PROCESS FOR REMOVING ACIDS FROM FLUIDS

Abstract: Acids can be removed from fruit juices by treating the juice with a filter apparatus comprising a pre-coat cake con­ taining a functionally effective amount of weak base resin parti­ culates. The sizes of the particulates are such that substan­ tially all of said particulates range from 0.25 to 0.125 mm. The weak base resin is most desirably one wherein the amount of strong base functionalities are less than about 5 percent, based on the total number of strong and weak base functional­ ities. Juices treated using the pre-coat cake taste sweet and the essential character thereof is not altered.

Description: The present invention relates to the removal of acids from fluids, and in particular to the removal of acids from fluids such as clarified food streams and/or fruit juices using particulate matter comprising weak base functionalities. In the processing of fluids, such as food streams and fruit juices, it is desirable to remove certain acids from the fluid. For example, it is desirable to remove certain amounts of acids, such as citric acid, malic acid, lactic acid and tartaric acid, which may be present in various juices before and/or during processing. The removal of such acids can be effected using conventional ion exchange technology, and in particular using weak base ion exchange resins as taught, for example, in US-A-4,522,836, US-A-4 514 427 and Journal of the science of food and agriculture, vol.33, no.3 (1982) 287-293. The use of weak base ion exchange resins is desirable due to the fact that such resins do not substantially change the chemical nature of the juice thus introducing an undesirable bad taste to the fluid which is treated. Unfortunately, conventional weak base ion exchange resins are employed in bead form in relatively large size columns. Such columns require relatively large amounts of weak base resins, making such columns not cost effective. In addition, pre-treatment of resins in columns prior to use, and post-treatment of resins in columns are both time consuming. In view of the known deficiencies which are apparent in the treatment and processing of fluids such as juices, it is highly desirable to provide a process for removing acids from such fluids which can be performed in a highly effective and efficient manner. Subject matter of the present invention is a process for removing acids from fluids such as clarified food streams and/or fruit juices according to claim 1. Preferred embodiments thereof are subject matter of claims 2 to 9. The process of this invention employs weak base resin particulates wherein substantially all of said particulates form a size distribution within which the sizes thereof range from 0.25 to 0.125 mm. Surprisingly, the particulates which are employed in the process of this invention can exhibit deacidification capacity at least as great or higher than particulates having a size in the range from .074 to .037 mm. In addition, the particulates which are employed in the process of this invention exhibit deacidification capacity at least as great or higher than standard particulates having a size in the range from 0.84 to 0.42 mm. Surprisingly, the process of this invention allows the skilled artisan to remove undesirable acids from a wide variety of fluids in an efficient and effective manner. In particular, the process for removing acids from fluids such as juices allows the skilled artisan to provide a sweeter tasting juice without altering the essential character of the juice, without introducing an undesirable odor or taste to the juice, and without substantially changing the color of the juice. The process of this invention is employed in treating and processing a wide variety of fluids. In particular, fluids such as fruit and vegetable juices are efficiently and effectively treated. Of particular interest are juices such as orange, pear, apple, cranberry, grape, pineapple, grapefruit, tomato, and the like. Other fluids which are of particular interest include, for example, sugar cane syrups, beet syrups and high fructose corn syrups. Filter apparatus useful in the process of this invention are those filter devices which can be equipped with small size mesh screens which can support a filter cake, and in particular as pre-coat cake, of weak base resin. Examples of suitable filter devices include the horizontal and vertical leaf filters such as sparkler filters; vacuum filters; tubular filters; rotary vacuum filters and plate and frame filters. Typically, such filter devices comprise a screen having mesh sizes which range from 0.59 to 0.105 mm, preferably from 0.297 to 0.149 mm. Weak base resins of this invention can vary, provided however, that the weak base resins comprise a majority of weak base functionalities as opposed to strong base functionalities. Typically, the resins are polymeric matrices comprising weak base functionalities in the free base form. Preferred resins are the epichlorohydrin based epoxy amine resins comprising weak base functionalities in the free base form. Such resins are commercially available as Dowex® WGR ion exchange resins sold by The Dow Chemical Company. Also useful are the epoxy polyamine resins which are commercially available as Amberlite® IRA-45, 47, 47.5, 48 and 60 by Rohm & Haas; Ionac® A-300 by Sybron; Dianion® A-365 by Mitsubishi; Lewatit® MIH by Bayer; and Duolite® A-30B, 340, 377 and 561 by Rohm and Haas. Also useful are those weak base resins which solid particulates are the styrene/divinylbenzene type, the phenolformaldehyde type or the acrylic type. The weak base resins which are employed are those resins which are typically in the free base form and which have as low an amount of strong base functionalities as is possible (i.e., are absent of substantial amounts of strong base functionalities). Desirable weak base resins are those which are provided by reacting polymeric matrices having haloalkylated functionalities with polyaminoalkylene amines such as 1,3-diaminopropane, 3,3'-imino-bispropylamine, 1,4-diaminobutane, 1,6-diaminohexane, and 2,4-diamino-2-methylpentane. Such resins can be described as resins having a high weak base capacity and high resistance to oxidation. The weak base capacity of resins can range from 1 to 2. The amount of strong base functionalities relative to weak base functionalities is less than 20 percent, preferably less than 10 percent, more preferably less than 5 percent, most preferably less than 2 percent, based on the total number of strong and weak base functionalities. The weak base resin particulates are particulates which are of a size suitable to form a cake in the previously described filter devices. The particulates are preferably of a size such that said particulates can form a pre-coat cake on the previously described screen of the filter devices. The particulates can have a uniform size distribution or a size distribution which is quite broad. For purposes of this invention, the weak base resin particulates have sizes such that there is provided a size distribution wherein substantially all of said particulates are in a range from 0.25 to 0.125 mm. By the term "size distribution wherein substantially all of said particulates are in a range from 0.25 to 0.125 mm" is meant that a relatively minor amount of the total number of particulates have a size less than 0.125 mm or larger than 0.25 mm. In particular, substantially all of said particulates include greater than 80, preferably greater than 90, percent by volume of the resin particulates. For example, a highly preferred weak base resin particulate sample exhibits a size distribution such that about 85 percent by volume of resin particulates is in a size range within 0.177 to 0.149 mm, the most preferred range being from 0.163 to 0.149 mm. The weak base particulates can be provided by a variety of means. For example, weak base resins can be ground to the desired size particulates by shearing a slurry of resin beads in a shearing device such as a high shear blender, by grinding using a mortar and pestle, by centrifugal grinding, by air impingement techniques, by using a ball mill or hammer mill, and the like. By the term "pre-coat cake" is meant a relatively uniform build-up or layer of particulate resin which forms on the filter screen. Typically, such a pre-coat cake is provided by preparing a slurry of particulates in a liquid (e.g., water) and circulating the slurry through the filter screen. The pre-coat particulates are maintained on the filter screen and circulation of the slurry is continued until the layer of particulate builds up on the filter screen to the desired consistency and thickness. The pre-coat cake of weak base particulates in the filter apparatus can be provided using a variety of techniques. For example, an aqueous slurry (comprising from 5 to 20 weight percent particulate and from 80 to 95 weight percent deionized water) can be contacted with the filter apparatus using known techniques. The pre-coat cake can be employed in a wet form in providing the process of this invention without further pretreatment. A functionally effective amount of weak base resin particulates is employed in forming the cake. The amount of particulate which is employed can depend upon a variety of factors including the weak base capacity of the particulates, the size of the particulates, and the like. Typically, the thickness of the cake ranges from 0.32 to 2.54 cm, preferably from 0.32 to 1.27 cm. The fluid is treated using the filter apparatus. Typically, the fluid is in liquid form and exhibits a viscosity which is low enough as to not create a large pressure drop during treatment with the filter cake. Preferably, the liquid exhibits a viscosity similar to a fluid which is treated using conventional filtration techniques. Typically, the flow rate of the fluid which is treated through the filter cake ranges from 0.1 to 6 gallons per minute per square foot (gpm/sq. ft.) (4.1 to 244.5 l/min/m²), preferably from 0.1 to 2 gpm/sq. ft (4.1 to 81.5 l/min/m²). The pressure drop of the fluid which is treated typically ranges from 0.91 x 10⁵ Pa to 9.1 x 10⁵ Pa (0.91 to 9.1 kg) and depends upon factors such as the flow rate of the fluid and the viscosity of the fluid at a given temperature. Typically, the fluid is treated at a temperature below 80°C, preferably from 25°C to 80°C. The amount of juice which can be treated per amount of resin particulate can vary depending upon factors such as the type of juice which is being treated, the viscosity of the juice, the acidity of the juice, etc. For example, 300 kgs of a sample of pineapple juice can be treated per kg of resin particulate, which particulate has a size distribution of 0.25 mm to 0.125 mm as defined hereinbefore. The resin particulate in the filter device can be regenerated after exhaustion. From 1 to 5 bed volumes, preferably 2 bed volumes, of water can be employed to rinse the juice from the filter cake prior to regeneration. For example, 1 to 5 bed volumes, preferably 2 bed volumes, of an aqueous basic solution is contacted with the resin. Advantageously, 3 to 10 percent active ammonium hydroxide can be employed in the aqueous solution. The resin is then rinsed with relatively pure water in order to provide a regenerated resin which is wetted by an aqueous liquid having a relatively neutral pH. The process of this invention allows the skilled artisan to remove varying amounts of acids such as organic acids from fluids such as juices. Such fluids are preferably those juices which contain dissolved solids and, more preferably, suspended solids of less than 25 µm diameter, most preferably, less than 0.5 µm diameter. The process of this invention is desirable in that the character (i.e., flavor, odor and nutrient content) of the juice which is treated is not substantially altered during treatment. In addition, undesirable impurities such as salts or hydroxide ions are not introduced to the juice during treatment. If desired, the fluid can be treated with a column or filter apparatus containing a cation exchange resin prior to the treatment using the process of this invention. Such a treatment allows the skilled artisan to also remove nitrogenous materials and certain minerals from the juice. If desired, the fluid can be also treated with a column or filter apparatus containing a styrene/divinylbenzene type adsorbent using the process of this invention. Such treatment allows the skilled artisan to also remove bitter components such as limonin and naringin from the juice. The fluid which is obtained using the process of this invention can be employed as is, can be further treated, can be concentrated, or can be blended with unblended fluid. The process of this invention in employing particulates wherein substantially all of said particulates are in a size range from 0.25 mm to 0.125 mm can provide a surprisingly high deacidification capacity over particulates of a much smaller size. In addition, the particulates having such a predominate size distribution exhibit numerous other advantages over much smaller size particulates. For example, in the process of this invention dusting problems are minimized, conventional size screens can be employed, a diatomaceous earth pre-cake is not required, in situ regeneration of resin can be accomplished without major resin loss, low amounts of regenerant are required during resin regeneration (while maintaining the ability of the resins to be regenerated to about 80 percent of capacity), and a low pressure drop in the filter apparatus is provided. The following example is given to further illustrate the invention. All parts and percentages are by weight unless otherwise indicated. Example Into a column is placed weak base resin of an epichlorohydrin based epoxy amine resin sold commercially as Dowex® WGR resin by The Dow Chemical Company having a particle size of from 0.84 to 0.42 mm. The resin is treated with 5 percent active aqueous hydrochloric acid followed by a rinse using deionized water until an essentially neutral rinse is obtained. The resin is further treated using a 4 percent active aqueous ammonium hydroxide solution followed by a rinse with deionized water. This treatment is repeated two more times. The resin is ground using a ball mill, and the resulting particulates are screened to a 0.25 to 0.125 mm size. The particulates are dried using a vacuum oven until the particulates have a 20 percent moisture content. The particulates have an approximate size distribution as follows: less than 1 volume percent are larger than 0.297 mm, less than 5 volume percent are between 0.297 and 0.25 mm, 85 volume percent are 0.25 mm to 0.163 mm, less than 5 volume percent are 0.163 to 0.149 mm, and less than 5 volume percent are 0.149 to 0.125 mm. Into 100 g deionized water is slurried 10 g of the particulate. The slurry is pumped into a 47 mm inner diameter Gelman pressure leaf filter having a 0.149 mm screen. After pumping the slurry through the filter device, a cake of 0.96 cm develops. The slurry is recirculated through the filter device for 0.2 hours until the aqueous medium becomes clear, thereby indicating the absence of resin particulates. It is most desirable to avoid dehydration or cracking of the cake. Into the filter apparatus is introduced a clarified pineapple juice stream having a pH of 4.12. The juice has a density of 1.044 g/cm³ (a °Brix of 17°), a citric acid content of 1.383 percent, and a sugar/acid ratio of 12.29 percent. The juice is treated and collected until the pH of the juice effluent becomes as low as 4.25. The juice is no longer introduced to the filter apparatus and the filter apparatus is flushed with water. The system is then contacted with the 4 percent active aqueous ammonium hydroxide solution and backwashed. When the pH of the effluent reaches 10, the stream is reversed and deionized water is introduced to the system in order to reform the filter cake. The system is washed with water until the effluent is neutral, at which point juice is reintroduced for treatment. About 300 kgs of juice per kg of resin particulate are treated before regeneration is required. The treated sample has a density of 1.044 g/cm³ (a °Brix of 17°), a citric acid content which ranges from 0.085 to 0.113, and a sugar/acid ratio which ranges from 150 to 200. For comparison purposes, a juice sample is similarly treated using similar resin but having a particle size distribution in the range from 0.84 to 0.42 mm. About 15 kgs of juice per kg of resin particulate are treated before regeneration is required. For further comparison a juice sample is similarly treated using similar resin but having a particle size distribution in the range from 0.074 to 0.037 mm. Surprisingly, only 56 kgs of juice per kg of resin particulate are treated before regeneration is required.

Claims: A process for removing acids from fluids, comprising treating the fluid with a filter apparatus comprising a pre-coat cake containing base resin particulates wherein the particulates have an amount of strong base functionalities relative to weak base functionalities in the resin of less than 20 percent based on the total number of strong and weak functionalities in the resin, and greater than 80 percent by volume of the resin particulates have a particle size of from 0.25 to 0.125 mm. The process of Claim 1 wherein the fluid is a juice. The process of Claim 2 wherein greater than 90 percent by volume of the resin particulates form a size distribution within which the sizes thereof range from 0.25 mm to 0.125 mm. The process of Claim 2 wherein greater than 85 percent by volume of the resin particulates form a size distribution within which the sizes thereof range from 0.177 to 0.149 mm. The process of Claim 1 wherein the weak base resin is an epichlorohydrin based epoxy amine resin. The process of Claim 1 wherein the amount of strong base functionalities relative to weak base functionalities in the resin is less than 5 percent based on the total number of strong and weak base functionalities in the resin. The process of Claim 1 wherein the amount of strong base functionalities relative to weak base functionalities in the resin is less than 2 percent based on the total number of strong and weak base functionalities in the resin. The process of Claim 1 wherein the pre-coat cake has a thickness which ranges from 0.32 cm to 2.54 cm. The process of Claim 1 wherein the flow rate of the fluid through the pre-coat cake ranges from 4.1 to 244.5 liters per minute per square meter.

Inventors: NORMAN, SETH I., O'BRIEN, KATHLEEN F.
Applicants: THE DOW CHEMICAL COMPANY
Application year: 1986
Main classification: A23L2
IPC codes: A23L2, B01J20