使固态化学反应100%完成的方法

Route map for 100% completion of solid-state reactions

无溶液形成的固态化学反应具有“一旦发生,就必完全”的特质,但因为固体的非流动性,它常常会因严重的传质困难而有始无终。为了克服这个困难,作者提出了少溶剂固态化学反应(LSR)的概念,即通过使用少量的溶剂赋予固体流动性,使反应物固体部分溶解,再使用搅拌反应器解决其“三传”问题,使之完全反应,从而达到使一些化学工业过程绿色化的目的。本文用平衡热力学数值计算的方法图解了几种代表性LSR的Gibbs自由能随反应进度的关系,进而指出:LSR的中间阶段如同没有溶液形成的固态化学反应,两端像溶液化学反应,因此,LSR虽继承了混合自由能导致的化学平衡,但其平衡点比溶液化学反应更接近100%完全。特别地,在LSR即将结束时,通过逐步移除溶剂以使反应物和产物固体持续存在而延长中段,能推动反应达到100%完全;对于连串反应,LSR仍有可能通过控制反应物的物质的量之比来获得中间产物;对于Δ_rG_m~?略小于零的反应,可以通过使用较多的溶剂跨越可能的早期平衡态,或者使用大量的产物固体“种子”使所有的产物一直与其饱和溶液平衡,最终通过逐渐蒸发溶剂推动反应进行到底;LSR的反应速度与反应物或产物的溶解度关系不大,但与反应物的溶解速度、化学反应速度和产物的结晶速度紧密相关。本文还讨论了使一些竞争反应、非自发反应进行到底的方法,获得高度的反应控制能力。

Although thermodynamics tells us that solid-state reactions without solution will not stop until 100% completion,they may stop far before the exhaust of reactants because of the difficulty of mass transfer among the solid particles.To solve this problem,the author has publicized a novel technique called the less solvent solid-state reaction(LSR),which makes small parts of the solid reactants dissolve and react in a small amount of solvent,thus making the reaction proceed faster and more complete in a stirred reactor.Consequently,LSR could make some of the industrial processes greener.By using numerical calculating and charting of its Gibbs energies with respect to its extent of reaction,this paper proves that(ⅰ) an LSR is a combination of a reaction thermodynamically equivalent to a solution-free solid-state reaction in the middle and semi-solution reactions at both ends.Although the LSR does reach an equilibrium eventually,it goes much further to the 100% completion than the solution reaction;if the solvent is removed gradually at the ending period of the reaction,the LSR can be pushed to 100% completion;(ⅱ) for the consecutive reactions,it is possible to get the sole intermediate product by controlling the molar ratio of the reactants as its stoichiometric ratio;(ⅲ) it is possible to make an LSR with near-zero negative Δ_rG_m(?) 100% completed by using more solvent or using the solid products as seeds;(ⅳ) it is the dissolution speed of reactants,the speed of chemical reaction,and crystallization speed of products,rather than the solubilities of the substances that control the speed of an LSR.Measures for 100% completion and selection of LSRs of non-spontaneous or coexisting competitive reactions are also discussed.