ABSTRACT
The fouling of equipment surfaces by suspended matter and precipitated scale forming salts is a critical concern to water technologists and plant operators. Certain feed waters, especially surface waters, require far more extensive pretreatment than sources such as deep wells. Polymeric dispersants are used in water treatment formulations to control fouling of equipment surfaces. This paper compares the performance of commercially available polymers as dispersants for a variety of suspended matter i.e., corrosion products, hydroxyapatite, clay, etc., under stressed industrial water system conditions. Results reveal that various factors including polymer architecture, water chemistry, nature of the substrates affect the performance of polymers. It has been observed that presence of water treatment formulation components i.e., homopolymers and phosphonates exhibit marked antagonistic effect on high performance dispersant performance. Additionally, zeta potential data on iron oxide suspensions show that the presence of copolymers compared to homopolymers results in marked increase in the negative charge of iron oxide particles. Based on the data collected, the performance of polymers may be ranked as follows: terpolymer > -copolymer > homopolymer > hybrid polymer.
INTRODCUTION
Deposition of undesirable materials such as mineral scales, microbiological growth, corrosion products, and particulate matter on equipment and reverse osmosis (RO) membrane surfaces often cause numerous technical and economic challenges in different facets of industrial processes and domestic installations. Affected application areas include boiler, cooling, geothermal, power generation, gas and oil productions, desalination of sea/brackish water (distillation or membrane-based processes). The problems associated with these deposits include: a) partial or total obstruction of pipes and clogging of membrane pores leading to a decrease flow rate, b) reduced heat transfer due to the insulated characteristics of the deposits c) increased energy cost, d) under deposit corrosion, and e) premature equipment replacement.
Metal ions (e.g., Al, Cu, Mn, Fe, Zn) present in the feed water may get oxidized by oxidizing biocides and/or may form insoluble oxide/hydroxide salts such as Al(OH)3, Cu(OH)2, Fe(OH)3, Zn(OH)2, and MnO2. Maintaining these hydrolyzed and/or oxidized metal ions in soluble and dispersed forms can prevent the buildup of unwanted deposits on various substrates. Iron based deposits typically are in the form of FeO, Fe2O3, Fe3O4, FeS, iron silicate, etc. Often manganese salts are also detected in these deposits. Iron fouling occurs as a result of corrosion processes throughout the system. Thus, it is important to implement a good corrosion program. In cooling waters, Fe2O3 (hematite) and FeOOH are the two most common iron deposits. Magnetite (Fe3O4) is rarely encountered in cooling systems. Magnetite needs high temperature and anaerobic conditions. Most magnetite found in cooling systems arrives via airborne or water borne deposits.