Sorbents artificial

As discussed in Chapter 3, at least trace amounts of arsenic commonly occur in rocks, soils, sediments, sludges and spent sorbents from water treatment systems, coal ashes, industrial wastes, and many other natural and artificial solids. Depending upon whether they are considered regulatory hazards (Appendix E), solid materials may require treatment before disposal (waste management) or remediation if they are located at a contaminated site. For solids, arsenic treatment may involve reducing the arsenic concentrations in the materials so that they are no longer hazardous (for example, soil washing). However, because arsenic cannot be destroyed, eventually the element will require permanent disposal in a manner that does not... 

The combustion efficiency of these low-capacity CFB combustors varies from 93% to 96%, with 20% excess air at the furnace exit. Measurements have shown that CO concentration in the flue gas could be reduced from 1,000-2,000 ppm to 100-200 ppm through the separator, indicating continued and rather efficient combustion in the separator. With an artificial sorbent (see Section V), the S02 removal could reach 83-93% at a Ca/S ratio of 1.4-1.7. The NO, in the exit gas is about 100 mg/Nm3. 

Another recourse is to develop artificial sorbents with more favorable pore structure. Figure 45 compares the desulfurization characteristics of... 

Fig. 45. Desulphurization characteristics of natural limestone and artificial sorbent.

Fig. 48. Reaction characteristics along diameter of artificial sorbent.

Liver. The liver performs a wide variety of chemical reactions in the body and is the main locus of detoxification. Successful liver transplantation is somewhat rare, and no true artificial liver seems likely in the near future. The process of hemoperfusion, which is sometimes termed an artificial liver, can be used to supplement or relieve the normal liver functions for short time periods. In this technique, the patient s blood is passed through a column or bed of some sorbent material that removes toxic chemicals from the blood. This technique is often used in cases of drug overdose, poisoning, and acute hepatitis. The sorbent material can be charcoal, ion-exchange resins, immobilized hepatic material, or liver material enclosed in artificial cells (microcapsules, usually made from a polyamide). The column is usually a plastic material, and plastic tubing is used to direct the blood flow to and from the device ( 1, 57, M). 

The liver Is the main detoxification organ in the body and therefore comes Into contact with nearly every poison and toxin that enters the body. These materials could occur in case of poisoning, drug overdose, acute hepatitis, and allergies. While no true artificial liver has been developed, and transplantation is rare and difficult, several approaches have been attempted to replace and/or assist the function of the liver. The most common method is hemoperfusion in which the blood is passed through a column or bed of some sorbent material which can remove the poisons. The sorbents that have been used include charcoal, ion-exchange resins, affinity chromatography resins, immobilized enzymes and hepatic material or pieces of liver enclosed in artificial cells (9, 52). 

Bioactive sorbents represent the simplest form of artificial cells already used in routine clinical applications for humans. Sorbents such as activated charcoal, resins, and immunosorbents could not be used in direct blood perfusion because particulate embolism and blood cells were removed. However, sorbents such as activated charcoal inside artificial cells no longer cause particulate embolism and blood cells removal. This application was developed and used successfully in patients. For example, the hemoperfusion device now used in patients contains 70 g of artificial cells. Each artificial cell is formed by applying an ultrathin coating of collodion membrane or other polymer membranes on each of the 100-p-diameter activated-charcoal microspheres. The mass transfer for this small device is many times higher than that for a standard dialysis machine. 

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. ... 

Tijink et al. [52] suggested that besides removal of protein-boimd toxins, the MMM might also be useful in liver failure or sepsis by combining renal support and targeted adsorption. The MMM might be useful for a wearable artificial kidney due to the incorporation of sorbents within a membrane. However, their development is still in an early stage. The MMMs prepared by phase inversion, using mixture polymer (cellulose acetate, polyethersulfone (PES)/polyvinylpyrrolidone (PVP) polymer blend) and activated carbon, were successfully applied for removal of creatinine. 

---