DEVELOPMENT OF AN INDUSTRIAL TECHNOLOGY FOR THE PRODUCTION OF SOLUBLE HUMATES

N. M. SMOLYANINOVA, S. I. KHOROSHKO, A. N. MOSKALCHUK

(Presented at the scientific-methodological seminar of the Faculty of Chemical Technology)

Recently, humic acids have been finding ever wider application in various branches of the national economy. In the form of soluble sodium salts (humates), they are successfully used as stabilizers for clay solutions employed in drilling oil wells, and also for preparing a dye for wood. Possessing good surface-active properties, humic acids have found application in the storage-battery industry as an expander for the positive plates of batteries. Finally, the use of humic acids in the form of soluble humates in agriculture as growth stimulants is very promising. Their high effectiveness has been demonstrated in numerous works by Professor L. A. Khristeva and her collaborators, and by other authors [1, 2].

At present, industrial production of humic acids is carried out at the Tyumen Battery Plant.

Solid sodium humates for the needs of the furniture industry are produced in small quantities in Latvia at an industrial combine. Both products are in short supply.

Taking into account the increased demand for humic preparations, it is necessary to organize their large-scale industrial production. This will make it possible more quickly to introduce humic acids and other preparations based on them into industry and agriculture.

The existing technological schemes have a number of serious shortcomings, namely: 1) the periodic nature of the process and, as a consequence, the cumbersome design of the equipment, the difficulty of automation, the low productivity of the installations, and high operating costs; 2) high heat consumption; 3) large product losses and a low coefficient of extraction of humic acids.

Of course, if the question is posed of industrial production of acids at the modern level, then only a continuous process can be considered.

The main difficulty in developing a continuous technology for obtaining humates or humic acids is the extremely long duration of the process of extracting them from the fuel, caused by the low diffusion rates of the active part of the alkaline reagent into the solid particles and of the humates formed from the solid substance into solution, as well as by the very specificity of humic acids as high-molecular organic acids possessing the properties of a colloid. In addition,

The separation of unreacted raw material from the humate solution is difficult, since the ground fuel, especially peat, swells strongly and is partially peptized in the alkaline solution, forming a very stable suspension that settles very slowly and is practically impossible to filter.

One of the factors that makes it possible to intensify this process is temperature. It is known that heating a peat–alkali suspension to a temperature of 80–100°C makes it possible to increase significantly the rate of formation and dissolution of humates.

Of considerable interest is the so-called dispersion method for extracting humic acids, based on fine grinding of the initial raw material in an alkaline medium without heating. According to G. M. Volkov [2, 3], this technique provides an increase in product yield and a reduction in process duration, making it possible to reduce costs substantially.

In some cases, the ultrasonic method of obtaining humates may have great prospects. A. P. Grishin and V. Yu. Zorin [4] showed that under the action of an ultrasonic field the process of extracting humic acids from brown coal in an alkaline medium is accelerated approximately 20-fold.

In the peat problem laboratory of the TPI, studies were carried out to determine the possibilities of dispersion and ultrasonic methods for intensifying the process as applied to peat. The influence of the type of alkaline reagent, process temperature, and intensity of mixing of the peat–alkali mixture, as well as the degree of dispersion of the peat, on the rate of extraction of humic acids was studied. In addition, various methods of separating the peat–humate suspension were tested—settling, filtration, centrifugation, and the action of polyacrylamide (as a flocculant) [5].

On the basis of the results obtained by us, as well as an analysis of the operation of existing enterprises and literature data [1, 2, 3], the following conclusions were drawn.

1. The use of ultrasound gives a certain positive effect; however, orientation toward the use of this method in industry is at present inadvisable because of the absence of practically acceptable designs of ultrasonic reactors.

2. Mechanical dispersion of peat in an alkaline medium makes it possible to intensify significantly the process of extracting humic acids from peat and may be used as the basis of the technological process being developed in combination with subsequent heating of the finely dispersed peat–alkali suspension to a temperature of 80–100°C. This will make it possible to reduce the duration of the process of treating peat with an alkaline solution to 30–60 minutes and to carry out extraction at a peat-to-alkaline-solution ratio of 1:10 instead of 1:100.

3. Solutions of caustic soda or soda ash may be used as the reagent; the latter is considerably cheaper, and its use is more economical.

4. For separating the humate solution from the peat residue, it is advisable to use a settling-type centrifuge.

5. It is advisable to organize the production of solid humate or of its concentrated solution, which is more economical when centrally supplying various consumers (agriculture, the furniture industry, oil fields). Concentration of the solution is easily accomplished by evaporation.

The conclusions presented were used as the basis for developing a continuous version of the technological scheme for the process of obtaining humates on the basis of

peat from the Tagan deposit in Tomsk Oblast. The capacity of the plant was determined approximately, based on the demand for humates in the main districts of the oblast with developed vegetable growing, since the use of humic fertilizers is most effective specifically for vegetable crops.

On the basis of the application rates recommended by L. A. Khristeva [1], the annual demand for 100% humates was determined to be 60 tons. With a humic-acid content in air-dry peat of 20.6%, peat consumption is 260 t/year.

A 2% solution of calcined soda was used as the reagent; it is considerably cheaper than sodium hydroxide. Despite its lower activity, soda provides a sufficient degree of extraction of humic acids when fine dispersion of the peat in an alkaline medium is combined with subsequent heating of the mixture to 80–100°C for 0.5–1.0 hour with intensive stirring. The ratio of the weight of peat to the volume of soda solution is 1 : 10.

For separation of the peat–alkali suspension, a settling centrifuge 2NOGSh-300 (6) is used.

The technological flow scheme of the process is shown in Fig. 1.

Air-dry peat in the form of crumb is fed from the hopper (1) by a bucket elevator (2), through an intermediate hopper (3), into a hammer crusher (4), where it is comminuted to pieces no larger than

Fig. 1. Technological flow scheme for obtaining sodium humates. 1—raw-material hopper; 2—elevator; 3—intermediate hopper; 4—hammer crusher; 5—screw mixer; 6—tank for alkali solution; 7—tank for preparing the alkaline solution; 8—mechanical disperser; 9—reactor; 10—settling centrifuge; 11—evaporator; 12—surface condenser; 13—vacuum pump; 14—humate receiver; 15—pump; 16—ejector.

1–2 mm. The comminuted peat is mixed in the screw mixer (5) with the soda solution supplied from the tank (6). Then the peat–alkali mixture enters the mechanical disperser (8), from which it is fed to the reactor (9). In the reactor, final extraction of the humic acids takes place while the suspension is heated and stirred with live steam entering through the ejector (16). The unreacted peat is separated from the humate solution in a settling-type centrifuge (10). The latter

has two screws, which makes it possible to wash the precipitate with a separate discharge of the wash waters, which (in order to reduce losses of humates) are fed into vessel (7) for preparing the soda solution.

The washed precipitate goes to the dump, while the weak solution of humates (2.0%) is evaporated in the evaporator (11) to a concentration of 15% and enters the receiver (14).

The secondary steam from the evaporator is condensed in the surface condenser (12). The hot condensate can be used for washing the precipitate in the centrifuge. Vacuum in the system is created by a vacuum pump (13).

As the economic calculation showed, the full cost of the humates was 465 rubles per ton. The high cost of the product is explained by the low productivity of the unit, since a large part of the costs (about 60%) falls on wages and operating expenses. These costs can be reduced by constructing larger units.

The economic effect from the use of sodium humates averaged 8–10 rubles per hectare of sown area.

LITERATURE

1. Collection, Humic Fertilizers. Theory and Practice of Their Application. Part I. Selkhozizdat of the Ukrainian SSR, Kiev, 1957.

2. Collection, Humic Fertilizers. Theory and Practice of Their Application. Part II. Selkhozizdat of the Ukrainian SSR, Kiev, 1962.

3. G. M. Volkov. On the technology of producing humic acids. Proceedings of the Institute of Fossil Fuels, Academy of Sciences of the USSR, vol. XII, 65–76, 1961.

4. A. P. Grishin, V. Yu. Zorin. Ultrasonic method for isolating humic substances. Proceedings of the Grozny Petroleum Institute, coll. 25, No. 3, 59–62, 1961.

5. N. M. Smolyaninova, A. N. Moskalchuk. Study of the process of obtaining humic acids from peat. Izvestiya TPI (in press).

6. Development of a technology for obtaining humic acids based on peat. Report on topic 162/63, Tomsk, 1965.

7. Centrifuges. Catalog-reference book. Mashgiz, 1955.