Time filter

Source Type

Houston, TX, United States

Vahid A.,University of Akron | Gray N.H.,Chemstations Inc. | Elliott J.R.,University of Akron
Macromolecules | Year: 2014

Polymeric mixtures of hydrocarbons and alcohols have been simulated with discontinuous potential models to characterize the Helmholtz energy of the repulsive reference fluids. This quantity is equivalent to the athermal mixture entropy. The reference compressibility factor and Helmholtz free energy have been correlated for various molecular structures from single to infinite chain lengths. The mixtures included small n-alkanes, branched alkanes, aromatics, and alcohols, with polymeric molecules of: n-alkanes, ethyl-styrenes, ethyl-propylenes, and isoprenes. We find that the athermal entropy of mixing at constant packing fraction deviates significantly from ideality as the volume ratio increases, but the nonideality is fairly insensitive to structural details like branching and rings. Volume ratio alone does not provide a complete characterization, however. For example, a mixture of C40 and C80 would yield a small deviation whereas a mixture of C2 and C4 would provide a relatively large deviation. This observation leads to the introduction of a characteristic parameter in terms of entropy density, designated as an entropic solubility parameter. In both ideal and nonideal solutions, the trends still follow van der Waals (vdW) mixing. This leads to an accurate characterization of the entropic contribution to the χ parameter (χS) of Flory-Huggins theory for mixtures of all sizes, shapes, and compositions of molecular structures. A general rule is developed for predicting the athermal entropy of mixing based on knowledge of the volume ratios and entropic solubility parameter of the constituent molecules. The simulations are compared to Flory-Huggins (FH), group contribution lattice fluid theory (GCLF), statistical associating fluid theory (SAFT), Sanchez-Lacombe (SL), and Guggenheim-Staverman (GS) theories of polymer chains. © 2014 American Chemical Society.

Hill D.,Chemstations Inc. | Matsuoka K.,INPEX Corporation
Chemical Engineering | Year: 2010

One of the best ways to realize value from your process data is to use those data - both real-time and historical - in a process simulator. The many applications for doing so are generally categorized into offline and online categories. A discussion covers process simulators; modern distributed control systems; reasons for integrating process simulators with control system data; example applications, which include a natural gas pipeline that had two looped branches and additional third loop to expand capacity, a chemical producer that integrated a steady-state simulator as a software sensor for its control system, and a company that wants to calculate fouling factors throughout a heat exchanger network; determination of capabilities; and implementation of a data connection.

Herrick A.,Chemstations Inc.
AIChE Annual Meeting, Conference Proceedings | Year: 2013

Design and scale-up of new batch processes presents a unique set of challenges versus design of continuous processes. One key difference is optimization of the time required for each process step. Rules of thumb are often used due to lack of data or tools. Improvements in dynamic simulation software have allowed for more rigorous modeling of increasingly complex systems and scenarios. Modeling of batch process steps in the design phase can highlight potential problem areas such as heat balance limitations, short residence times, reversal of flows, and pressure/flow dependencies. This allows for efficient optimization of step scheduling using the latest dynamic simulation techniques. Examples of batch designs are presented using CHEMCAD simulation software. A new method is included for simplification of handling any number of process steps and control elements.

Hill D.,Technical Support Inc. | Herrick A.,Chemstations Inc. | Matsuoka K.,INPEX Corporation
11AIChE - 2011 AIChE Spring Meeting and 7th Global Congress on Process Safety, Conference Proceedings | Year: 2011

Chemstations has advised on several modeling projects for LNG processes. Dynamic simulation has helped engineers gather insight into such processes. A discussion of scenarios was put forward, including what was achieved by the engineers modeling them. This is an abstract of a paper presented at the 2011 AIChE Spring Meeting & 7th Global Congress on Process Safety (Chicago, IL 3/13-17/2011).

Chemstations Inc. | Date: 2009-04-28

computer software for process simulation applications for use in chemical, petrochemical, oil and gas, and pharmaceutical industrial operations.

Discover hidden collaborations