Knowledge Management System Of Institute of process engineering,CAS
|关键词||有机酸 清洁生产 沉淀置换 酸碱再生 过程耦合|
有机酸的传统钙盐法生产伴生大量酸性硫酸钙固体废弃物，给环境带来较大压力，但钙碱对有机酸发酵菌体友好，是某些有机酸浓度积累不可缺少的物质，钙盐沉淀步骤有利于提升有机酸产品的纯度。本论文针对传统钙盐发酵生产有机酸过程中产生大量固体废弃物的共性问题，研究采用有机酸钙盐与可溶性碳酸盐进行沉淀置换反应，拟解决有机酸生产过程产生硫酸钙固体废弃物、实现清洁生产。以乳酸和柠檬酸为研究对象，重点研究沉淀置换、离子交换、酸碱再生等步骤的问题和解决方法，在此基础上构建具有一定普适性的有机酸清洁生产新工艺。首先研究乳酸钙和柠檬酸钙与碳酸铵进行沉淀置换反应的可行性，考察了反应条件对沉淀置换反应及碳酸钙颗粒粒度的影响。结果表明，碳酸铵的加入量是乳酸钙发酵液中钙的物质的量的1.06倍为佳，钙离子去除率可达99%以上，乳酸钙与碳酸铵之间的沉淀置换反应可在15 min内完成。碳酸铵与柠檬酸钙中钙的比值为1:1时，柠檬酸回收率达95%以上，柠檬酸钙与碳酸铵之间的沉淀置换反应所需的时间较长，本实验条件下所需的反应时间在2.5 h以上。沉淀置换反应得到的悬浊液可采用自然沉降、再用板框过滤的方式进行固液分离。考察了离子交换法提取乳酸钙沉淀置换上清液中的乳酸的工艺条件。乳酸钙沉淀置换上清液的pH较高，使D319树脂对乳酸的吸附量变小，残留的碳酸根可被吸附到树脂上，随后用盐酸洗脱时产生二氧化碳气体，造成离子交换过程无法稳定运行。提出的解决方法为：用乳酸调节沉淀置换上清液的pH值至7.0以下，然后采用加热减压法和离子交换法可有效去除残留碳酸根。根据柠檬酸钙沉淀置换上清液的特性，选择“盐-碱”两室双极膜膜堆结构进行酸碱再生，考察了残留钙离子对酸碱再生的影响、钙的存在形态及其去除方法。柠檬酸钙沉淀置换上清液中的残留钙浓度有8.0 g/L以上，酸碱再生过程中可在盐室产生柠檬酸钙盐固体。选择草酸沉淀去除残留钙离子，钙去除率约为60%。草酸沉淀法除钙后的沉淀置换上清液的酸碱再生过程中，盐室液仍会产生草酸钙，沉积于隔网和离子交换膜表面。发现盐室液开始出现浑浊与草酸钙固体在膜堆内沉积之间有一定的时间差，由此建立了间歇式堆外沉淀法去除残留钙离子的方法，可有效避免草酸钙盐在膜堆内沉积，铵离子跨膜迁移的平均电流效率、膜通量和能耗分别达到95%、12.5 mol/(m2·h)和60 kWh/kmol，与柠檬酸铵水溶液的酸碱再生参数相当。考察了沉淀置换剂制备与沉淀置换反应两步骤的耦合，表明耦合可降低体系中的产物（碳酸铵）浓度，从而增大碳酸铵的表观生成速率。考察了乳酸生产工艺中的酸碱再生步骤与离子交换的洗脱步骤的耦合，表明耦合可有效降低酸室液中游离H+和Cl-浓度，缓解了酸室中H+渗漏的程度，使Cl-的跨膜迁移通量提高了3.5%，平均电流效率提高了56.25%，能耗降低了29.61%。考察了碳酸钙（沉淀置换步骤得到的碳酸钙）循环利用的效果，表明使用循环碳酸钙进行乳酸发酵可大幅提高乳酸发酵水平，乳酸浓度增加了32.41%，产酸速率提高了33.17%，菌体浓度提高了19.34%；循环碳酸钙的比表面积大，具有较好的pH维持能力，颗粒内含有少量氮元素，且乳酸杆菌可在颗粒上形成洞状结构，为其自身提供较好的微环境，有效提高了乳酸发酵水平。在实验室规模下，对乳酸和柠檬酸的清洁生产工艺进行串联，结果表明，乳酸总收率可达90%以上；乳酸清洁生产新工艺的估算成本约为6782.5元，与传统钙盐法生产乳酸的成本相当；乳酸清洁生产工艺得到的精制乳酸符合某聚乳酸生产企业的原料采购要求。草酸脱钙后的柠檬酸沉淀置换上清液经酸碱再生得到的盐室终点液，经阳离子交换树脂除杂、常规减压浓缩、结晶得到柠檬酸固体，其中未检出草酸、铵离子和钙离子。;
A large amount of acidic calcium sulphate as by-product is produced during the traditional extraction of organic acids from fermentation broth, which is detrimental to the environment. However, calcium alkali is a mild neutralizer for lactic acid bacteria and yields a high lactic acid concentration when added to the broth, and the precipitation of the calcium salt of organic acid plays an important role in promotion of product purity. In this thesis, the precipitation replacement reaction between the calcium salt of organic acid and the soluble carbonate was investigated to solve the problem of calcium sulfate disposal. The problems occurred in precipitation replacement reaction, ion exchange and acid/base regeneration, as well as the corresponding solutions were studied intensively. Based on the results, a new and universal technology for cleaner production of organic acids was established.Firstly, the feasibility of precipitation replacement reaction, and the effects of reaction conditions on the replacement efficiency and the particle size of calcium carbonate were examined. The experimental results showed that the removal rate of calcium was more than 99% when the ratio of ammonium carbonate to calcium lactate was 1.06:1, and such reaction could be completed in 15 min. When the ratio of ammonium carbonate to calcium citrate was 1:1, the recovery rate of citric acid could reach more than 95%, while this reaction happened slowly and took above 2.5 h. Natural sedimentation followed by plate and frame filter press could be used for the solid-liquid separation of the suspension solution obtained in the precipitation replacement reaction. The process parameters in lactic acid separation from supernatant by ion-exchange method were optimized. The results showed that the high pH of supernatant and the residual carbonate ion were detrimental to the connection between precipitation replacement reaction and ion exchange. In order to solve these problems, adjusting pH value to above 7.0 using lactic acid, followed by the heating-decompression (60 °C) was used as a pre-treatment step to remove residual carbonate by ion exchange (resin D319). According to the properties of calcium citrate supernatant, the “salt-base” two-cell-BMED was used to regenerate acid/base from supernatant. Since the concentration of residual calcium in supernatant was too high (above 8.0 g/L), the resulting calcium citrate precipitates during the acid/base regeneration. Thus, oxalic acid precipitation was selected and the removal rate of calcium was about 60%. However, the calcium oxalic could also pollute the membrane stack. We found that during the process of regeneration of acid/base, there was a certain time lag between turbidity occurrence and calcium oxalate deposition in the membrane stack. Based on this phenomenon, batch-type-precipitation-out-stack method was established. The experimental results showed that this method could effectively avoid the deposition of calcium oxalate salt solid in membrane stack, and the average current efficiency, flux of NH4+, and energy consumption were 95%, 12.5 mol/(m2·h), 60 kWh/kmol, respectively.The integration of precipitation displacer production and precipitation replacement reaction could greatly reduce the concentration of displacer in system, thus increasing the apparent formation rate of ammonium carbonate. Meanwhile, the integration of acid/base regeneration and elution step for ion exchange during lactic acid production could also reduce the concentration of H+ and Cl- in solution of acid cell. Moreover, the performance of acid/base regeneration was significantly improved: the flux of Cl- through anion exchange membrane increased by 3.5%, the average current efficiency increased by 56.25%, and energy consumption reduced by 29.61%.The recycling of calcium carbonate during the lactic acid cleaner production was explored. Because of its unique granule structure and constitute, the recycled calcium carbonate could increase the concentration of lactic acid by 32.41%, enhance the productivity of lactic acid by 33.17%, and elevate the cell dry weight by19.34%.The experimental results at laboratory scale showed that the recovery rate of lactic acid could reach above 90%, and the estimated cost of lactic acid by this cleaner production technology was 6782.5 Yuan/ton. The obtained lactic acid could meet the demands of raw material in some polylactic acid plant. The analysis results of citric acid showed that the impurities, such as oxalic acid, ammonium and calcium ion, were not detected.
|杨鹏波. 基于沉淀置换的发酵法生产有机酸的清洁工艺过程[D]. 北京. 中国科学院研究生院,2015.|
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