Development of Bioenergy from Chromium-Copper-Arsenate (CCA) Treated Wood Wastes

用铬化砷酸铜（CCA）防腐剂处理的木材的处理已成为世界上一个严重的问题。必须开发对环境无害的处置技术。我们试图找到CCA处理木材的热解条件，以便最大限度地保留木炭中的砷，并获得高产油量。2002年，对经过CCA处理的样品在450℃下额外热处理10分钟进行了彻底的研究，以确定在挥发之前砷在热解残渣中被捕获的反应细节。利用透射电镜对热解残渣中金属化合物的组成和结构进行了分析。大量的颗粒直径在10到100纳米之间。较小的大多是球形的，有时是多面的。较大的是块状的。用选择区电子衍射法对CCA化合物及其反应产物Cr_2As_4O_<12 bbb_和As_2O_3进行了常规透射电镜鉴定。在高分辨率下，纳米颗粒表现出晶格条纹，表明其单晶特征，如Cr的d_<210> = 0.204 nm。在温度高达500℃，时间长达1小时的情况下，用XRF （x射线荧光）分析测量了CCA处理木材热解过程中砷的挥发性。测定了热解残渣在HMO_3中溶解后的质量变化和砷含量。300℃时砷已损失20%以上，这可能是As_2O_5中的As(V)还原为As_2O_3中的As（III）后未反应的砷化合物挥发所致。砷可能以As_4O_6的形式释放，As_4O_6很难捕获且有毒。通过额外的热处理可以防止这种还原，并且可以允许金属的干分离

Disposal of woods treated with chromated copper arsenate (CCA) preservatives has become a serious problem in the world. Environmentally benign disposal technologies have to be developed. We have tried to find pyrolysis conditions for CCA treated wood in order to maximize the retention of arsenic in wood charcoal along with a high oil yield. In 2002, a CCA treated sample given an extra heat treatment at 450℃ for 10 min was thoroughly investigated in order to establish the details of the reaction in which arsenic is captured in the pyrolysis residue prior to volatilization. Composition and structure of the metal compounds in the pyrolysis residue were examined by transmission electron microscopy. Alarge number of particles were found of variable diameter between 10 and 100 nm. The smaller ones were mostly spherical, sometimes faceted. The larger ones were lumpy. CCA compounds and their reaction products like Cr_2As_4O_<12> and As_2O_3 were identified in conventional TEM by Selected Area Electron Diffraction. In high resolution, the nanoparticles exhibited lattice fringes as indication of their mono crystalline character, fitting, e.g. the d_<210> = 0.204 nm of Cr. The volatility of arsenic during pyrolysis of CCA treated wood was measured by XRF (X-Ray Fluorescence) analysis at temperatures up to 500℃ and at times up to one hour. Weight change and arsenic content of the pyrolysis residue were measured after dissolution in HMO_3. More than 20 % of arsenic was already lost at 300℃, which may have been caused mainly by the volanlization of the unreacted arsenic compound after reduction of As(V) in As_2O_5 to As(III) in As_2O_3. Arsenic is probably released as As_4O_6, which is very difficult to capture and toxic. By an additional heat treatment this reduction can be prevented and the dry separation of the metals may be allowed