Organic matter occupies an important place in our lives. They are the main component of the polymers that surround us everywhere: these are plastic bags and rubber, as well as many other materials. Polypropylene is not the last step in this series. It is also part of various materials and is used in a number of industries, such as construction, and has domestic use as a material for plastic cups and other small (but not in scale of production) needs. Before we talk about a process such as hydration of propylene (thanks to which, by the way, we can get isopropyl alcohol), we turn to the history of the discovery of this substance necessary for industry.
History
As such, the propylene does not have an opening date. However, its polymer - polypropylene - was actually discovered in 1936 by the famous German chemist Otto Bayer. Of course, it was theoretically known how such important material could be obtained, but it was practically impossible to do so. This was possible only in the mid-twentieth century, when the German and Italian chemists Ziegler and Nutt discovered the catalyst for the polymerization of unsaturated hydrocarbons (having one or more multiple bonds), which was later called the Ziegler-Natta catalyst. Up to this point, it was decidedly impossible to make the polymerization reaction of such substances proceed. Polycondensation reactions were known when, without the action of a catalyst, substances were combined into a polymer chain, thereby forming by-products. But with unsaturated hydrocarbons this could not be done.
Another important process associated with this substance was its hydration. Propylene in the years of the beginning of its use was quite a lot. And all this is due to invented by various oil and gas processing companies methods for treating propene (this is also sometimes called the described substance). When cracking oil, it was a by-product, and when it turned out that its derivative, isopropyl alcohol, was the basis for the synthesis of many substances useful to mankind, many companies, such as BASF, patented their method of production and began mass trade in this compound. Hydration of propylene was tested and applied before polymerization, which is why acetone, hydrogen peroxide, isopropylamine began to be produced before polypropylene.
The process of separation of propene from oil is very interesting. It is to him that we will now turn.
Propylene recovery
In fact, in the theoretical sense, the main method is only one process: the pyrolysis of oil and associated gases. But technological implementations are just a sea. The fact is that each company seeks to obtain a unique method and protect it with a patent, while other similar companies are also looking for their own ways to still produce and sell propene as raw materials or to turn it into various products.
Pyrolysis (pyro means fire, lysis means destruction) is a chemical process of decomposition of a complex and large molecule into smaller ones under the influence of high temperature and a catalyst. Oil, as you know, is a mixture of hydrocarbons and consists of light, medium and heavy fractions. Of the first, the most low molecular weight, and get propene and ethane by pyrolysis. This process is carried out in special furnaces. For the most advanced manufacturing companies this process is technologically different: some use sand as a heat carrier, others use quartz, and others use coke; furnaces can also be divided by their structure: there are tube and ordinary, as they are called, reactors.
But the pyrolysis process allows you to get not enough pure propene, since, in addition to it, a huge number of hydrocarbons are formed there, which then have to be separated using fairly energy-intensive methods. Therefore, to obtain a cleaner substance for subsequent hydration, alkane dehydrogenation is also used: in our case, propane. Just like polymerization, the above process just does not happen. The elimination of hydrogen from a molecule of a saturated hydrocarbon occurs under the influence of catalysts: trivalent chromium oxide and alumina.
Well, before moving on to the story of how the process of hydration occurs, let us turn to the structure of our unsaturated hydrocarbon.
Structural Features of Propylene
Propene itself is only the second member of a series of alkenes (hydrocarbons with one double bond). In terms of ease, it is second only to ethylene (from which, as you might guess, polyethylene is made - the most massive polymer in the world). In the usual state, propene is a gas, like its "relative" from the alkane family, propane.
But the essential difference between propane and propene is that the latter has a double bond in its composition, which radically changes its chemical properties. It allows you to attach other substances to the unsaturated hydrocarbon molecule, resulting in compounds with completely different properties, often very important for industry and everyday life.
The time has come to talk about the theory of reaction, which, in fact, is the subject of this article. In the next section, you will learn that during the hydration of propylene one of the most industrially important products is formed, as well as how this reaction occurs and what nuances it contains.
Hydration theory
To begin with, we turn to a more general process - solvation - which also includes the reaction described above. This is a chemical transformation that involves the addition of solvent molecules to solute molecules. Moreover, they can form new molecules, or so-called solvates, particles consisting of molecules of a dissolved substance and a solvent connected by electrostatic interaction. We are only interested in the first type of substances, because during the hydration of propylene such a product is mainly formed.
When solvation is carried out as described above, the solvent molecules are attached to the dissolved substance, and a new compound is obtained. In organic chemistry, hydration primarily produces alcohols, ketones and aldehydes, but there are several other cases, such as the formation of glycols, but we will not touch on them. In fact, this process is very simple, but at the same time quite complicated.
Hydration mechanism
The double bond, as is known, consists of two types of compound of atoms: pi- and sigma-bonds. During the hydration reaction, the pi-bond is always broken first, since it is less durable (has lower binding energy). When it breaks, two vacant orbitals are formed at two neighboring carbon atoms, which can form new bonds. A water molecule that exists in a solution in the form of two particles: a hydroxide ion and a proton, is capable of joining via a broken double bond. In this case, the hydroxide ion joins the central carbon atom, and the proton - to the second, extreme. Thus, during hydration of propylene, propanol 1, or isopropyl alcohol, is predominantly formed. This is a very important substance, since when it is oxidized, acetone can be massively used in our world. We said that it is formed mainly, but this is not entirely true. I must say this: the only product is formed during the hydration of propylene, and this is isopropyl alcohol.
This, of course, is all the subtlety. In fact, everything can be described much easier. And now we will learn how a process such as hydration of propylene is recorded in a school course.
Reaction: how does it happen
In chemistry, it is customary to denote everything simply: using reaction equations. So the chemical transformation of the substance under discussion can be described in this way. Hydration of propylene, the reaction equation of which is very simple, takes place in two stages. First, the pi bond, which is part of the double bond, is broken. Then a water molecule in the form of two particles, a hydroxide anion and a hydrogen cation, approaches a propylene molecule, which currently has two vacant sites for the formation of bonds. The hydroxide ion forms a bond with a less hydrogenated carbon atom (that is, with one to which fewer hydrogen atoms are attached), and the proton, respectively, with the remaining extreme one. Thus, one single product is obtained: isopropanol saturated monohydroxy alcohol .
How to record a reaction?
Now we will learn how to write a chemical language for a reaction that reflects a process such as hydration of propylene. The formula that comes in handy is: CH 2 = CH - CH 3 . This is the formula of the starting material - propene. As you can see, he has a double bond, indicated by the sign "=", and it is in this place that water will join in when the hydration of propylene takes place. The reaction equation can be written as follows: CH 2 = CH - CH 3 + H 2 O = CH 3 - CH (OH) - CH 3 . The hydroxyl group in brackets means that this part is not in the plane of the formula, but lower or higher. Here we cannot show the angles between the three groups extending from the middle carbon atom, but we will say that they are approximately equal to each other and amount to 120 degrees.
Where does this apply?
We have already said that the substance obtained during the reaction is actively used for the synthesis of other substances vital to us. It is very similar in structure to acetone, from which it differs only in that instead of the hydroxo group there is a keto group (that is, an oxygen atom connected by a double bond with a nitrogen atom). As you know, acetone itself is used in solvents and varnishes, but, in addition, it is used as a reagent for the further synthesis of more complex substances, such as polyurethanes, epoxies, acetic anhydride and so on.
Acetone reaction
We think it would be useful to describe the conversion of isopropyl alcohol to acetone, especially since this reaction is not so complicated. To begin with, propanol is evaporated and oxidized with oxygen on a special catalyst at 400-600 degrees Celsius. A very pure product is obtained by carrying out the reaction on a silver mesh.
Reaction equation
We will not go into details of the mechanism of the reaction of the oxidation of propanol to acetone, since it is very complex. We restrict ourselves to the usual equation of chemical transformation: CH 3 - CH (OH) - CH 3 + O 2 = CH 3 - C (O) - CH 3 + H 2 O. As you can see, everything is quite simple in the diagram, but it’s worth going deeper into the process, and we will face a number of difficulties.
Conclusion
So we examined the process of hydration of propylene and studied the reaction equation and its mechanism. The considered technological principles underlie the real processes occurring in production. As it turned out, they are not very complicated, but they have real benefits for our daily lives.