JP7651108B2 - How to recycle food waste - Google Patents

Description

(1) Date: March 1, 2021 (2) Name and location of the meeting: 2020 National University Corporation Yamanashi University, Faculty of Engineering, Department of Applied Chemistry Graduation Thesis Presentation, Room A2-21, Faculty of Engineering, Yamanashi University (4-4-37 Takeda, Kofu, Yamanashi Prefecture)

The present invention relates to a method for recycling food waste, for example by extracting higher fatty acids from coffee grounds and green tea leaves, and by making effective use of the residue.

The treatment of municipal waste has become an important issue from the standpoint of cost and environmental concerns, and there is a need for the development of various recycling technologies as part of biomass utilization technology.

Conventional techniques relating to the processing of coffee husks include the inventions described in the following Patent Documents 1 to 3, for example.

Patent Document 1 discloses a method for producing carbonized material at a relatively low temperature with a high recovery rate by hydrothermally carbonizing plant-based raw materials including coffee husks in ion-exchanged water at a temperature of 150 to 350°C.

Patent Document 2 discloses a biomass processing method that efficiently ferments biomass such as coffee grounds into methane.

Patent Document 3 discloses a methane fermentation method using coffee grounds, which involves solubilizing the coffee grounds by heating them at 60°C or higher and adding a dilution medium in an amount equivalent to 5 to 10 times the dry weight of the coffee grounds.

JP 2016-150894 A JP 2015-003280 A JP 2011-206737 A

The coffee grounds processing technologies described in the above-mentioned Patent Documents 1 to 3 are basically aimed at producing carbonized material and using it effectively as fuel.

However, when taking into consideration the manufacturing costs of the carbonized material, its value and effectiveness as a fuel, and its impact on the environment, it cannot necessarily be said to be an efficient recycling technology.

The present invention aims to provide a more efficient recycling method for the treatment of food waste such as coffee grounds and green tea leaves and for the effective use of the treated materials.

The food waste recycling method of the present invention is characterized by producing hydrothermal char containing higher fatty acids by hydrothermal treatment of food waste.

In the present invention, food waste that can be used includes, for example, coffee grounds and grounds from tea extracts such as green tea, black tea, and barley tea.

By extracting higher fatty acids from the hydrothermal char obtained by the present invention, depending on the type of higher fatty acid, it can be effectively used as a raw material for cosmetics, detergents, paints, synthetic resins, etc. In addition, the residue from which the higher fatty acids are extracted can be used for fuel recycling and as carbonized materials such as activated carbon.

Hydrothermal treatment is carried out at heating at about 150 to 220°C, preferably 150 to 200°C. The yield of hydrothermal char is high when the hydrothermal treatment temperature is around 180°C, but the yield tends to decrease when the temperature exceeds 220°C.

The hydrothermal treatment time varies depending on the type of food waste, but is preferably about 3 to 48 hours, more preferably about 3 to 24 hours. The longer the hydrothermal treatment time, the higher the yield of hydrothermal char tends to be, but depending on the type of food waste, the rate of increase in yield is low or unclear, and long treatment times are not efficient. In addition, when attempting to utilize the organic acid in the residual liquid, for example, for dissolving slag or eluting metals, the longer the hydrothermal treatment time, the lower the acidity (the higher the pH), so the hydrothermal treatment time is preferably within 24 hours, or within 12 hours.

According to the present invention, by subjecting food waste such as coffee grounds and green tea grounds to hydrothermal treatment, it is possible to produce hydrothermal char containing higher fatty acids such as palmitic acid, and higher fatty acids can be obtained. By extracting higher fatty acids from this hydrothermal char, they can be effectively used as raw materials for cosmetics, detergents, paints, synthetic resins, etc., depending on the type of higher fatty acid. In addition, the residue from which the higher fatty acids have been extracted can be used as fuel, etc.

This graph shows the hydrothermal char yield for coffee grounds, green tea grounds, barley tea grounds, and black tea grounds in tests related to the food waste recycling method of the present invention, when the hydrothermal treatment temperatures were 180°C and 220°C. 2 is a graph showing the pH of the residual liquid after hydrothermal treatment in the test of FIG. 1. This is a graph showing the structural analysis by X-ray diffraction of hydrothermal char obtained by hydrothermal treatment for 24 hours for coffee grounds, black tea grounds, green tea grounds, and barley tea grounds in the food waste recycling method of the present invention. This graph shows the structural analysis by X-ray diffraction of hydrothermal char obtained at various treatment temperatures (180°C, 220°C) and times (3 hours to 24 hours) when coffee grounds were hydrothermally treated. This is a graph showing the structural analysis by X-ray diffraction of hydrothermal char for each treatment temperature (180°C, 220°C) and time (12 hours, 24 hours) when green tea was hydrothermally treated. This is an SEM photograph taken with a scanning electron microscope (hereinafter referred to as SEM) of coffee grounds char after coffee grounds were hydrothermally treated at 220°C for 24 hours (1 day). 1 is a graph of X-ray diffraction intensities of palmitic acid and cetanol.

Tests conducted to confirm the effects of the present invention will now be described.
Raw material husks: coffee, green tea, barley tea husks, black tea husks Hydrothermal treatment conditions: 180°C, 220°C, 3 to 24 hours Solvent: H ₂ O

After the synthesis, the black residue (hydrothermal char) was recovered by solid-liquid separation.
The test results are shown in Figures 1 to 5.

Figure 1 is a graph showing the hydrothermal char yields for coffee grounds, green tea grounds, barley tea grounds, and black tea grounds when the hydrothermal treatment temperatures are 180°C and 220°C, and Figure 2 is a graph showing the pH of the residual liquid after hydrothermal treatment.

In these graphs, coffee grounds are marked with a ● when hydrothermally treated at 180°C, a ◯ when hydrothermally treated at 220°C, green tea grounds are marked with a ▲ when hydrothermally treated at 180°C, a △ when hydrothermally treated at 220°C, barley tea grounds are marked with a ■ when hydrothermally treated at 180°C, a □ when hydrothermally treated at 220°C, black tea grounds are marked with a ▼ when hydrothermally treated at 180°C, and a ▽ when hydrothermally treated at 220°C.

When coffee grounds were hydrothermally treated at 180°C (●) versus 220°C (◯), the yield of hydrothermal char was higher when hydrothermally treated at 180°C.

When coffee grounds were hydrothermally treated at 180°C, the yield of hydrothermal char was highest when hydrothermally treated for 24 hours. When coffee grounds were hydrothermally treated at 220°C, the yield of hydrothermal char was highest when hydrothermally treated for 12 hours, but the difference due to the difference in treatment time was not very clear.

The pH of the organic acids in the residual liquid from the coffee grounds tended to be slightly higher at 220°C than at 180°C, but no significant difference was observed in relation to the hydrothermal treatment time.

When green tea leaves were hydrothermally treated at 180°C (▲) and 220°C (△), the yield of hydrothermal char was higher when hydrothermally treated at 180°C.

For green tea leaves, the yield tended to decrease when hydrothermal treatment was performed for a long period of time at both 180°C and 220°C. The pH of the organic acids in the residual liquid from green tea leaves tended to be higher the longer the treatment (shorter treatment was more acidic). From this, it is believed that for green tea leaves, hydrothermal treatment for a period of 3 to 12 hours is preferable rather than 24 hours.

Figure 2 also shows that when comparing coffee grounds and green tea grounds, the pH of the organic acids derived from coffee grounds is lower.

Although the amount of data for barley tea leaves and black tea leaves was not necessarily sufficient, results for black tea leaves were similar to those for green tea leaves, and results for barley tea leaves were intermediate between those for coffee leaves and green tea leaves.

Figure 3 shows a graph of the structure analysis by X-ray diffraction of hydrothermal chars obtained by hydrothermal treatment of coffee grounds (CF), black tea grounds (ET), green tea grounds (GT), and barley tea grounds (BT) at 220°C for 24 hours. E represents those washed with ethanol.

In CF220/24, which is a hydrothermal char obtained from coffee husks, two highly intense diffraction peaks (shown by dotted lines in Figure 3) were observed at around 21.4° and 23.7°.

The characteristic high intensity peaks of palmitic acid are 2.7°, 7.22°, 21.5°, and 24.1°, and palmitic acid was detected by gas chromatography. As for higher fatty acids, stearic acid was detected in addition to palmitic acid. For reference, the X-ray diffraction intensity graphs of palmitic acid (upper side) and cetanol (lower side) are shown in Figure 7.

Two intense diffraction peaks were observed around 21.4° and 23.7° for GT220/24, which was obtained by hydrothermal char from green tea leaves.

In the case of CF220/24E and GT220/24E, higher fatty acids such as palmitic acid were removed from the hydrothermal char by washing with ethanol, so the diffraction peaks of palmitic acid, etc. disappeared from the hydrothermally treated char.

Figure 4 is a graph showing X-ray diffraction analysis of coffee grounds hydrothermally treated at 220°C for 3, 6, and 24 hours, and at 180°C for 12 and 24 hours. The coffee grounds hydrothermally treated at 220°C are shown as CF220/3, CF220/6, and CF220/24, while the coffee grounds hydrothermally treated at 180°C for 12 and 24 hours are shown as CF180/12 and CF180/24.

Chars hydrothermally treated at 220°C showed clear peaks at around 2.5° and 21.4° for CF220/3 and CF220/6, and peaks were also observed for CF220/24.

Char hydrothermally treated at 180°C has a clearer peak than char hydrothermally treated at 220°C, and in addition to the peaks near 2.5° and 21.4°, a weak peak is also seen near 23.5°. Between CF180/12 and CF180/24, the peak is clearer in the case of CF180/12.

Figure 5 is a graph showing the X-ray diffraction analysis of green tea leaves that were hydrothermally treated. The samples that were hydrothermally treated at 220°C for 24 hours are shown as GT220/24, and the samples that were hydrothermally treated at 180°C for 12 and 24 hours are shown as GT180/12 and CF180/24.

In GT220/24, a relatively clear peak is seen at around 21.4°, but in GT180/24 and CF180/12, the X-ray diffraction intensity at the peak is higher, and peaks can be confirmed at around 2.5°, 21.4°, and 23.5°.

From the above test results, it was confirmed that hydrothermal char obtained by hydrothermal treatment of coffee grounds, green tea grounds, etc. contains higher fatty acids such as palmitic acid.

Figure 6 shows an SEM image of coffee husks hydrothermally treated at 220°C for 24 hours. (b) is an enlarged image of (a).

The generation of spherical char was also observed in the photograph of Figure 6. Therefore, it is expected that the carbonaceous material derived from coffee can be used as porous carbon, for example, for ethylene adsorption.

Claims (3)

A method for recycling food waste, which comprises hydrothermal treating the food waste to produce hydrothermal char containing higher fatty acids, characterized in that the hydrothermal treatment is carried out at a temperature of 150 to 200°C for 3 to 48 hours . The food waste recycling method according to claim 1, characterized in that the higher fatty acids are extracted from the hydrothermal char. 3. The method for recycling food waste according to claim 1 or 2 , wherein the food waste is coffee or green tea extract grounds.