Refining , refining or refining refers in the general sense to a technical process for cleaning, refining, separating or concentrating raw materials , foodstuffs and technical products (in the case of wines , this process is called refinement ). The result of a refining is the raffinate and possibly waste substances. A refinery has facilities for refining sugar , crude oil , metals or other substances.
Types of refining classified according to substance groups
After the fractional (vacuum) distillation of petroleum, hydrocarbons still contain undesirable substances containing sulfur , oxygen and nitrogen, as well as other undesirable substances, for example alkenes . In lubricants, these impurities can lead to signs of aging such as darkening, increase in viscosity , the formation of acids or oil sludge after only a short period of use . They are removed by hydrogenation during refining in a petroleum refinery , which leads to a quality improvement. Alternative purification processes (furfural extraction, oleum refining) are also used. Furthermore, the cleaning of base oils in lubricant production, in which the base oils are filtered with the help of various clays , is referred to as refining.
Vegetable oils or fats
The refining of vegetable oil is a processing step in the manufacture of these products; it takes place after hot pressing and / or solvent extraction . During refining, unwanted accompanying substances are removed from the previously produced crude oil (trub oil) (e.g. pigments, odor, taste and bitter substances), which can influence the quality of the products. This is essentially about taste, shelf life, technical processing, smell and color. Refining is associated with a loss of usable vegetable oil of around 4 to 8%.
Two methods of refining are used alternatively. First, there is chemical refining with the processing steps:
- possibly delecithination (water, heat, possibly diluted phosphoric acid )
- Degumming ( English Degumming ) (salt solutions, acids, phosphoric acid)
- Neutralization (deacidification) (caustic soda)
- Bleaching (discoloration) ( activated carbon , fuller's earth )
- additional winterization to remove waxes and high-boiling triglycerides is necessary for some vegetable oils.
- Deodorization (steaming) (water vapor)
Second, the physical refining with the processing steps:
- Degumming → discoloration → bleaching ( citric acid , phosphoric acid and fuller's earth), possibly winterization
- Damping → deodorization → distillative deacidification (pressure, heat)
During chemical refining, degumming first removes phospholipids , glycolipids , free sugars and metal ions from the oil. During the neutralization, free fatty acids , which are 0.3 to 0.6% in the oil, are separated off; the bleaching removes most of the colorants as well as residues of mucilage, soaps, trace metals and oxidation products. Steam distillation takes place during steaming in order to remove accompanying substances with an intense odor and taste.
Physical refining separates the fatty acids by distillation and therefore combines this treatment step with steaming. The oil must be completely degummed beforehand. The discoloration takes place either afterwards or coupled with the degumming. So far, chemical refining has been widespread, but with increasing environmental regulations, physical refining is becoming more important, as fewer chemicals are required for this, lower refining losses and wastewater are incurred, and the separated fatty acids in this process together with the distillate from deodorization for animal nutrition can be used. After refining, “fully refined vegetable oils” are available. Because of the high temperatures during deodorization, the content of certain desired accompanying substances and the nutritionally positive tocopherols in the oil is reduced.
In contrast to the hot pressing process, in which the crude oils (trub oils) are refined, this step is omitted with cold pressing , which is mainly used in decentralized oil mills . In this process, the crude oil (lees) is only filtered.
3-MCPD fatty acid esters can be found in all refined, i.e. purified, vegetable oils, the contents of which differ greatly in some cases. In 2011, 3-MCPD was classified as a "possible human carcinogen " by the International Agency for Research on Cancer (IARC) .
When refining the sugar, the raw sugar is pre-cleaned by washing with syrup and centrifugation ( affination ) and the affinade is further processed by dissolving it in water, decolorizing it with activated charcoal or kieselguhr and concentrating it in a vacuum. The white sugar (refined sugar) is brought to crystallization and obtained by centrifugation. Higher degrees of purity can be achieved through the (repeated) sequence of the process steps dissolving, decolorizing, filtering, crystallizing and centrifuging. In the thus obtained granulated sugar , the sugar refined sugar, is chemically almost pure sucrose (99.8 percent). Refined sugar or refined sugar is the legally protected name of a type of sugar .
In metallurgical practice, a fundamental distinction is made between fire refining and electrolytic refining. In fire refining, unwanted elements are removed either by converter processes or by oxidizing melting, depending on their degree of oxygen affinity . This then requires oxidizing furnace operation, supplemented by oxidizing melt additives ( melt treatment agents ). Electrolytic refining is used for higher degrees of purity. The respective raw metal, e.g. B. converter copper , becomes the anode and goes into solution , the electrolyte consists of a salt solution of the metal in question, and is deposited as a pure metal on the cathode . During electrolysis, even less noble accompanying elements go into solution, but without being deposited cathodically, nobler companions fall out as anode sludge (see electrochemical series ). Considerable amounts of silver and gold are obtained from the anode sludge, especially during copper refining . Electrolytic refining is used particularly for copper and nickel , but also for silver, lead and zinc , see Electrolytic Refining of Copper and Electrolytic Lead Refining .
Metals such as sodium or aluminum , the melting point of which is not very high, can also be obtained by melt refining, i.e. H. in liquid state, cleaned, e.g. B. by filtration using a ceramic filter or purge gas treatment or flotation . A more recent refining method is the zone melting process , which is used to obtain the purest silicon or silicon single crystals .
The refining of sea salt refers to the washing of the "raw salt" , which is mostly contaminated by the industrial harvest, in saturated brine , the renewed crystallization, centrifugation, drying and the addition of brighteners, flow aids and artificial iodination after grinding . After this treatment, the sea salt cannot be distinguished from rock salt , which is also refined, visually or in taste . Brine obtained through liquid mining is processed into evaporated salt using similar cleaning processes. Critics of the refining process criticize that the refining process loses minerals that are important to the body.
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