# 4. physical chemistry

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PHYSICAL CHEMISTRY

Engr. Yvonne Ligaya F. Musico

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Why is Physical Chemistry important in the study of Environmental Engineering?

Applied physical chemistry procedures is used to solve common environmental engineering problems.

Engr. Yvonne Ligaya F. Musico

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TOPICS

Gas Laws and Relationships Stoichiometry Equilibrium Chemistry Common Treatment Processes in Environmental Engineering

Engr. Yvonne Ligaya F. Musico

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GAS LAWS AND RELATIONSHIPS

Engr. Yvonne Ligaya F. Musico

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Gases

Indefinite shapeIndefinite volume Take the shape and volume of container Particles are far apart Particles move fast high Kinetic Energy - particles can separate and move throughout container

Engr. Yvonne Ligaya F. Musico

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Henrys Law

It states that the amount of gas that dissolves in a liquid is proportional to the partial pressure that the gas exerts on the surface of the equation

Engr. Yvonne Ligaya F. Musico

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Henrys LawCA WhereCA = concentration of A [mol/L] or [mg/L] KH = Henrys Law constant [mol/L.atm] or [mg/L.atm] PA = partial pressure of A [atm]

=

KHPA

Engr. Yvonne Ligaya F. Musico

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Sample Problem 1

Summer water temperatures of 25 to 30oC are typical for many surface waters in United States. The Henrys law constant for oxygen in water is 61.2 mg/L.atm at 5oC and 40.2 mg/L at 25oC. What is the solubility of oxygen at 5oC and at 25oC?

Engr. Yvonne Ligaya F. Musico

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Air Stripping

It is a common method of removing dissolved gases from water and wastewater. Gases commonly removed include ammonia, carbon dioxide, and hydrogen sulfide.

Engr. Yvonne Ligaya F. Musico

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Sample Problem 2

An air-stripping tower is used to remove dissolved carbon dioxide from a groundwater supply. If the tower lowers the level to twice the equilibrium concentration, what amount of dissolve gas will remain in the water after treatment? The partial pressure of carbon dioxide in the atmosphere is 1 x 10-3.5 atm.Engr. Yvonne Ligaya F. Musico 10

Ideal Gas LawPV = nRT WhereP = absolute pressure [atm]

V = volume [L] n = number of moles [mol] T = absolute temperature [K] R = gas constant [0.0821 L.atm/mol.K]

Engr. Yvonne Ligaya F. Musico

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Sample Problem 3Anaerobic microorganisms metabolize organic matter to carbon dioxide and methane gases. Estimate the volume of gas produced (at atmospheric pressure and 25oC) from the anaerobic decomposition of 1 mol of glucose. The reaction is C6H1206 3CH4 + 3CO212

Engr. Yvonne Ligaya F. Musico

Daltons Law of Partial PressureDalton's Law The total pressure of a mixture of gases is equal to the sum of the partial pressures of the gases in a mixture Ptotal = PA + PB + PC + ..Pi

Engr. Yvonne Ligaya F. Musico

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Stoichiometry

It deals with numerical relationships between reactants and products in chemical reactions. Stoichiometric analysis can be used to determine the product yield for a given amount of reactant converted.

Engr. Yvonne Ligaya F. Musico

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Example of Stochiometric Analysis

Nuetralization of hydrochloric acid with lime 2HCl + Ca(OH)2 CaCl2 + 2H2O Oxidation of acetic acid to carbon dioxide and water. CH3COOH + 2O2 2CO2 + 2H2O

Engr. Yvonne Ligaya F. Musico

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Theoretical Oxygen Demand (ThOD)

It is an environmental engineering application of stoichiometry. The estimation of the amount of oxygen a known organic chemical will consume as it is converted to carbon dioxide and water. It is simply the amount of oxygen required to convert the material to carbon dioxide and water.Engr. Yvonne Ligaya F. Musico 16

Equilibrium Chemistry

It can be used to analyze a variety of different aqueous reactions of interest to the environmental engineer or the environmental engineering student.

Engr. Yvonne Ligaya F. Musico

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Equilibrium ChemistryExample: 1. Determining the amount of base to add to an acid spill 2. The amount of acid to neutralize a basic process wastewater 3. The solubility of metal in a chemical waste stream 4. Estimating the removal of phosphorus in a wastewater treated with lime 5. Solubility of mercury complexed in seawater.

Engr. Yvonne Ligaya F. Musico

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Mass Balances

A mass balance is written statement or equation that describes the different species in which a component may exists.

Engr. Yvonne Ligaya F. Musico

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The Carbonate System

Carbon dioxide and carbonates are crucial in water chemistry.

Engr. Yvonne Ligaya F. Musico

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Units of Expression

Molarity Normality

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It is a surface phenomenon in which a solute (soluble material) concentrates or collects at a surface. This contrasts with ABSORPTION, which a substance penetrates the material.

Engr. Yvonne Ligaya F. Musico

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Adsorption is a process that occurs when a gas or liquid solute accumulates on the surface of a solid or a liquid (adsorbent), forming a film of molecules or atoms (the adsorbate).

Engr. Yvonne Ligaya F. Musico

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Adsorbents are used usually in the form of spherical pellets, rods, moldings, or monoliths with hydrodynamic diameters between 0.5 and 10 mm.

Engr. Yvonne Ligaya F. Musico

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They must have high abrasion resistance, high thermal stability and small pore diameters, which results in higher exposed surface area and hence high surface capacity for adsorption.

Engr. Yvonne Ligaya F. Musico

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The adsorbents must also have a distinct pore structure which enables fast transport of the gaseous vapors.

Engr. Yvonne Ligaya F. Musico

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Silica gel is a chemically inert, nontoxic, polar and dimensionally stable (< 400 C) amorphous form of SiO2. Zeolites are natural or synthetic crystalline aluminosilicates which have a repeating pore network and release water at high temperature.Engr. Yvonne Ligaya F. Musico 27

Activated carbon is a highly porous, amorphous solid consisting of microcrystallites with a graphite lattice, usually prepared in small pellets or a powder. It is non-polar and cheap.

Engr. Yvonne Ligaya F. Musico

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Activated carbon can be used to remove toxic organics from both water and air. It is commonly used in aquarium filters.

Engr. Yvonne Ligaya F. Musico

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It is used in some potable water plants to remove organics before or after chlorination, in industrial wastewater treatment to remove a variety of organics, and occasionally to remove residual organics following conventional wastewater treatment.

Engr. Yvonne Ligaya F. Musico

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It is used in air pollution control to remove organic contaminants from contaminated air before discharge.

Engr. Yvonne Ligaya F. Musico

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Mathematical Models to Predict the Mass of Solute Removed per Mass of Adsorbent

Freundlich Isotherm Langmuir Isotherm

Engr. Yvonne Ligaya F. Musico

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Freundlich IsothermqeWhere: qe = x m K n = = = ==

_x_ m

=

KCe1/n

mass of solute adsorbed per mass of adsorbent used [mg adsorbed/mg carbon] mass of solute adsorbed [mg or mol] mass of adsorbent [mg] experimental constant experimental constantEngr. Yvonne Ligaya F. Musico 33

Linearized Freundlich Equationlog (x/m) = log K + (1/n) log Ce If log (x/m) is plotted versus log Ce, the data should fit a straight line.

Engr. Yvonne Ligaya F. Musico

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Langmuir IsothermqeWhere: qe = x m K Q0 = = = ==

_x_ m

=

_KQ0Ce__ 1 + KCe

mass of solute adsorbed per mass of adsorbent used [mg adsorbed/mg carbon] mass of solute adsorbed [mg or mol] mass of adsorbent [mg] experimental constant [L/mg] constant representing the mass of solute adsorbed per mass of adsorbent at saturation

Engr. Yvonne Ligaya F. Musico

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Linearized Langmuir Isotherm_1__ x/m = _1_ + Q0 _1_ KQ0 _1_ Ce

If (1/qe) is plotted versus (1/Ce), the data fit a straight line.

Engr. Yvonne Ligaya F. Musico

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Linearized Langmuir Isotherm

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Sample Problem 1A pharmaceutical manufacturer plans to install a new industrial production process. The waste stream for the process is expected to have a concentration of 7.5 mg/L methylene blue at a flow rate of 25 gpm. The company plans to use carbon adsorption data were obtained from the laboratory. The liquid volume in each flask was 200 mL. Determine if either or both isotherms are applicable (plot a straight line in linearized form). Find both the Freundlich parameter K and 1/n and Langmuir parameters K and Qo if applicable. Estimate the amount of activated carbon require to remove the contaminant each year if the carbon is removed by an adsorption column that reaches the equilibrium with at the carbon at the 7.5 mg/L concentration.

Engr. Yvonne Ligaya F. Musico

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Sample Problem 1Mass of Adsorbent, mg 98.6 58.1 26.3 15.7 8.8 2.9 0.8 Blank Initial Concentration, mg/L 25 25 25 25 25 25 25 25Engr. Yvonne Ligaya F. Musico

Final Concentration, mg/L 0.04 0.11 0.49 1.2 3.2 10.2 19.7

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