Some new reactive polymers for the immobilization of enzymes.
From poly(vinyl alcohol) precursors, various reactive carriers for the immobilization of enzymes were synthesized. As insoluble starting polymers, the following products were used: poly(vinyl alcohol), gels crosslinked with terephthalaldehyde, hydrolyzed beads of crosslinked poly(vinyl acetate), poly(vinyl acetate-co- ethylene) tubes coated with poly(vinyl alcohol), and poly(vinyl alcohol)-containing synthetic pulp. Reactive groups introduced into these carriers or methods for their activation included the diazonium- and isothiocyanato group, and the glutardialdehyde-, BrCN, 2, 4, 6-trichloro-s-triazien, and p-benzoquinone methods. Furthermore, SH-specific reactive groups such as N-substituted maleimide groups or activated mixed disulfides with 2-thiopyridyl groups could be introduced into PVA-polymers. Enzymes like hydrolases (e.g. papain, trypsin, chymotrypsin, urease), oxidoreductases (e.g. glucose oxydase, catalase, glucose-6-phosphate dehydrogenase) as well as the example of transferase hexokinase coimmobilized with glucose-6-phosphate dehydrogenase, were immobilized by reactive poly(vinyl alcohol) carriers. The properties of the immobilized enzymes were investigated.
An polyvinylalkoholträgern immobilisierte enzyme
Aus mit Terephthalaldehyd vernetztem Polyvinylalkohol wurden durch Umsetzung mit 2,4,6-Trichlor-s-triazin, 4-Nitrobenzylchlorid beziehungsweise 2-(3-Aminophenyl)-1,3-dioxolan und Folgereaktionen reaktive Trager hergestellt, die mit Papain, Trypsin und Glucose-Oxydase aktive Enzympraparate ergaben. 
 
 
 
Das Bindungsvermogen des letztgenannten Tragers fur die Enzyme wurde in Abhangigkeit von der zur Immobilisierung eingesetzten Enzymmenge sowie fur Papain vom Gehalt an reaktiven Gruppen des Tragers untersucht. 
 
 
 
Fur die immobilisierten Hydrolasen wurden die Eigenschaften wie Aktivitat, pH-Aktivitats-Profil, KM(app.)-Werte, Lager- und Thermostabilitat, sowie Stabilitat bei wiederholtem Einsatz bestimmt. 
 
 
 
Poly(vinyl alcohol) was crosslinked with terephthalaldehyde and was reacted with 2,4,6-trichloro-s-triazine, resp. 4-nitrobenzyl chloride, resp. 2-(3-aminophenyl)-1,3-dioxolane. Subsequent reactions gave reactive carriers, which could be used to obtain active immobilized enzymes with papain, trypsin, and glucose oxidase. 
 
 
 
The binding ability of the last carrier for the enzymes was investigated as a function of the offered amount of the enzyme during the immobilization. In the case of papain also the dependence of the content of reactive groups on the binding ability was investigate. 
 
 
 
Some properties of the immobilized hydrolases as activity, pH-activity profile, KM(app.)-values, storage- and thermostability, and stability after repeated application were determined.
Prevention of Barite Sag in Oil-Based Drilling Fluids Using a Mixture of Barite and Ilmenite as Weighting Material
Drilling high-pressure high-temperature (HPHT) wells requires a special fluid formulation that is capable of controlling the high pressure and is stable under the high downhole temperature. Barite-weighted fluids are common for such purpose because of the good properties of barite, its low cost, and its availability. However, solids settlement is a major problem encountered with this type of fluids, especially at elevated downhole temperatures. This phenomenon is known as barite sag, and it is encountered in vertical and directional wells under static or dynamic conditions leading to serious well control issues. This study aims to evaluate the use of barite-ilmenite mixture as a weighting agent to prevent solids sag in oil-based muds at elevated temperatures. Sag test was conducted under static conditions (vertical and inclined) at 350 °F and under dynamic conditions at 120 °F to determine the optimum ilmenite concentration. Afterward, a complete evaluation of the drilling fluid was performed by monitoring density, electrical stability, rheological and viscoelastic properties, and filtration performance to study the impact of adding ilmenite on drilling fluid performance. The results of this study showed that adding ilmenite reduces sag tendency, and only 40 wt.% ilmenite (from the total weighting material) was adequate to eliminate barite sag under both static and dynamic conditions with a sag factor of around 0.51. Adding ilmenite enhanced the rheological and viscoelastic properties and the suspension of solid particles in the drilling fluid, which confirmed sag test results. Adding ilmenite slightly increased the density of the drilling fluid, with a slight decrease in the electrical stability within the acceptable range of field applications. Moreover, a minor improvement in the filtration performance of the drilling fluid and filter cake sealing properties was observed with the combined weighting agent. The findings of this study provide a practical solution to the barite sag issue in oil-based fluids using a combination of barite and ilmenite powder as a weighting agent to drill HPHT oil and gas wells safely and efficiently with such type of fluids.