Abstract:
A method of transalkoxylation of nucleophilic compounds in which an alkoxylated and a nucleophilic compound are combined in a suitable vessel and reacted in the presence of a heterogeneous catalyst under conditions capable of transferring at least one hydroxyalkyl group from the alkoxylated compound to the nucleophilic compound. The method is especially useful in the transalkoxylation of alkanolamines to transfer a hydroxyalkyl group from an alkanolamine having a greater number of hydroxyalkyl groups to an alkanolamine having a lesser number of hydroxyalkyl groups.

Description:
PRIORITY 
     The present non-provisional patent Application claims benefit from U.S. Provisional Patent Application having Ser. No. 61/195,456, filed on Oct. 6, 2008, by Stephen W. King, and titled TRANSALKOXYLATION OF NUCLEOPHILIC COMPOUNDS, wherein the entirety of said provisional patent application is incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to the transalkoxylation of nucleophilic compounds, especially the transoxylation of compounds having heteroatoms. 
     BACKGROUND 
     The preparation of alkoxylated compounds is well known. Typically, the method used to prepare alkoxylated compounds produces a mixture of products that is less than ideal. This is especially in the case in the preparation of alkoxylated, nitrogen compounds such as alkanolamines. 
     For example, alkanolamines, such as monoethanolamine (MEA), diethanolamine (DEA), and triethanolamine (TEA) are often prepared by reacting ethylene oxide with ammonia. The resulting product is a mixture of MEA, DEA, and TEA. While changing the stoichiometry of the reactants can vary the ratio of these amines in the final product mixture, the reaction is still not sufficiently selective to produce a high level of DEA. 
     Various approaches have been used to overcome this problem. For example, U.S. Pat. No. 4,264,776 (to Monsanto), Apr. 28, 1981, discloses the catalytic oxidation of tertiary amines with oxygen to form secondary amines in the presence of an active carbon catalyst. An example is provided which treats TEA over active carbon at 115° C. in the presence of oxygen with 60% conversion to DEA. 
     U.S. Pat. No. 4,328,370 (to TDCC), May 4, 1982, discloses the use of hydrogenation catalysts (Pd, Pt, Rh, Ru) at super-atmospheric pressure under anhydrous conditions. For example, TEA is treated with ammonia in the presence of Pd/C or Pd/Al 2 O 3 , optionally in the presence of hydrogen, at 200-300° C. to give MEA and DEA. 
     U.S. Pat. No. 6,469,214 B2 (to BASF) Oct. 22, 2002, discloses the preparation of DEA from a mixture of MEA and TEA in the presence of a strong base and, optionally, ammonia. The preferred strong bases are alkali metal and alkaline earth metal hydroxides, or an alkali metal alkoxide. 
     WO 2007/093514 A1 (to BASF), Aug. 23, 2007, discloses the conversion of monoethylene glycol into MEA and DEA via a reductive amination. 
     U.S. Pat. No. 6,169,207 (to Nippon Shokubai Kagaku Kogyo (NSKK)), 2001, discloses selective ethoxylation. 
     There remains a need for a more efficient method for the preparation of, for example, secondary alkanolamines. 
     SUMMARY OF THE INVENTION 
     The present invention provides a method for the transalkoxylation of nucleophilic compounds in which a hydroxyalkyl group on a heteroatom of one compound is transferred to another compound. The method can be practiced with or without the use of additional nucleophiles. 
     In one embodiment, the present invention provides a method of transferring a hydroxyalkyl group from an alkoxyated compound to a nucleophilic compound comprising the steps of
         a) providing the alkoxylated and nucleophilic compounds;   b) combining the alkoxylated and nucleophilic compounds in a suitable vessel;   c) reacting the alkoxylated and nucleophilic compounds in the presence of a heterogeneous catalyst under conditions capable of transferring at least one hydroxyalkyl group from the alkoxylated compound to the nucleophilic compound.       

     In another embodiment, the present invention provides a method of transalkoxylating an alkoxylated compound comprising the steps of:
         a) providing a first and a second alkoxylated compound;   b) combining the first and second alkoxylated compounds in a suitable reaction vessel;   c) reacting the first and second alkoxylated compounds in the presence of a heterogeneous catalyst under conditions capable of transferring at least one hydroxyalkyl group from one of the alkoxylated compounds to the other of the alkoxylated compounds.       

     In yet another embodiment, the present invention provides a method of transalkoxylating an alkanolamine compound comprising the steps of:
         a) providing a first and a second alkanolamine, each alkanolamine having a different degree of substitution;   b) combining the first and second alkanolamines in a suitable reaction vessel;   c) reacting the alkanolamines in the presence of a heterogeneous catalyst under conditions capable of transferring at least one hydroxyalkyl group from one of the alkanolamines to the other of the alkanolamines.       

     In a further embodiment of the invention, the first and second alkanolamines are selected from (i) a primary and a tertiary alkanolamine, or (ii) a secondary and a tertiary alkanol amine, or (iii) a primary and a secondary alkanolamine. 
     In the present invention, the transfer of the hydroxyaklyl group is preferably from the compound that has the greater degree of substitution to the compound that has the lesser degree of substitution. 
     The method of the present invention provides several advantages over the prior art. For example, it eliminates the need to employ strong bases and therefore avoids the problems associated with salt formation during the process. Additionally, it provides a mechanism by which desired alkanolamines, especially DEA, may be produced with high selectivity. 
     Additionally, the method of the invention is economical in that it can be used with conventional equipment. Furthermore, the present invention employs non-precious metal catalysts, thereby eliminating the need for the use of such materials. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates the effect of the gaseous atmosphere on the area percentage of products produced. 
         FIG. 2  illustrates the influence of changing the flow rate of the gas feed on the percentage of products produced. 
         FIG. 3  illustrates the influence of changing the flow rate of the liquid feed on the area percentage of products produced using different liquid feed rates. 
         FIG. 4 . illustrates the influence of reaction temperature on the percentage of products produced. 
         FIG. 5 . illustrates the influence of the catalyst surface area on the area percentage of products produced. 
         FIG. 6 . illustrates the influence of recycle on the quantity of product produced over time. 
     
    
    
     DETAILED DESCRIPTION 
     The materials required in the process of the invention include an alkoxylated compound, a nucleophile and a heterogeneous catalyst. The alkoxylated compound may be any heteroatom-containing compound in which the heteroatom is substituted with a hydroxyalkyl group. Preferably, the heteroatom is nitrogen (also referred to herein by its chemical symbol “N”). The most preferred alkoxylated compound for use in the present invention is an alkanolamine that may be represented the formula
 
(R 1 )(R 2 )(R 3 )N
 
wherein R 1  is a hydroxyalkyl group having from 2-20 carbon atoms, and each of R 2 , and R 3  group is independently selected from hydrogen, alkyl groups having from 1 to 20 carbon atoms, and hydroxyalkyl groups having from 2-20 carbon atoms. Preferably, each of R 1 , R 2 , and R 3  contain from 1-5 carbon atoms, and more preferably from 1-3 carbon atoms. A preferred subclass of alkanolamines for use in the present invention is selected from one or more of MEA, DEA, and TEA.
 
     Any nucleophilic compound may be employed in the process of the present invention. The nucleophilic compound is preferably selected from one or more of an alkanolamine of the formula (R 1 )(R 2 )(R 3 )N, wherein R 1 , R 2 , and R 3  are as defined above in all respects, an alkyleneamine, an alkylamine, water and an alcohol. The alkylene and alkyl groups of the alkyleneamine and alkylamine compounds preferable contain from 1-20 carbon atoms. Preferably, the nucleophilic compound comprises an alkanolamine compound. A preferred subclass of alkanolamines for use as the nucleophilic compound in the present invention is selected from one or more of MEA, DEA, and TEA. 
     The catalyst used in the present invention may be any heterogeneous catalyst. Preferably the catalyst is not a hydrogenation catalyst. Also the catalyst used in the present invention is preferably not a precious metal catalyst. 
     A particularly preferred catalyst for use in the present invention is zirconium dioxide (ZrO 2 ), also sometimes referred to as zirconia. Zirconia is a slightly acidic metal oxide compound. Zirconia useful in the present invention may have any surface area. Typically it has a surface area of from about 40-100 m 2 /g. Preferably the zirconia has a surface area of from about 50-90 m 2 /g, and more preferably of from about 50-75 m 2 /g. 
     The catalyst may also include other materials that enhance the performance of the method of the invention. While the mechanism of the enhancement is not fully understood, it has been found that when certain additives are used in combination with the heterogeneous catalyst the formation of certain impurities is suppressed. These additives include metal oxides that may be oxides of the Group IA, the Group IIA, the Lanthanide series, and the Actinide series of the Periodic Table of the Elements. Preferably the additives are selected from oxides of sodium, potassium, cesium, magnesium, and calcium. The additive generally comprises from about 0.5-15% by weight of the catalyst. Preferably it comprises from about 1-10% by weight, and more preferably from about 1-5% by weight, of the catalyst. 
     The method of the invention will now be discussed with respect to the transalkoxylation of alkanolamines. Specifically, the method will be discussed with respect to the transethoxylation of MEA by TEA to produce DEA. It is to be understood that this is not intended to limit the present invention, but rather to facilitate the discussion and understanding of the present invention. 
     The transethoxylation of MEA by TEA to produce DEA may be represented by the general scheme 
     
       
                 
         
             
             
         
      
     
     In the process, a feed of an alkoxylated compound (here TEA) and a nucleophilic compound (here MEA) is provided to a suitable reactor. One of the compounds has a higher degree of substitution than the other of the compounds. When the feed comprises two alkanolamines, it preferably comprises one of (i) a primary and a tertiary alkanolamine, (ii) a secondary and a tertiary alkanol amine, or (iii) a primary and a secondary alkanolamine. 
     Typically, the compounds of the feed are dissolved in a suitable solvent prior to being fed to the reactor. Suitable solvents include ethers, acetonitrile, methanol, ethylene glycol, and water. 
     The compounds may be dissolved in the solvent at a molar ratio of from about 10:1 to about 1:10 of the alkoxylated compound to the nucleophilic compound, preferably at a ratio of from about 5:1 to about 1:5, and more preferably at a ratio of from about 2:1 to about 1:2. The solution typically comprises from about 1% to about 100% by weight of the reactants. Preferably it comprises from about 5% to about 50% by weight of the reactants. More preferably it comprises from about 10% to about 30% by weight of the reactants. 
     Once dissolved, the reactants may be fed to a reactor, such as a tubular reactor, and passed over the catalyst. The reaction may be carried out in an inert atmosphere. Alternatively, it may be carried out in an oxygen-containing atmosphere. In either event, the reaction is carried out in an atmosphere that does not adversely affect it. Preferably, the reaction is carried out by simultaneously feeding the dissolved reactants and the gas to the reactor. Suitable gasses include nitrogen alone, or nitrogen with up to 25% by volume of oxygen. Preferably the gas is selected from nitrogen and nitrogen with from about 1-10% (more preferably from 3-5%) by volume oxygen. 
     The flow rates of the reactants and the gas are adjusted so that the reactants held in the reactor for a time and under conditions capable of transferring at least one hydroxyalkyl group from the more substituted compound to the less substituted compound. While these conditions can be varied to suit the individual reactions, they typically comprise the following: 
     Hourly Liquid Space Velocity of Reactant Solution (HLSV):
         0.3-3.5 hr −1 , preferably 0.6-2.7 hr −1 , more preferably 1-2 hr −1 .       

     Hourly Gas Space Velocity of Gas (HGSV):
         100-600 hr −1 , preferably 100-500 hr −1 , more preferably 160-400 hr −1 .       

     Reaction Temperature:
         200-400° C., preferably 250-380° C., more preferably 300-350° C.       

     The pressure at which the reaction is carried out is not critical to the invention. It may be carried out under vacuum or at super atmospheric pressure. Preferably it is carried out at atmospheric pressure. 
     In some embodiments, the most preferable operating conditions are: 
     
       
         
               
               
               
             
               
               
               
               
             
               
               
               
             
           
               
                   
                   
               
               
                   
                 Variable 
                 Conditions 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 Gas Feed 
                 5% 
                 O 2 /N 2   
               
               
                   
                 Catalyst 
                 72 
                 m 2 /g ZrO 2   
               
               
                   
                 HGSV 
                 200 
                 hr −1   
               
               
                   
                 HLSV 
                 1 
                 hr −1   
               
               
                   
                 Temperature 
                 325° 
                 C. 
               
             
          
           
               
                   
                 Pressure 
                 Atmospheric 
               
               
                   
                   
               
             
          
         
       
     
     EXAMPLES 
     General Procedure. Approximately 3 g of catalyst was charged to a ⅜″ O.D. 304 SS tube that was placed in a microfurnace at atmospheric pressure. A 1:1 mol ratio of MEA and TEA was dissolved in water to make a 30 wt % solution and this was fed over the catalyst at the following conditions: 
     
       
         
               
               
               
               
             
               
               
               
             
               
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 Temperature 
                 325° 
                 C. 
               
             
          
           
               
                   
                 Pressure 
                 atmospheric 
               
               
                   
                 Liquid feed 
                 30 wt % in water 
               
               
                   
                 Gas feed 
                 5% O 2  in N 2   
               
             
          
           
               
                   
                 Liquid feed rate 
                 3 
                 mL/h 
               
               
                   
                 Gas feed rate 
                 10 
                 cc/min 
               
               
                   
                   
               
             
          
         
       
     
     The reaction products were collected neat in a glass container packed with wet ice. The concentration of DEA manufactured was determined using gas chromotography and reported as area percent of product. 
     Example 1 
     The above general procedure was followed using medium surface area zirconia (72 m 2 /g). In one experiment, the gas feed was nitrogen, and in another the gas feed contained 5% oxygen. The results of these reactions are given in Table 1. 
     
       
         
               
               
             
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Area % DEA 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 N 2   
                 3-6 
               
               
                   
                 5% O 2 /N 2   
                 13-20 
               
               
                   
                   
               
             
          
         
       
     
     Example 2 
     The general procedure was repeated with the O 2 /N 2  feed as in Example 1, except that various metal oxide additives were incorporated into the zirconia catalyst (72 m 2 /g surface area). These additives reduced the amount of the major by-product, hydroxyethylmorpholine (HEM). With no additive, the DEA/HEM ratio was only 2.3, but 2 wt % Na raised this ratio to 10.6. The results are given in Table 2. 
     
       
         
               
             
               
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 Effect of Catalyst Additives 
               
             
          
           
               
                   
                 Area Percent 
               
             
          
           
               
                   
                 Additive 
                 DEA 
                 HEM 
                 DEA/HEM 
               
               
                   
                   
               
             
          
           
               
                   
                 none 
                 18.5 
                 7.9 
                 2.3 
               
               
                   
                 5% Ce 
                 11.3 
                 1.7 
                 6.6 
               
               
                   
                 7% Y 
                 21.4 
                 4.1 
                 5.2 
               
               
                   
                 10% La 
                 8.7 
                 1.5 
                 5.9 
               
               
                   
                 2% K 
                 13.8 
                 3.6 
                 3.9 
               
               
                   
                 2% Na 
                 13.0 
                 1.2 
                 10.6 
               
               
                   
                 4% K 
                 15.2 
                 4.2 
                 3.6 
               
               
                   
                 1% Mg 
                 13.5 
                 1.7 
                 7.9 
               
               
                   
                   
               
             
          
         
       
     
     Example 3 
     The general procedure was repeated except that the liquid flow was 6 mL/hr and the gas flow was 13 mL/min. In one experiment the gas feed was nitrogen. In the other experiment the gas feed contained 5% oxygen. The influence of oxygen concentration in the gas feed on the quantity of various reaction products produced is shown in  FIG. 1 . HEM is the acronym for hydroxyethylmorpholine. 
     Example 4 
     The general procedure was repeated using a 5% O 2 /N gas feed except that the gas flow rate was varied and the reaction was run at 350° C. The influence of gas flow rate on the quantity of the reaction products produced is shown in  FIG. 2 . 
     Example 5 
     The general procedure was repeated except that the liquid flow rate was varied. The influence of liquid feed rate on the quantity of the reaction products produced is shown in  FIG. 3 . 
     Example 6 
     The general procedure was repeated except that the reaction temperature was started at 300° C. and increased to 360° C. slowly. The influence of reaction temperature on the quantity of the products produced is shown in  FIG. 4 . 
     Example 7 
     The general procedure was repeated except that zirconia having three different surface areas were used: high (HSA 98 m 2 /g), medium (MSA 72 m 2 /g), and typical surface area (Zr0 2  52 m 2 /g). The influence of the surface area of zirconia catalyst on the quantity of the products produced is shown in  FIG. 5 . 
     Example 8 
     A recycle experiment was performed. The feed contained, in area percent, 15.6% MEA, 33.1% TEA, 13.1% DEA, 7.1% HEM, and 4.4% dihydroxyethylpiperazine (DHEP). The recycle feed was charged to the tubular reactor and reacted under the operating conditions of Example 1 except that the residence time was varied. The influence of recycle on the quantity of products produced is shown in  FIG. 6 . As shown, the amount of DEA increased over time. 
     Example 9 
     The general procedure of Example 2 was followed except that a 15 wt % aqueous TEA solution was fed at 15 mL/h. The catalyst was a medium surface area zirconia with 10 wt % CeO 2 . The results are shown in Table 3. 
     
       
         
               
             
               
               
             
               
               
               
             
           
               
                 TABLE 3 
               
             
             
               
                   
               
               
                 Results of 15% aqueous TEA Feed 
               
             
          
           
               
                   
                 GC Area % 
               
               
                   
                   
               
             
          
           
               
                   
                 TEA 
                 61 
               
               
                   
                 DEA 
                 26 
               
               
                   
                 EG 
                 1.6 
               
               
                   
                 HEM 
                 3.8