2/20/2014 2014 Training Seminars WATER CHEMISTRY Colin Frayne CWT AQUASSURANCE, INC. 2 Why is Water used as a Process Fluid? • Liquid water and gaseous steam forms of H2O are commonly employed as heat-transfer vehicles for the transport of heat to some distant point of use, or for the uptake/ removal/ rejection of heat . Also, for use in a wide variety of industrial processes. • Water has a high heat capacity • It’s a good solvent and medium for chemical reactions Apart from boilers and cooling systems, we use water for: • Washing , Cleaning ,Rinsing, Dying, Melting, Quenching, Stripping, Scrubbing, Cooking, Hydrolyzing reactions • We can obtain water for reuse from: Distillers, Evaporators, Condensates, Boiler Blowdown, Softener/Filter Rinsing, RO-Reject, Neutralization, Electronics, Formation/Produced Water, Refinery Sour Waters, Mining, Treated Wastewater, Rainwater 3 1 2/20/2014 Heat Capacity of Water is measured in Btu’s (unless we go Metric/SI!) • What is a Btu? • Provide a definition? • How many Btu’s required to raise 1lb. of water from 32oF to 212oF at sea level? • What is the heat content of 1 lb. of steam at sea level (from and at 212oF)? • What is the air pressure at sea level? For Metric/SI: 1 Btu/lb = 4.177 kJ/kg, or 0.516 calories/gram 4 Heat Capacity of Water • Btu is a British Thermal Unit • It is amount of energy required to raise temperature of 1 lb water by 1oF • 212-32 = 180 Btu • Enthalpy of evaporation (latent heat of vaporization) = 970 Btu/lb. So, heat content = 180 + 970 = 1150 Btu • Atmospheric pressure = 14.7 psiatm (Approx 1 Bar) • Absolute pressure (psia) = psiatm + psig • 1 Btu/lb = 4.177kJ/kg • 970 Btu/lb = 2257 kJ/kg • Latent Heat of Vaporization of water = 1150 Btu/lb (2260 kJ/kg, 593cal/g) @ 100oC o • Latent Heat of Fusion of water = 144 Btu/lb (334 kJ/kg, 79.7cal/g) @ 0 C 5 Why is Water Treatment vital? Effects of poor water treatment! 6 2 2/20/2014 Because Water is a “universal solvent”! • Natural impurities and introduced contaminants can promote many types of problems in water systems Effects are: • Hinders heat-transfer and steam gen. processes • Adversely affects quality and purity of steam • Primary instigator in metals corrosion/wastage. • Deposits crystalline/non-crystal scales/sludges • Produces foulants, and encourages biofoulants • Promote hygiene and infection hazards 7 So, understanding basic chemistry is critcally important in water treatment! Dissolved minerals + concentration effects + local operating conditions & stresses = risks of water-side problems 8 Chemistry Basics: 1 Matter – Anything with space/weight (mass) -solids, liquids gases. Elements – 92 naturally occurring types of matter, perhaps 117 in total. They consist of: protons and neutrons in a nucleus, plus electrons surrounding nucleus in elliptical, circular and spherical orbits. (Plus other sub- atomic particles) 9 3 2/20/2014 Chemistry Basics: 2 Allotropes – Some elements exist in different atomic geometric arrangements, e.g. Carbon exists as diamond, graphite and amorphous carbon (charcoal) - which confers different properties. We now know that carbon also exists as graphene – sheets of single atom thickness carbon and the basis of nanotubes and fullerenes (used in nano-technology) 10 Chemistry Basics: 3 Atom – Smallest unit of element capable of chemical combination. Example = elemental nitrogen N, elemental hydrogen H Proton “+” charged, sub-atomic particulate(s) found in atomic core. Atomic Weight = 1 Neutron Non-charged, sub-atomic particulate(s) found in atomic core. Atomic Weight = 1 Electron “-”charged particulate(s), surrounding atomic core. Atomic Weight = 0 Q: What is the real mass of an electron? (mass = weight at constant gravity) A: 9.1093821545 × 10-31 kilograms (Kg) 11 Chemistry Basics: 4 Electrons surround atomic nucleus in discrete, 3- dimensional, quantum energy “shells”, filling inner “shells” first, (holding 2, 2+6, 2+6+10, 2+6+10+14, 2+6+10, etc. electrons). Isotope – Two or more atoms of element with same At. No. and properties, but different At.Wt’s, due to increased number of neutrons. Isotopes decay over time, down to a stable energy level. (e.g. 14C 12C). Some isotopes exhibit radioactive decay! (e.g. U232/U238) Almost every element has multiple isotopes. NUCLEAR FUEL PLANT TO EXTRACT DEUTERIUM ISOTOPE FROM WATER 12 4 2/20/2014 Chemistry Basics: 5 Molecule – The smallest unit of chemical substance retaining all chemical identity. e.g. molecular nitrogen N2 hydrogen H2 and ammonia NH3. - Many elemental atoms unite, forming molecules for more stability (i.e to produce lower energy levels) e.g. O2 gas - They combine (bond) with other elements in different ways and via different types of bonds - Some elements are sufficiently stable to exist as single atoms (e.g. gold, platinum) Periodic Table – Each element is unique and is placed in a table reflecting common properties 13 Periodic Table of Elements 14 Chemistry Basics: 6 Radical – Group of elements with unsatisfied “valance” [space for electron(s) in outermost energy-level shell]. Acts as single element in reaction. e.g. + ammonium radical: (NH4) Valency – The number of bonds formed by an atom of a given element. i.e. “combining power” of an atom. Example: O atom (with a valency of 2 – or a space to accept two electrons) combines with 2 x H’s (each with a valency of 1) ,to form water - H2O Ion – Atom or molecule that has either gained or lost an electron. Salt (NaCl) consists of two ionic atoms = Na+Cl- 15 5 2/20/2014 Chemistry Basics: 7 Some types of molecular bonds • Ionic bond- combination of electronegative and electropositive attraction. Salts forms ionic bond • Metallic bond - lattices/crystals in metals • Covalent bond – sharing of electron pairs by atoms • Coordinate bonds – bonding of metals by a chelant, forming a complex • Hydrogen bonding – electrostatic attraction of atoms gto those in different molecules , linking the molecules together by the attractive force 16 Water Molecule: H20 molecular wt = 18, Dipolar Hydrogen atom Oxygen Atom Hydrogen atom = Electron = Proton The atoms in a water molecule = Neutron are covalently bonded. = Hydrogen bond attractions • How many protons, neutrons and electrons in each atom? Note: This model reflects a simplified version of a combination of Bohr & Schrodinger quantum physics theories, where shells represent discrete quantum energy levels, and changes in energy result in photonic electromagnetic radiation 17 HYDROGEN BOND – ACTUAL PICTURE! Atomic force microscopy (AFM) picture of (antiseptic) 8-hydroxyquinoline molecules (C9H7NO), showing hydrogen bonding, whereby electropositive hydrogen atoms form a bridge between two electronegative species X and Y, (i.e. X-H-Y). Color code: Green = C, Blue = N, Red = Oxygen, White = Hydrogen) 6 2/20/2014 Why is valency and bonding important? –Because molecular physics defines the structure and properties of chemicals, and the physical world The result is reflected in: • High heat capacity of water - hydrogen bonding • Leakage of sodium cations through a demineralizer • Difficult to remove non-reactive silica from water • Corrosive nature of chloride and sulfate anions • Different forms and colors of iron oxide rusting • Hardness of diamond and softness of graphite • The loss of carbon dioxide from bicarbonate, and resulting scale 19 Chemical Basics 8: Compounds/Mixtures: Compounds –2 or more elements bonded by reaction, forming new product. Not easily reversed. Examples: Salt - NaCl (sodium, Na and chlorine, Cl) Sulfuric acid - H2SO4 (hydrogen, H; sulfur, S; oxygen, O) Mixtures – 2 or more elements, compounds, or both, brought together in any combination, without bonding or chemical reaction. Capable of separation. Examples: Air -(O2, N2, CO2, H2O, SO2, inert gases) Chemical treatment - (caustic, polymers, phosphonates, tolyltriazole, molybdate) 20 Chemical Basics 9: Acids, Bases and Salts Acids/Bases/Salts – Early chemistry denoted acids as sour. Also, soda or potash bases (soluble alkalis) reacted with acids to form salts. Acids – Substances releasing hydrogen ions (H+) in water. (hydrogen that has lost an electron) + 2- • Sulfuric: a strong acid, dissociates to 2H and SO4 + 2- • Carbonic: weak acid, limited dissociation, 2H and CO3 Bases – (Alkali) Substance dissociating in water, producing hydroxyl ions (OH-) • Sodium hydroxide: (NaOH), a strong base. Readily dissociates, producing Na+ and OH-. + - • Ammonium hydroxide: weak base. Forms some NH4 OH 21 7 2/20/2014 Chemistry Basics: 10 - Salts Acid + Base = Salt + Water HCl + KOH KCl + H2O Hydrochloric potassium potassium water acid hydroxide chloride 22 Chemistry Basics 11: Inorganic/Organic Inorganic chemistry – non-organic (i.e. non-living) e.g. caustic soda, sulfuric acid Organic chemistry –originally, chemistry of living organisms – Carbon chemistry!, e.g. polymers. Carbon chemistry - forms long chain compounds with single/double/triple bonds (Aliphatic chemistry) - e.g. propane, gasoline, kerosene Also, sharing of unpaired electrons provides for resonating ring-structures, and (Aromatic chemistry) e.g. Benzene, Toluene, Xylene (BTX) Silica also has wide range of chemistries like carbon! 23 2013 Water Chemistry: Water is a “universal solvent”, formula H2O. MW 18. Hydrogen bonding causes molecular attraction, high latent heat, surface tension. Ionization potential water only slightly ionizes, which makes it a poor conductor. Dissolves ionic solids – leading to increase in TDS. pH: A logarithmic scale (from 0 to 14) of acidity (H+ concentration) of water. Each unit change indicates