Natural Pectin and Commercial Luvicap-Bio as Green Kinetic Hydrate Inhibitors: A Comparative Evaluation by Crystal Growth Inhibition Methods

Low dosage kinetic hydrate inhibitors (KHIs) are a cost-effective technique for the prevention of solid gas hydrate plug formation problems in the oil and gas industry. Although many commercial KHI polymers (e.g., poly-n-vinylcaprolactam, PVCap) have been used successfully in the field, in the past decade, considerable effort has been put into developing more eco-friendly KHIs due to environmental concerns around the non-biodegradability of traditional chemistries. Recently, natural pectin-a structural acidic heteropolysaccharide found in fruits-has been reported as a potential green KHI with good hydrate inhibition properties. In this work, crystal growth inhibition (CGI) methods have been used to assess the KHI performance of aqueous food grade apple pectin for pure methane and a multicomponent natural gas, with results compared to the commercial biodegradable KHI polymer Luvicap Bio. Results show that Luvicap Bio can offer significant inhibition to high subcoolings (e.g., 9.1 degrees C for the complete inhibition region in the natural gas system). In contrast, data show that pectin lacks the ability to significantly inhibit hydrate crystal growth, with it only showing some anti-nucleation properties, namely, through the ability to remove hydrate "history" (relic nuclei/water structuring). This "history removal" behavior highlights why it is crucial to ensure the presence of seeds (nuclei/water structures)-and ideally viable hydrate crystals-ahead of recooling cycles for the reliable assessment of KHIs by CGI type methods. An inadvertent lack of such "seeding" could potentially result in misleadingly strong apparent inhibition performance results, as recently found in related studies of some commercial KHIs.