Category: Chemistry Notes PPT

Petroleum is also known as ‘Black Gold.’ This name provides a clear indication as to how important Petroleum is for everyone. Students should also know that crude oil is also considered to be a highly valued commodity.

It is also referred to as the ‘mother of all commodities.’ This is mainly due to the fact that crude oil is used for the production of gasoline, plastics, pharmaceutical products, synthetic fabrics, and many other things. Petroleum or oil has also been the leading source of energy in the entire world since the 1950s!

Petroleum is usually found in the form of a liquid that occurs naturally during rock formation. It consists of a complex mixture of several molecules of hydrocarbons and other organic compounds. Fossil fuels are also used for obtaining some chemical compounds that are produced by petroleum.

Petrochemicals are produced at only a few manufacturing sites around the world! This means that the use of petroleum as a raw material is highly valuable. One might also find it interesting to note that the word petroleum basically translates to ‘rock oil.’ This word is derived from the Greek word ‘petra’ and the Latin word ‘oleum.’

Petroleum is known as crude oil when it is directly drilled from the ground. Even though human beings have existed on Earth for the last 4000 years, crude oil was pumped from the ground only around 2500 years ago in China. Students should remember that the first crude oil well in the world was drilled in Pennsylvania, United States of America (USA) in 1859.

Also, when it comes to India, then Petroleum or mineral oil is the biggest energy source that is available right after coal. Petroleum is used for supplying heat, lighting power, lubricants for machines, and raw materials for several other products that are required in the manufacturing industry.

Petroleum refineries for fertilizers, synthetic fabric, and other chemical industries also act the role of a ‘nodal industry.’ A large chunk of India’s petroleum also occurs in association with anticlines and fault traps in the tertiary age rock formation. It is known to be present in anticlines, domes, folding regions, and where oil is stuck in unfold crests.

What is Petroleum Refining?

According to several sources, petroleum refineries are huge industrial complexes that require lots of processing units and auxiliary installations, including storage tanks and utility units. In this section, we will explain the process of formation of petroleum.

Petroleum refineries also have their specific arrangements and a combination of processes that are required for refining. This process is also largely dependent on the location of the refinery, the economic considerations, and the target products.

Similarly, an oil or petroleum refinery is part of the facility of industrial manufacturing. This is where crude oil is successfully extracted and converted into goods that have a higher value, including gasoline, jet fuel, petroleum naphtha, heating oil, asphalt foundation, liquefied gas, and petroleum kerosene.

It should be noted that in most cases, oil refineries are rather huge. These refineries have massive industrial facilities that are built with extensive pipelines that are running throughout the refinery while holding fluid streams in between.

Students should remember that because of several factors, there are no two refineries that are identical to one another. That being said, there are several characteristics related to petroleum and its refiners that students should be familiar with. Some of those characteristics are:

• Petroleum is a mixture of several subjects, including kerosene, diesel, gas, petrol, paraffin wax, and lubricating oil.

• It is important to separate all the constituents of petroleum. This process is known as the refining of crude oil. It is also referred to as the petroleum refining process.

• Petroleum refining is done in oil refineries and there are three main steps required during the process.

• In the first step, one has to separate the crude oil into several components by going through the distillation process, During the distillation process, the heavier constituents remain at the bottom while the lighter particulars will rise in the form of vapour of remaining liquid.

• After that, the components that are very heavy are converted into a gaseous form, diesel, or gasoline. The last step is known as the conversion.

• There are also several impurities in the products that are received till now. These impurities are removed or treated to obtain the purest form of all the products.

It is important to mention here that the oldest and common way of separating anything into its different parts, components, or factions is with the help of the boiling temperature difference. That process is known as fractional distillation.

There is also a method known as conversion. In this method, chemical processing is used on certain fractions. This helps those components produce other components. This explains the answer to the question of how is petroleum extracted. A good example of this is how chemical processing can help in splitting lengthier chains into smaller chains.

In the final examination, students can be asked to draw a clear diagram of a petroleum refinery. This is why it is suggested that students should go prepared for this question by referring to the image that is attached below.

Students should also remember that in the industry, the refining process is normally known as the ‘downstream’ sector. On the other hand, the ‘upstream’ section has the raw crude oil output. Here, the term downstream is somewhat similar to the idea of sending oil down the supply chain for the idea of sending oil down the supply chain for a commodity.

This is sent to an oil refinery so that the product can be refined into petrol. The downstream phase also consists of the actual sale of petroleum products. This is done to other companies, private individuals, and the government.

The Formation of Petroleum in Nature

It should be noted that petroleum is formed for the remains of dead animals and plants. This happens when any plant or animal dies and they sink to settle on the seabed. After that, it takes millions of years for that life to decompose of organic matter that is mixed with silt and salt.

There are also different bacterias that help in the decomposition of organic matter. It results in various important chemical changes. During the refining process, components that are usually left behind are hydrogen and carbon atoms of larger size.

Also, when it comes to the bottom of the sea, then the matter is not sufficiently decomposed. This is due to a lack of oxygen. It remains on the seabed and is covered by several layers of slip and sand. This entire process of refining takes millions of years of high pressure and temperature. But whenever it does happen, the organic matters decompose and form oil. Students should be familiar with petroleum refining by-products and their uses. Remembering the petroleum products list is also helpful.

Fun Facts about the Uses of Petroleum

Did you know that there are several uses of petroleum? This is true and we have created a list of all the major uses of petroleum. And that list is mentioned below.

• LPG or Liquefied Petroleum Gas is used every day in the households and professional industry.

• Petrol and diesel as used in vehicles as fuels. When it comes to heavy motor vehicles, then diesel is preferred.

• Petrol is used in the dry cleaning process as a solver. Diesel, on the other hand, can be used for running generators.

• Jet planes and stoves rely on kerosene as their fuels.

• Wear, tear, and corrosion of machines can be reduced by using lubricants.

• Ointments, ink, candles, and crayons can be made by using paraffin wax.

• Roads are made by using asphalt or Bitumen.

We see different types of physical and chemical changes in our surroundings like dissolving sugar and water, burning of coal, rusting, melting an ice cube, boiling water, different shape and size of the Moon, etc., change is occurring all around us every time. Have you ever tried to understand these changes? We should try to understand the terms that are physical and chemical changes and examples, reversible and irreversible changes before knowing the scientific reason for changes. There are many reasons for these physical and chemical changes. We will understand more about this by starting with the physical change definition.

What is a Physical Change?

Properties such as shape, size, volume, colour, appearance, and state of a substance (solid, liquid, and gas) are called physical properties. A change in which a substance undergoes a change in its physical properties is termed physical change.  Physical changes only change the appearance of a substance, not the chemical composition. Examples of physical changes: boiling water, breaking a glass, melting an ice cube, freezing water, mixing sand and water, crumpling of paper, and melting a sugar cube.

Physical changes are the changes that influence the type of a synthetic substance, yet not its compound creation. Physical changes are utilized to isolate blends into their part compounds yet can not typically be utilized to isolate compounds into synthetic components.

Physical changes happen when articles or substances go through a change that doesn’t change their compound creation. This differentiates with the idea of synthetic change wherein the structure of a substance changes or at least one substance consolidates or separated to shape new substances. Overall a physical change is reversible utilizing physical means. For instance, salt dissolved in water can be recuperated by permitting the water to vanish.

A physical change includes a change in physical properties. Instances of physical properties incorporate softening, progress to a gas, change of solidarity, change of sturdiness, changes to gem structure, textural change, shape, size, shading, volume, and thickness.

An illustration of a physical change is the most common way of treating steel to frame a blade sharp edge. A steel clear is over and again warmed and pounded which changes the hardness of the steel, its adaptability, and its capacity to keep a sharp edge.

Numerous physical changes additionally include the adjustment of molecules most discernibly in the development of precious stones. Numerous substance changes are irreversible, and numerous physical changes are reversible; however, reversibility is anything but a specific standard for order. Albeit compound changes might be perceived by a sign, for example, scent, shading change, or creation of gas, all of these pointers can result from the physical change.

What is a Chemical Change?

A chemical change is said to happen when one chemical substance is transformed into one or more different substances, or chemical changes happen when a substance consolidates with one or more to shape another substance, called the chemical union, or, on the other hand, chemical decay into at least two distinct substances. These cycles are called chemical responses and, by and large, are not reversible besides by additional chemical responses. A few responses produce heat and are called exothermic responses.

At the point when chemical responses occur, the molecules are modified and the response is joined by an energy change as new items are produced. An illustration of a chemical change is the response between sodium and water to create sodium hydroxide and hydrogen. Such a lot of energy is delivered that the hydrogen gas delivered suddenly consumes in the air. This is an illustration of a chemical change on the grounds that the finished results are chemically not quite the same as the substances before the chemical response. Chemical changes occur by the process of chemical reactions, and the resulting substances have different properties because their atoms and molecules are arranged differently. Examples of chemical changes: rusting of iron, burning of coal, digestion of food, germination of seeds, adding vinegar to baking soda, ripening of fruits, fermenting of grapes, cooking an egg, etc.

The below table shows the major differences between physical and chemical change.

Difference Between Physical Change and Chemical Change

Fun Facts 

Introduction

We know that corrosions simply mean rusting. However, the question is what is pitting corrosion. Pitting Corrosion is the form of corrosion that particularly occurs at one spot. We can call it localized corrosion also. It only affects a particular part of the metal surface. Initially, it forms a layer of rust which later forms the holes in the material. It is proven to be more harmful than corrosion because it is hard to detect and work against. The depth of the corrosion is measured using a calibrated microscope. In this article, we will discuss what is pitting corrosion, its mechanism, test, damages caused by pitting corrosion, and how to prevent it.

Causes of Pitting Corrosion

Now, We know that Pitting corrosion is a kind of corrosion that is confined to a small area. However, the question arises what causes this pitting corrosion? The answer is the Environment. Gases present in the atmosphere, reactive chemical species in free form like chlorides. Chloride is the main source of this pitting corrosion. It attacks the passive layer of metal and breaks the bonds of oxides. 

If the metal surface is exposed to the water. Water droplets can form a layer over the metal surface. Ions present in the water droplets react and initiate the process of corrosion.

So, there are two factors – Environmental and metallurgy. These two factors determine if this can be stopped or not. If we restrict the aeration (oxygen supply to the surface) and prevent the surface from getting wet, Pitting corrosion can be prevented.

Pitting Corrosion Mechanism

Pitting corrosion is initiated by the oxidation process. Exposure of the passive layer of metal with air and water initiates the oxidation process at the localized part. This leads to the acidification of ions formed by oxidation. These two processes are part of an electrochemical reaction.

Oxidation occurs at the anodic part and reduction occurs at the cathodic part. These half cells constitute the electrochemical cell, which forms at a small site.

The reaction occurring at the anodic site is shown below:

Fe → Fe2+ + 2e– 

The reaction occurring at the cathodic site is shown below:

½ O2 +H2O + 2e– → 2(OH–)

Overall, the reaction is shown below:

FeCl2 + 2H2O →Fe(OH)2 + 2HCl

The HCl formed in the pit increases the acidity. A potential gradient is also set in this localized pit region. It attracts the ions from the other nearby sites. The holes which are formed at the surface of the metal, get filled with the side product of the corrosion process.

In the presence of chlorine ions, holes keep on growing via an autocatalytic mechanism. 

Pitting Corrosion Test

A number of tests are available to detect pitting corrosion. A few of them are listed below:

ASMT-G48 Practice A and E are the toughest tests that are being conducted on stainless steel, while CPT is the most commonly used method.

Damages Caused by Pitting Corrosion

As we already know, it affects a localized part of the metal. It creates a rusty layer over the metal surface, eventually forming holes in it. It reduces the thickness of metal. This leads to structural defects and metal cannot handle stress. Finally, cracking starts and metal becomes totally useless. Pitting corrosion causes pipe leakages, electric short circuits and major machinery faults if not prevented.

Corrosion damage causes an economical loss of about ＄300 billion annually in U.S. Industries. 

Pitting Corrosion Prevention

Till now, we understood what is pitting corrosion, what are the causes and damages. Now, we will discuss the ways to prevent it.

• We should use such materials that are resistant to environmental factors such as aeration and moisture exposure.

• We can apply anodic or cathodic protection layers over the metal surfaces.

• We can paint the metal surface or apply industrial coatings.

• The zinc spray metalizing process is extensively used to cover the metal layer with the layer of zinc because it is prone to environmental factors. 

• We should keep the metal materials in an environment with less moisture exposure, optimum temperature and aeration should be controlled.

Conclusion

In this article, we discussed the pitting corrosion definition, pitting corrosion examples, causes, mechanism, damages, and prevention methods. It is a localized kind of corrosion that is caused by environmental factors. It forms holes and causes thickness loss. There are a number of tests available to detect it. It could be prevented by using alloys rather than pure metals, painting the metal surface, using rust-prone materials, and maintaining the protective film over the metal surface.

Polyethylene (PE) is a light and versatile synthetic resin. This compound is made from the polymerization of ethylene. Polyethylene is an important family member of polyolefin resins. Also, it is the world’s most widely used plastic, being made into products ranging from shopping bags and clear food wrap to automobile fuel tanks and detergent bottles. In addition, it can be spun or slit into synthetic fibres or modified to take on the elastic properties of the rubber.

Chemical Composition and Molecular Structure

Ethylene, having the chemical formula as C2H4, is a gaseous hydrocarbon, which is commonly produced by ethane cracking, which, in turn, is a primary constituent of natural gas or can be distilled from petroleum. Essentially, ethylene molecules are composed of two methylene units – CH2,  together with a double bond between the carbon atoms, where the structure is represented using the formula CH2=CH2. Under the polymerization catalyst influence, the double bond is broken, and the resultant extra single bond can be used to link to a carbon atom in the other ethylene molecule. Therefore, made into the repeating unit of a large, polymeric (multiple-unit) molecule and the ethylene, which has the chemical structure as given below:

CH2-CH2

The secret to polyethylene properties is the simplest structure, which is replicated thousands of times in a single molecule. Big, chain-like molecules with hydrogen atoms bound to a carbon backbone may be made in branched or linear shapes. Branched versions are called linear low density polyethylene (LLDPE) or low density polyethylene (LDPE); linear versions are called ultrahigh-molecular-weight polyethylene (UHMWPE) and high density polyethylene (HDPE).

The basic polyethylene composition is modified by including the other elements or chemical groups, as in the chlorosulfonated and chlorinated polyethylene cases. Additionally, ethylene is copolymerized with other monomers such as propylene or vinyl acetate to produce a number of ethylene copolymers.

Major Polyethylene Compounds

Low Density Polyethylene

LDPE can be prepared from the gaseous ethylene under more high pressures (up to around 50,000 pounds per square inch or around 350 megapascals) and high temperatures (up to 350 °C) in the presence of oxide initiators. These processes yield a polymer-type structure with both short and long branches.

Since the branches prevent the polyethylene molecules from closely packing together in stiff, hard, and crystalline arrangements, LDPE is given as a very flexible material. Its melting point is given as nearly 110 °C. Principal uses of this compound are in packaging film, grocery and trash bags, agricultural mulch, cable and wire insulation, toys, housewares, and squeeze bottles. #4 is the LDPE’s plastic (polyethylene plastic) recycling code.

Linear Low Density Polyethylene

Structurally, LLDPE is the same as LDPE. It is produced by copolymerization the ethylene with 1-butene and fewer amounts of 1-octene and 1-hexene, using metallocene or Ziegler-Natta catalysts. The resulting structure has a linear backbone, but uniform, short branches that keep the polymer chains from packed together tightly, similar to LDPE’s longer branches.

Overall, LLDPE contains the same properties as LDPE and competes for similar markets. The major advantages of LLDPE are given as the polymerization conditions are less energy-intensive and that the properties of the polymer can be altered by differentiating the amount and type of its chemical ingredients. #4 is LLDPE’s plastic  (polyethylene plastic) recycling code.

High Density Polyethylene

HDPE is made at low pressures and temperatures, using the metallocene catalysts and Ziegler-Natta or activated chromium oxide (which is called Phillips catalyst). In its structure, the lack of branches allows the polymer chains to be closely packed together by resulting in a dense, highly crystalline material of moderate and high strength stiffness.

It can withstand prolonged exposure to 120 °C because it has a melting point greater than 20 °C and is higher than LDPE. The products are blow-moulded bottles for household cleaners and milk, blow-extruded grocery bags, agricultural mulch, and construction film, and injection-moulded pails, appliance housings, toys, and caps. #2 is HDPE’s plastic recycling code.

Ultra High-Molecular-Weight Polyethylene

Ultrahigh-molecular-weight variants of linear polyethylene are available, with molecular weights ranging from 3,000,000 to 6,000,000 atomic units, compared to 500,000 atomic units for HDPE. These polymers are spun into fibres and, after that, stretched, or drawn, into a highly crystalline state by resulting in tensile strength and high stiffness several times that of steel. Yarns, which are made from these fibres, are woven into bulletproof vests.

Ethylene Copolymers

Ethylene is copolymerized with many other compounds. Also, ethylene-vinyl acetate copolymer (EVA), for suppose, is produced by the copolymerization of vinyl acetate and ethylene under pressure, using the free-radical catalysts. Several various grades are manufactured, with the vinyl acetate content differing from 5 to 50% by weight. The copolymers of EVA are more permeable to the gases and moisture than that of polyethylene, but they are more transparent and very less crystalline, and they represent better grease and oil resistance. Principal uses of this compound are adhesives, packaging film, tubing, toys, wire coatings, gaskets, carpet backing, and drum liners.

Polyvinylidene chloride (PVDC) is defined as a synthetic resin, which is produced by the polymerization of vinylidene chloride. It can be used principally inflexible, clear, and impermeable plastic food wrap.

Properties of Polyvinylidene Chloride

Vinylidene chloride (with the bonding CH2=CCl2) is a colourless, clear, and toxic liquid. It is obtained from trichloroethane (CH2=CHCl3) via dehydrochlorination (the removal of hydrogen chloride [HCl]) of that compound by alkali treatment. In water, the liquid can be suspended either as fine droplets for PVDC processing, or else, it is treated with soaplike surfactants and also dispersed as an emulsion of smaller particles in water.

The vinylidene-chloride monomers (small and single-unit molecules) can be joined together to form large and multiple-unit polymers using the free-radical initiator action. The polymer is obtained from the water phase either as beads or dry powder, which may be melted for extrusion into the plastic film.

The outstanding property of PVDC is given as its low permeability to the water vapour and gases – making it ideal in food packaging. Copolymers of vinylidene chloride, including the other monomers, are also marketed. The well-known is Saran, which is a copolymer consisting of around 87% vinylidene chloride and 13% vinyl chloride. The Dow Chemical Company first introduced Saran in 1939, and it is still a common transparent food wrap today.

Polyvinylidene Chloride Structure

Let us look at the polyvinylidene chloride structure below.

The chemical structure of Polyvinylidene chloride can be represented as follows:

Fiber Types

Saran fibre is available in monofilament, multifilament-twist, and staple types. Thermochromic (colour changing) and luminescent (glow in the dark) fibres are also available.

Characteristics

Let us look at a few of the characteristics of Polyvinylidene chloride:

Compatibility With Additives

The chemical structure of PVC’s Chlorine polar groups, as well as its amorphous nature, allows it to easily mix with a variety of substances. Several qualities can be imbued in products based on the additives used in PVC manufacturing, including anti-mist, different colours, fire inhibiting, elasticity, impact resistance, durability, and microbe prevention.

Durability

The factor which most strongly affects the product’s durability under conditions of typical use is the resistance to oxidation by atmospheric oxygen. PVC has excellent longevity due to its high resistance to oxidative reactions. In a test performed by the Japan PVC Pipe and Fittings Association, for example, 35-year-old underground pipes showed no signs of deterioration. This specific durability applies even through the process of recycling because the re-converted product’s physical properties are virtually similar to those made from virgin PVC resin.

Fire Resistance

Fire resistance is one of the major qualities of PVC that make it popular in several industries like building products. Also, PVC is a thermoplastic, which is made of 57% chlorine derived from common salt, and when ignited, its chlorine content will extinguish the flames. PVC has a high ignition temperature of 455°C. Because the heat released by the PVC when ignited is much lower compared to the temperatures released by other plastics such as PP and PE, it is less likely to spread the fire to other materials that increase the desirability of building products.

Electrical Insulation

PVC holds a good dielectric strength. It means it can withstand a considerable amount of electric field strength without breaking down its insulation properties. When combined with the fire-retardant properties of PVC, this dialectic strength makes it ideal for usage in insulation tape, communication cables, switch boxes, residential electrical cables, and wire covering.

Oil and Chemical Resistance

Although PVC swells or dissolves in aromatic hydrocarbons, cyclic, and ketone ethers, it is difficult, not easy, to dissolve in other organic chemicals. Also, it is almost resistant to all the inorganic chemicals. This makes it more ideal for the usage in gas exhaust pipes or tubes and ducts of all kinds, including medical applications.

Forms

PVC is available in two basic forms: Rigid (at the time, abbreviated as PVC) and versatile. Polyvinyl Chloride (Vinyl or PVC) is given as a versatile and cheap thermoplastic polymer, which is widely utilized in the housing and building industry to supply window and door profiles, pipes (waste-water and drinking water), cable and wire insulation, medical devices, and more.

Polyvinylidene Chloride Uses

Various polyvinylidene chloride uses are given below.

Packaging

Polyvinylidene chloride can be applied as a water-based coating to the other plastic films such as polyethylene terephthalate (PET) and biaxially-oriented polypropylene (BOPP). This coating will increase the film’s barrier properties, reducing the permeability of the film to the oxygen and flavours and hence extending the shelf life of the food, which is inside the package. It may also impart a high-gloss finish, which can be aesthetically pleasing and also provides a higher degree of scuff resistance if it is applied overprint.

Household

Polyvinylidene chloride can be used for household purposes such as cleaning cloths, screens, filters, shower curtains, tape, and garden furniture.

Industry

Polyvinylidene chloride is useful for industrial uses such as artificial turf, screens, underground materials, and waste-water treatment materials.

Miscellaneous

PVC is also much useful for various uses such as stuffed animals, doll hair, fishnet, fabrics, pyrotechnics, shoe insoles.