Razgovorov P.B., Razgovorova M.P., Gordina N.E., Prokof’ev V.Yu.

Ivanovo State University of Chemical and Technology, Russia

Granulated Sorbents Based on Kaolin Clay and Adsorption of Undesirable Impurities from Sunflower Oil

Sorbents based on natural clay, which are often referred to as bleaching earths, are widely used for fine refining of vegetable oils. In an industrial scale, montmorillonite clay is most widely used as bleaching earth to remove color and odor from oils of vegetable and animal origin, e.g. cottonseed, sunflower or rapeseed oils. As an alternative to montmorillonite clay, kaolin clays have been used to bleach vegetable oils. With chemical positions, the introduction of kaolin clay in oil is reasonable because there are both acidic and basic sites on the surface. Clay minerals can be modified in different ways in order to obtain the desired properties. Typically, solutions of mineral acids and alkalis are used for these purposes. Often, for acid modification clay, sulfuric or hydrochloric acids are employed. However, treatment with strong acid provoke an amorphization resulting in the formation of an amorphous silica type phase.

The objective is to study the effect of kaolin clay modification with “soft” acid and base on the acid-base properties of the surface, porous structure and adsorption of undesirable impurities from sunflower oil on the granulated sorbent dynamically.

In this work, clay from the Veselovskoe deposit (Ukraine) was used. It was a form of the pale gray powder. As modifiers of the above clay we used glacial acetic acid and liquid sodium glass with concentration 20 wt% and silicate modulus 3.0. Sample preparation included mixing a clay with the liquid phase (water, acetic acid, or liquid sodium glass) to optimal molding moisture, molding on the piston extruder into cylindrical granules with the size 3×3 mm, dry-curing, and drying for 4 h at 100–110°С. The combined modification included the treatment with acetic acid, drying, and mixing with a solution of alkaline agent. Forming and drying the granules were analogous.

It was shown that the surface of kaolin clay of the Veselovskoe deposit has all kinds of surface centers, namely, the Lewis and Brönsted acidic and basic sites. The modification of clay with acetic acid increase the number of Brönsted sites, which are formed by the acid molecules adsorbed in monodetante form. The composition of clay and liquid sodium glass (alkaline agent) is characterized by the basic sites and mobile exchange cation. The composition of the clay modified with acetic acid and the liquid sodium glass produces all kinds of surface sites, which are listed above.

It was found that the modification of clay with acetic acid yields granular sorbent with a developed surface area. The alkali treatment leads to the disappearance of micropores [1]. As a result, the specific surface area and porosity significantly decrease. The acid and then alkali treatment of the clay yields the bipore structure with a reasonably high specific surface area (Tabl. 1).

Table 1 Physical properties and pore structure (by data on the sorption-desorption of nitrogen at 77 K) of the sorbents prepared from clay of the Veselovskoe deposit

N	Modi-fier*	Appa-rent density by water, g/cm^3	Strength of granule, MPa	Oil absorp-tion, wt%	Average pore diameter, nm	Micro-pore volume, mm^3/g	Total pore volume, cm^3/g	Speci-fic surface area, S, m^2/g
1	Water	1.87	3.1	9.57	19.0	4.47	0.126	26.7
2	AA	1.27	2.1	16.45	19.7	3.12	0.141	28.7
3	LSG	2.43	17.3	1.44	18.7	0.39	0.007	1.6
4	AA and LSG	1.93	4.5	14.31	22.1	6.69	0.112	20.2

* AA – acetic acid; LSG – liquid sodium glass

Table 2 Sunflower oil indices after adsorptive refining on the sorbents prepared from clay of the Veselovskoe deposit

No	Modifier of the clay	Oil indices (refining degree, %)
		acid value, mg KOH/l	peroxide value, mmol/l	phosphorated substances content, mg/l
1	Water	1.9 ± 0.06 (61.9)	1.9 ± 0.05 (68.3)	2.46 ± 0.09 (0.3)
2	AA	3.0 ± 0.07 (39.1)	1.8 ± 0.05 (70.0)	0.26 ± 0.03 (89.4)
3	LSG	0.6 ± 0.04 (87.7)	5.1 ± 0.07 (15.0)	0.56 ± 0.04 (77.2)
4	AA and LSG	0.8 ± 0.04 (84.6)	1.1 ± 0.04 (81.7)	0.38 ± 0.04 (84.6)
Original sunflower oil		4.9 ± 0.08	6.0 ± 0.08	2.46 ± 0.09

It was shown that the adsorption of free fatty acids from sunflower oil occurs on Lewis acid sites and basic sites on the surface of the sorbent (Tabl 2). Peroxide compounds are adsorbed on Brönsted and Lewis acid sites. Phosphorated substances interact with indicated above sites on the surface of the sorbent.

Reference:

1. Prokof’ev V.Yu. at. al. // Rus. J. Appl. Chem. 2011. 84 (11). pp. 1866-1870. DOI: 10.1134/S107042721111005X