WO2009048927A1

WO2009048927A1 - Vernonia oil polyols

Info

Publication number: WO2009048927A1
Application number: PCT/US2008/079167
Authority: WO
Inventors: James W. Rawlins; Sharathkumar K. Mendon; Yuan Liu
Original assignee: University Of Southern Mississippi
Priority date: 2007-10-08
Filing date: 2008-10-08
Publication date: 2009-04-16

Abstract

The present invention discloses polyols synthesized from vemonia oil. The process for synthesizing a vemonia oil-based polyol involves reducing vernonia oil to vernolic acid; heating the vernolic acid at elevated temperatures to form oligomers; and forming the polyol by transesterification of the oligomers with glycerol. The polyols synthesized according to the present invention have lower viscosity values at similar hydroxyl values compared to polyols synthesized from other vegetable oils. The lower viscosity values are of importance in the synthesis of foams as it promotes foam growth.

Description

VERNONIA OIL POLYOLS

BACKGROUND OF THE INVENTION

[0001] Polyols commonly used in rigid polyurethane (PU) foam manufacture have hydroxyl number of 350-650 mg KOH / g, and viscosities (@25°C) of 300-35000 cP. Rigid polyurethane (PU) foams are widely used in appliances, construction, insulation, transportation, packaging, and sporting goods. PU foams are prepared by reacting isocyanates with polyols in the presence of blowing agents (1). Most polyols utilized in foam manufacture are petrochemical derivatives. Rising petroleum costs, environmental sustainability and long term supply concerns have promoted interest in developing renewable resource based polyols such as vegetable oil derivatives. There are three main methods to synthesize vegetable oil-based polyols for rigid PU foams. The first is epoxidation of vegetable oil double bonds followed by hydroxylation. Polyols synthesized by this method yield solid polyols when the hydroxyl number exceeds 200 mg KOH/g (2). The second is hydroformylation of the double bonds and subsequent hydrogenation of the aldehyde to yield hydroxyl groups. However, it is difficult to obtain polyols with hydroxyl number higher than 230 mg KOH/g by this method (3). The final method is transesterification of vegetable oils with multifunctional hydroxyl compounds such as glycerin and sorbitol. Polyols with high hydroxyl number (up to 420 mg KOH/g) prepared by this method have high viscosity and high metal soap content (4). Polyols commonly used in rigid PU foam manufacture have hydroxyl number of 350-650 mg KOH/g and viscosities (@25°C) of 300- 35000 cP (1).

[0002] Polyols prepared from castor oil, the most commonly used vegetable oil in the PU foam industry, still have undesirable characteristics, specifically either relatively low hydroxyl numbers or high viscosity values.(5) Lower viscosity values are of critical importance in the synthesis of foams as it promotes foam growth. As described in U.S. Patent No. 7,125,950, polyols with high hydroxyl values (> 250 mg KOH/g) are difficult to obtain. Moreover, polyols with high hydroxyl values usually exhibit proportionately higher viscosity due to the increased hydrogen bonding afforded by the hydroxyl groups, and some are even solids. There still exists a need for improved renewable resource based polyols. An improvement in the field would provide a method for synthesizing renewable resource based polyols that have lower viscosity values at similar hydroxyl values than commercial polyols currently used in foam manufacture.

SUMMARY OF THE INVENTION

[0003] The present invention provides a method for synthesizing polyols from vernonia oil. Polyols synthesized from vernonia oil as provided in the present invention have lower viscosity values at similar hydroxyl values compared to polyols synthesized from other vegetable oils. Polyols prepared from castor oil, the most commonly used vegetable oil in PU foam industry, have either much lower hydroxyl number or much higher viscosity than that of vernonia oil- based polyol. Vernonia oil primarily differs from corn and soybean oils via its major constituent, i.e., namely vernolic acid. Corn and soybean oils do not contain any vernolic acid. The average composition of corn oil is 11% palmitic acid, 2% stearic acid, 28% oleic acid, 58% linoleic acid, and 1% linolenic acid. Similarly, the average composition of soybean oil is 11% palmitic acid, 4% stearic acid, 24% oleic acid, 54% linoleic acid, and 7% linolenic acid. A key feature of vernonia oil is that it is much lower in viscosity than the synthetic analog polyols such as materials resulting from epoxidized soybean oil. Corn and soybean oil can be epoxidized to incorporate the epoxide functionality naturally present in vernonia oil, however, such synthetically epoxidized oils are much higher in viscosity than vernonia oil. Because lower viscosity values are of critical importance in the synthesis of foams for promoting foam growth, and vernonia oil is a renewable resource, the present invention provides significant improvements over the manufacture of polyols from either petrochemical derivatives or the vegetable oils presently used in making polyols.

[0004] According to the present invention, a process for synthesizing a vernonia oil based polyol is provided, comprising: reducing vernonia oil to vernolic acid; heating the vernolic acid at elevated temperatures sufficient for refluxing to form oligomers; and forming a polyol by transesterification of the formed oligomers with glycerol. Polyols produced according to this method can be used in the manufacture of rigid foams.

[0005] Li another aspect of the invention, a method for synthesizing a vegetable oil polyol for use in flexible foams is provided. According to the method, lesquerella oil is reduced to lesquerolic acid. The lesquerolic acid is mixed with vernonia oil and catalyst, heated, and further reacted to form a vegetable oil polyol useful for synthesizing flexible foams.

DETAILED DESCRIPTION OF THE INVENTION

[0006] The present invention provides a process for the production of a vernonia oil polyol, depicted in Scheme 1. Vernonia oil was first reduced to vernolic acid. Carboxyl groups of vernolic acid reacted with the epoxy groups of vernolic acid at elevated temperatures to form oligomers. Vernonia oil has an average fatty acid composition of vernolic acid (62.7%), palmitic acid (4.4%), stearic acid (4.9%), oleic acid (10.6%), and linoleic acid (17.4%).[6] The final product is formed by transesteriflcation of vernonia oligomers and glycerin in solvent. A preferred solvent is dimethylformamide (DMF). Using DMF as a solvent facilitates transesteriflcation, significantly increasing the hydroxyl number of polyols. A suitable solvent can be used in place of DMF based on cost, non-reactivity, and boiling point. [0007] In a preferred embodiment the transesteriflcation of the oligomers is conducted by heating a mixture of the oligomers, glycerol, dimethylformamide, and dibutyltin oxide at 180 ⁰C. hi a more preferred embodiment, the heating of the mixture occurs for at least forty-eight hours. [0008] hi one aspect, the vernonia oil is reduced to vernolic acid by hydrolyzing the vernonia oil with a basic solution and acidifying the hydrolyzed vernonia oil to prepare the vernolic acid. [0009] hi another aspect, the oligomers are formed by heating vernolic acid with glycerin, an inert solvent, and butyltin hydroxide oxide. The reaction is continued until the desired acid value is achieved (preferably < 2 mg KOH/g). The inert solvent can be selected by one of skill in the art, for example, toluene, heptane, chlorobenzene, benzotrifluoride, and chlorobenzotrifluoride, or xylene, hi a preferred embodiment, the inert solvent is xylene. - A -

[0010] The hydroxyl number of the vernonia polyol produced by the present process preferably has a hydroxyl number of between about 350 and 500 mg KOH/g and an acid value of < 2 mg KOH/g.

Scheme 1. Vernonia Polyol synthesis

R -fatty acid

[0011] The present invention also provides a method for producing a lesquerella oil and vernonia oil based polyol. According to the method, lesquerella oil is blended with NaOH, heated, and subsequently acidified to yield lesquerolic acid. Lesquerolic acid and vernonia oil are then reacted with catalyst and heated at elevated temperatures, reducing the epoxy content. The final product is formed by adding an esterification catalyst to the lesquerolic acid and vernonia oil mixture and heating until the desired acid value (preferably < 2 mg KOH/g) is achieved. In a preferred embodiment, the transesterification catalyst is butyltin hydroxide oxide. The ratio of lesquerolic acid and vernonia oil can be varied to synthesize polyols with varying hydroxyl values and molecular weights. The lesquerella oil and vernonia oil based polyol produced by the process of the present invention preferably has a hydroxyl number of about 40 to about 100 mg KOH/g. The polyols synthesized according to this method are particularly useful in the synthesis of flexible foams. EXAMPLES

[0012] Example 1: Preparation of vernonia oil-based polyols (Polyol E, Table 1). Vernonia oil was hydrolyzed by NaOH solution (4%) at 8O⁰C and then neutralized using hydrochloric acid to provide vernolic acid. Alternatively, a KOH solution of similar concentration can also be used. A number of processes are known industrially to convert vegetable oils into their constituent fatty acids, for example, U.S. Patent Application Serial No. 10/923,968, entitled "Continuous splitting process to produce free fatty acids" describes several known industrial processes of synthesizing fatty acids. Vernolic acid (50.0 g), glycerin (50.0 g), xylene (100.0 g), and butyltin hydroxide oxide (0.2 g) were charged to a three-necked flask equipped with Dean- Stark trap and heated to refluxing temperatures (135 - 145°C). The reaction was continued until an acid value of < 2 mg KOH/g was reached. Xylene was then removed by distillation. DMF (50.0 g) and dibutyltin oxide (0.2 weight % on oil) were charged to the reactor, and the temperature was raised to 180⁰C. After 48 hours of reaction at 18O⁰C, the DMF was removed by distillation. A suitable solvent can be used in place of DMF based on cost, non-reactivity, and boiling point. The polyol phase separated from the unreacted glycerin and was washed with brine, and dried with MgSO₄ to yield the final product. While butyltin hydroxide oxide is employed as the catalyst, any of numerous esterification catalysts well-known in the art can be used in the reaction. Similarly, xylene is employed as the solvent, and any inert solvent with the appropriate boiling point can be used in the synthesis. For example, toluene, heptane, chlorobenzene, benzotrifluoride, and chlorobenzotrifluoride are several solvents that can be employed in the reaction.

[0013] Comparative Example 2: Preparation of castor oil-based polyols. Castor oil, multifunctional hydroxyl compounds, solvent, and dibutyltin oxide (0.2 weight % on oil) were charged into a flask and then heated to 180⁰C with stirring under nitrogen atmosphere. After 24 hours of reaction at 180⁰C, the solvent was removed by distillation. The polyol that phase separated from the multifunctional hydroxyl compound was washed with brine, and dried with MgSO₄ to provide the final product.

[0014] Table 1 provides the preparation and properties of vegetable oil-based polyols. The table demonstrates that polyols prepared from castor oil, the most commonly used vegetable oil in PU foam industry, have either a much lower hydroxyl number or a much higher viscosity than that of vernonia oil-based polyol. Polyol C was not evaluated because it was a solid at 25°C. Using DMF as a solvent can facilitate transesterification reaction, increasing significantly the hydroxyl number of polyols. Any inert solvent with appropriate boiling point can be used for the transesterification reaction as long as the solvent's polarity is high enough to encourage transesterification. Solvents of this nature can be easily identified by those of skill in the art, examples include dimethyl acetamide, dimethyl sulfoxide and diisopropyl ethylamine.

Table 1. Preparation and properties of vegetable oil-based polyols

[0015] Example 3: Preparation of polyurethane foams. Polyols, glycerin, catalysts, water, and surfactant were charged into a paper cup and agitated with a high speed mixer for 20 seconds. After addition of pMDI, the agitation was continued for another 10 seconds, and then quickly poured into a large paper bucket. The free-rise foams were cured at ambient temperature for one week before evaluating their mechanical properties. Table 2 provides the resultant properties of the PU foams. As seen from Table 2, PU foams prepared from vernonia oil-based polyol have significantly higher compressive modulus and flexural modulus than foams made from the castor oil-based polyol. Table 2: PU foams

[0016] Example 4: Preparation of a lesquerella oil and vernonia oil polyol

Polyol F was prepared by blending lesquerella oil (100.0 g) with 200 mL of NaOH solution (1.8 N) under mechanical agitation. The system was heated to 8O⁰C for 5 hours and then acidified with dilute sulfuric acid to pH 3.6. The organic layer was dried using magnesium sulfate and filtered to yield lesquerolic acid. Lesquerolic acid (84.0 g), vernonia oil (60.0 g), and AMC-2 (0.1 g) catalyst (AMC-2, Aerojet Chemicals, Rancho Cordova, CA, is a mixture of 50% trivalent organic chromium complexes and 50% phthalate esters) were charged into a three-necked flask and heated to 14O⁰C. Once the epoxy content was reduced to < 1%, butyltin hydroxide oxide was added, and the reaction mixture was heated to 18O⁰C under nitrogen. The reaction was stopped when the acid value was reduced to < 2 mg KOH/g. The resulting polyol had a molecular weight of 2600, hydroxyl value 56 mg KOH/g, and viscosity 3000 cP. The ratio of lesquerolic acid to vernonia oil can be varied to synthesize polyols with varying hydroxyl values and molecular weights. The resulting polyol was employed in synthesizing flexible foams following the procedure described in Example 3. The composition and properties of the resulting foam are shown in Table 3 below. Table 3

REFERENCES

1. Oertel, G.; Polyurethane Handbook 2^nd Ed., Hansen Munich, Germany, 1994.

2. Guo, A.; Javni, L; Petrovic Z., J. Appl. Polyni. Sei. 2000, 77, 467-473.

3. Guo, A.; Demydov, D.; Zhang W., Petrovic Z., J. Polym. Environ. 2002, 10, 49-52.

4. Dwan'Isa, J. L.; Drzal L. T.; Mohanty A. K.; Misra M. WO 2004/099227, 2004.

5. G.R. O'Shea Company, Caspol^® Castor Oil Polyols brochure, found at website: groshea.com/caschem/caspol.html.

6. Mohamed A. L, Mebrahtu T., and Andebrhan T., Perspectives on New Crops and New Uses. 1999, J. Janick (Ed.), ASHS Press, Alexandria, VA.

Claims

WHAT IS CLAIMED IS:

1. A process for synthesizing a vernonia oil-based polyol comprising: a) reducing vernonia oil to vernolic acid; b) heating the vernolic acid at an elevated temperature sufficient for refluxing to form oligomers; and c) forming the polyol by transesterification of the oligomers with glycerol.

2. The process of claim 1 wherein dimethylformamide is used as a solvent in forming the polyol by transesterification.

3. The process of claim 1 wherein the vernonia oil is reduced to vernolic acid by hydrolyzing the vernonia oil with a basic solution and acidifying the hydrolyzed vernonia oil to prepare the vemolic acid.

4. The process of claim 1 wherein the oligomers are formed by heating the vernolic acid with glycerin, xylene and dibutyltin oxide.

5. The process of claim 2 wherein the transesterification of the oligomers is conducted by heating a mixture of the oligomers, glycerol, dimethylformamide, and dibutyltin oxide at 180°C.

6. The process of claim 5 wherein the heating of the mixture occurs for at least forty-eight hours.

7. A vernonia polyol produced by the process of claim 1.

8. The vernonia polyol of claim 7 having an acid value of < 2 mg KOH/g.

9. The vernonia polyol of claim 7 having a hydroxyl number from about 350 - 500 mg KOH/g.

10. A polyurethane foam prepared from a vernonia polyol produced by the process of claim 1.

11. A process for synthesizing a lesquerella oil and vernonia oil based polyol: a) reducing lesquerella oil to lesquerolic acid; b) mixing lesquerolic acid, vernonia oil, and a catalyst, and heating said mixture to refluxing temperatures; d) adding an esterification catalyst to the mixture and heating to 180⁰C to yield the polyol.

12. The process of claim 11 wherein the esterification catalyst is butyltin hydroxide oxide.

13. A lesquerella oil and vernonia oil based polyol produced by the process of claim 11.

14. A flexible foam prepared from a lesquerella oil and vernonia oil based polyol produced by the process of claim 11.

15. The lesquerella oil and vernonia oil based polyol of claim 13 wherein the acid value of the polyol is < 2 mg KOH/g.

16. The lesquerella oil and vernonia oil based polyol of claim 13 with a hydroxyl number of about 40-100 mg KOH/g.