| 1. |
- Axelsson, Jan Peter, et al.
(författare)
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Substrate Control of Biotechnical Fedbatch Processes. Robustness and the Role of Adaptivity
- 1990
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Konferensbidrag (refereegranskat)abstract
- Results from experiments on laboratory scale fedbatch processes are presented as well as analysis and design of the control system. The main reason for control is to track the drastic growth in feed demand during a cultivation. Variations in the amount and quality of the inocculum makes precalculated dosage schemes of limited value to obtain reproducible cultivation conditions. Two processes have been studied on a laboratory scale, production of bakers' yeast, and production of the enzyme salicylate hydroxylase using a strain of bacteria. Direct measurement was used to monitor the feed demand. A regulator structure is proposed based on an observer for the exponentially growing feed demand. It can be viewed as a modified PID regulator around a dosage scheme, but it is less sensitive to errors in the dosage scheme than conventional PID control. The a priori knowledge of the feed profile is further relaxed by introduction of adaptation of the growth rate parameter. The obtained non-linear control system has a simple structure and stability is garanteed for a wide range of initial values using the technique of Liapunov function. The linearized system is analysed in the frequency domain and the adaptation is shown to have negligible influence on the loop phase margin. The adaptive regulator is tested in simulation against real feed profiles and shows good results.
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| 2. |
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| 3. |
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| 4. |
- Holst, Olle, et al.
(författare)
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Substrate Control in Fed-Batch Cultivations Using a Model-Based Modification of a PI-Controller
- 1992
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Ingår i: Proceedings of the 2nd IFAC Symposium on Modelling and Control of Biotechnical Processes.
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Konferensbidrag (refereegranskat)abstract
- A fedbatch process shows exponential growth under ideal conditions. To obtain good substrate concentration control it is necessary that the regulator can track an exponentially growing feed demand, and standard PI-control has to be supplemented with an estimated basic dosage to get reasonable control. However, an exponentially growing concentration error is impossible to avoid. An I-term could be interpreted as an observer of a constant demand, and we have proposed to replace it with a model-based observer for an exponentially growing demand. In the resulting controller the integrator is replaced by an unstable pole at s = μ, the specific growth rate, and the initial condition of this term is equivalent to the basic dosage part. The regulator can now track the exponentially growing feed demand without error. Pseudomonas cepacia was grown on salicylate as sole carbon and energy source. Salicylate is a toxic substrate, so it is important to have good substrate control. On-line measurement of salicylate concentration was carried out using a filtration system from which cell-free permeate was passed to a flow-through spectrophotometer. Introducing more instability into the controller requires attention to the anti-windup features. No such problems were found during the cultivations or in simulations of the effect of conceivable disturbances like pump-failure, air-bubbles in the spectrofotometer, and low oxygen concentration induced growth-rate reduction.
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| 5. |
- Bowman, Lawrence E., et al.
(författare)
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A single photon timing instrument that covers a broad temporal range in the reversed timing configuration
- 1993
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Ingår i: Review of Scientific Instruments. - : AIP Publishing. - 0034-6748 .- 1089-7623. ; 64:2, s. 338-341
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Tidskriftsartikel (refereegranskat)abstract
- A versatile single-photon timing instrument based on the reversed timing configuration has been constructed. Unlike similar instruments, the apparatus described here is capable of recording a broad range of excited-state decay times owing to a switched fiber optic delay. This allows the user to readily collect time-resolved luminescence data over a variable time window in the reversed-timing configuration. With proper adjustment of the appropriate components, one can acquire a luminescence decay over a variable time range from less than 1 ns to nearly 1 μs. The full width at half-maximum of the instrument response function is 42 ps. The utility of a switched fiber optic delay is discussed and the device's construction is described.
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| 6. |
- Cerreta, M.K., et al.
(författare)
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Contact nuclei formation in aqueous dextrose solutions
- 1990
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Ingår i: Journal of Crystal Growth. - 0022-0248 .- 1873-5002. ; 102:4, s. 869-876
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Tidskriftsartikel (refereegranskat)abstract
- A laser Raman microprobe was used in situ to observe the growth of alpha dextrose monohydrate on alpha anhydrous dextrose crystals. The Raman spectra indicate growth of the monohydrate below 28.1°C, but the presence of only the anhydrous form above 40.5°C. Contact nucleation experiments with parent anhydrous crystals yielded only monohydrate nuclei below 28.1°C, while contacts in solutions between 34.5 and 41.0°C produced both crystalline forms, and contacts in solutions above 43.5°C produced only anhydrous nuclei. The inability of the monohydrate to grow on anhydrous crystals in the same solution that forms the two crystalline phases with a single contact precludes a simple attrition mechanism of nuclei formation. For the same reason, the hypothetical mechanism involving parent crystal stabilization of pre-crystalline clusters, allowing the clusters to grow into nuclei, is also contradicted. A third, mechanism, which may be a combination of the two, is believed to apply.
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| 7. |
- Chakraborty, Reena, et al.
(författare)
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Steady state fluorescence spectroscopy of pyranine as a trace extrinsic probe to study structure in aqueous sugar solutions
- 1992
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Ingår i: Journal of Crystal Growth. - 0022-0248 .- 1873-5002. ; 125:1-2, s. 81-96
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Tidskriftsartikel (refereegranskat)abstract
- The steady state fluorescence behavior of pyranine has been monitored in aqueous solutions of sucrose, glucose, fructose, and lactose. In each case it is possible to use the ratio of peak intensities at 440 and 511 nm (the PIR) as an indicator of the degree of supersaturation of the sugar solutions. We observed both bulk water and water of solvation in all solutions examined, regardless of degree of sapersaturation. In each case the amounts of bulk water and water of solvation per molecule of sugar appear to be nearly equal at saturation. We did not observe any evidence of solvent exclusive clusters in any of the systems we studied
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| 8. |
- Chakraborty, Reena, et al.
(författare)
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Use of pyranine as a trace fluorescent probe to study structure in aqueous sucrose solutions
- 1991
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Ingår i: Particle design via crystallization. - Washington, DC : American Institute of Chemical Engineers. - 0816905533 ; , s. 114-123
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Konferensbidrag (refereegranskat)abstract
- Emission spectroscopy using pyranine as a trace fluorescent probe was evaluated as a means of studying solution structure in aqueous sucrose solutions. Spectra of pyranine doped sucrose solutions of 0-70 wt% were obtained, indicating two microenvironments. The peak intensity ratio (defined as the ratio of peak intensities at 440 nm and 511 nm) was observed to be a very sensitive function of the water content in supersaturated solutions. The two microenvironments were designated as bulk water and that near the solvated sucrose molecules. Calculations yielded six water molecules of solvation per molecule of sucrose. This is in agreement with values in literature. The number of molecules of water per molecule of sucrose in the bulk water environment varies exponentially from 165 in a 10% solution to three for a 70% solution at 20 degrees C. These results indicate that this technique can be used successfully to measure water content in supersaturated solutions.
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| 9. |
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| 10. |
- Dunuwila, Dilum D., et al.
(författare)
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An investigation of the applicability of attenuated total reflection infrared spectroscopy for measurement of solubility and supersaturation of aqueous citric acid solutions
- 1994
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Ingår i: Journal of Crystal Growth. - : Elsevier BV. - 0022-0248 .- 1873-5002. ; 137:3-4, s. 561-568
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Tidskriftsartikel (refereegranskat)abstract
- Currently applied methods for measurement of solubility and supersaturation based on viscometry, refractometry, interferometry and density require the separation of phases prior to measurement. ATR (attenuated total reflection) infrared spectroscopy provides a unique configuration in which the infrared spectrum of a liquid phase can be obtained in a slurry without phase separation. The applicability of the technique was investigated using a micro Circle® open boat cell equipped with a ZnSe (zinc selenide) ATR rod. Experiments conducted with aqueous citric acid proved that ATR infrared spectroscopy can be successfully employed to determine solubility and supersaturation.
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| 11. |
- Dunuwila, Dilum D., et al.
(författare)
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Application of controlled hydrolysis of titanium(IV) isopropoxide to produce sol-gel-derived thin films
- 1994
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Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 0897-4756 .- 1520-5002. ; 6:9, s. 1556-1562
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Tidskriftsartikel (refereegranskat)abstract
- A variety of porous optically transparent titanium carboxylate films that can be supported on silicate glass substrates have been developed. These films were made by spin casting polymeric solutions of titanium carboxylates processed using sol-gel techniques. The stability and the quality of these films have been qualitatively correlated to the extent of control of hydrolysis exerted by carboxylate modification of the precursor titanium(IV) isopropoxide. A series of carboxylic acids ranging from acetic acid to myristic acid has been used, and their effects on film quality and stability are presented.
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| 12. |
- Dunuwila, Dilum D., et al.
(författare)
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Sol-gel derived titanium carboxylate thin films for optical detection of analytes
- 1994
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Ingår i: Analytical Chemistry. - : American Chemical Society (ACS). - 0003-2700 .- 1520-6882. ; 66:17, s. 2739-2744
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Tidskriftsartikel (refereegranskat)abstract
- The feasibility of using a sol-gel derived titanium carboxylate thin film, which can be supported on glass, for the fabrication of optical test strips was investigated using a model probe/ analyte combination. The porous films, being optically transparent and baring the capability to host probe molecules, provided an excellent system to investigate the possibility of making optical test strips. A colorimetric reagent, an iron(III) porpohyrin, was chosen as the probe molecule to detect free cyanide ion concentrations in aqueous solutions. Entrapment of the porphyrin in the film was accomplished by direct dissolution of the porphyrin in the sol-gel solutions. Chemically induced structural modifications of the polymer were carried out to stabilize the encapsulated metalloporphyrin within the sol-gel derived matrix. The syntheses of this model analyte detection system and its response are presented. An optical parameter reflective of the chemical changes that occur in the system was selected as the measurement tool; its response asymptotically increased over the cyanide ion concentration range of 40-25 000 ppm.
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| 13. |
- Miranda, A., et al.
(författare)
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Recovery of Clostridium thermosulfurogenes produced β-amylase by (hydroxypropyl)methylcellulose partition
- 1990
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Ingår i: Biotechnology progress (Print). - : Wiley. - 8756-7938 .- 1520-6033. ; 6:3, s. 214-219
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Tidskriftsartikel (refereegranskat)abstract
- A procedure for recovering Clostridium thermosulfurogenes produced β-amylase from fermentation broth by partition was developed. The partition was achieved by addition of ammonium sulfate to an aqueous solution of the enzyme with (hydroxypropyl)methylcellulose. The β-amylase-containing pellet formed upon centrifugation could be redissolved and the polymer recovered by a second salt addition. The process was not dependent on polymer/enzyme solution pH, but it was affected by temperature, polymer nominal molecular weight and loading, and fermentation carbon source. Unlike more traditional aqueous-phase partitions, such as poly(ethylene glycol)/dextran, the current approach appeared to be biospecific.
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| 14. |
- Miranda, Everson A., et al.
(författare)
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Evaluation of column flotation in the downstream processing of fermentation products : recovery of a genetically engineered α-amylase
- 1993
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Ingår i: Biotechnology progress (Print). - : Wiley. - 8756-7938 .- 1520-6033. ; 9:4, s. 411-420
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Tidskriftsartikel (refereegranskat)abstract
- Flotation is a simple, inexpensive, and versatile unit operation with a largely unexplored potential in biotechnology. There is a general lack of research concerning biotechnological applications in this area, especially in the recovery of fermentation products. Moreover, the few reports in the literature do not consider the modern concept of column flotation as practiced in the mineral industry. We report herein the application of column flotation for the recovery of a Bacillus stearothermophilus α-amylase expressed in Escherichia coli by the use of a food-grade polymer, (hydroxypropyl)methylcellulose (HPMC), and ammonium sulfate. First, the enzyme was removed from the liquid phase by partition to a salted-out HPMC phase. The enzyme-containing polymer flocs were then floated from the liquid. Recovery of active enzyme was as high as 90%, with throughput as high as 94 m3/(h·m2). The floatability of the enzyme from a periplasmic extract was higher than extracellular enzyme in the broth due to the presence of depressors of molecular weight lower than 10 000 in the broth.
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| 15. |
- Ofoli, R., et al.
(författare)
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Extrusion liquefaction and saccharification of carbohydrate substrates
- 1990
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Ingår i: Food biotechnology. - 0890-5436 .- 1532-4249. ; 4:1, s. 365-
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Tidskriftsartikel (refereegranskat)abstract
- The objective of this study was to assess the feasibility of accomplishing enzymatic liquefaction and saccharification of carbohydrate formulations during one pass in a twin-screw food extruder. The combined liquefaction and saccharification process was carried out on a cereal grain formulation in a pilot-scale twin screw Baker Perkins extruder, using thermophilic α- and β-amylase. The biggest limitation on the process was the short residence times characteristic of the extruder. This problem was partially overcome by a combination of screw configurations, mass flow rates and RPM which extended the residence times and enhanced the extent of reaction. Results indicate that this type of technology may provide some opportunities for the food and biochemical industry.
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| 16. |
- Pan, Borlan, et al.
(författare)
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Time resolved fluorescence and anisotropy of 1-pyrene butyric acid and pyranine as probes of solvent organization in sucrose solutions
- 1993
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Ingår i: Journal of Crystal Growth. - 0022-0248 .- 1873-5002. ; 130:3-4, s. 587-599
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Tidskriftsartikel (refereegranskat)abstract
- The microenvironment of solute-solvent interactions in aqueous sucrose solutions, ranging from 0 to 80 wt% in concentration, was investigated using time resolved fluorescence techniques. The fluorescence lifetimes and rotational correlation times of the trace fluorescent probes, PBA (1-pyrene butyric acid) and pyranine (trisodium 8-hydroxy-1,3,6-pyrenetrisulfonate), were measured in sucrose solutions. The behavior of the fluorescence lifetimes and the increase in the rotational correlation times with increasing sucrose concentration provided no evidence for the formation of water exclusive solute clusters in the metastable solutions. Instead, the results indicated the formation of a network of hydrogen bonding interactions between dispersed sucrose molecules.
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| 17. |
- Severin, Kathryn G., et al.
(författare)
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Characterization of titanium and zirconium valerate sol-gel films
- 1994
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Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 0897-4756 .- 1520-5002. ; 6:7, s. 890-898
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Tidskriftsartikel (refereegranskat)abstract
- FTIR and XPS have been used to characterize titanium and zirconium valerate thin films prepared using sol-gel techniques. Films were prepared by hydrolysis of titanium(IV) isopropoxide or zirconium(IV) n-propoxide in excess valeric acid at room temperature. Film solution chemistry, from precursors to cast films, was followed with FTIR. The structure and chemical composition of films spin cast from fresh and day-old solutions were determined. Results of these studies suggest that all films consist of a metal-oxygen polymer backbone coordinated with bidentate valerate ligands. No evidence for the presence of alkoxide ligands has been found. A small amount of water is present in all cast films. While solution aging experiments indicate that the zirconium film structure does not change with solution reaction time, carboxylate ligand concentrations are higher in titanium films made from aged solutions. Titanium films made from aged solutions contain slightly less than 1.5 valerate ligands/titanium atom. Zirconium films are more highly carboxylated with almost two valerate groups per metal center.
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| 18. |
- Shiau, Lie-Ding, et al.
(författare)
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Growth rate dispersion in batch crystallization
- 1990
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Ingår i: AIChE Journal. - : Wiley. - 0001-1541 .- 1547-5905. ; 36:11, s. 1669-1679
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Tidskriftsartikel (refereegranskat)abstract
- A method for describing the crystal size distribution of a batch crystallizer in the presence of growth rate dispersion is presented. The analysis is based on the assumption that individual crystals have inherent constant growth rates, but the growth rate may vary from crystal to crystal, resulting in a distribution of growth rates. The method requires the availability of growth rate, growth rate dispersion, and nucleation rate expressions for prediction of the crystal size distribution. These required rate expressions can be recovered by the use of simple linear regressions from the CSD moment data. Prediction of the unsteady-state CSD was demonstrated using rate expressions for the sucrose-water system. Batch fructose experiments were analyzed to demonstrate the recovery of the growth and nucleation rates from the size distribution data.
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