Regeneration method of solid catalyst

Abstract

The present invention aims to provide a regeneration method capable of sufficiently restoring the catalytic performance of a solid catalyst used in a dehydration reaction of lactic acid and derivatives thereof. The present invention relates to a method for regenerating a solid catalyst used in a dehydration reaction of lactic acid and derivatives of lactic acid, the method including a contacting step of bringing a solid catalyst containing a component that forms a molten salt in the presence of steam into contact with oxygen and steam under pressure.

Claims

1. A method comprising a contacting step of bringing a solid catalyst containing a component that forms a molten salt in the presence of steam into contact with oxygen and steam, wherein the steam in the contacting step has a partial pressure of 0.3 to 10 MPa.

2. The method according to claim 1, wherein the component that forms a molten salt contains a condensed phosphate.

3. The method according to claim 1, wherein the contacting step is performed at 200° C. to 700° C.

4. The method according to claim 2, wherein the contacting step is performed at 200° C. to 700° C.

5. The method according to claim 2, wherein the condensed phosphate is a mixture of an alkali metal salt and an alkaline-earth metal salt.

6. The method according to claim 2, wherein the condensed phosphate is at least one compound selected from the group consisting of Na.sub.4P.sub.2O.sub.7, Na.sub.2H.sub.2P.sub.2O.sub.7, (NaPO.sub.3).sub.n, K.sub.4P.sub.2O.sub.7, K.sub.2H.sub.2P.sub.2O.sub.7, (KPO.sub.3).sub.n, Ca.sub.2P.sub.2O.sub.7, CaH.sub.2P.sub.2O.sub.7, Ca(PO.sub.3).sub.2, Ca.sub.3(PO.sub.4).sub.2, Ba.sub.2P.sub.2O.sub.7, BaH.sub.2P.sub.2O.sub.7, Ba(PO.sub.3).sub.2, Ca.sub.2-x-sK.sub.2xH.sub.2sP.sub.2O.sub.7 and Ba.sub.2-x-sK.sub.2xH.sub.2sP.sub.2O.sub.7, wherein n is a positive integer, x and s are each 0 or more and less than 0.5.

7. The method according to claim 2, wherein the condensed phosphate is at least one compound selected from the group consisting of K.sub.4P.sub.2O.sub.7, K.sub.2H.sub.2P.sub.2O.sub.7, (KPO.sub.3).sub.n, Ba.sub.2P.sub.2O.sub.7, BaH.sub.2P.sub.2O.sub.7, Ba(PO.sub.3).sub.2 and Ba.sub.2-x-sK.sub.2xH.sub.2sP.sub.2O.sub.7, wherein n is a positive integer, x and s are each 0 or more and less than 0.5.

8. The method according to claim 2, wherein the condensed phosphate is at least one compound selected from the group consisting of Ba.sub.2P.sub.2O.sub.7, (KPO.sub.3).sub.n and Ba.sub.2-x-sK.sub.2xH.sub.2sP.sub.2O.sub.7, wherein n is a positive integer, x and s are each 0 or more and less than 0.5.

9. The method according to claim 2, wherein the condensed phosphate is a mixture of Ba.sub.2P.sub.2O.sub.7 and (KPO.sub.3).sub.n.

10. The method according to claim 2, wherein when a mixture of an alkali metal salt and an alkaline-earth metal salt is used as the condensed phosphate, the molar ratio of the alkali metal to the alkaline-earth metal (alkali metal/alkaline-earth metal) is 0.5 to 2.0.

11. The method according to claim 1, wherein the solid catalyst is supported on a carrier, and wherein the carrier is at least one selected from the group consisting of silica, diatomite, alumina, silica alumina, silica magnesia, zirconia, titania, magnesia, niobia, ceria, zeolite, silicon carbide and carbide.

12. The method according to claim 1, wherein the steam in the contacting step has a partial pressure of 0.3 to 5.0 MPa.

13. The method according to claim 1, wherein the steam in the contacting step has a partial pressure of 0.3 to 1.0 MPa.

14. The method according to claim 1, wherein the oxygen partial pressure is more than 0 MPa and not more than 1.0 MPa.

15. The method according to claim 1, wherein the oxygen concentration in the gas component other than steam in the contacting step is 50% by volume or less.

16. The method according to claim 1, wherein the amount of the steam in the contacting step relative to 100% by volume of oxygen is 1% to 100000% by volume.

17. The method according to claim 1, wherein the contacting step is performed at 250° C. to 650° C.

18. The method according to claim 1, wherein the contacting step is performed at 300° C. to 600° C.

Description

DESCRIPTION OF EMBODIMENTS

(1) The present invention is described in more detail below with reference to, but not limited to, the following examples. Unless otherwise specified, “parts” means “parts by weights”, and “%” means “% by mass”.

(2) <Measurement of Amount of Coke Remaining on Solid Catalyst>

(3) A catalyst was heated in the air using a differential high temperature differential thermal balance (TG-DTA2020SA, Bruker AXS), and the amount of coke on the catalyst was calculated from the weight reduction.

Production Example 1: Production of Catalyst

(4) A potassium metaphosphate-barium pyrophosphate (molar ratio:K/Ba/P=0.4/0.6/1.0) powder was prepared with reference to Example 1 in JP 2014-518874 T. To the resulting potassium metaphosphate-barium pyrophosphate powder was added an inorganic carrier component and a binder containing 122% by mass of SiO.sub.2. The resulting mixture was extruded and molded into a 4 mm diameter article, and cut into pellets with a 4 mm length. The pellets were burned in an air atmosphere at 600° C. for 12 hours. Thus, a catalyst was obtained.

Production Example 2: Production of Acrylic Acid

(5) Acrylic acid was produced by the dehydration of lactic acid through a gas-phase fixed-bed flow reaction system under pressure using the catalyst prepared in Production Example 1.

(6) First, a titanium-coated stainless-steel reaction tube (inner diameter: 24.5 mm, length: 620 mm) was filled with 142 mL of the catalyst to prepare a fixed-bed flow reactor, and then this reactor was immersed in a salt bath at 375° C. Thereafter, nitrogen gas was circulated in the reactor at a flow rate of 0.70 NL/min for 30 minutes, and the pressure was increased to 0.50 MPa. The supply of nitrogen gas was stopped after the pressure in the reactor was stabilized, and a reactant gas of a 35% by mass aqueous solution of lactic acid (the composition of the reactant gas:lactic acid 10 mol %, water 90 mol %) was circulated at a flow rate (GHSV) of 480 hr.sup.−1 for 48 hours.

(7) After the reactant gas was circulated in the reactor, the flowing gas was condensed to a liquid by cooling and collected. The liquid was drawn at specific time intervals. Hereinafter, the liquid condensed by cooling and drawn refers to an “effluent”. Part of the effluent was taken and qualitatively and quantitatively analyzed using a gas chromatography (GC) apparatus (GC-2010, Shimadzu Corporation) equipped with a FID detector and a liquid chromatography (LC) apparatus (ACQUITY UPLC system, Waters) equipped with a UV detector. The quantitative analysis by GC or LC was performed by an internal standard method. Acrylic acid and by-products such as propionic acid were analyzed by GC, and lactic acid was analyzed by LC. The conversion of lactic acid (LA conversion), selectivity to acrylic acid (AA selectivity), and selectivity to propionic acid (PA selectivity) were calculated from the results of the quantitative analysis using the following equations.
LA conversion=(1−(the number of moles of lactic acid in effluent)/(the number of moles of lactic acid supplied to reactor))×100
AA selectivity=(((the number of moles of acrylic acid in effluent)/(the number of moles of lactic acid supplied to reactor))×100)/(conversion of lactic acid×100)
PA selectivity=(((the number of moles of propionic acid in effluent)/(the number of moles of lactic acid supplied to reactor))×100)/(conversion of lactic acid×100)

Reference Example: Regeneration of Solid Catalyst in the Absence of Steam and Production of Acrylic Acid

(8) Acrylic acid was produced in accordance with Production Example 2, and the production was stopped after 48 hours from the start of the production. The catalyst was left in the reactor. Thereafter, the pressure was returned to atmospheric pressure while only nitrogen gas was circulated in the fixed-bed flow reactor at a flow rate of 0.70 NL/min for 1 hour, and a reactant gas and a product gas remaining in the reactor were discharged. Thereafter, while the pressure was maintained at atmospheric pressure and the temperature of the salt bath was maintained at 375° C., a gas mixture of nitrogen at a flow rate of 0.60 NL/min and air at a flow rate of 0.10 NL/min was circulated in the reactor for 15 minutes, and subsequently, a gas mixture of nitrogen at a flow rate of 0.40 NL/min and air at a flow rate of 0.30 NL/min was circulated for 45 minutes. Then, only air was circulated at a flow rate of 0.70 NL/min for 23 hours, and carbonaceous deposits (organic matter deposits) or the like on the catalyst were burned off. Thus, the catalyst was regenerated.

(9) After the cycle of the production of acrylic acid and the regeneration of the catalyst in the absence of steam was repeated six times (cycles), the seventh production of acrylic acid was performed for 48 hours. The LA conversion, AA selectivity, and PA selectivity in each cycle were shown in Table 1. The conditions of the regeneration of the solid catalyst were shown in Table 2.

(10) Table 1 shows that in the seventh production of acrylic acid after the repetition of the regeneration of the solid catalyst in the absence of steam, the selectivity to acrylic acid significantly deteriorated, and the selectivity to propionic acid significantly increased.

(11) TABLE-US-00001 TABLE 1 LA AA PA Production time conversion [%] selectivity [%] selectivity [%] Cycle of acrylic acid (h) 1 h 48 h Ave. 1 h 48 h Ave. 1 h 48 h Ave. 1  0-48 98.5 94.5 96.5 80.8 79.4 84.3 0.3 1.6 0.9 2 48-96 94.1 90.9 92.9 83.7 77.6 78.4 0.8 2.2 1.7 3  96-144 96.0 91.9 94.1 84.9 78.6 81.4 0.7 2.0 1.5 4 144-192 96.7 91.4 94.3 85.0 78.7 82.0 0.8 1.9 1.3 5 192-240 95.9 90.2 93.8 83.2 77.4 80.9 0.6 1.7 1.2 6 240-288 96.3 93.1 94.3 84.4 85.9 84.8 1.1 2.3 1.5 7 288-336 96.6 93.5 95.7 75.9 70.9 72.9 2.3 2.5 2.3

Example 1: Regeneration of Solid Catalyst in the Presence of Steam and Production of Acrylic Acid

(12) The seventh production of acrylic acid in Reference Example was stopped after 48 hours from the start of the production. The catalyst was left in the reactor. Thereafter, the pressure was returned to atmospheric pressure while only nitrogen gas was circulated in the fixed-bed flow reactor at a flow rate of 0.70 NL/min for 1 hour, and a reactant gas and a product gas remaining in the reactor were discharged. Thereafter, the pressure was increased to 0.55 MPa. The temperature of the salt bath was maintained at 375° C., and the supply of nitrogen gas was stopped after the internal pressure of the reactor was stabilized. Then, a mixture of steam at a flow rate of 1.3 g/min and air at a flow rate of 0.35 NL/min was circulated for 24 hours, and carbonaceous deposits or the like on the catalyst were burned off. Thus, the catalyst was regenerated. The temperature of the salt bath in which the fixed-bed flow reactor was immersed was increased to 450° C. in 6 hours from the start of the circulation of steam, and the temperature was maintained. The conditions of the regeneration of the solid catalyst were shown in Table 2.

(13) Subsequently, the temperature of the salt bath was reduced to 375° C., and acrylic acid was continuously produced for 48 hours in accordance with Production Example 2. The LA conversion, AA selectivity, and PA selectivity in the production of acrylic acid were shown in Table 3.

(14) The amount of coke remaining on the regenerated catalyst was measured. The result was shown in Table 4. The amount of the coke remaining was calculated from the following equation.
Amount of coke remaining (% by mass)=reduced weight determined by TG analysis/weight of regenerated catalyst×100

(15) After the production of acrylic acid, the catalyst was regenerated again and taken out from the reactor. The crushing strength of the catalyst was measured using a compact table-top universal tester (EZ Test, Shimadzu Corporation) to be 170 N on average. The lateral strength of each pellet was measured.

Example 2: Regeneration of Solid Catalyst in the Presence of Steam and Production of Acrylic Acid

(16) A solid catalyst was regenerated and acrylic acid was produced as in Example 1 except that the pressure during the regeneration was 0.40 MPa and the flow rates of steam and air were 0.83 g/min and 0.35 NL/min, respectively. The conditions of the regeneration of the solid catalyst were shown in Table 2. The LA conversion, AA selectivity, and PA selectivity in the production of acrylic acid were shown in Table 3.

Comparative Example 1: Regeneration of Solid Catalyst in the Absence of Steam and Production of Acrylic Acid

(17) The seventh production of acrylic acid in Reference Example was stopped after 48 hours from the start of the production. Thereafter, the solid catalyst was regenerated under the same catalyst regeneration conditions as in the first to sixth regeneration treatments in Reference Example.

(18) Subsequently, acrylic acid was continuously produced for 48 hours in accordance with Production Example 2. The LA conversion, AA selectivity, and PA selectivity in the production of acrylic acid were shown in Table 3.

(19) The amount of coke on the regenerated catalyst was measured as in Example 1. The results were shown in Table 4.

(20) After the production of acrylic acid, the catalyst was regenerated again and taken out from the reactor. The crushing strength of the catalyst measured was 150N on average. The result demonstrates that the strength of the catalyst was lower than the strength of the catalyst in Example 1.

(21) TABLE-US-00002 TABLE 2 Steam in Reaction temperature P.sub.total regenerated P.sub.H2O (temperature of [MPa] gas [vol %] [MPa] salt bath) [° C.] Example 1 0.55 82 0.45 375-450 Example 2 0.40 75 0.3 375-450 Comparative 0.10 0 0 375 Example 1

(22) TABLE-US-00003 TABLE 3 Production LA AA PA time of acrylic conversion [%] selectivity [%] selectivity [%] acid (h) 1 h 48 h Ave. 1 h 48 h Ave. 1 h 48 h Ave. Example 1 336-384 98.8 97.9 98.4 80.6 79.8 81.3 1.1 1.5 1.3 Example 2 336-384 98.0 96.2 97.0 78.8 75.6 77.1 1.5 2.0 1.8 Comparative 336-384 96.5 93.5 95.6 72.0 68.3 70.1 2.5 2.8 2.6 Example 1

(23) TABLE-US-00004 TABLE 4 Amount of coke remaining (% by mass) Reference Example 3.0 (catalyst after 7 cycles of reaction) Example 1 0.3 Comparative Example 1 0.9

(24) As is clear from the comparison between the amounts of coke on the regenerated catalysts in Example 1 and Comparative Example 1 shown in Table 4, coke was burned off more efficiently in Example 1 than in Comparative Example 1. Further, Table 3 showed that the selectivity to acrylic acid was more enhanced and the selectivity to propionic acid was more reduced in Examples 1 and 2 in which the regeneration was performed in the presence of steam than in Comparative Example 1.

(25) These results demonstrate that in the solid catalyst regeneration method of the present invention, coke deposits on a catalyst can be sufficiently burned off by regeneration treatment of bringing the catalyst into contact with oxygen and steam under pressure, the selectivity to propionic acid produced as a by-product is reduced and the selectivity to acrylic acid that is mainly produced is enhanced, leading to sufficient restoration of the catalytic performance.