Method for producing formic acid by CO2 hydrogenation

Abstract

The invention relates to a continuous method for producing formic acid from CO.sub.2 and extracting the formic acid using compressed CO.sub.2.

Claims

1. A method of continuously hydrogenating CO.sub.2 to formic acid, comprising the following steps: a) producing formic acid by a catalytic reaction of CO.sub.2 with hydrogen in the presence of a base, in a reaction area; b) at least partially discharging the produced formic acid using compressed CO.sub.2, which is compressed during the reaction in step a), from the reaction area of step (a); and c) releasing the formic acid while removing the CO.sub.2 from step (b); wherein the base is an amine bonded to a fixed carrier.

2. The method of claim 1, wherein the CO.sub.2 is available in a compressed state during the reaction in step (a).

3. The method of claim 1, wherein the base in step (a) comprises an ionic liquid.

4. The method of claim 3, wherein the ionic liquid is imidazolines, quaternary ammonium salts, quaternary phosphonium salts or mixtures thereof.

5. The method of claim 1, wherein the base in step (a) is a high molecular-weight amine.

6. The method of claim 1, wherein the hydrogenation in step (a) takes place in the presence of a transition metal catalyst.

7. The method of claim 1, wherein at least step (a) is carried out with a CO.sub.2 pressure of 10 bar.

8. The method of claim 1, wherein at least a part of the CO.sub.2 extracted in step (c) is fed back in step (a) or (b).

9. A method for hydrogenation of CO.sub.2 to formic acid, comprising the following steps: a) producing formic acid by a catalytic reaction of CO.sub.2 with hydrogen in the presence of a base bonded to a fixed carrier, in a reaction area, wherein the base is an amine; b) at least partially discharging the produced formic acid using compressed CO.sub.2, which is compressed during the reaction in step a), from the reaction area of step (a); and c) releasing the formic acid while removing the CO.sub.2 from step (b).

10. The method of claim 9, wherein the CO.sub.2 is available in compressed state during the reaction in step (a).

11. The method of claim 9, wherein at least a part of the CO.sub.2 extracted in step (c) is fed back to step (a) and/or (b).

Description

BRIEF DESCRIPTION

(1) Further details, features and advantages of the object of the invention are obtained from the dependent claims as well as the following description of the corresponding drawings, in which several exemplary embodiments of the method according to the invention are presented as examples. The drawings show:

(2) FIG. 1 shows a flow diagram of an arrangement for carrying out the method pursuant to the invention according to a first embodiment of the invention (Example I);

(3) FIG. 2 shows a diagram which illustrates the TON (Turnover Number), the verifiable amount of formic acid in the CO.sub.2 flow relative to the metal content of the catalyst (mol/mol) during the implementation of the method on the basis of Example I;

(4) FIG. 3 shows a diagram which illustrates the progression of the total turnover number (TTON) and the turnover frequency (TOF) plotted against time during the implementation of the method on the basis of Example II;

(5) FIG. 4 shows an NMR spectrum of a sample during the method on the basis of Example II; and

(6) FIG. 5 also shows a diagram which illustrates the progression of the total turnover number (TTON) and the turnover frequency (TOF) plotted against time during the implementation of the method on the basis of Example III;

DETAILED DESCRIPTION

Example I

(7) The invention will be analyzed on the basis of Example I, which is to be understood purely as an example.

(8) FIG. 1 shows a flow diagram of an arrangement for carrying out the method pursuant to the invention according to a first embodiment of the invention (Example I), wherein:

(9) F0=compressed air (6 bar), F1=liquid CO.sub.2, F2=H.sub.2, F3=N.sub.2, F4=liquid CO.sub.2 (approx. 40-70 bar), F5=H.sub.2, PR=reduction valve, MFC=mass flow controller, LFM=flowmeter, GFM=gas flowmeter, H=heat, PI=pressure indicator, PV=proportional valve, CV=check valve, BV=ball valve, AB=incubator, V=lockable valve, M=mix chamber, S=reservoir for cosolvents or derivatization reagent, BA=scale, P=piston pump, SY=flushing syringe, TW=three-way valve, R=reactor, VC=high pressure visual cell, TI=temperature indicator, BPR=back pressure regulator valve, MTV=magnetic tunneling valve, MV=metering valve, CT=cold trap, VE=ventilation, SV=high pressure switchover valve, HE=heat exchanger, SFC=supercritical fluid chromatograph.

(10) The method according to the invention is (essentially) carried out in the incubator AB. The CO.sub.2 is first mixed with the CO.sub.2 in the mixing chamber M (a solvent can also be supplied via suitable lines, such as, for example, F0, if required). The hydrogenation subsequently takes place in the reactor R, and the produced formic acid then exits (for the most part) the reaction area together with the nonreacted CO.sub.2. A chromatograph SFCwhich can also be omitted in commercial applications or other exemplary embodimentsis provided in order to control the reaction. Then if required, a separation of CO.sub.2 takes place in the pressure stabilizer BPR by decompression of the compressed mobile phase, which can be discharged via the proportional valve PV2 and can again be fed back at PV1 for further hydrogenation. Then in the cold trap CT together with the ventilation VE, the separation of the (pure) formic acid from the CO.sub.2 takes place. The separated CO.sub.2 can here again be fed back, depending on the application.

(11) Physical Description of Progress of the Experiment

(12) 1. Production of the Immobilized Catalyst

(13) Aminated silica gel SiliaBond Diethylamine (SiliCyle Inc., particle size 40-63 nm, average pore size 600 nm, surface area 500 m.sup.2/g, pore volume 0.8 ml/g) was dried for 3 hours at 80 C. and at 0.1 mbar and stored under argon atmosphere. A parent solutions [sic] were [sic] applied under argon atmosphere for the exact dosage of the metal complex. For this purpose, 40 mol of [Ru(Cl.sub.2)(COD)].sub.n were weighed and dissolved in exactly 5 ml of DCM (c=8 mol/ml). From this was removed 0.34 ml (2.701 mol) which was added to a 3 equivalent PBu.sub.4TPPMS. The mixture was evaporated in a high vacuum until dry and was then dissolved in [EMIM][NTf.sub.2] (c.sub.Ru=0.0027 mol/l). The precursor dissolved in [EMIM][NTf.sub.2] was now blended with silica gel SiliaBond Diethylamine mixed with DCM and dried in a high vacuum, so that the charge of the carrier amounted to 44.2% by weight. A two-hour drying process at 0.1 mbar and 50 C. took place after this. The supported catalyst/stabilizer system was obtained as a powder.

(14) 2. Implementation of the Hydrogenation

(15) A hydrogenation was carried out within a test setup utilizing the solid carrier of I pursuant to the flow diagram of FIG. 1. The procedure was carried out as follows:

(16) Filling of the Reactor

(17) The filling of the tube reactor was carried out under an argon atmosphere. The reaction tube was opened at one end for this purpose and closed with 1 cm of glass wool. The desired amount of supported catalyst/stabilizer system (m=4.257 g, V=9.36 cm.sup.3, n.sub.catalyst=2.701 mol) was then added and held in place with 1 cm glass wool and the reaction tube was closed and installed in the apparatus.

(18) Startup and Operation of the Apparatus

(19) The ball valves in the reactor remained initially closed and the bypass was opened in order to start the apparatus. The CO.sub.2 volume flow was set to 150 ml.sub.N/min and the BPR was set to 200 mbar. Once the desired pressure was reached, it was switched over to the reactor in order to preset herein a pressure of 200 bar. Once the pressure was reached, it was switched over again to the bypass and the H.sub.2 volume flow was dosed. Once this system pressure was reached, then the CO.sub.2 volume flow was set to 100 ml.sub.N/min and the H.sub.2 volume flow was set to 10 ml.sub.N/min. Once the values remained constant, the flow was switched from the bypass to the reactor. This was the time point at which the reaction was started. The reaction temperature amounted to 50 C. The reaction was ended after 137 hours of operation.

(20) Sampling

(21) In order to sample the product, which was continuously extracted with the aid of the CO.sub.2, the extraction flow was fed toward the BPR via a steel capillary in a cold trap filled with purified water and glass beads. The cold trap was periodically replaced and the content was analyzed as to formic acid.

(22) FIG. 2 shows the progression of the turnover number plotted against time. Turnover numbers (TON) with a maximum TON=214 with 137 hours of continuous operation were achieved (with still fully non-optimized conditions).

Example II

(23) The same reaction apparatus as in Example I and shown in FIG. 1 is used in the example described herein, wherein a continuously stirred tank reactor is utilized instead of a flow tube. The catalyst provided herein is homogeneously dissolved in an ionic liquid phase.

(24) 1. Production of the Catalyst Solution

(25) For the exact dosage of the metal complex 24 mol of [Ru(cod)(methallyl).sub.2] and 84 mol of PBu.sub.4TPPMS (ratio 1:3.5) were dissolved under argon atmosphere in 3 ml of DCM, and of this amount 0.25 ml (2 mol of [Ru]) were transferred into another Schlenk flask. In addition, 2 equivalents of EMIMC1 were added by means of a parent solution in DCM. Then was added 1 ml of the ionic liquid 1-(N,N-dethylaminoethyl)-[sic] 2,3-dimethylimidazolium bis(trifluoromethylsulfonyl)imide ([EAMMIM][BTA]) and the mixture was stirred for 2 h at 70 C. in a high vacuum to remove the DCM.

(26) 2. Implementation of the Hydrogenation

(27) A hydrogenation within a test setup was carried out according to the flow diagram of FIG. 1 using the catalyst/stabilizer solution produced in step 1. The procedure was carried out therein as follows:

(28) Filling of the Reactor

(29) The catalyst/stabilizer solution was transferred under an argon atmosphere into a 10 ml stirred tank reactor and its ball valves were closed. The reactor prepared in this way was installed in the apparatus.

(30) Startup and Operation of the Apparatus

(31) The startup and operation of the apparatus took place as described in Example I with the following difference: A constant CO.sub.2 volume flow of 200 ml.sub.N/min and a H.sub.2 volume flow of 20 ml.sub.N/min at 200 bar were set in the bypass operation. The flow was switched over from bypass to reactor and the reactor was thus flushed for 30 minutes in order to equalize the atmosphere in the reactor with that during the continuous operation. The flow was then again switched over to bypass for 20 h in order to allow a balanced concentration of formic acid in the reactor, which improves the extraction from the beginning. The CO.sub.2 and H.sub.2 flow was again fed through the reactor after 20 h. This time point will be considered below as the starting point of the continuous reaction. The reaction was stopped after 211 hours of operation.

(32) Sampling

(33) The sampling was carried out as described in Example I.

(34) FIG. 3 shows the progression of the total turnover number (TTON) and the turnover frequency (TOF) plotted against time. A TTON of 358 could be reached therein after 211 hours of continuous operation. FIG. 4 shows as an example the .sup.1H-NMR analysis of the cold trap content with dioxane as internal standard. With the signal at 3.2 ppm there are traces of methanol, with which the apparatus was previously cleaned.

Example III

(35) The example described herein, like Example II, uses only a heterogeneous polymer-bound amine QuadraPure-DMA instead of an amino functionalized ionic liquid.

(36) 1. Production of the Catalyst Solution

(37) For the exact dosage of the metal complex an amount of 24 mol of [Ru(cod)(methallyl).sub.2] and 84 mol of PBu.sub.4TPPMS (ratio 1:3.5) was dissolved in 3 ml of DCM under an argon atmosphere and 0.25 ml (2 mol of [Ru]) were transferred into another Schlenk flask. As additive were added 2 equivalents of EMIMC1, likewise by means of a parent solution in DCM. Then 1 ml of the ionic liquid ([EAMMIM][BTA]) was added and the mixture was stirred for 2 h at 70 C. in a high vacuum to remove the DCM.

(38) 2. Implementation of the Hydrogenation

(39) A hydrogenation was carried out within a test setup according to the flow diagram of FIG. 1 using the catalyst/stabilizer solution produced in 1. The procedure was carried out as follows:

(40) Filling of the Reactor

(41) Into the 10 ml stirred tank reactor was added 0.5 g of QuadraPure-DMA as well as the catalyst/stabilizer solution under an argon atmosphere and its ball valves were closed. The reactor prepared in this way was installed in the apparatus.

(42) Startup and Operation of the Apparatus

(43) The startup and operation of the apparatus took place as described in Example II with the following difference: A constant CO.sub.2 volume flow of 200 ml.sub.N/min and a H.sub.2 volume flow of 20 ml.sub.N/min at 200 bar were set in the bypass operation. The flow was switched over from bypass to reactor in order to start the continuous operation. The reaction was stopped after 190 hours of operation.

(44) Sampling

(45) The sampling was carried out as described in Example I.

(46) FIG. 5 shows the progression of the total turnover number (TTON) and the turnover frequency (TOF) plotted against time. A TTON of 485 could be reached therein after 190 hours of continuous operation.

(47) The individual combinations of the components and the features of the already-mentioned embodiments are exemplary; the replacement and substitution of these teachings with other teachings contained in this publication and with those of the cited publications are likewise expressly contemplated. The person skilled in the art realizes that variations, modifications and other embodiments than those described herein can likewise be implemented without deviating from the spirit and scope of the invention. The above-mentioned description is accordingly exemplary and is not to be seen as a limitation. The wording used in the claims does not exclude further components or steps. The indefinite article a does not exclude the meaning of a plural. The mere fact that specific measurements are recited in different claims does not signify that a combination of these measurements cannot be advantageously used. The scope of the invention is defined in the following claims and the corresponding equivalents thereof.