Study on the application of KOH to produce activated carbon to realize the utilization of distiller’s grains

The distiller’s grains in a liquor factory are selected as the main material to study the preparation of activated carbon with KOH activation. The solid-to-liquid ratio A, KOH concentration B, activation temperature C, activation time D are regarded as variables to produce single factor experiment. The results show that the best preparation conditions of various factors are: 50% KOH concentration, solid-liquid ratio of 1:4, activation temperature of 750°, activation time of 2.0h. The L9 (34) orthogonal experiment is carried out by selecting three levels from each single factor, showing that the importance order of the factors is: B > A > C > D. In addition, when KOH solution concentration is 60%, the solid-liquid ratio is 1:5, activation temperature is 700°, and activation time is 2.0h, the performance of the preparation of activated carbon is the best.


Introduction
Many plants are widely used as materials for the preparation of activated carbon, for example, corncob, coconut, almond shell, peanut shell, bamboo, etc.Huang Lihua [1] used residual activated sludge to prepare activated carbon , studied the effect of preparation conditions on the adsorption performance and yield of activated carbon by using different activated method to prepare activated carbon. Song Lei [2] used waste tea to prepare activated carbon, studied the best preparation conditions and the control of pore structure. Xie Xinping [3] used phosphoric acid activating eucalyptus chips to prepare activated carbon and so on.
The lees are the main byproducts of the brewing industry. In addition to the consumption of carbohydrates after fermentation, protein, fat, vitamins, organic acids, amino acids, nucleic acids and many other substances content all be increased [4][5] . Therefore, the lees are usually used to make animal feed and its additives [6][7] , pit mud fermentation nutrient, cultivation of edible fungus [8] , brewed soy sauce and vinegar [9][10][11] , fertilizer [12] and so on.
China is a big producer of liquor. As a subsidiary products with a large amount, lees will rot if they are not treated timely. It will not only be a waste of resources, but also will seriously pollute the environment. Therefore, using lees for the preparation of activated carbon can realize "ecological" to the enterprise and have a vital significance for China's resources recycling and environmental protection.

Experimental methods
In this experiment, KOH activation method was used to prepare activated carbon, the main influencing factors of activated carbon's final yield and quality are as follows: (1) the concentration of KOH--A; (2) solid-liquid ratio of distiller's grains and KOH solution--B; (3) the activation temperature -T; (4) activation time-t.
Through the investigation of each influence factor, we can find out a data range can meet the orthogonal experiment, and finally get the best method of the preparation of activated carbon by orthogonal experiment. The experimental procedure is shown in figure 1.

Effect of KOH solution concentration on activated carbon.
Under the conditions of solid-liquid ratio of 1: 4, activation temperature of 750 ℃ and activation time of 2h, the concentration of KOH solution was 10%, 20%, 30%, 40%, 50% and 60% to prepare activated carbon.
It can be seen from Figure 2 that with the increase of the concentration of KOH solution, the adsorption value of iodine and methylene blue of the activated carbon increased and then decreased, and reached the highest yield of 24.48% at the concentration of 40%, the maximum iodine adsorption value and the highest methylene blue adsorption value of 1521.94mg / g and 21.28 (10mL / g) at the concentration of 50%. The purpose of KOH activation is to activate the mesopores and micropores of activated carbon. In the internal pore structure of activated carbon, the more developed micropores, the higher the adsorption value of iodine and methylene blue. When the concentration of KOH is less than 40%, the degree of activation of distillers is low, but with the increase of KOH concentration, the micropores are more developed in the internal void structure of activated carbon. When the concentration of KOH reaches 50%, the pore structure is the most developed. When the concentration of KOH is higher than 50%, due to excessive activation, the internal structure of activated carbon is destroyed, part of the microporous turn into large pores. In the case of comprehensive consideration of the yield and the adsorption value, the three levels of KOH solution concentration, which have a great influence on the preparation of activated carbon, were selected as follows: 40%, 50%, and 60%.  and the highest iodine adsorption value were obtained when the solid-liquid ratio was 1: 4, and the highest adsorption value of methylene blue (10mL/g) was obtained at the solid-liquid ratio of 1: 5.
When the solid-liquid ratio is greater than 1: 4, the charred distiller's grains are not completely immersed in the KOH solution and can not be fully contacted with the KOH, so the degree of activation of the distiller's grains is low. With the increase in the amount of KOH, distiller's grains and KOH solution are in full contact,so the activation degree is improved and the pores tend to develop. When the solid-liquid ratio reached 1: 4, it achieves the best activation state. When the solid-liquid ratio is less than 1: 4, the specific surface area of the activated carbon is relatively reduced due to excessive excess of KOH.
In the case of comprehensive consideration of the yield and the adsorption value, the three levels of solid-liquid ratio, which have a great influence on the preparation of activated carbon, were selected as follows: 1∶4, 1∶5, 1∶6.

Effect of activation temperature on activated carbon.Under the condition of KOH solution
concentration of 50%, solid-liquid ratio of 1: 4 and activation time of 2h, the activation temperature of the control variable was controlled at the activation temperature of 600 ℃, 650 ℃, 700 ℃, 750 ℃, 800 ℃, 850 ℃ to prepare activated carbon.  It can be seen from Figure 4 that with the increase of calcination temperature, the adsorption value of iodine and methylene blue of the activated carbon increased first and then decreased, but the final yield has been decreasing. The maximum adsorption value is reached at the activation temperature of 750℃. Distiller's grains and activator KOH can react at high temperature. With the increase of temperature, the reaction speed is accelerated, so the activation is accelerated. When the temperature is over 750℃, the temperature is too high, resulting in uneven activation of activated carbon and decreased adsorption performance.
In the case of comprehensive consideration of the yield and the adsorption value, the three levels of calcination temperature, which have a great influence on the preparation of activated carbon, were selected as follows: 700℃,750℃ , and 800℃.  As can be seen from Figure 5, with the increase of activation time, the iodine adsorption value and methylene blue adsorption value of activated carbon increased first and then decreased, and the maximum value was obtained at 2 hours, but the yield of activated carbon shew a decreasing trend. With the increase of time, the reaction between KOH and the lees is more and more abundant, and the pore structure is more and more developed, so the quality of activated carbon is reduced. When the reaction time reaches 2 hours, it reaches the peak of the micro -and mesopore structure, and the adsorption performance is the best. When the activation time is more than 2 hours, with the increase of time, the reaction is still continuing, so the micro hole is destroyed, the pore becomes larger, and the adsorption performance decreases.
In the case of comprehensive consideration of the yield and the adsorption value, the three levels of calcination time, which have a great influence on the preparation of activated carbon, were selected as follows: 1.5h,2.0h,2.5h.  Table 2, orthogonal experiment was carried out by L9 (3 4 ) orthogonal table.  Table 3.  Table 4.

Importance of factors B>A>C>D
Note: Kij----the average value of all test results of leval(i) of factor(j).
The data of yeild show that, the variance is A > C > B > D, iodine adsorption value is B > D > C >