Organic substances occupy 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 found in various materials and is used in a number of industries such as construction, domestic use as a material for plastic cups, and other small (but not industrial scale) uses. Before we talk about such a process as the hydration of propylene (thanks to which, by the way, we can get isopropyl alcohol), let's turn to the history of the discovery of this substance necessary for industry.
History
As such, propylene has no 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 not possible to do it in practice. This was only possible in the middle of the twentieth century, when the German and Italian chemists Ziegler and Natt discovered a catalyst for the polymerization of unsaturated hydrocarbons (having one or more multiple bonds), whichlater they called it the Ziegler-Natta catalyst. Until that moment, it was absolutely 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, forming by-products. But it was not possible to do this with unsaturated hydrocarbons.
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 thanks to the methods of recovering propene invented by various oil and gas processing companies (this is sometimes also called the described substance). When oil was cracked, it was a by-product, and when it turned out that its derivative, isopropyl alcohol, is the basis for the synthesis of many substances useful to mankind, many companies, such as BASF, patented their method of producing it and began mass trading this compound. Propylene hydration was tried and applied before polymerization, which is why acetone, hydrogen peroxide, isopropylamine began to be produced before polypropylene.
The process of separating propene from oil is very interesting. It is to him that we now turn.
Separation of propylene
In fact, in a 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 every company strives to get a unique way and protect it.patent, and other such companies are also looking for their own ways to still produce and sell propene as a raw material or turn it into various products.
Pyrolysis ("pyro" - fire, "lysis" - destruction) is a chemical process of breaking up 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 lowest molecular weight, propene and ethane are obtained during pyrolysis. This process is carried out in special ovens. For the most advanced manufacturing companies, this process is technologically different: some use sand as a heat carrier, others use quartz, others use coke; you can also divide furnaces according to their structure: there are tubular and conventional, as they are called, reactors.
But the pyrolysis process makes it possible to obtain insufficiently pure propene, since, in addition to it, a huge number of hydrocarbons are formed there, which then have to be separated in rather energy-consuming ways. Therefore, to obtain a purer substance for subsequent hydration, dehydrogenation of alkanes is also used: in our case, propane. Just like polymerization, the above process does not just happen. The splitting off of hydrogen from a molecule of a saturated hydrocarbon occurs under the action of catalysts: trivalent chromium oxide and aluminum oxide.
Well, before moving on to the story of how the hydration process occurs, let's turn to the structure of our unsaturated hydrocarbon.
Features of the structure of propylene
Propene itself is only the second member of the alkene series (hydrocarbons with one double bond). In terms of lightness, it is second only to ethylene (from which, as you might guess, polyethylene is made - the most massive polymer in the world). In its normal 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 an unsaturated hydrocarbon molecule, resulting in compounds with completely different properties, often very important for industry and everyday life.
It's time to talk about reaction theory, which, in fact, is the subject of this article. In the next section, you will learn that the hydration of propylene produces one of the most industrially important products, as well as how this reaction occurs and what are the nuances in it.
Hydration Theory
First, let's turn to a more general process - solvation - which also includes the reaction described above. This is a chemical transformation, which consists in the addition of solvent molecules to solute molecules. At the same time, they can form new molecules, or the so-called solvates, particles consisting of molecules of a solute and a solvent connected by electrostatic interaction. We are only interestedthe first type of substances, because during the hydration of propylene, just such a product is predominantly formed.
When solvating in the manner described above, the solvent molecules are attached to the solute, a new compound is obtained. In organic chemistry, hydration predominantly forms alcohols, ketones, and aldehydes, but there are a few 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
Double bond, as you know, consists of two types of connection of atoms: pi- and sigma-bonds. The pi-bond is always the first to break during the hydration reaction, since it is less strong (it has a lower binding energy). When it breaks, two vacant orbitals are formed at two neighboring carbon atoms, which can form new bonds. The water molecule, which exists in solution in the form of two particles: a hydroxide ion and a proton, is capable of joining along a broken double bond. In this case, the hydroxide ion is attached to the central carbon atom, and the proton - to the second, extreme. Thus, during the 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 obtained, which is widely used in our world. We said that it is formed predominantly, but this is not entirely true. I must say this: the only product formed during the hydration of propylene, and this is isopropyl alcohol.
This is, of course, all the subtleties. In fact, everything can be described much easier. And now we will find out how such a process as propylene hydration is recorded in the school course.
Reaction: how it happens
In chemistry, everything is usually denoted simply: with the help of reaction equations. So the chemical transformation of the substance under discussion can be described in this way. The hydration of propylene, whose reaction equation is very simple, proceeds in two stages. First, the pi bond, which is part of the double, is broken. Then a water molecule in the form of two particles, a hydroxide anion and a hydrogen cation, approaches the propylene molecule, which currently has two vacant sites for the formation of bonds. The hydroxide ion forms a bond with the less hydrogenated carbon atom (that is, with the one to which fewer hydrogen atoms are attached), and the proton, respectively, with the remaining extreme. Thus, one single product is obtained: the saturated monohydric alcohol isopropanol.
How to record a reaction?
Now we will learn how to write down in chemical language a reaction that reflects a process such as the hydration of propylene. The formula we need is: CH2 =CH - CH3. This is the formula of the original substance - propene. As you can see, it has a double bond, marked with "=", and this is where water will be added when the propylene is hydrated. The reaction equation can be written like this: CH2 =CH - CH3 + H2O=CH 3 - CH(OH) - CH3. The hydroxyl group in brackets meansthat this part is not in the plane of the formula, but below or above. 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 are 120 degrees each.
Where does it apply?
We have already said that the substance obtained during the reaction is actively used for the synthesis of other vital substances. It is very similar in structure to acetone, from which it differs only in that instead of a hydroxo group there is a keto group (that is, an oxygen atom connected by a double bond to 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, epoxy resins, acetic anhydride, and so on.
Acetone production reaction
We think it would be useful to describe the transformation of isopropyl alcohol into acetone, especially since this reaction is not so complicated. To begin with, propanol is evaporated and oxidized with oxygen at 400-600 degrees Celsius on a special catalyst. 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 oxidation of propanol to acetone, as it is very complicated. We restrict ourselves to the usual chemical transformation equation: CH3 - CH(OH) - CH3 + O2=CH3 - C(O) - CH3 +H2O. As you can see, everything is quite simple on the diagram, but it is worth delving into the process, and we will encounter a number of difficulties.
Conclusion
So we analyzed the process of propylene hydration and studied the reaction equation and the mechanism of its occurrence. The considered technological principles underlie the real processes occurring in production. As it turned out, they are not very difficult, but they have real benefits for our daily life.
