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grow. The rotating particles develop layer by layer into
larger spherical particles. After drying, the green spheres
are calcined to obtain higher mechanical strength.
Sometimes some binder and cement are used to make
the layers adhere better. As smaller particles can be made
more easily by granulation or extrusion than by tabletting,
these are the preferred methods of forming. Figure 14
shows a typical machine used to form catalyst particles by
granulation.
Figure 13: A Typical Machine Used to Extrude Catalysts
圖 13: 擠 壓 催 化 劑 的 典 型 機 器
(D) Spray drying
Spray drying is a technique which is used to produce
spherical materials. It can be used as an intermediate
process for drying and producing free-flowing powders,
or as a real shaping technique producing
attrition-resistant spherical particles with a diameter
between 10 and 100 m.
In spray drying, a hydrogel or sol solution is sprayed
through nozzles into a heated zone. Depending on the
temperature, either drying or both drying and calcination
occur as the drops fall. Two different types of spray
dryers are shown in Figure 15 for reference. The
difference between the two types is the way in which the
small droplets are formed or atomized. The type of liquid
atomizer is very important for the maximum attainable
particle size and the broadness of the particle size
distribution. Spray drying is also an important technique
for catalyst forming.
(Source 資 料 來 源 :http://www.cabofswitzerland.com/,
7 Feb, 2012)
Figure 14: A Typical Machine Used to Form Catalyst
Particles by Granulation
圖 14: 製 造 催 化 劑 顆 粒 的 典 型 機 器
The formation of catalysts involves many steps and unit
operations, which are preparation of the support,
formulation of the support particles, deposition of the
active components, and catalyst activation. After the
formation of catalysts, there are several general
approaches to their finishing, including washing, drying,
calcination, and activation.
3.3 Emerging Rare Earth Fine Chemical
Technologies
3.3.1 Separation and Purification Technologies
into Purified Metals
Unlike common metals like copper and zinc with standard
and well-established separation processes from rocks as
single-phase minerals, the REEs are usually found in two
or more mineral phases with multiple REEs co-existing in
the same mineral, resulting in a series of steps of
separation processes to obtain pure metals of REEs.
Consequently, the refinement of REEs requires
extraction, smelting and separation processing steps that
are tailored for a particular ore, which usually result in an
inherent increase in development cost. The technical
aspects of these processes have become even more
complex, pushing the costs up further, because the ores
of REEs often possess radioactive elements, such as
thorium and uranium, requiring special environmental and
disposal handling procedures in accordance with the
increasingly strict environmental regulations.
(Source 資 料 來 源 :Hong Kong Productivity Council 香 港 生
產 力 促 進 局 )
(D) 噴 霧 乾 燥
噴 霧 乾 燥 法 是 一 種 用 來 生 產 球 形 材 料 的 技 術 , 它 可 以 用 來
弄 乾 及 製 備 自 流 粉 末 的 中 間 過 程 或 作 為 一 個 真 正 的 成 型
技 術 , 以 生 產 耐 磨 及 球 形 直 徑 為 10-100 微 米 的 顆 粒 。
在 噴 霧 乾 燥 過 程 中 , 通 過 噴 嘴 把 水 凝 膠 或 溶 膠 溶 液 噴 塗 到
一 個 加 熱 區 。 當 被 噴 塗 的 材 料 降 下 , 因 應 著 不 同 的 溫 度 會
出 現 乾 燥 或 乾 燥 和 焙 燒 的 過 程 。 圖 15 展 示 兩 個 不 同 類 型
的 噴 霧 乾 燥 器 。 兩 種 類 型 霧 化 之 間 的 差 別 在 於 它 們 把 噴 塗
液 形 成 或 粒 子 化 的 方 式 。 因 為 要 怎 樣 才 可 得 到 最 高 可 粒 徑
和 細 微 性 分 佈 的 廣 泛 性 , 是 取 決 於 採 用 哪 種 方 法 。 此 外 ,
噴 霧 乾 燥 是 形 成 催 化 劑 的 一 個 重 要 技 術 。
催 化 劑 的 成 型 涉 及 許 多 步 驟 和 單 元 操 作 , 包 括 製 造 載 體 、
研 製 載 體 粒 子 、 活 性 成 分 沉 積 及 催 化 劑 活 化 。 催 化 劑 成 型
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