湿法磷酸制备高品质活性炭的技术研究

【作者】 张丽；

【导师】 林倩；

【作者基本信息】 贵州大学 ， 化学工程与技术， 2023， 硕士

【摘要】 活性炭因具有较高的比表面积、丰富的孔径结构以及表面化学性质,已经顺应时代潮流被广泛应用于各行各业。活性炭制备方法有物理法、化学法和其他方法。化学活化法常用的活化剂为氢氧化钾、氯化锌和磷酸,其中磷酸法因污染低、能耗低和回收简单等优点,成为目前工业上生物质基活性炭制备的主要方法。生产活性炭的磷酸分为热法磷酸和湿法磷酸,与热法磷酸相比,湿法磷酸制备所得活性炭存在灰分高、金属杂质含量高以及吸附性能不佳等缺点,限制了湿法磷酸在高端活性炭制备领域的应用。因此,研究以湿法磷酸为活化剂制备低灰分、高性能活性炭,无论是节能降耗减排,还是拓宽湿法磷酸应用领域都具有极大的社会经济意义。针对上述问题,本研究提出以湿法磷酸为活化剂、废木屑为碳源,通过化学活化法制备活性炭。通过ICP、粘度分析仪、离子交换法等对湿法/热法磷酸进行差异原因分析,具体判断湿法磷酸代替热法磷酸用于活性炭生产的可行性;通过TG、FTIR、XPS、XRF和SEM等对湿法/热法磷酸制备的活性炭差异进行分析,找出两者差异的具体影响因素;研究活化工艺和洗涤工艺条件对生产活性炭灰分的影响,找出最佳制备条件;最后是在较低的活化温度下,通过加入助剂的方式帮助活化,提升活性炭的品质。主要结果如下:（1）对湿法/热法磷酸性质及其制备活性炭的差异原因分析。通过开展湿法/热法磷酸新酸及返酸性质研究、明确了湿法磷酸相较于热法磷酸存在离子含量和多聚磷酸含量高等问题;研究离子对磷酸中正磷酸含量的影响,原液中正磷酸含量（P₂O₅）为46.35%,加入多种离子为44.69%,加入Mg²⁺后变为44.67%,结果表明,Mg²⁺是影响湿法磷酸中正磷酸含量减少的主要因素;采取加入助剂和预加热处理的方式,结果显示,预加热70℃,10 min可使溶液中正磷酸含量从37.93%增加到41.63%;最后对湿法/热法磷酸制备的活性炭进行表征分析,结果表明,湿法磷酸含有较多的杂质离子和多聚磷酸,使得湿法磷酸活性炭灰分较高、吸附性能较差。（2）对活性炭生产参数进行优化,降低湿法磷酸活性炭的灰分含量。研究活化工艺过程的温度、磷酸浓度、酸屑比和气氛;洗涤工艺过程中洗涤介质、洗涤温度、酸浓度、洗涤次数、洗涤剂用量和洗涤时间等活性炭灰分及性能的影响。结果表明,难溶性磷酸盐是活性炭灰分产生的主要因素,通过控制活性炭制备工艺和洗涤工艺可调控难溶性磷酸盐含量,从而调控活性炭灰分、碘值和亚甲蓝值。最佳工艺条件:活化温度500℃、磷酸浓度76%、酸屑比2:1、活化时间60 min和N₂保护;洗涤液用量100 ml、洗涤液浓度20%、洗涤介质H₃PO₄、洗涤温度80℃和洗涤时间60 min,此时制备的活性炭灰分1.07%、碘值1241.4 mg/g、亚甲蓝值19 ml/0.1g、比表面积2290.54 m²·g^-1,说明该技术制备的活性炭具有应用于食品、医药等高端行业领域的潜质。（3）提升湿法磷酸活性炭性能的研究。研究降低活化温度并加入助剂的方式,避免在较高温度下生成多聚磷酸进一步形成灰分,同时加入助剂帮助活化,提升活性炭的吸附性能。本研究考察了单一助剂、助剂用量以及混合助剂对湿法新酸和湿法返酸活性炭的作用,成功制备出灰分较低、碘值较大的高品质活性炭,与企业生产的高品质商用活性炭相比,具有更优秀的品质。其中,在湿法新酸中添加5%-C（助剂）制备的活性炭其碘值为1349.58 mg/g、比表面积高达2252.18m²/g、微孔率0.9295 cm³/g、且灰分小于3%,添加混合助剂2%-B+2%D制备的活性炭其碘值为1310.3 mg/g,灰分1.68%,高于高品质商用活性炭（碘值为1211.58 mg/g、灰分2.69%、比表面积1965.89 m²/g、微孔率0.9295 cm³/g）;在湿法返酸中添加2%-B+2%D制备的活性炭其碘值从原来的906.4增加到1116.6mg/g,灰分从4.21下降到2.75%。本研究具有一定的指导意义。更多还原

【Abstract】 Activated carbon has gained widespread use in various industries due to its high specific surface area,diverse pore size structure,and unique surface chemistry.Activated carbon is prepared using physical,chemical,and other methods.The commonly used activators for chemical activation are potassium hydroxide,zinc chloride,and phosphoric acid.Among these,phosphoric acid is currently the primary method for preparing biomass-based activated carbon in industry due to its advantages of low pollution,low energy consumption,and easy recycling.The phosphoric acid used in the production of activated carbon is classified into two types:hot and wet phosphoric acid.Compared to hot phosphoric acid,activated carbon prepared using wet phosphoric acid has several disadvantages.These include high ash content,high metal impurity content,and poor adsorption performance.These limitations restrict the application of wet phosphoric acid in the field of high-end activated carbon preparation.Therefore,studying the use of wet phosphoric acid as an activator for preparing low ash and high-performance activated carbon is of significant socio-economic importance.This research can lead to energy savings and emission reductions,as well as expanding the application area of wet phosphoric acid.In response to the aforementioned issues,this study proposes the production of activated carbon through a chemical activation method that utilizes wet phosphoric acid as an activator and waste wood chips as the carbon source.The differences between hot and wet phosphoric acid were analyzed using ICP,viscosity analyzer,and ion exchange methods to determine the feasibility of using wet phosphoric acid for activated carbon production.The study also analyzed the differences between activated carbon prepared using wet and hot phosphoric acid using TG,FTIR,XPS,and XRF to identify the specific factors that influence the differences between them.Additionally,the study investigated the effect of activation and washing process conditions on the ash content of the activated carbon.Carbon was investigated to determine the optimal preparation conditions.Ultimately,the quality of the activated carbon was enhanced by incorporating additives to facilitate activation at a lower temperature.The main results are as follows:（1）An analysis of the properties of wet/hot process phosphoric acid and the reasons for the differences in the preparation of activated carbon will be conducted.Through research on the properties of new and recycled wet/thermal phosphoric acid,it was discovered that wet phosphoric acid has higher levels of ionic and polyphosphate content compared to hot phosphoric acid.The impact of ions on the orthophosphoric acid content in phosphoric acid was also investigated.The original solution had an orthophosphoric acid content（P₂O₅）of 46.35%,which decreased to 44.69%with the addition of various ions.The addition of Mg²⁺further reduced the content to 44.67%.These results indicate that Mg²⁺is the primary factor responsible for the reduction of orthophosphoric acid content in wet phosphoric acid.Through the use of additives and pre-heating treatments,the study found that pre-heating at 70°C for 10 min increased the orthophosphoric acid content in the solution from 37.93%to 41.63%.The activated carbon produced through wet/thermal phosphoric acid was then analyzed and characterized.The results indicated that the wet phosphoric acid contained more impurity ions and polyphosphoric acid,resulting in a higher ash content and poorer adsorption performance of the wet phosphoric acid activated carbon.（2）Optimization of the parameters for producing activated carbon to reduce the ash content of activated carbon made from wet process phosphoric acid.The study investigated the impact of temperature,phosphoric acid concentration,acid-to-chip ratio,and atmosphere during the activation process,as well as the effects of washing medium,washing temperature,acid concentration,washing frequency,detergent dosage,and washing time during the washing process on the ash content and performance of activated carbon.The results indicate that the production of activated carbon ash is primarily caused by insoluble phosphate.However,the content of insoluble phosphate can be managed by controlling the preparation and washing processes of activated carbon.This regulation can effectively control the ash,iodine,and methylene blue values of the activated carbon.The optimal process conditions were as follows:an activation temperature of 500°C,a phosphoric acid concentration of 76%,an acid to chip ratio of 2:1,an activation time of 60 min,and N₂ protection.The washing solution dosage was 100 ml,with a washing solution concentration of 20%,using H₃PO₄ as the washing medium.The washing temperature was set at 80°C,and the washing time was 60 min.The activated carbon prepared has an ash content of 1.07%,an iodine value of 1241.4 mg/g,a methylene blue value of 19 ml/0.1g,and a specific surface area of 2290.54 m²/g.These results indicate that the activated carbon produced using this technology has the potential to be utilized in high-end industries such as food and medicine.（3）A study aimed at improving the performance of activated carbon through wet process phosphoric acid activation.The study investigated the reduction of the activation temperature and the use of additives to prevent additional ash formation from polyphosphoric acid at higher temperatures.The addition of additives also improved the activation process and increased the adsorption capacity of the activated carbon.In this study,we investigated the effects of single additives,additives dosage,and mixed additives on wet fresh acid and wet reacid activated carbons.As a result,we successfully prepared high-quality activated carbons with lower ash and larger iodine values.These activated carbons have better quality compared to the high-quality commercial activated carbons produced by companies.The activated carbon’s iodine value was measured after adding 5%-C to the wet reacid,resulting in a value of 1349.58mg/g.The specific surface area was found to be 2252.18 m²/g,with a microporosity of0.9295 cm³/g.The ash content was less than 3%.On the other hand,the activated carbon prepared by adding a mixed additive of 2%B+2%D had an iodine value of 1310.3mg/g and an ash content of 1.68%.However,the ash content was still higher than that of high-quality activated carbon.The iodine value of the activated carbon,prepared with the addition of 2%B+2%D,increased from 906.4 to 1116.6 mg/g.Additionally,the ash content decreased from 4.21%to 2.75%.This study provides some guidance.更多还原