Classifications

• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C51/00—Preparation of carboxylic acids or their salts, halides or anhydrides
  • C07C51/42—Separation; Purification; Stabilisation; Use of additives
  • C07C51/47—Separation; Purification; Stabilisation; Use of additives by solid-liquid treatment; by chemisorption

Definitions

• the field of art of this invention is the solid bed adsorptive separation of citric acid from fermentation broths containing citric acid, an organic acid such as gluconic acid or aconitic acid, carbohydrates, amino acids, proteins and salts. More specifically, the invention relates to a process for separating citric acid from gluconic acid which process employs an adsorbent comprising particular polymers which selectively adsorb citric acid from a fermentation mixture containing citric acid and gluconic acid.
• Citric acid is used as a food acidulant, and in pharmaceutical, industrial and detergent formulations.
• the increased popularity of liquid detergents formulated with citric acid has been primarily responsible for growth of worldwide production of citric acid to about 700 million pounds per year which is expected to continue in the future.
• Citric acid is produced by a submerged culture fermentation process which employs molasses as feed and the microorganism, Aspergillus-Niger.
• the fermentation product will contain organic acids such as gluconic acid or aconitic acid carbohydrates, amino acids, proteins and salts as well as citric acid, which must be separated from the fermentation broth.
• the patent literature has suggested a possible third method for separating citric acid from the fermentation broth, which involves membrane filtration to remove raw materials or high molecular weight impurities and then adsorption of contaminants onto a nonionic resin based on polystyrene or polyacrylic resins and collection of the citric acid in the rejected phase or raffinate and crystallization of the citric acid after concentrating the solution, or by precipitating the citric acid as the calcium salts then acidifying with H 2 SO 4 , separating the CaSO 4 and contacting cation- and anion-exchangers.
• This method disclosed in EP 151,470, is also a rather complex and lengthy method for separating the citric acid.
• the citric acid is adsorbed selectively by the adsorbent and purified citric acid is desorbed by a desorbent, for example, water or a dilute acid, sulfuric acid, hydrochloric acid, nitric acid, or phosphoric acid.
• a desorbent for example, water or a dilute acid, sulfuric acid, hydrochloric acid, nitric acid, or phosphoric acid.
• This invention relates to a process for adsorbing citric acid from a fermentation broth containing an organic acid selected from the group consisting of gluconic acid and aconitic acid or a mixture thereof onto a strongly basic, macroreticular or gel type, water- insoluble, anionic exchange resin matrix possessing quaternary ammonium functional groups or onto a weakly basic, macroreticular or gel type, water-insoluble, anionic exchange resin matrix possessing tertiary amine or pyridine functional groups.
• the resin matrix is either acrylic or styrene, cross-linked with divinylbenzene.
• the citric acid is recovered by desorption with a water or a dilute inorganic acid, especially sulfuric acid, desorbent under desorption conditions.
• Concentrations of inorganic acid of about 0.0 IN to about 1.0N can be used in the invention, preferably 0.1 to 0.2N. These resins result in an improved separation over the neutral resins disclosed earlier. They are superior in the adsorption separation of citric acid in their increased stability to deactivation by impurities in the feed.
• One aspect of the invention is in the discovery that complete separation of citric acid from salts and carbohydrates is only achieved by adjusting and maintaining the pH of the feed solution lower than the first ionization constant (pKaO of citric acid (3.13). However, pHs in the range of 0.5 to 2.5 are preferred and 1.5 to 2.2 are more preferred.
• the invention also relates to a process for separating citric acid from a feed mixture comprising a fermentation broth containing gluconic acid or aconitic acid or both, which process employs a water-insoluble, macroreticular or gel strongly basic anionic exchange resin possessing quaternary ammonium functional groups, or weakly basic anionic exchange resin possessing tertiary amine or pyridine functional groups said anionic exchange resin having a cross-linked acrylic or styrene resin matrix, which comprises the steps of: (a) maintaining net fluid flow through a column of said adsorbent in a single direction, which column contains at least three zones having separate operational functions occurring therein and being serially interconnected with the terminal zones of said column connected to provide a continuous connection of said zones; (b) maintaining an ad
• At least a portion of said raffinate stream may be passed to a separation means at separation conditions, thereby separating at least a portion of said desorbent material, to produce a raffinate product having a reduced concentration of desorbent material.
• a buffer zone may be maintained immediately upstream from said desorption zone, said buffer zone defined as the adsorbent located between the desorbent input stream at a downstream boundary of said buffer zone and the raffinate output stream at an upstream boundary of said buffer zone.
• FIG. 1 is a plot of concentration of various citric acid species versus the pH of citric acid dissociation which shows the shifting of the equilibrium point of the citric acid dissociation by varying the concentration of citric acid, citrate anions and the hydrogen ion.
• FIG. 2 is the plot of the pulse test in Example I using quaternary amine functionality in a cross-linked acrylic resin matrix to separate citric acid from a feed at a pH of 2.2 containing 15% citric acid and 7% gluconic acid, desorbed with dilute sulfuric acid.
• FIG. 3 is the plot of the pulse test in Example II using quaternary amine functionality in a cross-linked acrylic resin matrix to separate citric acid from a feed at a pH of 2.2 containing 20% citric acid and aconitic acid (below detection limits of analytical instrumentation), desorbed with dilute sulfuric acid.
• a "feed mixture” is a mixture containing one or more extract components and one or more raffinate components to be separated by the process.
• the term “feed stream” indicates a stream of a feed mixture which passes to the adsorbent used in the process.
• An "extract component” is a compound or type of compound that is more selectively adsorbed by the adsorbent while a “raffinate component” is a compound or type of compound that is less selectively adsorbed.
• citric acid is an extract component and proteins, amino acids, salts and carbohydrates are raffinate components.
• desorbent material shall mean generally a material capable of desorbing an extract component.
• desorbent stream or “desorbent input stream” indicates the stream through which desorbent material passes to the adsorbent.
• raffinate stream or “raffinate output stream” means a stream through which a raffinate component is removed from the adsorbent.
• the composition of the raffinate stream can vary from essentially 100% desorbent material to essentially 100% raffinate components.
• extract stream or “extract output stream” shall mean a stream through which an extract material which has been desorbed by a desorbent material is removed from the adsorbent.
• the composition of the extract stream can vary from essentially 100% desorbent material to essentially 100% extract components. At least a portion of the extract stream and preferably at least a portion of the raffinate stream from the separation process are passed to separation means, typically fractionators, where at least a portion of desorbent material is separated to produce an extract product and a raffinate product.
• separation means typically fractionators
• extract product and raffinate product mean products produced by the process containing, respectively, an extract component and a raffinate component in higher concentrations than those found in the extract stream and the raffinate stream.
• the ratio of the concentration of citric acid to that of the less selectively adsorbed components will be lowest in the raffinate stream, next highest in the feed mixture, and the highest in the extract stream.
• the ratio of the concentration of the less selectively adsorbed components to that of the more selectively adsorbed citric acid will be highest in the raffinate stream, next highest in the feed mixture, and the lowest in the extract stream.
• selective pore volume of the adsorbent is defined as the volume of the adsorbent which selectively adsorbs an extract component from the feed mixture.
• nonselective void volume of the adsorbent is the volume of the adsorbent which does not selectively retain an extract component from the feed mixture. This volume includes the cavities of the adsorbent which contain no adsorptive sites and the interstitial void spaces between adsorbent particles.
• the selective pore volume and the nonselective void volume are generally expressed in volumetric quantities and are of importance in determining the proper flow rates of fluid required to be passed into an operational zone for efficient operations to take place for a given quantity of adsorbent.
• adsorbent When adsorbent "passes" into an operational zone (hereinafter defined and described) employed in one embodiment of this process its nonselective void volume together with its selective pore volume carries fluid into that zone.
• the nonselective void volume is utilized in determining the amount of fluid which should pass into the same zone in a countercurrent direction to the adsorbent to displace the fluid present in the nonselective void volume. If the fluid flow rate passing into a zone is smaller than the nonselective void volume rate of adsorbent material passing into that zone, there is a net entrainment of liquid into the zone by the adsorbent.
• this net entrainment is a fluid present in nonselective void volume of the adsorbent, it in most instances comprises less selectively retained feed components.
• the selective pore volume of an adsorbent can in certain instances adsorb portions of raffinate material from the fluid surrounding the adsorbent since in certain instances there is competition between extract material and raffinate material for adsorptive sites within the selective pore volume. If a large quantity of raffinate material with respect to extract material surrounds the adsorbent, raffinate material can be competitive enough to be adsorbed by the adsorbent.
• the feed material contemplated in this invention is the fermentation product containing citric acid and gluconic acid, and possibly aconitic acid, obtained from the submerged culture fermentation of molasses by the microorganism, Aspergillus Niger.
• the fermentation product will have a composition exemplified by the following: Citric Acid 10 mass %
• the salts will be K, Na, Ca, Mg and Fe.
• the carbohydrates are sugars including glucose, xylose, mannose, oligosaccharides of DP2 and DP3 plus as many as 12 or more unidentified saccharides.
• the composition of the feedstock may vary from that given above and still be used in the invention. However, juices such as citrus fruit juices, are not 5 acceptable or contemplated because other materials contained therein will be adsorbed at the same time rather than citric acid alone. Johnson, J. Sci. Food Agric, VoI 33 (3) pp 287-93.
• the separation of citric acid can be enhanced significantly by adjusting the pH of the feed to a level below the first ionization constant of citric acid.
• the first ionization constant (pKai) of citric acid is 3.13, Handbook of
• the quaternary amine has a positive charge and can form an0 ionic bond with the sulfate ion.
• the sulfate form of quaternary ammonium anion exchange resin has a weakly basic property, which in turn, can adsorb citric acid through an acid-base interaction P- N + (R) 3 (1)
• the lone pair electron from the nitrogen atom can hydrogen bond to the citric aid either directly or through a sulfate ion, as for example, with a tertiary amine
• Desorbent materials used in various prior art adsorptive separation processes vary depending upon such factors as the type of operation employed. In the swing bed system, in which the selectively adsorbed feed component is removed from the adsorbent by a purge stream, desorbent selection is not as critical and desorbent materials comprising gaseous hydrocarbons such as methane, ethane, etc., or other types of gases such as nitrogen or hydrogen may be used at elevated temperatures or reduced pressures or both to effectively purge the adsorbed feed component from the adsorbent.
• the desorbent material in adsorptive separation processes which are generally operated continuously at substantially constant pressures and temperatures to insure liquid phase, the desorbent material must be judiciously selected to satisfy many criteria.
• the desorbent material should displace an extract component from the adsorbent with reasonable mass flow rates without itself being so strongly adsorbed as to unduly prevent an extract component from displacing the desorbent material in a following adsorption cycle.
• the selectivity it is preferred that the adsorbent be more selective for all of the extract components with respect to a raffinate component than it is for the desorbent material with respect to a raffinate component.
• desorbent materials must be compatible with the particular adsorbent and the particular feed mixture. More specifically, they must not reduce or destroy the critical selectivity of the adsorbent for an extract component with respect to a raffinate component.
• Desorbent materials should additionally be substances which are easily separable from the feed mixture that is passed into the process. Both the raffinate stream and the extract stream are removed from the adsorbent in admixture with desorbent material and without a method of separating at least a portion of the desorbent material the purity of the extract product and the raffinate product would not be very high, nor would the desorbent material be available for reuse in the process.
• any desorbent material used in this process will preferably have a substantially different average boiling point than that of the feed mixture to allow separation of at least a portion of the desorbent material from feed components in the extract and raffinate streams by simple fractional distillation thereby permitting reuse of desorbent material in the process.
• the term "substantially different” as used herein shall mean that the difference between the average boiling points between the desorbent material and the feed mixture shall be at least about 5°C.
• the boiling range of the desorbent material may be higher or lower than that of the feed mixture.
• desorbent materials should also be materials which are readily available and therefore reasonable in cost. In the preferred isothermal, isobaric, liquid phase operation of the process of the invention, dilute sulfuric acid, 0.01 to 1.0N, is a particularly effective desorbent material.
• dilute inorganic acids such as hydrochloric acid, nitric acid, phosphoric acid, and water may be used as a desorbent, but may be less effective.
• adsorbents are highly desirable to the successful operation of a selective adsorption process. Such characteristics are equally important to this process. Among such characteristics are: (1) adsorptive capacity for some volume of an extract component per volume of adsorbent; (2) the selective adsorption of an extract component with respect to a raffinate component and the desorbent material; and (3) sufficiently fast rates of adsorption and desorption of an extract component to and from the adsorbent. Capacity of the adsorbent for adsorbing a specific volume of an extract component is, of course, a necessity; without such capacity the adsorbent is useless for adsorptive separation.
• Increased capacity of a particular adsorbent makes it possible to reduce the amount of adsorbent needed to separate an extract component of known concentration contained in a particular charge rate of feed mixture.
• a reduction in the amount of adsorbent required for a specific adsorptive separation reduces the cost of the separation process. It is important that the good initial capacity of the adsorbent be maintained during actual use in the separation process over some economically desirable life.
• the second necessary adsorbent characteristic is the ability of the adsorbent to separate components of the feed; or, in other words, that the adsorbent possess adsorptive selectivity, ( ⁇ ), for one component as compared to another component.
• Relative selectivity can be expressed not only for one feed component as compared to another but can also be expressed between any feed mixture component and the desorbent material.
• the selectivity, ( ⁇ ), as used throughout this specification is defined as the ratio of the two components of the adsorbed phase over the ratio of the same two components in the unadsorbed phase at equilibrium conditions. Relative selectivity is shown as Equation 1 below:
• ⁇ becomes less than or greater than 1.0 there is a preferential adsorption by the adsorbent for one component with respect to the other.
• a ⁇ larger than 1.0 indicates preferential adsorption of component C within the adsorbent.
• a ⁇ less than 1.0 would indicate that component D is preferentially adsorbed leaving an unadsorbed phase richer in component C and an adsorbed phase richer in component D.
• desorbent materials should have a selectivity equal to about 1 or slightly less than 1 with respect to all extract components so that all of the extract components can be desorbed as a class with reasonable flow rates of desorbent material and so that extract components can displace desorbent material in a subsequent adsorption step. While separation of an extract component from a raffinate component is theoretically possible when the selectivity of the adsorbent for the extract component with respect to the raffinate component is greater than 1, it is preferred that such selectivity approach a value of 2. Like relative volatility, the higher the selectivity, the easier the separation is to perform. Higher selectivities permit a smaller amount of adsorbent to be used.
• the third important characteristic is the rate of exchange of the extract component of the feed mixture material or, in other words, the relative rate of desorption of the extract component.
• This characteristic relates directly to the amount of desorbent material that must be employed in the process to recover the extract component from the adsorbent; faster rates of exchange reduce the amount of desorbent material needed to remove the extract component and therefore permit a reduction in the operating cost of the process. With faster rates of exchange, less desorbent material has to be pumped through the process and separated from the extract stream for reuse in the process.
• a dynamic testing apparatus is employed to test various adsorbents with a particular feed mixture and desorbent material to measure the adsorbent characteristics of adsorptive capacity, selectivity and exchange rate.
• the apparatus consists of an adsorbent chamber comprising a straight or helical column of approximately 70 cc volume having inlet and outlet portions at opposite ends of the chamber.
• the chamber is contained within a temperature control means and, in addition, pressure control equipment is used to operate the chamber at a constant predetermined pressure.
• Quantitative and qualitative analytical equipment such as refractometers, polarimeters and chromatographs can be attached to the outlet line of the chamber and used to detect quantitatively or determine qualitatively one or more components in the effluent stream leaving the adsorbent chamber.
• a pulse test performed using this apparatus and the following general procedure, is used to determine selectivities and other data for various adsorbent systems.
• the adsorbent is filled to equilibrium with a particular desorbent material by passing the desorbent material through the adsorbent chamber.
• a pulse of feed containing known concentrations of a tracer and of a particular extract component or of a raffinate component or both, all diluted in desorbent, is injected for a duration of several minutes.
• Desorbent flow is resumed, and the tracer and the extract component or the raffinate component (or both) are eluted as in a liquid- solid chromatographic operation.
• the effluent can be analyzed on-stream or, alternatively, effluent samples can be collected periodically and later analyzed.
• performance can be in terms of void volume, retention volume for an extract or a raffinate component, selectivity for one component with respect to the other, and the rate of desorption of an extract component by the desorbent.
• the retention volume of an extract or a raffinate component may be characterized by the distance between the center of the peak envelope of an extract or a raffinate component and the peak envelope of the tracer component or some other known reference point. It is expressed in terms of the volume in cubic centimeters of desorbent pumped during this time interval represented by the distance between the peak envelopes.
• Selectivity, ( ⁇ ), for an extract component with respect to a raffinate component may be characterized by the ratio of the distance between the center of the extract component peak envelope and the tracer peak envelope (or other reference point) to the corresponding distance between the center of the raffinate component peak envelope and the tracer peak envelope.
• the rate of exchange of an extract component with the desorbent can generally be characterized by the width of the peak envelopes at half intensity. The narrower the peak width, the faster the desorption rate.
• the desorption rate can also be characterized by the distance between the center of the tracer peak envelope and the disappearance of an extract component which has just been desorbed. This distance is again the volume of desorbent pumped during this time interval.
• Adsorbents to be used in the process of this invention will comprise strongly or weakly basic anion exchange resins possessing quaternary ammonium, tertiary amine, or pyridine functionality in a cross-linked polymeric matrix, e.g., divinylbenzene cross-linked acrylic or styrene resins. They are especially suitable when produced in bead form and have a high degree of uniform polymeric porosity and exhibit chemical and physical stability.
• the resins can be gelular (or "gel-type") or "macroreticular” as the term is used in some recent literature, namely Kunin and Hetherington, A Progress Report on the Removal of Colloids From Water by Macroreticular Ion Exchange Resins, paper presented at the International Water Conference, Pittsburg, PA, October 1969, reprinted by Rohm & Haas Co.
• the term microreticular refers to the gel structure per se, size of the pores which are of atomic dimensions and depend upon the swelling properties of the gel” while “macroreticular pores and true porosity refer to structures in which the pores are larger than atomic distances and are not part of the gel structure.
• microporous and macroporous normally refer to those pores less than 20 A and greater than 200 A, respectively. Pores of diameters between 20 A and 200 A are referred to as transitional pores.”
• the former refers to the distances between the chains and crosslinks of the swollen gel structure and the latter to the pores that are not part of the actual chemical structure.
• the macroretical portion of structure may actually consist of micro, macro, and transitional-pores depending upon the pore size distribution.” (Quotes are from page 1 of the Kunin et al. article).
• the macroreticular structured adsorbents also have good resistance to attrition (not common to conventional macroreticular resins). In this application, therefore, all reference to "macroreticular” indicates adsorbent of the types described above having the dual porosity defined by Kunin and Hethesing. "Gel” and "gel-type” are used in their conventional sense.
• Adsorbents such as just described are manufactured by the Rohm and Haas Company, and sold under the trade name "Amberlite.”
• the types of Amberlite polymers known to be effective for use by this invention are referred to in Rohm and Haas Company literature as Amberlite IRA 400 and 900 series adsorbents and XE-275 (IRA-35), IRA-68 adsorbents and described in the literature as "insoluble in all common solvents and having open structure for effective adsorption and desorption of large molecules without loss of capacity, due to organic fouling.”
• intermediate base ion exchange which are mixtures of strong and weak base exchange resins.
• these are the following commercially available resins: Bio-Rex 5 (Bio-Rad 1); Amberlite IRA-47 and Duolite A-340 (both Rohm & Haas).
• Bio-Rex 5 Bio-Rad 1
• Amberlite IRA-47 and Duolite A-340 both Rohm & Haas
• they may be useful where a basic ion exchange resin is needed which is not as basic as the strong base resins, or one which is more basic than the weakly basic resins.
• the various types of polymeric adsorbents of these classes available will differ somewhat in physical properties such as porosity volume percent, skeletal density and nominal mesh sizes, and perhaps more so in surface area, average pore diameter and dipole moment.
• the preferred adsorbents will have a surface area of 10-2000 square meters per gram and preferably from 100-1000 m 2 /g. Specific properties of the materials listed above can be found in company literature and technical brochures, such as those in the following Table 1. Others of the general class are also available. TABLE 1
• the adsorbent may be employed in the form of a dense compact fixed bed which is alternatively contacted with the feed mixture and desorbent materials.
• the adsorbent is employed in the form of a single static bed, in which case the process is only semicontinuous.
• a set of two or more static beds may be employed in fixed bed contacting with appropriate valving so that the feed mixture is passed through one or more adsorbent beds while the desorbent materials can be passed through one or more of the other beds in the set.
• the flow of feed mixture and desorbent materials may be either up or down through the desorbent. Any of the conventional apparatus employed in static bed fluid-solid contacting may be used.
• Countercurrent moving bed or simulated moving bed countercurrent flow systems have a much greater separation efficiency than fixed adsorbent bed systems and are therefore preferred.
• the adsorption and desorption operations are continuously taking place which allows both continuous production of an extract and a raffinate stream and the continual use of feed and desorbent streams.
• One preferred embodiment of this process utilizes what is known in the art as the simulated moving bed countercurrent flow system.
• the operating principles and sequence of such a flow system are described in US 2,985,589 incorporated herein by reference. In such a system it is the progressive movement of multiple liquid access points down an adsorbent chamber that simulates the upward movement of adsorbent contained in the chamber.
• the active liquid access points effectively divided the adsorbent chamber into separate zones, each of which has a different function. In this embodiment of my process it is generally necessary that three separate operational zones be present in order for the process to take place although in some instances an optional fourth zone may be used.
• the adsorption zone, zone 1 is defined as the adsorbent located between the feed inlet stream and the raffinate outlet stream. In this zone, the feedstock contacts the adsorbent, extract component is adsorbed, and a raffinate stream is withdrawn.
• zone 2 Immediately upstream with respect to fluid flow in zone 1 is the purification zone, zone 2.
• the purification zone is defined as the adsorbent between the extract outlet stream and the feed inlet stream.
• the basic operations taking place in zone 2 are the displacement from the nonselective void volume of the adsorbent of any raffinate material carried into zone
• zone 2 is in a downstream direction from the extract stream to the feed inlet stream.
• the desorption zone is defined as the adsorbent between the desorbent inlet and the extract outlet stream.
• the function of the desorption zone is to allow a desorbent material which passes into this zone to displace the extract component which was adsorbed upon the adsorbent during a previous contact with feed in zone 1 in a prior cycle of operation.
• the flow of fluid in zone 3 is essentially in the same direction as that of zones 1 and 2.
• zone 4 an optional buffer zone, zone 4, may be utilized.
• This zone defined as the adsorbent between the raffinate outlet stream and the desorbent inlet stream, if used, is located immediately upstream with respect to the fluid flow to zone 3.
• Zone 4 would be utilized to conserve the amount of desorbent utilized in the desorption step since a portion of the raffinate stream which is removed from zone 1 can be passed into zone 4 to displace desorbent material present in that zone out of that zone into the desorption zone.
• Zone 4 will contain enough adsorbent so that raffinate material present in the raff ⁇ nate stream passing out of zone 1 and into zone 4 can be prevented from passing into zone 3 thereby contaminating extract stream removed from zone 3.
• the raffinate stream passed from zone 1 to zone 4 must be carefully monitored in order that the flow directly from zone 1 to zone 3 can be stopped when there is an appreciable quantity of raffinate material present in the raffinate stream passing from zone 1 into zone 3 so that the extract outlet stream is not contaminated.
• a cyclic advancement of the input and output streams through the fixed bed of adsorbent can be accomplished by utilizing a manifold system in which the valves in the manifold are operated in a sequential manner to effect the shifting of the input and output streams thereby allowing a flow of fluid with respect to solid adsorbent in a countercurrent manner.
• Another mode of operation which can effect the countercurrent flow of solid adsorbent with respect to fluid involves the use of a rotating disc valve in which the input and output streams are connected to the valve and the lines through which feed input, extract output, desorbent input and raffinate output streams pass are advanced in the same direction through the adsorbent bed. Both the manifold arrangement and disc valve are known in the art.
• one operational zone will contain a much larger quantity of adsorbent than some other operational zone.
• the buffer zone can contain a minor amount of adsorbent as compared to the adsorbent required for the adsorption and purification zones. It can also be seen that in instances in which desorbent is used which can easily desorb extract material from the adsorbent that a relatively small amount of adsorbent will be needed in a desorption zone as compared to the adsorbent needed in the buffer zone or adsorption zone or purification zone or all of them.
• the apparatus which can be utilized to effect the process of this invention can also contain a series of individual beds connected by connecting conduits upon which are placed input or output taps to which the various input or output streams can be attached and alternately and periodically shifted to effect continuous operation.
• the connecting conduits can be connected to transfer taps which during the normal operations do not function as a conduit through which material passes into or out of the process.
• At least a portion of the extract output stream will pass into a separation means wherein at least a portion of the desorbent material can be separated to produce an extract product containing a reduced concentration of desorbent material.
• At least a portion of the raffinate output stream will also be passed to a separation means wherein at least a portion of the desorbent material can be separated to produce a desorbent stream which can be reused in the process and a raffinate product containing a reduced concentration of desorbent material.
• the separation means will typically be a fractionation column, the design and operation of which is well-known to the separation art.
• Desorption conditions will include the same range of temperatures and pressures as used for adsorption conditions.
• the size of the units which can utilize the process of this invention can vary anywhere from those of pilot plant scale (see for example US 3,706,812, incorporated herein by reference) to those of commercial scale and can range in flow rates from as little as few cc an hour up to many thousands of gallons per hour.
• P is acrylic cross-linked with divinylbenzene.
• the test was run at a temperature of 60 0 C. Citric acid was desorbed with 0.1 N solution of sulfuric acid.
• the fermentation feed mixture had the following composition:
• Retention volumes and separation factor were obtained using the pulse test apparatus and procedure previously described. Specifically, the adsorbent was tested in a 70 cc straight column using the following sequence of operations for the pulse test. Desorbent material was continuously run upwardly through the column containing the adsorbent at a nominal liquid hourly space velocity (LHSV) of about 1.0. Void volume was determined by observing the volume of desorbent required to fill the packed dry column. At a convenient time, the flow of desorbent material was stopped, and a 5 cc sample of feed mixture was injected into the column via a sample loop and the flow of desorbent material was resumed.
• LHSV liquid hourly space velocity

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