She has been removed for allegedly bringing the party into disrepute.
Ms Patterson recently criticised the party's decision to overlook her for the South Belfast assembly seat vacated by Jimmy Spratt, and instead appointing former special adviser Emma Pengelly.
Mr Robinson said Ms Patterson has a right to appeal her expulsion.
He said party officers "unanimously decided to expel her earlier this week".
He added that he believed "there has been some correspondence" between the party and Ms Patterson since she was informed of the decision.
Ms Pengelly took her place in the Northern Ireland Assembly in September through the co-option system, which allows parties to replace departing MLAs with a party colleague without a by-election.
It has been used extensively by many of the parties in the assembly.
Within a month of her selection as an MLA for South Belfast, Ms Pengelly was appointed as a junior minister in the Office of the First Minister and deputy First Minister.
She had previously worked in the department as a special adviser to the first minister for almost nine years.
Last month, Ms Patterson, a former deputy lord mayor of Belfast, said she had been annoyed by Ms Pengelly's dual promotion.
"There is a principle, in my book, of giving someone who has earned something the chance, rather than someone who does not have one solitary vote, who has never stood for election, who has never run the gauntlet of an election," she said.
"It it not sour grapes. Anyone in my position would feel exactly the same - not surprised, but let down.
"I thought I was worth a little more."
Ms Patterson also said last month that her party's return to the Northern Ireland Executive after the publication of a report on paramilitaries had shocked her "to the core".
She said she had major difficulties with the move, and had been considering her position in the party.

The 25-year-old England international has played just twice since he picked up the injury in the 2-1 loss to Manchester United on 22 March.
"Just want to let the world know I've had a successful operation on my hip and I want to thank God for allowing that to be possible," Sturridge said.
"Onwards and upwards from here. Thanks for the support."
Sturridge scored 24 goals from 33 appearances last season but has been blighted by injuries this term, appearing in only 18 matches.
It is the second time this season he has travelled to the States in an attempt to rectify his fitness problems.
Towards the end of a five-month absence with a thigh problem sustained on international duty in early September - which was then followed by a calf strain - he spent 10 days in Los Angeles as part of his rehabilitation.
The striker has not featured since playing 85 minutes of the FA Cup quarter-final replay at Blackburn on 8 April.
Liverpool manager Brendan Rodgers last week said the club's medical team believed they had made a breakthrough in the diagnosis of Sturridge's injuries, which the player has previously suggested may be hereditary.
"I think we have found some underlying issues that maybe relate to Daniel's problems this season and the ongoing ones he's had," Rodgers said.

Liverpool will host FA Cup finalists Notts County in the other semi-final, with the dates for both ties in October still to be confirmed.
Three-time winners Arsenal's quarter-final with City was postponed after City were charged with fielding an ineligible player in the group stage.
The charge was found to be unproven and the tie is still to be re-arranged.
Two-time finalists Birmingham knocked out Women's Super League One leaders Chelsea in the last eight.
Liverpool thrashed Bristol Academy in the quarter-finals, while Notts saw off WSL 2 side Reading.
The final of the cup, now in its fifth year, will be held at Rotherham's New York Stadium on Sunday, 1 November.
The full semi-final draw is as follows:
Liverpool Ladies v Notts County Ladies
Arsenal Ladies or Manchester City Women v Birmingham City Ladies
Belfast councillor Ruth Patterson has been expelled from the Democratic Unionist Party (DUP), its leader Peter Robinson has told the BBC.
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Liverpool striker Daniel Sturridge has had "successful" surgery on a hip injury in the United States.
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Holders Manchester City or Arsenal will host Birmingham City in the semi-finals of this year's Women's Continental Cup.