An excess gibbs free energy model is applied to investigate the influence of n-paraffin composition on the aging behavior of wax-oil gel deposits known to form in subsea petroleum transport pipelines.The aging of wax-oil gels occurs by a counterdiffusion process where wax molecules with carbon numbers greater than a critical carbon number(CCN) diffuse into the gel matrix,and vice versa.Model crude oils were formulated to exhibit varying decreasing exponential distributions of n-paraffin components in the range n-C_9 to n-C_53.Deposition experiments ere conducted using a laboratory cold finger apparatus simulating the cold wall fo a subsea pipeline.Gas chromatography analysis of gel deposit compositions yielded experimented CCN values.a solid-liquid-phase equilibrium model,employing a modified version of UNIQUAC to compute solid-phase component activity coefficients,was able to successfully predict the critical carbon number for a variety of model oil n-paraffin compositions.
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