Petrochemistry

Petrochemistry. Industry that is fundamentally based on oil refining and the manufacture of polymers that are derived from oil, during these processes several different products are derived such as methane, ethane, propane, etc …

Summary

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  • 1 Background
  • 2 Products made by petrochemicals.
    • 1 Polymers
  • 3 How did oil form?
    • 1 What is oil?
  • 4 Oil hydrocarbons?
    • 1 Petrochemical raw materials
  • 5 Potential environmental impacts
  • 6 External links
  • 7 Sources

Background

From oil, certain compounds are obtained that are the basis of various production chains that determine a wide range of products called petrochemicals that are used in the fertilizer , plastics , food, pharmaceutical, chemical and textile industries, among others. The main petrochemical chains are those of natural gas, light olefins ( ethylene , propylene and Butene ) and that of aromatics.

Synthesis gas is produced from natural gas, which enables the large-scale production of hydrogen, making possible the subsequent production of ammonia by its reaction with nitrogen, and of methanol, the raw material in the production of methyl tert-butyl ether, among other compounds.

A large number of derivatives are produced from ethylene , such as the different classes of polyethylene , vinyl chloride, chlorinated compounds, ethylene oxides, styrene monomers, among others, that have application in plastics, coatings, molds, etc.

From propylene, compounds such as isopropyl alcohol, polypropylene and acrylonitrile are produced, which have great application in the industry of solvents, paints and synthetic fibers. By dehydrogenation of butenes, or as a by-product of the ethylene manufacturing process, 1,3-butadiene is obtained, which is a fundamental raw material in the elastomer industry, for the manufacture of tires, seals, etc.

A fundamental chain in the petrochemical industry is based on aromatics (benzene, toluene and xylenes). Benzene is the production base for cyclohexane and the nylon industry; as well as cumene for the industrial production of acetone and phenol . Xylenes are the start of various petrochemical chains, mainly those of synthetic fibers.

Products made by petrochemicals.

Products can be divided according to their use into:

  • Solvents, among which are various alcohols, acetone and others that are used in the extraction of essences for perfumes or oilseed oils, cleaning clothes, etc.:

 

  • Industrial chemicals, such as carbon black for paints and tires; sulfur to prepare sulfuric acid; naphtha additives; antifreeze for radiators, etc.

 

  • Detergents, which largely replace soaps and are more effective when using hard water;

 

  • Agricultural chemicals, such as fertilizers and herbicides, the use of which determines increases in the yield of cultivated land; insecticides to combat predators such as lobsters and insects that carry various diseases;

 

  • Plastics, such as polyethylene, polypropylene, polyvinyl chloride, etc., which when molded allow the manufacture of innumerable objects: tubes, containers, waterproof covers, toys, construction materials;

 

  • Synthetic fibers, varieties of plastics that are transformed into continuous filaments by the passage through fine holes; for example: nylon, dacron, polyester, etc.

 

Polymers

Chemical substance, made up of repeated structural units: plastic is made of polymers. Molecule consisting of the repetition of simpler chemical units linked by covalent bond. The formation of these macromolecules can be carried out by reaction of simpler molecules (polymerization reaction) called monomers.

Most polymers used as plastics, fibers and rubbers have molecular weights (product of the repeating unit molecular weight times the degree of polymerization) ranging from 10,000 to 1,000,000 (for example, polyethylene of molecular weight between 1,000 and 5,000 is a waxy solid that only acquires useful properties when its molecular weight is greater than 10,000).

The useful properties of polymers, such as their mechanical resistance, high glass transition temperature (for amorphous plastics), high melting temperature (for semi-crystalline fibers and films), are due to their high molecular weight. Due to polymerization processes (both synthetic and natural polymers) in which the length of each chain is determined by random events, each polymer will be made up of a set of chains of different degrees of polymerization (macromolecules with different lengths). This chain length is determined by the time the chain grows before the termination stage occurs.

The atoms that make up polymer chains and their substituents are of paramount importance in the properties of polymers. In addition polymers, the polarity and volume of the substituent have a great influence on properties and characteristics such as glass transition temperature, crystallization, chain flexibility, etc.

In the case of condensation polymers, the types of atoms of the functions that form the main chain of the polymer will determine a large number of its characteristics. Also, the substituents introduced in the main chain will influence the stiffness of the chain (as in the case of aromatic rings), the melting point (in crystalline polymers), etc. The bonding bonds between atoms of the main chain and of the substituents are of the covalent type. The secondary bonding forces that occur between macromolecular chains play an important role in the texture of the polymers and in their thermal and mechanical properties.

Chains with weak intermolecular forces and little lateral adaptation power to form ordered structures are characteristic of rubbers or elastomers. If the intermolecular attraction is strong and the spatial arrangement of the substituents is such that it allows the chains to adapt to form an ordered structure (crystallinity), the structural conditions of a fiber exist.

The market for these products is characterized by its wide variety of applications. Petrochemicals are mainly used as raw materials in the chemical and petrochemical industries, as well as in the solvents, paints, coatings, food, pharmaceuticals, glues and adhesives, propellants, hydrogen production, polystyrene expanders and polymerization solvents, industry rubber, aluminum rolling and dyeing for printing and industrial oils and greases, etc. On the other hand, sulfur is used in sugar mills and for the production of fertilizers, manufacture of caprolactam, chemicals, soaps and detergents, production of sulfuric and hydrochloric acids, among others.

The products have to comply with a series of specifications that ensure their satisfactory behavior. This is achieved with a series of chemical transformations that occur in the various processes that constitute a refinery, where the structure of hydrocarbons is modified.

How did oil form?

There are several theories about the formation of oil. However, the most accepted is the organic theory that assumes that it originated from the decomposition of the remains of animals and microscopic algae accumulated at the bottom of the lagoons and in the lower course of the rivers. This organic matter was gradually covered with increasingly thick layers of sediment, under which, under certain conditions of pressure, temperature and time, it was slowly transformed into hydrocarbons (compounds formed from carbon and hydrogen), with small amounts of sulfur. , oxygen, nitrogen, and traces of metals such as iron, chromium, nickel, and vanadium, whose mixture constitutes crude oil.

These conclusions are based on the location of the oil layers, since they are all located in sedimentary lands. Furthermore, the compounds that make up the aforementioned elements are characteristic of living organisms.

Now, there are people who do not accept this theory. Their main argument lies in the inexplicable fact that if it is true that there are more than 30,000 oil fields in the entire world, so far only 33 of them constitute large fields. Of these large deposits, 25 are in the Middle East and contain more than 60% of our planet’s proven reserves.

One wonders then: How is it possible that so many animals have died in less than 1% of the earth’s crust, which is the percentage that corresponds to the Middle East? Undoubtedly, the answer to this question, if the organic theory is valid, can only be found in the Bible, where Eden is described as a place surrounded by four rivers (one of them being the Euphrates), in whose center is the “Tree of Life”. This answer probably doesn’t sound very scientific, but doesn’t it justify the fact that the Middle East contains the world’s largest animal cemetery, the source of its oil reserves, if the organic theory is true?

Naturally, there are other theories that hold that the oil is of inorganic or mineral origin. Soviet scientists have been most concerned with testing this hypothesis. However, these propositions have not been accepted in their entirety either. An interesting version of this topic is the one published by Thomas Gold in 1986. This European scientist says that natural gas (methane), which is usually found in large quantities in oil fields, may have been generated from meteorites that fell during the formation of the Earth millions of years ago. The arguments it presents are based on the fact that more than 40 chemicals similar to kerogen, which is supposed to be the precursor of oil, have been found in various meteorites. And since the latest discoveries from NASA have proven that the atmospheres of the other planets have a high methane content, it is not surprising that this theory is gaining more followers every day. We can conclude that despite the innumerable investigations that have been carried out, there is no infallible theory that undoubtedly explains the origin of oil since this would imply being able to discover the origins of life itself.

What is oil?

Anyone with a certain sense of observation can describe oil as a viscous liquid whose color varies from yellow and dark brown to black, with green reflections. It also has a characteristic odor and floats on water. But if you want to know everything that can be done with oil, this definition is not enough. It is necessary to deepen the knowledge to determine not only its physical properties but also the chemical properties of its components. As we said before, petroleum is a mixture of hydrocarbons, compounds that contain carbon and hydrogen in their molecular structure mainly.

The number of carbon atoms and the way they are placed within the molecules of different compounds gives oil different physical and chemical properties. Thus we have that the hydrocarbons composed of one to four carbon atoms are gaseous, those containing 5 to 20 are liquid, and those with more than 20 are solid at room temperature. Crude oil varies greatly in its composition, which depends on the type of field where it comes from, but on average we can consider that it contains between 83 and 86% carbon and between 11 and 13% hydrogen.

The greater the carbon content in relation to that of hydrogen, the greater the quantity of heavy products that crude oil has. This depends on the age and some characteristics of the deposits. However, it has been found that the older they are, the more gaseous and solid hydrocarbons and less liquids enter their composition. Some crudes contain compounds of up to 30 to 40 carbon atoms.

Oil hydrocarbons?

Any chemical classification of oil presupposes that the type of compounds that form it has been established in advance. For this, hydrocarbons from oil are classified into three large series.

The first series is made up of saturated acyclic hydrocarbons, also called paraffinic. They are so called because they do not readily react with other compounds. Its name comes from the Greek roots “parum”, small and “affinis”, affinity. Its general formula is C n H 2n + 2 (n is a positive integer).

The first four hydrocarbons in this series are methane , ethane, and butane and are the main components of petroleum gases.

The second series includes saturated or naphthenic cyclic hydrocarbons of general formula, such as cyclopentane and cyclohexane. The third series is made up of unsaturated cyclic hydrocarbons, better known as aromatic hydrocarbons, whose general formula is CnH2n-6. The simplest compound in this series is benzene, which has six carbon atoms linked by alternating double bonds forming a ring. The hydrocarbons of the latter series, which are found in crude oil in general, are made up of so-called polyaromatics, which are several benzene rings linked together and which are mainly found in heavy fractions.

However, apart from the three series mentioned above, there are other hydrocarbons in small quantities such as unsaturated acyclics, also called ethylenes or olefins, of general formula, diolefins, acetylenics, in addition to other hydrocarbons formed by the combination of rings and strings that may resemble several of the preceding series. As we said earlier, crude oil contains almost no light benzene hydrocarbons such as benzene, toluene, and xylenes. It also does not have a large amount of olefins or low carbon diolefins such as ethylene, propylene, butenes, butadiene and isoprene. Only through specific processes or separating them when manufacturing gasoline, is it possible to obtain these important hydrocarbons.

Petrochemical raw materials

The petrochemical industry primarily uses olefins and aromatics obtained from natural gas and petroleum refining products as basic raw materials: ethylene, propylene, butylenes, and some pentenes among olefins, and benzene, toluene and xylenes as aromatic hydrocarbons.

However, in some cases, the low availability of these hydrocarbons due to the alternate use they have in the manufacture of high octane gasoline has forced the industry to use special processes to produce them. Therefore, if it is desired to produce petrochemicals from the virgin hydrocarbons contained in the oil, it is necessary to subject them to a series of reactions, according to the following steps:

1.Transform virgin hydrocarbons into products with a higher chemical reactivity, such as ethane, propane, butanes, pentanes, hexanes, etc., which are the paraffins that petroleum contains, and convert them to ethylene, propylene, butylenes, butadiene , isoprene, and the aromatics already mentioned.

  1. Incorporate other heteroatoms such as chlorine, oxygen, nitrogen, etc. into the olefins and aromatics obtained in the first stage, thus obtaining second generation intermediate products. This is the case of ethylene, which when reacting with oxygen produces acetaldehyde and acetic acid.

 

  1. Carry out at this stage the final operations that make up consumer products. For this, the particular formations are required so that their properties correspond to the uses they provide.

Some examples of this third stage are polyurethanes, which, depending on the specific formulations, can be used to make artificial mattresses, lifeguards, or hearts. Acrylic resins can be used to make rugs , lamp soffits, dentures and paints.

Another typical case is that of acetaldehyde that is produced by oxidizing ethylene and that finds application as a solvent for lacquers and synthetic resins, in the manufacture of flavorings and perfumes, in the manufacture of artificial leather for inks, cements, photographic films and fibers such as acetate of cellulose and vinyl acetate.

This classification has numerous exceptions, sometimes, for example, the number of stages to make the final product is reduced. It is necessary to mention other products that are considered basic petrochemicals without being hydrocarbons , such as carbon black and sulfur. These can be obtained from natural gas and oil . Next we will try to explain how the products of the first stage are obtained, among which we will consider not only the obtaining of olefins and aromatics, but also that of carbon black and sulfur from these crudes.

Potential environmental impacts

Most of the materials used in chemical and petrochemical manufacturing are flammable and explosive. While many of the chemicals and petrochemicals are toxic, some are also carcinogenic. The potential explosion risks are more severe compared, for example, to the refining industry, because the compounds are highly reactive and the pressures that occur during their manufacture and handling are high.

Highly toxic materials that cause immediate injury, such as phosgene or chlorine, would be classified as a safety hazard. Others cause long-term effects, sometimes at very low concentrations. In studies of chemical production and its environmental impact, toxicity, hazard and operability considerations were found to play an important role. Possible wastes and emissions depend on the types of compounds that are manufactured and the wide variety of processes and chemicals that are used in their manufacture.

The negative environmental impact of chemical production can be very severe. To provide information on chemical and health risks, the National Institute for Occupational Safety and Health (NIOSH), a division of the US Department of Health and Human Resources (HHS) has published a guide book. The Dow and Fire and Explosion Index, published by the American Institute of Chemical Engineers (AICE), is used to obtain information on fire and explosion risks.

Large amounts of water are used in the chemical industry for the process, cooling and washing. Often during chemical production, water is contaminated with these or by-products. The US Environmental Protection Agency (EPA) has published a list of compounds for which effluent guidelines have been established. Pollutants that can pose a hazard if discharged to rivers and underground aquifers include toxic materials, carcinogenic compounds, suspended solids, and substances that manifest a high demand for biochemical and chemical oxygen.

Groundwater and surface water resources can be adversely affected by rainwater from tank yards, product discharge and processing areas, pipelines, cooling water purge, flushing and cleaning water, and casual spills from raw materials and finished products. Normally, to avoid these negative impacts, it is necessary to implement measures to control runoff, including the use of rainwater detention containers, which receive treatment before discharging it.

Depending on the process used, atmospheric pollutants include particles and a large number of gaseous compounds, such as sulfur oxides, carbon and nitrogen oxides from process boilers and furnaces, ammonia, nitrogen compounds and chlorinated compounds. These emissions come from various sources, including process equipment, storage facilities, pumps, valves, drains, and leaking retainers. Atmospheric emissions are controlled through the use of incineration (lighters), adsorption, gas scrubbing, and other absorption processes. The US Environmental Protection Agency It has developed standards for air quality , which regulate emissions from chemical factories.

Solid waste from the chemical industry can include remains of raw material, residual polymers, sludge from the boiler, cleaning of tanks or pollution control equipment, and ash produced during the operation of coal-fired boilers. The waste may be contaminated with chemicals from the processes. Disposal of spent catalysts can create an environmental problem in the petrochemical industries. Currently, catalyst suppliers offer the service of receiving, once again, spent catalysts.

 

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