Study On Decolouring Technology Of Waste Oils In Catering Industry By Activated Clay

- Jan 22, 2018 -

The waste oil from the restaurant industry is extracted from the sump of the hotel and restaurant. After simple heating and dehydration, the oil extracted from the residue, neutralization and sedimentation is called "Huangshui Oil" by Cantonese. Its appearance is brown, with a special smell, contains many harmful ingredients, is inedible waste oil. In recent years, many have been infiltrated with edible oil by lawless elements or directly used for frying food, causing great harm to the general public's physical and mental health. It has also had a tremendous negative impact on the image of our country both at home and abroad. If not recycled, not only wasting valuable natural resources, but also cause secondary pollution. In view of this, the method of deep processing and comprehensive utilization of waste oil is studied, and it is proposed to fundamentally solve the problem of waste oil returning into the market of edible oil, polluting the environment and wasting resources.


Catering industry, the source of waste oil is more complex, recycling and simple refining of waste oil is still relatively deep color, and a strong special smell, a variety of impurities is also relatively large. Waste pigments affect the stability of waste oil and industrial use, hinder the deep processing of waste oil. In order to ensure the quality of waste oil to meet the color requirements of comprehensive utilization, it must be pretreated bleaching, saponification and preparation of detergent. Degradation of waste oil, not all the pigment off theoretically, but rather through the removal of pigments, trace metals, soap tablets, gums to get the improvement of the color of waste grease, waste oil for the processing of qualified raw materials.


In this paper, waste oil from the restaurant industry as raw materials, the use of activated clay adsorption decolorization of the decolorization effect on the various factors have been studied to determine a reasonable restaurant waste oil decolorization process conditions for the comprehensive utilization of waste oil saponification production of washing powder to provide qualified Suitable raw materials.


1 materials and methods

The amount and residual solute concentration are in accordance with the mathematical formula derived by Freundlich:

x / m = kCn

Where: x is the amount of adsorbed material; m is the amount of adsorbent; C is the amount of residual material; k, n is a constant. According to different k value, n value of the theoretical decolorization curve shows that the greater the k value of the adsorbent decolorization effect is better; n value is better, but can not therefore reduce the k value.


1.2 Experimental equipment and reagents


SA RT O RIU S-BS210S analytical balance; 721 spectrophotometer; electric mixer; oven temperature; EAF; restaurant waste oil; activated clay.

1.3 experimental method


1.3.1 Adsorbent selection


Decolorization is divided into adsorption decoloration and chemical decolorization, oil pretreatment generally used adsorption decolorization. Decolorization effect of a direct impact on product quality and cost, so the choice of suitable adsorbent is extremely important.


Commonly used adsorbents are activated carbon and clay. Activated carbon as adsorbent can selectively adsorb pigment and odor, but activated carbon adsorbent is expensive, high oil rate. White clay, also known as drift soil, the surface area of the acidification greatly increased after adsorption greatly enhance the performance, this clay called activated clay (or acid clay). Clay is commonly used in oil refining decolorizing agent. Activated clay than the natural clay k value, so the experiment using activated clay as a decolorizing agent, the decolorization of waste oil to explore the best decolorization process conditions.


1. 3. 2 Determination of waste oil color Currently there are two common international methods to assess the grease color or test off


1.1 Experimental principle


Adsorption method is to remove the pigment dissolved in the oil or colloidal particles dispersed in the oil is an effective method. Adsorption is a phenomenon of surface adsorption, which depends on the special affinity between the solute and the adsorbent. At a certain temperature, adsorption

Color process effect of the standard. For the light crude oil, deacidification oil, and more to Rover Pongere standard oil tank measured yellow and red chromaticity to represent; for dark grease, because the Lovibond colorimeter can not meet the colorimetric requirements, the more light The light transmission curve measured by a photometer or the light transmission rate measured at a fixed wavelength. Catering industry waste oil appearance was brown, are dark oil, so the choice of spectrophotometer colorimetric decolorization.


1. 3. 3 activated clay activation and dehydration Although the commercially available activated clay is finished product has been processed, but in the process of loading, transportation and so on will still inevitably absorb moisture in the air, so that the ability of decoloration of activated clay Reduced. To this end, the need to heat the activated clay before the experiment to remove moisture, improve the ability of decoloration of activated clay.


In this experiment, the activation and dehydration time of activated clay was selected by oven method. The method is as follows: accurately weighed about 5 g of activated clay placed in a crucible, dried in an oven at 150 to remove moisture. Heat different times, respectively, and then placed in a desiccator to cool and weigh. Finally, according to the formula: Moisture% (wt) = [(C- D) / (C-B)] × 100 to calculate the moisture content to determine the optimal activation time of activated clay. B is the mass of crucible lid (g); C is the crucible lid and the original mass (g); D is the crucible lid and the quality of the sample (g). Activation time is short, incomplete removal of water; activation time is too long, active clay easily degeneration and inactivation. Taking the above factors into consideration, the optimal activation time is 2 h.


1. 3. 4 activated clay bleaching process Waste oil in the laboratory under normal pressure bleaching, heating before adding clay, can reduce the oil due to oxidation of the darker. Product color under normal pressure bleaching get good color. The experiment is carried out atmospheric pressure decolorization, in order to avoid oxidation of the pigment, the color becomes darker, the use of activated clay before heating waste oil. 3.5 Determination of decolorization rate With distilled water as a reference, the absorbance was measured at a wavelength of 700 nm using a 1 cm cuvette. And the decolorization rate was calculated as [(A0 - A1) / A0] × 100, where A0 is the absorbance of the oil before decolorization and A1 is the absorbance of the oil after decolorization.

2 results and discussion


2.1 Determination of the maximum absorption wavelength

Absorbance of the test oil were measured at different wavelengths to determine the maximum absorption wavelength of waste oil, the results shown in Figure 1. The maximum absorption wavelength of waste grease is 700 nm.


The amount of activated clay on the decolorization rate


As can be seen from Figure 2, the decolorization rate of waste oil increased with the increase of the amount of activated clay. When the dosage was 5% ~ 6%, the decolorization rate reached more than 90% and slowly decreased. The reason may be because with the increase of the amount of activated clay, the amount of adsorbed pigment also increased; but with the continued increase in the amount of decolorization effect is not obvious. Therefore, the optimum amount of activated clay is 5%.

2.3 decolorization temperature on the decolorization rate


Research shows that when grease is in contact with a decolorizing agent, temperature has a significant effect on the decolorization process. Generally can not simply increase the temperature to improve the efficiency and effectiveness of decolorization, oil decolorization should have an optimum temperature range, it is necessary to optimize the upper and lower limits of decolorization temperature.


The effect of the initial decolorization temperature on the decolorization rate when added to the clay The initial decolorization temperature refers to the temperature at which the adsorbent comes into contact with the grease initially and has a significant effect on the decolorization effect.





It can be seen from Fig. 3 that when the initial temperature is low, the adsorption of pigment on the clay is poor due to the higher viscosity of the oil, and the decoloration effect of the clay is not good at the higher temperature, which may be due to the higher temperature Oil in the warming process can not be obtained when the evaporation of white clay water vapor escape caused by the role of pigment fixation caused by the lower thermal stability and produce new pigments and polymerization, isomerization, etc .; also accelerate the desorption, adsorption and decolorization effect Decline, fuel consumption increases; and high temperature contact with the adsorbent grease over time may occur double bond conjugation of fatty acids, and oils and fats to bring odor (soil taste), the operation is not economical. In addition, when the temperature is high, the free water in the activated clay evaporates rapidly, causing the crystal lattice of the bentonite or the montmorillonite, which is the main component of the activated clay, to be disintegrated. As a result, the activated clay loses part of the active surface before it has a chance to absorb the pigment. The decolorization effect of the same adsorbent dosage is lower than that of the cold oil addition adsorbent. It is determined that the best starting temperature for decolorization of waste oil in the catering industry is 60 .


The effect of final decolorization temperature on decoloration rate after addition of clay The final decoloration temperature is the final contact temperature at which the adsorbent decolorizes the oil. In a certain temperature range, increasing the contact temperature is conducive to the diffusion of acidic oxidation products to the surface of the adsorbent, but with the increase of temperature, the oxidation rate of the grease accelerates and the acidic oxidation product increases. Under a certain adsorbent, Rise, the decolorization effect rises. After a certain temperature, the decolorization effect but decreased. Therefore, the final decolorization temperature after adding clay on the decolorization rate also plays a decisive role, the results shown in Figure 4.



It can be seen from Figure 4 that when the final decoloring temperature is 70 , the decolorization rate is the lowest. The reason may be that the temperature is too low and the mass transfer rate is slow. When the temperature exceeds 120 , mass transfer is not the decisive factor, At the same time accelerated the accelerated oxidation of fat, the color will deepen, so the final decolorization temperature of 120 is appropriate.


2.4 decolorization time decolorization rate


Decolorization time affect the decolorization rate of waste oil, affecting the adsorbent and pigment adsorption equilibrium. With proper stirring, the activated clay can quickly reach equilibrium with the pigment, without decolorization for a long time. The effect of decolorization time on decolorization rate is shown in Figure 5.



It can be seen from Figure 5 that the decoloration rate increases with the extension of time within the range of 10 ~ 25 min. The longer the stirring time, the more contact of the adsorbent with the oil, the more the diffusion of acidic oxides to the adsorbent surface, the faster the mass transfer rate, Adsorption increased, so the adsorption effect increased significantly.

When the decolorization time exceeds 25 min, the adsorption effect decreases. This is probably because the adsorbent is saturated and the fading rate slows down. Further lengthening the mixing time will accelerate the oxidation rate of waste grease, which will lead to the deterioration of the quality of waste grease, including the recovery of oil color and the rise of acid value, so the decolorization rate will decrease instead.


In summary, decolorization time of 25 min, the highest decolorization rate. So choose 25 min for the best decolorization time.



After discoloring of waste oil saponification value greater than 185 mg / g, in line with the oil industry soap requirements, is the soap soap industry's main raw material. Made of soap-based detergent products with strong detergency, foam thick and durable characteristics (another study). The decolorization of the main components of the restaurant waste oil analysis shows that the waste oil is a natural fat restaurant, is a mixture of various vegetable and animal fats and oils, is C16 to C18 fatty acid triglycerides. Waste oil into the waste oil (also known as water) and fried oil. The complexity of the sources of waste oil, chemical composition is complex, is a mixture of a variety of natural oils, at room temperature is a thick semi-solid, with a special smell, no fragrance, not edible. After decolorization of the old oil chemical composition is relatively simple. Such as the collection of western fast food restaurant frying the old oil, its main chemical composition is palmitic acid (C16 H32 O2) ester, stearic acid (C18 H36 O2) ester and oleic acid (C18 H34 O2) ester, Similarly, the fatty acid carbon chain length is mainly C16 and C18, can be saponified into fatty acid sodium or potassium fatty acid (potassium salt soluble, but the price is higher, generally do not) and other surfactants to replace the environment and Eco-damaging sodium dodecyl benzene sulfonate (LAS) and nonylphenol ethoxylates (TX-10) surfactants produce detergent. In the saponification directly into other detergent aids such as sodium carbonate, sodium tripolyphosphate (ST PP), sodium metasilicate, sodium chloride can be made of high performance washing powder.


Fat is a renewable natural resource. Oil and its saponified various components easily biodegradable, and vulnerable to microbial decomposition during sewage treatment, rivers, lakes and other water pollution less, which is the biggest feature of waste oil made washing powder, at the same time , The low price of waste oil, compared with the organic synthetic detergent also has great economic advantages.


2.5 stirring speed on the decolorization rate


During decolorization, the adsorption of pigment on the adsorbent is carried out on the surface of the adsorbent, which belongs to the non-uniform physicochemical reaction. Experimental studies have shown that a good mixing oil and adsorbent can make uniform contact opportunities, which is conducive to the establishment of adsorption equilibrium, and avoid local long-term exposure caused by deterioration of oil quality. Atmospheric pressure decolorization operation, the stirring intensity to achieve uniform suspension of the adsorbent in the oil can be, not too strong, to reduce the introduction of air mixing and oxidation of oil, color deepening.


2. 6 activated clay added on the decolorization rate of the impact


A certain amount of adsorbent added in batches of oil in a full amount of oil into the decolorization effect. This can be thought of as a "concentration effect" that causes a new balance between adsorbent and pigment. A total investment of adsorbent can only establish an equilibrium adsorption, and batch addition of adsorbent, it will play a new adsorbent activity, with the balance of the previous balance of the remaining dye to establish a new adsorption equilibrium. Experimental results show that the amount of clay used under certain circumstances, the use of 3 times the method of adding activated clay can improve the decolorization rate.


2. 7 decolorization of waste oil composition, quality and saponification product application prospects


As the waste oil in the collection, storage, processing, refining process with water, air, microorganisms and other effects, resulting in hydrolysis, oxidation, acidification, cracking and other reactions, resulting in deterioration of the fat. Although the appearance and physico-chemical indexes of waste oil in the catering industry have changed after decolorization, the content of waste oil in the restaurant industry has been changed by GC-MS, TLC, column chromatography, IR, A ES), atomic absorption spectroscopy (AAS) and other instrumental means of waste oil and cooking oil were analyzed and compared, found in decolorization of waste oil still exists

3 Conclusion


Experimental studies show that the activated clay can take off the pigment of waste oil. The optimum conditions of decoloration are as follows: the amount of activated clay is 5%; the initial decolorization temperature is 60 ; the final decolorization temperature is 120 ; the decolorization time is 25 min. Decolourized waste oil color and physical and chemical indicators have reached the requirements of saponification production of washing powder. Waste oil production of detergent can reduce the pollution of food waste water on the environment, while its products with low cost, good washing performance and environmental pollution characteristics.

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