GB2062660A - Method of recovering and reproducing raw materials from polyurethanes - Google Patents

Abstract

The method comprises adding an inorganic or organic compound capable of generating ammonia gas at 50-200 DEG C to a polyurethane, in the presence or absence of a solvent, and heating the resulting mixture at 50-200 DEG C to conduct ammonia decomposition of the polyurethane. Suitable compounds include ammonium carbonate or bicarbonate and urea. The solvent may be water or methyl alcohol.

Description

SPECIFICATION Method of recovering and reproducing raw materials from polyurethanes The present invention relates to a method of recovering and reproducing raw materials from polyurethanes.

Polyurethane is presently produced industrially on a massive scale. As a result, the waste disposal of the product loss produced in the production of polyurethane and the expired products is a great problem having regard to public nuisance as well as resource reuse.

As methods of reusing such wastes, there are known two main methods, i.e. (A) a physical treatment wherein the waste is chipped for reuse and (B) a chemical treatment wherein the waste is thermally decomposed to recover the raw material polyol therefrom.

The present invention is concerned with chemical treatment of the above type (B). There have hitherto been proposed many methods of chemical treatment, which are broadly classified into the following five methods: (1) Hydrolysis with steam at high temperature and high pressure; (2) thermal hydrolysis by addition of an alkali metal; (3) thermal amine decomposition by addition of an organic amine compound; (4) thermal ammonia decomposition with urea or ammonia; and (5) any one of the above methods (1 )-(4) using aliphatic polyol inclusive of raw polyol as a solvent.

According to these methods, however, it is necessary to recover polyol having as high a purity as possible, so that there are caused the following problems.

(i) The decomposition product should be completely liquid at room temperature, so that the thermal decomposition conditions (temperature and decomposition time) become more severe and consequently a greater than expected amount of thermal energy for decomposition is required; and (ii) The aromatic amine compounds such as toluene diamine (TDA) and diphenylmethane (MDA), which are by-produced in the recovery of polyol, should be separated from the polyol product, so that a special after-treatment refining step is required.

As mentioned above, the recovery of polyol according to the prior art is not always economical. In particular, when adopting the above method (5) (using an aliphatic polyol such as raw polyol as a solvent), the industrial economy or profitability must be ignored.

The present inventors have made various studies in order to solve the aforementioned drawbacks of the prior art while seriously considering the industrial economy; and have found that raw materials can be recovered and reproduced from polyurethanes by using an ammonia decomposition process which is economical and safe in operation, without requiring the polyurethane to be completely decomposed to such an extent that the decomposition product is always liquid at room temperature as required in the prior art and without requiring a special after-treatment refining step for removing aromatic amine compounds.

According to the present invention, there is provided a method of recovering and reproducing raw materials from polyurethanes, which comprises adding an inorganic or organic compound capable of generating ammonia gas at a decomposition temperature of 50-2000C to a polyurethane, in the presence or absence of a solvent, and heating the resulting mixture at a temperature of 50-2000C to conduct ammonia decomposition of the polyurethane.

That is, the present invention lies in the ammonia decomposition of polyurethane by an addition of an inorganic or organic compound, which can generate ammonia gas at the decomposition temperature of 50--2000C, to the polyurethane in the presence or absence of a solvent as described above, and is particularly related to the aforementioned chemical treatment methods (4) and (5). In connection with these methods, there have hitherto been known various methods described, for example, in U.S. Patent Specification No. 4,162,995 and Japanese Patent Laid Open No. 4,098/78, No. 78,797/79 and No.

78,798/79. However, U.S. Patent Specification No. 4,1 62,995 discloses a method wherein polyurethane is completely liquified in an anhydrous state by treating it with an hydros ammonia or ammonia gas so as to recover raw materials therefrom, while the present invention adopts an ammonia decomposition process using no ammonia involving danger in handling and may suitably further promote the ammonia decomposition reaction by using a solvent, particularly water.

The Japanese Patent Laid Open No. 4,098/78 discloses a method wherein polyurethane is decomposed with ammonia gas or ammonium hydroxide by using polyol or ethylene glycol as a solvent so as to recover the raw polyol, while the present invention does not use ammonia gas or ammonium hydroxide involving danger in handling and suitably uses water as a solvent for the acceleration of the decomposition reaction.

In Japanese Patent Laid Open No. 78,797/79 and No. 78,798/79, there is disclosed a method wherein polyurethane is decomposed by heating in a mixture of a polyhydroxyl compound and urea or in an addition product of an alkylene oxide-urea. In this method it is necessary to use an aliphatic polyol such as raw polyol in addition to urea or to add alkylene oxide as a synthetic starting material in the polyurethane decomposition. Therefore, this method is not an economical technique for polyurethane decomposition.

The present invention will be described in greater detail below.

By the polyurethane to be subjected to ammonia decomposition in the present invention, there is meant a polymer having a urethane bond in its molecule. More particularly, the polyurethane is a polymer having a urethane bond produced by a polycondensation or polyaddition reaction of an active hydrogen compound, which contains at least a polyoxyalkylene polyol as an essential ingredient, with a polyisocyanate. This polymer may have an allophanate bond, a urea bond, a biuret bond or an isocyanurate bond in addition to the urethane bond. Typical examples of such polymers are polyurethane elastomers containing a polyoxyalkylene polyol as an essential ingredient, rigid polyurethane foams, and flexible polyurethane foams.

According to the present invention, the polyurethane is subjected to an ammonia decomposition reaction. Although the exact mechanism for thermal ammonia decomposition of polyurethane is not clear in detail, it is generally considered to take the following reaction course, as deduced from the chemical reaction behaviour of the resulting decomposition products.

In order to conduct the thermal ammonia decomposition of polyurethane according to the present invention, there is used an inorganic or organic compound capable of generating ammonia gas at a decomposition temperature of 50--200"C, for example an inorganic ammonium salt such as ammonium carbonate, which is a cheap industrial material, or ammonium bicarbonate, or urea.

Among these compounds, ammonium bicarbonate begins to decompose at a temperature of about 60CC to produce ammonia gas. On the other hand, ammonium carbonate, considered as a generic term for a mixture of ammonium bicarbonate and ammonium carbonate, begins to gradually decompose at a temperature of about 300C and fully decomposes at 55-600C so as to produce ammonia gas.

Urea begins to thermally decompose at a temperature of 150--1600C. By thermal decomposition of urea are by-produced biuret (carbamyl urea) containing isocyanic acid as a reaction intermediate and cyanuric acid in addition to ammonia gas. In this case, these by-products easily incorporate into the polyurethane decomposition products.

The main reaction for polyurethane decomposition according to the present invention is a dissociation reaction of the urethane bond contained in the polyurethane polymer into a hydrogen group and a ureido group by ammonia decomposition of ammonia gas produced by the thermal decomposition of the above inorganic or organic compound.

In the case of rigid polyurethane foam, such a presumed reaction mechanism is expressed by the following reaction formula:

According to the present invention, raw polyol may optionally be used as a solvent. In particular, the thermal ammonia decomposition reaction according to the present invention is further accelerated by adding a small amount of water or methyl alcohol. The water is a good solvent for the inorganic ammonium salt and urea, which generate ammonia gas. The methyl alcohol is a good solvent for polyol recovered by the decomposition of polyurethane. It is particularly surprising that these solvents, i.e.

water and methyl alcohol, develop the effect of accelerating the decomposition reaction in respect of a small addition amount, but do not develop the acceleration effect when the addition amount is large.

Therefore, when using a small amount of the solvent, the amount of the inorganic ammonium salt or urea added may be reduced, which further improves the industrial economy of the polyurethane decomposition process according to the present invention.

The reason by the decomposition reaction is accelerated by adding a small amount of the solvent is not all-together clear.

In the aforementioned reaction formula for thermal ammonia decomposition, a decomposition product having a hydroxyl group is recovered as a liquid polyol at room temperature when the decomposition reaction is extremely advanced. According to the present invention, however, it is not necessary to decompose the polyurethane to such an extent that the decomposition product is always liquid at room temperature, but it is frequently sufficient to decompose the polyurethane from its original form to a viscous solid or a liquid, which is a noticeable feature as compared with the conventional recovering processes. Furthermore, this feature contributes not only to save the thermal energy required for the decomposition, but also to improve the industrial economy.Surprisingly, it has been found that the recovered raw materials improve the properties of polyurethanes produced therefrom as seen from the comparison of Reference Examples 1 and 2 as described below.

According to the reaction formula for thermal ammonia decomposition, the decomposition product having an ureido group is a compound produced by reacting a polyisocyanate residue of a polyurethane polymer with ammonia gas. In the present invention, when the polyurethane decomposition product is reused as a recovered raw material, it is not always required to undergo a special refining as an after-treatment, which is important having regard to industrial economy. The reason why the refining step is not required is because the method of the present invention produces the ureido group-containing compound and hydroxyl group-containing compound as a primary decomposition product but does not produce an aromatic amine compound as in the conventional recovering process.However, it is speculated that the ureido group-containing compound is converted into an aromatic amine compound as a secondary decomposition product as the thermal ammonia decomposition reaction proceeds further.

Therefore, in order to avoid tne requirement of special refining as the after-treatment, it is desirable to perform the thermal ammonia decomposition reaction according to the present invention under moderate conditions as far as possible.

When the recovered decomposition product obtained by the method according to the present invention used as a raw polyol, polyurethanes are frequently produced at a sufficiently fast rate without the addition of a catalyst, because the ureido group-containing compound included in the decomposition product or a part thereof is further decomposed to produce an aromatic amine compound, which develops a catalytic effect. In this case, it is considered that the catalytic activity of the ureido group-containing compound is lower than that of the aromatic amine compound. Therefore, even if the reactivity of the recovered raw material obtained in the method according to the present invention is excessively high, it is easy to adjust such a reactivity by the addition of a negative catalyst (reaction inhibitor) as compared with the conventional recovering process.

In the practice of the present invention, the amount of the inorganic or organic compound added as an ammonia gas source to the polyurethane, the amount of water or methyl alcohol added as a solvent, the reaction time, and the reaction temperature within a range of 50-2000C may be optionally selected in accordance with the form of the desired decomposition product, for example viscous solid or liquid. The addition amount of the inorganic or organic compound is preferably 30-1 50 parts by weight per 100 parts by weight of polyurethane having regard to the cost, reaction time and reaction temperature. Furthermore, the addition order of the inorganic or organic compound and the solvent is optional.

In order to efficiently perform the thermal ammonia decomposition reaction, it is preferable that the polyurethane to be decomposed is previously shaped into small chips or powder as far as possible.

Furthermore, it is preferred that the reaction is carried out in a closable-type pressure container to prevent the escape of the generated ammonia gas.

When the thermal ammonia decomposition reaction according to the present invention is carried out by using a solvent, the resulting decomposition product is separated from the solvent by any conventional manner after cooling to room temperature. For instance, when using water as a solvent, the decomposition product is completely separated from the water layer, so that it is thoroughly washed with water, dried and reused as a recovered polyol as it is. When using methyl alcohol as a solvent, the greater part of the decomposition product is dissolved in methyl alcohol, so that methyl alcohol can be removed by means of for example an evaporator so as to reuse the recovered polyol as it is. If it is intended to reuse the recovered polyol, the use of the recovered polyol alone is very rare.It is usual and preferable to blend the recovered polyol with a fresh raw polyol as shown in the following examples, if the reactivity of the blended polyol is fairly high, a negative catalyst may optionally be added to the blended polyol.

The invention will be further described with reference to the following illustrative Examples.

The polyurethanes to be decomposed in the following Examples and Comparative Examples have the following compounding recipe: (A) Rigid Polyurethane foam (parts by weight) GR-30 (aromatic amine-series polyether polyol, made by Takeda Yakuhin Kabushiki Kaisha, trade name) 100 Water 1.7 Trichloromonofluoromethane 39.0 DABCO-33LV (triethylene diamine solution, made by Sankyo Air Products Kabushiki Kaisha, trade name) 1.8 Dibutyltin diiaurate 0.18 VA-1 648 (Silicone surfactant, made by Gold Schmitt Co.Ltd., (trade name) 1.5 TCEP [tris(p-chloroethyl)phosphate] 7 Crude MDI (crude-p,p'-diphenylmethane diisocyanate) (NCO index) (110) Foam density 0.0245 (g/cm3 (B) Flexible polyurethane foam (parts by weight) DOW CP-301 0 (polyether polyol, made by Dow Japan Co. Ltd., trade name) 100 Water 4.0 DABCO (triethylene diamine, made by Sankyo Air Products Kabushiki Kaisha, trade name) 0.05 Stannous octoate 0.2 BF-2370 (silicone surfactant, made by Gold Schmitt Co. Ltd., trade name) 2.0 TDI-80 (mixture of 80% 2,4-toluene diisocyanate and 20% 2,6 toluene diisocyanate) (NCO index) (105) Foam density 0.0200 (g/cm3) EXAMPLES 1-4 Into a glass ceramic pressure container of 11 capacity (made by Taiatsu Gaishi Kogyo Kabushiki Kaisha, Model TEM-D1 000) provided with a pressure indicator, a safety valve and a purge valve were charged predetermined amounts of urea and water as shown in the following Table 1 to prepare a urea solution, to which was added 50 g (100 parts by weight) of a decomposing sample obtained by pressing a rigid polyurethane foam (A) 25 mm thick to a thickness of 2-3 mm and cutting it into chips of about 1 cm square and then the container was airtightly closed.

The container filled with the sample was placed in a silicon oil bath, where the rigid polyurethane foam (A) was subjected to an ammonia decomposition under the decomposition conditions as shown in Table 1. The light brown and rigid foam (A) was converted into a blackish brown liquid, while being boiled, with lapse of the decomposition time. The resulting decomposition product exhibited the property as shown in Table 1.

After naturally cooling to room temperature, the decomposition product was clearly separated from the water layer and changed into a state facilitating the after-treatment. Moreover, the infrared absorption spectrum of the decomposition product included an absorption peak group assigned to the raw polyol and an amino group absorption characteristic.

TABLE 1 Example 1 2 3 4 (parts by weight) rigid polyurethane foam (A) 100 100 100 100 urea 50 50 50 100 water 25 25 25 100 Decomposition conditions: temperature, 0C 150 165 165 150 time, hr 7 5 7 5 intemal pressure, kg/cm2 5.2 6.2 not 5.2 measured Property of decomposition product at room temperature: any products are blackish brown and viscous solid liquid liquid solid REFERENCE EXAMPLES 1-4., COMPARATIVE EXAMPLE 1 The blackish brown and viscous decomposition product of each of Examples 1-4 was changed into a liquid by heating at 80-900C.Twenty five parts by weight of such a liquid decomposition product was mixed with 75 parts by weight of aromatic amine series polyether polyol (GR-30, trade name, made by Takeda Yakuhin Kabushiki Kaisha) for the production of rigid polyurethane foam, which was heated at the same temperature, while stirring, to prepare a polyol blend. This polyol blend exhibited no two-layer separation even at room temperature and had a good compatibility.

The polyol blend was foamed according to the compound recipe as shown in the following Table 2 in the absence of a catalyst to produce a rigid polyurethane foam, the properties of which were measured to obtain a result as shown in Table 2. For comparison, the usual polyol was used alone to produce a rigid polyurethane foam, the properties of which are also shown in Table 2.

TABLE 2

Reference Example 1 2 3 4 Comparative Example 1 Compounding recipe: (parts by weight) Polyol blend 100 100 100 100 GR-30 100 (GR-30/recovered polyol*1 75/25) Water 1.9 2.0 1.5 2.0 Water 2.0 trichloromonofluoromethane 37.5 37.5 37.5 56.0 trichloromonofluoromethane 36.0 L-5420 * 2 2.0 2.0 2.0 2.8 VA-1648 1.5 DABCO-33LV 1.8 dibutyltin dilaurate 0.18 TCEP 7 Crude MDI 143.9 145.4 137.9 145.4 Crude MID (NCO index) (110) (NCO index) (110) (110) (110) (110) Foaming cream time, sec. 2#3 1#2 2#3 2#3 5#6 rise time, sec. 50#60 85 90 70 57 Properties foam density, g/cm 0.9209 0.0221 0.0253 0.0171 0.0238 thermal conductivity #, Kcal/mhr C 0.0165 0.0172 0.0175 0.0320 0.0173 compression strength, kg/cm # 0.95 0.82 0.82 0.62 0.66 # not not measured 0.99 measured 0.68 0.80 ratio of dimensional change at low temperature (-5 C, 24 hr) # -0.1 -0.4 -0.1 -0.1 0.1 # -0.2 -0.1 0 -0.1 -0.2 Note) *1: Calculation of active hydrogen equivalent for the recovered polyol Assuming that the hydroxyl number of the recovered polyol corresponds to the hydroxyl number of polyol GR-30 used in the rigid polyurethane foam (A) of 400, the hydroxyl equivalent of the recovered polyol is 140.0.

Further, assuming that the recovered polyol contains MDA (diphenylmethane diamine) corresponding to about 50% decomposition of crude MDI used in the foam (A) as a by-product, the hydroxyl equivalent of the recovered polyol is really about 93.3 by adding the amine equivalent of MDA.

*2: silicone surfactant, made by Nippon Unicar Kabushiki Kaisha, trade name.

From a comparison of Reference Examples 1 and 2 of Table 2, it can be seen that when recovering and reproducing the raw materials from the polyurethane by the thermal ammonia decomposition, there is a tendency to improve the properties of the polyurethane foam produced by using the recovered raw material when the decomposition of the polyurethane is incomplete. That is, the properties of the polyurethane foam produced from the polyol recovered by retaining a degree of polynierization of the polyurethane as far as possible, which corresponds to Reference Example 1, are superior to those of the polyurethane foam produced from the polyol recovered by completely decomposing the polyurethane, which corresponds to Reference Example 2.

That is, it can be said that when recovering and reproducing raw materials from polyurethane, if the ammonia decomposition reaction is stopped to an extent to obtain a reutilizable recovered raw material, for example an extent capable of blending the recovered polyol with the raw polyol, the use of the resulting decomposition product becomes advantageous having regard to the cost of the decomposition process and the properties of the polyurethane foam produced from the recovered decomposition product. Such an advantage of the present invention is a noteworthy characteristic as compared with the conventional polyurethane decomposition technique aiming at the production of a completely liquid decomposition product.

When the properties of Reference Examples 1-4 are compared with those of Comparative Example 1 using the usual polyol alone, it can be seen from Table 2 that the polyol recovered by the method of the present invention can be blended with the usual polyol without the after-treatment refining required for the conventional polyurethane decomposition technique and also the properties of the rigid polyurethane foam produced from the recovered polyol are substantially equal to rather superior to those of the usual foam.

EXAMPLES 5-11 Into a stainless reaction container of 200 ml capacity (made by Taiatsu Gaishi Kogyo Kabushiki Kaisha, Model TVS-1) provided with a safety valve and a purge valve were charged predetermined amounts of an inorganic ammonium salt or urea and water or methanol as shown in the following Table 3, to which was added 5.0 g (100 parts by weight) of a decomposing sample obtained by shaping the rigid polyurethane foam (A) or flexible polyurethane foam (B) into chips of about 1 cm square as described in Examples 1-4 and then the container was airtightly closed.

The container filled with the sample was placed in a silicone oil bath, where the foam (A) or (B) was subjected to an ammonia decomposition under the decomposition conditions as shown in Table 3.

From the data of Table 3, it can be seen that the foam (A) or (B) can be decomposed according to the method of the present invention.

TABLE 3 Example 5 6 7 8 9 10 11 (Parts by weight) Rigid polyurethane foam (A) 100 100 100 100 100 100 Flexible polyurethane foam (B) - - - - - - 100 Ammonium carbonate 100 40 50 - - - 40 Ammonium bicarbonate - - - 100 100 - Urea - - - - - 100 Water - 20 - - 100 - 20 Methyl alcohol - - 50 100 - 100 Decomposition conditions Temperature, C 150 150 130 150 150 150 150 time, hr 5 5 5 5 5 5 5 Property of decomposition Blackish Blackish Blackish Blackish Blackish Blackish Blackish product at room temperature brown brown brown brown brown brown brown viscous viscous viscous viscous viscous solution liquid liquid liquid solution solution liquid (water (water (water separation) separation) separation)

Claims (8)

1. A method of recovering and reproducing raw materials from polyurethanes, which comprises adding an inorganic or organic compound capable of generating ammonia gas at a decomposition temperature of 50-2000C to a polyurethane, and heating the resulting mixture at a temperature of 50-2000C to conduct ammonia decomposition of the polyurethane.

2. A method as claimed in claim 1, wherein the inorganic compound is ammonium carbonate or ammonium bicarbonate.

3. A method as claimed in claim 1, wherein the organic compound is urea.

4. A method as claimed in any of claims 1 to 3, wherein the inorganic or organic compound is added to the polyurethane in the presence of a solvent.

5. A method as claimed in claim 4, wherein the solvent is water or methyl alcohol.

6. A method as claimed in any of claims 1 to 3, wherein the inorganic or organic compound is added to the polyurethane in the absence of a solvent.

7. A method as claimed in any of claims 1 to 6, wherein the inorganic or organic compound is added in an amount of 30-1 50 parts by weight per 100 parts by weight of the polyurethane.

8. A method according to claim 1, substantially as herein described in any of the foregoing Examples.