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Unit I : Natural Sources and their Chemistry

Water Technology

Water exists in three states: solid, liquid and gaseous. The important sources of water are (i) rain water, (ii) ground water and (iii) sea water. Rain water carries all the reaches to water bodies such as ponds, lakes and rivers. Also, these impurities seep into underground and are stored as ground water. Sea water is highly alkaline due to the presence of dissolved salts.The natural water contains numerous organisms and dissolved gases (ex:
oxygen), which is essential for aquatic organisms. The pure water is one which is free from organisms. Water is required mainly for drinking and
cooking, also for industry, agriculture and many other activities. Pollution of water implies that it contains a lot of inorganic and organic substances
introduced by human activities, which change its quality, not suitable for any purposes and also harmful for living organisms. Any alteration in physical,
chemical or biological properties of water, as well as the addition of any foreign substance makes it unfit for health and which decreases the utility of water, is known as water pollution. The major impurities present in the water bodies are described below

Potable water
Water of sufficient quality to serve as drinking water or water that is safe for human consumption is called potable water. The following are characteristics of potable water It should be sparking clear, soft, pleasant in taste, perfectly cool and odourless Its turbidity level should not exceed 10 ppm Its alkalinity should not be high (pH = 8.0) The total dissolved solids should not exceed 500 ppm It should be free from heavy metals such as lead, arsenic, cadmium, chromium and manganese salts It should be free from dissolved gases such as hydrogen sulphide It should be free from disease producing micro-organisms.

Dissolved oxygen
Oxygen is poorly soluble in water. The solubility of water depends on the concentration of the salts and temperature. Dissolved oxygen is consumed by aquatic animals for their respiration. Aerobic bacteria consume the DO for the oxidation of biodegradable matter.
 
 
 
 
 
 
 


Winklers method of determination of Dissolved oxygen (https://youtu.be/PrvkV_Fmv8M )
​Biological Oxygen Demand( BOD)
Definition: the microorganism to bring about oxidation
of biological compounds present in 1 dm3 waste water
over a period of 5 days at 20 degree
The biodegradable impurities present in the waste water are
oxidizes by aerobic bacteria, using dissolved oxygen.
Biodegradable matter such as carbohydrates, proteins,
oils and fats utilized by bacteria as a source of energy
 


Chemical oxygen demand: (https://youtu.be/2mGykx1dqDA)
Definition:organic and inorganic compounds present in one ldm3 of waste water by using strong oxidizing agent such as K2Cr2O7. r
Principle
A known volume of waste water sample ifs refluxed with excess of K2Cr2O7 solution in sulphuric acid medium in the presence of Ag2SO4 and HgSO4. K2Cr2O7 acts as oxidizing agent in acidic media which oxidizes all the oxadizable impurities present in waste water. The amount of unreacted K2Cr2O7 is determined by titration with known strength FAS (Ferrous ammonium sulfate). The amount of K2Cr2O7 consumed for the oxidation corresponds to COD of waste water. In this titration Ferroin is used as indicator. This indicator is redox indicator which contains Fe+2 ions. This indicator is red in colour. Oxidizing agents oxidizes the iron in the indicator to +3 oxidation state which is in pale blue colour.
 
 
 
 
 
 
 
 
 

Note
Ag2SO4 acts as catalyst in the oxidation of long chain fatty acids and pyridine like impurities
The role of HgSO4 is to avoid the Chloride ion hindrance

Hard water
Water which does not produce sufficient lather with soap solution
readily but forms a white or grey precipitate. The soap (potassium
or sodium salts of fatty acids like stearate) gets precipitated in
the form of insoluble salts of calcium and magnesium which is
termed as scum. Determination of total hardness of water
can be done using EDTA titrations


Calcium carbonate equivalence
Any sample of water contains various types of impurity in various amounts. The degree of harness due to all these substances are unified in the forms of CaCO3
Reasons for representing in calcium carbonate equivalence
  • CaCO3 is water insoluble
  • CaCO3 Doesn't impart hardness
  • Its molecular weight is 100 which make calculation easy
Due to this reason harness is expressed in calcium carbonate equivalence


Alkalinity
Alkalinity of water is due to the presence of the substance which increases
the concentration of OH- , either by hydrolysis or by dissociation.
Alkalinity measures the acidneutralizing capacity of water sample.
It is an aggregate property of water sample and can be interpreted
in terms of specific substance only when a complete chemical composition
of the sample is also performed. The alkalinity of the water sample is due
to carbonate (CO32-),, bicarbonate (HCO3 -) and hydroxide (OH-), content.
Alkalinity may also be includes contribution from borates, phosphates,
silicates (SiO32- ), or other bases. This alkalinity is very important parameter
and it is very essential for water to use in irrigation, industrial and domestic use.

Fluoride (SPADNS method)
Fluoride is very important parameter in water if it is high in concentration causes dental fluorosis and lower concentration (<0.8 mg/L) causes dental caries. A fluoride concentration of approximately 1 mg/L in drinking water is acceptable. Fluorides present in bore well water much more than river water and this is because water comes in contact with mineral as CaF2(Fluorospar) and Na3AlF6(Cryolite). But fluorides largely occur in industrial wastes such as coke, glass, ceramics and electronic industries. Thus determination of fluoride is essential. The determination of amount of fluoride
in the water can estimated using SPADNS method. (sulpha phenyl azo dihydoxy naphthalene disodium sulfonate).
Principle: In this method SPADNS molecule made to react with the zirconium chloride in acidic media which forms a red coloured complex. When this red coloured comlex made to react with fluoride present in the water sample then forms colourless ZrF6 leaving behind SPADNS which is of yellow in colour. As amount of fluoride increases red colour decreases and yellow colour (absorption maxima is 570 nm) of SPADNS increases. By colorimetric
estimation absorption of yellow colour is measured and hence amount of fluoride can be calculated using calibration plot method.
 
 
 
 
 
 
 
 
 
 

Membrane Technology
Membrane also known as selective barrier between two phases that have thin barrier that permits selective mass transport and the phase that acts as a barrier to prevent mass movement, but allows restricted and / or regulated passage of one or more species

Reverse osmosis
Many company of drinking water in our country used the concept of Reverse Osmosis (RO). Reverse Osmosis (RO) is a process for desalting water
that uses membranes that are permeable to water but essentially impermeable to salt. Pressurized water containing dissolved salts contacts the feed side of the membrane; water depleted of salt is withdrawn as a low-pressure permeates. The ability of membranes to separate small solutes from water has been known for a very long time. In 1931the process was patented as a method of desalting water and the term reverse osmosis was coined. This Reverse Osmosis has the smallest pores 0.0001- 0.001 microns and has the highest-pressure requirement 10-100 bar. The movement of solution molecule through semi permeable membrane from higher concentration to lower concentration or the process which reverse to the natural spontaneous osmosis is called reverse osmosis. RO system tube contains a semi permeable membrane made up of polymethylacrylate and polyamide. Brackish water and fresh water is separated by semi permeable membrane. When the brackish water (1000ppm) supplied with
high pressure, water flow from brackish water to fresh water, Fresh water is collect from fresh water outlet and brackish water (2000ppm) is discharged in to the environment. The flow of pure water propositional to the applied pressure.

 

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Chemical Fuels
As most of the fuels contain carbon or carbon and hydrogen, the combustion involves the oxidation of carbon to carbon dioxide and hydrogen to water. Sulphur, if present, is oxidized to sulphur dioxide while the mineral matter forms the ash.
Chemical fuels are classified as primary and secondary fuels. Fuels, which occur in nature, are called primary fuels. Fuels, which are derived from
primary fuels, are called secondary fuels. Chemical fuels are further classified as solids, liquids and gases
Characteristics of a Good/ideal fuel:
1. It should possess high calorific value.
2. It should have proper ignition temperature. The ignition temperature of the fuel
should neither be too low nor too high.
3. It should not produce poisonous products during combustion. In other words, it
should not cause pollution o combustion.
4. It should have moderate rate of combustion.
5. Combustion should be easily controllable i.e., combustion of fuel should be easy to
start or stop as and when required.
6. It should not leave behind much ash on combustion.
7. It should be easily available in plenty.
8. It should have low moisture content.
9. It should be cheap.
10. It should be easy to handle and transport
Calorific value
It is an important parameter of fuels is calorific value. It gives useful information about its heating efficiency. The performance of a fuel is expressed in terms of its calorific value. Calorific fuel s defined as the amount of heat released when unit quantity (mass or volume) of a fuel is burnt completely in air oxygen
Gross Calorific Value (G.C.V.)
It is defined as the amount of heat obtained on complete combustion of unit mass of a solid or liquid fuel or unit volume of a gaseous fuel (STP) and on cooling the products of combustion are cooled to room temperature (298K)
Net Calorific Value (N.C.V.)
It is defined as the amount of heat released when unit quantity of a fuel is completely burnt in air or oxygen and the products of combustion are let off into the atmosphere

Determination G.C.V. of Solid, Liquid Fuels by Bomb Calorimeter

Principle: A known weight of solid / liquid fuel is burnt completely and the
heat liberated is effectively absorbed into a known weight of water.
By recording the rise in the temperate of water and knowing specific heat
of water, calorific value is calculated. Construction: It consists of a strong
cylindrical stainless steel bomb in which combustion of the fuel takes place.
The bomb has a lid which is screwed to the body of the bomb to make a
perfect gas tight seal. The lid has two stainless steel electrodes and an
oxygen inlet valve (See Figure). To one of the electrodes a small ring is
attached on which a stainless steel crucible is supported. The bomb is
placed in a copper calorimeter surrounded by air and water jacket
(which prevents heat loss due to radiation). An electrically operated
stirrer and a Beckmann's thermometer (which measures bath of a degree)
is placed in the water jacket to maintain uniform distribution of heat
and measure the increase in temperature respectively


Knocking of IC engine
In petrol engines, the mixture of petrol and air is drawn in to the cylinder. The fuel air mixture is compressed by the piston and is ignited by an electric spark. As the flame front travels in the combustion chamber, rapidly expanding combustion products compress the remaining unburnt fuel and raise its temperature. If the flame front travels rapidly at an optimum speed, the combustion of unburnt fuel takes place smoothly. On the other hand, if
the flame front travels too slowly, the entire last portion of fuel mixture may get heated up beyond its ignition temperature and undergo instantaneous explosive combustion. This result Knocking is the rattling noise or metallic sound produced in an internal combustion engine due to uneven combustion (detonation) of fuel and air mixture
 
 
 
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working of Four stroke engine
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Knocking in diesel engines
It works on the principle of compression ignition. Air is drawn into the cylinder and compressed to a pressure of about 3.5 X 10-3 kg m-2.During compression cylinder gets heated around 350 °C. Then diesel is introduced in the form of spray which is spontaneously get ignited and burns producing pressure on the piston. It takes some time for the fuel to get ignited. The time interval between the fuel injection and ignition is called ignition delay. It will be milliseconds. The shorter ignition delay leads to burning of the fuel at the rate which it is injected. Whereas longer ignition delay results in accumulation of the fuel in the engine and this causes an explosive combustion when ignited. As a result the diesel engine knocks.
Octane and cetane number
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Power alcohol
When ethyl alcohol is used as fuel in internal combustion engine, it is called as power alcohol.It contains 25% of alcohol and 75% petrol.
Advantages of Power Alcohol
(i) Ethyl alcohol has good antiknocking property and its octane number is 90, while the octane number of petrol is about 65. Therefore addition of ethyl alcohol to petrol, increases its octane number.
(ii) Alcohol has property of absorbing any traces of water if present in petrol.
(iii) If a specially designed engine with higher compression ratio is used, then the disadvantage of lower C.V. of ethyl alcohol can be overcome.
alcohol and the polluting emissions of CO, hydrocarbon, particulates are reduced largely.
(v) Use of ethyl alcohol in petrol reduces our dependence on foreign countries for petrol and saves foreign currency considerably.
(vi) Power alcohol is cheaper than petrol.
Disadvantages of Power Alcohol
(i) Ethyl alcohol has C.V. 7000 cal/gm much lower than C.V. of petrol 11500 cal/gm.Use of power alcohol reduces power output upto 35%.
(ii) Ethyl alcohol has high surface tension and its atomisation, especially at lower temperatures, is difficult causing starting trouble.
(iii) Ethyl alcohol may undergo oxidation to form acetic acid, which corrodes engine parts.
(iv) Ethyl alcohol obtained by fermentation process directly cannot be mixed with petrol but it has to be dehydrated first. combustion of power alcohol is lesser and therefore carburettor and engine needs to be adjusted or modified, when only ethyl alcohol is used as fuel.
 
 
 
 
 
 
 
 
 
 
 
 
 
 


Biodiesel
Chemically biodiesel is the mixture of methyl esters of long chain carboxylic acids. It is eco friendly fuel obtained from renewable sources like vegetable oils and animal fats. Common vegetable (edible and Non-edible) oils used are Soyabean oil, palm oil, peanut oil, cotton seed oil, corn oil, pongamial oil, Jatropha oil etc. Vegetable oils are the triglycerides, which have high viscosity, flash point and low heating value. Hence they cannot be used as
such in diesel engine. Triglycerides are need to be converted into biodiesel by a process is called Transesterification. During the transesterification, the triglyceride is treated with methanol or ethanol in the presence of a base like KOH/NaOH, forms methyl or ethyl esters of fatty acids (biodiesel)
Conditions: Temperature: 55-60 C, Catalyst-KOH/NaOH, Reaction time-1-8 hrs.
Trans esterification

 
Advantages of Biodiesel:
(i) Biodiesel is cheaper, as it is manufactured from cheap, non-edible or waste oil or animal fats.
(ii) It has high cetane numbers 46 to 54 and high C.V of about 40 kJ/gm.
(iii) It is regenerative and environment friendly.
(iv) It does not give out particulate and CO pollutants, as Oxygen atoms in biodiesel help for complete combustion.
(v) It has certain extent of lubricity, due to higher oiliness of the esters.
(vi) Its use provides good market to vegetable oils and reduces our dependence on diesel on foreign countries, saving currency.
(vii) It is clean to use biodiesel in diesel engines.
Limitations of Biodiesel:
(i) Cloud and pour points of biodiesel are higher than diesel and can cause problem in fuel flow line. So it cannot be used in cold regions.
(ii) Biodiesel may have dissolving action rubber hoses, gaskets.
(iii) There is shortage of vegetable oils and the starting material if costly, the biodiesel will be costly.
(iv) Biodiesel strongly adheres on metals and can become gummy
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Photovoltaics
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Working of DSSC
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