Nitrogen rejection from natural gas is a capital intensive process. The most widely used technology, cryogenic distillation, is uneconomical for gas wells in remote areas or with small production rate. In this work, a detailed simulation and optimization is carried out to explore the feasibility of pressure-vacuum swing adsorption (PVSA) technology for on-site nitrogen rejection at remote/low-throughput gas wells. The designed PVSA unit possesses high mobility at a cost that scales well with low throughput. A nonisothermal and nonisobaric simulation model including detailed description of both micropore and barrier resistances in a kinetically selective carbon molecular sieve adsorbent has been used for process optimization. The process parameters constitute the decision variables of the optimization problem, with recovery and productivity as the objective functions, and industrial pipeline purity specification as an inequality constraint. Starting with a 6-step PVSA cycle, it is shown that a modified 9-step PVSA cycle promises to improve further the process performance. The process simulation model is the most comprehensive model for kinetically controlled PSA processes to date and the optimum results exceed the performances expected from the trends revealed in parametric studies published so far. Preliminary costing of the optimized process reveals that the modified PSA cycle has the potential to produce the desired product at a lower cost than the competing alternatives.

We introduce a framework for analyzing and designing EIS inversion algorithms. Our framework stems from the observation of four features common to well-defined EIS inversion algorithms, namely (1) the representation of unknown distributions, (2) the minimization of a metric of error to estimate parameters arising from the chosen representation, subject to constraints on (3) the complexity control parameters, and (4) a means for choosing optimal control parameter values. These features must be present to overcome the ill-posed nature of EIS inversion problems. We review three established EIS inversion algorithms to illustrate the pervasiveness of these features, and show the utility of the framework by resolving ambiguities concerning three more algorithms. Our framework is then used to design the generalized EIS inversion (gEISi) algorithm, which uses Gaussian basis function representation, modality control parameter, and cross-validation for choosing the optimal control parameter value. The gEISi algorithm is applicable to the generalized EIS inversion problem, which allows for a wider range of underlying models. We also considered the construction of credible intervals for distributions arising from the algorithm. The algorithm is able to accurately reproduce distributions which have been difficult to obtain using existing algorithms. It is provided gratis on the repository https:// github.com/suryaeff/gEISi.git.

A variety of polymeric surfaces, such as anti-corrosion coatings and polymer-modified asphalts, are prone to blistering when exposed to moisture and air. As water and oxygen diffuse through the material,...

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Conventional propylene/propane separation via distillation is capital- and energy-intensive. Pressure vacuum swing adsorption (PVSA) is a potential low-cost alternative to C3 distillation. In this work, a new 7-step PVSA cycle is developed using 4A zeolite as the adsorbent, capable of separating 84.4/15.6 propylene/propane (wt %) mixture to produce high purity (>99.5 wt %), high recovery (>99%) propylene at a low energy consumption. The proposed PVSA unit is simulated and costed together with its peripheral units using industrially relevant feed condition and product specifications. The lost opportunity cost arising from the presence of propylene in the raffinate product is also included in the costing algorithm. The proposed PVSA unit is optimized using a global stochastic optimizer, giving a minimum total cost of US$20.86 per tonne of propylene. This is significantly lower than the cost of an equivalent distillation unit, which is found to be US$41.07 per tonne of propylene. The use of PVSA for propylene/propane separation can thus lead to a significant improvement in profitability. The net present value (NPV) of PVSA over distillation for a 450 KTA propylene plant is found to be US$76.79M.