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Mechanical degradation of polyacrylamide at ultra high deformation rates during hydraulic fracturing
Environmental Science: Water Research & Technology ( IF 3.5 ) Pub Date : 2019-11-18 , DOI: 10.1039/c9ew00530g Boya Xiong 1, 2, 3, 4, 5 , Prakash Purswani 3, 6, 7 , Taylor Pawlik 3, 7, 8 , Laxmicharan Samineni 3, 7, 8 , Zuleima T. Karpyn 3, 6, 7 , Andrew L. Zydney 3, 7, 8 , Manish Kumar 1, 3, 7, 7, 8
Environmental Science: Water Research & Technology ( IF 3.5 ) Pub Date : 2019-11-18 , DOI: 10.1039/c9ew00530g Boya Xiong 1, 2, 3, 4, 5 , Prakash Purswani 3, 6, 7 , Taylor Pawlik 3, 7, 8 , Laxmicharan Samineni 3, 7, 8 , Zuleima T. Karpyn 3, 6, 7 , Andrew L. Zydney 3, 7, 8 , Manish Kumar 1, 3, 7, 7, 8
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Degradation of drag reducer polyacrylamide under high volume hydraulic fracturing (HVHF) conditions alters its polymer size, distribution and chemical composition, potentially affecting the toxicity and treatability of the resulting wastewater. This study focused on a non-chemical pathway-mechanical degradation of polyacrylamide under ultra-high fluid strain conditions (∼107 s−1) that uniquely exist during HVHF but has not yet been explored experimentally. PAM solutions were subjected to an abrupt contraction into a narrow capillary driven by a high-pressure precision pump (∼10 000 psi). The change in polyacrylamide size distribution was evaluated by size exclusion chromatography. The peak polymer molecular weight (MW) after a single-pass through the capillary decreased from 107 to 7 × 105 Da at deformation rate 
= 4 × 106 s−1. The extent of degradation increased with 
, approximately following an empirical scaling relationship of 
for the polyacrylamide with an initial MW ≈ 107 Da. Degraded PAM with lower MW (<106 Da) showed minimal degradation during multiple flow passes even at high deformation rates, suggesting that most mechanical degradation occurs at the first entrance into the fracture. Relative to chemical degradation, mechanical degradation caused a narrowing of the MW distribution due to greater degradation of the larger MW polymers and preferential mid-chain polymer scission. In addition, we saw no detectable change in chemical composition during mechanical scission, in contrast to the generation of carbonyl groups during oxygenic radical induced chemical degradation. Combining both chemical and mechanical mechanisms during HVHF operation, we propose an initial mechanical breakage of polymer chain by fluid strain, followed by chemical degradation under the high temperature and appropriate mineralogical conditions. These findings provide critical information for understanding the nature of degradation byproducts from polyacrylamide, and the treatability of polyacrylamide fragment-containing wastewaters.
中文翻译：
水力压裂过程中聚丙烯酰胺在超高变形速率下的机械降解
减阻剂聚丙烯酰胺在高容量水力压裂（HVHF）条件下的降解会改变其聚合物尺寸，分布和化学组成，从而可能影响所得废水的毒性和可处理性。这项研究的重点是在超高流体应变条件（〜10 7 s -1）下，聚丙烯酰胺的非化学途径机械降解，该条件在HVHF过程中是唯一存在的，但尚未进行实验探索。PAM溶液突然收缩成由高压精密泵（〜10000 psi）驱动的狭窄毛细管。通过尺寸排阻色谱法评价聚丙烯酰胺尺寸分布的变化。单次通过毛细管后的峰值聚合物分子量（MW）从10降低7〜7×10 5达在变形率= 4×10 6小号-1。降解程度随着的增加而增加，大约遵循初始MW≈10 7 Da的聚丙烯酰胺的经验比例关系。降低的MW（<10 6）的PAM降级Da）在多次流动过程中即使在高变形率下也显示出最小的退化，这表明大多数机械退化发生在裂缝的第一个入口。相对于化学降解，由于较大的MW聚合物的降解程度更高和优先的中链聚合物断裂，机械降解导致MW分布变窄。此外，与在氧自由基诱导的化学降解过程中产生羰基相反，在机械断裂过程中化学成分没有发现可检测的变化。结合HVHF操作过程中的化学和机械机理，我们提出了由流体应变引起的聚合物链的初始机械断裂，然后在高温和适当的矿物学条件下化学降解。
更新日期：2019-11-18
= 4 × 106 s−1. The extent of degradation increased with , approximately following an empirical scaling relationship of for the polyacrylamide with an initial MW ≈ 107 Da. Degraded PAM with lower MW (<106 Da) showed minimal degradation during multiple flow passes even at high deformation rates, suggesting that most mechanical degradation occurs at the first entrance into the fracture. Relative to chemical degradation, mechanical degradation caused a narrowing of the MW distribution due to greater degradation of the larger MW polymers and preferential mid-chain polymer scission. In addition, we saw no detectable change in chemical composition during mechanical scission, in contrast to the generation of carbonyl groups during oxygenic radical induced chemical degradation. Combining both chemical and mechanical mechanisms during HVHF operation, we propose an initial mechanical breakage of polymer chain by fluid strain, followed by chemical degradation under the high temperature and appropriate mineralogical conditions. These findings provide critical information for understanding the nature of degradation byproducts from polyacrylamide, and the treatability of polyacrylamide fragment-containing wastewaters.
中文翻译：
水力压裂过程中聚丙烯酰胺在超高变形速率下的机械降解
减阻剂聚丙烯酰胺在高容量水力压裂（HVHF）条件下的降解会改变其聚合物尺寸，分布和化学组成，从而可能影响所得废水的毒性和可处理性。这项研究的重点是在超高流体应变条件（〜10 7 s -1）下，聚丙烯酰胺的非化学途径机械降解，该条件在HVHF过程中是唯一存在的，但尚未进行实验探索。PAM溶液突然收缩成由高压精密泵（〜10000 psi）驱动的狭窄毛细管。通过尺寸排阻色谱法评价聚丙烯酰胺尺寸分布的变化。单次通过毛细管后的峰值聚合物分子量（MW）从10降低7〜7×10 5达在变形率
= 4×10 6小号-1。降解程度随着的增加而增加，大约遵循初始MW≈10 7 Da的聚丙烯酰胺的经验比例关系。降低的MW（<10 6）的PAM降级Da）在多次流动过程中即使在高变形率下也显示出最小的退化，这表明大多数机械退化发生在裂缝的第一个入口。相对于化学降解，由于较大的MW聚合物的降解程度更高和优先的中链聚合物断裂，机械降解导致MW分布变窄。此外，与在氧自由基诱导的化学降解过程中产生羰基相反，在机械断裂过程中化学成分没有发现可检测的变化。结合HVHF操作过程中的化学和机械机理，我们提出了由流体应变引起的聚合物链的初始机械断裂，然后在高温和适当的矿物学条件下化学降解。
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