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membranes that can play effective role in separation of these com-
ponents are microfiltration, ultrafiltration, nanofiltration, reverse
osmosis and electrodialysis membranes. Microbial cells and pro-
teins can quickly foul all membranes though extent of fouling
may be far less in microfiltration membranes compared to that
in nanofiltration or reverse osmosis membranes. However, mem-
branes used in some particular modules may be operated for
long without much fouling. Microfiltration membranes having the
largest pore size (0.1–0.2m) among the categories can separate
microbial cells for their subsequent recycling to the bioreactor to
ensure high cell concentration and thus high productivity. Ultrafil-
tration membranes with average pore size much less than that of
the microfiltration membranes can retain cells and proteins. Sepa-
ration bymicrofiltration and ultrafiltrationmembranes is based on
size exclusion and for effective cell harvesting, at least 100–300 kDa
molecular weight cut off (MWCO) value should be ensured [17] for
this. Nanofiltration membranes being in between reverse osmo-
sis and ultrafiltration membranes with average pore size of 1 nm
can separate cells, proteins, nutrients, salts, and unconverted car-
bon sources from lactic acid. Reverse osmosis normally known
as nonporous membrane where separation is based on solution
diffusion mechanism can separate the same components from fer-
mentation broth as nanofiltration membranes do but at much
higher operating pressure than what is needed in nanofiltration.
The schematic flow diagram in Fig. 3. shows how such micro,
ultra, nano or reverse osmosis membrane modules can be cou-
pled with a fermentor permitting continuous removal of acid from
the broth and separation of cells, nutrients or unconverted car-
bon sources for their subsequent recycle. The scheme in the Fig. 3
shows a single stage integration of a membrane module as has
been investigated in several studies over the last two decades.
Separation and recycle of the components depends on the type
of membrane used. For example, if a microfiltration membrane
module is coupled, only cells are likely to be retained while per-
mitting acids, unconverted carbon sources, proteins nutrients and
water to pass to the permeate side. This however, ensures con-
tinuous removal of acid from the fermentor helping to arrest文章概述
乳酸hydroxy-carboxylic酸发生历来最广泛用作食品防腐剂和acidulent。这么长时间,通过化学合成路线或生产发酵路线后者主导的一个。尽管其巨大潜力的大规模生产和使用各种各样的应用程序,具有成本效益的生产高纯度乳酸几十年来始终是一个挑战,这主要是由于下游处理成本高。近年来,集成的可能性高选择性膜与传统fermentors为完整的商业开发打开了一个黄金机会不知道化学的巨大的应用潜力。论述了最新发展的膜过程代表过程集约化生产的单体年级乳酸而提出有前途的生产计划。
1． 简介
化学和盟军过程工业世界各地现在面对的重大挑战生存的产品创新和过程在一个瘦弱的利润率在高度全球化的时代贸易竞争和快速发展的环境约束。因此通过革命发展过程强化新产品和流程,确保材料和减少能源消耗和降低环境影响,同时提供更大的灵活性在经营规模的需要。单体的生产级乳酸(2-hydroxypropanoic酸)传统食品防腐剂和acidulent已经在过去的几十年里,吸引了全世界研究者的注意。论文网
凭借独特的羟基和羧酸团体、乳酸可以参与各种各样的化学物质反应如酯化、缩合、聚合,减少和替代,这导致了其巨大的潜力作为一个平台的一系列化学产品非常大规模的用于工业生产和消费产品。可生物降解的热塑性塑料(聚乳酸),与这些过程相关的主要问题,然后绿色溶剂(乙、丙、丁lactates)和氧化的化学——地(丙二醇)的几个例子乳酸acid-derived产品,市场需求是呈指数型增长多年来[1]。开发其潜力,然而,在很大程度上取决于是多么低成本生产高纯度。的主要技术障碍具有成本效益的生产高纯度乳酸是其投入品分离和纯化。在这里,膜过程是介入。在模块化设计、膜后产生在生产规模提供极大的灵活性取决于市场需求。膜的选择性高,可以确保高水平的分离和纯化。选择膜的选择性和渗透性与传统fermentors,可以很容易地集成膜过程允许在同一单位同时生产和净化。这消除了需要单独净化单元和紧凑的设计,减少资本投资。膜分离、净化(除非渗透蒸发)涉及没有相变确保减少能源消耗。因此这些过程可以满足所有目标的过程强化。在本文中,我们首先简要讨论传统流程高——光与这些过程相关的主要问题,然后检查膜的发展过程,试图克服传统流程的问题。目标是确定一个环保,简单,经济上可行的和持续的制造方案。