Recovery of lactic acid

Abstract: Process for recovering lactic acid from a medium, comprising contacting the medium with a solid-phase free base polymer having tertiary amino or pyridine groups to absorb the lactic acid. The lactic acid is desorbed using, respectively a stronger acid or hot water.

Description: BACKGROUND The present invention relates generally to the recovery of lactic acid from mediums in which it is contained. More particularly, it relates to methods for adsorptive recovery of lactic acid. Phytic acid (inositolhexaphosphoric acid) occurs naturally in plant tissues, and, of particular commercial interest, in the seeds of many cereal grains. Generally, this phytic acid occurs as its insoluble calcium-magnesium salt, also known as "phytin". At present, commercially available phytic acid is derived largely from corn steep liquor and/or rice bran, which typically contains phytin at levels corresponding to about 2 weight % phytic acid. Other valuable materials also occur in mediums containing phytic acid. For instance, lactic acid occurs along with phytic acid in corn steep liquor. Lactic acid has also long been used in the food industry, in the production of confectionary products, soft drinks, beers, wines, dairy products, baby foods, jams, salad dressings, etc. Lactic acid is also used in the preparation of pharmaceuticals, cosmetics, agrichemicals, etc. Recently, there has been substantial academic and commercial interest in lactic acid as a potential raw material for producing biodegradable plastics. See, for instance, Lipinsky, E.S., and Sinclair, R.G., Chem. Eng. Prog., August, 26 , (1986). Commercially, lactic acid is at present produced via both synthetic and fermentation processes. The synthetic process converts lactonitrile to lactic acid, with the lactonitrile starting material being available as a byproduct in acrylonitrile production. Van Ness, J.H., "Hydroxy Carboxylic Acids," in Encyclopedia of Chemical Technology , 3rd Ed., Wiley, Volume 13, pp. 80-103 (1981). On the other hand, in traditional fermentation processes, lactic acid bacteria produce free lactic acid as they metabolize carbohydrate raw materials. As it is formed, the lactic acid is typically neutralized by an alkali such as NaOH, NH 4 OH or more commonly CaCO 3 to prevent a pH drop in the fermentation broth. Following the fermentation, the broth is acidified to convert the lactate salt to free lactic acid which is then separated from the broth. See, Buchta, K., "Lactic Acid", Biotechnology , H. Dellweg. Ed.), 3 , 409 (1985). However, as has been recognized, this separation and purification is particularly cumbersome and inefficient. Atkinson, B. and Mavituna, F., Biochemical Engineering and Biotechnology Handbook , the Nature Press, N.Y. (1983). Thus, the search for new commercially attractive lactic acid sources and recoveries has continued for some time. US patent no.4552905 discloses a sorbent for removing acid substances from aqueous solutions, based on a cross-linked polymer having N-vinyl amide groups. It is in light of this extensive background that the applicants have applied themselves in an effort to address the continuing need and demand for truly convenient and effective recovery of lactic acid. Through their discoveries, the applicants have now succeeded in addressing these needs. According to one aspect of the invention we provide a process for treating a medium to recover lactic acid therein contained, comprising contacting the medium with a solid-phase free base polymer having tertiary amine functions to adsorb the lactic acid, desorbing said lactic acid by displacement on the polymer with a stronger acid, and recovering a lactic acid fraction substantially free from contamination by the stronger acid. We also provide a process for treating a medium to recover lactic acid therein contained, comprising contacting the medium with a solid-phase free base polymer having pyridine groups to adsorb the lactic acid, and desorbing the lactic acid with hot water at a temperature of at least about 75°C. For the purposes of promoting an understanding of the principles of the invention, reference will now be made to certain embodiments and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations, further modifications and applications of the principles of the invention as described herein being contemplated as would normally occur to one skilled in the art to which the invention pertains. As indicated above, in a preferred mode of this embodiment, the medium to be treated contains both phytic and lactic acid. Again, this medium is contacted with a solid-phase free base polymer having tertiary amine functions. A fraction predominant in phytic acid product, and a separate fraction predominant in lactic acid product, are then recovered from the polymer. The separate fractions are then preferably concentrated in their respective predominant products. This process thus enables effective and convenient winning of two highly valuable materials from the medium. As before, the preferred medium for this embodiment is corn steep liquor which, in addition to containing phytic acid, also contains about 1% or more lactic acid prior to any concentration. Polymers employed, mode of contacting, desorption, rinse and other preferred parameters for this embodiment are similar to those set forth above, as modified or expanded by the following discussion. Single or multiple columns containing resin beds can be used to provide processes in accordance with this mode. For instance, the medium containing phytic acid and lactic acid can be passed through a single column as in Example 2 below. The free base polymer will preferentially bind the phytic acid over the lactic acid, and thus the effluent will be rich in lactic acid while the adsorbed material on the resin will at least predominantly comprise phytic acid. The loaded polymer can then be treated with a desorbent to obtain a separate fraction predominant in the phytic acid. In this regard, the term "predominant in phytic acid" is intended to mean that the fraction contains more moles of phytic acid than lactic acid. Of course, then, "predominant in lactic acid" means the fraction contains more moles lactic acid than phytic acid. Favored are processes in which the medium contains the predominating material in at least twice the molar amount of the other material, and more preferably at least ten times the molar amount. As an example, the preferred work illustrated in Example 2 below achieved a fraction having a lactic acid/phytic acid molar ratio of greater than 200:1 (Fraction 1), and a phytic acid-containing fraction in which no lactic acid was detected (Fraction 3). This and other work by applicants has demonstrated the highly advantageous recoveries and separations achieved by this preferred process and highlighted the magnitude of their discovery. In another preferred process mode, the medium is passed in series through a plurality of columns containing the polymer. In this manner, columns toward the beginning of the series will adsorb predominantly the phytic acid, and those later in the series will adsorb predominantly the lactic acid. Fractions can then be obtained from the respective columns which predominate in either the lactic acid or the phytic acid. In a preferred feature, a column or columns central in a series (i.e. having at least one column before and after) and containing substantial amounts of both lactic acid and phytic acid can go untreated, and simply be used at or near the beginning of the series in a subsequent run. These columns will then of course become rich in the phytic acid as lactic acid is displaced, carried downstream and for example adsorbed on a subsequent column. As such, fractions very highly predominant in the respective desired macerials can be obtained. For instance, in Example 3 below, Fraction 1 exhibited a lactic acid/phytic acid ratio of about 132:1, and Fraction 3 exhibited a physic acid/lactic acid ratio of greater than 20:1. The phytic acid can be desorbed from the polymers as described above. The lactic acid may be desorbed from a preferred pyridine-containing polymer using hot water at a temperature of about 75°C or above, and more preferably about 85° to 100°C. Higher temperatures can also be used, for instance up to about 150°C or more using steam and/or under pressure. By this discovery a greatly simplified product workup can be achieved, as compared to that incurred using known desorptions employing polar organic materials such as methanol. In another favored process, a polymer bed containing adsorbed phytic acid as well as lactic acid can be subjected to a selective desorption treatment to separate the materials. First, the lactic acid is desorbed using hot water as described above. During this procedure, no significant amounts of phytic acid are removed from the polymer. As such, the polymer can then be treated with desorbents effective to remove the phytic acid (e.g. as described above), and thereby separate fractions predominant in phytic acid and lactic acid, respectively, can be obtained. As with phytic acid, the applicants have discovered that lactic acid can also be advantageously desorbed from a free base polymer having tertiary amine groups, using a stronger acid, for instance desirably H 2 SO 4 or HCl. In this case, a lactic acid-containing fraction substantially free from the stronger acid may be obtained. In order to promote a further understanding of the invention and its preferred features and advantages, the following specific Examples are provided. It will be understood that these Examples are intended to be illustrative and not restrictive in character In the Examples, percents given are percents by weight unless otherwise specified or suggested in context. The aqueous solutions of phytic acid or salts of phytic acid obtained in the Examples below were analyzed by HPLC. Samples containing sodium phytate were acidified before analysis. Further, although sometimes recovered from the columns as its sodium salt, quantities of phytic acid are reported as grams of the free acid. EXAMPLE 1 Acid Separation by Selective Desorption From Column An experiment was conducted to illustrate the ability to simultaneously recover and separate phytic and lactic acids by selectively desorbing them from a resin bed. As such, the procedure of Example 2 was repeated, except passage of the steep liquor through the column was stopped when equal amounts of lactic acid in the effluent and influent were observed. The resin bed was rinsed with cold CO 2 water as in Example 2, whereafter 120 mL of water was added to the column. A gentle flow of compressed air was passed upflow through the column to agitate the bed, and hot water was circulated through the column jacket until the internal column temperature reached 85°C. Thereafter, the flow of compressed air was stopped and the hot water in the column quickly drained. This step was repeated, and the two fractions thus collected were designated fraction 1 and fraction 2. Afterwards, the resin was backwashed with a minimum of water, the bed settled, and the liquid level adjusted to just above the resin. A 5% solution of sodium hydroxide was then passed through the resin as in Example 1 and another fraction collected as fraction 3. The phytic and lactic acid composition of the fractions, as determined by HPLC, are given in Table 2. Fraction Volume (mL) Lactic Acid (g) Phytic Acid (g) 1 123 1.8 0.1 2 121 0.4 0.1 3 320 .02 3.1 It was thus demonstrated that phytic and lactic acids could very effectively be simultaneously recovered and then separated in accordance with the invention. Further, after collection and analysis, fraction 3 was refluxed so as to hydrolyze phytic acid to inositol. EXAMPLE 2 Multiple Column Selective Adsorption and Desorption of Lactic and Phytic Acids A series of three columns was prepared as follows. An aqueous slurry containing 80 mL of REILLEX™ 425 polymer (26.7 g of dry resin) was added to a 1 inch I.D. jacketed, glass column. The resin column was backwashed and the resin bed allowed to settle. A sample of corn steep liquor was filtered to remove suspended solids, and its pH adjusted to 1.8 with concentrated HCl. Upon analysis by HPLC, the solution was found to contain 0.8% phytic acid and 1.6% lactic acid. This corn steep liquor was passed through the three columns in series. When the third column in the series was saturated with lactic acid, flow was stopped, and all three columns were rinsed in series with cold CO 2 water as before. The first and third columns were then isolated and treated separately as follows: Column 1: The resin in this column was rinsed with 3 bed volumes of 5% sodium hydroxide as in the Examples above, and the neutral and basic fractions collected. The two fractions were combined to give 250 mL of solution that contained 9.4 g of phytic acid and 1.1 g of lactic acid. Column 3: The resin in column 3 was slurried with 140 mL of water and agitated with an upflow stream of compressed air. Hot water was circulated through the column jacket until the internal column temperature reached 90°C. The flow of air was stopped and, after the bed settled, the hot water quickly drained from the column. This hot water desorption procedure was repeated to give a second fraction. The two fractions were combined to give 286 mL of solution containing 3.2 g of lactic acid and less than 0.1 g of phytic acid. Nothing was removed from column 2, which becomes column 1 in a subsequent cycle followed by the two freshly regenerated columns. In this manner, a highly effective recovery and separation process is performed, thus advantageously obtaining two valuable materials from the steep liquor. EXAMPLE 3 Lactic and Phytic Acid Desorption with Strong Acid The adsorption and rinse procedures of Example 4 were repeated and columns 1 and 3 again isolated. Columns 1 and 3 were then treated as follows: Column 1: A 10% solution of sulfuric acid was prepared and passed through the resin bed in column 1. The pH of the column effluent was monitored. After the pH dropped to 0.6, flow was discontinued. HPLC analysis of the solution indicated that it contained 10.1 g of phytic acid and very little lactic acid. The solution remaining after analysis was refluxed for 18 hours to effect the hydrolysis of phytic acid to inositol. The resin in Column 1 was treated with either aqueous sodium hydroxide or ammonia and could then be used again. Column 3: A 5% solution of HC1 was prepared and passed through the resin in column 3. The pH of the effluent was monitored. Two fractions were collected. Fraction 1 was collected until the pH of the column effluent dropped below 2. Fraction 2 was collected thereafter. Upon analysis, fraction 1 was shown to contain 2.9 g lactic acid, and fraction 2 0.4 g lactic acid, each containing little phytic acid. The lactic acid in fraction 1 can be recovered as an 80% solution by decolorization and concentration. The pH of the second fraction is preferably adjusted to between 1.8 and 4.0, and processed with a subsequent portion of corn steep liquor to recover its lactic acid component. EXAMPLE 4 Recovery of Phytic And Lactic Acid Using Resin With N-Aliphatic Tertiary Amine Functions A series of three columns, each containing about 80mL of Amberlyst A-21 instead of a crosslinked polyvinylpyridine were prepared and assembled as described in Example 2. Corn steep liquor was prepared and passed through the three resin columns as in this earlier experiment until the third column was saturated with lactic acid. The first and third columns were isolated, rinsed with cold water, and treated as follows: Column 1: The resin in this column was rinsed with 3 bed volumes of 5% sodium hydroxide and then 1 bed volume of water. The rinse water was combined with the basic solution to give 310 mL of solution that contained 8.4 g of phytic acid (as sodium phytate) and 0.6 g of lactic acid (as sodium lactate). Column 3: The resin in column 3 was rinsed with 10% sulfuric acid and a major fraction collected until a significant drop in the pH was observed. The major fraction contained 2.9 g of lactic acid and only a minor amount of sulfuric acid. The last acidic fraction of lactic acid can be recycled into fresh corn steep liquor upon adjustment of its pH to about 3 with aqueous base. The resin was reused after passing aqueous sodium hydroxide or ammonia through the column followed with a water rinse. EXAMPLE 5 Steam Desorption of Lactic Acid A steam desorption apparatus was constructed including a 3.675cm (1½ inch) outer diameter stainless steel pipe about 51cm (about 20 inches) long. The upper end of the pipe was fitted with a valved steam inlet port and a pressure gauge. The lower end was fitted with a pressure regulation valve. A 35.6cm (14 inch) stainless steel water cooled condenser was also attached below the pressure regulation valve. A fine stainless steel wire mesh was positioned in the lower end of the pipe to hold the polymer within the pipe. The apparatus was attached to a pressure regulated high pressure steam line. One liter of a 6% aqueous solution lactic acid was prepared. 59.52 grams (dry basis) REILLEX™ 425 polymer were added to the solution and the solution stirred for about 2 hours at ambient temperature. The polymer was filtered off and washed with 250 ml of 10°C carbonated water. The filtrate was analyzed by titration, whereby it was determined that 6.84 grams of lactic acid had been loaded onto the polymer (e.g. acid loading = grams acid in original solution less grams acid in filtrate). The loaded polymer was then placed into the steam desorption apparatus (filling about 2/3 the volume of the pipe), and the outer surface of the apparatus was then heated with live steam. After this, steam was passed through the apparatus at (8-15 psig) and a flow rate was passed through the apparatus at 0.55-1.03 x 10 5 Nm -2 (8-15 psig) and a flow rate of about 6 bed volumes per hour (as measured by rate of liquid collection). 100 ml fractions were collected, and each was titrated with 0.1N NaOH. Upon analysis, it was determined that 4.50 g of lactic acid were recovered within the first 3 bed volumes of steam collected. This represents a 65.8% recovery of lactic acid from the polymer in the first 3 bed volumes, demonstrating the high efficacy of the steam desorption procedure.

Claims: A process for treating a medium to recover lactic acid therein contained, comprising contacting the medium with a solid-phase free base polymer having tertiary amine functions to adsorb the lactic acid, desorbing said lactic acid by displacement on the polymer with a stronger acid, and recovering a lactic acid fraction substantially free from contamination by the stronger acid. A process for treating a medium to recover lactic acid therein contained, comprising contacting the medium with a solid-phase free base polymer having pyridine groups to adsorb the lactic acid, and desorbing the lactic acid with hot water at a temperature of at least about 75°C.

Inventors: BAILEY THOMAS D, CROWE ERNEST, FITZPATRICK GINA, MARSTON CHARLES K, MCOUIGG DONALD, MURUGAN RAMIAH, VORHIES SUSAN, BAILEY, THOMAS D., CROWE, ERNEST, FITZPATRICK, GINA, MARSTON, CHARLES K., MCOUIGG, DONALD, MURUGAN, RAMIAH, VORHIES, SUSAN
Applicants: REILLY IND INC, REILLY INDUSTRIES
Application year: 1992
Main classification: C07C59
IPC codes: C07C51