HK1120025B - Improved process for preparing unsaturated carboxylic anhydrides - Google Patents

Description

Improved process for preparing unsaturated carboxylic acid anhydrides

Technical Field

The present invention relates to an improved process for the preparation of unsaturated carboxylic acid anhydrides, and in particular to the reaction of unsaturated carboxylic acids with low molecular weight aliphatic carboxylic acid anhydrides.

Background

DE-A-3510035 describes a process for preparing unsaturated carboxylic anhydrides by carrying out an acid-catalyzed transanhydridation of acetic anhydride with an unsaturated carboxylic acid in the middle of a distillation column. The catalysts given are homogeneous catalysts, preferably sulfuric acid, aliphatic or aromatic sulfonic acids or phosphoric acid. In order to achieve complete conversion, acetic anhydride is used in an excess of from 0.1 to 0.5mol per mol of carboxylic acid, in which case a mixture of acetic acid and acetic anhydride is produced at the top of the column, i.e. pure acetic acid is not obtained.

In addition, a product is formed which is contaminated with the catalyst which has to be removed in a further process step.

US-A-4,857,239 describes A process for the preparation of methacrylic anhydride wherein the molar ratio of methacrylic acid to acetic anhydride is from 2.1 to 3 and A polymerization inhibitor is added to the distillation column. The disadvantage is that the reactants used in excess are present in an unused form. In addition, no catalyst is used to accelerate the reaction.

US-A-2003/0018217 describes A process for the preparation of methacrylic anhydride wherein the initial molar ratio of methacrylic acid to acetic anhydride is preferably in the range of 9 to 11. The acetic acid formed was immediately discharged and the freed reactor content space was filled with acetic anhydride. To avoid polymerization, a polymerization inhibitor is added to the reactor and column. A number of by-products are formed which cannot be completely removed. Also produced as a by-product is an intermediate acetyl (meth) acrylate (mixed anhydride of acetic anhydride and (meth) acrylic anhydride). No catalyst is used here either.

Disclosure of Invention

The object of the present invention is to provide an improved process for preparing unsaturated carboxylic anhydrides in which a stoichiometric excess of one of the reactants is avoided, the formation of side components is suppressed as far as possible and a complete conversion of the reactants is achieved. In addition, polymerization should be avoided to a large extent in all regions and the space-time yield of the reaction should be increased.

The present invention provides an improved process for the preparation of unsaturated carboxylic acid anhydrides of the general formula I,

R-C(O)-O-C(O)-R (I)

wherein R is an unsaturated organic group containing 2 to 12 carbon atoms or a 9, 12-octadecadienyl group,

the process is carried out by transanhydridating an aliphatic carboxylic anhydride with a carboxylic acid of the general formula II in an apparatus consisting of a reaction zone and a rectification column,

R-COOH (II)

wherein R is as defined above, characterized in that

a) Feeding the reactants into a reaction zone in stoichiometric ratios,

b) the carboxylic acid formed as a by-product is discharged from the reaction mixture,

c) the carboxylic anhydride of the formula I formed is then discharged,

d) the unconverted reactants are recycled to the reaction zone,

e) the reaction zone comprises a heterogeneous catalyst, and

f) one or more polymerization inhibitors are added.

Complete conversion of the reactants is achieved by these technical features, the space-time yield is significantly increased and polymerization in all regions is largely avoided. Furthermore, there is no need to perform the separation and removal of the catalyst in an additional separation apparatus.

The carboxylic acids suitable for the process according to the invention have unsaturated organic groups having from 2 to 12, preferably from 2 to 6, more preferably from 2 to 4, carbon atoms. Suitable alkenyl groups are vinyl, allyl, 2-methyl-2-propenyl, 2-butenyl, 2-pentenyl, 2-decenyl, 1-undecenyl and 9, 12-octadecadienyl. Vinyl and allyl groups are particularly preferred.

Particularly preferred carboxylic acids include in particular (meth) acrylic acid. The term "(meth) acrylic acid" is known in the art and is understood herein to mean, in addition to acrylic acid and methacrylic acid, derivatives of these acids. These derivatives include, in particular, beta-methacrylic acid (crotonic acid ), alpha, beta-dimethylacrylic acid, beta-ethylacrylic acid, alpha-chloroacrylic acid, alpha-cyanoacrylic acid, 1- (trifluoromethyl) acrylic acid and beta, beta-dimethylacrylic acid. Acrylic acid and methacrylic acid (2-methacrylic acid) are preferred.

Suitable carboxylic anhydrides for the process according to the invention are likewise known in the art. Preferred compounds have the general formula III: r ' -C (O) -O-C (O) -R ' (III), wherein R ' is C₁-C₄-an alkyl group. Acetic anhydride is preferably used.

According to the invention, a stoichiometric ratio is understood to mean a molar ratio of carboxylic acid to carboxylic anhydride of from 1.9 to 2.1: 1.

For the separation of the product stream according to the invention, any rectification column having from 5 to 50 separation stages can be used. The number of separation stages is preferably 20 to 30. In the context of the present invention, the number of separation stages is the number of trays in a tray column multiplied by the tray efficiency, either in a packed column (Packungskolone) or with packing (F ü llk)rpern), refers to the number of theoretical separation stages.

Examples of rectification columns having trays include those such as bubble cap trays, sieve trays, tunnel cap trays, valve trays, slotted sieve trays, bubble cap trays, jet trays, centrifuge trays; examples of the rectification column having a packing include those such as a raschig ring, a leicin ring, a pall ring, a bell saddle, a trough saddle; examples of rectification columns with packings include those of the Mellapak type (Sulzer), the Rombopak type (Ku hni), the Montz-Pak type (Montz), and packings with catalyst bags (taschen), for example Katapak (Sulzer).

It is likewise possible to use rectification columns having a combination of tray regions, packing regions and/or packed body regions.

Preference is given to using rectification columns having packings and/or packings (packingen).

The rectification column can be made of any material suitable therefor. They include, inter alia, stainless steel and inert materials.

The apparatus has at least one zone, hereinafter referred to as a reaction zone, in which preferably at least one catalyst has been provided. This reaction zone may be inside the rectification column and/or outside the rectification column. However, this reaction zone is preferably arranged outside the rectification column, wherein one of these preferred embodiments is described in detail in fig. 1.

The reaction is preferably carried out at a temperature of from 30 to 120 deg.C, more preferably from 40 to 100 deg.C, especially from 50 to 80 deg.C. The reaction temperature here depends on the system pressure set. In the case of a reaction zone arranged inside the column, the reaction is preferably carried out at a pressure in the range from 5 to 100 mbar (absolute), in particular at from 10 to 50 mbar (absolute), more preferably from 20 to 40 mbar (absolute).

If the reaction zone is present outside the column, different pressure and temperature conditions can be selected there than in the column. This has the advantage that the reaction parameters of the reactor can be adjusted independently of the operating conditions in the column.

In the case of producing (meth) acrylic anhydride from acetic anhydride and (meth) acrylic acid, the reaction temperature is preferably 40 to 100 ℃, more preferably 50 to 90 ℃, most preferably 70 to 85 ℃.

The reaction mixture may contain, in addition to the reactants, other ingredients such as solvents, catalysts and inhibitors.

Preferably, a heterogeneous catalyst is used in the reaction zone. Particularly suitable heterogeneous catalysts are acidic fixed bed catalysts, especially acidic ion exchangers.

It has surprisingly been found that with these acidic ion exchangers the formation of the intermediate acetyl (meth) acrylate (mixed anhydride of acetic anhydride and (meth) acrylic anhydride) is minimized and is present in the carboxylic anhydride of the formula I only in trace amounts.

Particularly suitable acidic ion exchangers include in particular cation exchange resins, for example styrene-divinylbenzene polymers containing sulfonic acid groups. Suitable cation exchange resins can be obtained from Rohm&Haas under the trade name AmberlystFrom Dow under the trade name DowexAnd Lewatit from Lanxess under the trade name LewatitAnd (4) carrying out commercial purchase.

The amount of catalyst in L is preferably from 1/100 up to 1/1, more preferably from 1/30 to 1/5 of the reaction zone.

Polymerization inhibitors which can preferably be used include, in particular, octadecyl-3- (3, 5-di-tert-butyl-4-hydroxyphenyl) propionate, phenothiazine, hydroquinone monomethyl ether, 4-hydroxy-2, 2, 6, 6-Tetramethylpiperidinooxy (TEMPOL), 2, 4-dimethyl-6-tert-butylphenol, 2, 6-di-tert-butyl-4-methylphenol, para-substituted phenylenediamines, for example N, N' -diphenyl-p-phenylenediamine, 1, 4-benzoquinone, 2, 6-di-tert-butyl-alpha- (dimethyl-amino) -p-cresol, 2, 5-di-tert-butylhydroquinone or mixtures of two or more of these stabilizers. Very particular preference is given to phenothiazine.

The polymerization inhibitor can be metered into the feed upstream of the reaction zone and/or can be metered into the rectification column, preferably at the top of the rectification column.

According to the invention, the transanhydridation is carried out in an apparatus in which the reactants are fed to the reaction zone. At the top of the rectification column, the newly formed carboxylic acid is discharged as the lowest-boiling reaction component, preferably under reduced pressure.

The unconverted reactants and the intermediate products formed are recirculated to the reaction zone, for example by means of a pump.

Once the newly formed carboxylic acid has been completely discharged, the unsaturated carboxylic anhydride of the formula I is then discharged at the top of the rectification column, preferably under reduced pressure.

The catalyst is provided in a separate section or in the entire reaction zone of the apparatus. A separate arrangement of the catalyst is preferred, in which case unconverted reactants and formed intermediate products are recycled into the catalyst-filled section. As a result, an unsaturated carboxylic acid anhydride such as (meth) acrylic anhydride, and a newly formed carboxylic acid such as acetic acid are continuously formed.

A preferred embodiment of the process according to the invention is illustrated in fig. 1. Reaction zone 1 has a gray background in fig. 1 and comprises a reaction zone main portion 1a, a reaction zone dividing portion 1b and input and output lines.

Firstly, (meth) acrylic acid (═ M) AS) and acetic anhydride (═ Ac)₂O) is fed into the main reaction zone portion 1 a.

The entire apparatus is then placed under reduced pressure and the reaction mixture in the main part of the reaction zone is heated by means of the heat exchanger 2 until the rectification column 3 located above the main part of the reaction zone has been completely filled with vapor and liquid.

The heat exchanger 2 is preferably installed separately and connected to the reaction zone main body portion 1a via a pipeline. The reaction mixture is preferably pumped continuously through the heat exchanger 2 by means of a pump 4.

The pump 5 leading to the reaction zone dividing section is now activated and the reaction mixture is also continuously led through the reaction zone dividing section 1 b.

The divided part is preferably a flow tube reactor containing an acidic fixed bed catalyst, more preferably an acidic ion exchanger.

The waste stream 6 is recycled back to the main reaction zone portion 1 a.

In the rectification column 3, separation of components takes place. To avoid polymerization, it is preferred to meter in the polymerization inhibitor at the top of the column.

At the top 7 of the rectification column, the acetic acid formed is first discharged as the lowest-boiling component. Subsequently, the formed (meth) acrylic anhydride was discharged.

Detailed Description

Hereinafter, the present invention will be described in detail with reference to examples.

Example 1: preparation of methacrylic anhydride

In order to prepare methacrylic anhydride by reaction of methacrylic acid and acetic anhydride, a test apparatus according to fig. 1 was constructed.

The rectification column 3 has about 25 separation stages. The column with the top condenser was about 3.5m high, had an internal diameter of 100mm and was equipped with packings of the type CY from Sulzer. The polymerization inhibitor used is phenothiazine. The discharge at the top 7 of the column and the heating capacity of the heat exchanger 2 were controlled by adjusting the appropriate temperature and internal recycle stream in the test apparatus. The reaction zone main body part 1a is a glass vessel having a volume of 10L. The heat exchanger 2 used is a falling-film evaporator.

The experiments were carried out without (experiment 1.1) and with a heterogeneous fixed bed catalyst (experiment 1.2) in the reaction zone partition 1 b. The heterogeneous fixed bed catalyst used was the 500mL acidic ion exchanger Lewatit K2431 from Lanxess. Before the start of the test, the ion exchanger was washed with methacrylic acid to rinse off the water present in the ion exchanger. The methacrylic acid is subsequently sucked off from the ion exchanger substantially completely through a filter.

Methacrylic acid and acetic anhydride are first fed to the main reaction zone portion 1 a. The pressure in the apparatus is then reduced to 20 bar at the top of the column and the reaction mixture is continuously conducted through a heat exchanger 2 and heated by means of a pump 4. Once the rectification column has been completely filled with vapor and liquid, the pump 5 leading to the reaction zone section 1b and the discharge at the top 7 of the column are started.

The following table shows the test results obtained in a comparative manner:

test of		1.1	1.2
				MAS used	mol	72.92	72.92
Ac2O used	mol	36.46	36.46
				MAS used	kg	6.28	6.28
Ac2O used	kg	3.72	3.72
				Amount of ion exchanger	mL	0	500
Time until pump start (0)	h	1.0	1.0
				AcOH discharge time	h	8.5	2.0
Purity of AcOH discharged acetic anhydride methacrylic acid acetyl methacrylate methacrylic anhydride	wt％ wt％ wt％ wt％ wt％	74.21 6.04 13.44 4.86 1.44	93.14 1.32 3.15 1.39 1.00
				Amount of AcOH discharged	kg	5.23	4.59
MAAH discharge time	h	3.0	2.5
				Purity of discharged MAAH acetic anhydride methacrylic acid acetyl methacrylate methacrylic anhydride high boiling point compound	wt％ wt％ wt％ wt％ wt％ wt％	0.06 0.22 0.45 0.80 96.35 2.12	0.04 0.18 0.39 0.23 98.91 0.25
Amount of MAAH discharged	kg	4.49	5.18
				Yield of discharged MAAH	％	79.8	92.1
Residue in reaction zone 1 after the end of the run	kg	0.28	0.23

In the case of the use of an ion exchanger (run 1.2),

a) significantly less by-products (high boilers and acetyl methacrylate) are formed,

b) the test time can be reduced from a total of 12.5h to 5.5h,

c) less unconverted reactants (Ac2O and MAS) were present in the vented AcOH and vented mahh,

d) the yield is significantly higher.

Example 2: preparation of acrylic anhydride

To prepare acrylic anhydride by reaction of acrylic acid and acetic anhydride, the same experimental set-up as described in example 1 was used.

The test conditions and the operating procedure were in accordance with the description given in example 1.

The experiments were carried out in the reaction zone subsection 1b without (experiment 2.1) and with a heterogeneous fixed bed catalyst (experiment 2.2). The heterogeneous fixed bed catalyst used was the 500mL acidic ion exchanger Lewatit K2431 from Lanxess. Before the start of the test, the ion exchanger was washed with acrylic acid to rinse off the water present in the ion exchanger. The acrylic acid is subsequently sucked off from the ion exchanger substantially completely through a filter.

The following table shows the test results obtained in a comparative manner:

test of		2.1	2.2
				Use ofAS of	mol	81.23	81.23
Ac2O used	mol	40.62	40.62
				AS used	kg	5.85	5.85
Ac2O used	kg	4.15	4.15
				Amount of ion exchanger	mL	0	500
Time until pump start (0)	h	1	1
				AcOH discharge time	h	10	2.25
Purity of discharged AcOH Acacetic anhydride Acrylacrylic Acetylacrylate acrylic anhydride	wt％wt％wt％wt％wt％	72.15 7.71 13.94 4.86 1.35	90.03 2.81 4.79 1.32 1.06
				Amount of AcOH discharged	kg	5.82	5.19
AAH discharge time	h	2.35	2.0
				High boiling point compound of acetic anhydride acrylic acid acetyl acrylate acrylic anhydride of purity of discharged AAH	wt％wt％wt％wt％wt％wt％	0.07 0.25 0.51 0.97 95.88 2.32	0.03 0.23 0.50 0.37 98.55 0.32
Amount of discharged AAH	kg	3.92	4.58
				Yield of discharged AAH	％	76.6	89.5
Residue in reaction zone 1 after the end of the run	kg	0.26	0.23

In the case of the use of an ion exchanger (run 2.2),

e) significantly less by-products (high boilers and acetyl acrylates) are formed,

f) the test time can be reduced from a total of 13.35h to 5.25h,

g) less unconverted reactants (Ac2O and AS) were present in the vented AcOH and vented AAH,

h) the yield is significantly higher.

Claims (4)

1. An improved process for the preparation of unsaturated carboxylic acid anhydrides of the general formula I,

R-C(O)-O-C(O)-R (I)

wherein R is a vinyl group or an allyl group,

the process is carried out by transanhydridating an aliphatic carboxylic anhydride with a carboxylic acid of the general formula II in an apparatus consisting of a reaction zone and a rectification column,

R-COOH (II)

wherein R is as defined above, and wherein,

it is characterized in that

a) Feeding the reactants into a reaction zone in stoichiometric ratios,

b) removing carboxylic acid formed as a by-product from the reaction mixture,

c) the carboxylic anhydride of the formula I formed is subsequently discharged,

d) the unconverted reactants are recycled to the reaction zone,

e) the reaction zone contains a heterogeneous catalyst, the heterogeneous catalyst is an acidic ion exchanger, and the acidic ion exchanger is a cation exchange resin, and

f) one or more polymerization inhibitors are added.

2. The process according to claim 1, characterized in that a heterogeneous catalyst is used in the entire reaction zone or in a part of the reaction zone.

3. The process according to claim 1 or 2, characterized in that the catalyst is present in a separate zone of the reaction zone.

4. A process according to any one of claims 1 to 3, characterized in that the unsaturated carboxylic acid anhydride of formula I is (meth) acrylic anhydride, which is prepared by transanhydridation of acetic anhydride and (meth) acrylic acid.