Formation of an external char layer during subcritical water hydrolysis of biomass,Sustainable Energy & Fuels

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Formation of an external char layer during subcritical water hydrolysis of biomass
Sustainable Energy & Fuels ( IF 5.0 ) Pub Date : 2017-09-05 00:00:00 , DOI: 10.1039/c7se00260b
Zijian Ma _{1,

2,

3,

4} , Patricia Guerra _{1,

2,

3,

4} , Maksim Tyufekchiev _{1,

2,

3,

4} , Azadeh Zaker _{1,

2,

3,

4} , Geoffrey A. Tompsett _{1,

2,

3,

4} , P. C. Torres Mayanga _{5,

6,

7,

8} , Tânia Forster-Carneiro _{5,

6,

7,

8} , Peng Wang _{4,

9,

10,

11} , Michael T. Timko _{1,

2,

3,

4}

Affiliation

Flow-through subcritical water hydrolysis (FT-SWH) consists of flowing hot liquid water over a fixed bed packed with biomass particles to produce fermentable carbohydrates and other valuable small molecules. In this work, we studied FT-SWH of green coffee powder as a model lignocellulosic feed, investigating temperatures in the range from 150 to 250 °C and 22.5 MPa. Batch SWH was performed as a basis of comparison for the FT-SWH tests. The focus of the study was characterization of the treated solids; specifically, bulk (primarily thermogravimetric analysis, TGA) and surface (both attenuated total reflectance infrared Fourier transform spectroscopy, ATR-FTIR, and Raman microscopy) methods were used to investigate the hemicellulose, cellulose, and lignin content of the solids. Bulk analysis indicated that the solids treated under FT-SWH conditions retained substantial holocellulose content, even when treated under the most aggresisve FT-SWH conditions studied here (250 °C). On the other hand, surface analysis indicated that the treated materials were primarily composed of char, with the surface content of bound carboxylic acids also increasing with increasing hydrolysis temperature. To understand the apparent discrepancy between bulk and surface analysis, the cross sections of the treated samples were analyzed using both FTIR and Raman microscopy. These techniques confirmed that the surface consisted of a char material, whereas the particle interior was primarily holocellulose. Formation of the external char layer seems to prevent hydrolysis of the internal holocellulose, limiting sugar yields. In comparison with FT-SWH, batch SWH at a similar severity factor resulted in reduced sugar yields, decreased the onset temperature for formation of detectable char quantities, and increased char formation. Comparison with batch conditions suggests that flow conditions reduce external char formation but do not prevent it. This study explains the benefits of FT-SWH and inform development and refinement of pretreatment technologies that can reduce char formation rates.

中文翻译：

亚临界水分解生物质过程中外部炭层的形成

流通式亚临界水水解（FT-SWH）包括使热水流过固定有生物质颗粒的固定床，以产生可发酵的碳水化合物和其他有价值的小分子。在这项工作中，我们研究了作为模型木质纤维素饲料的生咖啡粉的FT-SWH，研究温度范围为150至250°C和22.5 MPa。进行批次SWH作为FT-SWH测试的比较基础。研究的重点是处理过的固体的表征。具体来说，采用体积法（主要是热重分析，TGA）和表面法（衰减的全反射红外傅里叶变换光谱法，ATR-FTIR和拉曼显微镜）来研究固体的半纤维素，纤维素和木质素含量。本体分析表明，即使在此处研究的最苛刻的FT-SWH条件下（250°C）处理，在FT-SWH条件下处理的固体仍保留了大量的全纤维素含量。另一方面，表面分析表明，经处理的材料主要由炭组成，结合的羧酸的表面含量也随着水解温度的升高而增加。为了理解本体分析和表面分析之间的明显差异，使用FTIR和拉曼显微镜对被处理样品的横截面进行了分析。这些技术证实了表面由炭材料组成，而粒子内部主要是全纤维素。外部炭层的形成似乎阻止了内部全纤维素的水解，限制了糖的产量。与FT-SWH相比，批次SWH在类似的严重性因子下导致糖产量降低，形成可检测焦炭的起始温度降低以及焦炭形成增加。与批料条件的比较表明，流动条件减少了外部炭的形成，但没有阻止这种形成。这项研究解释了FT-SWH的好处，并为可降低炭形成率的预处理技术的开发和完善提供了信息。

更新日期：2017-09-13

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