Urea removal

The mixture was prepared and allowed to achieve equilibrium to it was added an excess of urea which caused the immediate precipitation as urea nitrate of the free nitric acid present. As a result of the sudden removal of the nitric acid from the mixture, the system underwent change to re-establish the equilibrium however, the use of an excess of urea removed the nitric acid as it was produced from acetyl nitrate and acetic acid, and the consumption of acetyl nitrate proceeded to completion. Thus, by following the production of urea nitrate with the time from the addition of urea, the rate of the back reaction could be determined, and by extrapolating the results to zero time the equilibrium... 

Schollenberger added 2% of a polycarbodiimide additive to the same poly(tetra-methylene adipate) urethane with the high level of acid (AN = 3.66). After 9 weeks of 70°C water immersion, the urethane was reported to retain 84% of its original strength. Carbodiimides react quickly with residual acid to form an acyl urea, removing the acid catalysis contributing to the hydrolysis. New carbodiimides have been developed to prevent hydrolysis of polyester thermoplastics. Carbodiimides are also reported to react with residual water, which may contribute to hydrolysis when the urethane is exposed to high temperatures in an extruder [90]. 

Eiroa, M., Kennes, C., and Veiga, M.C., Formaldehyde and urea removal in a denitrifying granular sludge blanket reactor, Water Res., 38, 3495-3502, 2004. 

Ayhan, F., Yousefi Rad, A., and Ayhan, H. (2002) Biocompatibility investigation and urea removal from blood by urease-immobilized HEMA incorporated poly(ethyleneglycol dimethacrylate) microbeads. J. Biomed. Mater. Res. B Appl. Biomat. 64B(1), 13-18. 

When either ammonia or urea is injected into flue gases at temperatures of about 870°C-1,100°C for ammonia and 900°C-1,150°C for urea, removal can reach as high as 50 percent. 

In general, although the fluxes in corresponding membrane systems may be lower than those with conventional commercially available urea-removing hemodialysis membranes, the selectivity may be much higher [140]. 

The treatment of submitochondrial particles, which are prepared from the inner mitochondrial membrane by sonication and which have the orientation of their membrane reversed (See Figure 18.26, which shows a structure analogous to a submitochondrial particle), with urea removes subunits. When these treated particles are incubated in air with an oxidizable substrate and calcium ion, the concentration of calcium inside the particles increases. 

A preliminary long-term clinical evaluation has demonstrated the safety and effectiveness of this approach [18]. The completion of this system will have to wait for the development of a urea removal system. Recently, a composite artificial kidney has been formed, combining artificial cells and dialysis or artificial cells and an ultraflltrator [19]. 

Urease Bacterial Urea removal from blood (enzymatic artificial kidney) Qin and Cabral (2002)... 

Thus, in 4 hr, which is a typical treatment time, the urea concentrate has been reduced by 45%. It is left as an exercise at the end of this chapter for a study of the effect on the rate of urea removal of changing the hemodialyzer geometry, the blood and dialysate flow rates to the dialyzer, the rate of waste withdrawal, the volume of the dialysate tank, and the sensitivity of the rate of urea mass transfer to the mass-transfer coefficient. In particular, the above estimate of the coefficient on the shell side may be low because the entry to and exit fi om the hemodialyzer of the dialysate is normal to, rather than parallel to the fibers. This should enhance the shell-side coefficient. ... 

Artificial Internal Organs and Related Fields.— There has been a marked increase in certain aspects of the literature here, notably in the haemoperfusion field and in total artificial heart replacement. Some recent advances in haemodialysis techniques have been described involving high rates of ultra-filtration combined with optimal diffusion, the use of a resin-sorbent system for dialysate regeneration and the use of urease (E.C. 3.5.1.5) and an expanded polytetrafluoroethylene membrane in the development of a new method of urea removal. The effects of different membranes in the onset of haemodialysis-induced leucopenia have been discussed. ... 

In this model, there are mass transfer eflFects between the CSF and extracellular compartments (given by the mass transfer coefficient K2) and between the extracellular compartment and the intracellular compartment (Ki). G is the natural rate of generation of the contaminant urea, L is the flow rate of CSF fluid that flows directly into the extracellular fluid, and F is the rate of urea removal due to dialysis with an artificial kidney. 

OuGH, C.S. and G. Trioli. 1988. Urea removal from wine by an acid urease. Am. J. Enol. Vitic. 39 303-307. 

Requirements for Adequate Dialysis The quantitative assessment of efficacy of dialysis therapy and renal function is based on the small solutes, even though the molecular weights range over 3 orders of magnitude. Urea and creatinine are eonsidered to be representative or surrogates for the small molecules and easily measured. Three different methods of accessing urea removal rates are currently used ... 

A new protocol, involving the addition of a bifunctional urea to the reaction mixtnre, increased significantly the reaction rate [92], The origin of the increased reaction rate was dne to a hydrogen bond interaction between the bifunctional thio-nrea and the possible oxazolidine intermediate formed [93] which enhanced the rate of the enamine formation. Moreover, the addition of urea removed the aforementioned antoindnction behavior, and therefore, an alternative catalytic cycle conld take place in the presence of the urea. 

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