…A few words about UNIFAC…

Interaction parameters for VLE

■ Fredenslund A, Gmehling J, Rasmussen P. 1977. Vapor-Liquid Equilibria Using UNIFAC. Elsevier, Amsterdam.

■ Hansen HK, et sl. 1991. Ind. Eng. Chem. Res. 30:2352–2355

■ Wittig R, et al. 2003. Ind. Eng. Chem. Res. 42:183–188

Interaction parameters for LLE

■ Magnussen T, et al., HK, et sl. 1981. Ind. Eng. Chem. Fund.20:331–339

Interaction parameters for heats of mixing

■ Dang D, Tassios DP. 1986. Ind. Eng. Chem. Process Des. Dev.25:22–31

Interactionparameters(for VLE)

Smithet al.1996

Poling et al. 2001

CH3OH + H2O

Soup of CH3, OH and H2O groups

Soup of CH3OH and H2O groups (molecules)

CH3

CH3

OH

Design Project: Polylactic Acid

Preliminary design and economic analysis for a plant producing 300 million lb/yr of polylactic acid polymer from a feed stream of crude lactic acid.

Technical and economic aspects of design

Procedural aspects of course

Technical and economic aspects of design

Advantages of polylactic acid

Biodegradable thermoplastic polymer. To be addressed by YOU in Interim Report #0

Direct polymerization of lactic acid? Um… NO!

PolymerizationCondensation reaction

Rate decreases with increasing MW

Depolymerization reactionCreates cyclic dimer lactide(“dilactide”)

Polymerization of lactide

PolymerizationRing opening

Low-MW poly(lactic acid) = pre-polymer = source of lactide

Pre-polymer MW 1,000–5,000 (400–2500) ➔ 1,000

Decent high-MW PLA: MW > 100,000

Poly(L-lactic acid), PLLA

“The L-isomer constitutes the main fraction of PLA derived from renewable sources since the majority of lactic acid frombiological sources exists in this form.”

“PLA polymers with L-content greater than ∼90% tend to be crystalline while those with lower optical purity are amorphous.”

Lim LT, et al. 2008. Progress in Polymer Science 33:820–852

“PLA articles which require heat resistant properties can be injection molded using PLA resins of less than 1% D-isomer.”

(Lim LT, et al. 2008. Progress in Polymer Science 33:820–852)

Design project

Pretend as if L-isomer is the only one that exists. Can use D-properties.

Real life: minimize racemization by minimizing residence time and avoiding high temperature (< ~200 oC for PLLA)

Process

(22) + (38)

Gruber PR, et at. 2001. US Patent No. 6,326,458 B1

Evaporator/pre-polymer reactor

Falling film, agitated thin-film, wiped film

Multiple effects

Vacuum to reduce minimize racemization

E.g. falling film – one pass down innerwalls of tube. Good for heat sensitivematerials, viscous liquids.

Less detail in design (except for five-member groups)

Evaporators

Falling film

Horizontal wiped film

McCabe LT, et al. 2001.

Towler G, Sinnott R. 2008.

Lactide reactor (evaporator)

Will be supplying more information about reaction and catalyst (tin(IV) butyl-tin tris(2-ethylhexanoate); FASCAT® 9102, Atochem North America Inc.). Watch Update page.

Feed 180–250 oC

Pressure 2–60 mm Hg

Residence time 2 – 10 min

Film thickness 0.5–8 mm

Physical properties

Lim LT, et al. 2008. Progress in Polymer Science 33:820–852

Distillation

Components: lactide, lactic acid, water

Condenser temperature (and therefore pressure) is limited by cooling water temperature

Reboiler temperature (and therefore pressure) is limited by maximum tolerable temperature (avoid decomposition, polymerization)

Avoid freezing of all components

Must establish all pure-component phase diagrams, and find suitable operating window

Must feed UniSim accurate vapor pressure and activity coefficient parameters

Consider pressure drop (trays versus packing)

Points to watch for

Low pressure process. Lecture on vacuum systems. Tight system.

Energy integration.

Required level of detail in technical design

Evaporators/reactors

Specify type; size/dimensions; temperature, pressure and composition of input and output lactic acid/polylactic acid streams, and output vapor stream; and required amount of steam. The requirements for your design of the evaporator/pre-polymer reactor (i.e., the unit combining the functions of (22) and (38)) are relaxed in the sense that it may be a rough estimate. For the lactide reactor (60) you must present a more detailed design. In particular, you must specifically determine a film thickness based on mass transfer considerations, and incorporate this choice into your design.

The choice of lactic acid feed, and the pressure and basic configuration for the evaporator/pre-polymer reactor and lactide reactor must be established by Interim Report 1 (Decision Point 1).

Note: five-member groups must develop a more detailed design also for the evaporator/pre-polymer reactor.

Distillation column

You must develop a detailed design of the distillation column specifying reflux ratio and boilup ratio; temperature, pressure and composition of feed, distillate and bottom product streams; column height above feed and below feed, and column diameter; type of packing or trays; and thermal duty and heat transfer area for reboiler and condenser.

The distillation is a particularly important part of the process. Calculations can be made by yourself or using UniSim. If you use UniSim, then you must provide it with substantial amounts of physicochemical property data on lactide, which is not included in the library of available components. Relying on the base estimation package based only on MW and boiling point will be grossly inaccurate and therefore unacceptable.

You must also carefully check the properties of lactic acid, and augment them as necessary. Start the distillation model early to be sure you produce a converged model that reasonably approximates reality.

Do not underestimate the amount of work involved in getting this unit operation right. If you use UniSim, then you must also prepare one or more McCabe-Thiele diagrams that explain your design and roughly check the numbers.

The pressure, VLE data and configuration for your distillation process must be reported by Interim Report 2 (Decision Point 2).

Heat exchangers

Determine and state thermal duty, heat transfer area, temperature and pressure of input and output streams, and type of heat exchanger.

Fluid lines

Your design must include sizes of all lines between units (must be standard sizes), and pump power for each line. These specifications must be reported by 20 April (Decision Point 3). You must also specifically select the pump for the line from the hold tank (44) to the lactide reactor (60). (The term “fluid transfer mechanism” used throughout Gruber et al.’s patent means pump.)

Flow sheet

Your completed design (and in particular, report) must contain a neat, computer-generated, detailed flow diagram. It should resemble Towler and Sinnott’s Figure 2.8 (p. 39). It may not be a UniSim flowsheet.

Streams must be labeled, with information about each stream (temperature, pressure, phase, composition) tabulated below by number. Information must be given in units customary among engineers in this country, i.e., flow rates in lb/h or kg/h, pressures in psi or kPa, temperatures in °F or °C, dimensions in ft or m, and pipe sizes in in.

Although you might use other units in calculations, they must be converted into acceptable units in your final presentation. Also, you should retain extra significant figures in order not to let round-off error corrupt your calculations. However, you should ultimately report only a reasonable number of digits. Net: a flow rate expressed as, e.g., 1.344789002 × 108 g/week WILL NOT FLY.

Givens

(a) Materials availableLactic acid at $0.69/lb for 50% solution, $0.78/lb for 88%

solution, f.o.b.FASCAT® at $12/lb, f.o.b.

(b) Services availableSteam, 150 psig, saturated: $15 / 1000 kgCooling water, 60 psig, 30 °C supply, 40 °C return:

$0.20 / 1000 galProcess water (chilled), 60 psig, 15 °C: $1.50 / 1000 galElectricity: $0.06 / kWhWastewater treatment: $3.00 / 1000 gal

(c) Product specificationPolylactic acid (PLA), 200,000 MW, sells for $2.00/lb

(d) On stream timeAssume 8000 hours / year

Economic analysis

Assume 20-year project life, 6% annual effective interest rate, 40% tax rate.

Results and criteria specifically to be addressed in your final report are: fixed and working capital investment, manufacturing cost, and revenue; return on investment (minimum acceptable 15% after income tax), and net present value.

Base capital cost estimates mainly on tables in Towler and Sinnott (especially Table 7.1 (pp. 314–317) and Table 7.2 (pp. 322–324)), which yield reasonable study estimates. Do NOT expend effort contacting actual vendors for quotations on specific pieces of equipment.

As with process stream variables, figures from the economic analysis should be reported with a reasonable number of digits, especially as your cost estimates will be subject to ±30% error or more. In other words, report e.g. a net present value as $12,400,000, not $12,364,078.92.

Industrial participants

Paul Ameis (VanDeMark Chemical)

Jennifer Barnes (VanDeMark Chemical)

Dr. Mahesh Biradir (Linde)

Larry Coleman (private consultant)

Dr. Rich Fickelscherer (Falconeer)

Dr. John Peck (Linde)

Dr. William Scharmach (Linde)

Regular meetings and progress reports

Meetings with project advisors

Schedule

Sign-up will be done with Doodle Polls, watch for email with links; sign up early

Must talk with four different supervisors during semester

All members of group must be present at meeting (grade penalty for absence)

Bring questions

Progress reports

Schedule &contents

Must be received in time for supervisors to have a look before meeting.

Composition of grade for design project

Calendar

Haven’t I seen this somewhere before?

Yes I have… several times!

CE 317

CE 318

CE 427 fall 2014

Lactide process safety

Chemical hazards

Evaporation

Distillation