**7.2. Application of straw industrial lignin**

Although being a highly abundant aromatic feedstock, lignin is still largely regarded simply as a source for heat and power for the biorefining or pulping process that liberates the lignin. The lack of established processes that add value to the lignin component can be largely attributed to its chemical recalcitrance and structural complexity. Adding to this complexity, the lignin structure is highly dependent on both the feedstock and lignin isolation process [30]. However, a part of lignin could be converted into value-added products including bio-based aromatic chemicals, as well as building blocks for materials [31]. The soda lignin has more value than kraft lignin from wheat straw in manufacturing lignin-derivative compounds in terms of the industrial lignin structure and the lignin recovery cost [30, 32]. Lignosulfonates and their modified products have always been traditionally and extensively employed as a class of thinning agent for drilling fluids. SFP lignin is a kind of lignosulfonate in the waste liquor from the pulping of wheat straw with Na<sup>2</sup> SO3 , HCHO, and AQ [33, 34]. Experimental results showed that SFP lignin exerts three effects on drilling fluid dilution, foaming, and flocculation. Therefore, SFP lignin and its modified products can be used as a thinning and foaming agent for drilling fluids, as well as a flocculating agent for treating waste drilling fluids [34, 35].
