The urea extraction crystallization is a process for separating linear paraffins (n-paraffins, n-alkanes) from hydrocarbon mixtures through the formation of urea-n-paraffin-clathrates. The process is primarily used to lower the pour point of petroleum products, by-products of the process are n-paraffins in high purity. The method may also applied for the separation of fatty acids and fatty alcohols. In addition to urea also thiourea is used in the process.
In addition to the n-alkanes are also unbranched fatty acids with more than four carbon atoms, their esters and unbranched fatty alcohols can migrate into the channels of the crystallized urea and form a clathrate. The initial discovery of the method was based on a study of the fats in milk. [2] A deviation from the linear molecular geometry, for example, by C=C-double bonds in the molecule, leads to a less stable inclusion compound. Thus stearic acid (C18: 0) forms more stable urea adducts compared to oleic acid (C18: 1 cis -9) or linoleic acid (C18: 2 cis -9, cis -12). A branching in the fatty acid molecule or an autoxidation result in a large deviation from the straight-chain molecular structure, so that these compounds do not form urea adducts. This is used as part of the fatty acid analysis and for the separation or enrichment of specific fatty acids. [3]
For the separation of n-paraffins from other hydrocarbon compounds, urea is added with an approximately 20-fold molar excess. The urea crystallizes in a hexagonal crystal structure with about 5.5 to 5.8 Å wide channels. In these channels the n-paraffins are included. If the concentration of n-paraffins in the mixture is too high, the mixture is diluted with a solvent.
In general, the reaction proceeds according to the scheme:
The equilibrium of the reaction is dependent on the concentrations of the reactants, the solvent and the temperature. [4] The necessary quantity of urea for the formation of inclusion compounds varies from about 1 to 0.8 mole of urea per methyl- and methylene group in a carbon chain. [4] The urea is added as a supersaturated aqueous solution to compensate for losses due to adduct formation during the process. In order to avoid a too high concentrations of adducts in the dewaxed oil a solvent such as methyl isobutyl ketone or methylene chloride is used for dilution. The ratio of oil to water phase is about 1 to 0.5. The mixing of the oil and water phases occurs at slightly elevated temperatures of about 35 °C. In the course of the reaction the mixture is cooled to room temperature. Lower temperatures are advantageous for the formation of inclusion complexes. [4]
The urea-paraffin-adduct can be filtered off and thereby separated from the iso-paraffins and other non-paraffinic components. By washing with a solvent a solid adduct residue is obtained. The washing of the clathrates with hot water at about 75 °C breaks up the clathrates and releases the paraffins. The obtained n-paraffins have a purity of about 99%. Losses of urea are small, the hot urea solution can be returned directly back into the process.
In organic chemistry, an alkane, or paraffin, is an acyclic saturated hydrocarbon. In other words, an alkane consists of hydrogen and carbon atoms arranged in a tree structure in which all the carbon–carbon bonds are single. Alkanes have the general chemical formula CnH2n+2. The alkanes range in complexity from the simplest case of methane, where n = 1, to arbitrarily large and complex molecules, like pentacontane or 6-ethyl-2-methyl-5-(1-methylethyl) octane, an isomer of tetradecane.
In chemistry, a solution is a special type of homogeneous mixture composed of two or more substances. In such a mixture, a solute is a substance dissolved in another substance, known as a solvent. If the attractive forces between the solvent and solute particles are greater than the attractive forces holding the solute particles together, the solvent particles pull the solute particles apart and surround them. These surrounded solute particles then move away from the solid solute and out into the solution. The mixing process of a solution happens at a scale where the effects of chemical polarity are involved, resulting in interactions that are specific to solvation. The solution usually has the state of the solvent when the solvent is the larger fraction of the mixture, as is commonly the case. One important parameter of a solution is the concentration, which is a measure of the amount of solute in a given amount of solution or solvent. The term "aqueous solution" is used when one of the solvents is water.
Urea, also called carbamide, is an organic compound with chemical formula CO(NH2)2. This amide has two amino groups joined by a carbonyl functional group. It is thus the simplest amide of carbamic acid.
A triglyceride is an ester derived from glycerol and three fatty acids. Triglycerides are the main constituents of body fat in humans and other vertebrates, as well as vegetable fat. They are also present in the blood to enable the bidirectional transference of adipose fat and blood glucose from the liver, and are a major component of human skin oils.
Waxes are a diverse class of organic compounds that are lipophilic, malleable solids near ambient temperatures. They include higher alkanes and lipids, typically with melting points above about 40 °C (104 °F), melting to give low viscosity liquids. Waxes are insoluble in water but soluble in nonpolar organic solvents such as hexane, benzene and chloroform. Natural waxes of different types are produced by plants and animals and occur in petroleum.
Dichloromethane is an organochlorine compound with the formula CH2Cl2. This colorless, volatile liquid with a chloroform-like, sweet odor is widely used as a solvent. Although it is not miscible with water, it is slightly polar, and miscible with many organic solvents.
A micelle or micella is an aggregate of surfactant amphipathic lipid molecules dispersed in a liquid, forming a colloidal suspension. A typical micelle in water forms an aggregate with the hydrophilic "head" regions in contact with surrounding solvent, sequestering the hydrophobic single-tail regions in the micelle centre.
Pentane is an organic compound with the formula C5H12—that is, an alkane with five carbon atoms. The term may refer to any of three structural isomers, or to a mixture of them: in the IUPAC nomenclature, however, pentane means exclusively the n-pentane isomer, in which case pentanes refers to a mixture of them; the other two are called isopentane (methylbutane) and neopentane (dimethylpropane). Cyclopentane is not an isomer of pentane because it has only 10 hydrogen atoms where pentane has 12.
A clathrate is a chemical substance consisting of a lattice that traps or contains molecules. The word clathrate is derived from the Latin clathratus, meaning 'with bars, latticed'. Most clathrate compounds are polymeric and completely envelop the guest molecule, but in modern usage clathrates also include host–guest complexes and inclusion compounds. According to IUPAC, clathrates are inclusion compounds "in which the guest molecule is in a cage formed by the host molecule or by a lattice of host molecules." The term refers to many molecular hosts, including calixarenes and cyclodextrins and even some inorganic polymers such as zeolites.
Crystallization is the process by which solid forms, where the atoms or molecules are highly organized into a structure known as a crystal. Some ways by which crystals form are precipitating from a solution, freezing, or more rarely deposition directly from a gas. Attributes of the resulting crystal depend largely on factors such as temperature, air pressure, and in the case of liquid crystals, time of fluid evaporation.
In host-guest chemistry, cucurbiturils are macrocyclic molecules made of glycoluril monomers linked by methylene bridges. The oxygen atoms are located along the edges of the band and are tilted inwards, forming a partly enclosed cavity (cavitand). The name is derived from the resemblance of this molecule with a pumpkin of the family of Cucurbitaceae.
Sulfamic acid, also known as amidosulfonic acid, amidosulfuric acid, aminosulfonic acid, sulphamic acid and sulfamidic acid, is a molecular compound with the formula H3NSO3. This colourless, water-soluble compound finds many applications. Sulfamic acid melts at 205 °C before decomposing at higher temperatures to water, sulfur trioxide, sulfur dioxide and nitrogen.
Hot-melt adhesive (HMA), also known as hot glue, is a form of thermoplastic adhesive that is commonly sold as solid cylindrical sticks of various diameters designed to be applied using a hot glue gun. The gun uses a continuous-duty heating element to melt the plastic glue, which the user pushes through the gun either with a mechanical trigger mechanism on the gun, or with direct finger pressure. The glue squeezed out of the heated nozzle is initially hot enough to burn and even blister skin. The glue is sticky when hot, and solidifies in a few seconds to one minute. Hot-melt adhesives can also be applied by dipping or spraying, and are popular with hobbyists and crafters both for affixing and as an inexpensive alternative to resin casting.
Nitrosobenzene is the organic compound with the formula C6H5NO. It is one of the prototypical organic nitroso compounds. Characteristic of its functional group, it is a dark green species that exists in equilibrium with its pale yellow dimer. Both monomer and dimer are diamagnetic.
In chemistry, fractional crystallization is a stage-wise separation technique that relies on the liquid-solid phase change. It fractionates via differences in crystallization temperature and enables the purification of multi-component mixtures, as long as none of the constituents can act as solvents to the others. Due to the high selectivity of the solid - liquid equilibrium, very high purities can be achieved for the selected component.
This glossary of chemistry terms is a list of terms and definitions relevant to chemistry, including chemical laws, diagrams and formulae, laboratory tools, glassware, and equipment. Chemistry is a physical science concerned with the composition, structure, and properties of matter, as well as the changes it undergoes during chemical reactions; it features an extensive vocabulary and a significant amount of jargon.
Winterization of oil is a process that uses a solvent and cold temperatures to separate lipids and other desired oil compounds from waxes. Winterization is a type of fractionation, the general process of separating the triglycerides found in fats and oils, using the difference in their melting points, solubility, and volatility.
Paraffin oxidation is a historical industrial process for the production of synthetic fatty acids. The fatty acids are further processed to consumer products such as soaps and fats as well as to lubricating greases for technical applications. Coal slack wax, a saturated, high molecular weight hydrocarbon mixture and by-product of the Fischer–Tropsch process was used as raw material. Side products were a wide range of carboxylic acids and oxidation products such as alcohols, aldehydes, esters, or ketones. The oxidation of paraffins was carried out in the liquid phase by molecular oxygen, e.g. by aerating with oxygen or atmospheric air, in the presence of catalysts such as permanganates, e.g. 0.1% - 0.3% potassium permanganate, at temperatures in the range of about 100 to 120 °C and under atmospheric pressure.
Gas chromatography–vacuum ultraviolet spectroscopy (GC-VUV) is a universal detection technique for gas chromatography. VUV detection provides both qualitative and quantitative spectral information for most gas phase compounds.
Urea can crystallise with other compounds. These can be called urea adducts or if a solvent is involved, a urea solvate, and the process is called urea extraction crystallization. Urea can also be a neutral ligand if it is coordinated to a central metal atom. Urea can form hydrogen bonds to other oxygen and nitrogen atoms in the substance it crystallises with. This stiffens the solid and raises the melting point. T