4 Conclusion

Methyl glucoside addition (5-10°/o) facilitated the glass transition and melting of corn starch at relatively low mois- ture contents (6-1 lO/o). But, the degree of depression of glass transition temperature (T,) or onset temperature for melting was not significantly dependent on the methyl glucoside con- tent. Methyl glucoside addition caused the biphasic melting and the additional peak around 2 O O O C in DSC thermogram.

Acknowledgement

poration for supplying corn starch and methyl glucoside, resp. The authors thank Cerestar USA, Inc. and Grain Processing Cor-

Bibliography

Roos, Y. H.: Glass transition-related physicochemical changes in foods. Food Technol. 10 (1995), 97. Lirn, S., and J. Jane: Storage stability of injection-molded starch- zein plastics under dry and humid conditions. J. Environ. Polym. Deg. 2(2) (1994), 111. Anonymous: Additives and modifiers. 93/94 Red book, Plastics Compounding 9 (1993/1994), 41. Lelikvre, J.: Thermal analysis of carbohydrates as illustrated by aqueous starch systems, in: Developments in Carbohydrate Chemistry. Eds. R. J. Alexander and H. F. Zobel. The American Association of Cereal Chemists, St. Paul 1992, pp. 137-161. Donovan, J. W : Phase transition of starch-water systems. Biopolymers 16 (1979), 263. Biliaderis, C. G.: The structure and interaction of starch with food constituents. Can. J. Physol. Pharmcol. 69 (1990), 60. Lay, G., J . Rehm, R. E: Stepto, and M . Thoma: Polymeric materials made from destructurized starch and at least one synthetic ther- moplastic polymeric material. European Patent Application 0327505 A2.

[8] F/ory, P. J.: Principles of Polymer Chemistry. Cornell University Press, New York 1953.

[9] Slade, L. , and H . Levine: Recent advances in starch retrograda- tion, in: Industrial Polysaccharides. Eds. S. S., Stivala, V. Cres- cenzi and 1. C. M. Dea. Gordon and Breach Science Publishers, New York 1987, p. 387.

[lo] Slade, L., and H. Levine: Non-equilibrium melting of native granular starch. Part I. Temperature location of the glass transi- tion associated with the gelatinization of A-type cereal starches. Carbohydr. Polym. 8 (1988), 183.

[ l l ] Slade, L. , and H. Levine: Beyond water activity: Recent advances based on an alternative approach to the assessment of food qual- ity and safety. Crit. Rev. Food Sci. Nutr. 30 (1991), 115.

[12] Shogren, R. L.: Effect of moisture content on the melting and subsequent physical aging of cornstarch. Carbohydr. Polym. 19 (1992), 83.

[13] Shogren, R . L. , G . E: Fanta, and W: M . Doane: Development of starch-based plastics-a reexamination of selected polymer sys- tems in historical perspective. StarchBtarke 45 (1993), 276.

[14] Shogren, R . L. , and B. K . Jasberg: Properties of extruded high amylose starch. J. Environ. Polym. Degradation. 2 (1994), 99.

[15] Biliaderis, C. G., and H. D. Seneviratne: On the supermolecular structure and metastability of glycerol monstearate-amylose complex. Carbohydr. Polym. 13 (1990), 185.

[I61 Gordon, M., and J. S. Tay1or:Ideal copolymers and the second-or- der transitions of synthetic rubbers. I. Non-crystalline copoly- mers. J. Appl. Chem. 2 (1952), 493.

[17] Zeleznak, K. J., and R. C. Hoseney: The glass transition in starch. Cereal Chem. 64 (1987), 121.

[I81 Stevens, M. P.: Chemical structure and polymer properties, in: Polymer Chemistry, an Introduction. Oxford University Press, New York 1990, pp. 110-145.

Addresses of authors: Seung-Taik Lirn, Associate Professor, Center for Advanced Food Science and Technology, Graduate School of Bio- technology, Korea University, 5-1 Anam-dong, Sungbuk-ku, Seoul, Korea 136-701. Jay-lin Jane, Professor, Department of Food Science and Human Nutrition, Center for Crops Utilization Research, Food Science Building, Iowa State University, Ames, Iowa 5001 I, USA. (Received: July 26, 1996).

Gas Chromatographic Determination of Free Adipic Acid in Adipyl Cross-linked Starches

Peter Sanders and Kommer Brunt, G r o n i n g e n (The Net h e r I a n d s)

The performance of two different procedures for the extraction of the free adipic acid present in acetylated adipyl cross-linked starches, was compared. It concerns a single extraction with a methanol-acetic acid mixture and, a two step extraction procedure based upon a sin- gle aqueous extraction of the starch, followed by four extractions with ethyl acetate of the obtained aqueous extract. Apparently, some compounds - probably sodium salts -were present in the dry resi- due of the methanolic extract, which interfered with the silylation re- action of the adipic and pimelic (internal standard) acid. This re- sulted in a less reliable gas chromatographic determination of the adipic acid content in the dry extraction residues. The aqueous/ethyl acetate extraction procedure results in a better isolation of the al- kanedioic acids from the interfering residues present in the starch sample. The standard deviation in the determination of the free adipic acid in the starch adipates, based on 55 independent duplicates, is 1.6ppm. The free adipic acid concentrations in the analyzed wheat and corn starch samples varied from 0-360ppm.

Gaschrornatographische Bestimrnung von freier Adipinsaure in adipylvernetzten Starken. Die Durchfuhrbarkeit von zwei verschei- denen Verfahren zur Extraktion der freien Adipinsaure in acetylier- ten, adipalvernetzten Starken wurde verglichen. Es umfaDt eine ein- zelne Extraktion mit einem Methanol-Essigsaure-Gemisch und ein zweistufiges Extraktionsverfahren, basierend auf einer einzelnen waorigen Extraktion der Starke, gefolgt von vier Extraktionen des er- haltenen walrigen Extraktes mit Ethylacetat. Offenbar waren einige Verbindungen - moglicherweise Natriumsalze - in der Trockensub- stanz des methanolischen Extraktes anwesend, welche sich mit der Silylierungsreaktion der Adipin- und Pimelinsaure (interner Stan- dard) iiberlagerten. Dies fuhrte zu einer weniger zuveriassigen gas- chromatographischen Bestimmung des Adipinsauregehaltes in den trocknen Extraktionsresten. Das waDrig/Ethylacetat-Extraktionsver- fahren ergibt eine bessere Isolierung der Alkandicarboxy-Sauren aus den in den Starkeproben anwesenden storenden Resten. Die Stan- dardabweichung bei der Bestimmung der freien Adipinsaure in den Starkeadipaten, basierend auf 55 unabhangigen Duplikaten, betragt 1,6ppm. Die Konzentrationen an freier Adipinsaure in den analysier- ten Weizen- und Maisstarkeproben variierte von 0-360ppm.

448 StarchlStiirke 48 (1996) Nr. 11/12. S. 448-452 0 VCH Verlagsgesellschaft mbH, D-69451 Weinheim, 1996 0038-9056/96/1111-0448$10.00+.25/0

1 Introduction

In a previous paper we have described an improved method for the determination of the total adipyl content in acetylated adipyl cross-linked starches [ 11. The current paper describes a comparison of two miniaturized extraction proto- cols for the determination of the free adipic acid content in adipyl crosslinked starches. It is assumed that the extractable adipic acid is equivalent to the amount of non-esterified adipic acid, present in the adipyl cross-linked starch samples. In the past a concept protocol has been prepared for the deter- mination of the free adipic acid content in adipyl crosslinked starches both by the STEX (Starch Expert Group) [2] as well as by I S 0 [3].

The STEX method is based on extraction of the free adipic acid with a mixture of methanol-acetic acid. The obtained ex- tract is evaporated to dryness and the adipic acid in the dry re- sidu is derivatised into its corresponding di(trimethylsily1) ester and quantified by gas chromatography.

The I S 0 draft protocol appeared to be rather laborious. In this method a two-step extraction procedure is applied for the isolation of the adipic acid. First, an aqueous extraction of the starch sample is effected. After filtration the starch free aque- ous extract is acidified, and the dissolved free adipic acid is ex- tracted with ethyl acetate. After phase separation the ethyl acetate is evaporated with a rotary evaporator, and the remain- ing adipic acid in the dry residue is derivatised into its corre- sponding di(trimethylsily1)ester and quantified by gas chro- matograp hy.

In both protocols a relatively large sample weight is used. Just as we have done for the total adipate determination [l], we have first modified the extraction procedure, especially with respect to the amount of organic solvent needed, by de- creasing the sample weight. As with the total adipate determi- nation, pimelic acid is used as the internal standard. The ex- tractions are carried out in screw cap closed glass reaction tubes with a volume of about 15m1, avoiding the use of 250ml Erlenmeyer flasks and 250ml glass separatory funnels. Thanks to the considerable reduction in the volumes of the organic solvents compared to both the STEX and the I S 0 extraction procedure, a simple evaporation device can be applied now. Simultaneous evaporation of the extraction solvent in 27 sam- ples is done instead of single samples in a rotary evaporator. This results in a considerable increase in the daily analysis ca- pacity.

2 Experimental Section

2.1 Chemicals The following chemicals were used:

- concentrated hydrochloric acid (Merck, Darmstadt), - ethyl acetate (Merck, Darmstadt), - methanol (Merck, Darmstadt), - acetic acid, 96% (Merck, Darmstadt), - adipic acid (hexanedioic acid) (Merck, Darmstadt), - pimelic acid (heptanedioic acid) (Merck, Darmstadt), - acetonitrile (Lab-Scan), - bis-(trimethylsily1)-trifluoroacetamide (B STFA) which in-

cludes 1% trimethylchlorosilane (TMCS) (Pierce), - nitrogen gas (Hoek-Loos).

2.2 Apparatus - glass reaction tubes (10Ox16mm) with screw cap fitted

with PTFE covered rubber seals. Used for saponification,

extraction, evaporation, and silylation of the sample, re- spectively the analyte,

- home made rotary shaker, - adjustable Finn pipettes 0.2-1 .Oml, - waterbath adjusted to 3OoC, - Pierce Reacti-Vap I11 evaporation device. To evaporate to

dryness the sample solutions simultaneously in 27 tubes with a stream of nitrogen,

- ultrasonic bath, - Carlo Erba Vega gas chromatograph equipped with a cold on-column injection system, and a flame ionisation detector (temperature 3OO0C, hydrogen pressure OSbar, air pressure 1.0bar). The separation was performed on a WCOT-fused sil- ica CP-sil 5CB capillary column (length 50m, internal diame- ter 0.32mm, film thickness 0.12pm) with helium as the carrier gas (pressure 0.7bar). During the separation the temperature of the column oven was programmed as follows: after injec- tion, the temperature was kept constant at 13OOC for lmin, then the temperature was raised at S°C/min up to 19OoC, im- mediately followed by a fast temperature rise of 2S°C/min to 290OC. The temperature was kept at 29OOC for Smin, and then the oven was cooled down to 13OOC in order to prepare the in- strument for the next injection. The retention times of the adipic and pimelic acid derivates are 10.3min and 12.2min, re- spectively.

2.3 Extraction method The investigations as described in this paper have resulted

in the following extraction protocols for the determination of the free adipic acid content in acetylated adipyl cross-linked starches.

2.3.1 Aqueous extraction 500mg of the acetylated adipic cross-linked starch sample

is weighed accurately (0.lmg) in a glass reaction tube, and 4.0ml distilled water and 1.0ml of an aqueous solution con- taining O.OSmg pimelic acid are added. The tube is closed and the adipic acid is extracted by rotating the tube continuously during 16h. Then the aqueous suspensions are centrifuged for lOmin at about 2900g. The starch-free aqueous solution is transferred into a clean reaction tube. After addition of loop1 6M hydrochloric acid and 5ml ethyl acetate, the tube is closed, and shaken vigorously for at least lmin to extract the adipic and pimelic acid into the ethyl acetate. After phase separation the (upper) ethyl acetate layer is transferred with a glass Pus- teurpipette into a clean glass reaction tube. The ethyl acetate extraction of the aqueous solution is repeated three times and the ethyl acetate fractions are collected. These collected frac- tions are evaporated to dryness with a nitrogen stream in a Pierce Reacti-Vap evaporator at a temperature of 30°C in a wa- terbath.

2.3.2 Methanol-acetic acid extraction 500mg of the acetylated adipic cross-linked starch sample

is weighed accurately (O.1mg) in a glass reaction tube, and 4.0ml methanol, 1.0ml of a solution of pimelic acid in metha- nol (0.05mg pimelic acid/ml), and loop1 acetic acid are added. The tube is closed and the adipic acid is extracted by rotating the tube continuously during 16h. Then the suspension is cen- trifuged for lOmin at about 2900g. The starch-free superna- tant is transferred into a clean tube and evaporated to dryness with a nitrogen stream in a Pierce Reacti-Vap evaporator at a temperature of 3OoC in a waterbath.

Starch/Stiirke 48 (1996) Nr. 11/12, S . 448-452 449

2.3.3 Silylation 0.3ml of acetonitrile is added to the dry residue, and the re-

action tube is placed in an ultrasonic bath for several minutes to dissolve the residue. 0.3ml of BSTFA/l% TMCS solution is added, and the mixture is homogenized again in the ultra- sonic bath for several minutes. After a reaction time of at least 30min in a waterbath at a temperature of 30°C, 0 .3~1 of the re- action mixture is injected in the capillary gas chromatograph.

2.4 Calibration Five 500mg samples of waxy corn starch are weighed into

five glass reaction tubes. Then 1.0ml aqueous or methanolic pimelic acid solution containing 0.05mg pimelic acid is added to each tube. This is followed by the addition of 0.00, 0.25, 0.50,0.75, and 1.00ml adipic acid solution in water or metha- nol, containing 0.05mg adipic acid/ml, into the respective tubes. The volume is adjusted to 5.0ml with the extraction sol- vent and the extraction procedure is carried out as described above, beginning with “The tube is closed and the adipic acid is extracted by rotating the tube continuously during 16h”.

3 Results and Discussion Both extraction procedures of the free adipic acid have

been tested with two samples of adipyl cross-linked maize starches and one sample of adipyl cross-linked wheat starch.

3.1 Aqueous extraction followed by the extraction with ethyl acetate

As we have established before [l], the adipic acid and the internal standard pimelic acid in aqueous solution will be fully extracted by four extractions with ethyl acetate and cor- rectly quantified by the gas chromatographic method. Now we have investigated the performance of the aqueous extraction of the free adipic acid from the adipyl cross-linked starch sam- ple. First the calibration method was evaluated. Known amounts of adipic acid and the internal standard pimelic acid were added to waxy maize starch, and analyzed as described for the calibration procedure (single extraction by rotating continuously during 16h). The analytical results were com- pared with those of model solutions of adipic and pimelic acid. For both the calibration samples and the model solu- tions, the relative response factor was calculated. This factor is defined as the quotient between the ratio of the peak area of the analyte and the internal standard and the ratio of the weights of the analyte and the internal standard. The average response factor for the model solutions was 1.01+0.02 (n=4) and for the calibration samples 0.99+0.01 (n=20). These fig- ures are in good agreement with each other and fit very well with the expected theoretical value of 1.00, calculated by us- ing the effective carbon number [5] of the trimethylsilyl de- rivatives of both alkanedioic acids. Subsequently the adipyl cross-linked starch samples were analyzed. The free adipic acid and the internal standard pimelic acid were extracted by single aqueous extractions, and by two successive aqueous ex- tractions. The total duration of the extractions ranged from 2 to 48h in which each of the two successive extractions had a duration of half of the total time of extraction. In the case of two successive extractions, the aqueous extracts were pooled before starting the four successive extractions with ethyl ace- tate. The results are summarized in Figure 1. It appears that, in principle, a single extraction of two hours is sufficient to isolate all the free adipic acid present in the starch samples. Prolonged and/or repeated extractions of the sample do not improve the results.

IL” I

401

corn 1, single 0 corn 1, double f corn 2, single

3 corn 2. double + wheat, single x wheat, double

0 10 20 30 40 Extraction time in h

0

Fig. 1. The effect of the applied aqueous extraction procedure (total extraction time and single or double extractions) upon the measured content of free adipic acid in one acetylated adipyl cross-linked wheat starch and two acetylated adipyl cross-linked corn starch (corn 1 and corn 2) samples.

3.2 Methanol-acetic acid extraction The modified STEX method, based on the extraction of

the free adipic acid with a mixture of methanol-acetic acid as described in the experimental section, was also tested with calibration samples and with the two adipyl cross-linked maize starch and the wheat starch samples which had been used for the evaluation of the aqueous extraction method. The obtained methanolic extracts were evaporated to dryness and the adipic and pimelic acid in the dry residues were deri- vatised into their corresponding di(trimethylsily1) esters and quantified by gas chromatography.

The adipic acid determination in the waxy maize calibra- tion samples, to which different amounts of adipic acid and the internal standard pimelic acid were added, gave no prob- lems. The average response factor for these calibration sam- ples was 0.99f0.01 (n=16), which is in good agreement with the results of the aqueous extraction method of the calibra- tion samples.

However, problems were encountered in the analysis of the adipyl cross-linked starch samples. These problems espe- cially concern the reproducibility of the gas chromatographic determination of the alkanedioic acids. The methanolic ex- traction method resulted in larger amounts of dry residue than the aqueous extraction procedure in combination with the four successive ethyl acetate extractions. It appears that sodium salt residues present in the dry residues, originating from the industrial derivatizing process, inhibit to a certain extent the silylation reaction of the alkanedioic acids with the B STFAITMCS reagent. Our findings confirm the previous ex- periences of Mitchell [6]. The degree of inhibition of the silyla- tion reaction hardly differs for the adipic acid and the pimelic acid, indicating that pimelic acid behaves as might be ex- pected of an internal standard compound. Therefore it should be possible to quantify the free adipic acid content in most adipyl cross-linked starch samples by applying the methanolic extraction procedure, as long as the sodium salt residue in the dry residue is not too high. However, due to the inhibition, the chromatographic peaks of the adipic and pimelic acid are

450 Starch/Stike 48 (1996) Nr. 11/12, S. 448-452

Tab. 1. The Measured Free Adipic Acid Content in Acetylated Adipyl Cross-linked Starches Depending upon the Applied Extraction Proce- dure: The Methanolic Extraction or the Aqueous Extraction Followed by the Ethyl Acetate Extraction.

Sample Number of Extraction Measured range in free Mean content Duplicate Standard matrix samples method adipic acid content adipic acid differences deviation

min. max. min. max.

Wheat 18 methanolic 0.0 352.5 46.6 0.6 40.8 8.0 aqueous 0.4 361.9 50.5 0.1 6.0 2.1

Corn 37 methanolic 8.0 172.8 60.6 0.0 12.8 3.1 aqueous 11.7 187.2 68.4 0.0 8.2 1.4

Wheat and 55 methanolic 0.0 352.5 56.0 0.0 40.8 4.4 corn aqueous 0.4 361.9 62.5 0.0 8.2 1.6

smaller than in the case of the aqueous extraction method. Thus, compared with the aqueous extraction, the methanolic extraction method results in a decrease in sensitivity, and con- sequently also in a decrease in accuracy and reproducibility as will be demonstrated below.

3.3 Comparison of the performance of both extraction methods

The performance of both methods has been investigated. With each method, 18 acetylated adipyl cross-linked wheat starches and 37 acetylated adipyl cross-linked corn starches have been analyzed as independent duplicates. The duplicate differences were used to calculate the standard deviation in the respective methods.

The results are summarized in Table 1. As can be seen in this table the methanolic extraction procedure results in lower measured contents of the free adipic acid in the starch samples than the aqueous extraction followed by the ethyl acetate extraction procedure. Both the minimum and the maximum free adipic acid content in the starch samples, and the average content of all samples, are lower than those found by applying the aqueous extraction procedure. These differ- ences are statistically significant (e.g. paired t-tests and regres- sion analysis, a=0.05). The difference between both methods is also illustrated in Figure 2. In this figure a correlation plot is

.- 0 wheat starch 2 160

120

100 s I i - E m 0 .- 0

a a Q

/+-

I ,

-0 20 40 60 80 100 120 140 160 180 ppm adipic acid (aqueous extraction)

Fig. 2. Comparison between the free adipic acid content as measured by applying the aqueous and the methanolic extraction procedure on 18 acetylated adipyl cross-linking wheat starches and 37 acetylated adipyl cross-linked corn starches.

given of the mean duplicate values of the free adipic acid con- tent in the starch samples, as measured by applying the respec- tive extraction procedures.

The precision in the determination of the free adipic acid content depends upon the applied extraction procedure. In case of the aqueous extraction procedure the duplicate differ- ences in the respective starch samples were smaller than when applying the methanolic extraction. The methanolic extrac- tion procedure resulted in a significantly higher standard de- viation (F-test, a=0.05) than the aqueous extraction proce- dure (Table 1). This is most probably caused by the foremen- tioned problems with the reproducibility of the silylation reac- tion of the alkanedioic acid due to the presence of sodium salts in the methanolic extraction procedure. It was noticed that when the methanolic extraction procedure was used, the chromatographic peak of the internal standard pimelic acid was lower than expected in several samples. In two samples both the adipic acid and internal standard peak had complete- ly vanished.

4 Closing Remarks Although not discussed in detail in this paper, the reduc-

tion in sample weight compared to the original concept proto- col, [2,3] resulted in a considerable reduction in the amount of organic solvent needed per determination. This was also the case in the improved determination of the total adipyl content in acetylated adipyl cross-linked starches [l]. It was therefore possible to use a simple evaporation device, which allows simultaneous evaporation of the extraction solvent in 27 samples instead of one sample at a time in a rotary evapora- tor. This has resulted in a considerable increase in the daily ca- pacity of analysis, and in a reduction in the costs per determi- nation.

5 Summarizing Conclusions 1. For the determination of the free adipic acid content in

acetylated adipyl cross-linked starches, it is advised to use water followed by an extraction of the water four times with ethyl acetate for the extraction of the free adipic acid, instead of applying a single extraction with a methanol - acetic acid solution.

2. Advantages of the miniaturized method with respect to the original method are: 0 increase in daily analysis capacity from about 8 sam-

ples to about 25 samples 0 considerable decrease in the consumption of organic

solvent per determination; instead of 300m1, only 20ml of ethyl acetate are needed per determination.

Starch/Stiirke 48 (1996) Nr. 11/12, S. 448-452 45 1

Acknowledgement The authors are indebted to Mr. G . A . Mitchell from Eridania Be-

ghin-Say, Vilvoorde, Belgium, for the constructive discussions con- cerning the adipate determination and his critical reviewing of the manuscript.

Bibliography [l] Sanders, P., and K . Brunr: Improved method for the determina-

tion of the total adipyl content in acetylated adipyl cross-linked starches. StarchIStarke 46 (1994), 255-259. Gunten, D. von, and D. Korduba: Determination of free adipic acid in acetylated di-starch adipate products. Circular letter STEX 13/84, June ZOth, 1984.

[3] Whitehouse, D. B.: Starch - Determination of the total adipate content and the free adipic acid content in adipate crossbonded

[2]

starches (first draft). ISO/TC 93 WG2 document N20, March 16th, 1989.

[4] Mitchell, G. A . , M. J. Vanderbist, and R R Meert: Gas-liquid chro- matographic determination of the adipate content of acetylated di-starch adipate. J. Assoc. Off. Anal. Chem. 65 (1982), 238-240. Scanlon, J . Z, and D. E. Willis: Calculation of flame ionization detector relative response factors using the effective carbon number concept. J. Chromatogr. Sci. 23 (1985), 333-340.

[6] Mitchell, G. A. : Personal communication.

[5]

Address of authors: Dr. K. Brunt (corresponding author) and P. Sanders, Department of Analytical Chemistry and Raw Materials, Netherlands Institute for Carbohydrate Research TNO, Rouaanstraat 27, 9723 CC Groningen, The Netherlands.

(Received: October 3, 1996).

Dynamic Simulation of a Simulated- Moving-Bed Chromatographic Reactor for the Inversion of Sucrose

Markus Meurer, Ulf Altenhoner, Jochen Strube, Armand Untiedt, und Henner Schmidt-Traub, Dortmund (Germany)

The combination of a chemical or biochemical reaction and a chro- matographic separation process in a single unit-operation allows higher yields and a better separation performance not only for revers- ible decomposition reactions but also for irreversible reactions. A continuous Simulated-Moving-Bed (SMB) chromatographic reactor for the irreversible enzymatic inversion of sucrose is presented. In addition, a simulation based strategy for the design and optimization of chromatographic reactors is explained. Dynamic simulation stud- ies using a rigorous model of the SMB process, illustrate the advan- tages of the continuous chromatographic reactor in comparison to conventional chromatographic processes for the inversion of su- crose. Reaching at least the same product purity as comparable conventional processes, the new reactor allows not only the reduc- tion of capital costs but also a reduced desorbent rate and a higher productivity in terms of the converted amount of sucrose.

Dynamische Simulation eines Simulated-Moving-Bed Chromato- graphie-Reaktors zur lnvertierung von Saccharose. Die Kombina- tion von Reaktion und chromatographischer Trennung in einem ge- meinsamen Verfahrensschritt fuhrt im Vergleich zu konventionellen Verfahren auch bei irreversiblen Zerfallsreaktionen zu Umsatzerho- hungen bei gleichzeitig verbesserten Trennergebnissen. Am Beispiel der enzymkatalysierten Invertierung von Saccharose wird ein konti- nuierlicher Simulated-Moving-Bed (SMB)-Chromatographie-Reak- tor sowie eine Strategie zur simulationsgestutzten Auslegung und Optimierung chromatographischer Reaktoren vorgestellt. In Simula- tionsstudien mit einem rigorosen dynamischen Model1 werden die Vorteile des SMB-Reaktors im Vergleich zu einem konventionellen Invertierungsreaktor mit nachgeschalteter Batch-Trennung bzw. ei- nem Reaktor mit nachgeschaltetem SMB-Trennverfahren aufgezeigt. Bei gleicher Produktqualitat ist die Produktivitat des neuen Prozes- ses bei gleichzeitig geringerem Desorbensverbrauch und somit nied- rigeren Aufarbeitungskosten fur die Produkte hoher.

1 Introduction

Integration of chemical or biochemical reactions in chro- matographic separation processes has been discussed since the early sixties [l, 21. In addition to financial benefits achie- ved by process integration, the application of chromatogra- phic reactors promises an improved course of reaction and en- hanced separation efficiency. For instance, in reversible reac- tions, where higher conversions can be achieved by separating educts and products from each other and thus shifting the re- action equilibrium, the use of combined reactor-separators is promising. Other fields of application exist for the removal of inhibitors, poisons, or acceptor products to improve reaction yields.

Figure 1 shows the operating principle of a chrornatogra- phic reactor for a reversible decomposition reaction. A sharp pulse of component A is fed into the column. Educt A reacts to the product components B and C until chemical equilib- rium is established. Because of their different adsorbability,

A + Desorbent B C Figure 1. Batch chromatographic reactor operating principle.

452 StarchlStZrke 48 (1994) Nr. 11/12. S. 452-457 @ VCH Vedagsgesellschaft mbH, D-69451 Weinheim, 1994 0038-9056/96/1111-0452%10.00+.25/0