塑料化学分解回收
发布日期：2014-04-11
阅读量：3509
用化学法分解塑料废弃物也是可行的。化学分解法比热分解法有诸多优越性：分解产物均匀且易于控制；在一般情况下，产物不需进行分离和纯化；生产设备投资少等。但化学分解法不适用于混杂型废旧塑料，一是因为所用试剂均有严格的选择性；二是因为它对废旧塑料预处理的清洁度和品种均匀性皆有较高的要求。因此，化学分解法更适用于较单一品种的无污染型废旧塑料。化学分解法对多种塑料都是可行的，但目前主要是处理聚氨酯、热塑性聚酯、聚酰胺类等极性类废旧塑料。
一、水解法
水解法适用于含有水解敏感基团的高聚物，这类高聚物多由缩聚反应制得，水解反应其实质是缩合反应的逆向反应。现以聚氨酯沫塑料为例，略述水解反应工艺条件及主要水解产品。图1为聚氨酯(PU)泡沫塑料连续水解反应工艺流程，主要的水解反应装置是双螺杆挤出机。
水解工艺流程为：
PU泡沫塑料→粉碎→进料（双螺杆挤出机）→300℃→高温挤塑→中间加料口送水→混合浆料→水解→分离产物双螺杆挤出机既是制浆混炼室，又是水解反应器，制浆和水解反应约需5~30min。当螺杆低速旋转时，将加入的泡沫塑料进行塑化并在向前推进中与水掺混形成浆料，边混边进行水解，通过温度和反应时间控制水解程度。其水解产物主要是聚酯和由异氰酸酯产生的二胺，经分离可得到均一的产品。混合产物的分离可采取蒸馏法，先蒸出二胺，后纯化聚酯，也可采用往混合产物中加入酸与胺反应使之沉淀，经过滤所得滤液为聚酯，沉淀物则含二胺。
二、 醇解法
醇解法的操作比较简单，它既适用于分解聚氨酯泡沫塑料，又适用于分解聚氨酯软质或硬质制品。聚氨酯废旧制品的醇解可通过有机金属化合物或叔胺类催化剂进行。聚氨酯泡沫塑料的醇解条件较温和，在适量的乙二醇存在下，于185~200℃即可进行醇解，其反应产物主要是混合多元醇。工业上醇解工艺比较简单和易于操作，具体过程是将预先切碎的泡沫塑料送人用氮气保护的反应器内，以乙二醇为醇解剂，醇解温度可控制在185~210℃之间。由于泡沫塑料密度小，易浮于醇解剂的液面上，因此需要进行有效地搅拌与掺混，使醇解反应充分。如此制得的多元醇生产成本低，有较高的经济效益和社会效益。
三、废聚酯的解聚
废旧聚酯（如PRT等）在复合催化剂的作用下，于常温常压下进行解聚，解聚产物主要是聚酯的原单体，此单体不需掺和新单体即可直接缩聚成纺丝级聚酯。所选用的复合催化剂为乙酸锌0.15%、乙酸钙0.05%、乙酸锂0.02%。
综上所述，回收的废旧塑料的化学分解主要是通过粉碎、清洗、干燥后，再进行化学处理，从而得到有用的化工原料或油品的过程。
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