Optimization Of The Preparation Of Calcium Acetate,Calcium Citrate And Calcium Propionate From Waste Eggshell By Response Surface Method

As the world's largest poultry producer,China's annual product of eggs is 25million tons.Eggshells account for 10%of the total weight of eggs.While most of the eggshells are discarded and buried,only a small part of them are used as feeding additives.The discarded eggshells caused not only serious environmental problems,but also a huge waste of resources.Calcium carbonate is the major component of eggshells,and calcium accounts for 37%of the total weight of eggshells.In this study,eggshells were used as resource to obtain calcium and produce materials important for the food industry,including calcium acetate,calcium citrate and calcium propionate,under the condition of secondary reaction.Single factor and response surface were utilized to optimize the production processes and the processes that separated the eggshell membrane from the eggshells and purified the calcium-containing products.We investigated factors that were important for the efficiency of separation of eggshell membranes from eggshells,including reaction temperature,stirring time,stirring speed,solid-liquid ratio,standing time and times of separation.We used the method of response surface to analyze these factors and obtained the optimized process conditions was:21°C,reaction temperature;16 minutes,stirring time;550rpm,stirring speed;1:8,solid-liquid ratio;16 minutes,standing time;3 times,times of separation.The yield of pure eggshells from raw eggshells was over 95%,and the optimized process could be used in industrialized production.The feasibility of producing calcium acetate from eggshells with the secondary reaction was investigated.The factors important for the producing efficiency,including reaction temperature,acetic acid dosage,solid-liquid ratio,primary reaction time and secondary reaction time,were analyzed separately by single factor analysis.Furthermore,the optimized process conditions were obtained by a comprehensive analysis with the method of response surface:39°C,reaction temperature;1:12,solid-liquid ratio;159%,acetic acid dosage;1.5 hours,primary reaction time;80minutes,secondary reaction time.The yield of calcium acetate from eggshells reached96.5%,which could be used in industrialized mass production.The feasibility of producing calcium citrate from eggshells with the secondary reaction was investigated.The factors important for the producing efficiency,including reaction temperature,citric acid dosage,solid-liquid ratio,primary reaction time and secondary reaction time,were analyzed separately by single factor analysis.Furthermore,the optimized process conditions were obtained by a comprehensive analysis with the method of response surface:72°C,reaction temperature;1:11,solid-liquid ratio;2.15 mol/L,the concentration of citric acid;1.0 hour,primary reaction time;41 minutes,secondary reaction time.The yield of calcium acetate from eggshells reached 96.5%.The feasibility of producing calcium propionate from eggshells with the ultrasonic-assisted secondary reaction was investigated.The factors important for the producing efficiency,including reaction temperature,solid-liquid ratio,ultrasonic power,propionic acid dosage,primary reaction time and secondary reaction time were analyzed separately by single factor analysis.Furthermore,the optimized process conditions were obtained by comprehensive analysis with the method of response surface:85°C,reaction temperature;1:16,solid-liquid ratio;176%,the propionic acid dosage;150W,ultrasonic power;2 minutes,ultrasonic time,1 hour,the primary reaction time;64 minutes,the second reaction time.The yield of calcium propionate from eggshells reached 96.5%,which could be used in industrialized mass production.The process of purification of the crude calcium product was investigated using calcium acetate as an example.The factors important for the purification efficiency,including the amount of flocculant,reaction temperature,Ca?OH?₂ dosage,ethanol dosage and reaction time,were analyzed separately by single factor analysis.Furthermore,the optimized purification conditions were obtained by comprehensive analysis with the method of response surface:0.002%,amount of coagulant;82°C,reaction temperature;0.82g,Ca?OH?₂ dosage;15 minutes,reaction time;1.96mL,ethanol dosage.The purity of the calcium acetate reached 96.05%after the purification.In this study,we improved the production efficiency of calcium acetate,calcium citrate and calcium propionate from eggshells using secondary reaction or ultrasonic-assisted secondary reaction,and optimized the production process using single factor analysis and the method of response surface,which can be used in the industrialized mass production.Through the full utilization of discarded eggshells,our study will improve the utilization efficiency of wasted resources and promote the sustained economic growth.