Rheologi

Dr. Widya Rukmi PADSORPTION AND ABSORPTIONDFOOD PHYSICAL CHEMISTRYDWIDYA DWI RUKMI PUTRI

SORPTIONSorptionis a physical and chemical process by which one substance become attached to another. Specific cases of sorption are treated in the following :Adsorption : the physical adherence or bonding of ions and molecules onto the surface of another phaseAbsorption : the incorporation of a substance in one state into another of a different state (e.g., liquid being absorbed by a solid or gases being absorbed by a liquid)

ADSORPTION VS ABSORPTION3ADSORPTION VS ABSORPTION4Adsorption of a solute molecule from a liquid solution to the surface of a solid matrix depends on the followingThe size, shape and molecular weight of soluteElectrostatic charge on the surface of solute molecule and the site of the solid matrix where adsorption takes placeShape of the binding site of the solid matrixPolarity of the solute molecule and the binding site of the solid matrixADSORPTIONThe following physical binding and physical interactions may be involved in the adsorption process :PartitioningVan der Waals forcesElectrostantic interactionsHydrogen bondingHydrophobic interactionsADSORPTION MECHANISM

The surface of a solid shows a strong affinity for molecules that come into contact with it.Certain solid materials concentrate specific substances from a solution onto their surfaces.ADSORPTON PHENOMENONPhysical adsorption (physisorption): Physical attractive forces (van der Waals forces)e.g. Carbon ads, Activated aluminaAdsorption PhenomenonChemical adsorption (chemisorption): the adsorbed molecules are held to the surface by covalent forces.(little application in water waste treatment)Adsorbents in Natural & Engineered SystemsNatural SystemsSediments SoilsEngineered SystemsActivated carbonMetal oxides (iron and aluminum as coagulants)Ion exchange resinsBiosolids9Ion Exchange

Ion exchange is an adsorption phenomenon where the mechanism of adsorption is electrostatic. Electrostatic forces hold ions to charged functional groups on the surface of the ion exchange resin. The adsorbed ions replace ions that are on the resin surface on a 1:1 charge basis.

Adsorption applicationWATER & WASTE WATER TREATMENTS

Applications of ion exchange in water & wastewaterCa, Mg (hardness removal) exchange with Na or H.Fe, Mn removal from groundwater.Recovery of valuable waste products Ag, Au, UDemineralization (exchange all cations for H all anions for OH)Removal of NO3, NH4, PO4 (nutrient removal).Ion Exchangers (types)

Natural: Proteins, Soils, Lignin, Coal, Metal oxides, Aluminosilicates (zeolites) (NaOAl2O3.4SiO2).Synthetic zeolite gels and most common -polymeric resins (macroreticular, large pores).

Resin

Absorptionis a physical or chemical phenomenon or process in which atoms, molecules or ions enter some bulk phase gas, liquid or solid material. Molecules undergoing absorption are taken up by the volume, not by the surface. Physical absorption or non-reactive absorption is made between two phases of matter: a liquid absorbs a gas, or a solid absorbs a liquid.Chemical absorption or reactive absorption is a chemical reaction between the absorbed and the absorbing substances. Sometimes it combines with physical absorption. ABSORPTIONPHYSICAL ABSORPTIONWhen a liquid solvent absorbs a gas mixture or part of it, a mass of gas moves into the liquid. For example, water may absorb oxygen from the air. This type of absorption depends on the solubility of gases, the pressure and the temperature. The rate and amount of absorption also depend on the surface area of the interface and its duration in time.

PHYSICAL ABSORPTIONWhen a solid absorbs a liquid mixture or part of it, a mass of liquid moves into the solid. Absorption is essentially a molecule attaching themselves to a substance and will not be attracted from other molecules.

FOOD ABSORPTION IN THE BODY

WATER ACTIVITY AND MOISTURE SORPTION ISOTERMMOISTURE CONTENT AND WATER ACTIVITYMoisture content :It is a measurements of the total water contained in a foodIt is usually expressed as a percentage of the total weight

Water activity :Water has different levels of binding and thus activity or availability in a food sampleWater activity (aw) helps to explain the relationship between perishability and moisture content

MOISTURE SORPTION ISOTERMThe relationship between water activity and moisture content at a given temperature is called the moisture sorption isotherm. This relationship is complex and unique for each product due to different interactions (colligative, capillary, and surface effects) between the water and the solid components at different moisture contentsKnowledge of the sorption properties of foods is of great importance in food dehydration, especially in the quantitative approach to the prediction of the shelf life of dried foodsSorption isotherms can be generated from an adsorption process or a desorption process; the difference between these curves is defined as hysteresis.Water adsorption by food products is a process in which water molecules progressively and reversibly mix together with food solids via chemisorption, physical adsorption, and multilayer condensation. MOISTURE SORPTION ISOTERMMOISTURE SORPTION ISOTERM

An isotherm can be typically divided into three regions;1. The water in region A represents strongly bound water, and the enthalpy of vaporization is considerably higher than the one of pure water. The bound water includes structural water (H-bonded water) and monolayer water, which is sorbed by the hydrophilic and polar groups of food components (polysaccharides, proteins, etc.). Bound water is unfreezable and it is not available for chemical reactions.

MOISTURE SORPTION ISOTERM

2. In region B, water molecules bind less firmly than in the first zone, they usually present in small capillaries. The vaporization enthalpy is slightly higher than the one of pure water. This class of constituent water can be looked upon as the continuous transition from bound to free water. MOISTURE SORPTION ISOTERM2. The properties of water in region C are similar to those of the free water that is held in voids, large capillaries, crevices; and the water in this region loosely binds to food materials MOISTURE SORPTION ISOTERM