Abstract:
A biohydraulic fluid which has high performance attributes and which is environmentally acceptable includes trimethylolpropane (TMP) esterified to monounsaturated fatty acids of unsaturated vegetable oils or vegetable oil blends. The process for making the TMP esters can be accomplished in a manner similar to biodiesel production wherein methyl oleates obtained from reacting methanol with the vegetable oils or vegetable oil blends are reacted with TMP. Production of the TMP esters can be achieved without the use of catalysts.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims benefit of priority of U.S. Provisional Patent Application 61/751,042, filed Jan. 10, 2013, and the complete contents of this prior application is hereby incorporated by reference in its entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The invention is generally directed to environmentally acceptable hydraulic fluids, and more particularly, biohydraulic fluids which employ unsaturated vegetable oils esterified with trimethylolpropane (TMP). 
       BACKGROUND 
       [0003]    The purpose of a lubricant is generally to minimize friction and wear of metals. Lubricants generally consist of a base fluid and additives selected to improve the lubricating properties or other properties of the lubricant (e.g., stability, performance at low or high temperature, etc.). With industrialization, mineral based lubricants became important in the market. Most existing heavy duty lubricating oils used for construction equipment and the like contain mineral oils as a main a component. For example, hydraulic systems found in farm tractors, backhoes, excavators, garbage trucks, snow plows and other heavy equipments generally use mineral oil based fluids as lubricants. Mineral oils have the advantages of lubricity, longevity, and corrosion resistance. 
         [0004]    The drawbacks of mineral based lubricants are that they are toxic, they have long term residual properties making them difficult to dispose of safely (i.e., long term, they have very low biodegradability), and they are very difficult to clean if there is an accidental spill. Unauthorized release and spill of mineral oil based lubricants can have significant adverse impacts on terrestrial and aquatic environments, as well as underground sources of drinking water. Furthermore, scattering and leakage of oil is generally difficult to avoid during usage; hence, mineral oil usage inevitably leads to at least some contamination of the environment. Spillage clean up can require removing the top layer of the grass or soil and containment for proper disposal which involves significant labor hours and additional costs. 
         [0005]    Because of the risks associated with mineral based oils, efforts have been made to identify environmentally friendly alternatives. One area which has been explored is replacement of mineral oils with vegetable oils. The advantages of vegetable oils include being non-toxic, being biodegradable (i.e., they breakdown quickly and can be consumed by naturally occurring organisms in water, earth, and air), being renewable, and they do not accumulate in nature and thus do not impact the natural food chain. Exemplary vegetable oils which may be suitable as lubricants include rapeseed, rape, soybean, castor, olive, coconut; palm, tall, maize, walnut, flaxseed, and cotton, and sunflower, sesame and almond oils. 
         [0006]    However, vegetable oils have limitations which make them not good candidates for many environments where mineral oils are used. Specifically, vegetable oils typically have poor stability (i.e., they breakdown over relatively short periods of time), they have unsatisfactory behavior at low temperature. The attributes poor thermal and oxidative stability are generally due to the presence of unsaturated and polyunsaturated fatty acids, and the unsatisfactory behavior or vegetable oils at low temperature is generally due to the saturated fraction of fatty acids (U.S. Pat. No. 5,885,946). 
         [0007]    Van der Waal and Kenbeek have presented a process for the preparation of synthetic esters from vegetable and/or animal fats (Proceedings of the Tribology 2000, 8 th  International Colloquium, Technische Akademie Esslingen, Germany, 14-16 Jun. 1992, Vol II, pp 13.3-8). However, the costs of the process are extremely high due to the multistage separation and purification reaction and the most severe conditions (high pressure and temperature) required by the reaction. 
         [0008]    U.S. Pat. No. 5,885,946 describes a process of preparing synthetic ester from a vegetable oil which employes a two stage transesterification process. 
         [0009]    There is a need for making improved vegetable oil based alternatives which have performance qualities making them usable in industrial applications, and for being able to manufacture the lubricants at reasonable costs. 
       SUMMARY 
       [0010]    A high performance environmentally acceptable biohydraulic fluid includes a synthetic oil, and optionally stable vegetable oils (unsaturated), and additives. The high performance, environmentally acceptable biohydraulic fluid is designed for excellent low temperature performance and maximum life time. The synthetic oil includes trimethylolphosphate (TMP) esters of predominantly mono unsaturated vegetable oils. By “predominantly mono unsaturated”, it should be understood that at least 70% of the fatty acid moieties are mono unsaturated fatty acids. For example, in an embodiment, high oleic sunflower oil is used, and high oleic sunflower oil includes mainly triglycerides derived from oleic acid which is a mono unsaturated fatty acid (i.e., having only one carbon carbon double bond). The synthetic oil may also be formed from vegetable oils or vegetable oil blends which have low levels of saturated fatty acids (i.e., no carbon carbon double bonds) and/or low levels of polyunsaturated fatty acids (i.e., two or more carbon carbon double bonds). 
         [0011]    In a particular embodiment, the synthetic oil functions as a base fluid (TMP base fluid) in the biohydraulic fluid. That is, the TMP base fluid containing TMP esterified vegetable oil or vegetable oil blends, is further diluted with vegetable oils or vegetable oil blends (which may be the same or different from those used to make the TMP base fluid. The vegetable oil or vegetable oil blends which dilute the TMP base fluid preferably comprise 20% or more by weight of the biohydraulic fluid. 
         [0012]    The biohydraulic fluid has lower toxicity compared to other high quality lubricants, it provides excellent lubricity, does not gel at low temperatures, is stable over long storage times, has low foaming tendency, low emulsion tendency, it is non corrosive, and has a high flash point. The process used to make the biohydraulic fluid as well as the materials employed allow for low production cost. 
         [0013]    In the preparation of high performance biohydraulic fluid, unsaturated vegetable oil (triglycerides with predominantly mono unsaturated fatty acids) is converted to a trimethylphosphate (TMP) ester base fluid. The vegetable oil is reacted with methanol and the glycerol produced is separated from, e.g., methyl oleates. The methyl oleate is converted to TMP ester and is washed to collect the TMP base fluid. The production method does not require a catalyst. 
         [0014]    The TMP base fluid is preferably, combined with additional unsaturated vegetable oils preferably at a weight percentage of at least 60% TMP base fluid and at least 20% additional unsaturated vegetable oils. In a particularly preferred formulation the TMP base fluid is present at a weight percentage of 72.7%. The unsaturated vegetable oils combined with the TMP base fluid can be the same or different from those used to produce the TMP base fluid. Various additives such as antioxidants, antiwear agents, corrosion inhibitors, pour point depressants, and antifoam agents can be added to suit the needs of the application. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0015]      FIG. 1  is a schematic drawing showing the production of TMP base fluid used in the biohydraulic fluids of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0016]    The invention is directed to a biohydraulic fluid formulation and method for its production. 
         [0017]    The biohydraulic fluid uses natural or synthetic vegetable oils, or mixtures of the same, which are preferably highly unsaturated. Natural vegetable oils are glyceride esters, i.e., tri-, di- or monoesters of glycerol and straight chain saturated and unsaturated fatty acids. Exemplary vegetable oils which may be suitable for use in the formulation include rapeseed, rape, soybean, castor, olive, coconut; palm, tall, maize, walnut, flaxseed, and cotton, sunflower, safflower, sesame, almond, and canola oil. The preferred base oils used in the invention include mixtures of oils obtained from chemical products producers such as Cargill. One product which has shown very good results as described below is sold by Cargill under the trade name Agri-Pure (AP) 85. Cargill AP 85 includes both sunflower and safflower oils. The vegetable oils used in the practice of this invention will be predominantly monosaturated (i.e., they have only one carbon-carbon double bond in the fatty acid moiety); however, in some formulations, low levels of polyunsaturated vegetable oil may be employed. 
         [0018]    A particularly preferred recipe within the practice of the invention is set forth in Table 1. 
         [0000]    
       
         
               
             
               
               
               
             
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Composition of exemplary lubricant referred to as “EA-2” 
               
             
          
           
               
                   
                 %, by mass 
                 Role in formulation 
               
               
                   
                   
               
             
          
           
               
                 Synthetic TMP Ester prepared 
                 72.7% 
                 Base fluid 
               
               
                 from Cargill AP85, using 
               
               
                 procedures similar to biodiesel 
               
               
                 production 
               
               
                 Cargill AP85 
                 24.2% 
                 Base fluid 
               
               
                 NA-lube 1208 
                 2.0% 
                 Antioxidant/Antiwear/ 
               
               
                   
                   
                 Corrosion Inhibitor 
               
               
                 Viscoplex B171 
                 1.0% 
                 Pour point depressant 
               
               
                 Viscoplex 14-515 
                 0.1% 
                 Antifoam 
               
               
                   
               
             
          
         
       
     
         [0019]    Table 2 presents a more detailed explanation of the role of each constituent in the formulation. 
         [0000]    
       
         
               
             
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 Role of ingredients in EA-2 
               
             
          
           
               
                   
                 Role in formulation 
               
               
                   
               
               
                 Synthetic TMP Ester 
                 This base fluid has a lower gel point than vegetable oil. It also has 
               
               
                   
                 a long lifetime since it contains a very low percentage of 
               
               
                   
                 polyunsaturated fatty acid groups. 
               
               
                 Cargill AP85 
                 Including this lowers the overall fluid cost, but it is used in low 
               
               
                   
                 enough concentration so that the low temperature gelling 
               
               
                   
                 properties are not compromised. 
               
               
                 NA-Lube 1208 
                 This is a combination of antioxidants, antiwear agents, and 
               
               
                   
                 corrosion inhibitors. This complex proprietary mixture 
               
               
                   
                 outperforms various additive combinations that were evaluated. 
               
               
                 Viscoplex B171 
                 This pour point depressant was found to be the most effective, by 
               
               
                   
                 far, compared to alternative additives. Without this additive, the 
               
               
                   
                 fluid will gel up at −29° C. 
               
               
                 Viscoplex 14-515 
                 This is an antifoaming agent. It counteracts the side effect of the 
               
               
                   
                 pour point depressant. 
               
               
                   
               
             
          
         
       
     
         [0020]    The formulation described in Tables 1 and 2 has the following desirable attributes:
       1) The formulation is readily biodegradable   2) The formulation has a toxicity comparable to other high quality environmentally acceptable (EA) lubricants   3) The formulation does not gel at −29° C. (−20° F.), even after several weeks of storage at this temperature   4) The “lifetime” for use of the lubricant is estimated to be as long or longer than all other readily biodegradable lubricants, based on accelerated lab testing   5) The formulation has excellent lubricity, low foaming tendancy, low emulsion teneanch, it is non-corrosive, it does not swell rubber O-rings, it has a high flash point, and has a high viscosity index.   6) The formulation is made from materials and using processes which are low in cost.       
 
         [0027]    The ISO viscosity grade of EA-2 was found to be between ISO32 and ISO46. It is possible to adjust the viscosity up or down to closely match one of these viscosity grades without significantly changing other properties. The API Gravity and Density of EA-2 were determined to be 22.4 and 0.918 g/cm 3 , respectively. The Flash Point of EA-2 was determined to be 191° C. The pour point for EA-2 was determined to be −52° C. (the pour point is the industry standard for indicating the lowest operating temperature of a fluid—as a general rule a fluid will operate well when it is 10 to 15 degrees above its pour point). EA-2 also did not gel when stored for &gt;two days at −29° C. Pour point depressants can help interfere with crystal growth and help prevent gelling. The water content of EA 2 was determined to be 223 ppm. Foaming characteristics represent a fluids ability to release air and reduce the risk of introducing unwanted air bubbles into the hydraulic system. Foaming performance for EA 2 was generally good, with some foaming tendencies being introduced by the pour point additive. The EA-2 fluids also passed the rust test according to ASTM D665 standards. In the rust test, 10% deionized water is added to the oil which is heated to 60° C., and polished steel rods are inserted into the heated mixture for 24 hours before final inspection. The copper corrosion properties of EA 2 were found to be acceptable with only a slight discoloration when a polished copper strip is immersed into a heated oil bath for a period of time. The oxidative stability (lifetime) according to rotating pressure vessel oxidation test (RPVOT) for EA 2 was determined to be 282 minutes which is deemed to be quite good for biodegradable fluids and outperforms most other commercially available fluids that are readily biodegradable. The Acid number for EA-2 was determined to be low (0.28 mg KOH/g). The Base number was 0.09. Water contamination in hydraulic systems can lead to a host of problems including loss of lubricity, corrosion, additive degradation, and filter plugging. Thus, water should be removed from the fluid as quickly as possible. A water separability test for EA 2 showed that it met the highest score for separability (a standard not met by many hydraulic fluids). A four ball wear test was used to measure EA-2 lubricants ability to protect metal surfaces as they slide relative to one another. The four ball wear test showed that EA 2 performed significantly better than other vegetable oils and obtained scar diameters in the desired range of approximately 0.3 mm. Biodegradability testing demonstrated EA 2 to be readily biodegradable under ASTM 5864 testing. 
         [0028]    Other vegetable oil based formulations can be made within the practice of the invention. For example, suitable biohydraulic fluids can be formulated with the practice of the invention to have 60% or more by weight of a synthetic trimethylol propane (TMP) esterified with fatty acids of vegetable oils from any single source or blend, as long as the reagent oil comprises &gt;70% esters of monounsaturated fatty acid. 
         [0029]    Each of the ingredients in the exemplary formulation of Tables 1 and 2 (EA-2) are commercially available, except the synthetic TMP base fluid. The TMP base fluid, such as that in EA-2 and or in other formulations within the practice of the invention which utilize other unsaturated vegetable oils, can be manufactured easily using a process similar to that used for biodiesel production. This process alignment with readily available biodiesel manufacturing infrastructure will lower production cost of this fluid. 
         [0030]      FIG. 1  provides a schematic of the chemistry which can be used to make the TMP base fluid. In  FIG. 1 , vegetable oil (triglycerides containing predominantly mono unsaturated fatty acids) is converted to a TMP ester. Conversion to a TMP ester is important as it prevents low temperature gelling. In  FIG. 1 , it can be seen that the process has been streamlined and avoids several purification steps. The process of  FIG. 1  has been found to produce better TMP base fluid for use in the biohydraulic fluid of the present invention in a manner that can be easily scaled up. The methanol and biodiesel produced as part of the process in  FIG. 1  are recyclable materials as indicated by the arrows. As the “biodiesel” is not the target product of the TMP conversion process, this product might best be considered simply as methyloleates and other waste products. The biodiesel can contain some traces of unreacted oils (e.g., as much as 2%), as well as hydroxides and sulfates depending on the chemistry and/or catalysts (an advantage of the process of the present invention is that it does not require catalysts). The waste products from the process of  FIG. 1  include glycerol and water. 
         [0031]    In  FIG. 1 , the ratio of methanol to vegetable oil (AP85) can be fairly high (12:1 molar ratio) to drive the triglyceride to biodiesel conversion to completion; however, lower levels of methanol can also be employed. The reaction of methanol with the vegetable oil produces glycerol (a waste product for this process) and biodiesel (methyl oleate; (Z)-9-octadecanoic acid methyl ester) 
         [0032]    For the conversion of biodiesel to raw TMP ester, a slight excess of biodiesel to TMP was used to drive the reaction to completion. However, if a large excess of biodiesel is used, then there will be excess biodiesel in the final product which will lower viscosity (which may be useful in some applications). Conversely, there may be reason to reduce biodiesel content in the final product in order to reduce the flash point or to get a higher viscosity. 
         [0033]    Table 3 summarizes the TMP conversion process 
         [0000]    
       
         
               
             
               
               
             
           
               
                 TABLE 3 
               
               
                   
               
               
                 Overview of the TMP conversion process* 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 1. Reaction of vegetable oil with methanol 
               
               
                   
                 2. Separation of glycerol from methyl oleate (i.e., biodiesel) 
               
               
                   
                 3. Reaction of methyl oleate with TMP 
               
               
                   
                 4. Washing of TMP ester 
               
               
                   
                 5. Heating of TMP ester to evaporate water 
               
               
                   
                 6. Further heating to drive off excess methyl oleate 
               
               
                   
                   
               
               
                   
                 *It is noted that conventional biodiesel production would involve these same steps, except not step 3 and 6. 
               
             
          
         
       
     
         [0034]    Table 4 provides a more detailed presentation of the TMP conversion process, as it pertains to the exemplary EA-2 product described in Tables 1 and 2. 
         [0000]    
       
         
               
             
               
               
               
             
           
               
                   
               
               
                 Detailed Summary of the TMP conversion process 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 1. 
                 Vegetable oil → 
                 Combine: 
               
               
                   
                 Biodiesel 
                 5 kg of Cargill AP85 
               
               
                   
                   
                 0.913 kg of methanol 
               
               
                   
                   
                 25 g of potassium hydroxide 
               
               
                   
                   
                 Stir vigorously, heat to 60° C. (not above 70° C.) for ≦3 hours. 
               
               
                   
                   
                 Vacuum not required. It is noted that the reaction is likely complete 
               
               
                   
                   
                 in 30 min, but this has not been investigated yet. 
               
               
                 2. 
                 Glycerol removal 
                 Transfer the reaction product to a separation vessel. Leave it 
               
               
                   
                   
                 overnight. The glycerol and some methanol will phase separate into 
               
               
                   
                   
                 a distinct viscous orange layer on the bottom, which is to be drained 
               
               
                   
                   
                 off and discarded. The above recipe should yield approximately 650 mL 
               
               
                   
                   
                 of glycerol. Care should be taken to remove as much glycerol as 
               
               
                   
                   
                 possible, otherwise it will interfere with subsequent steps. For 
               
               
                   
                   
                 perspective, each gallon of oil creates ~½ pint of glycerol 
               
               
                   
                   
                 byproduct. 
               
               
                 3. 
                 Biodiesel → TMP 
                 The top layer in step 2 should be a low viscosity yellow liquid, 
               
               
                   
                 Ester 
                 which is methyl oleate (i.e., biodiesel). Transfer this to the 
               
               
                   
                   
                 reactor. 
               
               
                   
                   
                 Add 580 grams of TMP. 
               
               
                   
                   
                 Heat the reaction and pull vacuum. Moderately strong vacuum 
               
               
                   
                   
                 pressure is required (~25 inches Hg). A cold trap to condense and 
               
               
                   
                   
                 collect methanol vapors is needed. Approximately 1 L of 
               
               
                   
                   
                 methanol will be collected for the above recipe. Although we do 
               
               
                   
                   
                 not currently reuse this methanol, it is anticipated that it can be 
               
               
                   
                   
                 reused in scaled-up production, thereby reducing waste and cost. 
               
               
                   
                   
                 As the reaction heats, the TMP will melt and dissolve at ~80° C. 
               
               
                   
                   
                 Excess methanol from step 1 will boil off at ~90° C. Once the 
               
               
                   
                   
                 reaction reaches 120° C., the TMP reaction will initiate. Maintain 
               
               
                   
                   
                 the temperature at 140° C. 
               
               
                   
                   
                 The reaction will be complete in approximately 3 hours. Reaction 
               
               
                   
                   
                 for additional time does not appear to help, since this equilibrium 
               
               
                   
                   
                 reaction can go forwards or backwards. 
               
               
                 4. 
                 Washing 
                 The product from step 3 is partially cooled and transferred to a 
               
               
                   
                   
                 separation tank. Warm deionized water is misted over the oil. 
               
               
                   
                   
                 Approximately 2-5 gallons of water are used for washing. The water 
               
               
                   
                   
                 separates to a distinct bottom layer in ~20 min, and can be drained 
               
               
                   
                   
                 off and discarded. 
               
               
                 5. 
                 Drying 
                 The washed oil from step 4 is transferred to the reaction flask, and 
               
               
                   
                   
                 heated to 100° C. under vacuum, while stirring, to pull off water. 
               
               
                 6. 
                 Distilling methyl 
                 The dried oil is further heated to ~200° C. to pull off excess methyl 
               
               
                   
                 oleate 
                 oleate. It is noted that it may be tolerable (or even desirable) to omit 
               
               
                   
                   
                 this step. In principle, there is no significant drawback to leaving 
               
               
                   
                   
                 ~20% methyl oleate in the biohydraulic fluid. For now, it was 
               
               
                   
                   
                 included for the sake of being thorough. 
               
               
                   
               
             
          
         
       
     
         [0035]    The TMP conversion process has a number of benefits, including without limitation:
       1) Higher performance: The process makes TMP fluids that are more stable than commercially available TMP fluids, because it preferably starts with high oleic vegetable oil (e.g., sunflower oil with mono unsaturated oleic acid as the fatty acid moiety). This assures that the fluids will have a longer lifetime. That is, common vegetable oils contain polyunsaturated fatty acid esters, which are easily oxidized and therefore lead to short lifetime fluids. In contrast, the present invention uses vegetable oils which include at least 70% mono unsaturated fatty acids such as oleic acid (which is particularly preferred). Also, the process illustrated in  FIG. 1  avoids production of fatty acids, which would otherwise cause the TMP based fluid to be corrosive and perform poorly on emulsion tests. At least one commercially available TMP ester contains very high fatty acid concentrations. In contrast, the residual unreacted constituent in the process illustrated in  FIG. 1  is biodiesel, which does not hurt biohydraulic fluid performance. In fact, residual biodiesel can be a desirable ingredient to include in the formulation to obtain a lower viscosity. Also, since the saturated fatty acid esters are omitted or are only present at low levels (e.g. 2% or less by weight), it is feasible to prevent low temperature gelling of formulated fluids made with this TMP ester.   2) Potential Cost Savings: High stability vegetable oils (≦$1.05/lb) are relatively cheap, even when compared to low stability TMP esters (e.g., Cargill AP560, $2.50/lb).   3) Flexibility: Vegetable oil can be obtained from countless sources, including farmer co-ops, whereas TMP fluids (which have lower performance characteristics) are sold only by a few suppliers.       
 
         [0039]    The TMP base fluid can be combined with one or more vegetable oils to produce a biohydraulic fluid. In Table 1 and 2, the TMP base fluid, in a preferred embodiment, is present at approximately 72% by weight and the vegetable oil which it is combined with is present at approximately 24% by weight. By “approximately” it should be understood to mean plus or minus 2% by weight of either constituent. As discussed in detail above, the ratios can be varied. However, within the practice of a preferred embodiment of the invention the TMP base fluid should be at least 60% by weight of the biohydraulic fluid. 
         [0040]    Various additives can be added to the final mixture to comply with state and federal laws or to adjust the properties of the biohydraulic fluid (e.g., reduce the freezing point, change the combustibility, include detergents, etc.). As noted above, for example, the biohydraulic fluid could include antioxidants, antiwear agents (e.g., zinc dithiophosphates, etc.), corrosion inhibitors, pour point depressants, and antifoam agents. 
         [0041]    Antioxidants inhibit the oxidation of hydraulic oils by scavenging free radicals. Vegetable oil based hydraulic fluids often contain substantial amounts of polyunsaturated oils to lower the pour point, and these oils are highly reactive with free radicals. When free radical react with polyunsaturated oils, cross linking or polymerization can occur, which increases viscosity. In extreme cases a rubbery residue is formed. While a number of antioxidants can be used in the practice of this invention, the two best performing antioxidants were N, N′ Di sec butyl p-phenylenediamine and Vanlube 961. Many antioxidant additives have synergistic effects when mixed together. We have found that mixing hindered phenols with aromatic amines provides synergistic improvement. 
         [0042]    Pour point additives can be beneficial to biohydraulic liquids. These polymer additives co-crystallize with the saturated oils, thereby dispersing them as particles small enough to avoid gelling. The co-crystallization process is sensitive to the chemical structures of the fluid and additive. 
         [0043]    While the invention has been described in terms of its preferred embodiments, the invention may be practiced with modifications within the spirit and scope of the appended claims.