloy component Amount [wt%] Cu 5 to 35 Fe 0.5 to 18 Ni 5 to 40 Mn 0.5 to 6 Cr 5 to 40 Not a word 1 to 35 W 0.5 to 5 V 1 to 22 Nb 1 to 20 Ti 0.5 to 8 Si 0.1 to 3 C 0.1 to 4 P 0.1 to 3
• the Co base alloys of the second embodiment particularly preferred are those containing 5 to 40% by weight, in particular 7 to 30% by weight, of Cr as a further alloying constituent. These alloys are referred to below as group 2.1.
• the base alloys of group 2.1 may contain one or more of the following alloying constituents in an amount of up to 40% by weight, in particular up to 35% by weight: Fe, Ni, Mn, Cu, Mo, W, V, Nb, Ti, Si, C and P.
• the further alloying ingredient, if present will be present in an amount shown in Table 2.
• the Co base alloys of group 2.1 particular preference is given to those which contain Mo, W and / or Fe as a further alloying constituent, in particular in a total amount of from 1 to 30% by weight.
• the total amount of Si, C and P will preferably not exceed 10% by weight.
• Typical proportions of the further alloying constituents which may be contained in Fe-based alloys in a quantity significant for the alloy are given in the following Table 3: Table 3: Further alloy constituents of Fe base alloys Alloy component Amount [wt%] Cu 1 to 18 Co 1 to 23 Ni 5 to 45 Mn 0.2 to 2 Cr 3 to 30 Not a word 1 to 30 V 1 to 22 Nb 1 to 20 Ti 0.1 to 1 Si 0.1 to 3 C 0.1 to 4 P 0.1 to 4 S 0.1 to 4
• the base alloys of group 3.1 may contain one or more of the following alloying ingredients in an amount of up to 40% by weight, in particular up to 35% by weight: Co, Ni, Mn, Cu, Mo, V, Nb, Ti, Si, C, S and P.
• the further alloying ingredient, if present will be present in an amount shown in Table 3.
• Fe base alloys of group 3.1 are chromium steels, eg X12Cr13, X6Cr17 and X20Cr13, chromium-nickel steels, eg X2CrNi12, X5CrNi18-10, X8CrNiS18-9, X2CrNi19-11, X2CrNi18-9, X10CrNi18-8, X1CrNi19-9, X2CrNiMo17-12-2, X2CrNiMo19-12, X2CrNiMo18-14-3, X2CrNiMoN18-14-3, X13CrNiMoN22-5-3, X6CrNiTi18-10, X6CrNiMoTi17-12-2, GX5CrNiMoNb19-11-2 and X15CrNiSi25-21 Chromium-molybdenum steels
• Group 3.1 Cu base alloys are nickel silver (alloy of 62 wt.% Cu, 18 wt.% Ni and 20 wt.% Zn) and cupronickel (alloy of 75 wt.% Cu and 25 wt. % Ni).
• any type of electrode known to the person skilled in the art can be used as the anode.
• This may consist entirely of the respective base alloy or be a carrier electrode having a carrier which is coated with the base alloy. Preference is given to electrodes which consist of the respective base alloy.
• the electrodes used as the anode may, for example, be electrodes in the form of expanded metals, nets or sheets.
• any electrode known to the person skilled in the art and suitable for the electrolysis of aqueous systems can be used as the cathode. Since reduction processes take place at the cathode and the lignin is oxidized at the anode, when using a heavy metal electrode such as a nickel cathode, the loading of vanillin with this heavy metal is so low that the vanillin obtained can be used without problem in the food industry. Preferably, the electrode materials exhibit a low hydrogen overvoltage.
• electrodes comprising an electrode material selected from nickel, Ni-based alloys, Co-based alloys, Fe-based alloys, Cu-based alloys, silver, Ag-based alloys, ie silver-rich alloys having a silver content of at least 50 wt .-%, RuO x TiO x mixed oxides, platinized titanium, platinum, graphite or carbon.
• the electrode material of the cathode is selected from Ni base alloys, Co base alloys, Fe base alloys, Cu base alloys, more preferably Ni base alloys, Co base alloys and Fe base alloys and especially among the base alloys of groups 1.1, 1.2, 1.3, 2.1 and 3.1.
• any type of electrode known to the person skilled in the art can be used as the cathode.
• This may consist entirely of the respective electrode material or be a carrier electrode having an electrically conductive carrier which is coated with the electrode material.
• Preference is given to electrodes which consist of the respective electrode material, in particular of one of the abovementioned base alloys, especially one of the base alloys of groups 1.1, 1.2, 1.3, 2.1 and 3.1.
• the electrodes used as the cathode may, for example, be electrodes in the form of expanded metals, nets or sheets.
• the arrangement of anode and cathode is not limited and includes, for example, arrangements of planar gratings and / or plates, which may also be arranged in the form of several, alternately poled stacks and cylindrical arrangements of cylindrically shaped networks, gratings or tubes, which also in the form of several , alternately polarized cylinder can be arranged.
• a bipolar arrangement of a plurality of electrodes an arrangement in which a rod-shaped anode is comprised by a cylindrical cathode, or an arrangement in which both the cathode and the anode consist of a wire mesh and these wire nets are superimposed and rolled up cylindrical.
• the anode and cathode are separated by a separator.
• a separator Basically, all separators commonly used in electrolysis cells are suitable as separators.
• the separator is typically a porous sheet placed between the electrodes, e.g. a grid, mesh, woven or nonwoven fabric made of an electrically nonconductive material that is inert under the electrolysis conditions, e.g. a plastic material, in particular a Teflon material or a Teflon-coated plastic material.
• any of the electrolysis cells known to those skilled in the art can be used, such as divided or undivided flow cell, capillary gap cell or plate stack cell.
• the undivided flow cell for example a flow cell with circulation, in which the electrolyte is continuously circulated past the electrodes. The process can be carried out with good success both batchwise and continuously.
• the contents of the electrolytic cell is mixed.
• any mechanical stirrer known to those skilled in the art can be used.
• the use of other mixing methods such as the use of Ultraturrax, ultrasound, jet nozzles or circulation or combinations of these measures is also preferred.
• the electrolysis voltage By applying the electrolysis voltage to the anodes and cathodes, electric current is passed through the electrolyte.
• a current density of 1000 mA / cm 2 In order to avoid side reactions such as overoxidation and oxyhydrogen gas formation, one will generally not exceed a current density of 1000 mA / cm 2 , in particular 100 mA / cm 2 .
• the current densities at which the process is carried out are generally 1 to 1000 mA / cm 2 , preferably 1 to 100 mA / cm 2 .
• the process according to the invention is particularly preferably carried out at current densities between 1 and 50 mA / cm 2 .
• the total duration of the electrolysis naturally depends on the electrolytic cell, the electrodes used and the current density. An optimum duration can be determined by the skilled person by routine tests, e.g. by sampling during electrolysis.
• the polarity can be changed at short intervals.
• the polarity reversal can take place in an interval of 30 seconds to 10 minutes, an interval of 30 seconds to 2 minutes is preferred.
• the anode and cathode are made of the same material.
• the electrolysis is carried out according to the inventive method usually at a temperature in a range of 0 to 100 ° C, preferably 50 to 95 ° C, especially 70 to 90 ° C.
• the electrolysis is generally carried out at a pressure below 2000 kPa, preferably below 1000 kPa, in particular below 150 kPa, e.g. in the range of 50 to 1000 kPa, especially 80 to 150 kPa performed. It is particularly preferred to carry out the process according to the invention at a pressure in the range of atmospheric pressure (101 ⁇ 20 kPa).
• the inventive method is carried out at a temperature in the range of 50 to 95 ° C, in particular 70 to 90 ° C and in the range of atmospheric pressure (101 ⁇ 20 kPa).
• the aqueous, lignin-containing suspension or solution generally contains 0.5 to 30 wt .-%, preferably 1 to 15 wt .-%, in particular 1 to 10 wt .-% lignin based on the total weight of the aqueous, lignin-containing suspension or solution.
• an aqueous, alkaline suspension or solution is electrolyzed to produce the vanillin.
• aqueous and alkaline lignin-containing solutions or suspensions is here and below understood an aqueous solution or suspension containing lignin or lignin derivatives, such as lignin sulfate, lignin, kraft lignin, alkali lignin or Organosolv lignin or mixtures thereof, as a lignin component and an alkaline pH, preferably at least pH 10, in particular at least pH 12 and especially at least pH 13.
• the aqueous, alkaline solution or suspension may be an aqueous solution or suspension which is obtained as a by-product in a technical process such as pulp, pulp or cellulose production, for example black liquor, and the lignin-containing wastewater streams from US Pat Sulfite process, from the sulfate process, from the Organocell or Organosolv process, from the ASAM process, from the Kraft process or from the Natural-Pulping process.
• the aqueous, alkaline solution or suspension may be an aqueous solution or suspension which is prepared by dissolving a lignin or lignin derivative in aqueous alkali or in water with addition of a base, for example lignin sulfate, lignin sulphonate, kraft lignin, Alkalignin or Organosolv lignin, or a lignin that in a technical process such as pulp, pulp or cellulose production eg lignin from black liquor, from the sulfite process, from the sulfate process, from the organocell or organosolv process, from the ASAM process, from the kraft process or from the natural pulping process.
• a base for example lignin sulfate, lignin sulphonate, kraft lignin, Alkalignin or Organosolv lignin, or a lignin that in a technical process such as pulp, pulp or cellulose production eg
• lignin-containing wastewater streams are produced. These may, if appropriate after setting an alkaline pH, be used as aqueous, lignin-containing suspension or solution in the process according to the invention.
• the effluent streams of the papermaking sulfite process often contain lignin as lignosulfonic acid. Lignosulfonic acid can be used directly in the process of the invention or first hydrolyzed alkaline.
• lignin-containing wastewater streams fall e.g. in the form of black liquor.
• organocell process which will become more important in the future because of its environmental friendliness, lignin is an organosolvLignin. Ligninsulfonkla or Organosolv lignin-containing wastewater streams and black liquor are particularly suitable as aqueous, alkaline lignin-containing suspensions or solutions for the process of the invention.
• the aqueous lignin-containing suspensions or solutions may also be prepared by dissolving or suspending at least one lignin-containing material in aqueous alkali, i. H. in an aqueous solution of a suitable base or in water with the addition of base.
• the lignin-containing material preferably contains at least 10% by weight, in particular at least 15% by weight and particularly preferably at least 20% by weight of lignin, based on the total weight of the lignin-containing material.
• the lignin-containing material is preferably selected from Kraft lignin, lignin sulfonate, oxidized lignin, Organosolv lignin or other lignin-containing residues from the paper industry or fiber production, in particular Kraft-lignin, lignin sulfonate and oxidized lignin, which is used in an electrochemical oxidation of non-oxidized lignin accrues.
• inorganic bases can be used, for example alkali metal hydroxides such as NaOH or KOH, ammonium salts such as ammonium hydroxide and alkali metal carbonates such as sodium carbonate, for example in the form of soda. Preference is given to alkali metal hydroxides, in particular NaOH and KOH.
• concentration of inorganic bases in the aqueous, lignin-containing suspension or solution should not exceed 5 mol / L and in particular 4 mol / L and is typically in the range from 0.01 to 5 mol / L and in particular in the range from 0.1 to 4 minor.
• oxidized lignin is used which originates from a previous electrolysis cycle. It has proved to be advantageous to use oxidized lignin in at least one further electrolysis cycle, preferably in at least two further electrolysis cycles and in particular in at least three further electrolysis cycles.
• An advantage of this repeated use of the oxidized lignin is that repeated vanillin can be obtained. Thus, the yield of vanillin, based on the amount of lignin originally used, significantly increased and therefore increases the efficiency of the overall process.
• the concentration of oxidation-sensitive vanillin in the electrolyte per oxidation process can be kept so low that the undesirable side reactions such as over oxidation can be effectively suppressed, while the overall yield of vanillin increases over the overall process (multiple electrolysis cycles).
• effluent streams or residues from paper and pulp production in particular black liquor or kraft lignin.
• further preferred embodiments relate to a process according to the invention in which the aqueous, alkaline lignin-containing suspension or solution is selected from wastewater streams from paper and pulp production, in particular black liquor or solutions of kraft lignin.
• the viscosity of the solution or suspension can increase greatly and the solubility of the lignin can be very low.
• a prehydrolysis of the lignin this in an aqueous alkali metal hydroxide solution heated to above 100 ° C.
• the concentration of the alkali metal hydroxide is preferably 0.5 to 5 mol / L, more preferably 1.0 to 3.5 mol / L.
• sodium hydroxide or potassium hydroxide is used.
• the lignin-containing alkali metal hydroxide solution is heated to a temperature of 150 to 250 ° C, in particular 170 to 190 ° C and stirred vigorously for 1 to 10 h, preferably for 2 to 4 h.
• the pre-hydrolyzed lignin can be separated from the alkali metal hydroxide solution prior to electrochemical oxidation. Alternatively, it is possible to carry out the electrochemical oxidation directly with the lignin-containing alkali metal hydroxide solution.
• the aqueous, alkaline lignin-containing suspension or solution may contain a conductive salt to improve the conductivity.
• a conductive salt to improve the conductivity.
• alkali metal salts such as salts of Li, Na, K or quaternary ammonium salts such as tetra (C 1 -C 6 alkyl) ammonium or tri (C 1 -C 6 alkyl) methylammonium salts.
• Suitable counterions are sulfate, hydrogensulfate, alkyl sulfates, aryl sulfates, halides, phosphates, carbonates, alkyl phosphates, alkyl carbonates, nitrates, alcoholates, tetrafluoroborate, hexafluorophosphate, perchlorate, bis-triflates and bis-triflimide.
• ionic liquids ionic liquids
• electrochemically stable ionic liquids are described in “ Ionic Liquids in Synthesis ", ed. Peter Wasserscheid, Tom Welton, Verlag Wiley-VCH 2003, Chapters 1 to 3 ,
• a metal-containing or metal-free mediator can be added to the aqueous, alkaline lignin-containing suspension or solution.
• Mediators are understood as meaning redox pairs which allow indirect electrochemical oxidation.
• the mediator is electrochemically transferred to the higher oxidation state, then acts as an oxidant and then regenerates again by electrochemical oxidation. It is therefore an indirect electrochemical oxidation of the organic compound, since the mediator is the oxidizing agent.
• the oxidation of the organic compound with the mediator in the oxidized form can be carried out in the electrolysis cell in which the mediator was converted into the oxidized form, or in one or more separate reactors ("ex-cell method"). The latter method has the advantage that any remaining traces of the organic compound to be oxidized do not interfere with the production or regeneration of the mediator.
• Suitable mediators are compounds which can be present in two oxidation states, act as oxidants in the higher oxidation state and can be regenerated electrochemically.
• salts or complexes of the following redox couples can be used as mediators: Ce (III / IV), Cr (II / III), Cr (III / VI), Ti (II / III), V (II / III), V ( III / IV), V (IV / V), Ag (I / II), AgO + / AgO -, (Cu (I / II), Sn II / IV), Co (II / III), Mn (II / (III), Mn II / IV), Os (IV / VIII) (Os III / IV), Br 2 / Br - / BrO 3, I- / I 2, I 3 + / 3 + I 2 IO / IO 4 , Fremy's salt (dipotassium nitrosodisulfonate) or organic mediators such as ABTS (2
• the method according to the invention is carried out without the addition of mediators.
• the aqueous, alkaline lignin-containing suspension or solution may further contain an inert solvent.
• Suitable solvents are polar-aprotic solvents having high electrochemical stability, such as acetonitrile, propionitrile, adiponitrile, suberonitrile, propylene carbonate, ethylene carbonate, N-methylpyrrolidone, hexamethylphosphoric triamide, dimethyl sulfoxide and dimethylpropyleneurea (DMPU).
• polar-aprotic solvents having high electrochemical stability, such as acetonitrile, propionitrile, adiponitrile, suberonitrile, propylene carbonate, ethylene carbonate, N-methylpyrrolidone, hexamethylphosphoric triamide, dimethyl sulfoxide and dimethylpropyleneurea (DMPU).
• DMPU dimethylpropyleneurea
• inert solvents are generally used in an amount of not more than 60% by weight, preferably not more than 30% by weight, in particular not more than 20% by weight, e.g. 2.5 to 30 wt .-% or 5 to 20 wt .-%, based on the total amount of the aqueous, lignin-containing suspension or solution used.
• the vanillin obtained by the process according to the invention can be obtained from the aqueous, lignin-containing solution by methods known to the person skilled in the art.
• the vanillin formed in the electrolysis can be removed or depleted by distillation or extraction of the aqueous, lignin-containing suspension or solution.
• Suitable distillative methods are distillation processes known to those skilled in the art, e.g. Vacuum distillation, distillation under a protective gas atmosphere or steam distillation.
• An advantage of vanillin separation via distillative processes is that the vanillin is not contacted with potentially hazardous organic solvents.
• Vanillin can also be removed by extraction from the aqueous, lignin-containing suspension or solution. This is particularly advantageous because the sensitive vanillin is not exposed to any further thermal stress.
• extraction processes known to those skilled in the art are suitable.
• aqueous, lignin-containing suspension or solution can be added to the extraction, for example with an organic solvent, so as to separate the vanillin formed (liquid-liquid extraction).
• organic solvents are water-immiscible organic solvents such as hydrocarbons having 5 to 12 carbon atoms such as hexane or octane, chlorinated hydrocarbons having 1 to 10 carbon atoms such as dichloromethane or chloroform, aliphatic ethers having 2 to 10 carbon atoms such as diethyl ether or diisopropyl ether, cyclic ethers or aliphatic esters such as ethyl ethanoate. Halogen-free organic solvents are preferred.
• supercritical CO 2 is suitable for this purpose.
• the lignin formed can also be removed by solid phase extraction from the aqueous lignin-containing suspension or solution.
• solid phase extractants are added to the aqueous, lignin-containing suspension or solution.
• the vanillin (vanillate) adsorbed to the extractant may then be treated with polar organic solvents known to those skilled in the art, e.g. Methanol are eluted from the solid phase.
• polar organic solvents e.g. Methanol are eluted from the solid phase.
• polar organic solvents e.g. Methanol
• a solid phase extraction analogous to the solid phase synthesis is possible.
• the vanillin is covalently bound as vanillate to the solid phase.
• the vanillin is released again by dissolving the covalent bond.
• a concentrated crude product is obtained, which can then be purified and isolated by distillation easier.
• the vanillin produced is obtained by treatment with a basic adsorbent, in particular an anion exchanger, from the aqueous, alkaline, lignin-containing solution or suspension obtained in the electrolysis (hereinafter alkaline electrolysate). won. Since in the alkaline electrolysate the vanillin is present in anionic form as vanillate, it is adsorbed by the basic adsorbent, for example an anion exchanger, and can subsequently be treated by treating the vanillate-loaded anion exchanger with acid, preferably a dilute solution of a mineral acid or an organic acid an organic solvent or in an aqueous-organic solvent mixture are released.
• a basic adsorbent in particular an anion exchanger
• the adsorbent e.g. the anion exchanger into which alkaline electrolyzate obtained in the electrolysis give, after a certain residence time, the adsorbent, e.g. Separate the anion exchanger from the alkaline electrolysate and then release the adsorbed adsorbent vanillin by treating the adsorbent with acid.
• the alkaline electrolysate is first passed through a bed of that of the adsorbent, especially a bed of anion exchanger, for example by one or more, with the adsorbent, e.g. pass an anion exchanger, packed columns and then pass through the bed of the adsorbent a dilute solution of an acid, in particular a mineral acid or an organic acid, thereby eluting the vanillin.
• Suitable adsorbents are basically all substances which have basic groups or are treated with hydroxide ions. These include alkalized activated carbons, basic aluminas, clays, basic adsorber resins, in particular anion exchangers or anion exchanger resins.
• Anionic or anion exchange resins generally have functional groups which are selected from tertiary amino groups, quaternary ammonium groups and quaternary phosphonium groups.
• the anion exchangers preferably used for this purpose are generally crosslinked, organic polymer resins which preferably have quaternary ammonium groups or phosphonium groups.
• the anion exchangers which are preferably used are preferably those from the group of crosslinked polystyrene resins in which part of the phenyl rings of the crosslinked polystyrene carry quaternary ammonium groups, for example trialkylammonium groups bonded via alkylene groups, especially trimethylammonium groups bonded via a methylene group.
• Crosslinked polyvinylpyridines in which some of the pyridine groups are present quaternized, for example as 1-alkylpyridinium, especially as 1-methylpyridinium, and crosslinked acrylate, the trialkylammonium groups bonded via alkylene groups, especially over a 1.2 -Ethandiyl- or 1,3-propanediyl bound trimethylammonium wear.
• this is Charge density, ie the number of ionic groups in accordance with the invention suitable anion exchanger in the range of 0.5 to 6 mmol / g, in particular 1 to 5 mmol / g ion exchange resin or 0.1 to 3 eq / L (molar equivalents per liter, wet).
• Suitable adsorbents are also polymers which have NC 1 -C 8 -Alkylimidazolium fate.
• the NC 1 -C 8 -Alkylimidazolium phenomenon are bound directly or via a spacer to the polymer backbone.
• Such polymers can be obtained by polymer-analogous reaction with NC 1 -C 8 -alkylimidazole compounds, for example by reacting haloalkyl groups, in particular polymers containing chlorobenzyl groups, for example copolymers of styrene and chloromethylstryrene, with NC 1 -C 8 -alkylimidazoles.
• Such polymers are known and described for example by J. Yuan, M. Antonietti, Polymer 2011, 52, 1469-1482 ; J. Huang, C. Tao, Q. An, W. Zhang, Y. Wu, X. Li, D. Shen, G. Li, Chem. Comm. 2010, 46, 967 ; R. Marcilla, J. Alberto Blazquez, J. Rodriguez, JA Pomposo, D. Mecerreyes, J. Pol. Sci. A: Pol.Chem.2004, 42, 208-212 ; Tang, H. Tang, W. Sun, M. Radosz, Y. Shen, J. Pol. Sci. A: Pol. Chem. 2005, 43, 5477-5489 ; Tang, Y. Shen, M. Radosz, W. Sun, Ind. Eng. Chem. Res. 2009, 48, 9113-9118 ,
• Diluted solutions of mineral acids such as hydrochloric acid, sulfuric acid or phosphoric acid
• organic solvents and dilute solutions of mineral acids in organic-aqueous solvent mixtures are particularly suitable for the elution of vanillin from the basic adsorbent (for example an anion exchanger).
• Diluted solutions of organic acids such as trifluoromethanesulfonic acid, acetic acid, formic acid or propionic acid, in organic solvents and dilute solutions of organic acids in organic-aqueous solvent mixtures are particularly suitable for the elution of vanillin from the basic adsorbent (for example an anion exchanger).
• Suitable organic solvents are, above all, those which are immiscible with water at 22 ° C. indefinitely or at least dissolve in water in an amount of at least 200 g / l at 22 ° C.
• These include above all dimethyl sulfoxide, acetone, C 1 -C 4 alkanols such as methanol, ethanol, isopropanol, n-propanol, 1-butanol, 2-butanol and tert-butanol, alkanediols such as glycol and 1,4-butanediol, glycerol, but also cyclic ethers such as dioxane, methyltetrahydrofuran or tetrahydrofuran, nitrogen heterocycles such as pyridine or N-methylpyrrolidine and mixtures. Preference is given to C 1 -C 4 -alkanols and especially to methanol.
• Suitable acids are especially mineral acids such as hydrochloric acid, phosphoric acid, and in particular sulfuric acid and organic acids such as methanesulfonic acid, formic acid, acetic acid and propionic acid.
• the solution of the acid preferably has a concentration of acid in the range from 0.01 to 10 mol kg -1 , in particular from 0.1 to 5 mol kg -1 .
• the eluate obtained during the elution can be subjected to further purification steps, for example crystallization, filtration or chromatography.
• the separation of vanillin can be continuous or discontinuous. It is particularly advantageous to remove the vanillin continuously or at intervals from the aqueous, lignin-containing suspension or solution during the electrochemical oxidation.
• a partial stream of the electrolysate can be discharged from the electrolysis arrangement and the lignin contained therein can be depleted, for example by continuous (solid phase) extraction or by steam distillation.
• the vanillin is continuously or at intervals isolated from the electrolysate using an anion exchanger.
• anode materials used in the process according to the invention show no appreciable corrosion under the reaction conditions, has the thus prepared Vanillin no or no significant heavy metal pollution and can therefore be used in the food industry.
• Another object of the invention is thus the use of vanillin, which was obtained by the process according to the invention, as a flavoring in the food industry.
• the aqueous, lignin-containing suspension or solution contains oxidized lignin in addition to the vanillin formed.
• the oxidized lignin can be obtained by drying the aqueous, lignin-containing solution.
• a lignin produced in this way can advantageously be used as an additive in the building material industry, for example as a cement or concrete additive.
• the stationary phase used was an HP-5 column from Agilent with a length of 30 m, a diameter of 0.25 mm and a layer thickness of 1 ⁇ m. This column is heated by means of a temperature program of 50 ° C within 10 min at 10 ° C / min to 290 ° C. This temperature is held for 15 min.
• the carrier gas used was hydrogen at a flow rate of 46.5 mL / min.
• Electrode materials electrode material composition Monel 400K 65% by weight Ni, 30% Cu, 2% by weight Fe Monel 500K 63% by weight of Ni, 30% by weight of Cu, 2% by weight of Fe, 1.5% by weight of Mn, 0.5% by weight of Ti Hastelloy® C 276 57 wt .-% Ni, 17 wt .-% Mo, 16 wt .-% Cr and Fe, W and Mn Inconel® 625 61% by weight of Ni, 9% by weight of Mo, 22% by weight of Cr, 5% by weight of Fe nickel silver 62% by weight of Cu, 18% by weight of Ni, 20% by weight of Zn cupronickel 75% by weight of Cu, 25% by weight of Ni NiCrFe 72-76 wt% Ni, 18-21 wt% Cr, 0.08-0.13 wt% C, 5 wt% Fe Stellite® 4 53% by weight of Co, 31% by weight of Cr, 14% by weight of Fe, 1.2% by weight of C Stellite®
• a standard n- hexadecane
• the electrolysis was carried out analogously to Example 1 with the following change:
• the electrolyte used was 3 M aqueous sodium hydroxide solution.
• the electrodes used were plates (thickness: 3 mm) of various Ni and Cu base alloys (see Table 5) with dimensions of 3.0 ⁇ 4.0 cm 2 , which were arranged at a distance of 0.5 cm from one another.
• the maximum cell voltage during the electrolysis was 2.9 V.
• Table 5 The results are summarized in Table 5.
• the electrolysis was carried out analogously to Example 1 with the following change:
• the electrolyte used was 3 M aqueous sodium hydroxide solution.
• the electrodes used were plates (thickness: 3 mm) of various Co base alloys (see Table 6) (dimension 3.0 ⁇ 4.0 cm 2 ) with a maximum usable electrode surface area of 9 cm 2 , spaced 0.5 cm apart were arranged to each other.
• the maximum cell voltage during the electrolysis was 2.9 V.
• Table 6 The results are summarized in Table 6.
• the electrolysis was carried out analogously to Example 1 with the following change:
• the electrolyte used was 3 M aqueous sodium hydroxide solution.
• the electrodes used were plates (thickness: 1 mm) of Co (dimension 3.0 ⁇ 4.0 cm 2 ) with a maximum usable electrode surface area of 9 cm 2 , which were arranged at a distance of 0.5 cm from each other.
• the maximum cell voltage during the electrolysis was 3.1 V.
• the maximum clamping voltage during the reaction was 4.1 V.
• Example 16 Electrolysis of a lignin solution on electrodes made of stainless steel
• the electrolysis was carried out analogously to Comparative Example 1 with the following change.
• Stainless steel nets were used as electrodes (binding: fallen body Bdg. 555, mesh: 200, Mw: 0.077, wire diameter: 0.050, material: 1.4404, manufacturer: GKD, item no .: 29370850; 3.0 ⁇ 4.0 cm 2 ).
• Example 2 The procedure was analogous to Example 1 with the following variation: 525-526 mg of kraft lignin were dissolved in 85 g of electrolyte in an undivided cell with stirring.
• the electrolyte used was 3 M aqueous sodium hydroxide solution.
• the cell was provided with an anode and a cathode, which consisted of platinum and had a maximum usable electrode surface of about 12 cm 2 .
• the maximum cell voltage during the reaction was 3.1 V.
• the yield of vanillin was 0.48 wt .-%, based on the applied power-Lginin the yield of acetovanillon 0.06 wt .-%.

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