Compositional modeling of wax formation in petroleum mixtures

Heavy organics deposition is a common problem in oil industry, especially in oil production, transportation and processing. Wax or solid paraffin series are examples of heavy organics that deposit. Precipitation and crystallization of wax causes major difficulties in different processes. Based on multi-solid theory, a basic model is modified in this paper for wax precipitation in different oils. Four oil samples with paraffin/naphthene/aromatic (PNA) analysis are used. Two-parameter gamma function is used for molecular weight distribution of C7+ fraction. Since all samples in original multi-solid model were dead oil with vapor phase being ignored, the pressure and composition effects on wax precipitation were, therefore, impossible (existence of vapor phase). When considering vapor phase in this work, the proposed modification (i.e. solution method) is well able to predict pressure and composition (addition of different solvents) effects on wax appearance point (WAP). The results obtained agree very well with the experimental and previous investigator's results.