定义Definition
过滤是利用多孔介质（滤纸、滤膜、砂芯等）使液体或气体通过而截留其中固体颗粒的分离操作。实验室中常用漏斗和滤纸进行常压过滤，用布氏漏斗进行减压过滤（抽滤）。
Filtration separates solid particles from a liquid or gas by passing the fluid through a porous medium such as filter paper, a membrane or sintered glass, which retains the solids. In the laboratory gravity filtration uses a funnel and filter paper, and suction filtration uses a Büchner funnel.
原理与操作Principle and practice
过滤介质孔径小于颗粒尺寸，颗粒被截留形成滤饼，透过的液体称为滤液。常压过滤“一贴二低三靠”：滤纸紧贴漏斗内壁；滤纸边缘低于漏斗边缘、液面低于滤纸边缘；烧杯口靠玻璃棒、玻璃棒靠三层滤纸处、漏斗下端尖嘴靠烧杯内壁。折叠成扇形（菊花形）的滤纸过滤面积大，适合热过滤。
The medium's pores are smaller than the particles, which collect as a filter cake while the liquid passes through as filtrate. For gravity filtration, keep the paper flat against the funnel, keep its edge below the funnel rim and the liquid below the paper edge, pour down a glass rod resting on the triple-thickness side of the paper, and let the funnel stem touch the inside of the receiving beaker. Fluted paper has a larger area and suits hot filtration.
滤纸与滤材Filter media
定性滤纸用于一般分离，定量滤纸灰分极低（< 0.01%）用于重量分析；砂芯漏斗适合强酸和氧化性溶液；微孔滤膜（0.22 μm、0.45 μm）用于除菌和 HPLC 样品预处理；硅藻土助滤剂用于过滤细小或胶状沉淀。
Qualitative paper serves general separations, while ashless quantitative paper (below 0.01% ash) is used in gravimetric analysis; sintered-glass funnels suit strong acids and oxidising solutions; membrane filters of 0.22 or 0.45 μm sterilise liquids and clean HPLC samples; and diatomaceous-earth filter aid handles fine or gelatinous precipitates.
应用Applications
过滤用于分离沉淀、除去不溶杂质、重结晶热过滤、饮用水和废水处理（砂滤、膜过滤、反渗透）、空气净化（高效空气过滤器 HEPA、口罩熔喷布）和制药无菌过滤。
Filtration separates precipitates, removes insoluble impurities, is used in hot filtration during recrystallisation, treats drinking water and wastewater (sand filters, membranes, reverse osmosis), cleans air (HEPA filters, melt-blown mask layers) and sterilises pharmaceuticals.
年表Timeline
- 古代
用布和沙过滤水
Cloth and sand are used to filter water
- 1804
苏格兰佩斯利建成首座城市砂滤水厂
Paisley, Scotland, builds the first municipal sand-filtration plant
- 1940s
HEPA 过滤器为曼哈顿计划开发
HEPA filters are developed for the Manhattan Project