KR101467202B1 - Shaped Catalyst For Direct Preparation of Lactide from Lactic Acid and Preparation of the Shaped Catalyst - Google Patents

Abstract

According to the present invention, provided is a shaped catalyst for preparing lactide from lactic acid including a tin-based catalyst and inorganic oxide binder used in a direct conversion from lactic acid to lactide, wherein the tin-based catalyst is selected from a tin compound, preferably tin oxide, having a tetravalent tin oxide state, and the inorganic oxide binder is preferably selected from colloidal silica.

Description

TECHNICAL FIELD The present invention relates to a lactide-forming catalyst for lactide production, and a method for producing lactide from lactic acid,

The present invention relates to a shaped catalyst for the production of lactide from lactic acid comprising a tin catalyst and an inorganic oxide binder used in a one-step conversion reaction from lactic acid to lactide and a method for producing the same, and more particularly to a tin / And a process for producing the same.

Lactide is a cyclic dimer of lactic acid, a useful monomer for biomass-based environmentally friendly polymeric material, Polylactic Acid (PLA). Direct polymerization of lactic acid or lactic acid ester can give low molecular weight oligomers, but it is difficult to obtain high molecular weight PLA. When lactide, which is a cyclic dimer of lactic acid, is used, high molecular weight PLA can be easily produced.

Lactide can theoretically be synthesized in one step by dehydration cyclization of two molecules of lactic acid, but oligomers can be produced simultaneously by dehydration polymerization under the same reaction conditions. It has been investigated so far that oligomers are more produced in the dehydration reaction or the generated lactide is decomposed. Therefore, lactide is not directly produced from lactic acid, but lactic acid ester or lactic acid oligomer is first prepared and then subjected to depolymerization reaction Lactide. ≪ / RTI >

At present, in a commercial process of lactide, a method of producing lactide by first polymerizing lactic acid under a reduced pressure to prepare a prepolymer or oligomer having a molecular weight of about 500 to 5,000 and then depolymerizing the prepolymer or oligomer in the presence of a catalyst . (US Patent No. 5274073, US Patent No. 5247059, US Patent No. 5274127, US Patent No. 6277951)

On the other hand, according to the present inventors, there has been proposed a method for converting lactic acid directly to lactide at a temperature of 200 ° C or higher in the presence of a tin catalyst without passing through a prepolymer or oligomer of lactic acid (Korean Patent Application No. 10-2012-0090883 number).

In the one-step conversion reaction from lactic acid to lactide described in the above-mentioned patent application, tin oxide or a composite oxide of tin and silicon is used in the form of powder as a tin catalyst, and lactide is obtained in high yield by using such tin catalyst It is proven that it can do. However, in order to apply the above-described catalyst to a commercial process, it is necessary to produce or form a block form instead of a powder form. Such a block type catalyst is required to have various mechanical properties while maintaining the catalytic activity in the powder form as it is , The reworking or shaping of the catalyst into a form suitable for a commercial process is often the subject of further research.

It is necessary to prepare or form the tin catalyst used in the one-step conversion reaction of lactide in the form of a block in powder form. It is an object of the present invention to provide a process for the preparation of a tin-based catalyst for use in lactide-based one-step conversion of lactide in the form of a block in powder form, And to develop a method for producing a shaped catalyst having excellent mechanical properties.

The present inventors have studied to develop a method of preparing or molding a tin-based catalyst used as a block-form in powder form for use in lactide-based one-step conversion of lactide. As a result, it has been found that SiO ₂ , TiO ₂ , ZrO ₂ , Al ₂ O ₃ or the like as a binder and mixing with the above-mentioned tin catalyst in the form of powder to prepare a block-shaped catalyst. The block-shaped catalyst thus prepared is in powder form The present inventors have found that the tin catalysts of the present invention have sufficient mechanical properties such that they can not only maintain the excellent catalytic properties of tin catalysts as they are, but also can be applied to commercial processes.

A shaping catalyst having sufficient mechanical properties such that it can be applied to a commercial process while keeping the catalytic property of the tin catalyst used in the first stage conversion reaction of lactide from lactic acid as it is or at the maximum, Can be manufactured.

1 is an X-ray diffraction spectrum of a tin / silicon composite oxide of Production Example 1,
2 is a gas chromatographic analysis result of the final product of Test Example 1,
3 is a photograph of a molding catalyst produced by extrusion molding in Example 1,
4 is a photograph of a shaped catalyst extruded in the form of a cylinder in Example 2,
5 is a photograph of a molding catalyst compressed in a cylinder form in Comparative Example 1. Fig.

A first object of the present invention is to provide a shaped catalyst for the production of lactide, which comprises a tin catalyst and an inorganic oxide binder used in the one-step conversion reaction of lactide in lactic acid.

In one embodiment, the tin catalyst used in the one-step conversion reaction of lactide in the aforementioned lactic acid may be selected from tin compounds having a tetravalent tin oxidation state, preferably SnO ₂ .

In a preferred embodiment, the tin catalyst or tin compound used in the one-step conversion of lactide in the aforementioned lactic acid is selected from the group consisting of Si, Ti, Al, Zn, Zr, V, Cr, Mn, Or in the form of a mixed oxide or a complex oxide, in a form supported on an oxide of at least one selected metal.

In the present invention, the term mixed oxides and complex oxides can be distinguished by chemical formulas. For example, in silicon and titanium, the mixed oxide may be expressed in the form of SiO ₂ + TiO ₂ or SiO ₂ / TiO ₂ , and the complex oxide may be expressed in the formula of SiTiO ₄ . As another example, in tin and silicon, a mixed oxide of tin and silicon can be expressed in the form of SnO ₂ + SiO ₂ or SnO ₂ / SiO ₂ , and a composite oxide of tin and silicon is expressed in the formula of SnSiO ₄ . The separation of the mixed oxide and the composite oxide by the above-mentioned expression or chemical formula is commonly used in the art and can be easily understood by those skilled in the art.

In the present invention, the above-mentioned inorganic oxide binder may be an oxide of at least one metal selected from the group consisting of Si, Ti, Al, Zn, Zr, V, Cr, Mn, Fe and Mo.

The above-mentioned inorganic oxide binder may be contained in an amount of 0.1 to 50% by weight, preferably 0.5 to 40% by weight, more preferably 1 to 30% by weight, based on the total weight of the catalyst including the tin catalyst and the binder .

A second object of the present invention is to provide a method for producing a catalyst preform for the direct production of lactide, which comprises a tin catalyst and an inorganic oxide binder used in a one-step conversion reaction of lactide in lactic acid, (3): < RTI ID = 0.0 >

(1) preparing a solid catalyst comprising a tin catalyst used in a one-step conversion reaction of lactide in lactic acid,

(2) mixing the solid catalyst obtained in the step (1) with an inorganic oxide precursor,

(3) Molding and firing the mixture obtained in step (2).

In one embodiment, the above-described inorganic oxide precursor used as a binder is at least one selected from the group consisting of chlorides, hydroxides, hydroxides, hydroxides, hydroxides, hydroxides, hydroxides and the like of at least one metal selected from the group consisting of Si, Ti, Al, Zn, Zr, V, Cr, Sulfur oxides, nitrates, silicates or mixtures thereof.

According to one variant of the present invention, a sol-like inorganic oxide on the surface can be used as an inorganic oxide precursor which is a binder. The inorganic oxide in the form of a sol has an oxide form inside but a large number of reactive groups such as a hydroxyl group on the surface, and thus can serve as a binder according to the present invention. Examples of such sols of inorganic oxides may include colloidal silica and colloidal alumina. Colloidal silica having a particle size of 1 to 200 nm, preferably 2 to 100 nm, can preferably be used.

In one embodiment, the catalyst formed in step (3) described above is dried and calcined at a temperature of from 100 to 500 ° C, preferably from 150 to 450 ° C, more specifically from 200 to 400 ° C.

The shape of the catalyst is not limited, and the catalyst may be formed into any shape such as a spherical shape, a cylindrical shape, a prismatic shape, a hollow block shape, or the like.

The size of the shaped catalyst is not particularly limited and can be manufactured according to the size of the general catalyst shaped bodies. For example, in the case of a spherical shape, 10 mm to 5 cm, particularly 20 mm to 2 cm, 1 cm. ≪ / RTI >

In the present invention, tin-based catalysts that can be used for one-step conversion (reaction) from lactic acid to lactide or for the direct preparation of lactide from lactic acid include Korean Patent Application 10-2012-0090883 (filed on August 20, 2012) , Which patent application is incorporated herein by reference.

In the present invention, the one-step conversion (reaction) from lactic acid to lactide or the direct preparation of lactide from lactic acid means that two molecules of lactic acid are converted into one molecule of lactide in the chemical reaction formula, It does not necessarily mean that there is little. However, when using the tin catalyst of the present invention, it may be understood that lactic acid is converted to lactide into the first stage because there is little or no oligomer formation.

On the other hand, some catalysts capable of directly producing lactide from lactic acid have been reported in the prior art, but the reactivity (conversion of lactic acid) and yield (lactide selectivity) are low and the selectivity of the lactic acid oligomer, And productivity and economical efficiency were low, so that it could not be actually applied.

When lactide is produced from lactic acid using the tin catalyst used in the present invention, little or no lactic acid oligomer with high reactivity (conversion of lactic acid) and yield (selectivity of lactide) is difficult to be separated, Which is very useful as a catalyst for producing lactide directly or in one step, and is very valuable industrially and commercially.

According to the present invention, tin-based catalysts exhibiting excellent catalytic properties in the reaction of directly producing lactide from lactic acid in the form of powder are formed into a block form using a binder to produce lactide directly from lactic acid It is possible to produce a block shaped catalyst exhibiting excellent catalytic properties in the reaction, and that the shaped catalyst thus prepared has sufficient mechanical strength for commercial use.

In the process of directly producing lactide from lactic acid, the tin catalyst in powder form used in the present invention has not been reported in the past and has excellent catalytic properties. For example, , The conversion of lactic acid is 80% or more, preferably 90% or more, and the selectivity of lactide is 90% or more, preferably 94% or more and the selectivity of meso-lactide is 5% or less and the selectivity of lactic acid oligomer is 5% .

In the process of directly producing lactide from lactic acid, the block-shaped shaped catalyst according to the present invention also has a very excellent catalytic property. For example, the conversion of lactic acid is 80% or more, preferably 90% The selectivity of tide is 90% or more, preferably 94% or more, the selectivity of meso-lactide is 5% or less and the selectivity of lactic acid oligomer is 5% or less. Therefore, it can be confirmed that the block-shaped catalyst according to the present invention has the catalytic properties of the solid catalyst in powder state as it is or at the maximum.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited thereto.

Production Example 1: Preparation of tin / silicon composite oxide powder

SnCl ₄ ^. 950 g of 5H ₂ O and 351 g of silica sol (Ludox, SM30) were placed in a beaker maintained at 5 ° C and adjusted to pH 8.5 with 2.0 M NaOH while stirring. The temperature was then raised to 70 < 0 > C and then further stirred for 4 hours. The resulting precipitate was filtered, dried at 100 ° C. for 5 hours, and finally calcined at 450 ° C. for 2 hours to prepare 510 g of a tin / silicon composite oxide powder.

As a result of confirming the powder by X-ray diffraction analysis, the peaks related to the tin compound identified on the X-ray diffraction spectrum mainly corresponded to the peaks corresponding to the SnO ₂ phase (FIG. 1).

Test Example 1: Direct preparation of lactide from lactic acid using Sn / Si composite oxide powder as a catalyst

1 g of the Sn / Si composite oxide (500 mesh) prepared in Production Example 1 was charged into a fixed bed reactor and 75% L-lactic acid aqueous solution (Aldrich) was fed into the reactor at a feed rate of 1.5 g / h, Was added at a rate of 250 ml / ml. The reaction was continuously carried out for 280 hours while maintaining the temperature of the reactor filled with the catalyst at 240 캜 and the pressure of the reactor at the normal pressure.

The obtained product was analyzed by gas chromatography to find that the conversion of L-lactic acid was 95%, the selectivity of L-lactide was 97%, the selectivity of meso-lactide was 2%, and the selectivity to lactic acid oligomer was 1% or less (FIG. 2).

Example 1: Preparation of Molded Catalyst (1) from Sn / Si composite oxide and preparation of lactide using the same

(1) Production of molded catalyst 1 from Sn / Si composite oxide

75 g of the tin / silicon composite oxide prepared in Preparation Example 1 was mixed with 750 ml of an aqueous solution containing 2% by weight of colloidal silica, and water was removed with stirring at 70 ° C.

The slurry was extruded using a mesh of 3 mm size and ball milled for 24 hours and then calcined at 450 degrees for 6 hours (FIG. 3).

(2) Production of lactide using a molding catalyst (1)

1 g of the shaped catalyst prepared in (1) above was charged into a fixed-bed reactor, 75% L-lactic acid aqueous solution (Aldrich) was fed into the reactor at a feed rate of 1.5 g / h, Flow rate. The reaction was continuously carried out for 120 hours while maintaining the temperature of the reactor filled with the catalyst at 240 ° C. and the pressure of the reactor at the normal pressure.

The obtained product was analyzed by gas chromatography to confirm that the conversion of L-lactic acid was 93%, the selectivity of L-lactide was 97%, the selectivity of meso-lactide was 2%, and the selectivity of lactic acid oligomer was 1% or less.

Example 2: Production of molded catalyst 2 from Sn / Si composite oxide

A shaped catalyst 2 was prepared in the same manner as in Example 1, except that 4 wt% was used instead of 2 wt% of colloidal silica.

The reaction was continued under the same reaction conditions as in Example 1 for 120 hours continuously. Gas chromatographic analysis of the obtained product confirmed that the conversion of L-lactic acid was 91%, selectivity of L-lactide was 97%, selectivity of meso-lactide was 2%, and selectivity to lactic acid oligomer was 1%.

Example 3: Production of molded catalyst (3) from Sn / Si composite oxide

A shaped catalyst 3 was prepared in the same manner as in Example 1, except that 6 wt% was used instead of 2 wt% of colloidal silica.

The reaction was continued under the same reaction conditions as in Example 1 for 120 hours continuously. The gas chromatographic analysis of the obtained product confirmed that the conversion of L-lactic acid was 90%, the selectivity of L-lactide was 97%, the selectivity of meso-lactide was 2%, and the selectivity of lactic acid oligomer was 1% or less.

Example 4: Preparation of molded catalyst (4) from Sn / Si composite oxide

A shaped catalyst 3 was prepared in the same manner as in Example 1, except that 10 wt% was used instead of 2 wt% of colloidal silica.

The reaction was continued under the same reaction conditions as in Example 1 for 120 hours continuously. The gas chromatographic analysis of the obtained product confirmed that the conversion of L-lactic acid was 87%, the selectivity of L-lactide was 97%, the selectivity of meso-lactide was 2%, and the selectivity to lactic acid oligomer was 1% or less.

Example 5: Preparation of molded catalyst 5 from Sn / Si composite oxide

(1) Production of molded catalyst 5 from Sn / Si composite oxide

75 g of the tin / silicon composite oxide prepared in Preparation Example 1 was mixed with 750 ml of an aqueous solution containing 1% by weight of colloidal silica, and water was removed with stirring at 70 ° C.

The slurry was molded into a cylinder using an extruder and dried at 110 DEG C for 24 hours (FIG. 4).

(2) Production of lactide using a molding catalyst (5)

1 g of the shaped catalyst prepared in (1) above was charged into a fixed-bed reactor and 75% L-lactic acid aqueous solution was fed into the reactor at a feed rate of 1.5 g / h. At the same time, nitrogen was fed at a flow rate of 250 ml / min Respectively. The reaction was continuously carried out for 120 hours while maintaining the temperature of the reactor filled with the catalyst at 240 ° C. and the pressure of the reactor at the normal pressure.

The obtained product was analyzed by gas chromatography to confirm that the conversion of L-lactic acid was 95%, the selectivity of L-lactide was 97%, the selectivity of meso-lactide was 2%, and the selectivity of lactic acid oligomer was 1% or less.

In the above-mentioned Examples 1 to 5, a molded article produced by molding a Sn / Si composite oxide powder using colloidal silica as a binder has a good impact strength.

At this time, as the concentration of the silica binder increases, the impact strength of the molded body increases, but the conversion of lactic acid is slightly decreased. The content of the silica binder may preferably be 40% or less with respect to the total weight of the Sn / Si composite oxide.

Example 6: Preparation of molded catalyst (6) from Sn / Si composite oxide

A shaped catalyst 6 in the form of a cylinder was prepared in the same manner as in Example 5, except that 2 wt% of gamma alumina was used instead of 1 wt% of colloidal silica.

The reaction was continued under the same reaction conditions as in Example 5 for 120 hours continuously. The gas chromatographic analysis of the obtained product confirmed that the conversion of L-lactic acid was 88%, the selectivity of L-lactide was 96%, the selectivity of meso-lactide was 2%, and the selectivity to lactic acid oligomer was 2% or less.

Example 7: Preparation of molded catalyst 7 from Sn / Si composite oxide

A shaped catalyst 7 in the form of a cylinder was prepared in the same manner as in Example 5 except that 2 wt% of silica was used instead of 1 wt% of colloidal silica.

The reaction was continued under the same reaction conditions as in Example 5 for 120 hours continuously. The gas chromatographic analysis of the obtained product confirmed that the conversion of L-lactic acid was 91%, the selectivity of L-lactide was 95%, the selectivity of meso-lactide was 2%, and the selectivity of lactic acid oligomer was 3% or less.

Examples 6 and 7 show that alumina and other types of silica can be used as well as colloidal silica as a binder for forming Sn / Si composite oxides.

Comparative Example 1: Production of lactide using graphite binder / compression molding

50 g of the Sn / Si composite oxide prepared in Example 1 was mixed with 1.5 g of graphite, compressed at a pressure of 300 kg / cm < 2 >

The reaction was continued under the same reaction conditions as in Example 5 for 120 hours continuously. The gas chromatographic analysis of the obtained product confirmed that the conversion of L-lactic acid was 76%, selectivity of L-lactide was 95%, selectivity of meso-lactide was 2%, and selectivity of lactic acid oligomer was 3% or less.

It will be understood by those skilled in the art that various changes and modifications may be made therein without departing from the spirit and scope of the invention as defined in the appended claims. It is obvious to those who have. It is therefore intended that such variations and modifications fall within the scope of the appended claims.

The shaped catalyst for lactide production from lactic acid according to the present invention can be used in the lactide manufacturing process.

Claims (12)

A catalyst formed body for producing lactide from a lactic acid comprising a tin catalyst and an inorganic oxide binder used in a one-step conversion reaction of lactide in lactic acid, wherein the tin catalyst is SnO ₂ , Catalyst compact for direct manufacturing. delete delete The method according to claim 1, wherein SnO ₂ as the above-mentioned tin catalyst is supported on or mixed with an oxide of at least one metal selected from the group consisting of Si, Ti, Al, Zn, Zr, V, Cr, Mn, Fe and Mo A catalyst preform for the direct production of lactide from lactic acid, characterized in that it is used in the form of a composite oxide. The method according to claim 1, wherein the inorganic oxide binder is an oxide of at least one metal selected from the group consisting of Si, Ti, Al, Zn, Zr, V, Cr, Mn, A catalyst preform for the direct production of lactide. The catalyst preform for direct production of lactide from lactic acid according to any one of claims 1, 4 and 5, characterized in that said inorganic oxide binder is contained in an amount of 1 to 40% by weight, based on the total weight of the catalyst. A process for producing a catalyst molded body for the production of lactide from lactic acid according to claim 1, which comprises the following steps (1) to (3).
(1) A solid catalyst comprising SnO ₂ as a tin catalyst used in the one-step conversion reaction of lactide in lactic acid was prepared,
(2) mixing the solid catalyst obtained in the step (1) with an inorganic oxide precursor,
(3) Molding and firing the mixture obtained in step (2). delete delete The method of claim 7, wherein SnO ₂ is supported on or mixed with an oxide of at least one metal selected from the group consisting of Si, Ti, Al, Zn, Zr, V, Cr, Mn, Fe and Mo Characterized in that the lactide is used in the form of a complex oxide. The method according to claim 7, wherein the inorganic oxide binder is an oxide of at least one metal selected from the group consisting of Si, Ti, Al, Zn, Zr, V, Cr, Mn, A process for producing a catalyst preform for the direct production of lactide. A catalyst formed article for the direct preparation of lactide from lactic acid according to any one of claims 7, 10 and 11, characterized in that the catalyst formed in step (3) described above is dried and calcined at a temperature of 100 to 500 ° C. Gt;

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