Tall oil is formed during sulphate pulping. Fatty acids, which are obtained from crude oil, are widely used: the production of soaps, coatings, epoxy resins, adhesives, use as additives in the manufacture of various materials (rubber, concrete, paper and others).
Description
Tall oil (sulfate) oil is a liquid mixture of organic compounds (mainly higher fatty and resin acids), which has a dark color and a pungent odor.
The substance has the following physicochemical characteristics:
- viscosity (at t = 40 ° C) - from 410 to 1660 cSt;
- density at +20 ° C - 994-1001 kg / m 3 ;
- heat capacity - from 1.6 to 4.1 kJ / (kg · K);
- acid number - 158-163;
- flash point - 221 ° ;
- autoignition temperature - 304-311 ° ;
- thermal conductivity at normal temperature - 0.13-0.15 W / (m · K).
The properties of tall oil (its solidification temperature, viscosity) are improved by adding additives from phenol-formaldehyde resins, alcohols and other compounds.
The density, content of resin acids, acid number and saponification number depend on the composition of wood raw materials (in the order of decreasing values of these indicators):
- conifers;
- a mixture of coniferous and hardwood;
- hardwood.
Tall oil acid salts are called tallates.
Getting
Sulphate pulping is carried out by treating wood chips with an aqueous solution of hydroxide and sodium sulfide. Currently, this technology is one of the leading in the pulp industry. Under the action of the above reagents, saponification of resin and fatty acids occurs. They turn into black liquor, which is a sulfate soap. The latter is fully used for processing into tall oil.
Evaporation of the liquor leads to the separation of the fraction of low density, which floats to the surface. The output of the substance is in the range of 100-140 kg per ton of raw material. Crude tall oil is obtained by 2 methods:
- Periodic. Sulphate soap is pumped into the reactor, where it is affected by a 30% H₂SO₄ solution. The decomposition process lasts 2-3 hours, then the same time the mixture settles directly in the reactor. The liquid exfoliates into 3 layers, the upper of which includes oil. It is pumped out for further washing and drying.
- Continuous. First, the soap is washed with a liquor solution, then passed through a homogenizer and filtered from solids. Mixing with H₂SO₄ is carried out continuously in the pump. Separation into fractions occurs in a separator, from which all components are quickly removed to tanks.
The amount of tall oil obtained depends on several parameters. It:
- composition of the source material;
- sulphate soap moisture;
- the quality of its washing;
- thorough separation of fractions (the middle fraction, consisting of lignin, can take with it up to 50% of the oil);
- decomposition technology.
Composition
The following main factors affect the chemical composition of the oil:
- type of wood and its species;
- time of year during which the harvesting of raw materials;
- the duration and method of storage of wood;
- process conditions.
Tall oil contains the following substances:
- resin or rosin acids (palustric, abietic, neo-abietic, dihydro- and tetrahydro-abietic) - 40-45%;
- unsaturated fatty acids (oleic, stearic, linolenic, linoleic, palmitic) - 40%;
- unsaponifiable substances (aliphatic, diterpenic hydrocarbons, stearin, phytosterol, alcohols and others) - 12%;
- hydroxycarboxylic acids - about 5%.
Purification without distillation
Of greatest practical value are the individual components of tall oil. The separation of fatty acids and other components is carried out in several ways:
- using solvents and mixtures thereof (liquid propane, furfural, diacetone alcohol, gasoline hydrocarbons and others);
- reaction with urea;
- decarboxylation (if you want to isolate only fatty acids);
Distillation
In industrial conditions, the separation of fractions is carried out according to a two-stage technology:
- Distillation. When heated to 200 ° C, volatile substances are distilled from tall oil.
- Rectification (separation of the mixture due to mass and heat exchange with steam).
Another way to modify the oil is oligomerization, which results in fatty acid dimers. In technological installations in the USA, this process is carried out at a temperature of 230-250 ° C, under pressure and in the presence of a catalyst, montmorillonite. In Russia, oligomerization is carried out by the method of autooxidation. Tall oil is heated to 195 ° C, while continuously passing air through it.
Application
After distillation and rectification, several types of organic compounds are obtained, which are widely used:
- Tall oil fatty acids with a purity of up to 97% (paint and printing industry).
- Tall oil rosin (paper and soap manufacture, manufacture of glues for cardboard and paper, cable industry).
- Distilled tall oil (soap making, production of varnishes, resins, paints, emulsifiers, linoleum; rubber regeneration, introduction of sand-clay injection molds as a binder).
- Tall pitch (production of asphalts, fiberboard).
Crude, non-distilled oil is used for the following purposes:
- fiberboard impregnation for hardening and hydrophobization;
- additive in the production of mineral and glass wool (improvement of strength properties in conditions of high humidity);
- manufacture of flotation agents-foaming agents;
- softening additive for rubbers;
- production of resins and paints and varnishes (paints, varnishes), plasticizers;
- lubricants and lubricants for processing textile materials;
- additive in bitumen to improve its adhesive properties.
Tallates are used in the manufacture of the following substances:
- oil paints and drying oils (an additive to accelerate their drying);
- chemical reaction catalysts;
- insecticides;
- wetting agents;
- hardeners of asphalt and waxes;
- waxed paper for corrosion protection.
Tall oil also contains a large amount of sterols (up to 3%) compared to other vegetable oils. These substances are biologically active and promising for use in medicine, cosmetology and the food industry.