High-pH cleaners

High-pH cleaners are typically used to address removal of the following species  

Note that performance fo the RO unit may be different after a high pH cleaning. Specifically, the flux may be higher and the rejection may be lower. This is a result of the membrane loosening at high pH and is a temporary condition. Performance should return to nominal within a couple of days. 

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Industrial grade amide with high free amine content. Used in high pH cleaners, degreasers, and floor strippers. Good foam boosters and stabilizers. 

The composition of the builders in an alkaline cleaner is dependent on the metal substrate from which the soil is to be removed. For steel (qv) or stainless steel aggressive, ie, high pH, alkaline salts such as sodium or potassium hydroxide can be used as the main alkaline builder. For aluminum, zinc, brass, or tin plate, less aggressive (lower pH) builders such as sodium or potassium siUcates, mono- and diphosphates, borates, and bicarbonates are used. 

Production of ammonia (NH ) Anhydrous (dry) ammonia is the fifth most produced industrial compound. The Haber-Bosch process uses steam on hot coke, which is mostly used in South Africa. In the United States, it is mostly produced from partial combustion of natural gas (methane) or by combining several gases using steam. Other methods use coke-oven gas, refinery gas (mostly methane), or even solar energy. Ammonia is toxic if inhaled and has a high pH value when mixed with water (hydration) to form ammonium hydroxide (NH OH), which has many uses, including as a household cleaner. Ammonia forms many compounds, including ammonium nitrate in fertilizer, rocket fuel, and explosives. Ammonia is also explosive when mixed with mercury or silver or when mixed as part of nitrocellulose. 

Sodium hydroxide (NaOH) is one of the most useful industrial sodium compounds. It is also known as lye or caustic soda and is one of the strongest base alkahs (high pH value) on the household market. It is used as a drain and oven cleaner, and it saponifies fats in the manufacture of soap. It must be used with care because it is also capable of producing serious skin burns. 

Potassium hydroxide (KOH) is commonly referred to as caustic potash or lye because of its extreme alkahnity (high pH value). It is produced in an electrolytic cell reaction (2KC1 + THfD —> Hj + CIj + 2KOH). It is used to manufacture soaps and as a caustic drain cleaner because it is strong enough to dissolve animal fats that clog household and restaurant drains. 

Completely clean the membranes with high pH and low pH cleaners prior to recirculating hydrogen peroxide. 

Figure 14.20 gives the pHs of some common materials. Notice the range of pHs from the low pH of lemon juice to the high pH of drain cleaner. 

The primary disadvantage of MEEs (or any ester ethoxylates) are that they will hydrolyse at pH levels above about 9. This makes these materials unacceptable for high pH (caustic) cleaners. 

One may argue with the designation of a bleach cleaner as an APC. Many household surfaces can potentially be damaged by bleach, some due to attack by the bleach itself, some by the high pH necessary to stabilize bleach in the formula. These include painted surfaces, aluminum, some ceramics, and wood. However, bleach formulas serve an important purpose in that they not only clean but also decolorize stains. If a stain cannot be cleaned off a surface it can be made less noticeable by decreasing its color, which the oxidizing action of the bleach does very well. 

First this discussion will tnm to the simplest of the specialty cleaners, those based on very high pH the oven and drain cleaners. Both are usually based on a high concentration of an alkaline ingredient such as sodium hydroxide. In both cases, the alkalinity of the formula is key to its ability to clean the soils encountered in these problems. The choice of snrfactant is somewhat limited, as the surfactant needs to be stable at pHs of 11-14, bnt there is still reasonable choice. The main function of the surfactant in these products relates primarily to their foaming. 

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