HF alkylation process
09739736 · 2017-08-22
Assignee
Inventors
Cpc classification
G01N25/00
PHYSICS
G01N9/36
PHYSICS
C10G29/205
CHEMISTRY; METALLURGY
B01J19/24
PERFORMING OPERATIONS; TRANSPORTING
International classification
G01N25/00
PHYSICS
C10G29/20
CHEMISTRY; METALLURGY
Abstract
An HF olefin/isoparaffin alkylation process is carried out in an alkylation unit with a settling vessel in which the alkylate product is separated from the HF acid catalyst containing water and acid soluble oil (ASO). The density of the liquids in the settling vessel is measured at different levels by means of a nuclear density profile analyzer. The acid strength of the acid phase is determined from the density measurement and an optional temperature measurement. The proportion of water in the acid phase may also be measured separately by measurement of its electrical conductivity to determine the respective contributions of the water and the ASO to the density of the HF acid phase.
Claims
1. In a method of determining the HF acid strength of the HF acid in an HF olefin/iso-paraffin alkylation unit having a settling vessel in which a hydrocarbon phase comprising alkylate and an HF acid phase containing acid soluble oil (ASO) and water are separated into a hydrocarbon phase and a denser HF acid phase with an interface between the two phases, the method comprising determining the density of the HF acid phase from the density profile of the hydrocarbon and HF acid phases in the settling vessel and from the density of the HF acid phase determining the proportion of water and ASO in the HF acid phase to determine the HF acid strength; wherein the HF acid strength is determined from measurements of the density of the HF acid phase, of the temperature and the proportion of water in the acid phase and the HF acid strength is determined from the measured density, temperature and water proportion of the HF acid phase according to the relationship:
c.sub.HF=A.Math.ρ+B.Math.c.sub.H.sub.
2. A method according to claim 1 in which the density of the HF acid phase is measured by means of a nuclear density profiler.
3. A method according to claim 1 in which the proportion of water in the HF acid phase is determined by means of a measurement of electrical conductivity.
4. A method according to claim 1 in which the temperature of the HF acid phase is measured.
5. A method according to claim 1 in which the density of the HF acid phase is determined at or below the interface between the hydrocarbon phase and the HF acid phase.
6. A method according to claim 1 in which the water concentration is determined by measurement of the conductivity of the HF acid phase.
7. In an olefin/isoparaffin HF alkylation process in which a C.sub.2 to C.sub.5 olefin is reacted with a C.sub.3-C.sub.6 isoparaffin in the presence of an HF acid catalyst to form a higher molecular weight alkylate reaction product comprising branched chain paraffins which is separated from an HF acid phase containing water and acid soluble oil (ASO) in a settling vessel, the method of determining the HF acid strength of the HF acid in the settling vessel by determining the density of the HF acid phase from the density profile of the hydrocarbon and HF acid phases in the settling vessel and from the density of the HF acid phase and determining the proportion of water and ASO in the HF acid phase to determine the HF acid strength; wherein the HF acid strength is determined from measurements of the density of the HF acid phase, of the temperature and the proportion of water in the HF acid phase and the HF acid strength is determined from the measured density, temperature and water proportion of the HF acid phase according to the relationship:
c.sub.HF=A.Math.ρ+B.Math.c.sub.H.sub.
8. A method according to claim 7 in which the density of the HF acid phase is measured by means of a nuclear density profiler.
9. A method according to claim 7 in which the proportion of water in the HF acid phase is determined by means of a measurement of electrical conductivity.
10. A method according to claim 7 in which the temperature of the HF acid phase is measured.
11. A method according to claim 7 in which the density of the HF acid phase is determined at or below the interface between the hydrocarbon phase and the HF acid phase.
12. An HF olefin/iso-paraffin alkylation unit comprising: a reactor in which a C.sub.2 to C.sub.5 olefin is reacted with a C.sub.4-C.sub.5 isoparaffin to form a higher molecular weight alkylate reaction product comprising branched chain paraffins; a settling vessel in which the reaction product is separated into a liquid hydrocarbon phase and a denser liquid HF acid phase containing acid soluble oil (ASO); a density profiler for measuring the density of the liquid phases at vertically spaced intervals in the settling vessel, means for determining the density of the HF acid phase from the density profile measured by the nuclear density profiler to determine the acid strength of the HF acid phase: and means for determining the HF acid strength from measurements of the density of the HF acid phase, of the temperature and the proportion of water of the HD acid phase and the HF acid strength is determined from the measured density, temperature and water proportion of the HF acid phase according to the relationship:
c.sub.HF=A.Math.ρ+B.Math.c.sub.H.sub.
13. An alkylation unit according to claim 12 which includes an electrical conductivity meter for measuring the electrical conductivity of the HF acid phase.
14. An alkylation unit according to claim 12 which includes a temperature sensor for measuring the temperature of the HF acid phase.
15. An alkylation unit according to claim 12 which includes a recirculation line extending from the lower portion of the settling vessel to an inlet of the reactor with an electrical conductivity meter located along the line for measuring the electrical conductivity of the HF acid phase in the line.
16. An alkylation unit according to claim 12 which includes a recirculation line extending from the lower portion of the settling vessel to an inlet of the reactor with a temperature sensor for measuring the temperature of the HF acid phase in the line.
17. An alkylation unit according to claim 12 which includes means for determining the density of the HF acid phase at an interface between the hydrocarbon phase and the HF acid phase.
Description
DRAWINGS
(1) The single FIGURE of the accompanying drawings is a simplified diagram of a settler vessel of an HF alkylation unit with a nuclear density profiler for monitoring the depths of the layers in the vessel.
DETAILED DESCRIPTION
(2) In recent years, nuclear density profile analyzers have become widely used commercially in the petroleum refining industry to measure the acid height in the settler vessel. The profile analyzer scans the vertical density profile in the settling tank and identifies the boundary between the light hydrocarbon(alkylate) phase and a denser acid phase. The three primary components of the acid phase are HF acid, water, and acid soluble oil (ASO) but because these components differ in density and, in addition, the density of the ASO may vary in a manner which is not predictable, the density measurement on the acid phase cannot directly determine the concentration of the acid relative to the ASO. In addition, water-HF mixtures are very non-ideal and the density of the mixture is significantly higher than the individual components.
(3) In the FIGURE, a nuclear density profile analyzer simultaneously measures the height of the acid phase in the acid settling tank and the position of the interface between the alkylate and the acid phase and in addition, obtains an indication of the HF acid strength by measuring the density of the HF acid phase which is dependent on the concentration of water and ASO in the acid phase. In the unit, the olefin/isoparaffin feed HC and the HF alkylation catalyst meet in reactor 10 and then pass through line 11 to settling tank 12 were the alkylate product phase and the denser HF acid phase are allowed to separate in the usual way under gravity with a supernatant alkylate phase and a denser acid phase. The alkylate phase 15 forms the least dense layer while the denser HF acid phase 17 accumulates in the lower portion of the settler. The HF acid/water stream is withdrawn through line 21 with its inlet in the lower portion of the settler and passes to the acid recovery unit in the usual manner. A slip stream is withdrawn from line 21 and passes through recirculation line 22 to conductivity meter 23 and an optional temperature measurement module 24 before being returned to line 21 by way of line 25, so providing for a continuously updated indication of the conductivity and optionally, the temperature of the acid phase in the settler.
(4) A nuclear density profile analyzer 30 is shown extending into the tank, e.g. in a dry well although an externally mounted profile analyzer may also be used. If the internal drywell type analyzer is used, the detectors may be mounted on the exterior of the vessel at various selected heights or a single detector may be scanned with the source in a separate drywell; if the density is measured at various depths where the acid/hydrocarbon interface is to be found, e.g. with more than one detector at the expected depth of the interface, the average density of the acid phase in the region may be used for the density determination. Typically, the density of the acid phase is measured at or just below the hydrocarbon/acid interface. The outputs from the conductivity meter 23, the temperature module 24 and the densitometer 30 are passed to a monitoring/control module 31 where the density and conductivity measurements are convolved together with the temperature measurement, if taken. The output representing the HF acid strength may then be read out through line 32.
(5) One type of nuclear density profiler is described in U.S. Pat. No. 6,633,625 (Jackson/Johnson Matthey) using collimated ionizing radiation beams with an axially distributed radiation detector array in which each detector is associated with one of the beams to produce an output signal in response to incident radiation. In a typical commercial density profiler a dip pipe extending into the vessel through a flange holds an array of low-energy gamma sources with a collimator with holes at each source level. These holes direct a narrow beam of radiation toward a selected detector so that each source is matched to the radiation source in the same plane. The liquid between the dip pipes will attenuate the radiation with the intensity of the detected radiation proportional to the density of the intervening liquid, this providing an output signal indicative of the liquid density at each source/detector plane. The outputs from the detectors are transmitted for analysis, for instance, by wire or fiber-optic link to a programmable logic controller that collects the information and calculates the density profile.
(6) Various nuclear density profilers are commercially available such as the Nitus™ system from Thermo Fisher Scientific, the Tracerco™ Profiler from Johnson Matthey, the Delta Controls IPT (Interface Position Transmitter) and the Ohmart Vega MDA FiberFlex® interface profiler as well as the Profile Vision device from Endress+Hauser. The profiler typically operates from an internal drywell with multi-level radiation sources with internal or external detectors for each interface level. The type with internal drywell detectors has the advantage of easy installation while the external detectors are less sensitive to temperature and do not require temperature control to preserve system integrity but since the acid density varies with temperature, a correlation with liquid temperature to provide a temperature correction is nevertheless desirable.
(7) The HF acid strength may then be determined from the measurements according to the following methodology:
(8) Assuming variations in concentration and temperature are relatively small, the density is a linear function of all of the components and temperature:
ρ=α.Math.c.sub.HF+β.Math.c.sub.H.sub.
where ρ is the measured density of the acid phase in the settler, c.sub.HF and c.sub.H2O are HF and water concentration, T is measured temperature, and α, β, γ, and δ are fitting parameters. The terms α and β represent the densities of HIP and water and the term γ accounts for the temperature-dependent solubility of hydrocarbon and also the temperature effects on density. The liquid density is also dependent on the ASO concentration but since c.sub.HF+c.sub.H2O+c.sub.ASO=1, the equation is simplified and reduced to a system of three unknowns with one constraint (components adding to unity) and two measurements (density and conductivity), so permitting a solution in which the acid strength is expressed as directly dependent on the water the density and water concentration.
c.sub.HF=A.Math.ρ+B.Math.c.sub.H.sub.
where, in this case, the fitting parameters are A, B C and D. Additional measurements, including the water concentration from the conductivity measurement and the temperature correction can be included in a model, which calculates the acid strength resulting from the various input variables.
ADDITIONAL EMBODIMENTS
Embodiment 1
(9) In a method of determining the HF acid strength of the HF acid in an HF olefin/iso-paraffin alkylation unit having a settling vessel in which a hydrocarbon phase comprising alkylate and an HF acid phase containing acid soluble oil (ASO) and water are separated into a hydrocarbon phase and a denser HF acid phase with an interface between the two phases, the method comprising determining the density of the HF acid phase from the density profile of the hydrocarbon and HF acid phases in the settling vessel and from the density of the HF acid phase determining the proportion of water and ASO in the HF acid phase to determine the HF acid strength.
Embodiment 2
(10) In an olefin/isoparaffin HF alkylation process in which a C.sub.2 to C.sub.5 olefin is reacted with a C.sub.3-C.sub.6 isoparaffin in the presence of an HF acid catalyst to form a higher molecular weight alkylate reaction product comprising branched chain paraffins which is separated from an HF acid phase containing water and acid soluble oil (ASO) in a settling vessel, the method of determining the HF acid strength of the HF acid in the settling vessel by determining the density of the HF acid phase from the density profile of the hydrocarbon and HF acid phases in the settling vessel and from the density of the HF acid phase and determining the proportion of water and ASO in the HF acid phase to determine the HF acid strength.
Embodiment 3
(11) A method according to Embodiment 1 or Embodiment 2 in which the density of the HF acid phase is measured by means of a nuclear density profiler.
Embodiment 4
(12) A method according to anyone of the previous Embodiments in which the proportion of water in the HF acid phase is determined by means of a measurement of electrical conductivity.
Embodiment 5
(13) A method according to anyone of the previous Embodiments in which the temperature of the HF acid phase is measured.
Embodiment 6
(14) A method according to anyone of the previous Embodiments in which the density of the HF acid phase is determined at or below the interface between the hydrocarbon phase and the HF acid phase.
Embodiment 7
(15) A method according to anyone of the previous Embodiments in which the HF acid strength is determined from measurements of the density of the HF acid phase, of the temperature and the proportion of water in the acid phase and the IV acid strength is determined from the measured density, temperature and water proportion of the HF acid phase according to the relationship:
c.sub.HF=A.Math.ρ+B.Math.c.sub.H.sub.
where c.sub.HF and c.sub.H2O are respectively, the HF and water concentration, ρ is the measured density, T is the measured temperature, and A, B, C, D are fitting parameters.
Embodiment 8
(16) An HF olefin/iso-paraffin alkylation unit comprising: a reactor in which a C.sub.2 to C.sub.5 olefin is reacted with a C.sub.4-C.sub.5 isoparaffin to form a higher molecular weight alkylate reaction product comprising branched chain paraffins; a settling vessel in which the reaction product is separated into a liquid hydrocarbon phase and a denser liquid HF acid phase containing acid soluble oil (ASO); a density profiler for measuring the density of the liquid phases at vertically spaced intervals in the settling vessel, means for determining the density of the HF acid phase from the density profile measured by the nuclear density profiler to determine the acid strength of the IV acid phase.
Embodiment 9
(17) An alkylation unit according to Embodiment 8 which includes an electrical conductivity meter for measuring the electrical conductivity of the HF acid phase.
Embodiment 10
(18) An alkylation unit according to any one of Embodiments 8 and 9 which includes a temperature sensor for measuring the temperature of the acid phase.
Embodiment 11
(19) An alkylation unit according to any one of Embodiments 8-10 which includes a recirculation line extending from the lower portion of the settling vessel to an inlet of the reactor with an electrical conductivity meter located along the line for measuring the electrical conductivity of the HF acid phase in the line.
Embodiment 12
(20) An alkylation unit according to any one of Embodiments 8-11 which includes a recirculation line extending from the lower portion of the settling vessel to an inlet of the reactor with a temperature sensor for measuring the temperature of the HF acid phase in the line.
Embodiment 13
(21) An alkylation unit according to any one of Embodiments 8-12 which includes means for determining the density of the HF acid phase at an interface between the hydrocarbon phase and the IV acid phase.
Embodiment 14
(22) An alkylation unit according to any one of Embodiments 8-13 which includes means for determining the HF acid strength from measurements of the density of the HF acid phase, of the temperature and the proportion of water of the HD acid phase and the HF acid strength is determined from the measured density, temperature and water proportion of the HF acid phase according to the relationship:
c.sub.HF=A.Math.ρ+B.Math.c.sub.H.sub.
where c.sub.HF and c.sub.H2O are respectively, the HF and water concentration, ρ is the measured density, T is the measured temperature, and A, B, C, D are fitting parameters.