Foulants inorganic

The type of membrane cleaning required depends on both the type and degree of fouling experienced, but typically it is either organic (bacterial slimes, natural organics, or process foulants and nutrients) or inorganic (silica, carbonate, sulfate, or phosphate deposits). 

Any of a number of insoluble materials laid down in a cooling system by a variety of mechanisms, such as scales and wind-blown minerals. Modem applied chemical technology has blurred the traditional notions of scales, corrosion debris, and inorganic mineral foulants as being separate problems, requiring individual chemical treatment, and now any of these may be referred to as a deposit. 

Solid inorganic foulants may also accumulate on the catalyst. Little can be done to remove such foulants except by mechanical means. This is usually inefficient, and replacement of catalyst is often necessary. 

Despite the aforementioned efforts, membrane flux decline due to fouling continues to be a major operational issue. Attempts have been made to modify inorganic membranes, mostly their surfaces, to render them less prone to foulant adsorption. One of the frequently encountered fouling problems in biotechnology and food applications is protein adsorption. In membrane reactor applications which are largely associated with hydrocarbons, carbonaceous deposits pose as one of the operational problems. 

Attenuated total reflection (ATR) Fourier transform infrared (FTIR) spectroscopy can provide insight into the chemical nature of deposits on membranes [46]. The spectra of the foulants can be easily distinguished from the spectra of the membrane material. ATR/FTIR can also indicate the presence of inorganic foulants as well as the ratio of inorganic-organic foulants. 

The particulate matter carried forward in gas streams can also cover a wide range of materials including inorganic mineral matter, organic particles and "natural" materials like wood particles. Inorganic substances possibly with carbon particles, are common foulants in combustion systems where fossil ftiels like oil and coal or waste materials like domestic refuse are burnt. Even with "clean" fuels such as natural gas, problems of fouling may arise as a result of poor combustion... 

Chlorine in the form of household bleach (4 ml of 55 bleach in 1 litre of 0.5 N caustic soda results in 200 ppm of chlorine) is an effective cleaner (not to be used for PA membranes) especially when the pores are fouled in the case of UF and MF membranes. The recommended dosage is 50 ppm for CA membranes, 20—400 ppm for polyether sul-phone membranes and 1000—2000 ppm for inorganic membranes. In the case of UF and MF polymeric membranes, chlorine action results in opening the pores that allows the foulant to be flushed out at high pressure. 

---