矿物质对生物炭形成及其碳稳定性的调控机制

Pyrolysis and carbonization is an effective technology of carbon sequestration. In this method, the biomass is pyrolyzed by heating in low O2 atmosphere and relative low temperature, and the carbon undergoes carbonization process to form a stable aromatic structure. This high polymeric product, biochar is input into soil, in which the carbon is regarded as being locked for hundreds or millennium years. In the long term this is a strategy of greenhouse gas emission reduction and climate change mitigation. However, during the carbonization the decomposition and polymerization occur synchronously, and only 50% carbon is retained in biochar. The stability of biochar-carbon in soil is also important for carbon sequestration. The inorganic minerals are widely distributed in biomasses. For example, there is a certain amount of KCl and Ca in straw, and other biomass wastes contain P, Al, Si, etc., which have been proved to be of potential influence on the evolution of microcosmic carbon molecular structure. This perhaps has relationship to the macroscopical carbon sequestration effect. In this proposal, the effect of indigenous minerals on biomass carbonization and the biochar formation will be exploited. And then, a novel idea is forwarded, which is adding exogenous inorganic minerals to regulate this process, thus enhance the carbon remaining in biochar and strengthen the biochar stability including physical stability, oxidation-resistance stability and mineralization stability. The aim is enhancing the total carbon-locking in soil. In detail, the study will focus on: the influence of minerals on the distribution of bio-oil, bio-gas and bio-char as well as their main compositions, the intervening of minerals on the decomposition and aromatization process of carbon cellulose structure, the bonding effect of minerals with C such as the formation of P-C compound and its "wrapping" on the carbon surface. This project will use the advanced instrumental analysis to observe the structural evolution of carbon molecular structure including transformation of turbostratic/order crystal phase, growth of mesoscopic and pore structure, change between cellulose and lignin microfibrils. Thus the interaction of the minerals and the carbon will be elucidated, and this would give an insight into the carbon remained in the biochar, as well as biochar stability.

通过热解炭化将生物质废物中的碳转为芳香化高聚合结构生物炭输入土壤，可实现长期碳封存和温室气体减排。但是，炭化过程同时发生碳分解和聚合，仅有50%的碳被保留在生物炭中，且其输入土壤后的稳定性对固碳效果也很重要。无机矿物组分广泛存在于生物质中，如秸秆中含有KCl、Ca等，P、Si、Al等也分布于一些生物质中，其在热解炭化过程中对碳的微观分子结构演变有潜在影响，并可能影响宏观的固碳效果。本项目研究内源矿物质对生物炭形成过程的诱导机制，并利用外加矿物质调控该过程，拟使更多碳保留于固相中，并有更好的物理、氧化和矿化稳定性。具体包括：对固、液、气三相分布及成分的影响，对碳纤维的分解和芳香化进程的干扰，与碳的键合作用，如P-C结合物的形成及对碳的“包裹”作用。利用先进仪器手段揭示矿物质对“碳”的乱层/有序晶相转化、介观结构和孔结构演变、纤维素和木质素微晶相转化的影响，探明热解中碳的保留及产物稳定性根源。

生物质废物大量产生及无序弃置，成为不可忽视的温室气体释放源。通过热解炭化将其转为芳香化高聚合结构生物炭输入土壤，可实现长期碳封存和温室气体减排。但是，炭化过程同时发生碳分解和聚合，仅有50%的碳被保留在生物炭中，其是否可实现真正的碳负性有所争议。无机矿物组分如K、Ca、P、Si等广泛存在于生物质中，其在热解过程中对碳的微观分子结构演变有潜在影响，并可能影响宏观固碳效果。本项目系统而全面地研究了内源矿物质对生物炭形成过程的诱导机制，并利用外加矿物质调控该过程，揭示了无机矿物与碳骨架的作用机制，从碳保留、碳无序结构、碳分解行为、小分子碳释放等各方面阐述了固碳效果。. 结果表明，无机矿物的存在能够催化碳分解过程，产生更多小分子组分进入气相中，诱导氧元素在生物炭上的截留，碳的固相保留率有所下降，从50%下降至45%左右，所得生物炭产物无序化程度加大，稳定性下降，这是对固碳不利的，但程度较小；而外加矿物则呈现了不同的影响，通过物理覆盖、化学吸收，以及与碳元素的键合等作用，强化了碳保留，从50%提高到70%左右。发现了制备镁复合生物炭、磷复合生物炭可同时强化固碳和污染物修复的能力，提升环境效益。为了进一步评估生物炭系统对温室效应的缓解潜势以及综合环境影响，我们在微观层面的研究基础上，同时开展了宏观碳足迹研究。基于Gabi生命周期评价软件，结合文献统计的大量数据，量化了生物炭系统的固碳潜势和环境效应。1 吨农业生物质残体用以制备生物炭，GWP100值达到-921.66 kgCO2e。抵消燃煤发电和生物炭田间应用是生物炭系统中最重要的固碳环节，而慢速热解是最大的排碳环节。我国可达到的年度固碳潜势为7.97×108 tCO2e，占2014年中国净温室气体排放量的7.12%。生物炭系统对于海洋生态毒性潜势、人体毒性潜势、酸化潜势等都有积极的改善和缓解。对热解过程中氮、磷元素的形态转化和环境行为进行了拓展研究，更加深入揭示了生物炭系统对于固碳和提升环境效益的微观和宏观机制。